Stone Wesley W, Wilson John T
U.S. Geological Survey, Indiana Water Science Center, 5957 Lakeside Blvd., Indianapolis, IN 46278, USA.
J Environ Qual. 2006 Aug 9;35(5):1825-35. doi: 10.2134/jeq2006.0068. Print 2006 Sep-Oct.
Agricultural subsurface drains, commonly referred to as tile drains, are potentially significant pathways for the movement of fertilizers and pesticides to streams and ditches in much of the Midwest. Preferential flow in the unsaturated zone provides a route for water and solutes to bypass the soil matrix and reach tile drains faster than predicted by traditional displacement theory. This paper uses chloride concentrations to estimate preferential flow contributions to a tile drain during two storms in May 2004. Chloride, a conservative anion, was selected as the tracer because of differences in chloride concentrations between the two sources of water to the tile drain, preferential and matrix flow. A strong correlation between specific conductance and chloride concentration provided a mechanism to estimate chloride concentrations in the tile drain throughout the storm hydrographs. A simple mixing analysis was used to identify the preferential flow component of the storm hydrograph. During two storms, preferential flow contributed 11 and 51% of total storm tile drain flow; the peak contributions, 40 and 81%, coincided with the peak tile drain flow. Positive relations between glyphosate [N-(phosphonomethyl)glycine] concentrations and preferential flow for the two storms suggest that preferential flow is an important transport pathway to the tile drain.
农业地下排水管道，通常称为瓦管，在中西部大部分地区可能是肥料和农药流入溪流和沟渠的重要潜在途径。非饱和带中的优先流为水和溶质提供了一条绕过土壤基质的路径，使其比传统置换理论预测的更快到达瓦管。本文利用2004年5月两次暴雨期间的氯化物浓度来估算优先流对瓦管排水的贡献。氯化物是一种保守阴离子，由于流入瓦管的优先流和基质流这两种水源的氯化物浓度存在差异，因此被选作示踪剂。电导率与氯化物浓度之间的强相关性为估算整个暴雨过程中瓦管排水中的氯化物浓度提供了一种方法。采用简单的混合分析来确定暴雨过程线中的优先流成分。在两次暴雨期间，优先流分别占暴雨期间瓦管排水总量的11%和51%；其峰值贡献分别为40%和81%，与瓦管排水流量峰值一致。两次暴雨期间草甘膦[N-(膦酰基甲基)甘氨酸]浓度与优先流之间的正相关关系表明优先流是瓦管排水的重要输送途径。
