Sediment community oxygen consumption and nutrient exchange in the central and eastern North Pacific1

ABSTRACT. In situ rates of oxygen uptake, carbon dioxide and inorganic nitrogen release from sediments at 34 m depth in St. Georges Bay, Nova Scotia (Canada) increased as temperature of bottom water increased between April and November. Rates of gas and nutrient exchange were linearly related to temperature and regressions were used to estimate daily rates of exchange between sediment and overlying water. Sedimentation of particulate organic carbon from the euphotic zone at depths above bottom which reduced collection of resuspended material was slightly less than carbon released by benthc aerobic respiration between April and November. Anaerobic microbial respiration corrected for aerobic oxygen uptake accounted for approximately 50 % of total carbon dioxide release. Nitrogen sedimentation from the euphotic zone exceeded regeneration of inorganic nitrogenous nutrients from sediments during periods of weak stratification but a balance existed when the water column was stratified. Total inorganic nitrogen release including N2 produced by denitrification was not measured but mineralization could have supplied approximately 20 % of phytoplankton requirements it nutrients released at the sediment were distributed homogeneously to the euphotic zone. Estimates of production by benthic macrofauna, calculated from biomass and assumed annual turnover ratios, equalled from 10 to 30 % of average particulate organic carbon sedimentation at 22 m for stratified and unstratified periods. Demersal fish production by a similar calculation amounted to from 1 to 7 % of estimated production of macrobenthos.

Section: Benthic Metabolism and Nutrient Regenerationsupporting

confidence: 49%

Dynamics of the benthic food web in St. Georges Bay, southern Gulf of St. Lawrence

Hargrave¹,

Phillips²

1986

“…The relationship between high abundance and biomass of benthic fauna on marine shelves and the deep sea and enhanced carbon flux to the sediments has been well documented (Zenkevitch 1963, Rowe 1971, Elmgren 1978, Smith et al 1983, Davies & Payne 1984, Valiela 1984). The quality and quantity of organic matter that descends to the sea floor as potential food is dependent on a variety of factors, including primary production, phytoplankton sinking rate, zooplankton grazing rate, mixed layer depth, overall water column depth and proximity to land runoff sources (Parsons et al 1977, Pace et al 1984, Wassman 1984.…”

Section: Introductionmentioning

confidence: 99%

Pelagic-benthic coupling on the shelf of the northern Bering and Chukchi Seas. I. Food supply source and benthic bio-mass

Grebmeier¹,

McRoy²,

Feder³

1988

364

191

The shelf waters of the northern Bering and Chukchi Seas are ice-covered for 7 mo of the year, but despite thls harsh environment, they are characterized by high benthic biomass. Coupling between water column primary production and the benthos was investigated in summers 1984 to 1986 by measurements of sediment characteristics in relation to those of the water column. Low surface sediment C/N ratios (5.8 to 7.6) suggested a higher quality, nitrogen-rich marine carbon supply to the benthos in the highly productive (ca 250 to 300 g C m-' yr-') Bering Shelf-Anadyr Water (BSAW) compared to lower quality, higher C/N ratios (7 7 to 14 0) in sediment under the less productive (ca 50 g C m-' yr-l) Alaska Coastal Water (ACW). Stable carbon isotope ratios suggested a manne origin for organic matter in BSAW compared to a mixture of manne and terrestrial input in ACW. Mean benthic biomass was significantly different between water locations, with mean benthic biomass decreasing from 20.2 g C m-* under BSAW to 6.3 g C m-2 under ACW Summer benthic biomass remained seasonally constant for the 3 yr. Benthic communities underlying BSAW received a high quality marine food supply on a regular basis interannually, while those in ACW received an interannually variable amount of temgenous organic matter in addition to marine organic matter. We conclude that the quality and quantity of organic carbon deposited to the benthos directly influence benthic biomass.

“…Pearson et al 1983), most benthic-pelagic coupling studies have examined infaunal response to organic matter input (i.e. phytodetritus) using community bulk measurements such as oxygen or carbon dioxide exchange (Smith et al 1983, heat or nutrient release (Smith et al 1983) or changes of bacterial biomass (ATP) (Drazen et al 1998). Limited attention has been given to responses of specific infaunal groups or individuals to variable organic matter inputs.…”

Section: Introductionmentioning

confidence: 99%

Spatial patterns in sedimentary macrofaunal communities on the south coast of Newfoundland in relation to surface oceanography and sediment characteristics

Ramey¹,

Snelgrove²

2003

This is the first comprehensive study of the community structure and spatial distribution of macrofauna in deep, muddy sediments of Placentia Bay, Newfoundland, and the adjacent shelf. The study examines the influence of water column (e.g. chlorophyll a [chl a], temperature and salinity) and sediment characteristics (e.g. grain size, carbon and nitrogen content) on infaunal patterns. Box-core samples were collected at 10 sites in June and July of 1998 from the head of the bay to the edge of the continental shelf. Multivariate analyses of community composition and environmental variation indicated inshore and offshore groupings. Inshore communities had lower species richness, diversity and densities. Fauna living deeper in the sediment were also more abundant in offshore areas. The inshore region was characterised by greater mixed-layer temperatures, higher surface chl a and large amounts of relatively fresh organic carbon (low C/N ratios) in sediments. Within the inshore sites, high levels of organic carbon influenced macrofaunal assemblages that were similar to those characteristic of organic-rich areas. Surface chl a concentration was positively correlated with sedimentary organic carbon, which was the most important predictor of infaunal abundance. At broad scales, surface chl a and sedimentary organic carbon were negatively related to infaunal abundance. Moreover, this pattern was confounded by particularly low densities at 3 inshore sites where organic levels were very high, and elevated densities at 1 productive offshore site. Low densities at these 3 inshore sites may be a result of sulphide production in sediments, or of poor food quality. Broad-scale patterns (inshore vs offshore) of community composition and abundance in Placentia Bay are largely influenced by surface oceanography through production export.