Nitrate loss from a restored floodplain on the lower Cosumnes River, California
Abstract
Floodplain habit was recreated on the lower Cosumnes River by breaching levees that previously protected agricultural lands from seasonal flooding. This study examined the ability of restored floodplains to retain nutrients from the river during flood events. The study looked at the potential for nitrate loss utilizing two techniques: (i) potential denitrification rates of floodplain soils and (ii) nitrate loss from floodplain waters during in situ microcosm experiments. Soils samples were collected from 13 locations within the floodplain and analyzed for denitrification potential. Denitrification potentials ranged from 0.06 to 27.5 nmol N2O cm-3 hr-1 and correlated with the concentrations of total N, organic C, sand and silt in the soils. Furthermore, denitrification potential correlated well with microbial respiration rates suggesting that concentrations of labile carbon strongly affect microbial activity and subsequent denitrification. Microcosm experiments were conducted by inserting polycarbonate tubes approximately 20 cm into the sediment. In addition, a replicate set of columns was studied which excluded the sediment layer to distinguish water column processes from those occurring within the sediments. The overlying water was spiked with nitrate and bromide to observe changing nitrate concentrations over time. Three different levels of nitrate were examined: ambient, +1 ppm nitrate, and +5 ppm nitrate. Results showed that nitrate loss from the water column was rapid and a function of the initial nitrate concentration. Nitrate was completely removed within 68 to 163 hours for the background and +5ppm treatments, respectively. Rates of nitrate disappearance were ~ 2.5 times greater in the sediment/water treatment, with approximately 20-30% of the nitrate being lost from water column alone. Results from this study document the potential role of these floodplain habitats to reduce the amount of nitrate that is transported downstream to sensitive aquatic ecosystems.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2002
- Bibcode:
- 2002AGUFM.H51D..06S
- Keywords:
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- 1800 HYDROLOGY;
- 1803 Anthropogenic effects;
- 1871 Surface water quality