HR: 09:45h
AN: H51F-06    [Abstracts]
TI: Climate Variability Impacts on Watershed Nutrient Delivery and Reservoir Production
AU: * White, J D
EM: joseph_d_white@baylor.edu
AF: Baylor University, Center for Reservoir and Aquatic Systems Research One Bear Place #97388, Waco, TX 76798 United States
AU: Prochnow, S J
EM: shane_prochnow@baylor.edu
AF: Baylor University, Center for Applied Spatial and Geographic Research, Waco, TX 76798 United States
AU: Zygo, L M
EM: lisa_zygo@baylor.edu
AF: Baylor University, Center for Applied Spatial and Geographic Research, Waco, TX 76798 United States
AU: Byars, B W
EM: bruce_byars@baylor.edu
AF: Baylor University, Center for Applied Spatial and Geographic Research, Waco, TX 76798 United States
AB: Reservoirs in agricultural dominated watersheds tend to exhibit pulse-system behavior especially if located in climates dominated by summer convective precipitation inputs. Concentration and bulk mass of nutrient and sediment inputs into reservoir systems vary in terms of timing and magnitude of delivery from watershed sources to reservoirs under these climate conditions. Reservoir management often focuses on long-term average inputs without considering short and long-term impacts of variation in loading. In this study we modeled a watershed-reservoir system to assess how climate variability affects reservoir primary production through shifts in external loading and internal recycling of limiting nutrients. The Bosque watershed encompasses 423,824 ha in central Texas which delivers water to Lake Waco, a 2900 ha reservoir that is the primary water source for the city of Waco and surrounding areas. Utilizing the Soil Water Assessment Tool for the watershed and river simulations and the CE-Qual-2e model for the reservoir, hydrologic and nutrient dynamics were simulated for a 10 year period encompassing two ENSO cycles. The models were calibrated based on point measurement of water quality attributes for a two year time period. Results indicated that watershed delivery of nutrients was affected by the presence and density of small flood-control structure in the watershed. However, considerable nitrogen and phosphorus loadings were derived from soils in the upper watershed which have had long-term waste-application from concentrated animal feeding operations. During El Niño years, nutrient and sediment loads increased by 3 times above non-El Niño years. The simulated response within the reservoir to these nutrient and sediment loads had both direct and indirect. Productivity evaluated from chlorophyll a and algal biomass increased under El Niño conditions, however species composition shifts were found with an increase in cyanobacteria dominance. In non-El Niño years, species composition was more evenly distributed. At the longer time scale, El Niño events with accompanying increase in nutrient loads were followed by years in which productivity declined below levels predicted solely by nutrient ratios. This was due to subtle shifts in organic matter decomposition where productive years are followed by increases in refractory material which sequesters nutrients and reduces internal loading.
UR: http://www3.baylor.edu/~Joseph_D_White/lakewaco.htm
DE: 1615 Biogeochemical processes (4805)
DE: 1806 Chemistry of fresh water
DE: 1857 Reservoirs (surface)
DE: 1860 Runoff and streamflow
SC: Hydrology [H]
MN: 2005 Joint Assembly