Orthophosphate-P in the nutrient impacted River Taw and its catchment (SW England) between 1990 and 2013

Abstract

Excess dissolved phosphorus (as orthophosphate-P) contributes to reduced river water quality within Europe and elsewhere. This study reports results from analysis of a 23 year (1990-2013) water quality dataset for orthophosphate-P in the rural Taw catchment (SW England). Orthophosphate-P and river flow relationships and temporal variations in orthophosphate-P concentrations indicate the significant contribution of sewage (across the catchment) and industrial effluent (upper R. Taw) to orthophosphate-P concentrations (up to 96%), particularly during the low flow summer months when maximum algal growth occurs. In contrast, concentrations of orthophosphate-P from diffuse sources within the catchment were more important (>80%) at highest river flows. The results from a 3 end-member mixing model incorporating effluent, groundwater and diffuse orthophosphate-P source terms suggested that sewage and/or industrial effluent contributes ≥50% of the orthophosphate-P load for 27-48% of the time across the catchment. The Water Framework Directive (WFD) Phase 2 standards for reactive phosphorus, introduced in 2015, showed the R. Taw to be generally classified as Poor to Moderate Ecological Status, with a Good Status occurring more frequently in the tributary rivers. Failure to achieve Good Ecological Status occurred even though, since the early-2000s, riverine orthophosphate-P concentrations have decreased (although the mechanism(s) responsible for this could not be identified). For the first time it has been demonstrated that sewage and industrial effluent sources of alkalinity to the river can give erroneous boundary concentrations of orthophosphate-P for WFD Ecological Status classification, the extent of which is dependent on the proportion of effluent alkalinity present. This is likely to be a European - wide issue which should be examined in more detail.

Forty-year trends in the flux and concentration of phosphorus in British rivers

“…Therefore, it can be proposed that these step changes were brought about by the implementation of the UWWTD. This is in agreement with other studies from individual British rivers which have assessed changes in P concentrations, fluxes and eutrophication risk since the 1990s (e.g., Bowes et al 2010, 2011, Whitehead et al, 2013Earl et al, 2014;Bussi et a, 2016, Tappin et al, 2016. Worrall et al (2016) could show that urban land use was the important contributor to the explanation of TP flux across the UK but did not consider change in this urban source over time.…”

“…Muscutt and Withers (1996) carried out a study among 98 rivers in England and Wales and reported that 80% of the rivers were failing a target limit of of 0.1 mg/l mean orthophosphate concentration (DoE, 1993). However, the UK has increased investment and accelerated implementation of the UWWTD at STWs in the last decade (Bowes, et al, 2010): investment in England was almost doubled from £9600 M in the period 1990 -2000 to £16100 M in the years between 2000 -2015; with a total investment of £39126 M on STWs overall in the UK for the years between 1990(DEFRA, 2015. These actions have started to pay off with considerable reduction of phosphorus concentrations in many UK rivers (Kinniburgh & Barnett, 2010;Bowes, et al, 2009;Neal, et al, 2010c).…”

The role of alkalinity in setting water quality metrics: phosphorus standards in United Kingdom rivers

“…These authors used ordinary least squares regression (OLS) to quantify the relationship between load and flow, but in the current work the robust parametric bisquare weights linear regression was used because it is less sensitive to heteroscedastic data and the presence of outliers than OLS. 19,20 Concentration and flow data for all years for each site were used to estimate the slope value because the sampling frequency was generally only ca. 12 samples y -1 and alkalinity data were not available for all years.…”

Higher Abundance of Sediment Methanogens and Methanotrophs Do Not Predict the Atmospheric Methane and Carbon Dioxide Flows in Eutrophic Tropical Freshwater Reservoirs

“…These results corroborate that pollution favors gaseous flows in water bodies (Gonzalez-Valencia et al, 2014;Silva et al, 2016), by supporting the microbial community acting in these flows, and reinforce the concept that management measures, aiming at preventing or reducing anthropogenic impacts, should also be considered to mitigate CH 4 and CO 2 emissions from reservoirs (Ometto et al, 2013). Domestic sewage discharges are the likely impact on these reservoirs, according to the values of P-PO 4 3− , EC, DTC, TSS, and BOD, and should be prevented or at least minimized (Shiddamallayya and Pratima, 2008;Tappin et al, 2016;Vigiak et al, 2019;Coelho et al, 2020). Although not innovative, such observations in environmental samples reinforce the robustness of our data and strengthen the remainder conclusions drawn in this research.…”