High-frequency monitoring of nitrogen and phosphorus response in three rural catchments to the end of the 2011–2012 drought in England

摘要

This paper uses high-frequency bankside measurements from three catchmentsselected as part of the UK government-funded Demonstration Test Catchments(DTC) project. We compare the hydrological and hydrochemical patterns duringthe water year 2011–2012 from the Wylye tributary of the River Avon with mixedland use, the Blackwater tributary of the River Wensum with arable land useand the Newby Beck tributary of the River Eden with grassland land use. Thebeginning of the hydrological year was unusually dry and all threecatchments were in states of drought. A sudden change to a wet summeroccurred in April 2012 when a heavy rainfall event affected all threecatchments. The year-long time series and the individual storm responsescaptured by in situ nutrient measurements of nitrate and phosphorus (totalphosphorus and total reactive phosphorus) concentrations at each site revealdifferent pollutant sources and pathways operating in each catchment. Largestorm-induced nutrient transfers of nitrogen and or phosphorus to each streamwere recorded at all three sites during the late April rainfall event.Hysteresis loops suggested transport-limited delivery of nitrate in theBlackwater and of total phosphorus in the Wylye and Newby Beck, which wasthought to be exacerbated by the dry antecedent conditions prior to thestorm. The high rate of nutrient transport in each system highlights thescale of the challenges faced by environmental managers when designingmitigation measures to reduce the flux of nutrients to rivers from diffuseagricultural sources. It also highlights the scale of the challenge inadapting to future extreme weather events under a changing climate.