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Vegetation and climate both play integral roles in water availability, particularly for arid to semi-arid regions. Changes in these variables can lead to extreme shortages in water for regions that rely on water for crop irrigation (i.e., the Great Plains). The objective of this study is to evaluate the impacts of vegetation on water availability in the Republican River basin in central Nebraska. Decreases in streamflow have been observed in the river basin for many years and, as a result, an invasive riparian plant species (Phragmites australis) is being removed in an effort to reduce evapotranspiration and reclaim surface water. Meteorological variables and energy balance data have been collected at a field site during the 2009 and 2010 growing seasons. Vegetation was sprayed with herbicide in July 2009, killing all P. australis in the wetland. Significant decreases in evapotranspiration were observed during the 2010 growing season due to the limited amount of transpiring vegetation in the wetland. Greenhouse growth experiments were also conducted with both invasive and native varieties of P. australis to determine basic plant physiological parameters. Nitrogen fertilizer was applied to half of the plants in each subset. Gas exchange (e.g., photosynthesis, stomatal conductance, and transpiration rates), and the efficiency of the water and nitrogen use, were assessed under variable light, temperature and CO2 concentrations. As well as providing specific vegetation parameters for modeling purposes, this study was interested in evaluating the differences in physiology and growth characteristics between the two varieties of P. australis present in Nebraska. Lastly, the plant physiological parameters were incorporated into Agro-IBIS, a dynamic vegetation model, and this model was evaluated using observed energy balance data from the wetland field site from 2009. Experiments were also performed for 2010 to assess the ability of the model to capture the response to vegetation removal.
Adviser: John Lenters
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