Phosphorus from Agriculture: Riverine Impact Study (PARIS)

PARIS flow gaugeThe way we manage our farm at Loddington affects the condition of the stream both within the farm, and downstream of it. Similarly, how farmers upstream from us manage their land influences the stream when it reaches us. Loddington is ideally placed, in the centre of the Eye Brook catchment, to explore catchment scale processes associated with water quality and ecology.

Our main research project on this issue is the Defra-funded project, PARIS (Phosphorus from Agriculture: Riverine Impacts Study), for which the Eye Brook is one of three study catchments in lowland England. Other projects (e.g. MOPS and SOWAP) research the processes operating within fields and in field drains and ditches. PARIS explores the processes in the next stage along the line, in the stream.

The project concentrates on two sub-catchments, one in the Eye Brook headwaters where the land use is pasture, and the other at Loddington where arable is the predominant land use. The research includes monitoring of flow and concentrations of a range of nutrients, aquatic invertebrate and diatom communities, and ecological processes such as respiration.

The focus is on the impact of phosphorus, as this is the main nutrient causing ecological problems in fresh water. There is a gradient of phosphorus concentration (from very low to very high) across the project’s study catchments, with the lowest being the Eye Brook headwater. Loddington sits in the middle of this range. The diversity of aquatic invertebrates and diatoms is highest in low phosphorus streams, and lowest in water with high phosphorus concentration. Diatom biomass is highest under high phosphorus conditions. Maximum biomass is reached at a phosphorus concentration of around 100µg/l, suggesting that this is the limit below which fresh water in agricultural catchments should be maintained.

Phosphorus is mainly associated with fine soil particles eroded from farmland. However, rural areas also contain numerous isolated houses with septic tanks. Our results reveal that these contribute high concentrations of phosphorus, at least locally and in summer when this domestic contribution is not diluted by water from other sources. Other sources are roads, tracks, farmyards and houses. Because of the large volumes of water involved and the association between rain storms and soil erosion, arable land is the greatest contributor of sediment and phosphorus to the stream.

Achieving targets for water quality and ecology is dependent on the knowledge and commitment of farmers and we are using the results of our research to inform training for farmers from across the country. However, such changes in attitudes to catchment management are also dependent on the knowledge and commitment of other members of the rural community, and we are building local knowledge of environmental management and use within the catchment through the Eye Brook Community Heritage Project.

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