HR: 1340h
AN: H13D-1546    [Abstracts]
TI: Subsurface Stream Processes and Spatiotemporal Controls on Nutrient Cycling Upper San Pedro River, AZ
AU: * Soto-López, C D
EM: csoto@hwr.arizona.edu
AF: The University of Arizona Department of Hydrology and Water Resources, JW Harshbarger, Rm 122 1133 E James E Rogers Way P.O. Box 210011, Tucson, AZ 85721-001, United States
AU: Meixner, T
EM: tmeixner@hwr.arizona.edu
AF: The University of Arizona Department of Hydrology and Water Resources, JW Harshbarger, Rm 122 1133 E James E Rogers Way P.O. Box 210011, Tucson, AZ 85721-001, United States
AB: In semi-arid lotic systems, little is known about the mechanisms that control nutrient variability and availability. Many studies have demonstrated that streambed upwelling zones are important for stream nutrient cycling while other evidence indicates that episodic floods carry high concentrations of organic matter and nutrients; as a result these nutrients are reflected in subsurface waters of the river and later return to the stream through upwelling. The main goal of this research is to answer the following question: How does the spatial and temporal variability of surface water nutrients change in relation to subsurface processes and time since last flood? To address this question, chemical measurements together with paired surface and sediment water temperature measurements were conducted using a nested hierarchy approach on a 10km river segment at various stages of post flood succession. Sulfate to chloride ratios of stream waters indicate that during non-flood periods the contributions of groundwater to stream flow become more dominant over winter or summer flood flows as the time since flood increases. A near stream spring found only in November 2006 sampling campaign shows that the sulfate to chloride ratios closely resemble baseflow water but with nitrate concentrations that where similar to the highest nitrate concentration in November samples. In addition, we have found that the spatial variability and availability of nitrate increases as time after flood increases and that this variability appears to be influenced by upward subsurface hydrologic flux. Moreover, location and spatial scale appears to influence these relationships; at larger scales the variability of nutrients is controlled and dampened by in-stream processes while at smaller scales is more variable and controlled by the direction of water exchange. Our results suggest that during post-flood succession upwelling waters, like the spring found on November 2006, develop into the dominant control of stream water chemistry in the San Pedro River.
DE: 1806 Chemistry of fresh water
DE: 1821 Floods
DE: 1830 Groundwater/surface water interaction
DE: 1839 Hydrologic scaling
DE: 1895 Instruments and techniques: monitoring
SC: Hydrology [H]
MN: 2007 Fall Meeting