J Environ Qual. 2019 Jan;48(1):64-72. doi: 10.2134/jeq2018.03.0104.
Cyanobacteria growth in Missisquoi Bay of Lake Champlain is triggered by the P load carried by tributaries in surrounding watersheds where agriculture is a dominant land use. The objective of this study was to apportion the total P (TP) load in streamflow from an agricultural subwatershed into distinct hydrologic pathways: groundwater resurgence, surface runoff, and tile drainage components (matrix flow and preferential flow). Stream discharge during peak flow was separated into these four components using electrical conductivity (EC)-discharge relationships developed from the stream water EC at the subwatershed outlet and from EC values of surface runoff and tile drain water in 10 fields within the subwatershed. The four-component hydrograph model revealed that 46 to 67% of the TP load at the outlet originated from surface runoff during peak flow. Preferential flow was responsible for most of the particulate P and dissolved reactive P loads lost through tile drainage. Groundwater resurgence was a minor source of TP, whereas other sources such as streambank erosion and resuspended sediments contributed up to 21% of the TP load and from 36 to 41% of the particulate P load at the subwatershed outlet. This work confirms that tile drainage contributes to the TP load in agricultural subwatersheds in the Missisquoi Bay region.
在尚普兰湖的米西索基湾，蓝藻的生长是由周围流域携带的磷负荷引发的，而农业是这些流域的主要土地利用方式。本研究的目的是将农业子流域的地表径流水总磷（TP）负荷分配到不同的水文路径中：地下水回升、地表径流和排水渠（基质流和优先流）组成部分。利用子流域出口处的地表水电导率（EC）值和子流域内 10 个田块的地表径流和排水渠水的 EC 值，通过电导率-流量关系，将峰值流量期间的流量分为这四个组成部分。四组分流量模型表明，出口处的 TP 负荷有 46%至 67%来源于地表径流。优先流是通过排水渠流失的大部分颗粒态磷和可溶解性反应磷的主要来源。地下水回升是 TP 的一个次要来源，而其他来源，如河岸侵蚀和再悬浮沉积物，对 TP 负荷的贡献率高达 21%，对颗粒态磷负荷的贡献率高达 36%至 41%。这项工作证实了排水渠对米西索基湾地区农业子流域的 TP 负荷有贡献。
