Irrigation canals are newly created streams of semi-arid agricultural regions

Abstract

The natural hydrologic processes that create and maintain the diversity of aquatic and riparian habitats along the World's streams and rivers have been profoundly altered by humans. Diversion of surface water to support production agriculture in arid and semi-arid regions has degraded ecosystems but also created potential habitat along and in canals specifically designed to transport water. The prevalence of canals and the immense amount of water used for agriculture have created these new artificial stream systems. This study demonstrates the potential for irrigation canals to support riparian and aquatic communities similar to natural streams in urban/residential and agricultural landscapes. We examined the hydrological and ecological characteristics of streams and irrigation canals in urban and agricultural landscapes in northeastern Colorado, typical of regions dominated by irrigation-supported agriculture. Flow patterns in canals depended on their size and had a range of patterns with potential ecological consequences such as rapidly rising and falling water stage, intermittent dry periods, and delayed peak and base flows compared to natural streams. Despite these hydrologic differences, the taxonomic and functional composition of riparian plant and aquatic macroinvertebrate communities indicated that ecological similarities exist between streams and canals, but are dependent, in part, on their landscape setting with stronger similarities in agricultural areas. We also tested the influence of characterizing taxa by functional groups using physiology, ecology and life history traits to explore attributes of habitats including woody canopy structure and water quality. We used a Habitat Quality Index (HQI) that combined physical and biological measures into a single index. Streams scored higher on average within agriculture and urban/residential settings compared to canals; however, one third of urban canals scored above the average of agricultural streams. This multidisciplinary study shows that irrigation canals can be valuable riparian and aquatic habitat, especially in regions with severely degraded streams.