Abstract：
Reducing phosphorus (P) concentrations in aquatic ecosystems, is necessary to improve water quality and reduce the occurrence of harmful cyanobacterial algal blooms. Managing P reduction requires information on the role rivers play in P transport from land to downstream water bodies, but we have a poor understanding of when and where river systems are P sources or sinks. During the summers of 2019 and 2021, we sampled streambed sediment at 78 sites throughout the Maumee River network (a major source of P loads to Lake Erie) focusing on the zero equilibrium P concentration (EPC0), the soluble reactive phosphorus (SRP) concentration at which sediment neither sorbs nor desorbs P. We used structural equation modeling to identify direct and indirect drivers of EPC0. Stream sediment was a P sink at 40 % and 67 % of sites in 2019 and 2021, respectively. During both years, spatial variation in EPC0 was shaped by stream water SRP concentrations, sediment P saturation, and sediment physicochemical characteristics. In turn, SRP concentrations and sediment P saturation (PSR) were influenced by agricultural land use and stream size. Effect of stream size differed among years with stream size having a greater effect on SRP in 2019 and on PSR in 2021. Streambed sediment is currently a net P sink across the sites sampled in the Maumee River network during summer, but sediment at these locations, especially sites in headwater streams, may become a P source if stream water SRP concentrations decrease. Our results improve the understanding of watershed- and reach-scale controls on EPC0 but also indicate the need for further research on how changes in SRP concentration as a result of conservation management implementation influences the role of streambed sediment in P transport to Lake Erie.
摘要：
降低水生生态系统中的磷（P）浓度，改善水质和减少有害蓝藻水华的发生是必要的。管理减少磷需要有关河流在从陆地到下游水体的磷运输中发挥的作用的信息，但是我们对河流系统何时何地是P源或汇的理解很差。在2019年和2021年的夏季，我们对Maumee河网（伊利湖的主要P负荷来源）的78个地点的河床沉积物进行了采样，重点是零平衡P浓度（EPC0），沉积物既不吸附也不解吸P的可溶性活性磷（SRP）浓度。我们使用结构方程模型来确定EPC0的直接和间接驱动因素。2019年和2021年，溪流沉积物是P汇，分别占站点的40%和67%。在这两年间,EPC0的空间变化由溪水SRP浓度决定，沉积物P饱和度,和沉积物的物理化学特征。反过来,SRP浓度和沉积物P饱和度（PSR）受农业土地利用和河流大小的影响。河流大小的影响因年份而异，河流大小对2019年的SRP和2021年的PSR的影响更大。河床沉积物目前是夏季Maumee河网采样地点的净P汇，但是这些地方的沉积物，尤其是在源头水流中的地方，如果溪水SRP浓度降低，则可能成为P源。我们的研究结果提高了对EPC0的水量和范围控制的理解，但也表明需要进一步研究由于实施保护管理而导致的SRP浓度变化如何影响河床沉积物在磷向伊利湖迁移中的作用。
