Interstitial water chemistry of anoxic Long Island Sound sediments. 1. Dissolved gases1

Abstract

Measurements of dissolved N2, Ar, CH4, and SO42− and salinity and temperature are used to examine the processes controlling their distributions in the interstitial waters of nearshore sediments. Where sulfate reduction is incomplete, dissolved N2 and Ar concentrations in the upper 10–30 cm appear to be controlled by macroinfaunal irrigation activities and vary in accordance with overlying water conditions. Below 30 cm, N2 and Ar concentrations appear to have been last affected by August through October irrigation. In harbor sediments where sulfate reduction is complete at shallow depths, low N2 and Ar concentrations result from in situ stripping by methane bubbles. Methane concentrations remain below about 0.1 mM until about 90% of seawater sulfate is removed. As sulfate concentrations approach zero, methane builds up to bubble saturation. Concave‐up methane depth distributions can be explained by methane consumption following first‐order kinetics in the zone of sulfate reduction. Laboratory jar experiments with natural sediments indicate no methane production during sulfate reduction, in agreement with previous models and distribution studies of sulfate reducing and methanogenic bacteria in lake sediments. Combined laboratory and field results support the hypothesis that methane is produced mainly after sulfate is depleted but is consumed within the sulfate reduction zone as it diffuses upward.

Gas transport from methane‐saturated, tidal freshwater and wetland sediments

“…These variations were due to seasonal changes in gas transport mechanisms. Dissolved nitrogen has been shown to be depleted in sedimentary pore water because it is removed by bubble stripping (Kipphut and Martens 1982;Martens and Berner 1977;Reeburgh 1969), and depletion of dissolved nitrogen relative to equilibrium with atmospheric nitrogen has also been observed in White Oak pore waters (Chanton unpubl. data).…”

“…Ebullition transports methane directly to the atmosphere, bypassing the mediating effects of an oxygenated water column (Martens and Klump 1980) or plant rhizome (Chanton and Martens 1988;Chanton et al 1988). In the process ofmethane bubble formation and release, other gases are stripped from sediments and transported to the atmosphere (Martens and Chanton 1989;Kipphut and Martens 1982;Martens and Berner 1977;Reeburgh 1969).…”

Anaerobic Metabolism: Linkages to Trace Gases and Aerobic Processes

“…Anaerobic CH 4 oxidation in marine sediments was first observed around the mid-1970s (Barnes and Goldberg, 1976;Reeburgh, 1976;Martens and Berner, 1977). The process was inferred from pore-water S0 4 and CH 4 profiles because it imparted the CH 4 profile with a strong "concave up" shape .…”

Fluxes associated with brine motion in growing sea ice

“…The distribution of snow cover on sea ice appears to control ice algae distributions (Alexander and Chapman 1981). Biological irrigation in sediments also varies in time and space and seems to be most active in late summer (Martens and Berner 1977;Elderfield et al 1981).…”