Relationship between Water Withdrawals and Freshwater Ecosystem Water Scarcity Quantified at Multiple Scales for a Great Lakes Watershed

Abstract

Even in relatively water-rich regions, withdrawal and consumption of water has the potential to create instream freshwater ecosystem water scarcity, especially at seasonal and local scales. Water resource policy must balance consumptive uses of water against corresponding ecosystem impacts of flow depletion. In this study, the concept of an adverse resource impact threshold, as established by the Michigan Water Withdrawal Assessment Process, is applied in conjunction with a water use database to identify the cause, location, and scale in space and time of instream freshwater ecosystem water scarcity caused by consumptive uses of water. The study results show that there is a strong multiscalar linear relationship between freshwater consumption, adverse resource impact ecological flow thresholds, and spatial scale. On average and at the whole-watershed scale, water scarcity does not exist in this watershed, but water scarcity does occur on a localized basis, especially in the summer and at small watershed scales of less than