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Description
DOMUSe project is determined to characterize microbial response to dissolved organic matter (DOM) supplied from the sediments to the near-bottom water of Baltic Sea Deeps. Our study will utilize outcomes of a parallel project, funded by Polish National Science Centre which focuses to determine the return DOM flux from sediment pore waters to near bottom waters.This project will supply an initial condition of supply rates of the DOM to the near-bottom waters. In DOMUSe, we will execute several studies, where part of the sediment and near-bottom waters will be enclosed in the anoxic atmosphere for a period of time. This way, we would like to assess the rates of microbial processes occurring in the near-bottom waters. We have chosen several proxies that will allow us to trace changes in quality and quantity of DOM, including chemical composition and optical DOM properties. We will use optical properties of DOM to assess changes in DOM quality. Optical properties of DOM, such as fluorescence, via statistical multivariate analyses, will allow to assess the DOM fractionation between humic-like (microbially reworked and mainly refractory) DOM and amino acid-like DOM, which is mainly associated to rapidly utilizable fresh DOM. We will use siderophores, ferric iron specific small organic molecules, as a proxy of microbial activity. Their production rates were previously shown to be affected by bioavailability of dissolved organic matter. Their production was previously associated to fresh labile organic matter sources, such as phytoplankton blooms, however, they were also found in the sediment pore waters. The measurements of oxygen respiration by bacteria and microbial nutrient utilization will fulfil the measurements of the microbial response to DOM release from sediments pore waters. Bacterial abundance will be also measured overtime to access bacterial growth associated to DOM supply by the sediments.