Research project: Phosphorus in the perennial headwaters of chalk streams
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.