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Medientyp:
E-Artikel
Titel:
Nitrate dynamics within the Pajaro River, a nutrient-rich, losing stream
Beteiligte:
Ruehl, Christopher R.;
Fisher, Andrew T.;
Huertos, Marc Los;
Wankel, Scott D.;
Wheat, C. Geoff;
Kendall, Carol;
Hatch, Christine E.;
Shennan, Carol
Erschienen:
The University of Chicago Press, 2007
Erschienen in:
Journal of the North American Benthological Society, 26 (2007) 2, Seite 191-206
Beschreibung:
Abstract The major ion chemistry of water from an 11.42-km reach of the Pajaro River, a losing stream in central coastal California, shows a consistent pattern of higher concentrations during the 2nd(dry) half of the water year. Most solutes are conserved during flow along the reach, but [NO3 −] decreases by ~30% and is accompanied by net loss of channel discharge and extensive surface–subsurface exchange. The corresponding net NO3 −uptake length is 37 ± 13 km (42 ± 12 km when normalized to the conservative solute Cl−), and the areal NO3 −uptake rate is 0.5 μmol m−2s−1. The observed reduction in [NO3 −] along the reach results from one or more internal sinks, not dilution by ground water, hill-slope water, or other water inputs. Observed reductions in [NO3 −] and channel discharge along the experimental reach result in a net loss of 200–400 kg/d of NO3 −-N, ~50% of the input load. High-resolution (temporal and spatial) sampling indicates that most of the NO3 −loss occurs along the lower part of the reach, where there is the greatest seepage loss and surface–subsurface exchange of water. Stable isotopes of NO3 −, total dissolved P concentrations, and streambed chemical profiles suggest that denitrification is the most significant NO3 −sink along the reach. Denitrification efficiency, as expressed through downstream enrichment in15N-NO3 −, varies considerably during the water year. When discharge is greater (typically earlier in the water year), denitrification is least efficient and downstream enrichment in15N-NO3 −is greatest. When discharge is lower, denitrification in the streambed appears to occur with greater efficiency, resulting in lower downstream enrichment in15N-NO3 −.