HR: 0830h
AN: H41D-1024    [PDF]
TI: River-floodplain Hydrologic Connectivity: Impact on Temporal and Spatial Floodplain Water Quality and Productivity Patterns
AU: * Gallo, E L
EM: elgallo@ucdavis.edu
AF: Dept. of Land, air and Water Resources, University of California, Davis One Shileds Ave., Davis, CA 95616 United States
AU: Ahearn, D
EM: dsahearn@ucdavis.edu
AF: Dept. of Land, air and Water Resources, University of California, Davis One Shileds Ave., Davis, CA 95616 United States
AU: Dahlgren, R A
EM: radahlgren@ucdavis.edu
AF: Dept. of Land, air and Water Resources, University of California, Davis One Shileds Ave., Davis, CA 95616 United States
AU: Grosholz, E
EM: tedgrosholz@ucdavis.edu
AF: Dept. of Environmetal Science and Policy, University of California, Davis One Shields Ave., Davis, CA 95695 United States
AB: Nutrient spiraling and cycling are critical processes for floodplain systems, but these have not been well studied in western North America. Floodplain production and function relies on the integrity of river-floodplain interactions, particularly during periods of hydrologic connectivity. The purpose of this study was to: (1) determine the importance of the timing and duration of river-floodplain hydrologic connectivity, (2) link flood event water quality to subsequent primary and secondary production, and (3) identify temporal and spatial patterns of floodplain production. The Cosumnes River watershed transports surface runoff and snowmelt from the Sierra Nevadas to the Sacramento-San Joaquin Delta. It is one of the few watersheds in California that has no major water diversions or impoundments; therefore the river responds to the natural watershed hydrology. The study site in southern Sacramento County is an unmanaged experimental floodplain, one of the few remaining floodplains in California. Weekly and flood-event water quality and macroinvertebrate sampling was conducted during the flood season from January through June in 2001 and 2002. Both water years were characterized by historically low river flows. On average, volatile suspended solids in the water column increased from 5 mg/l to 10 mg/l during early season periods of hydrologic connectivity (December - February), suggesting that during watershed flushing flood events, the river acts as a source of nutrients and organic matter to the floodplain. Following a flood event, invertebrate concentrations decreased on average from 26,000 individuals/m3 to 9,000 individuals/m3 for zooplankton and from 350 individuals/m2 to 65 individuals/m2 for benthic macro-invertebrate, suggesting a net dilution of invertebrates during flood events. Chlorophyll a (chl-a) levels were also diluted during flood events, on average from 25 ppb to 5 ppb. Zooplankton densities and chl-a levels quickly rose after flood events. On average, zooplankton densities and chl-a concentrations exceeded 150,000 individulas/m3 and 30 ppb respectively. However, as hydrologic residence time increased, chl-a levels decreased and were generally lowest following periods when macroinvertebrate population densities were highest, suggesting grazing pressure on planktonic algae. Total nitrogen to total phosphorous ratios (TN:TP) tended to be greater than 10 during periods of high hydrologic residence time, suggesting P limitation during periods of hydrologic disconnection, which coincides with the highest zooplankton densities and lowest chl-a levels observed. Following a flood event, TN:TP dramatically decreased, suggesting that during periods of river-floodplain connectivity, N tends to be the limiting nutrient. These data suggest that nutrients are replenished to the floodplain during periods of hydrologic connectivity, followed by periods of resource uptake and subsequent nutrient limitation. These patterns suggests that efforts directed towards restoration of river floodplain systems should attempt to reconstruct the naturally irregular and periodic connection cycle to enhance primary and secondary production.
DE: 1821 Floods
DE: 1860 Runoff and streamflow
DE: 1871 Surface water quality
DE: 1894 Instruments and techniques
SC: Hydrology [H]
MN: 2003 Fall Meeting