Magner J A, Payne G A, Steffen L J
Minnesota Pollution Control Agency, St. Paul, Minnesota, USA.
Environ Monit Assess. 2004 Feb;91(1-3):183-98. doi: 10.1023/b:emas.0000009235.50413.42.
Excessive nitrate-N in south-central Minnesota ditches and streams is related to land-use change, and may be contributing to the development of the zone of hypoxia in the Gulf of Mexico. Intensive land-use (agricultural management) has progressively increased as subsurface drainage has improved crop productivity over the past 25 years. We have examined water at varying scales for delta18O and, nitrate-N concentrations. Additionally, analysis of annual peak flows, and channel geomorphic features provided a measure of hydrologic change. Laboratory and field results indicate that agricultural drainage has influenced riverine source waters, concentrations of nitrate-N, channel dimensions and hydrology in the Blue Earth River (BER) Basin. At the mouth of the BER shallow ground water comprises the largest source water component. The highest nitrate-N concentrations in the BER and tributaries typically occurred in May and June and ranged from 7-34 mg L(-1). Peak flows for the 1.01-2-yr recurrence intervals increased by 20-to-206% over the past 25 years. Geomorphic data suggest that small channels (ditches) were entrenched by design, whereas, natural that are disconnected from an accessible riparian corridor. Frequent access to a functioning riparian zone is important for denitrification.
明尼苏达州中南部沟渠和溪流中过量的硝态氮与土地利用变化有关，可能导致墨西哥湾缺氧区的形成。在过去25年里，随着地下排水提高了作物产量，集约化土地利用（农业管理）逐渐增加。我们在不同尺度上检测了水的δ18O和硝态氮浓度。此外，对年峰值流量和河道地貌特征的分析提供了水文变化的度量。实验室和野外结果表明，农业排水影响了蓝地球河（BER）流域的河流水源、硝态氮浓度、河道尺寸和水文状况。在BER河口，浅层地下水是最大的水源组成部分。BER及其支流中硝态氮浓度最高值通常出现在5月和6月，范围为7 - 34 mg L(-1)。在过去25年里，1.01 - 2年重现期的峰值流量增加了20%至206%。地貌数据表明，小河道（沟渠）是特意开凿的，而天然河道与可进入的河岸走廊断开了联系。频繁进入功能正常的河岸带对于反硝化作用很重要。
