HR: 17:15h
AN: H32H-06    [PDF]
TI: Nutrient Flux from Mediterranean Coastal Streams: Carpinteria Valley, California
AU: * Robinson, T H
EM: trobinson@bren.ucsb.edu
AF: Bren School of Environmental Science and Management, UCSB, 4422 Bren Hall University of California, Santa Barbara, CA 93106-5131 United States
AU: Leydecker, A
EM: al.leydecker@cox.net
AF: Bren School of Environmental Science and Management, UCSB, 4422 Bren Hall University of California, Santa Barbara, CA 93106-5131 United States
AU: Melack, J M
EM: melack@lifesci.ucsb.edu
AF: Bren School of Environmental Science and Management, UCSB, 4422 Bren Hall University of California, Santa Barbara, CA 93106-5131 United States
AU: Keller, A A
EM: keller@bren.ucsb.edu
AF: Bren School of Environmental Science and Management, UCSB, 4422 Bren Hall University of California, Santa Barbara, CA 93106-5131 United States
AB: Along the southern California coast, near Santa Barbara, California, we are measuring nutrient export from specific land uses and developing a model to predict nutrient export at a watershed scale. The area is characterized by a Mediterranean-like climate and short steep catchments producing flashy runoff. The six land uses include chaparral, avocado orchards, greenhouse agriculture, open-field nurseries, and residential and commercial development. Sampling sites are located on defined drainages or storm drains that collect runoff from relatively homogeneous areas representing each land use. Stream water samples are taken once a week during the rainy season, every two weeks during the dry season and every one to four hours during storms. Samples are analyzed for ammonium, nitrate, phosphate, total dissolved nitrogen and particulate nitrogen and phosphorus. Intensive sampling at the thirteen sites of the study was conducted throughout Water Year (WY) 2002 and 2003. We determine discharge from measurements of stage derived from pressure transducers at all sampling sites. This information is then converted to flux at a high temporal resolution. Wet and dry season sampling has shown that nitrate baseflow concentrations vary over three orders of magnitude, from a few micromoles per liter in undeveloped catchments, to a few 100 æmol/L in agricultural and urban watersheds, to 1000 æmol/L where intensive "greenhouse" agriculture dominates. Nitrate loading ranged from a few moles per hectare per storm at undeveloped and residential sites to hundreds at the greenhouse site. Phosphate concentrations show a similar, but smaller, variation from 1 to 100 æmol/L, although the loading is comparable at 1-100 moles/ha-storm. Stormflow concentrations fluctuate with the storm hydrograph: phosphate increases with flow, while nitrate typically decreases due to dilution from runoff probably from impervious surfaces. Nitrate export patterns indicate a marked difference between land use type (1, 10, 100 g ha-1mm-1 for undisturbed, urban, and greenhouse sites respectively) and show little variance storm to storm during WY2002 and WY2003. The phosphate export pattern with successive storms is not as clear. Cumulative rainfall and/or runoff/rainfall ratios for nitrate and phosphate show promise as variables to simulate the magnitude of nutrient export for individual storms in non-monitored catchments.
DE: 1803 Anthropogenic effects
DE: 1806 Chemistry of fresh water
DE: 1871 Surface water quality
SC: Hydrology [H]
MN: 2003 Fall Meeting