Hydrochemical processes in lowland rivers: insights from in situ, high-resolution monitoring

Abstract

Abstract. This paper introduces new insights into the hydrochemical functioning of lowland river systems using fieldbased spectrophotometric and electrode technologies. The streamwater concentrations of nitrogen species and phosphorus fractions were measured at hourly intervals on a continuous basis at two contrasting sites on tributaries of the River Thames -one draining a rural catchment, the River Enborne, and one draining a more urban system, The Cut. The measurements complement those from an existing network of multi-parameter water quality sondes maintained across the Thames catchment and weekly monitoring based on grab samples. The results of the sub-daily monitoring show that streamwater phosphorus concentrations display highly complex dynamics under storm conditions dependent on the antecedent catchment wetness, and that diurnal phosphorus and nitrogen cycles occur under low flow conditions. The diurnal patterns highlight the dominance of sewage inputs in controlling the streamwater phosphorus and nitrogen concentrations at low flows, even at a distance of 7 km from the nearest sewage treatment works in the rural River Enborne. The time of sample collection is important when judging water quality against ecological thresholds or standards. An exhaustion of the supply of phosphorus from diffuse and multiple septic tank sources during storm events was evident and load estimation was not improved by sub-daily monitoring beyond that achieved by daily sampling because of the eventual reduction in the phosphorus mass entering the stream during events. The results highlight the utility of sub-daily water quality measurements and the discussion considers the practicalities and challenges of in situ, sub-daily monitoring.

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

“…The system was subjected to a weekly cleaning cycle, with automatic calibration with a 2 mg L -1 standard solution being performed daily. TP is determined colourimetrically following heating of the sample to 140ºC under pressure and being subjected to persulfate digestion, whilst molybdate-reactive phosphorus (TRP) concentrations are determined colourimetrically on an unfiltered sample (Elisenreich et al, 1975;Wade et al, 2012). TRP is an operationally defined measurement predominantly comprised of orthophosphate (PO4; SRP), although readily hydrolysable P species in the sample may also be present within this TRP fraction (Halliday et al, 2014).…”

“…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.…”

Evolution of physicochemical species concentration in streams based on heavy rainfall event data obtained for high-frequency monitoring

“…These technological developments provide rainfall measurements, stream flow, and physicochemical parameters in short time intervals (KIRCHNER et al, 2004), such as seven-hour intervals NEAL et al, 2013;NEAL et al, 2012), two-hour intervals (DONN; BARRON; BARR, 2012), hourly intervals (BOWES et al, 2015;HALLIDAY et al, 2014;JORDAN et al, 2007;RÜCKER;SCHRAUTZER, 2010;WADE et al, 2012), or in minutes (CASSIDY; JORDAN, 2011;DOWNING et al, 2009;MORAETIS et al, 2010;TERCIER-WAEBER et al, 2009). High frequency monitoring helps our understanding of the biogeochemical processes that occur in natural waters in short time intervals (MORAETIS et al, 2010;SANDFORD;EXENBERGER;WORSFOLD, 2007;WADE et al, 2012).…”

“…Studies with high frequency sampling of streams managed to correlate changes in the electrical conductivity to the water runoff (ROBSON et al, 1992), demonstrate the diurnal and seasonal dynamics of nutrients (BOWES; SMITH; NEAL, 2009;CASSIDY;JORDAN, 2011;DONN;BARRON;BARR, 2012;HALLIDAY et al, 2014HALLIDAY et al, , 2012MORAETIS et al, 2010;NEAL et al, 2012;SANDFORD;EXENBERGER;WORSFOLD, 2007;SCHOLEFIELD et al, 2005;WADE et al, 2012) and metal species (TERCIER-WAEBER et al, 2009), enable mass balances in watersheds (JORDAN et al, 2007;RÜCKER;SCHRAUTZER, 2010), and analyze the spatial and temporal variations of dissolved oxygen (MALCOLM; SOULSBY; YOUNGSON, 2006).…”