Professor Dave Nedwell

Research interests

ecology of aquatic microorganisms and the ecological role of sediment bacteria, particularly in estuarine and marine sediments, and in peat soils

cycling of C, N and S in estuaries, in mangrove swamps and in Antarctic environments

production of trace gases (CH4, N2O, DMS) by bacteria in aquatic environments, and their exchange with the atmosphere

processes controlling production and oxidation of CH4 by bacteria in peat bogs and in landfill sites

physiological response of bacteria to temperature, particularly low temperature

ecophysiology of denitrifying bacteria

influence of transient environmental conditions on competition and survival

multidisciplinary approaches to ecological research

Estuarine ecology

A large part of my current research is directed towards examining the importance of sedimentary (benthic) microbial communities on the fluxes of elements , primarily carbon, nitrogen, phosphorus and silicate, through estuaries. This is of fundamental ecological importance, but has many practical implications in the light of increasing loads of nutrients to estuaries because of human activities. We have 3 current research projects (funded by NERC, Dept of the Environment, EU MAST programme) examining the influence of benthic processes on N fluxes, and the influence of estuarine nutrients on primary production in estuaries. Important recent results have shown that in high nitrate estuaries on the East Coast of the UK a large part of the N load is removed by benthic denitrification, thereby reducing eutrophication. However, nitrous oxide, one of the products of denitrification, is a major green house gas, and high nitrate estuaries may be an important source of N2O to the atmosphere. Work on mangrove-lined estuaries has also been a long-term interest. Recent publications: - Nedwell,D.B., Blackburn,T.M., Wiebe,W.J. 1994. Dynamic nature of the turnover of organic carbon, nitrogen and sulfur in the sediments of a Jamaican mangrove forest. Marine Ecology Progress Series. 110, 223-231. - Nedwell,D.B., Trimmer,M.T. 1996.Nitrogen fluxes through the upper estuary of the Great Ouse, England: the role of the bottom sediments. Marine Ecology Progress Series, 142,273-286. - Ogilvie,B., Nedwell,D.B., Harrison,R.M., Robinson,A., Sage,A. 1997. High nitrate, muddy estuaries as nitrogen sinks: the nitrogen budget of the River Colne estuary (U.K.). Marine Ecology Progress Series. 150,217-228. - Trimmer,M., Nedwell,D.B., Sivyer,D., Malcolm,S. 1998. Nitrogen fluxes through the lower estuary of the river Great Ouse, England: the role of the bottom sediments. Marine Ecology Progress Series, in press. - Robinson,A.D., Nedwell,D.B., Harrison,R.M., Ogilvie,B.G. 1998. Hypernutrified estuaries as sources of N2O emission to the atmosphere: the estuary of the River Colne, Essex, U.K. Marine Ecology Progress Series, in press

Trace gas formation

Extensive work on the importance of bacteria in producing trace gases such as methane, nitrous oxide and dimethyl sulphide, and regulating their emission to the atmosphere. This regulation is often because other bacteria remove much of the gases before their emission to the atmosphere. Methane production and oxidation has been examined in landfill cover soil, and in peat bogs. It is clear that there may be intimate interactions between bacteria and plant roots which can markedly influence methane oxidation in the rhizosphere, and hence methane emission to the atmosphere. Other work has examined the production of nitrous oxide by bacteria during denitrification in estuarine sediments. This may be a major source of N2O emissions to the atmosphere. Recent publications: - Nedwell,D.B., Shabbeer,M.T., Harrison,R.M. 1994. Dimethyl sulphide in North Sea waters and sediments. Estuarine, Coastal and Shelf Science, 39,209-217. - Kightley,D., Nedwell,D.B., Cooper,M. 1995. Capacity for methane oxidation in landfill cover soils measured in laboratory scale microcosms. Applied and Environmental Microbiology. 61,592-601. - Nedwell,D.B., Watson,A. 1995. CH4 production, oxidation and emission in a UK ombrotrophic peat bog: influence of sulphate from acid rain. Soil Biology and Biochemistry, 27,893-903. - Watson,A., Stephen,K.D., Nedwell,D.B., Arah,J.R.M. 1997. Oxidation of methane in peat: kinetics of CH4 and O2 removal and the role of plant roots. Soil Biology and Biochemistry 29,1257-1267. - Robinson,A.D., Nedwell,D.B., Harrison,R.M., Ogilvie,B.G. 1998. Hypernutrified estuaries as sources of N2O emission to the atmosphere: the estuary of the River Colne, Essex, U.K. Marine Ecology Progress Series, in press

Antarctic microbiology

This work has focussed on examining the rates of microbial activity in Antarctic environments, particularly marine sediments, and the physiological adaptation of microorganisms to low temperature. We have shown that organic matter is broken down by microorganisms in the Antarctic at 0°C at rates as great as in temperate or tropical sediments, at much higher temperatures. Currently, funded by NERC, we are examining how low temperature affects the uptake by phytoplankton of nutrients such as nitrate or ammonium in the Southern Ocean. This may help to explain the reasons for very low oceanic primary production in the Antarctic. Recent publications: - Nedwell,D.B. et al, 1993. Measurements of seasonal rates and annual budgets of organic carbon fluxes in an Antarctic coastal environment at Signy Island, South Orkney Islands, suggest a broad balance between production and decomposition. Applied and Environmental Microbiology, 59,3989-3995. - Nedwell,D.B., Walker,T.R., 1995. Sediment-water fluxes of nutrients in an Antarctic coastal environment: influence of bioturbation. Polar Biology 15,57-64.

Application of molecular techniques in microbial ecology

Recently developed techniques of analysis of microbial community structure by using nucleotide sequences in 16S rRNA have provided new tools to investigate the structure and function of microbial communities in natural environments. In collaboration with Dr Martin Embley at the Natural History Museum, and funded by NERC, we have been applying this technology to communities of anaerobic bacteria in saltmarsh sediments, and currently in Antarctic environments, to provide new insights into how these communities function ecologically. Recent publications: - Purdy,K.J., Embley,T.M., Takii,S. Nedwell,D.B. 1996. Rapid extraction of DNA and rRNA from sediments by a novel hydroxyapatite spin-column method. Applied and Environmental Microbiology, 62,3905-3907. - Munson,M.A., Nedwell,D.B., Embley,T.M. 1997 Phylogenetic diversity of Archaea in sediment samples from a coastal salt marsh. Applied and Environmental. Microbiology. 63, 4729-4733. - Purdy,K.J., Nedwell,D.B.,Embley,T.M. and Takii,S. 1997 Use of 16S rRNS-targeted oligonucleotide probes to investigate the occurence and selection of sulphate-reducing bacteria in response to nutrient addition to