Estuaries gas exchange

In addition to gases produced naturally in the environment, estuaries tend to be enriched in byproducts of industry and other human activity. A few studies have investigated volatile organic pollutants such as chlorinated hydrocarbons (chloroform, tet-rachloromethane, 1,1-dichloroethane, 1,2-dichlor-oethane, 1,1,1-trichloroethane, trichloroethylene and tetrachloroethylene) and monocyclic aromatic hydrocarbons (benzene, toluene, ethylbenzene, o-xylene and m- and p-xylene). Concentrations of VOCs are controlled primarily by the location of the sources, dilution of river water with clean marine water within the estuary, gas exchange, and in some cases, adsorption onto suspended or settling solids. In some cases (for example, chloroform) there also may be natural biotic sources of the gas. Volatilization to the atmosphere can be an important cleansing mechanism for the estuary system. Since the only estuaries studied to date are heavily impacted by human activity (the Elbe and... 

The last include wet and dry deposition of particles and solutes and gas exchange across the air-sea interface. Because of proximity to source, coastal waters tend to be more polluted than the open ocean. A notable exception is the worldwide acidification of surface waters caused by CO2 emissions. Of all the coastal waters, estuaries tend to be the most impacted. This is due to high rates of pollutant loading and to natural processes that act to concentrate these pollutants in the local sediments and biota. This is most unfortunate as estuarine waters support the world s largest fisheries and are where recreation is concentrated. 

Radon-222 is an inert noble gas produced by alpha decay of 226Ra with a half-life of 3.85 d. The primary application of 222Rn in estuaries has been in estimating flux rates of pore waters across the sediment-water interface and the rate of gas exchange between the estuary and the atmosphere. 

Kremer, J.N., Nixon, S.W., Buckley, B., and Roques, P (2003b) Technical note conditions for using the floating chamber method to estimate air-water gas exchange. Estuaries 26, 985-990. 

Kremer, J.N., Reischauer, A., and D Avanzo, C. (2003a) Estuary-specific variation in the air-water gas exchange coefficient for oxygen. Estuaries 26, 829-836. 

Other volatile tracers have been used in estuaries to determine gas exchange coefficients. These tracers, such as chlorofluorocarbons (CFCs) or sulfur hexafluoride (SFg), are synthetic compounds with no known natural source. Unlike Rn, these gases are stable in solution. These tracers may be added to the aquatic system and the decrease of the gas due to flux across the air/water interface monitored over time. In some estuaries, point sources of these compounds may exist and the decrease of the tracer with distance downstream may be used to determine k or z values for the estuary. 

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