Comparing lake sediment records of landscape macronutrient loadings with N14CP model simulations: 200 years of change in British lakes

To fully understand coupling between P and other macronutrients it is necessary to have both long-term data sets and process models, combining empirical reality with numerical simulation of coupling processes. Here, lake sediment records of N and P from four UK lakes are compared with model output from N14CP, a long-term, large-scale model of cycling and export of macronutrients from the landscape. The sediment records at the three lakes that have substantial lowland contributions reveal strongly increasing N and P loading through the late 19^th century, with steady increases through the twentieth century. Corresponding changes in N and C isotopes are observed. However, the one mountain lake show maximum N and P loadings in the 19^th century, with declines through the twentieth, consistent with a wholly different land use history. The N14CP model shows N and P increasing from mid 19^th century for average lowland sites, in agreement with the lowland sediment records. The implications of these results for our knowledge about the history of P and N coupling and leaching from UK soils are discussed.