Use Of A Dynamic Simulation Model To Understand Nitrogen Cycling In The Middle Rio Grande Nm

Use of a Dynamic Simulation Model to Understand Nitrogen Cycling in the Middle Rio Grande, NM.

Water quality often limits the potential uses of scarce water resources in semiarid and arid regions. To best manage water quality one must understand the sources and sinks of both solutes and water to the river system. Nutrient concentration patterns can identify source and sink locations, but cannot always determine biotic processes that affect nutrient concentrations. Modeling tools can provide insight into these large-scale processes. To address questions about large-scale nitrogen removal in the Middle Rio Grande, NM, we created a system dynamics nitrate model using an existing integrated surface water--groundwater model of the region to evaluate our conceptual models of uptake and denitrification as potential nitrate removal mechanisms. We modeled denitrification in groundwater as a first-order process dependent only on concentration and used a 5% denitrification rate. Uptake was assumed to be proportional to transpiration and was modeled as a percentage of the evapotranspiration calculated within the model multiplied by the nitrate concentration in the water being transpired. We modeled riparian uptake as 90% and agricultural uptake as 50% of the respective evapotranspiration rates. Using these removal rates, our model results suggest that riparian uptake, agricultural uptake and denitrification in groundwater are all needed to produce the observed nitrate concentrations in the groundwater, conveyance channels, and river as well as the seasonal concentration patterns. The model results indicate that a total of 497 metric tons of nitrate-N are removed from the Middle Rio Grande annually. Where river nitrate concentrations are low and there are no large nitrate sources, nitrate behaves nearly conservatively and riparian and agricultural uptake are the most important removal mechanisms. Downstream of a large wastewater nitrate source, denitrification and agricultural uptake were responsible for approximately 90% of the nitrogen removal.

Rio Grande Ecosystems

These proceedings are an outcome of a symposium and workshop held June 2-5, 1998 in Albuquerque, NM. Hosted by the USDA Forest Service, Rocky Mountain Research Station and the U.S. Fish and Wildlife Service's Bosque Improvement Group, in collaboration with numerous partners from a variety of sectors, the symposium was designed to report on current research and development activities in the Middle Rio Grande Basin. The purpose of the meeting was to share information and develop ideas for sustaining and conserving Middle Rio Grande Basin ecosystems, especially those from Cochiti Dam to Elephant Butte Reservoir. Experts were invited to contribute oral presentations, posters, and papers that addressed five Basin themes. Theme one's session was designed to identify methods and opportunities to enhance communication and collaboration among researchers, managers, and communities. A second theme explored ideas and approaches for conserving water and riparian resources in relation to human needs and population growth. Theme three discussed how watershed processes form linkages and influence management of upland and river resources. A fourth session identified methods and strategies for restoring and monitoring basin ecosystems and discussed project successes and failures. Theme five reported on status of endangered and sensitive species, biological diversity, and opportunities for restoring and managing habitats to recover species. Management and understanding of the Middle Rio Grande Basin's natural resources and ecosystems require communication and cooperation of partners across cultural, landowner, and organizational boundaries. To produce a shared understanding of the current state and desired future state of the Middle Rio Grande Basin and to outline the steps needed to move toward the desired future, a facilitated workshop was held the last day of the conference. The results of this workshop are reported in the concluding section of this proceedings. The technical coordinators of the symposium and proceedings wish to acknowledge all the partners who have contributed to the research, restoration, technology development, educational outreach, and special events and activities designed to improve human and ecosystem conditions in the Basin. We hope this volume captures at least some of the excitement, ideas, and productivity generated by Basin projects over the past several years.

Cooperative Strategies for Forest Science Management and Leadership in an Increasingly Complex and Globalized World