Radioactive and stable isotope measurements reveal saline submarine groundwater discharge in a semiarid estuary

[摘要] There is little information on submarine groundwater discharge (SGD) in hypersaline estuaries in semi-arid climates where SGD may be the dominant nutrient source. Here, we assess the spatial and temporal variability of SGD in the hypersaline Baffin Bay (Texas) using radon [Rn-222], radium [Ra-226, Ra-224, and Ra-223], and water isotopes [delta O-18 and delta D]. Continuous electrical resistivity surveys revealed potential SGD at nearshore serpulid reefs. High spatial and temporal resolution radon measurements revealed slightly higher SGD inputs at the shoreline near course-grained sediments and relic serpulid reefs. Mass balance models of Rn-222 and Ra-226 produced equal SGD estimates within the range of uncertainty, while Ra-223 yielded substantially higher SGD rates. Baywide SGD rates from Ra-226, Ra-223, and Rn-222 ranged from 1.6 +/- 0.2 to 41.3 +/- 4.1. Larger SGD rates obtained from short-lived isotopes imply higher recirculated/saline SGD rates over short time scales. Radiogenic and stable isotopes as well as resistivity indicate that saline rather than freshwater accounts for most SGD in this hypersaline estuary. Because saline porewater exchange can play a significant role in coastal biogeochemical budgets, SGD inputs should be considered in management strategies in semi-arid areas where surface inflows are almost absent.

[发布日期] 2020-11-01

[关键词] Submarine groundwater discharge;Semiarid estuaries;Hypersaline system;Well-mixed estuaries;Baffin Bay