Introduction to the project OrgCarbon: Organic carbon in rivers – characterization, origin, and degradability – first results from the Ems estuary

Organic carbon drives key processes in estuaries and rivers like (micro)biological production, oxygen consumption, transport of pollutants, and the flocculation/agglomeration of suspended particulate matter. The OrgCarbon project aims for an in‑depth characterization of organic carbon in field samples by using both established and innovative methods. Oxygen consumption, microbial respiration, potential for sorption of pollutants, origin and composition of the organic matter will be determined. By testing a variety of cross-disciplinary methods, we aim to develop a standardized protocol for studying organic carbon in estuaries and rivers. The goal is to develop an easy-to-use and cost-effective protocol that can be implemented in existing monitoring programs. As a result, knowledge about the origin and degradability of organic carbon and thus oxygen consumption rates could, in future, be determined routinely and included in water quality management.

First results from the highly turbid Ems Estuary show strong gradients in dissolved organic carbon (DOC) and total organic carbon (TOC) along the salinity gradient. TOC, but also the ratio of DOC to particulate organic carbon (POC), increases along the gradient from marine to freshwater. Spectroscopic measurements and absorption indices (e.g., SUVA₂₅₄, S_R, S_275-295) provided first insights into organic carbon origin and composition and are easy to use and inexpensive. Additional analysis of microbial respiration and enzyme activity will provide information on organic carbon degradability and its role for the oxygen budget of rivers and estuaries.