Phosphorus and nitrogen limitation and impairment of headwater streams relative to rivers in Great Britain: A national perspective on eutrophication

Authors: JARVIE, HELEN - Centre For Ecology And Hydrology; Smith, Douglas; NORTON, LISA - Centre For Ecology And Hydrology; EDWARDS, FRANCOIS - Centre For Ecology And Hydrology; BOWES, MIKE - Centre For Ecology And Hydrology; KING, STEPHEN - Centre For Ecology And Hydrology; SCARLETT, PETER - Science And Technology Facilities Council; DAVIES, SIAN - Environment Agency; DILS, RACHAEL - Centre For Ecology And Hydrology; BACHILLER-JARENO, NURIA - Centre For Ecology And Hydrology

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/11/2017
Publication Date: 4/15/2018
Publication URL: https://handle.nal.usda.gov/10113/5979355
Citation: Jarvie, H.P., Smith, D.R., Norton, L., Edwards, F., Bowes, M., King, S.M., Scarlett, P., Davies, S., Dils, R., Bachiller-Jareno, N. 2018. Phosphorus and nitrogen limitation and impairment of headwater streams relative to rivers in Great Britain: A national perspective on eutrophication. Science of the Total Environment. 621:849-862. https://doi.org/10.1016/j.scitotenv.2017.11.128.
DOI: https://doi.org/10.1016/j.scitotenv.2017.11.128

Interpretive Summary: This study provides a first national-scale assessment of the nutrient status of British headwater streams within the wider river network based on analysis of two large databases. The results show that, while localized nutrient impairment of headwater streams can occur, there were markedly lower rates of phosphorus and nitrogen impairment of headwater streams relative to downstream rivers at the national scale. Nutrient source contributions, relative to hydrological dilution, increased with catchment scale, corresponding with increases in the range and complexity of agricultural and urban land-use. To explore the extent to which nutrients may potentially limit algal growth in streams and rivers, a novel approach was used, assessing the relative rations of carbon, nitrogen and phosphorus, as well as the absolute concentrations of nitrogen and phosphorus. Phosphorus limitation was more commonly seen in the rivers, compared to nitrogen limitation being observed more in the headwater streams. However, high levels of potential phosphorus and nitrogen co-limitation were found in the headwater streams. This suggests that managing both phosphorus and nitrogen inputs may be needed to minimize risks of degradation of these sensitive headwater stream environments. The estimated nutrient reductions needed to achieve compliance with European Water Framework Directive standards were greatest for rivers and streams in lowlands that also had high alkalinity. Preliminary assessments suggest that targeted reductions of phosphorus concentrations in headwater streams in lowlands with high alkalinity, and nitrogen concentrations in rivers found in uplands with low alkalinity, might offer greater overall benefits for water-quality remediation at the national scale, relative to the magnitude of nutrient reductions required. This approach could help inform the prioritization of nutrient remediation, as part of a directional approach to water quality management based on closing the gaps between current and target nutrient concentrations.

Technical Abstract: This study provides a first national-scale assessment of the nutrient status of British headwater streams within the wider river network, by joint analysis of the national Countryside Survey Headwater Stream and Harmonised River Monitoring Scheme datasets. The results show that, while localized nutrient impairment of headwater streams can occur, there were markedly lower rates of phosphorus (P) and nitrogen (N) impairment of headwater streams relative to downstream rivers at the national scale, particularly in the Lowland-High-Alkalinity catchments. Nutrient source contributions, relative to hydrological dilution, increased with catchment scale, corresponding with increases in the range and complexity of agricultural and urban land-use. To explore the extent to which nutrients may potentially limit primary production in headwater streams and rivers, a novel Nutrient Limitation Assessment was applied, coupling a ternary assessment of N, P and C depletion, with N:P stoichiometry, and threshold P and N concentrations. P limitation was more commonly seen in the rivers, compared to N limitation in the headwater streams. However, high levels of potential P and N co-limitation were found in the headwater streams, especially the Upland-Low-Alkalinity streams. This suggests that managing both P and N inputs may be needed to minimize risks of degradation of these sensitive headwater stream environments. The estimated nutrient reductions needed to achieve compliance with European Water Framework Directive standards, and to reach limiting concentrations, were greatest for the Lowland-High-Alkalinity rivers and streams. Preliminary assessments suggest that reducing P concentrations in the Lowland-High-Alkalinity headwater streams, and N concentrations in the Upland-Low-Alkalinity rivers, might offer greater overall benefits for water-quality remediation at the national scale, relative to the magnitude of nutrient reductions required. This approach could help inform the prioritization of nutrient remediation, as part of a directional approach to water quality management based on closing the gaps between current and target nutrient concentrations.