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Benthic microbial biomass dynamics in aquatic ecosystems of the Danube Delta

Sediments represent distinct ecological areas with a significant importance in transfer of matter and energy through aquatic ecosystems. Many heterogeneous groups of heterotrophic microorganisms coexist at sediment level and breakdown the detrital organic matter (DTOM) originated from excretes and dead bodies of aquatic organisms. Through the metabolic activity of heterotrophic microorganisms, the mineral elements from the DTOM composition are recycled and become available to primary consumers, being reintroduced into biogeochemical cycles. Assessment of total microbial biomass (TMB) can provide general information about the active microorganisms implied in energy and matter transformation. This paper presents several characteristics of TMB dynamics, evaluated during two research projects in sediments of several aquatic ecosystems from Danube Delta: three sections of Sf. Gheorghe branch in 2008-2010 period, and Roşu Lake, Mândra Lake and two adjacent channels in 2011-2013 period. The results show significant temporal and spatial variations of this parameter, with different tendencies in the studied ecosystems. Highest TMB was recorded in Mândra Lake (general average values of 966 g C g). Two statistical methods, hierarchical cluster analysis and ANOVA, were used to determine the grouping by similarity of ecosystems and areas, and, also, to evaluate the differences between obtained data series.