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The University of Southampton
Geography and Environmental Science

Research project: Phosphorus in the perennial headwaters of chalk streams

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English chalk streams represent Europe’s most significant chalk river resource and are of massive conservation importance. Anthropogenic pressures, however, on some chalk rivers are leading to their deterioration, displaying the symptoms of what has come to be called “chalk stream malaise”; including turbid water, silted gravel beds, declines in fauna (trout and salmon, coarse fish, and characteristic invertebrates), and enhanced growth of benthic and filamentous algae.   It is believed that eutrophication of chalk streams is a key underlying cause of this deterioration. The nitrogen–rich status of English chalk aquifers leads to chalk stream ecosystems being highly sensitive to P inputs. Increases in the supply of dissolved P may thus lead to excessive and rapid growth of filamentous algae in favour of characteristic chalk stream plants such as water crowfoot. It is recognised that release of P into chalk headwaters occurs via both point and diffuse effluent sources, particularly sewage-derived effluents and agriculture. Release of P will vary both spatially (i.e. reflecting the distribution and magnitude of sources) and temporally.   Variations in hydrology will likely affect both the interaction of river sediment with dissolved P on seasonal and rainfall-event timescales, leading to mobilisation and downstream movement of sediment-associated P. Variations in groundwater levels may also lead to sewers and sewerage acting as either sinks for groundwater or sources of sewage-derived contaminants when leakage occurs or systems are not fully sealed. Reduction or mitigation of impacts of P on chalk rivers can be most readily effected if the quantities of P released from these various sources are understood in the following terms: - Which source(s) deliver(s) the most P into chalk headwaters? - How does delivery of P into chalk headwaters vary over time in relation to (1) season, (2) rainfall and storm events, and (3) groundwater levels?   This project will comprise a three-year research programme on headwaters of the Rivers Test and Itchen, aiming to address these key issues and to identify cost-effective mitigation measures. In addition to sampling and analytical work (see research programme below), the programme will deploy autonomous monitoring instruments to acquire field data at high temporal resolution to maximise insight to the influences of hydrological and event-specific processes. This information will enable measures (both policies and infrastructure) to be identified that can help reduce and mitigate the impact of phosphorus on chalk waters by setting evidenced-based priorities. The insight provided by the project will help identify where investment can best be directed i.e. to where the benefit/cost relationships are at their most efficient.


Research aims
This project seeks to determine key processes that contribute phosphorus to chalk stream headwaters and thereby incur a risk to the integrity and quality of these diverse and valued ecosystems. The research will seek to establish the relative contributions of phosphorus sources (point and diffuse, sewerage- and agriculture-derived) to chalk streams, examining its speciation, composition and potential bioavailability in the water column and sediment. Specific attention will be paid to the role of fine sediments as a source or sink for phosphorus, and the relationship between sediment-bound and water column P.
Research methods
The programme of study will focus on perennial headwaters of the Rivers Test and Itchen; two internationally-renowned chalk rivers with small rural settlements and with varied land uses, agriculture, and aquaculture within their headwaters. The P content of surface water samples and sediments will be analysed using established colourimetric techniques, including the DOP fraction. Sediments will be sieved to determine overall physical composition, and fine sediments will be further fractionated by filtration (0.2µm to 10µm) to determine geochemical composition as a function of grain size, providing a proxy for mobility. Fine sediment particles of different size will be characterised and the potential bioavailability of associated P species determined. We will also establish through deployment of autonomous logging instrumentation the role of key environmental variables on the subsequent fate of phosphorus in chalk headwaters, thereby providing a holistic understanding of the processes and activities that determine the sources, pathways and targets of phosphorus as an agent of eutrophication. A mass balance model will be developed on the basis of these observations.
Expected outcomes
On completion of the project, it is envisaged that the project outcomes will enable prioritisation of programmes of measures to control P and mitigate impacts of its release into chalk headwaters at sub-catchment level. Recommendations arising from research outcomes and critical appraisal should form a template for the evaluation and management of P in perennial headwater chalk streams.
Research partners
This project is funded by the Vitacress Conservation Trust, the Test and Itchen Association, and the University of Southampton's Faculty of Engineering & the Environment.Other partners include the Hampshire and Isle of Wight Wildlife Trust, Environment Agency, and the Campaign to Protect Rural England.

Related research groups

Centre for Environmental Sciences
Water and Environmental Engineering Group
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