Reliable quantification of phosphorus (P) sources is critical for cost effective mitigation of freshwater eutrophication. At present, measures to reduce nutrient loading to aquatic systems are widely predicated on the assumption that in the absence of sewage inputs, agricultural sources, particularly those that persist in the catchment as legacy P, are the primary control. For example, landscape export coefficient models assign particularly high values to arable land, implying that fertilizer application rates are a key control. Long duration records of lake water total phosphorus (TP) offer a solution; by comparison with historical records of potential drivers, assumptions over the relative importance of each source can be tested. However, most directly measured TP records are not long enough to enable this. Here, lake sediment-inferred TP records (SI-TP) offer an alternative. We combine a 200-year SI-TP record from Crose Mere, a small eutrophic UK lake, with historical land-use data to test the assumed dominance of arable P sources in the lake P budget. We find 20th century chemical fertilizer usage has no direct influence on TP trends, highlighting the canonical assumption about the role of chemical agriculture in driving freshwater eutrophication need not be valid. This paves the way for a critical analysis of eutrophication drivers, and a recognition that export coefficient models cannot reliably use single values to represent arable land. This approach enables the impact of land use change on the lake P cycle to be quantified, bridging the terrestrial-aquatic divide.

Primary Presenter: Madeleine Moyle, University of Liverpool (maddy.moyle@liverpool.ac.uk)

Authors:

Madeleine Moyle, University of Liverpool  (maddy.moyle@liverpool.ac.uk)

John Boyle, University of Liverpool  (jfb@liverpool.ac.uk)