September 2023 – Chalk-Streams

The carbon-sequestering potential of floodplains in general and chalk streams in particular.

September 15, 2023September 18, 2023Posted in Uncategorized1 Comment

It’s taken me too long to publish news of this fascinating new paper from David Sear, Ben Pears and Immy Speck, the chalk team at Southampton University, also sponsored by Natural England.

CARBON STORAGE IN RIVER AND FLOODPLAIN SYSTEMS highlights the potential for C-storage in floodplain and river environments, and reviews the effectiveness of restoration actions in increasing carbon storage relative to current degraded states.

Fascinating factoids abound, but one is that almost 20% of English peat is stored in the top 15% of chalk stream floodplains. Another, that the carbon in this peat is very old (11,000 years) and that chalk stream floodplains are amongst the stable repositories because they are wet and they don’t move around much.

This paper should be a valuable tool for those making river restoration proposals and bids, especially if we think about hydrological connectivity and the restoration of the contiguous mosaic of wet habitats including spring flushes, calcareous fen and wet woodland, which support the chalk stream.

Well done and thank you to David and co.

Clearing up the confusion over chalk streams as UK BAP priority habitat.

September 11, 2023October 3, 2023Posted in UncategorizedLeave a comment

I’ve fielded a bit of correspondence lately because some people are confused about the status of chalk streams as a priority habitat. The confusion mostly arises out of the way in which the NE maps are published: there are several of them.

So, this is my attempt to bring a bit of clarity to the situation.

The original list of UK biodiversity action plan habitats was created between 1995 and 1999. Chalk rivers were the only riverine habitat. Other freshwater habitats included fens, machair, eutrophic standing waters and a few others.

The list was revised in 2007 in order to “ensure that the UK BAP remains focussed on the correct priorities for action and takes account of changes in the status of UK biodiversity in addition to new information and knowledge”.

The review added considerably to the list of priority habitats including other riverine habitats but the Report on the Species and Habitat Review made clear that in adding additional types of freshwater habitat, chalk rivers were not subtracted. Under the summary of major changes in Table 1 it clearly states under “rivers and streams – major changes”.

“New habitat, incorporating an existing habitat (Chalk Rivers). Further work by specialists is required to develop guidelines for the identification of river reaches which will be priorities for UK BAP action.”

That further work led to the current list of priority habitats HERE in the UK Biodiversity Action Plan Priority Habitat Descriptions – Rivers (Updated December 2011).

See the document for more detail but essentially the list of qualifying criteria in is:

1. Riverine water bodies of high hydromorphological / ecological status.

2. Headwaters (within 2.5km of its furthest source as marked with a blue line on Ordnance Survey (OS) maps at a scale of 1:50,000. Headwaters which have been significantly altered from their natural state are not included).

3. Occurrence of the EC Habitat Directive Annex I habitat (H3260 Watercourses of plain to montane levels with the Ranunculion fluitantis and Callitricho-Batrachion vegetation). The definition will include (but not be confined to) all river SACs designated for the feature.

4. Chalk Rivers (as given in the existing BAP definition).

5. Active shingle rivers. Data for this can come from River Habitat Surveys (Environment

Agency 2003) or indicator species of invertebrate (see criterion 7).

6. Areas or Sites of Special Scientific Interest designated for river species, riverine

features or fluvial geomorphology.

7. Species including:

i. Annex II Habitats Directive species 2

ii. BAP priority species

iii. Invertebrate species which are strongly indicative of river shingle

The BAP definition stated:

Chalk rivers have a characteristic plant community, often dominated in mid-channel by river water crowfoot Ranunculus penicillatus var pseudofluitans and starworts Callitriche obtusangula and C. platycarpa, and along the edges by watercress Rorippa nasturtium-aquaticum and lesser water-parsnip Berula erecta.

They have low banks which support a range of water-loving plants. This plan considers action required for the river channel and banks but not for the whole catchment or floodplain.

All chalk rivers are fed from groundwater aquifers, producing clear waters and a generally stable flow and temperature regime. These are conditions which support a rich diversity of invertebrate life and important game fisheries, notably for brown trout Salmo trutta, brook lamprey Lampetra planeri, salmon Salmo salar, crayfish Austropotamobius pallipes and otter Lutra lutra are among the species listed on Annex II of the EC Habitats Directive which chalk rivers support.

Most chalk rivers have ‘winterbourne’ stretches in their headwaters. These often run dry, or partially dry, in late summer because of lack of rainfall recharging the aquifer. A characteristic range of invertebrates has adapted to these conditions, as is the brook water crowfoot Ranunculus peltatus.

The list of priority habitats has not changed since that date, but the mapping has slowly caught up with the definition and in that mapping lies some confusion.

There are several maps of priority habitats: the one you will find easily if you google “river priority habitat” is – as it clearly states in the summary HERE – the map “of rivers and streams that exhibit a high degree of naturalness”.

The map which you won’t find easily is the MAP OF CHALK RIVERS which, as it clearly states in the summary is a map of:

“Priority Habitat Chalk Rivers, based on Environment Agency Detailed River Network v3. Data prepared Autumn 2021.Data shows the location of Priority Habitat Chalk rivers and Streams.”

There is also another map HERE where you can toggle on and off the different layers for different priority habitat types.

Chalk rivers were the proto riverine priority habitat and when they were designated as such it was because they supported communities of ranunculus, starwort and berula, because their low banks and high water-tables support varied communities of riparian water-loving plants, and because they are spring-fed, altogether meaning they support a very large bio-diverse community of designated flora and fauna (see my previous post).

Why I think chalk streams are ‘irreplaceable habitats’ and should be recognised as such

September 10, 2023September 15, 2023Posted in Uncategorized2 Comments

Biodiversity net gain is a new approach to development and land management which aims to protect the natural environment by ensuring it is measurably improved as part and parcel of any given development.

The National Planning Policy Framework (NPPF) states that development should contribute to and enhance the local environment, minimise impacts and provide net gains for biodiversity. Plans should:

‘promote the conservation, restoration and enhancement of priority habitats, ecological networks and the protection and recovery of priority species’.

The Environment Act sets out the key components of the biodiversity net gain system; essentially a minimum 10% net gain (assessed using a biodiversity metric) which may be delivered at or away from the development site, and which must be secured for a minimum of 30 years.

None of this changes or undermines existing legal protections.

Some habitats, however, are deemed to be too important for the principle of off-setting a loss via the net 10% gain that this processes entails.

Under the new system these special habitats will be called ‘irreplaceable habitats’. They have been defined in the NPPF as habitats that are ‘technically very challenging or time-consuming to restore, considering factors such as age, uniqueness, species diversity, or rarity’.

At the moment the “example” list of these habitats includes: ‘ancient woodland, ancient and veteran trees, blanket bog, limestone pavement, sand dunes, salt marsh and lowland fen’.

I very much hope when the final list is confirmed that chalk streams and their mosaic of supporting habitats – winterbournes, wet woodland, calcareous fen, spring-lines, peat-rich floodplains – will be on it. This would provide a higher level of protection and demand bespoke reports prepared as part of the planning application.

There is a very good case for putting chalk streams on the list, if not at the top of it.

Chalk streams are the most bio-diverse of any British freshwater system. So, if the river corridor is the most biodiverse, or potentially biodiverse part of any given landscape, chalk stream and their floodplains must – ipso facto – be more biodiverse than any other part of the English landscape.

Chalk streams are a lowland, cold-water, spring-fed river system, occupied in their upper reaches by rheophilic species of flora and fauna. They are home to a number of threatened species, not least a genetically distinct race of Atlantic salmon that are unique to the Wessex chalk streams: also the southern damselfly, Desmoulins whorl snail, the white-clawed crayfish. They are a global hotspot for species of invertebrate adapted to ephemeral streams: the scare brown sedge and the winterbourne stonefly.

Chalk streams are globally rare and – of course – most chalk streams are in England.

However, they are inherently vulnerable, as described in section 5 of English Nature’s 1999 publication Chalk Rivers Nature Conservation and Management:

• they feature flora and fauna communities adapted to stable flow regimes that are easily disrupted by abstraction, development, agriculture

• they are low energy systems that are less able to self-cleanse or self-repair

• they are located in parts of England with lower then average rainfall and high population density, imposing intrinsically high pressure on water resources

• historic management and development of chalk streams had left a legacy of modifications which can exacerbate modern environmental pressures

And by Sear et al in the paper Defining reference conditions for chalk stream and Fenland natural channels which shows that:

• the geomorphology and natural bed substrate of chalk streams are relics of processes which have long since retreated from our landscape.

• once gravel beds have been removed, there is an insufficient supply of gravel to replenish these through natural processes.

In other words, they are globally rare, biodiverse and home to threatened and rare species, but vulnerable to damage, and relatively incapable of self-repair, especially within time-scales that we can relate to. Once gravels are removed we would need to wait for another ice-age for the stream’s physical structure to be re-set.

What exactly constitutes an irreplaceable habitat has, unsurprisingly, sparked some debate, but there appears to consensus around the ideas that these habitats support rare or endangered species and provide critical ecosystem services, such as carbon sequestration, and flood prevention, while their loss or damage can result in significant, long-term, and sometimes irreversible negative impacts on local and regional ecosystems.

Again, you can’t do much better in those regards than to preserve and restore rivers, especially chalk streams.

A recent paper by Sear, Speck and Pears – Carbon storage in river and floodplain systems – shows that 18% of English peat is stored in the top 15cm of English chalk stream floodplains. Dig deeper and that % goes up: and you can dig deeper. At the river’s edge the peat is usually one meter deep in my experience on East Anglian streams, but up to three to four meters deep in certain parts of the catchments where marsh conditions once prevailed. Carbon storage in river floodplains is quantitatively comparable to other fens and marshes and need to be recognised as such. Carbon buried in floodplains is old, and in chalk streams, the oldest of all @ circa 11,000 years. It is sensitive to draining and drying. On the other hand, there is the potential to use floodplains, especially chalk stream flood-plains, to sequester and stably store carbon through the restoration of water-table levels, wet-woodland, calcareous fen and marsh: all exactly the kind of advanced river restoration prescriptions the chalk stream strategy is pushing for.

In other words, if we protect and restore chalk streams, surely we deliver the objectives of preserving and enhancing biodiversity and other ecosystems services about as effectively as it is possible to imagine?

***

Here’s a list of designated priority species supported by chalk streams and their riparian habitats (from EN chalk rivers conservation and management).

Plants

Ranunculion fluitantis

a) R. peltatus

b) R. penicillatus subsp pseudofluitans

c) R. fluitans

Oenanthe fluviatilis

Invertebrates

Austropotamobius pallipes (Crayfish)

Oulimnius troglodytes (Beetle)

Riolus cupreus (Beetle)

Riolus subviolaceus (Beetle)

Agabus biguttatus (Beetle)