Monitoring of nutrients and species relevant to the carbon cycle is of vital importance for tracing and understanding the mechanisms that drive aquatic ecosystem dynamics. Multiple harmful effects resulting from nutrient enrichment range from localized high concentrations of suspended algae to marked dissolved oxygen depletion and death of biota. Furthermore, the ocean surface pH has decreased significantly in the last few decades, leading to notable changes in structure and biodiversity of aquatic ecosystems. High quality monitoring of relevant chemical species is crucial in order to predict and to be able to deal with the consequences of anthropogenic influences. The main goal of this work has been the development of sensors, new tools, in-line setups and approaches for on-site and in-situ monitoring of nutrients and species relevant to the carbon cycle; integration of the proposed arrangements for the field analysis in freshwater and/or seawater with subsequent validation using laboratory measurements.