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Submarine Groundwater Discharge-Derived Nutrient Loads to San Francisco Bay: Implications to Future Ecosystem Changes |
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| Authors: | Kimberly A Null Natasha T Dimova Karen L Knee Bradley K Esser Peter W Swarzenski Michael J Singleton Mark Stacey Adina Paytan |
| Institution: | 1. Institute of Marine Sciences, University of California Santa Cruz, Santa Cruz, CA, USA 2. Department of Geological Sciences, University of Alabama, Tuscaloosa, AL, USA 3. Smithsonian Environmental Research Center, Edgewater, MD, USA 4. Lawrence Livermore National Laboratory, Livermore, CA, USA 5. US Geological Survey, Pacific Coastal and Marine Science Center, Santa Cruz, CA, USA 6. Department of Civil and Environmental Engineering, University of California Berkeley, Berkeley, CA, USA |
| Abstract: | Submarine groundwater discharge (SGD) was quantified at select sites in San Francisco Bay (SFB) from radium (223Ra and 224Ra) and radon (222Rn) activities measured in groundwater and surface water using simple mass balance box models. Based on these models, discharge rates in South and Central Bays were 0.3?C7.4?m3?day?1?m?1. Although SGD fluxes at the two regions (Central and South Bays) of SFB were of the same order of magnitude, the dissolved inorganic nitrogen (DIN) species associated with SGD were different. In the South Bay, ammonium (NH 4 + ) concentrations in groundwater were three-fold higher than in open bay waters, and NH 4 + was the primary DIN form discharged by SGD. At the Central Bay site, the primary DIN form in groundwater and associated discharge was nitrate (NO 3 ? ). The stable isotope signatures (??15NNO3 and ??18ONO3) of NO 3 ? in the South Bay groundwater and surface waters were both consistent with NO 3 ? derived from NH 4 + that was isotopically enriched in 15N by NH 4 + volatilization. Based on the calculated SGD fluxes and groundwater nutrient concentrations, nutrient fluxes associated with SGD can account for up to 16?% of DIN and 22?% of DIP in South and Central Bays. The form of DIN contributed to surface waters from SGD may impact the ratio of NO 3 ? to NH 4 + available to phytoplankton with implications to bay productivity, phytoplankton species distribution, and nutrient uptake rates. This assessment of nutrient delivery via groundwater discharge in SFB may provide vital information for future bay ecological wellbeing and sensitivity to future environmental stressors. |
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