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.

中文翻译：

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小型农业河流中河流悬浮和河床沉积物磷含量的变化

农业是淡水中沉积物和颗粒磷 (P) 输入的主要来源。区分沉积物中的 P 组分有助于了解其富营养化风险。尽管溪流和河流是农业集水区磷循环的重要组成部分，但对河床沉积物，尤其是河流悬浮沉积物 (FSS) 及其 P 组分的研究较少。为了解决这一知识差距，研究了瑞典三个农业源头集水区 2 年间 FSS P 组分的季节性变化及其与水质和河床沉积物的关系。顺序分馏用于表征河床沉积物和 FSS 中的 P 组分。所有流域都有相似的年磷损失（0.4–0.8 kg ha ^–1）、悬浮固体（124–183 mg L ^–1) 和 FSS 总磷浓度 (1.15–1.19 mg g ^–1 )。然而，FSS 中 P 组分和主要 P 组分的分布在流域之间存在差异（p < .05)，这很可能取决于流域地质、粘土含量、外部 P 源和流动条件的差异。在所有集水区中，最突出的季节性模式是铁结合磷，夏季低流量时浓度高，冬季高流量时浓度低。河床沉积物 P 组分的浓度范围与 FSS 中的浓度范围相同，流域之间的组分分布不同。本研究强调需要量化 P 部分，而不仅仅是 FSS 中的总 P，以便更全面地了解农业沉积物损失造成的富营养化风险。