The impact of agricultural intensification and fertilizer inputs on stream water quality were examined at different catchment scales for an area of mixed land use in Devon, England. Storm events were the main mechanism of sediment and solute transfer, with ammonium, phosphate, and suspended sediment mobilized in surface runoff and nitrate transfered in throughflow. Surface runoff from heavily grazed permanent pasture was 53% of the total rainfall input and delivered 0.5kgha_1 phosphorus, l ^ k g h a - 1 nitrogen and 0.5kgha -1 suspended sediment. For ungrazed land with intact vegetation cover, surface runoff was only 7% of the rainfall input. This significantly reduced sediment and solute delivery. An annual input of 260 tonnes NOa-N, 3 tonnes NrU-N, 2 tonnes PO4-P and 640 tonnes suspended sediment was recorded from the 46km2 catchment to Slapton Ley, a 0.8km2 freshwater lake. Although over 80% of this input "occured in'
winter it was less critical for lake eutrophication than the 20% delivered in summer when nutrient export from the lake is minimal.
Runoff, sediment, and solute delivery in agricultural drainage basins: a scale-dependent approach
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