Contrasting controls on the phosphorus concentration of suspended particulate matter under baseflow and storm event conditions in agricultural headwater streams

Abstract

11Whilst the processes involved in the cycling of dissolved phosphorus (P) in rivers have been 12 extensively studied, less is known about the mechanisms controlling particulate P concentrations 13 during small and large flows. This deficiency is addressed through an analysis of large numbers of 14 suspended particulate matter (SPM) samples collected under baseflow (n = 222) and storm event (n = 15 721) conditions over a 23-month period across three agricultural headwater catchments of the River 16 Wensum, UK. Relationships between clay mineral and metal oxyhydroxide associated elements were 17 assessed and multiple linear regression models for the prediction of SPM P concentration under 18 baseflow and storm event conditions were formulated. These models, which explained 71-96% of the 19 variation in SPM P concentration, revealed a pronounced shift in P association from iron (Fe) 20 dominated during baseflow conditions to particulate organic carbon (POC) dominated during storm 21 events. It is hypothesised this pronounced transition in P control mechanism, which is consistent 22 across the three study catchments, is driven by changes in SPM source area under differing 23 hydrological conditions. In particular, changes in SPM Fe-P ratios between small and large flows 24 suggest there are three distinct sources of SPM Fe -surface soils, subsurface sediments and 25 streambed iron sulphide. Further examination of weekly baseflow data also revealed seasonality in the 26Fe-P and aluminium oxalate-dithionate (Al ox-Aldi) ratios of SPM, indicating temporal variability in 27 2 sediment P sorption capacity. The results presented here significantly enhance our understanding of 28 SPM P associations with soil derived organic and inorganic fractions under different flow regimes and 29 has implications for the mitigation of P originating from different sources in agricultural catchments. 30

Challenges of Reducing Phosphorus Based Water Eutrophication in the Agricultural Landscapes of Northwest Europe

“…At the scale of the hyporheic zone, Van der Grift et al (2014 have shown that SRP via Fe(II) oxidatie at the groundwater-surface water interface can be followed by remobilization of newly formed particulate P. Thus, there can be an ambiguity in the location (proximal/distal) of the source of the particulate P, which can be attributed to a proximal source (the river bank) whereas it may stem from remobilization of a more distal primary source. Another example of ambiguity is the P release pulses observed in summer from river sediments whose ultimate source can be a mixture of several point and diffuse sources, located further upstream (Cooper et al, 2015a;Dupas et al, 2017;Smolders et al, 2017).…”

National Large-Scale Wetland Creation in Agricultural Areas—Potential versus Realized Effects on Nutrient Transports

“…Continuous automatic water sampling for estimation of nutrient removal has only been performed in a very restricted number of the wetlands created in agricultural field areas in Sweden. Further, estimations of annual phosphorus removal from water monitoring data in individual wetlands receiving water from agricultural fields are problematic due to that phosphorus transports are highly event-driven and concentration covaries strongly with water flow [14][15][16][17][18]. In this paper, we are approaching these problems.…”

“…In this paper, we are approaching these problems. Several studies have shown that in runoff from agricultural fields, phosphorus is transported largely as particulate phosphorus [15][16][17][19][20][21][22]. Therefore, sedimentation is likely to be the predominant phosphorus removal process in wetlands receiving high phosphorus loads [23][24][25][26][27].…”

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

“…This is because P sorption can only occur across the water-sediment interface and, as such, the specific surface area (SSA) of sediments strongly influences the rates of surface reactions and the ability of sediments to adsorb P (Evans et al 2004;Rawlins et al 2010). Sediments dominated by fine-grained particles have higher SSAs and tend to contain greater concentrations of clay minerals and metal oxyhydroxide complexes to which P has a high affinity, thus enhancing sorption rates (Hartikainen et al 2010;Cooper et al 2015). However, here EPC 0 values displayed no obvious relationship with either the bedrock/superficial geology ( …”