Using high-resolution phosphorus data to investigate mitigation measures in headwater river catchments

Abstract

Abstract. This study reports the use of high-resolution water quality monitoring to assess the influence of changes in land use management on total phosphorus (TP) transfers in two 5 km 2 agricultural sub-catchments. Specifically, the work investigates the issue of agricultural soil P management and subsequent diffuse transfers at high river flows over a 5-year timescale. The work also investigates the phenomenon of low flow P pollution from septic tank systems (STSs) and mitigation efforts -a key concern for catchment management. Results showed an inconsistent response to soil P management over 5 years with one catchment showing a convergence to optimum P concentrations and the other an overall increase. Both catchments indicated an overall increase in P concentration in defined high flow ranges. Low flow P concentration showed little change or higher P concentrations in defined low flow ranges despite replacement of defective systems and this is possibly due to a number of confounding reasons including increased housing densities due to new-builds. The work indicates fractured responses to catchment management advice and mitigation and that the short to medium term may be an insufficient time to expect the full implementation of policies (here defined as convergence to optimum soil P concentration and mitigation of STSs) and also to gauge their effectiveness.

High-resolution monitoring of nutrients in groundwater and surface waters: process understanding, quantification of loads and concentrations, and management applications

“…In contrast, highfrequency monitoring reduces the bias in concentration distributions derived from under-sampling of the concentration time series (e.g. Jordan et al, 2007;Rozemeijer et al, 2010b;Ernstsen et al, 2015;Campbell et al, 2015). High-frequency monitoring may also reveal artefacts produced by the fact that regular sampling is normally undertaken in the daytime, thus typically not capturing differences between daytime and night-time fluxes Van der Grift et al, 2016).…”

“…Besides revealing the time-dependent nutrient inputs from, for instance, sewage treatment facilities or leaking septic tanks (Wade et al, 2012a), the effects of mitigating measures can be followed by assessing changes in the duration or frequency of nutrient peaks in the time series before and after their implementation. Examples are given in Campbell et al (2015) and Greene et al (2011).…”

“…Despite the establishment of high-frequency monitoring, the effects of mitigation measures are often difficult to separate from those of natural variability created by meteorological conditions or from spatial variations in governing variables such as soil types and subsurface reactivity. Examples of monitoring the effects of mitigation measures in diffuse pollution settings are given in Campbell et al (2015), Ernstsen et al (2015), Van der Grift et al (2016), and Rozemeijer et al (2016), all included in this special issue, and Greene et al (2011). Given the slower dynamics of groundwater, other techniques such as age dating and lower monitoring frequencies are usually applied to reveal trends following implementation of mitigation measures (Broers and Van der Grift, 2004;Visser et al, 2007Visser et al, , 2009Hansen et al, 2012aHansen et al, , b, 2013).…”

“…Often, these rapid changes occur at timescales of less than 1 h and high-frequency monitoring is required in order to capture peaks and extreme values that would go undetected if applying only low-frequency monitoring (cf. Campbell et al, 2015;Skeffington et al, 2015;Van der Grift et al, 2016).…”

“…However, the design of monitoring strategies is often hampered by limited knowledge of, for instance, nutrient responses to weather conditions, land use, and agricultural practices. Moreover, the behaviour of nutrients shows large variability in both space and time (see, e.g., Campbell et al, 2015;Goyenola et al, 2015).…”