Ecological characteristics, environmental services and the potential for change in a semi-arid agricultural landscape in Colorado, U.S.A.
Date
2017
Authors
Carlson, Erick A., author
Cooper, David J., advisor
Kondratieff, Boris, committee member
Merritt, David M., committee member
Waskom, Reagan, committee member
Journal Title
Journal ISSN
Volume Title
Abstract
The conversion of native vegetation to cities and agriculture has caused a loss in habitat diversity with subsequent effects on plant and animal populations. Hydrologic modifications have increased land available for buildings and crops through drainage and irrigation, with largely negative effects on aquatic and wetland ecosystems. This work contributes to the growing literature of ecological benefits of anthropogenic ecosystems with two examples from the infrastructure and activities associated with irrigated agriculture, canal riparian habitat and nutrient mitigation processes of tailwater wetlands. The prevalence of canals in agricultural areas and the immense amount of water used for agriculture have created a new stream system in parts of the western U.S. In my study area in semi-arid, northcentral Colorado 1,906 km of canals supply water to 67,606 ha of irrigated agriculture and several cities and towns. Riparian vegetation bordering the canals was statistically similar for canals and streams in agricultural areas for composition of functional plant groups, yet dissimilar for species composition. In residential areas species composition was statistically different, though the p-value was borderline (p=0.05) and the functional groups were more strongly separated (p=0.013). Temporary aquatic habitat also provides suitable conditions for macroinvertebrate communities to colonize with statistically similarity between canals and streams in both land uses. In addition to the similarity to natural ecosystems, the length of canals can exceed that of natural streams in some regions, potentially creating more riparian habitat than would have naturally occurred and in new landscape positions. During high agricultural and municipal water use, more water could be flowing through artificial channels than natural streams, creating a paradigm shift and posing the concept that canals are the new rivers of the West. Wetlands can trap and process agricultural water pollutants, but landscape position is crucial to accumulate polluted runoff or groundwater and maintain hydrologic conditions favorable to biogeochemical processes for pollutant removal. Tailwater wetlands receiving excess irrigation water and surface runoff intercepted nutrient rich waters with nitrate (NO3-N) concentrations up to 54 mg/L, over five times the U.S. EPA and ten times the drinking water standard in Europe. Biotic, hydrologic, biochemical characteristics of tailwater wetlands were favorable for N transformation and uptake processes with shallow water tables creating anoxic conditions and sufficient organic matter and microbial communities for denitrification processes. Plant uptake was of greater importance at all wetland sites, especially those with Typha latifolia. The duration of saturated conditions supported wetland plants with high annual biomass for uptake of excess nutrients. A decline in irrigated agriculture could change the type, extent and quality of ecosystems services associated with canal infrastructure and tailwater wetlands. A one-third decline in irrigated agriculture in the study area was modeled through drying up irrigated land using several spatial prioritizations. These resulted in different location and intensity of effects on canal riparian and wetland ecosystem services. Results from these three studies identify two ecosystem services of the infrastructure and activities associated with irrigated agriculture and the potential unintended consequences of changes to the timing and amount of water distributed across the landscape.