Evaluating Ecosystem Services in Coupled Human-Natural Systems

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Although irrigation systems are generally assessed with respect to the quantity of water delivered and the cost-benefit ratio of transporting water, some irrigation systems may connect to natural environments and improve water quality through nutrient processing. Irrigation systems, as human-built systems, are not entirely separate from the natural watershed. Irrigation systems can play a role in nutrient transport and transformation, sediment transport, flood mitigation, maintaining water temperatures, and others. These processes may provide beneficial ecosystem services to the surrounding community. However, management of irrigation systems is typically complex and decentralized. For example, irrigation in Cache Valley is managed by approximately 25 different companies and each company is facing decisions on how to maintain their infrastructure. The Logan and Northern Canal, belonging to one of the larger irrigation companies, has relocated their diversion structure to a different location within the Logan River within the last three years, and completely enclosed the segment of the canal following the diversion. Other canal sections within Cache Valley have similar changes and enclosures proposed in the near future. Little is known about the water quality benefits provided currently or how they may change with proposed plans. This research will examine the role of water quality ecosystem services provided within the irrigation systems connected to the Logan River. First a general literature review of ecosystems services provided by streams and canals will inform us of the services we could expect to find within Cache Valley's irrigation system, and explore how these services have been modeled. A conceptual model will be created to organize current understanding of the system, highlight data gaps, and formulate hypotheses of system function. Two computer models will be developed to describe current system behavior, and predict outcomes for future decisions. One computer model will be a water quality simulation model, describing current conditions within the irrigation network. The second model will be a water quality and quantity management optimization model. The management model will estimate changes to nutrient processing and downstream water quality by evaluating how ecosystem services change with decisions to use dirt-lined, cement-lined or piped irrigation systems. These models will present an approach to not only estimate and manage water quality ecosystem services from changes to irrigation systems in Cache Valley, but also provide a generalizable approach that can be applied in a similar manner to other locations. Irrigation systems throughout the Wasatch Front and in many water-scarce regions of the American West are being updated to improve water use efficiency. Improvements to water quantity and possible impairments to water quality must be evaluated together for irrigation districts and water managers to make informed decisions. These models will be part of a larger set of analysis through iUTAH, an EPSCOR project, where they will be combined with other models of local water use to create a more complete understanding of how to best manage our limited natural resources.

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