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Marine Ecology Progress Series

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MEPS 178:169-177 (1999)  -  doi:10.3354/meps178169

Groundwater seepage in the marine environment: role for mass flux and bacterial activity

I. Bussmann1,*, P. R. Dando2,**, S. J. Niven2, E. Suess1

1GEOMAR, Wischhofstr. 1-3, D-24148 Kiel, Germany
2Marine Biological Association of the UK, Citadel Hill, Plymouth PL1 2PB, United Kingdom
Present addresses:
*University of Constance, Dep. Microbial Ecology, PO Box 5560, D-78457 Konstanz, Germany. E-mail:
**School of Ocean Sciences, University of Wales, Bangor, Menai Bridge, Anglesey LL59 5EY, United Kingdom

ABSTRACT: In Eckernförde Bay (western Baltic Sea) pockmark structures are induced by groundwater seeping out of the sediment. On 3 occasions in winter and spring 1993-94 we investigated the influence of groundwater on the reduction of salinity, on porewater chemistry, and on bacterial activities (methane oxidation and sulphate reduction). In 2 out of 3 sampling campaigns groundwater discharge could be detected. The concentration gradients of Cl- and SO4= are moved towards the sediment surface by the vertical advection of groundwater during seep times. Without groundwater discharge the porewater chemistry resembled the control site. Compared to the control site, the methane oxidation and sulphate reduction rates were elevated at the pockmark site, reaching maximum values of 49 and 269 µmol l-1 d-1 respectively. The groundwater venting from the pockmark had an end member composition of 80 mM Na+, 1.0 mM Ca++ and was depleted in Mg++. Due to mixing of these major cations along the groundwater/seawater interface, no CaCO3 precipitation was found around the pockmark site.

KEY WORDS: Methane oxidation rate · Sulphate reduction rate · Baltic Sea · Salinity · Sediments

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