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SOIL AND WATER IN HAMPSHIRE AND THE ISLE OF WIGHT

This section contains an introduction to the physical environment of Hampshire and provides a set of case studies divided between the main landscape areas of the county.

The areas to be covered will be added to with time and opportunity. The case studies include:

The Hampshire Chalklands
Afton Down, Isle of White
Sites in the Test and Itchen Valleys
The Warren and Crab Wood

The Hampshire Weald
The Upper Greensand Hangers
Shortheath Common
Petersfield Heath

The Hampshire part of the London Basin
Fleet Pond
Bramshill Forest
Odiham Common

The Hampshire Basin
Wickham Common
The Moors, Bishop’s Waltham
Emer Bog
NB. There is a separate section on the New Forest within this website.

The Coast
Farlington Marshes LNR

1. INTRODUCTION

Ron Allen started studying the soils, water and landscape of Hampshire 25 years ago in 1980. In a freezing January of that year, Ron and his wife Mary moved from Essex to Hampshire and came to live in Stroud village just outside of Petersfield. Petersfield is pivotal in an understanding of the landscape of southern England being at the extreme western end of the Wealden Horseshoe, one of the best known landscape features in the southern UK.

From 1980 to 1986, Ron mapped and wrote about the Soils of Hampshire during his time with the Soil Survey of England and Wales. From 1986 to 2005 Ron, while in private practice (see www.epcg.co.uk) has extended the soil work to also include water and wetland biodiversity (see www.biodiversity.co.uk).

This section summarises some of the many Hampshire studies undertaken during that time and are arranged as a series of case studies according to their landscape position.

New sections, and illustrations will added as opportunity arises.

2. GEOLOGICAL AND LANDSCAPE FRAMEWORK

To understand soils requires an understanding of geology and landscape and in Hampshire we are fortunate in having rocks laid from the Cretaceous Period through the Tertiary and the Quaternary Ice Ages and into the present time. During this time, the land of Hampshire has drifted northwards from warm temperate to temperate climate zones and erosion and deposition has created a wide range of landforms leading to a wide range of surface water forms and in turn a very wide range of soil and landscape types. And so we have high plateau with ancient interglacial soils right through to soils on modern sediments that have hardly started to form.

A good account of the structure and geology of Hampshire can be found in
‘The Flora of Hampshire’ by Anne Brewis, Paul Bowman and Francis Rose (Harley Books – 1996)

A wide-ranging review of the landscape of Hampshire can be found in:
‘The Hampshire Landscape’ Hampshire County Council (HCC) June 1993.

3. GEOLOGICAL AND LANDSCAPE DIVERSITY IN HAMPSHIRE

HCC 1993 divides Hampshire into two major landscape types and these can be increasingly subdivided according to their constituent landforms and geological structure.

A. The CHALKLANDS occupying about half of the county, link Salisbury Plain in Wiltshire to the South Downs of West Sussex and including the central spine of the Isle of Wight. Geologically, chalk forms the foundation, but the surface is modified to contain ancient clayey plateau remnants and younger valley formations.

B. The LOWLAND MOSAIC is formed over a wide variety of clayey, loamy and sandy deposits both older and younger than the Chalk.
The lowland mosaic is easily divisible into three areas.

B 1. The Hampshire part of the ‘Weald’
This occupies that part of East Hampshire District extending broadly from Liphook in the north, across Woolmer-Whitehill-Bordon to Petersfield in the south. This complex parcel of and is contained within the western part of chalkland horseshoe where the South and North Downs join the Hampshire Downs. The soils are formed on a variety of formations including the Upper Greensand, Gault Clay and the Lower Greensand together with a wide range of younger Drift deposits. A separate part of the ‘Weald’ is found in the southern half of the Isle of Wight.

B 2. Hampshire part of the ‘London Tertiary Basin’
That part of Hampshire within the southwest part of the London Tertiary Basin is found in the northeast of the county from north of Basingstoke east to Fleet in Hart District and from where the landform extends along the Thames across London and into south Essex and north Kent. The soils are formed on a wide variety of flinty, Loamy, clayey and sandy strata.

B 3. Hampshire part of the ‘Hampshire Basin’
Finally, is the major part of the Hampshire Basin occupying Tertiary and more recent Quaternary deposits across the New Forest, the Hampshire Coastal Plain from Southampton to Portsmouth, and the northern part of the Isle of Wight and extending into Dorset to the west and Sussex to the East. The soils are formed on a wide range of clays, loams, sands and silty materials.

4. SOIL AND WATER IN THE HAMPSHIRE CHALKLANDS

Case Study 4.1 Afton Down, Isle of Wight

Case Study 4.2 Winnall Moors Nature Reserve

4.2.1 INTRODUCTION

Winnall Moors is a nature reserve on the River Itchen Flood Plain just north of Winchester and managed by the Hampshire Wildlife Trust.

I visited the northern part of the site in August 1992 as part of The Wildlife Trusts Partnership (RSNC) Water for Wildlife Campaign 1992. This campaign was set up after a very dry summer in which water levels of many nature reserves were very low. The objective was to examine the soils and water regimes and to install dipwells to allow monitoring of the water table.

Winnall Moors is an area of one-time floated water meadows dived by a complex arrangement of ditches, ridges and furrows along which the meadows were formerly shallowly flooded in late winter to promote grass growth. The grasslands and water courses are now rich in a wide variety of plants and animals. The land lies at 35m AOD between the Itchen watercourses.

4.2.2 GEOLOGY

The Winchester sheet of the Geological Survey of Great Britain indicated that the floodplain was underlain by alluvium with low gravel terraces to either side the whole valley underlain by Upper Chalk.

Field surveys showed that 10-40cm of thin silty alluvium occurred at the surface but underlain be deep fen peat up to 3m deep and underlain by a thing 10-50cm thick layer of clayey alluvium over sand and gravels.

4.2.3 SOILS AND PEAT DEPOSITS

All the soils examined were developed on dark brown or black humified base-rich peat and placed by the Soil Survey of England and Wales into the Adventurer’s soil series, Earthy eutro-amorphous peat soils, indicating that drainage of the topsoils has occurred leading to some structural development.

Thin layers of silty alluvium occur within the peat but are seldom more than 40cm thick. Some deeper silty over peaty soils occur, Bressingham series, Calcareous alluvial gley soils.

The peat is typically 2-3m deep, well humified and with vegetable remains that are easily destroyed by rubbing between the fingers. Peat at depth is rich in Hydrogen sulphide giving it the characteristic ‘rotten eggs’ smell.

Most of the peat is of humified sedge remains with zones rich in the flattened rhizomes of Phragmites reeds and towards the base is often a layer of woody peat with twigs and wood fragments. Some localised areas of more fibrous peat occur (possibly of Sphagnum bog-mosses).

Included within the peat are thin bands of calcareous tufa containing freshwater shells and porous nodules of calcium carbonate.

The thin alluvial layer below the peat contains the remains of sedges and reeds and passes down to flint gravel.

Detailed studies of the peat deposits at Winnall Moors were made by P V Waton in his PhD studies and published in Waton P V (1982) Man’s impact on the Chalklands: some new pollen evidence; in Archaeological aspects of woodland ecology Eds M Bell and S Limbrey Br Arcaheol.Rep., International Series 146, 75-91. Evidence presented here indicates that the peat pollen sequence extends back to the Mesolithic and preserving pollen characteristics for the Post-glacial primaeval forests through to the present.

Detailed profile descriptions are provided in the 1992 report to RSNC.

4.2.4 HYDROLOGY

The Itchen is a chalk stream fed by springs off the Chalk and from water rising upwards into the river channel. The Itchen channel is thought to have been cut during the later stages of the Ice Ages, partly filled with gravel and then with peat as water levels rose during the Post-glacial period. Because the valley cuts through the chalk water table there is a continuous flow of water into the river (base flow).

Within Winnall Moors there a number of locations at which regular upwellings of water occur into the ditches; sometimes these upwellings have been reported as breaking out through the peaty meadow soils. The peats themselves are quite compact and form a confining layer across the valley floor inducing a slight artesian pressure which is released into ditches where they have caused thinning of the peat. This effect would be expected to be confined to the deeper ditches in thinner areas of peat.

Eight dipwells were installed in 1992 and since then the reserve manager has installed more.


Case Study 4.3 The Warren National Nature Reserve

4.3.1 INTRODUCTION

The Warren Local Nature Reserve (29ha)is owned and managed by Hampshire County Council, and is an outstanding area of ancient semi-natural woodland that 'tumbles' down both sides of a valley set into the East Hampshire Chalk Escarpment. I surveyed the geology and soils of the site for the Recreation Department of Hampshire County Council in 1988. About that time the Petersfield children’s Watch Group of the Hampshire Wildlife Trust (that my wife and I used to lead) adopted it as their woodland.

My 1988 report to Hampshire County Council contains maps of the geology and soils of The Warren and these are not reproduced here.

4.3.2 LOCATION AND LANDFORM

The Warren is an area of deciduous and yew woodland on the East Hampshire Chalk Escarpment in the parish of Colemore and Prior’s Dean and is about 5km NNW of Petersfield.

The woodlands are set along a steeply sloping valley head or ‘coombe’ cut into the easterly facing Chalk escarpment. At the highest point the woodland is at 235m AOD and descends a full 100m into the valley bottom at 135m AOD with slopes up to 45 degrees. The valley is mainly dry but with some damp areas of seepage near the base.

The valley can be divided into:

  • Plateau
  • Plateau margin
  • Escarpment face
  • Footslope
  • Low Terrace Bench
  • Valley Floor


4.3.3 GEOLOGY

The valley sides expose the sequence of Upper, Middle and Lower Chalk and these soft limestones are covered with various Drift Deposits.

The Upper Chalk is hard, white with flints. The Middle Chalk lacks the flints and the Lower Chalk is softer, grey and contains a high proportion of clayey material.

The Drift deposits include:

Clay-with-flints, occurring on the highest areas of the woodland on the edge of adjoining the Chalk Plateau surfaces. This reddish brown clay is thought to have been derived from interglacial weathering of the Reading Beds and particularly by the downward movement of clay particles onto the Chalk/Reading Beds interface.

Coombe Deposit, a compact silty and chalky deposit occurring on chalkland valley floors and derived from the downslope accumulation of frost shattered chalk fragments during late glacial times.

Clayey Drift, occurring above the Coombe Deposit on the valley bottom and low terrace features and most likely to have been derived from the erosion and downward accumulation of clay-with-flints material.

Silty Drift, a brownish and often flinty silty clay loam that thinly covers all other deposits to a depth of between 10 and 60cm.

4.3.4 THE SOILS AND VEGETATION

The soils are well drained and acidic on the plateau surface, well drained and alkaline on the chalk escarpment face and seasonally or permanently waterlogged and neutral on the terrace bench and valley floor.

The soils of each landscape facet are described below together with the soil series and soil classification subgroup a used in publications of the Soil Survey of England and Wales.

Plateau soils

Well drained very acidic with silty topsoils over reddish clayey subsoils over chalk at depth (Carstens series, Typical paleoargillic brown earths).

These soils are typical of the Hampshire ‘clay caps’ and have the reddish acidic subsoils typical of interglacially weathered soils. Silty upper layers are assumed to be of windblown (loessial) origin.

The acidic soils tend to support a calcifuge flora and much of this land has coppiced beech (probably planted) with some pedunculate oak, birch, hazel, holly with wood sorrel, foxglove, honeysuckle, bramble, broad buckler fern and bracken

Plateau margin soils

Well drained moderately acidic with silty or clayey topsoils over reddish clayey subsoils over Chalk at 40-80cm depth (Porton and Winchester series, Typical paleoargillic brown earths).

These soils are typical of the thinning edges of the clay-with-flints and have similar profiles to the Carstens soils but are shallower over chalk and in places (especially on slopes), the upper silty layer may be absent.

These soils have a wider variety of plants including the calcifuge species typical of the plateau as well as more moderately calcicolous species more typical of the escarpment face. This variety reflects the variable and generally slightly higher pH and shallow depth to chalk. The more calcicolous species include ash, field maple, dog’s mercury, sanicle and sweet woodruff.

Chalk Escarpment soils

Mostly well-drained neutral to alkaline shallow calcareous soils over chalk within 40cm. Some soils with clayey topsoils and most with thin humose, brown or chalky silty topsoils (Wallop, Andover, Icknield and Upton series, Brown, humic and grey rendzinas).

These are the soils on the main steep chalk escarpment face and comprise a mosaic of shallow soils, all with chalk or very chalky material within 40cm depth and often much shallower. Brown silty Andover soils are the most common, but in places where organic matter has accumulated there are Icknield soils thin dark humose topsoils. Where erosion has removed the surface layers, the soils are very chalky with thin pale extremely calcareous topsoils. On the uppermost escarpment face, the soils often have thin clayey topsoils derived from the clay-with-flints above (Wallop soils).

Much of the escarpment face has thick calcicolous yew woodland below beech and whitebeam with field maple, ash, hazel, holly, wych elm and clematis and a range of herbs typical of such woodlands on chalk.

Footslope soils

Well-drained neutral to alkaline calcareous shallow loamy soils over Lower Chalk (Wantage series, Grey rendzinas).

These soils are typical of the steeper slopes on grey Lower Chalk and where the solid chalk is often obscured by up to 80cm depth of extremely calcareous chalky drift.

The vegetation is generally similar to that of the escarpment face but can be more varied with a greater range of species, perhaps because of the greater rooting depth and more moisture retentive conditions. Typical species include field maple, ash and hazel coppice, wych elm, elder, beech and yew over dog’s mercury, yellow archangel, wood spurge, woodruff, large lords and ladies, ivy, clematis and male and hart’s tongue ferns.

Terrace bench soils

Moderately well drained neutral calcareous silty over clayey soils with slight seasonal waterlogging over drift deposits and with Lower Chalk below 80cm depth (Winterbourne series, Stagnogleyic brown calcareous earths).

These are unusual soils in the East Hampshire chalk escarpment and occur on a small area of gently sloping land which appears as a terrace-like feature. The soils are calcareous and grey mottling indicates a degree of impeded drainage and winter waterlogging, perhaps arising from seepages at the Middle and Lower Chalk interface.

Valley floor soils

This a complex area with a range of different soils that are unusual in these woodlands. They tend to be deeper than higher on the slope and provide a gradation of well drained soils on gentle slopes passing to wetter soils on valley bottom.

The lower slopes (in the absence of the terrace feature) have moderately deep well-drained neutral calcareous silty topsoils and subsoils over chalk rubble (Coombe Deposit) (Panholes series, Typical brown calcareous earths). These soils are typical of the sloping floors of valley heads of dry valleys and coombes on chalk escarpments.

Some lower-most slope areas have somewhat similar soils but there can be a clayey subsoil layer below the silty topsoils before reaching the chalk rubble (Yatesbury series, Typical brown calcareous earths).

In places the soil profiles lack the silty layers and are more clayey with chalky rubble within 80cm depth. These soils tent to have slight impeded drainage and very slight seasonal wetness (Blewbury series, Typical brown calcareous earths).

The lower-most valley floor has deep silty clay loam seasonally waterlogged soils on a thin strip of water lain alluvium. These soils are strongly grey and orange mottled and in places have humose topsoils, all indications of prolonged waterlogging during the winter and spring. (Thames series, Calcareous alluvial gley soils).

The drier well-drained soils support calcicolous woodland with ash and hazel coppice, dogwood and with a wide range of ancient woodland herbs typical of drier deep calcareous conditions.

As the soils become wetter there are other species typical of more moisture retentive and more wetter conditions. Such species include sallow, bugle, opposite-leaved golden-saxifrage (often luxuriant), cuckoo-flower, pendulous sedge and wood sedge.

Case Study 4.4 Crab Wood SSSI Sparsholt, Winchester, Hampshire

4.4.1 Introduction

Crab Wood (SU 438298), owned by Hampshire County Council and about 3 miles west of Winchester, is a fine example of ancient woodland and is both a Site of Special Scientific Interest and a Local Nature Reserve. The site has over 80 hectares (200 acres) of broadleaved woodland, hazel coppice with oak/ash over-storey, and rich with woodland flowers.

Crab Wood is part of Farley Mount Country Park, a 530 hectare (1300 acre) woodland and downland site, managed in conjunction with Forest Enterprise and the Hampshire and Isle of Wight Wildlife Trust.

The woodland is divided into a western part and an eastern part by the north-south Sparsholt Road

I visited Crab Wood in December 1984 describing the soils from 26 hand auger borings, and took ten topsoil samples for pH determination. Vegetation was described from quadrats around each auger boring. My draft report on ‘The soils and edaphic relations of Crab Wood’ was prepared early in 1985 and never completed. The information here is extracted from the draft report.

4.4.2 Relief, Geology and Drainage
Crab Wood has mostly gently or moderately sloping land and is within the central Hampshire Chalklands. While the substrate is Upper Chalk, gently sloping land is covered by silty and clayey Plateau Drift (Head and Clay-with-Flints). On valley sides, the Chalk is covered with thin silty drift (Head). Minor valley bottoms are infilled with thick silty drift.

Surface water mainly infiltrates into the Chalk and the valley system is dry.

4.4.3 Soils and Mapping Units

The soils are all well-drained, silty or silty over clayey and most overlie chalky rubble or Chalk at moderate depth less than 80cm or at shallow depth less than 30cm.

The site is divisible into three topographic units, each with a distinctive suite of contrasted soils and described in the next section.

4.4.4 Soils of the Map Units

Map Unit 1 Porton-Carstens-Garston Association

The most extensive area of the site with well drained non-calcareous silty over clayey or deeper silty soils developed in Plateau Drift (Head and Clay-with-Flints) over Chalk at 40-85cm depth occurring on gently sloping and level land on interfluves.

The soils have non-calcareous silty and sometimes flinty upper horizons overlying reddish clay and with chalky calcareous horizons at depth. The clayey subsoils have red and orange mottles typical of weathering during previous warm temporate interglacial climatic conditions (ie. they represent fossil soils or ‘palaeosols’). The silty upper layers are more recent and typical of having been deposited and weathered during the last glacial period and into the present Post-glacial period.

This association covers the level to gently sloping land occupying the higher northern and northeast areas of the land west of the Sparsholt Road and most of the eastern part of the reserve other than the small area of sloping land in the very south and just north of Crabwood House.

Description:
Well-drained, moderately deep or deep non-calcareous silty over clayey, or silty soils, overlying Chalk at 40-85cm depth.
Geology:
Plateau Drift and Head over Chalk or Chalk rubble
Soil Series and classification
Porton Series, Typical palaeo-argillic brown earths
Well-drained, moderately deep, non-calcareous flinty silty over clayey soils.
Carstens Series, Typical palaeo-argillic brown earths
Well-drained, deep, non-calcareous flinty silty over clayey soils.
Garston Series, Typical argillic brown earths
Well-drained, moderately deep, non-calcareous flinty silty soils over Chalk.


Map Unit 2 Andover-Panholes Association

This area occupying moderately sloping valley sides in the southern part of the site has well-drained calcareous silty soils developed in thin silty drift (Head) over Chalk at 25-80cm depth. Two soil series identified.

This association covers land between Map Unit 1 and the southern boundary along the Roman Road.

Description:
Well-drained, shallow or moderately deep calcareous silty soils, over Chalk.
Geology
Silty drift (Head) over Chalk or Chalk rubble
Soil Series and classification
Andover Series, Brown rendzinas
Well-drained, shallow, calcareous silty soils over chalk.
Panholes Series, Typical brown calcareous earths
Well-drained, deep, non-calcareous flinty silty soils over chalk at depth.


Map Unit 3 Charity Association

Well-drained deep non-calcareous silty soils developed in silty drift and confined to a single narrow valley floor in the west of the site. One soil series identified.

Well-drained, deep, non-calcareous flinty silty soils.
Geology
Silty drift (Head)
Soil Series and classification
Charity Series, Typical argillic brown earths
Well-drained, deep, non-calcareous flinty silty soils.

4.4.5 Topsoil pH

Topsoil reaction varied from alkaline to very acid with the highest pH values associated with the calcareous Andover and Panholes soils in Map Unit 2. Garston and Porton soils with non-calcareous upper horizons over Chalk were mostly neutral to moderately acid, while the deep non-calcareous Carstens soils were moderately to very acid.

Measured pH ranges (air dried soil determined in 1:2.5 water) were as follows:

Map Unit 2 Andover series 1 sample 8.0
Panholes series 2 samples 7.6-7.8

Map Unit 1 Garston series 1 sample 6.7
Porton series 6 samples 5.3-7.6
Carstens 2 samples 4.6-4.7

4.4.6 Edaphic Relations

Trees, shrubs and herbs were recorded from 1x1m and 30x30m plots around each of the soil auger borings and were divisible into five stand types (Peterkin 1980, 1981).

Ash-maple woodland (group 2) and Hazel-ash woodland (group 3) together occupied most of the soil auger boring locations. Coppiced hazel predominated in those stands occupied by Andover, Porton and most of the Garsten soils.

Birch-oak woodland (group 6) occurred mainly on the deeper acidic Carstens soils with a ground flora dominated by bramble and often with bracken

The calcareous Andover and Panholes soils with alkaline topsoils in Map Unit 2 in the south of the wood had mainly southern calcareous hazel-ash woods with some dry ash-maple woods. The ground flora was dominated by dog’s mercury with primrose, wild strawberry and others.

The non-calcareous silty over Chalk profiles of the Garston soils with neutral topsoils had mainly the light form of acid pedunculate oak-hazel-ash woods with a flora sharing the characteristics of the more alkaline and the more acidic soils.

The more acidic Porton soils had mostly dry ash-maple woods whereas the deeper Carstens soils with very acid topsoils had lowland hazel-pedunculate oakwoods.

4.4.7 Discussion

Crab Wood SSSI includes most of the soils characteristic of the central Hampshire Chalklands where there is only a thin cover of Plateau Drift over Chalk at shallow or moderate depth. The soils appear to be uncultivated.

West of the Sparsholt Road, the wood contains both shallow calcareous soils on Chalk and non-calcareous soils on Plateau Drift (Map Units 1, 2 and 3). East of the road, most of the soils are on Plateau Drift at moderate depth (Map Unit 1) with calcareous soils (Map Unit 2) confined to the extreme south.

The calcareous soils in Map Unit 2 (in the south of the wood) have alkaline surface horizons in contrast to the non-calcareous soils and which are neutral to very acid in their surface horizons.

The large area of non-calcareous soils in Crab Wood contrasts with the mainly calcareous soils in Winterdown Copse and North Park Wood and which sites together contain a range of shallow chalkland soils with none of the deep non-calcareous soils over Plateau Drift characteristic of the East Hampshire Chalk Plateau where there is no current woodland SSSIs.

A copy of the full draft report is being placed in the Hampshire Biodiversity Information Centre (HBIC) at Hampshire County Council.




5. SOIL AND WATER IN THE HAMPSHIRE WEALD

Case Study 5.1 The Greensand Hangers

5.1.1 INTRODUCTION

Forming a ring around the Wealden Edge in East Hampshire District, is a remarkable double escarpment. The upper and larger escarpment is that of the Chalk and lower and smaller escarpment is that of the Upper Greensand. Both escarpments are wooded, but the Upper Greensand escarpment has the wider range of woodland and soil types. The main wooded escarpment is between.

I visited many of the privately owned Greensand Hangers during 1987 in order to prepare a report on their geology, soils and vegetation for the East Hampshire Hangers Project and whose project officer at the time was John Ockendon based at East Hampshire District Council. The area examined was between the villages of Selborne in the north and Steep in the south.

5.1.2 SOILS

The East Hampshire Hanger woodlands (especially those on the Upper Greensand) were found to contain a remarkable range of contrasted soil types within very close proximity. These range from deep loamy soils to very thin soils directly over rock, from well-drained to seasonally waterlogged soils and from those on chalk to those on sandstone and on clay. Acidic and alkaline conditions can occur within a metre distance. These often rapidly changing conditions, in a varied and often land-slipped environment, explain the complex vegetation patterns found in these remarkable woodlands.

Descriptions were made of the following woodlands:

Moor’s Copse, Hawkley
The Slip, Hawkley
Farewell Hanger, Hawkley
Coombe Hanger, Hawkley
Longmead Copse, Hawkley
Wheatham Farm Woods including Roundabout Copse, Hazel Holt Copse and Naps Copse
Wheatham Farm Woods Main Wood
Mabbot’s Woods including Adam’s Wood, The Beeches and Crabtree Copse
Down Hanger, Hawkley
Oakshott Hanger, Hawkley
Juniper Hanger Hawkley

Descriptions to be added.

Case Study 5.2 Shortheath Common

5.2.1 INTRODUCTION

Shortheath Common (SU773365) is another magical spot, an area of heathland, open water, and acidic woodland surrounding a one time lake now covered by a floating layer of peat. The peat supports a spectacular floating Sphagnum bog with what is described in the Flora of Hampshire as having what is probably the largest population of cranberry in southern England.

I examined the area of the floating mire for Hampshire County Council towards the end of 2003 undertaking about 200 auger borings across the mire basin and taking seven water samples for analysis. These notes summarise the fully illustrated report.

The whole site is an SSSI and also a Special Area of Conservation (SAC) selected on the basis of Transition Mires and Quaking Bogs. The site owned by the Council and managed for nature conservation and public access.

The mire is variously covered with soft Sphagnum and Polytricum through which it is very easy to fall into the water below. There are also seasonal pools of open water, a permanent pool, and areas of wet bog woodland.

The hydrological system is remarkable in the Hampshire context and floating mires of the type found here are uncommon in lowland England.

5.2.2 TOPOGRAPY

The mire, at 75mAoD, is set into a shallow bowl shaped re-entrant cut into the eastern slopes of a high ridge rising to 85mAoD and has an outlet into the Kingsley Stream to the east at about 70mAOD.

5.2.3 GEOLOGY

The deposits below Shortheath Common comprises yellow and orange sandstones that weather to loose sand at the surface. The mire is directly underlain by sandy Head deposits laid down following Ice Age erosion of the upslope deposits.

5.2.4 HYDROLOGY

The present day fishing lake, Shortheath Pond, appears to have been cut out of the mire and has been extended into the mire at various times. Historically, the lake was joined to a series of marshy areas by drains although these are difficult to find today. Now the land between the marsh and mire has been built up with chalky material to form a rigid peninsular used by fisherman. This peninsular has substantially and hydrologically separated the mire from the lake. There is no clear flowing inlet and so the whole system is thought be groundwater fed.

An outfall drain is controlled by a modern weir and flows in a rather poor and (fortunately) silted channel to the Kingsley Stream. The small pond in the northeast of the mire area is at least 1.5m deep, appears to be relatively new, and is being grown over with floating Sphagnum bog-mosses and Polytrichum hair-mosses making the margins very difficult to access.

The main mire basin is up to 1.9m deep in places. The basin floor is highly irregular with three deeper areas. Where the basin floor undulations rise to the surface they form small heathy islands. In the southeast, the basin edge rises steeply suggesting an artificial margin.

A central tract of water appears to flow slowly across the deeper part of the mire. This originates in the west of the site as a series of shallow pools which coalesce into an area of wet willow bog woodland. Road runn-off is directed to this area. From here, the tract passess across the mire as a series of irregular pools. Water in the tract tends to be neutral as opposed to the acidic character of the main mire.

5.2.5 PEAT AND MINERAL SOILS

The mire basin is filled with mostly highly fluid watery peat and which at the surface grades into about 0.3m of only slightly firmer raw Sphagnum peat. The peat becomes humified and firmer where shallow towards the edges and directly underlain by the sandy substrate.

The better drained mineral soils have not been examined in detail but are generally sandy and sometimes podzolised. Of the wetter soils, there is a range from seasonally waterlogged wholly mineral soils to those with surface peaty layers up to 40cm thick and which are permanently wet. Most of the wetter soils are affected by groundwater rather than surface water.

The main survey report describes the soils of the different mire plant communities in more detail.

5.2.6 HYDROCHEMISTRY

Seven water samples were taken from flooded areas and open waters and determined for a wide range of nutrients and chemical parameters.

Water in the main fishing Shortheath Pond had a pH of 6.6-6.7 and this pond may have been limed in the past. Phosphorus levels were low, but nitrogen levels were relatively high. The outflow from the pond is more acidic suggesting interchange with the mire. Total phosphorus levels were higher than in the Pond although soluble phosphorus levels remained low.

The small pond at the edge of mire had a pH value of only 4.1 and so is strongly acidic.

The mire surface was too dry to sample, but the outflowing stream was moderately acidic at pH 5.4.

Wet pools at the upper end of the water tract had a slightly acidic pH value of 6.5 suggesting that the groundwater inflow into the mire was not strongly acidic. It is thus likely that the source of the acidity in the mire is the result of the hydrogen exchange capacity of the Sphagnum cover.

5.2.7 DISCUSSION

The mire vegetation is simply growing over a water column that may contain some suspended peat material and which is of variable depth. Lack of significant peat deposition suggests that the mire system is very young.

The mire is fed by circum-neutral or slightly acidic groundwater flowing into a valley side basin-like hollow and derived from a small catchment to the northwest. Water in the mire is retained by encircling higher land and which has only a single outlet serving both the mire and the main pond. Water exchange between Shortheath Pond and the mire is now reduced by the modern causeway.

The mire characteristics relate more to open water than peatland with exchange of water to the atmosphere and chemical characteristics controlled by the thin surface layer of floating peat. The acidity being generated by the Sphagnum bog-mosses.

Because the mire is fed by groundwater, it should technically be considerd a fen rather than a bog (which would be rainwater fed). Nutrients in the system are primarily derived from the surrounding catchment.

The mire system probably started as a slightly acidic body of open water retained in a shallow basin and modified by man to enclose more water than it would naturally do. Shortheath Pond has probably been dug out of the mire to create a large area of open water.

A full reference list is provided in the main report.



Case Study 5.3 Petersfield Heath

5.3.1 Introduction

Petersfield Heath is an area of heathland, acid grassland and open water on the southeast margin of Petersfield Town. The land is owned and managed by Petersfield Town Council assisted by the Friends of Petersfield Heath and Petersfield and District Angling Society. While the site contains wildlife habitats that meet the criteria for Sites of Special Scientific Interest, it is currently designated in the Local Plan as a non-statutory Site of Importance for Nature Conservation. None-the-less, the site is of outstanding interest for its landscape, heathland and acid grassland habitats and is valuable public open space. For about 100 years up to 2000 much of the site had been managed as golf course. Today it is managed for wildlife conservation.

Ron Allen undertook a study of the geology, hydrology, soils and edaphic relations in April 1993 for Hampshire County Council as a background study for site management proposals.

5.3.2 A diverse landscape

The historic landscape of Petersfield Heath is in the southwest corner of the Weald, an area of sandy, loamy and clayey land between the North and South Downs. Heath Pond is at the head of a small valley eroded into high land between two tributaries of the Rother, the outflowing stream running down the bottom of the valley and the heathland rising up the valley sides.

The upper slopes are on gravel terraces which surround the Heath on three sides like a horseshoe and on which run Heath Road and Sussex Road. The valley bottom is at about 54m above sea level, Heath Pond at about 56m and Music Hill rises to about 60m. The landscape is further diversified by the many Bronze Age barrows and the remaining golf course structures.

5.3.3 Geology

There was a borehole close to the old golf clubhouse. This extended to 8.3m depth and revealed 1m of gravel terrace deposits over sands and clayey sands of the Pulborough Sandrock.

The geology of the wider area is more complex. The youngest deposits are called Head and cover the lower parts of the land having slipped downhill during melting of frozen ground at the end of the last Ice Age.

The deeper rocks are all marine and Cretaceous in age. Because the deposits slope to the south at about 2-3 degrees from horizontal, different strata appear at the surface in different places. The oldest strata, the Sandgate Beds, underlie the Cricket Ground and surrounding woodlands. Here the upper and lower Marehill Clay, separated by a sandy layer, occur. The wetter clayey nature of the land here may explain why woodland has been allowed to develop. The central and southern parts of The Heath are underlain by sands and soft sandstones of the Folkestone Beds. In the very south of the site, on higher ground, is the feather-edge of the youngest stratum, the Gault Clay, and this may explain why small pools form in low-ways here after heavy winter rain.

5.3.4 Hydrology

Groundwater on The Heath is ‘perched’ on the gently sloping surface of the Marehill Clay and rises through the Folkestone Beds aquifer into Heath Pond and into the east flowing outlet stream. There is no inlet stream.

Heath Pond is an extensive but shallow lake and which has been dredge twice during the 20th Century. The Pond is thought to have been dug in the 18th Century to merge a series of wet pools on safety grounds. In March 1993 water in the pond had a neutral reaction with pH values of between 7.0 and 7.1.

The outlet stream leaves the pond via a sluice, passes through and out of the site and passes eventually to the River Rother. From the sluice the stream has been piped below a landscaped area formed from previous bunded lagoons and then into a straightened channel devoid of meanders or other natural features. In March 1993, water in the stream had a pH value of 6.3, slightly more acidic than the Pond suggesting interception of acidic groundwater off heathland.

Low-lying areas of Petersfield Heath, east of the Pond are drained by small shallow grips. Areas of springs close to the main car park had water in March 1993 with a moderately acidic pH value of 5.2.

Spring and seepage water arises at the junctions of the various clayey and sandy strata, the main spring being near the Nursery Car Park and which still flows in very wet conditions.

5.3.5 Soils

During the survey of The Heath, forty three 1.2m deep auger borings revealed six main soil types divided into three main groups, ‘podzols’, ‘surface water affected soils or surface water gley soils’ and ‘groundwater affected soils or ground water gley soils’.

The main soils, Podzols, are thought to have been created where woodland was cleared in the Bronze Age followed by several thousand years of leaching under heathland management. On drier land at Petersfield Heath, well-drained podzols have thin black topsoils over subsoils with pale lilac grey leached upper layers over black or brown layers over orange sandy substrates. Where the leached layers and are thin over clay, water is held in the surface layers forming seasonally waterlogged ‘stagnogley podzols’. On lower land, ground water can rise up into these soils creating ‘gley podzols’.

Two sub-types of clayey soils occur over the Marehill Clay. One type has sandy upper layers over clay and has regular winter waterlogging because the water cannot easily drain away. The other type has thin organic layers over loam and clay and which remain wet for most of the year.

Finally, there are two types of soils affected by rising groundwater such as around the Pond and stream. One type has dark humus-rich topsoils over strongly grey and orange mottled sandy subsoils indicative of prolonged waterlogging. The other type has wet peaty topsoils over permanently waterlogged sands.

Most of these soils are strongly acidic with pH values between 4 and 5. Some of the old fairways had slightly higher values and areas with brick rubble were slightly alkaline.


Reference:

The Heath – Petersfield: Geology, hydrology, soils and edaphic relations with special reference to heathland restoration. Ron Allen Associates for Hampshire County Council, 1993.

6. SOIL AND WATER IN THE HAMPSHIRE PART OF THE LONDON BASIN

Case Study 6.1 Fleet Pond and Surrounds

Case Study 6.2 Bramshill Forest

Case Study 6.3 Odiham Common


7. SOIL AND WATER IN THE HAMPSHIRE BASIN

Case Study 7.1 Wickham Common

Case Study 7.2 The Moors, Bishop’s Waltham

7.2.1 INTRODUCTION AND BRIEF

I have visited The Moors, Bishop’s Waltham, on a great many occasions, initially undertaking soil and hydrological surveys and installing dipwells and later undertaking studies examining the effects of water abstraction from nearby water company boreholes. As with Emer Bog, The Moors has been a regular location for hydro-ecological training courses. I know the site very will indeed.

The Moors, Bishop’s Waltham SSSI It lies at the very northern edge of the Hampshire Tertiary Basis and receives water from a series of artesian springs which flow out of one-time watercress into a series of watercourses flowing across a large area of damp mineral soils and fen peatland.

There are many surprises on site, from the upwellings creating moving swirling sandy circles in some stream beds, through highly calcareous springs depositing tufa, to areas of acidity with Sphagnum bog-mosses and the occasional tuft of cross-leaved heath. The soils are remarkable varied with drier and wetter mineral soils, some on Reading Beds clays but most on chalky and flinty Head deposits off the nearby chalk slopes. The fen peat deposits sit on this chalky Head which effectively prevents the upward flow of chalk groundwater into the site except at certain locations where the strata appear to be more sandy and permeable. The fenland fauna and flora is quite remarkable with no real parallels anywhere else in the UK.

Perhaps no-where else in Hampshire are the underground soil and hydrological site characteristics so important for understanding the ecology of the site.

The main semi-natural part of the site is owned by Hampshire County Council and managed by Peter Potts, Hampshire’s Countryside Sites Ranger and my thanks are due to Peter for his continuing enthusiasm for evermore knowledge of the reserve. Adjacent land in the The Moors hydrological system is in private ownership and my thanks go these landowners for access to their land.

7.2.2 THE MOORS SSSI

Some background

Studies at The Moors have been commissioned at various times by Hampshire County Council Countryside Department, partly funded by the County and partly by the Environment Agency. The work has been assisted considerably by Pete Potts who is responsible for so successfully managing the county owned part of this remarkable site and Local Nature Reserve. My thanks also go to the other landowners who manage other parts of The Moors hydrological system.

The Moors SSSI, at Bishops Waltham, is a nationally (if not a European) significant tract of alkaline wetland and open waters located south of the Chalk outcrop in southern Hampshire at the head of River Hamble displaying a good diversity of habitat types, plant and animal communities and rare species. As a result, not only is the majority of the site designated as a Site of Special Scientific Interest (SSSI) under the UK Wildlife and Countryside Act, but also as a Nature Conservation Review (NCR) site, in recognition of its special national interest.

The land comprises some 34ha mainly of hydrologically sensitive fen, fen meadow and wet woodland dissected by a series of south and west flowing streams and drains totalling some 1265m in length. Some of the drains originate from one-time watercress beds fed by clear chalk water springs and feed into either the Western Stream arising off the ‘Sand Boils’ or the Eastern Stream arising off Alexanders Moors. Both streams flow into Waltham Mill Pond and from where the water passes to The Moors Stream, a headwater of the River Hamble. The ‘Sand Boils’ is an area at the head of the West Stream in which upwelling spring water creates swirling sandy patches in the gravelly streambed.

Until recently, the adjacent pumping station was known to dramatically lower the chalk water table leading to reduced spring flow and drying of large parts of the site. Fortunately, pumping has now ceased and the future of the site is secure.

Topography

The major part of the SSSI comprises a shallow basin-shaped structure, open to the south and linked to a small valley system in the east. Land within the nature reserve rises gently from about 28m AOD in the southwest at the Mill Pond to a maximum of 35m AOD in the northeast, an overall change in relief of about 8m over a distance of 400m. A dry valley feeds into The Moors from the northwest within the built up area of Bishop’s Waltham. A further wet valley feeds into and through The Moors from the southeast, arising at Alexanders Moors.

7.2.3 GEOLOGY

The Moors is located at the northern edge of the Hampshire Tertiary Basin where it abuts the Chalk dipslope, and where the strata dip to the south at about 5 degrees. Detailed surveys (Ron Allen 1982, 2003) have shown that The Moors is underlain by a variety of drift deposits overlying the Reading Formation as follows:

Drift Deposits
Calcareous tufa and marl
Peat
Freshwater alluvium
Chalky Head
Flinty Head

Solid Deposits
Reading Beds
Upper Chalk (at depth)

The Reading Beds are overlain by Flinty Head and Chalky Head in an irregular mosaic. It is likely that the flinty material is derived from erosion of the Clay-with-flints and/or from decalcification of the Chalky Head. The Chalky Head is most likely to be derived from late glacial erosion of land on the Chalk dipslope and subsequent downwash and slumping.

Black amorphous peat, up to 1.75m deep, occurs especially towards the centre and lower parts of the nature reserve area where it almost always overlies very compact and only slightly moist Chalky Head. Thin loamy and chalky layers within the peat suggest that sporadic mineral sedimentation occurred during peat accumulation.

Freshwater alluvium is restricted to a narrow band of clayey material along the flood plain of the Eastern Stream. White or pale brown highly calcareous soft marl occurs locally being up to 60cm thick and often containing hard nodular calcareous concretions. This material is thought to have infilled former stream channels or pools. Nodular tufa is still being precipitated in streams on the site.

The Reading Beds directly overlie an eroded Chalk surface and comprise mostly brightly mottled clays and silty clays but include lenticular bodies of fine to medium-grained sands and loamy sands as well as interbedded sands and clays at various levels.

A borehole close to the Sand Boils drilled in September 1996 showed 9.5m of mainly light or dark grey clayey material over chalk but with a running sand layer from 6.0 to 7.5m depth.

7.2.4 SOILS

Soils have been examined in detail (1992 and 2002) across The Moors and adjacent areas and are surprisingly varied with 25 distinct soil profile types identified to date according to their underlying geological substrate and surface lithology, hydrology, and their landscape position.

Soils over most of The Moors are very poorly-drained and affected by either high groundwater perched over slowly permeable Chalky Head and Reading Beds at shallow depth or by impeded drainage where permeable surface deposits are absent or of negligible depth and slowly permeable substrates are within 0.5-1m of the ground surface.

The soils at The Moors can be divided into:

Mineral soils: on Flinty and Chalky Head and Alluvium;
Carbonatic soils: on calcareous Tufa and Marl;
Organic soils: on humified Peat.

These in turn can be divided into soils with different drainage regimes (areas also given):

Well-drained soils on the adjacent chalk dipslope
Moderately well-drained soils with impeded drainage (c.6.3ha)
Poorly-drained land affected by impeded drainage (c.10.8ha)
Very poorly-drained land affected by impeded drainage and likely to include some land directly affected by high groundwater(c.6.7ha)
Soils affected by high groundwater, mostly perched(c.8.8ha)

At The Moors, 8.8ha of land is directly affected by high groundwater, although most of this is perched over slowly permeable geological materials. A further 6.7ha of land is very poorly-drained and has upper peaty soil layers that are waterlogged for most of the year and likely to be in hydrological continuity with the land affected by high perched groundwater. The moderately and poorly-drained soils (totalling17.08ha) are affected primarily by surface water rather than groundwater.

About 15.5ha of land remain waterlogged for much of the year and most of this will either be directly due to perched groundwater or is likely to have a significant groundwater component. A detailed description of the individual soils can be found in Allen (2002).

7.2.5 HYDROLOGY

The Moors comprises the wetland area fed by springs and surface watercourses within the SSSI and adjacent land and which discharge into the Waltham Mill Pond. Water from the mill pond passes through Chase Mill and then downstream as The Moors Stream tributary to join the Northbrook Stream tributary of the River Hamble.

There appears to be no significant external surface-water catchment for the wetland area. This is because the higher land is well-drained and capable of absorbing rainfall and passing it directly into the underlying chalk aquifer. There are several storm drains off nearby housing that flow into The Moors and have caused local pollution events despite the presence of oil interceptors.

Around the edge of the wetland area are a series of twenty two spring fed pools and damp areas (some being one-time cress beds) with outlet streams feeding either into a western system or into an eastern system joining at the Mill Pond. The ‘Sandboils’ represent a source of more-or-less permanently upwelling water at the head of the Western Stream.

7.2.6 HYDROGEOLOGY

The Chalk, which crops out to the north of The Moors SSSI and passes below the site at depth, is a fine-grained white rock and which stores and transmits water. Water mainly moves in fissures throughout the Chalk creating an important regional aquifer and supplying water to springs and streams. Water from the Chalk is abstracted for public water supply.

The Chalk here responds naturally to annual recharge as seen at local boreholes and which in the past was impacted by abstraction. The Reading Beds and the overlying compact chalky head appear to restrict the upward flow of groundwater into the wetlands.

Most of the spring heads are on the fringes of the Reading Beds where these strata are thin. In contrast, the springs at the Sand Boils are known to occur over a thickness of 9.5m of Reading Beds over Chalk. Here, water wells up through sandy deposits at the head of the Western Stream. Similar upwelling waters can be seen at other springs in the Eastern System. Upwelling springs here are likely to be linked to areas of solution subsidence or water saturation in the Reading Beds.

7.2.7 HYDROCHEMISTRY

Analysis of water samples in 1992, indicated that the surface waters were mostly circum-neutral or slightly alkaline (pH 7.1 to 7.5) but with extremes of 6.7 (very slightly acidic) and 8.1 (moderately alkaline). The waters were high in calcium and bicarbonate and had moderately high levels of phosphorus, potassium and nitrate nitrogen. Such waters are typical of hyper-eutrophic calcareous conditions and would be expected to support high plant productivity. Typical chalk streams lack the high phosphorus levels found at The Moors and so there are processes acting on the water after it arises from the chalk and passes through the Reading Beds.

More detailed studies in June 2002 indicated that the pH values of the watercourses were generally between 7 and 8.2 with high calcium bicarbonate levels and high alkalinity. Nitrogen and Phosphorus levels were generally high, indicative of highly productive water systems. The source of high nitrogen and phosphorus levels may arise from external groundwater sources.

These high plant nutrient levels suggest that the habitat is eutrophic rather than oligotrophic. The high levels of nitrogen and phosphorus in some water samples are cause for concern and may be the cause of an algal bloom observed in summer 2002.

7.2.8 DISCUSSION AND SUMMARY

Wetlands at The Moors are supported by groundwater perched within peat deposits over underlying compact Head deposits and Tertiary clays. In contrast, open waters are supported by spring fed sources.

It is suggested that groundwater rises by artesian pressure into the northern margins of the site through limited areas of sandy strata within the feather-edge of the Reading Beds associated with solution hollows in the Chalk. This process leads to the development of the boundary springs fed by upwelling water. This water flows into a variety of drains and watercourses and so passes slowly towards the mill pond. The slope on these drains is slight and water seeps out of the drains laterally into the more permeable peat deposits.

The clayey nature of the substrate (which is almost dry or only slightly moist when augered) prevents any effective upward rise in water from groundwater in the chalk. Similarly, water cannot drain effectively downwards. This means that the whole wetland site is dependent upon locally upwelling groundwater.

The Moors SSSI is vulnerable particularly to adverse changes in artesian fed water supply, to enhanced nutrient levels off adjacent land, and also to the risk of pollution from off adjoining developed areas.

Wetlands at The Moors SSSI are dependent upon water held within peat deposits and derived from the underlying chalk aquifer. Water cannot rise directly into the site because of the slowly permeable and compact substrate and so all water here is likely to be perched. The source of the water arises from artesian springs fed by chalk groundwater rising through sandy lenses in the Reading Beds in areas affected by local solution subsidence in the Chalk. This artesian water flows along streams and spreads laterally into the peat deposits.

Water at The Moors is calcareous and locally causes deposition of nodular calcareous tufa. The open waters are also rich in total phosphorus and especially with inorganic nitrogen and these levels are also reflected in the groundwater chemistry. Soluble phosphorus however, is low in the groundwater. The source of high levels of total phosphorus, and particularly of nitrogen, appear to be related in part to flows off agricultural land adjacent to the head of eastern stream at Alexanders Moors and this can also have an adverse ecological effect.

7.2.9 REFERENCES

Allen R (1992) The Moors Nature Reserve: Geology, Hydrology, Soils and Edaphic Relations of the Wildlife Habitats. Report for Hampshire County Recreation Department.
Allen R (2002) Soils and Substrates of The Moors, Bishop’s Waltham, and adjoining areas. Draft report for Environment Agency and Hampshire County Council.
Allen R (2002) Water Chemistry: The Moors, Bishops Waltham and adjoining areas. Draft report for Environment Agency and Hampshire County Council.
Allen R (2004) Environmental Report on the The Moors SSSI drawing together ecological and hydrological data in relation to Hoe Pumping Station for Environment Agency and Hampshire County Council.
Allen R (2003) Soil Fertility: the Moors SSSI and adjoining areas, Bishop’s Waltham, Hampshire. Draft report for Environment Agency and Hampshire County Council.
Environment Agency: Water quality Guideline Phosphorus standards for SAC Rivers (see WQTAG048b 29th August 2002).
Lake R D et.al. Geological Report, The south-east Hampshire District: Fareham and Surrounding Areas. British Geological Survey 1985.
SSSI and NCR citations.
Environment Agency: General Quality Assessment of Rivers 2002.
Environment Agency: Phosphorus standards for rivers in England and Wales Pitt J, Phillips G and Mainstone C. 2002
Newbold C and Palmer M A (1979) Trophic Adaptions of Aquatic Plants, NCC CST Notes No. 18.
Palmer M A, Bell S L and Butterfield I (1992) A botanical classification of standing waters in Britain, applications for conservation and monitoring, Aquatic Conservation: Marine and Freshwater Ecosystems, Vol 2 125-143.
Palmer M A and Roy D B (2001) A method for estimating the extent of standing fresh waters of different trophic state in Great Britain, Aquatic Conservation: Marine and Freshwater Ecosystems Vol. 11 199-216.
Palmer M A and Roy D B (2001) An estimate of the extent of dystrophic, oligotrophic, mesotrophic and eutrophic standing freshwater in Great Britain, JNCC Report No 317
Potts P (2002-3) Personal communications.
Sanderson N A April 1992, Ecological Appraisal of proposed fishery improvements at The Moors. Report for English Nature.
1:25,000 Soils of England and Wales, Sheet 6, South East England, Ordnance Survey for Soil Survey of England and Wales 1983.
Legend for the 1:250 000 Soil Map of England and Wales, Lawes Agricultural Trust (Soil Survey of England and Wales) 1983.

Case Study 7.3 Emer Bog

7.3.1 INTRODUCTION

Emer Bog is a very special place in Hampshire; it has magical quality and is easily accessible via the boardwalk. In winter the centre of the site is very wet and the peat soft and treacherous. The site is owned and managed for nature conservation by the Hampshire Wildlife Trust. I have visited the site on several occasions undertaking peat and hydrological surveys for the Trust and for the Environment Agency and English Nature at various times. Also desk studies for Text Valley Borough Council with respect to the developing local plan. I have also used Emer for training courses prepared for English Nature, the Rivers and Otter Trust and a variety of other organisations.

The site was always thought to be an acidic mire, but various tests have shown that while the surrounding soils are strongly acidic, many parts of the mire are neutral and have a fen like vegetation.

7.3.2 EMER BOG cSAC

Emer Bog was recommended as a candidate Special Area of Conservation (EN 02/03/01) because: ‘it contains transition mires and quaking bogs which are rare or threatened within a European context and which are considered to be one of the best areas in the United Kingdom’. These are described as: ‘Very wet mires often identified by an unstable ‘quaking’ surface’ occurring in waterlogged situations where they receive nutrients from the surrounding catchment as well as from rainfall.

Sanderson describes the site as containing a sizeable central basin mire, eastern seepage mires and a western valley mire where the occurrence of Carex rostrata-Sphagnum squarrosa Mire (NVC=M5) and Carex-Potentilla Tall Herb Fen (NVC=S27) are regarded by JNCC as forming part of the Habitats Directive Annex-1 category: 54.5 Transition Mires and Quaking Bogs. S27 tall herb fen occupies a large western area passing to rush dominated M5 poor fen typical of basin mires together with a range of mire-edge communities, ponds and wet woodlands.

7.3.3TOPOGRAPHY

Emer Bog and the adjacent woodland occur within a broad U shaped structure set into the north and northwest facing slopes of the major interfluve between the Test and Itchen valleys. The land slopes appreciably at first within woodland and grassland and then very gently across the open mire and towards the Tadburn Lake stream. Total change in relief across the site from the highest land to the Tadburn Lake stream is 13m.

7.3.4 GEOLOGY

The site is in the northern part of the Hampshire Tertiary Basin and the strata probably dip at 1-2 degrees to the south. The area of Emer Bog is shown on the 1:10 000 geological map as being underlain by alluvium within a wide outcrop of Tertiary Wittering Formation. Land in the wider area also has a variety of river terrace deposits. In practice there is not much alluvium and the wetland area is mostly peaty. Mineral deposits of various kinds surround the peaty basin.

Peat

Auger borings made in 1996 and 2001 suggest that much of the alluvial area is underlain by peat over Head deposits. The character and location of the peat deposits, suggests that the wetlands are not formed on a floodplain, but have developed on the surface of two adjacent topographic basins.

The lower basin which is on level land, extending across wet woodland and the open swamp and mire habitats, has generally well-humified organic deposits from 1m to over 2m thick. The upper basin sits below wet woodland on the southern valley side and extends almost to the upper margin of the site. The gently sloping surface of the basin rises a total of 5m and the peat depth varies from about 0.3m to over 2m (I was using a 2m auger and so the full depth remains unknown).

Mineral Deposits

The surrounding area of heathland and acid grassland within the cSAC are shown on geological maps as underlain by the Wittering Formation with the overlying Earnley Sand occurring to the south. This same material underlies the peat deposits. The Wittering Formation is locally covered with thin loamy and flinty Head, arising from surface deposition from solifluction during the Quaternary period.

The Wittering Formation is described on the 1:10 000 scale Geological Map as: mainly brownish grey laminated clays; sands with clay bands; clayey sands; and beds of glauconitic sands.

Boreholes near to the site indicate that the Wittering Beds are of medium-grained sand with a few thin bands of extremely sandy clay, very sandy clay with lenticles and partings of very fine-grained sand, very sandy clay with thin lenses and partings of fine-grained sand, and sand with a few thin (2 to 3mm) bands and thicker bands of sandy clay.

Overall, the Wittering Beds appear to be of variable layers of fine sandy clay and clayey fine sand with bands of fine sandy and clayey material.

7.3.5 SOILS

Mineral soils

The mineral soils at Emer have not been examined directly, however they are included with the Wickham 3 Soil Association and which also includes much land in the New Forest. These soils occur where thin loamy drift covers Tertiary clays and loams on gently undulating land. Fine loamy or fine silty over clayey poorly drained soils on slowly permeable substrates are the most widespread, but similar coarse loamy over clayey soils occur where there is a source of superficial coarse loamy material. Footslopes and low-ways have deeper loamy soils affected by high groundwater.

Most of these soils have slowly permeable subsoils and, after prolonged periods of heavy rain in winter, excess water is disposed of by lateral flow. Where the soils are undrained, the loamy over clayey soils remain waterlogged for long periods in winter.

Peat soils within Emer Bog

The peat soils were examined in 1996 and 2002 when 46 auger borings were made in the wetland area. Within the open mire, peat depths were typically 40-100cm from the surface, increasing to over 200cm below the alder woodland to the north of the open swamp and mire.

Lower Peat Basin

Within the Carex-Potentilla Tall Herb Fen (S27), peat depth varied from less than 20cm at the edges to 100cm in the northern part. Within the Carex rostrata-Sphagnum Mire (M5) with Poor Fen, the peat was of intermediate depth at 60cm. At the small area of Juncus dominated Carex echinata-Sphagnum Mire (M6) the peat had further thinned to between 18 and 39cm. Passing east out of the wetter land onto the Molinia-Potentilla Mire (M25a) the peat depth had reduced from 13cm to 3cm.

In the open Tall Herb and Poor Fen area (S27 and M5), surface peat layers tend to be rich in fibrous Sphagnum or Molinia fragments, but with depth the peat is well humified sometimes with remains of grasses or sedges and sometimes with Phragmites leaves. Woody peat with twigs occurs occasionally. Within the Juncus dominated Poor Fen (M6), the shallow peats tended to be composed of fibrous Sphagnum remains throughout, but the profiles are disturbed by scrub clearance and layers have become mixed in places.

Within the birch, willow and alder woodland to the north of the open area, peat depths reached their maximum at over 200cm and the peat was well humified throughout.

Below the peat there is usually a layer of dark silty clay loam that is often rich in organic matter or has peaty layers, otherwise the peat usually passes to sandy clay loam, sometimes with flints. In places, the mineral substrate contained unidentified pale cream clayey material that was locally very slightly calcareous. When tested in 1996, the peat was typically strongly acidic (pH 4-5) in the surface but became neutral at depth.

Upper Peat Basin

Peat in the upper basin is almost wholly below wet willow woodland and at over 200cm deep in the upper part of the slope, was surprisingly deep. The peat is always well humified and contains woody fragments in places. Substrates tended to be fine-grained loams and clays.

Peat water levels

Two perforated dipwells have been installed to about 1m deep. Dipwell 1 is at the upper edge of the Molinia-Potentilla Mire close to the boundary with the Agrostis curtisii grassland upslope in the east of the site. Dipwell 2 is in the Carex-Potentilla Tall Herb Fen near the boardwalk in the west of the site. Water levels at each site were recorded, at about two weekly intervals during 2001 by the Hampshire Wildlife Trust, a period that was atypically wet. The data indicated that:

The groundwater table in the Molinia-Potentilla mire was at about ground level until the end of April 2001, when water levels began to drop to a maximum depth of 65cm below ground level in August. By early October, water levels had recovered and remained at about ground level to the end of the year. The groundwater table in the Carex Potentilla Tall Herb Fen was above ground level (ie. the site was flooded) to a height of 5-15cm above ground level until the end of June, after which the water table dropped to about 25cm below ground level during August after which levels again rose and the site became flooded from October onwards.

Groundwater fluctuations mirrored each other in both sites, but the Molinia mire site (which seldom flooded) was dry for about 41/2 months of that year and was considerably drier than the Tall Herb Fen site which was dry for about 21/2 months in that year and flooded for the remaining period.

7.3.6 HYDROLOGY

Surface wetness

Much of the site is seasonally wet at the surface and the main open mire remains waterlogged throughout most years and flooded in some winters. Some of the water appears to arise from seepages on higher land and some is likely to represent at least a proportion of groundwater. As well as surface streams and seepages, there are also two artificial ponds.

Inflows

There are three main inflowing sources. i. An area of seepage on slopes in the east develops a small winter water tract, which flows west into the mire. ii. Two winter streams arise off land-drains from the a grass field to the south and which flow into wet woodlands where they combine to feed an eastern open pond where the outflow passes into the open mire. iii. A western seasonal stream arising in part from seepage and in part from field edge drains ultimately flowing into an area of wet woodland and so into the mire.

Outflows

Winter floodwater in the open mire collects via a series of wooded distributaries to flow north towards the Tadburn Lake, a stream flowing to the northwest of the site. Surface water accumulating in wet woodland in the north of the site flows in very wet conditions north and east towards a seasonal boundary drain from where it again flows to the Tadburn Lake stream.

7.3.6 HYDROGEOLOGY

There are no boreholes within the site and hydrogeology is interpreted from other information. The 1:50 000 geological map indicates that the strata dip at 1-2 degrees to the south.

The London Clay aquiclude prevents upward or downward movement of groundwater below the site. The overlying Wittering Formation, which directly underlies the peat basins, is likely to have a low hydraulic conductivity. However, sandier seams within the Wittering Formation could provide conduits for locally enhanced rates of subsurface flow.

The presence of springs and extensive areas of seepage around the eastern and southern edges of the wetland area suggests that, despite the southerly dip, the general flow of groundwater is from the south. Seepage water from south flows into the upper valley side peat basin which becomes saturated creating surface water flows north towards the level land of the lower peat basin. The seasonal rise of water over the lower peat basin indicates that there is likely to be a groundwater component here. This suggests that in winter, groundwater effectively rises by upward seepage out of the Wittering Formation into the peat layers below the lower basin causing seasonal flooding. This rising groundwater is supplemented by surface flows off the higher peat basin and adjacent land in the south and east. Excess water then flows overland north towards the Tadburn Lake stream.

7.3.7 HYDROCHEMISTRY

Sampling

Initial sampling of waters was undertaken in 1996 and in more detail in 2002. The objective has been to determine the trophic state of the surface flows with a view to ascertaining the effect, if any, of inflows on water quality. It is acknowledged that in mire communities, plants are also abstracting nutrients from the substrate and that shallow surface waters can be enhanced by solution of nutrients from the substrate. Sample results referred to here are from deeper open waters, spring flows, and from shallow water pools over peat.

pH

Testing in December 1996 had indicated that surface waters in the open mire and eastern seepages were all very acidic with values from 4.1 to 5.5, typical of dystrophic and oligotrophic waters. In contrast, the ponds had higher values of 5.9 and 6.0. Overall, there was a marked acidity gradient from circum-neutral conditions in the south of the site through moderately acidic conditions in the open mire. Later sporadic testing between 1997 and 2000 indicated that open mire acidity had declined (becoming circum-neutral) and this was confirmed in very detailed sampling and analysis in the summer and again in the winter of 2002 when much of the open mire had increased in pH to between 6.0 and 6.4 and the only strongly acidic areas were in the east of the open mire and in the eastern seepages.

Alkalinity

In December 1996 alkalinity values (expressed as equivalent CaCO3) across the site were in the high to very high range and from 20 to 125 mg/lCaCO3, all within the range typical of eutrophic to hyper-eutrophic waters. The eastern seepage had the lowest value. In August 2002, typical values ranged from 45 to over 128 mg/lCaCO3 typical of eutrophic to highly calcareous hypertrophic waters.

In December 2002, a much greater number of samples revealed that the southern sources then had values of 33-35 mg/lCaCO3 (typical of eutrophic water), the western sources ranged from 15-23 mg/lCaCO3 (typical of mesotrophic water) and the eastern sources and eastern mire had values of 5-15 mg/lCaCO3 (typical of more oligotrophic water). There had thus been a small reduction between summer and winter, perhaps the result of dilution with rainwater.

Phosphorus

In 1996 total phosphorus values in water ranged from eutrophic levels of 0.04 to 0.05mg/l in the seepages to hyper-eutrophic levels of 0.2 to 0.6 mg/l in the ponds and a pool in the open mire. In August 2002, all 26 samples had total phosphorus levels within the hyper-eutrophic range of from 0.1 to 0.7mg/l. Much of the open mire (in the M27 area) had total phosphorus levels above 0.4mg/l.

Othophosphate phosphorus levels in August 2002 were also very variable ranging from 0.06 to 0.09mg/l (moderate) in the inflowing southern stream and part of the open mire to between 0.1 and 0.7 across the rest of the site (high to very high). In terms of the Environment Agency recommendations for cSAC Headwaters in Mesozoic clay vales and Tertiary Clays, these values all exceeded the ‘natural’ value and about half the samples exceeded the much higher ecological ‘threshold’ value. In December 2002, the values had declined somewhat and most values were in the low to moderate range from 0.04 to 0.06 with only small areas exceeding these values. However, none of the samples attained the ‘natural’ guide level and all samples exceeded both the ‘standard’ and ‘threshold’ levels indicating high levels of phosphorus overall.

Nitrogen

In December 1996 inorganic nitrogen (nitrate-N plus ammonia-N) levels ranged from 0.7mg/l in the eastern seepage to 5.23 in one of the open ponds. These are very high levels typical of eutrophic to hyper-eutrophic waters. In August 2002 the greater number of samples confirmed these very high levels of inorganic nitrogen from 0.9 to 5.09 mg/l. As would be expected from mire systems, a high proportion of the nitrogen was as ammonia and which attained a surprisingly high maximum of 4.4mg/l in a deep pool within the S27 community. By December, these high levels had declined slightly, perhaps as a result of dilution from rainwater, although levels generally remained at levels typical of eutrophic waters. The highest levels (2.46mg/l InorgN) were found in waters arising from land drains from off an adjacent grass field although levels declined within the reserve.

7.3.8 A HYDROLOGICAL CONCEPTUAL MODEL FOR EMER BOG cSAC

Emer Bog sits within a broad U shaped bowl-like structure, open to the north and set into the interfluve between the Test and Itchen Valleys in Hampshire. The bowl-shaped topography rises 13m from the out-flowing stream to the highest point on the SSSI. The basin structure is complex and contains a lower mostly level area underlain by up to 2m of peat and a higher gently sloping area containing a further body of peat. The peat is considered to be more permeable than the underlying Tertiary substrate and so controls the flow of water across the site.

Three surface inflows arise from open drains and under-drainage outfalls off agricultural grasslands to the south and to the west of the site. In winter, these flows pass in irregular shallow channels into and across the upper peat basin leading to one or other of two artificial ponds and on into the open mire of the lower peat basin. Further flows arise from springs in the east. These water sources recharge shallow perched water within the two peat bodies, and which are acidic to the east and slightly acidic to circum-neutral in the west. Water outflows through a further channel and (in wet weather) from easterly surface flows, and ultimately reaches a stream to the northwest.

The peat upper basin is also likely to be fed by seepages off the underlying Tertiary deposits and the lower peat basin contains perched groundwater held above the Tertiary substrate.

The agriculturally sourced flows tend to be only slightly acidic and the spring flows are strongly acidic. These contrasted flows create pH gradients across the site and which is reflected in plant community composition.

Open waters in the site are generally rich in nitrogen and phosphorus. Soluble phosphorous in particular exceeds target values for headwaters of cSAC streams and total nutrients are all high compared to expected values for these habitats. There is no evidence that these high nutrient levels are sourced from surface waters and so the source appears to be primarily from within the mire system itself, perhaps from the underlying peats or from nutrient rich groundwater.

7.3.10 GENERAL CONCLUSION

The mire system at Emer Bog is hydrologically complex and highly fertile. The site contains two adjacent peat basins and is fed in winter by waters arising from a strongly acidic source and two slightly acidic sources, together with water from higher-level seepages and lower-level perched groundwaters. The water is generally high in alkalinity, phosphorus and nitrogen. While it is possible that some of these high nutrient levels arise from external sources, it is most likely that most arise as an integral part of the mire and open water system.

Of concern however, is that an apparently one-time wholly acidic open mire, is now predominately only slightly acidic to circum-neutral. The remaining acidic mire vegetation is now restricted to the small area of M5 community and which is now possibly highly vulnerable to the apparent changes in water pH regime. Loss of the critical acidic M5 community would severely reduce the ecological interest of the site by removing the transitional character of this part of Emer Bog.

7.3.11 REFERENCES

1. Allen R H (1996), Emer Bog and Baddesley Common: Reconnaissance Hydro-ecological Study, for Hampshire Wildlife Trust.
2. Allen R H (2002) Desk Study: Hydro-ecological appraisal of Emer Bog cSAC, North Baddesley, Hampshire, for Test Valley Borough Council: Planning Service.
3. British Geological Survey 1:50 000 scale Sheet 315 Southampton.
4. English Nature, 1982 SSSI Citation Baddesley Common.
5. English Nature, 02/03/01, Reasons for recommendation as a candidate Special Area of Conservation.
6. Environment Agency: General Quality Assessment of Rivers 2002
7. Environment Agency: Phosphorus standards for rivers in England and Wales Pitt J, Phillips G and Mainstone 2002
8. Geological Survey of Great Britain 1:10 000 scale Sheet SU32 SE.
9. Geological Survey of Great Britain 1:10 000 scale Sheet SU42SW.
10. Geological Survey of Great Britain 1:50 000 scale Sheet 299 Winchester.
11. Hampshire Wildlife Trust, Water Level Records 2000.
12. Haslam S M (1994) Wetland differentiation and sensitivity to chemical pollutants (non-open water wetlands) DoE Report No DoE/HMIP/RR/040.
13. Jarvis M G, Allen R H, Fordham S J, Hazleden J, Moffat A J and Sturdy R G, Soils and their use in South East England, Soil survey of England and Wales Bulletin No 15, Harpenden 1984.
14. Legend to the 1:250,000 Soil Map of England and Wales, Soil Survey of England and Wales 1983.
15. Ordnance Survey 1:25 000 scale Explorer Sheet 131 Romsey, Andover and Test Valley.
16. Ordnance Survey 1:25 000 scale Explorer Sheet 132 Winchester.
17. Ordnance Survey 1:50 000 scale Landranger Sheet 185 Winchester and Basingstoke.
18. Ordnance Survey 1:50 000 scale Landranger Sheet 196 Solent and Isle of Wight.
19. Newbold C and Palmer M A (1979) Trophic Adaptions of Aquatic Plants, NCC CST Notes No. 18.
20. Palmer M A, Bell S L and Butterfield I (1992) A botanical classification of standing waters in Britain, applications for conservation and monitoring, Aquatic Conservation: Marine and Freshwater Ecosystems, Vol 2 125-143.
21. Palmer M A and Roy D B (2001) A method for estimating the extent of standing fresh waters of different trophic state in Great Britain, Aquatic Conservation: Marine and Freshwater Ecosystems Vol. 11 199-216.
22. Palmer M A and Roy D B (2001) An estimate of the extent of dystrophic, oligotrophic, mesotrophic and eutrophic standing freshwater in Great Britain, JNCC Report No 317
23. Sanderson NA December 1998, Vegetation Survey of Emer Bog, Hampshire, for Hampshire Wildlife Trust.
24. 1:25,000 Soils of England and Wales, Sheet 6, South East England, Ordnance Survey for Soil Survey of England and Wales 1983.


 
The Environmental Project Consulting Group
44A Winchester Road, Petersfield, Hampshire GU32 3PG
email: Ron Allen, tel: 01730 231019,
Copyright April 2005 Ron Allen
Geologist, Soil Scientist, Applied Ecologist, Hydro-ecologist, Chartered Environmentalist