RESUMEN
The combined effects of anthropogenic and biological CO2 inputs may lead to more rapid acidification in coastal waters compared to the open ocean. It is less clear, however, how redox reactions would contribute to acidification. Here we report estuarine acidification dynamics based on oxygen, hydrogen sulfide (H2S), pH, dissolved inorganic carbon and total alkalinity data from the Chesapeake Bay, where anthropogenic nutrient inputs have led to eutrophication, hypoxia and anoxia, and low pH. We show that a pH minimum occurs in mid-depths where acids are generated as a result of H2S oxidation in waters mixed upward from the anoxic depths. Our analyses also suggest a large synergistic effect from river-ocean mixing, global and local atmospheric CO2 uptake, and CO2 and acid production from respiration and other redox reactions. Together they lead to a poor acid buffering capacity, severe acidification and increased carbonate mineral dissolution in the USA's largest estuary.The potential contribution of redox reactions to acidification in coastal waters is unclear. Here, using measurements from the Chesapeake Bay, the authors show that pH minimum occurs at mid-depths where acids are produced via hydrogen sulfide oxidation in waters mixed upward from anoxic depths.
RESUMEN
The structure and metabolism of a soft-sediment estuarine macrofaunal community were measured over an annual cycle at two depth-contours in mesohaline Chesapeake Bay. Additional data for plankton productivity and respiration, as well as seston and sediment organics are also summarized for these communities. Benthic community respiration ranged from 0.24-3.38 g O2 m-2 d-1, and significant differences were detected between the two depths. Similarly, macroinfaunal standing stocks reached 11.2 and 32.3 g (ash free) m-2 for 3 m and 6 m depth communities, respectively, and both exhibited mid-summer declines in abundance. Inferences drawn from these data facilitated a partitioning of benthic community respiration into macrofaunal and meiofaunal/microbial components with a residual term, much of which could be explained statistically by interactions between these two components. A multi-variate statistical model developed from these data matched benthic respiration measurements within 1-2 S.E. Mass-balances of organic carbon were estimated for water column and benthos at the two depthcontours for early and late summer, as well as for an entire, time-weighted year. These various analyses led to the tentative conclusions that this benthic community was regulated by such internal factors as macrofaunal/meiofaunal grazing and "microbial gardening", and by external factors such as temperature and predation by nekton. However, it appears that the ultimate control for this community was the supply of energy from organic carbon.