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

Abstract

This paper uses high-frequency bankside measurements from three catchments selected as part of the UK government-funded Demonstration Test Catchments (DTC) project. We compare the hydrological and hydrochemical patterns during the water year 2011–2012 from the Wylye tributary of the River Avon with mixed land use, the Blackwater tributary of the River Wensum with arable land use and the Newby Beck tributary of the River Eden with grassland land use. The beginning of the hydrological year was unusually dry and all three catchments were in states of drought. A sudden change to a wet summer occurred in April 2012 when a heavy rainfall event affected all three catchments. The year-long time series and the individual storm responses captured by in situ nutrient measurements of nitrate and phosphorus (total phosphorus and total reactive phosphorus) concentrations at each site reveal different pollutant sources and pathways operating in each catchment. Large storm-induced nutrient transfers of nitrogen and or phosphorus to each stream were recorded at all three sites during the late April rainfall event. Hysteresis loops suggested transport-limited delivery of nitrate in the Blackwater and of total phosphorus in the Wylye and Newby Beck, which was thought to be exacerbated by the dry antecedent conditions prior to the storm. The high rate of nutrient transport in each system highlights the scale of the challenges faced by environmental managers when designing mitigation measures to reduce the flux of nutrients to rivers from diffuse agricultural sources. It also highlights the scale of the challenge in adapting to future extreme weather events under a changing climate

Riverbed sediments buffer phosphorus concentrations downstream of sewage treatment works across the River Wensum catchment, UK

“…The concentration increases observed here therefore strongly suggests diffuse P from agriculture was a more important source of P input into the River Wensum at the time of the September sampling due to precipitation-induced soil erosion and flushing of P sources from across the wider catchment (Quinton et al 2001). This is supported by previous studies which have shown up to 70% of annual riverine P load is transported from arable dominated sub-catchments of the River Wensum during storm events at mean rates of 0.1-0.2 kg P ha −1 (Outram et al 2014;Outram et al 2016). It is also likely that the elevated September discharge initiated the remobilisation of P-rich fines deposited on the riverbed during intervening periods of low flow when sediment and P retention times would have been greater.…”

Changing climate and nutrient transfers: Evidence from high temporal resolution concentration-flow dynamics in headwater catchments

“…There is, therefore, increasing interest in the use of in-stream high resolution water quality monitoring to assemble higher resolution catchment-scale datasets (e.g. Bowes et al, 2015;Halliday et al, 2012;Jordan et al, 2012;Mellander et al, 2012;Mellander et al, 2014;Outram et al, 2014;Skeffington et al, 2015;Wade et al, 2012), which can be used to understand key catchment processes in terms of hydrology, diffuse pollution transfer and trophic impacts and how these may alter under a changing climate.…”

Dominant mechanisms for the delivery of fine sediment and phosphorus to fluvial networks draining grassland dominated headwater catchments

“…Lefrançois et al, 2007;Naden, 2010;Outram et al, 2014;Smith and Dragovich, 2009). Small scale experiments, in which the pollutant transport processes are controlled, have successfully produced the expected hysteresis dynamics, offering support for this indirect approach (e.g.…”

“…Analysis of the process dynamics of multiple contaminants using this hysteresis framework enables commonalities in transport systems to be assessed, and maximum information to be extracted about pollutant and catchment response to hydrological events (e.g. Halliday et al, 2014;Mellander et al, 2012;Outram et al, 2014;Owen et al, 2012;Wade et al, 2012). Specifically, this framework enables an assessment of the complicating factors and influences on SS and P transfer at multiple scales (e.g.…”