Anthropogenic impacts on river food webs

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Southern Alberta is an area of acute water scarcity, where all aquatic resources are subjected to considerable anthropogenic influence.  In addition, it is an area, due to the shortage of lakes, where very work on aquatic foodwebs has been done.   A long-term goal is to address the spatial problems (both methodological and theoretical) of working with riverine food webs.  These arise from the linear geometry of rivers and the fact that they are usually open-ended hierarchical systems with strong directionality and strong upstream/downstream gradients in virtually every attribute (eg temperature, nutrients, and productivity).  As such the species compostion and dynamics  of the foodweb is gradually changing along the river continuum.   The proposal outlines three projects related to river food webs structure and function   (1)Mercury biomagnification in the SSRB food web.  The questions to be answered using a nested comparative approach within the watershed, are: (a) What is the gradient in mercury exposure along the river, (b) how important are activities such as coal mining, intensive agriculture, irrigation, and sewage as potential mercury sources, and (c) can levels of mercury seen in top predators be explained by local exposure and biomagnification, or is biotransport through fish movements from downstream areas an important factor.   (2)Ecological consequences of hybridization between introduced rainbow trout and native cutthroat trout. Cutthroat trout dominate the foodwebs of the headwater regions of many western rivers. Rainbow trout stocking has resulted in the formation and spread of hybrids that are rapidly expanding their range leaving very few genetically pure cutthroat trout populations. This study will explore ecological differences between hybrids and native cutthroat trout and their functional consequences. 3.)Organic matter and nutrients from domestic and animal sewage and its impact on river food webs.  In this project we will use stable isotopes to trace the magnitude and the extent of foodweb enrichment from these sources.