Eric R. Breuer

Bioturbation, sediment fluxes and benthic community structure around a salmon cage farm in Loch Creran, Scotland

Abstract This study examined bioturbation along an organic carbon gradient away from an Atlantic salmon farm and sought to determine relationships between benthic fluxes, mixing intensity and the infaunal community structure. Macrofaunal community structure, abundance and biomass were examined at stations with varying quantities and qualities of organic matter input. In situ benthic chambers were used to determine oxygen and nutrient fluxes and mixing parameters were derived from down core profiles of chlorophyll a (chl a ). Mean oxygen demand of sediments ranged between 8.8 and 467.8 mmol m −2 day −1 , being highest beneath the fish farm and indicating very high rates of community respiration and organic matter diagenesis. Oxygen and nutrient fluxes followed similar trends to community abundance and biomass, declining with increasing distance from the farm. Mixing intensity increased with distance from the farm until returning, at the farthest station, to values similar to those measured beneath the farm. The differences in the community structure between sediments beneath the farm and furthest from it suggest that similar diffusive mixing coefficients are generated by different mechanisms. These results generally follow the successional model of Pearson and Rosenberg [Oceanogr. Mar. Biol. Ann. Rev. 16 (1978) 229.], with the exception of the farthest station, but suggest that the bioturbation potential of the community over short time scales is greatest at stations with intermediate qualities and quantity of organic matter. However, the methods used here to assess mixing over short time scales (i.e. diffusive mixing coefficient and the mixed layer depth) do not account for the activities of deep burrowing infaunal animals, such as Maxmuelleria lankesteri , known to be present at the farthest station.

Assessment of metal concentrations found within a North Sea drill cuttings pile

North Sea drill cuttings piles are a distinct anthropogenic legacy resulting from the exploration and production of North Sea oil reserves. The need to understand metal cycling within the piles becomes increasingly important with the imminent decommissioning of many North Sea platforms and the subsequent fate of associated cuttings piles. This paper presents results of the simultaneous analysis of geochemical carrier substances (Mn and Fe oxyhydroxides), along with dissolved (<0.2 microm) and total (>0.2 microm) metal (Ba, Co, Cr, Cu, Mo, Pb, V) concentrations from a North Sea cuttings pile and surrounding sediment. These data are examined in conjunction with in situ measured porewater oxygen and sulfide. Results show a rapid removal of oxygen within the top few millimeters of the cuttings pile along with elevated concentrations of total hydrocarbons and solid phase metal concentrations compared to the surrounding environment.

Rates and Regulation of Microbially Mediated Aerobic and Anaerobic Carbon Oxidation Reactions in Continental Margin Sediments from the Northeastern Arabian Sea (Pakistan Margin)

Rates of microbially mediated C oxidation were measured at sites above, within, and below the oxygen minimum zone (OMZ) on the Pakistan margin of the Arabian Sea, before and after the southwest monsoon, with the goal of assessing how low bottom water O 2 concentration affects microbial C oxidation processes. Rates of C oxidation coupled to aerobic and anaerobic processes were measured at five depths: 140 m (seasonally hypoxic), 300 m (OMZ core), 940 m (OMZ transition), 1200 m (OMZ transition), and 1850 m (non-OMZ). Rates and mechanisms of C oxidation did not vary significantly between seasons. However, an exception was found at the 140-m site, which became hypoxic during the southwest monsoon. Considering both seasons, C oxidation rates ranged from 0.73 to 4.86 mmol C m ―2 d ―1 . Generally, OMZ sites and those on the OMZ transition had lower C oxidation rates (0.73―2.90 mmol C m ―2 d ―1 ) than those located below the OMZ (3.13―4.86 mmol C m ―2 d ―1 ). The relative importance of C oxidation via different terminal electron acceptors varied between sites according to the position and intensity of the OMZ. At all sites, a large proportion of measured O 2 consumption (30―100%) was coupled to the oxidation of reduced species; consequently, aerobic processes were essentially absent at low-0 2 sites. In contrast, under higher bottom water O 2 concentrations, aerobic processes accounted for 4―64% of C oxidation. Denitrification largely dominated carbon oxidation at all sites (36―99%). Rates of C oxidation coupled to microbial Mn 4+ and Fe 3+ reduction were quantitatively unimportant. Measured sulphate reduction rates at all sites across the margin were surprisingly low (0―0.45 mmol m ―2 d ―1 ) compared to rates measured on other margin environments.

Rates and regulation of microbially mediated aerobic and anaerobic carbon oxidation reactions in continental margin sediments from the Northeastern Arabian Sea (Pakistan Margin)

Rates of microbially mediated C oxidation were measured at sites above, within, and below the oxygen minimum zone (OMZ) on the Pakistan margin of the Arabian Sea, before and after the southwest monsoon, with the goal of assessing how low bottom water O 2 concentration affects microbial C oxidation processes. Rates of C oxidation coupled to aerobic and anaerobic processes were measured at five depths: 140 m (seasonally hypoxic), 300 m (OMZ core), 940 m (OMZ transition), 1200 m (OMZ transition), and 1850 m (non-OMZ). Rates and mechanisms of C oxidation did not vary significantly between seasons. However, an exception was found at the 140-m site, which became hypoxic during the southwest monsoon. Considering both seasons, C oxidation rates ranged from 0.73 to 4.86 mmol C m ―2 d ―1 . Generally, OMZ sites and those on the OMZ transition had lower C oxidation rates (0.73―2.90 mmol C m ―2 d ―1 ) than those located below the OMZ (3.13―4.86 mmol C m ―2 d ―1 ). The relative importance of C oxidation via different terminal electron acceptors varied between sites according to the position and intensity of the OMZ. At all sites, a large proportion of measured O 2 consumption (30―100%) was coupled to the oxidation of reduced species; consequently, aerobic processes were essentially absent at low-0 2 sites. In contrast, under higher bottom water O 2 concentrations, aerobic processes accounted for 4―64% of C oxidation. Denitrification largely dominated carbon oxidation at all sites (36―99%). Rates of C oxidation coupled to microbial Mn 4+ and Fe 3+ reduction were quantitatively unimportant. Measured sulphate reduction rates at all sites across the margin were surprisingly low (0―0.45 mmol m ―2 d ―1 ) compared to rates measured on other margin environments.

INDIAN OCEAN BIOGEOCHEMICAL PROCESSES AND ECOLOGICAL VARIABILITY

Rates of microbially mediated C oxidation were measured at sites above, within, and below the oxygen minimum zone (OMZ) on the Pakistan margin of the Arabian Sea, before and after the southwest monsoon, with the goal of assessing how low bottom water O 2 concentration affects microbial C oxidation processes. Rates of C oxidation coupled to aerobic and anaerobic processes were measured at five depths: 140 m (seasonally hypoxic), 300 m (OMZ core), 940 m (OMZ transition), 1200 m (OMZ transition), and 1850 m (non-OMZ). Rates and mechanisms of C oxidation did not vary significantly between seasons. However, an exception was found at the 140-m site, which became hypoxic during the southwest monsoon. Considering both seasons, C oxidation rates ranged from 0.73 to 4.86 mmol C m ―2 d ―1 . Generally, OMZ sites and those on the OMZ transition had lower C oxidation rates (0.73―2.90 mmol C m ―2 d ―1 ) than those located below the OMZ (3.13―4.86 mmol C m ―2 d ―1 ). The relative importance of C oxidation via different terminal electron acceptors varied between sites according to the position and intensity of the OMZ. At all sites, a large proportion of measured O 2 consumption (30―100%) was coupled to the oxidation of reduced species; consequently, aerobic processes were essentially absent at low-0 2 sites. In contrast, under higher bottom water O 2 concentrations, aerobic processes accounted for 4―64% of C oxidation. Denitrification largely dominated carbon oxidation at all sites (36―99%). Rates of C oxidation coupled to microbial Mn 4+ and Fe 3+ reduction were quantitatively unimportant. Measured sulphate reduction rates at all sites across the margin were surprisingly low (0―0.45 mmol m ―2 d ―1 ) compared to rates measured on other margin environments.