认识到源头床和悬浮沉积物减轻大湖下游的非点农业磷(P)负荷的能力,但是促进沉积物P保留或内部P释放的特定生物地球化学过程仍然知之甚少。为了阐明这些机制,位于安大略省南部优先流域内的三个源头段,加拿大,在2018-2020年的生长季节进行了采样。这项研究采用了平衡磷测定法以及对传统分水岭养分的新颖评估,氮(N)浓度,沉积物氧化还原,和微生物群落组成。20年的数据显示,在无机肥料和粪肥影响的地点,总磷(TP)和总氮(TN)升高,分别。总的来说,采样地点充当P汇;然而,与参考森林流域相比,农业沉积物的缓冲能力明显较低。通过时间积分采样收集细悬浮沉积物(<63µm),表明无机施肥地点的悬浮负荷已被P饱和,表明与床沉积物相比,磷释放到地表水中的潜力更大。通过沉积物微生物群落的垂直微传感器分析和DNA测序,确定了与不同P源事件相关的位点特异性因素.其中包括整个沉积物界面(SWI)的溶解氧(DO)的快速消耗,以及硝酸盐还原细菌和氨氧化古细菌(AOA)属的存在。这项研究为源头中P的动态提供了有价值的见解,P保持和释放时发光。了解这些过程对于旨在减轻大湖下游磷污染的有效管理策略至关重要。
The ability of headwater bed and suspended sediments to mitigate non-point agricultural phosphorus (P) loads to the lower Great Lakes is recognized, but the specific biogeochemical processes promoting sediment P retention or internal P release remain poorly understood. To elucidate these mechanisms, three headwater segments located within priority watersheds of Southern Ontario, Canada, were sampled through the growing season of 2018-2020. The study employed equilibrium P assays along with novel assessments of legacy watershed nutrients, nitrogen (N) concentrations, sediment
redox, and microbial community composition. 20-year data revealed elevated total P (TP) and total Nitrogen (TN) at an inorganic fertilizer and manure fertilizer-impacted site, respectively. Overall, sampled sites acted as P sinks; however, agricultural sediments exhibited significantly lower buffering capacity compared to a reference forested watershed. Collection of fine suspended sediment (<63 µm) through time-integrated sampling showed the suspended load at the inorganic-fertilized site was saturated with P, indicating a greater potential for P release into surface waters compared to bed sediments. Through vertical microsensor profiling and DNA sequencing of the sediment microbial community, site-specific factors associated with a distinct P-source event were identified. These included rapid depletion of dissolved oxygen (DO) across the sediment water interface (SWI), as well as the presence of nitrate-reducing bacterial and ammonia-oxidizing archaeal (AOA) genera. This research provides valuable insights into the dynamics of P in headwaters, shedding light on P retention and release. Understanding these processes is crucial for effective management strategies aimed at mitigating P pollution to the lower Great Lakes.