Bacterial Biomass and Heterotrophic Activity in Sediments and Overlying Waters

Abstract

Most studies of aquatic microbial ecology have been concerned with the water column. In comparison, little is known about the microbiology of sediments, although sediments are unquestionably an important part of coastal ecosystems. From the high bacterial biomass, which is about equal to the faunal standing crop (Dale 1974), it has been concluded that the bacteria have an important role in the nutrient cycles and the food web. Much of the research has been concentrated on nutrient cycles (nitrogen, sulfur) and methanogenesis, which will not be discussed in this connection. However, information on the microbiology of sediments (bacterial biomass, activity) is still limited. Most of the earlier publications deal with the enumeration and isolation of bacteria using the agar plate technique (e.g., Westheide 1968; Stevenson et al. 1974; Boeye et al. 1975; Litchfield et al. 1976; Rheinheimer 1977). However, bacteria growing on agar plates account for only a small fraction of the total number of bacteria present in sediments. A more direct insight into bacterial colonization and biomass in sediments was obtained by scanning electron microscopy (Weise and Rheinheimer 1978) or epifluorescence microscopy (e.g.. Dale 1974; Griffiths et al. 1978; Meyer-Reil et al. 1978; Jones 1980; Meyer-Reil and Faubel 1980). From these studies, the diversity of bacteria and their comparatively high biomass became obvious. In evaluating the role of bacteria as mineralizers and biomass producers, the determination of bacterial activity becomes important. However, only in a limited number of studies has the bacterial uptake of dissolved organic substrates been measured (Wood 1970; Harrison et al. 1971; Hall et al. 1972; Christian and Wiebe 1978; Griffiths et al. 1978; Hanson and Gardner 1978; Meyer-Reil et al. 1978, 1980; Litchfield et.a1. 1979; Novitsky and Kepkay 1981). Reports on the degradation of particulate organic matter by bacteria in sediments is even sparser (Ayyakkannu and Chandramohan 1971; Maeda and Taga 1973; Oshrain and Wiebe 1979; Sayler et a1. 1979; King and K1ug 1980, Meyer-Reil 1981).