Phosphorus storage in stream sediment over time, Lillån Västra Götaland (Bachelor/Master)

Eutrophication is one of the most challenging problems related to water today. Much effort is spent on reducing external sources of phosphorus (P) that might be transported to the water and also on mitigation measures, like P retention ponds to catch pollutants in the running water. However, there are also legacy sources of P where historical inputs are stored in the soils, riparian areas and lake- and stream sediment (Sharpley et al. 2009).

Legacy P could contribute to internal loading in water bodies, where stored P in the sediment is remobilized or released from which could contribute to eutrophication. This is a known problem in lakes, during certain conditions e.g. low oxygen conditions. P is often bound to particles; depending on what it is bound to, it might be more or less available for algal growth and primary production.

Studies have shown that legacy P are also stored in ditches and streams (Audette et al., 2018; SanClements et al., 2009). In some cases, these stores are comparable to P stored in lake sediment (Lannergård et al. 2020). Lillån is a nutrient-rich stream in an agricultural area in Västra Götaland. In a collaboration with Länsstyrelsen, a sediment sampling campaign have been carried out in 2023, where P fractions (analysed according to Hupfer et al. 2009) and TP concentrations was analysed. During 2024 some of these streams were maintained (dredged) and excessive sediment removed and dug out.

In this project, the same sites will be sampled a second time in Lillån catchment area. The field campaign will be done with local farmers and Länsstyrelsen i Västra Götaland. The samples will be analysed in the lab to determine P fractions and TP amounts and assess if internal loading of P in the stream is a prevailing risk. The results could be compared with the data from autumn 2023 to get an indication of change over time and change related to the maintenance of stream channels.

This project is a collaboration with Länsstyrelsen i Västra Götaland, as they work actively with farmers and mitigation measures to reduce eutrophication in the area. Field and lab work need to be carried out during autumn 2025, data analysis and writing could be more flexible.

References

Audette Y, O’Halloran IP, Nowell PM, Dyer R, Kelly R, Voroney RP. 2018. Speciation of Phosphorus from Agricultural Muck Soils to Stream and Lake Sediments. Journal of Environment Quality. 47(4):884. https://doi.org/10.2134/jeq2018.02.0068

Hupfer M, Zak D, Roβberg R, Herzog C, Pöthig R. 2009. Evaluation of a well-established sequential phosphorus fractionation technique for use in calcite-rich lake sediments: identification and prevention of artifacts due to apatite formation. Limnology and Oceanography: Methods. 7(6):399–410.

Lannergård EE, Agstam-Norlin O, Huser BJ, Sandström S, Rakovic J, Futter MN. 2020. New Insights Into Legacy Phosphorus From Fractionation of Streambed Sediment. Journal of Geophysical Research: Biogeosciences. 125(9):e2020JG005763. https://doi.org/10.1029/2020JG005763

SanClements MD, Fernandez IJ, Norton SA. 2009. Soil and sediment phosphorus fractions in a forested watershed at Acadia National Park, ME, USA. Forest Ecology and Management. 258(10):2318–2325. https://doi.org/10.1016/j.foreco.2009.03.016

Sharpley A, Jarvie HP, Buda A, May L, Spears B, Kleinman P. 2013. Phosphorus Legacy: Overcoming the Effects of Past Management Practices to Mitigate Future Water Quality Impairment. Journal of Environment Quality. 42(5):1308. https://doi.org/10.2134/jeq2013.03.0098