Core sub-sampling. A series of sampling ports were drilled at 20 cm intervals into the
plastic core tubes, which were then fitted with air tight seals. Samples were removed from
the core using disposable plastic syringes, transferred to gas tight tubes, and were stored in
the freezer prior to analysis for methane gas.
Pore water extraction from Holyhead harbour sediments. Pore water was extracted at
ambient temperature under nitrogen using six Reeburg squeezers operated off a single
manifold. 10 ml aliquots were retained for dissolved methane analysis (Mc Auliffe, 1971).
About 20 ml of the pore water was retained frozen for the analysis of dissolved organic
carbon, volatile organic carbon and sulphate ion.
Analytical techniques.
Methane. Concentrations of methane within Holyhead harbour and Western Irish sea
sediments were determined by gas chromatography. A Perkin Elmer F 11 (Perkin Elmer
Ltd., Beaconsfield) containing a 3 m glass lined metal column, packed with 80-100 mesh
Poropak N (Phase Separations Ltd., Queensferry) operated at 70° C, with OFN (BOC
Ltd., London) carrier gas flowing at 30 ml min ', was used for some analyses. Alternatively a Dani SPA 3 800 HR GC (Kontron instruments Ltd., St. Albans) containing a 1.5 m
pyrex column packed with Poropak QS (Phase Separations Ltd., Queensferry), operated
at 120°C, injector temperature 150°C, detector temperature 150°C, with OFN (BOC Ltd.,
London) carrier gas flowing at 30 ml min -1 was used for analysis. The FID detectors were
calibrated with standard gas mixtures (Phase Separations Ltd., Queensferry). Headspace
gases were sampled through septa with either 100 µl or 1 ml syringes and injected directly
onto the GC column.
Analysis of pore water from Holyhead harbour sediments.
Dissolved organic carbon. (DOC). The method of Collins and Williams (1977) was used.
Volatile organic carbon (VOC). VOC was determined by bubbling oxygen into 1-2 ml of
pore water (pH 11) in a specially adapted cell. The stripped volatiles were oxidised to
carbon dioxide whose concentration was estimated by an infra-red analyser.
Sulphate concentrations. Dissolved sulphate was determined gravimetrically as barium
sulphate on 2-5 ml interstitial water samples.
Microcosm incubations. Experimental treatments of natural mixed populations of bacteria in sediment microcosms were attempted. 1 ml plastic syringes were used to take
sediment from a Holyhead harbour core via the sampling ports, which were immediately
transferred to an anaerobic jar containing nitrogen. On return to the laboratory, the
sediment samples were transferred to 5 ml OFN flushed glass tubes fitted with gas tight
stoppers. Incubation temperatures were 10°C unless otherwise indicated.
The treatments were: (1) Incubation of the microcosms at 20°C or 30°C for 24 hours. (2)
Addition of acetate (2mM final concentration) or H 2 / CO 2 mixture, followed by incubation for 24 hours. (3) Addition of sulphate ( 1 m M final concentration) to tubes pretreated
with acetate or H
2 / CO
2 , followed by incubation for 24 hours. At the end of the incubations the headspace gases were analysed for methane.
RESULTS AND DISCUSSION.
Acoustic sub-bottom profiling of Holyhead harbour indicated that sediments were
38
plastic core tubes, which were then fitted with air tight seals. Samples were removed from
the core using disposable plastic syringes, transferred to gas tight tubes, and were stored in
the freezer prior to analysis for methane gas.
Pore water extraction from Holyhead harbour sediments. Pore water was extracted at
ambient temperature under nitrogen using six Reeburg squeezers operated off a single
manifold. 10 ml aliquots were retained for dissolved methane analysis (Mc Auliffe, 1971).
About 20 ml of the pore water was retained frozen for the analysis of dissolved organic
carbon, volatile organic carbon and sulphate ion.
Analytical techniques.
Methane. Concentrations of methane within Holyhead harbour and Western Irish sea
sediments were determined by gas chromatography. A Perkin Elmer F 11 (Perkin Elmer
Ltd., Beaconsfield) containing a 3 m glass lined metal column, packed with 80-100 mesh
Poropak N (Phase Separations Ltd., Queensferry) operated at 70° C, with OFN (BOC
Ltd., London) carrier gas flowing at 30 ml min ', was used for some analyses. Alternatively a Dani SPA 3 800 HR GC (Kontron instruments Ltd., St. Albans) containing a 1.5 m
pyrex column packed with Poropak QS (Phase Separations Ltd., Queensferry), operated
at 120°C, injector temperature 150°C, detector temperature 150°C, with OFN (BOC Ltd.,
London) carrier gas flowing at 30 ml min -1 was used for analysis. The FID detectors were
calibrated with standard gas mixtures (Phase Separations Ltd., Queensferry). Headspace
gases were sampled through septa with either 100 µl or 1 ml syringes and injected directly
onto the GC column.
Analysis of pore water from Holyhead harbour sediments.
Dissolved organic carbon. (DOC). The method of Collins and Williams (1977) was used.
Volatile organic carbon (VOC). VOC was determined by bubbling oxygen into 1-2 ml of
pore water (pH 11) in a specially adapted cell. The stripped volatiles were oxidised to
carbon dioxide whose concentration was estimated by an infra-red analyser.
Sulphate concentrations. Dissolved sulphate was determined gravimetrically as barium
sulphate on 2-5 ml interstitial water samples.
Microcosm incubations. Experimental treatments of natural mixed populations of bacteria in sediment microcosms were attempted. 1 ml plastic syringes were used to take
sediment from a Holyhead harbour core via the sampling ports, which were immediately
transferred to an anaerobic jar containing nitrogen. On return to the laboratory, the
sediment samples were transferred to 5 ml OFN flushed glass tubes fitted with gas tight
stoppers. Incubation temperatures were 10°C unless otherwise indicated.
The treatments were: (1) Incubation of the microcosms at 20°C or 30°C for 24 hours. (2)
Addition of acetate (2mM final concentration) or H 2 / CO 2 mixture, followed by incubation for 24 hours. (3) Addition of sulphate ( 1 m M final concentration) to tubes pretreated
with acetate or H
2 / CO
2 , followed by incubation for 24 hours. At the end of the incubations the headspace gases were analysed for methane.
RESULTS AND DISCUSSION.
Acoustic sub-bottom profiling of Holyhead harbour indicated that sediments were
38