Variability in fluvial suspended and streambed sediment phosphorus fractions among small agricultural streams

Abstract

Agriculture is a major source of sediment and particulate phosphorus (P) inputs to freshwaters. Distinguishing between P fractions in sediment can aid in understanding its eutrophication risk. Although streams and rivers are important parts of the P cycle in agricultural catchments, streambed sediment and especially fluvial suspended sediment (FSS) and its P fractions are less studied. To address this knowledge gap, seasonal variations in FSS P fractions and their relation to water quality and streambed sediment were examined in three Swedish agricultural headwater catchments over 2 yr. Sequential fractionation was used to characterize P fractions in both streambed sediment and FSS. All catchments had similar annual P losses (0.4-0.8 kg ha -1 ), suspended solids (124-183 mg L -1 ), and FSS total P concentrations (1.15-1.19 mg g -1 ). However, distribution of P fractions and the dominant P fractions in FSS differed among catchments (p < .05), which was most likely dependent on differences in catchment geology, clay content, external P sources, and flow conditions. The most prominent seasonal pattern in all catchments was found for iron-bound P, with high concentrations during low summer flows and low concentrations during winter high flows. Streambed sediment P fractions were in the same concentration ranges as in FSS, and the distribution of the fractions differed between catchments. This study highlights the need to quantify P fractions, not just total P in FSS, to obtain a more complete understanding of the eutrophication risk posed by agricultural sediment losses.

Phosphorus supply and floodplain design govern phosphorus reduction capacity in remediated agricultural streams

“…The range of TP content in channel bed sediments was consistent with other agricultural streams in Sweden (0.07-1.57 g P kg −1 , Lannergård et al, 2020; 0.35-1.85 g P kg −1 , Sandström et al, 2021), indicating that remediated streams do not promote P enrichment in channel beds compared with streams without floodplains. However, the proportions of labile P fractions were overall lower in our study, either explained by less deposition of these fractions or a more rapid turnover of labile P. In a comparable system, sediments were also dominated by recalcitrant fractions that were shown to be stable over seasons (Kindervater and Steinman, 2019).…”

“…Internal erosion from trapezoidal channels can therefore contribute with higher sediment and P loads compared with distal sediment sources in catchments (Simon and Rinaldi, 2006). Closely interlinked with sediment conveyance in channels is the instream transport and storage of P, governed by fluvial processes (deposition/resuspension of sediment-bound P; Ballantine et al, 2009;Noe et al, 2019), redox processes (adsorption/desorption of soluble reactive P [SRP] to SS; Sandström et al, 2021) and geomorphic stability (streambank erosion;Fox et al, 2016). Channel bed sediments can store high amounts of P (Ballantine et al, 2009) and although deposition has been found to dominate in headwater reaches owing to stream power limitation (Worrall et al, 2020), sediment-bound P becomes susceptible to remobilization during high flow events (Bowes et al, 2003).…”

How to Achieve a 50% Reduction in Nutrient Loads from Agricultural Catchments under Different Climate Trajectories?

“…The lack of TP load response to a reduction in phosphorus fertilisation corresponded with results by Capell et al (2021) in the Baltic sea region, but contrasted with the outcomes from Ockenden et al (2017) in England. The strong binding of phosphate to finetextured soils and sediments in the study sites might form an explanation (Sandström et al, 2021).…”

The impact of external plant carbon sources on nitrogen removal and microbial community structure in vertical flow constructed wetlands

“…Agricultural production efforts generate large volumes of rainfall-runoff derived from farmlands that (Leng et al, 2021), owing to the excessive application of chemical fertilizers and pesticides, carry large amounts of nitrogen (N) that can cause serious surface water pollution (Butkovskyi et al, 2021). Nutrient levels in surface bodies of water that are derived from such receding farmland water runoff can rise as high as 60%-80% (Hu, Yang, Han and Wang, 2019), making these waters the primary non-point source of agriculture-associated pollution (Lavrnić et al, 2018;Jabbar and Grote, 2019;Kaandorp et al, 2021;Sandström et al, 2021). China is a large nation with an extensive agricultural system that relies on the use of large quantities of chemical fertilizers, posing a major risk to Chinese surface water quality owing to the potential for farmland-derived runoff pollution.…”