Scale effect in nutrient transport along a rural river system : the river Eden, Cumbria UK

Abstract

Many research studies on nutrient transfer are conducted at small scale and transferring such findings to the large scale at which planners and catchment managers work faces uncertainties because of non-linearity. There is a need therefore for multiscale studies, which define and link the transfer mechanisms across spatial scales. Such a study may also provide the answers on the processes driving it and test the answers further by using a model. Experimental data to support the study were collected from two complementary research programmes in the Eden catchment. Spatial scale variations were investigated through seasonal and spot samples down a sequence of nested catchments, area 1 – 1400 km2, from the NERC-funded Catchment Hydrology and Sustainable Management project (CHASM). Soil samples were also taken. These samples were analysed in the laboratories for nitrate, phosphates and suspended sediment using standard methods. The explanation of spatial variation was then supported by data from two contrasting 10 km2 catchments of the DEFRA-funded Demonstration Test Catchments (DTC) project. A generalisation of the findings was carried out by deploying the TOPCAT-NP model. The nitrate, phosphorus and the suspended sediment concentration, load and yield increased downstream relative to the headwaters. Nitrate sources were complex and appear dominated by groundwater source whereas phosphorus and suspended sediment were from diffuse sources. Nitrate showed the clearest increasing pattern downstream when compared with the other nutrients. A downstream increase in nutrient transfer relates to a downstream increase in flow, agricultural land use and soil type. Hydrology of Morland was adequately represented by the model but the nutrients were less accurate leading to suggestions on model improvement. By carrying out a spatial scale related study of the Eden catchment, analysing the DTC high resolution data and modelling the data, insights into how, where and when nutrients losses occur have been gained. This encourages us, in that targeted land management and a better understanding of the hydrological processes that drive nutrient losses may be an effective way to reduce the problem.