Sediment carbon, nitrogen and phosphorus cycling in an anoxic fjord, Effingham Inlet, British Columbia

Abstract

Sediment geochemistry, as well as benthic exchange of nutrients, was investigated in Effingham Inlet, a fjord located on the west coast of Vancouver Island in Barkley Sound. The effect of bottom-water oxygenation on sediment carbon, nitrogen and phosphorus cycling was compared at sites overlain by oxic and anoxic bottom waters. The sites, separated by only 3 kilometers, were similar in terms of key diagenetic parameters including mass accumulation rate and bulk sediment organic carbon content, thus allowing a focus on diagenetic effects attributable to depositional oxygen availability. Benthic flux chamber incubations, sulfate reduction rate measurements, measurements of solid-phase and pore water chemical profiles were compared for the sites. These comparisons reveal that diagenetic processes in the site overlain by oxic waters act to retain more phosphorus in the sediment relative to the anoxic site. Differences in phosphorus benthic fluxes and burial between the two sites most likely result from differences in organic matter cycling under aerobic versus anaerobic conditions and are not strongly influenced by cycling of P associated with metal oxide phases.