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 δ18O 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 channels incised. Increased frequent peak flows in the BER have created laterally confined channels that are disconnected from an accessible riparian corridor. Frequent access to a functioning riparian zone is important for denitrification.
|Original language||English (US)|
|Number of pages||16|
|Journal||Environmental Monitoring and Assessment|
|State||Published - Feb 2004|
Bibliographical noteFunding Information:
Funding for this work was provided by the Minnesota State legislature and the U.S.Geological Survey Cooperative Grant Program. The authors wish to thank Steve Komor for his assistance in data collection and interpretation and Larry Gunderson for the construction of Figure 1. This manuscript was improved by the thoughtful comments of: Tim Larson, Don Hansen, Tom Keep and two anonymous reviewers.
Copyright 2008 Elsevier B.V., All rights reserved.
- Channel geomorphology
- Peak flow