Main Research Interests Roger Carvalho da Silva

The processing of dissolved organic matter (DOM) in submarine groundwater discharge (SGD): Implications for land-ocean fluxes of organic carbon.

The land-ocean interface is of particular importance for global biogeochemical cycles and the processing and transport of organic matter, nutrients, and trace metals. Much of the continental flux of organic matter and inorganic nutrients occurs through rivers and estuaries. Over the past years, it became more and more evident that subterranean fluxes are of major importance, and in some regions the submarine groundwater discharge (SGD) of nutrients rivals that of rivers.

The geochemistry of SGD is influenced by the chemistry of the recirculating seawater and fresh, terrestrial groundwater endmembers. The SGD can fuel primary production, influence benthic community structures, trigger harmful algal blooms, and induce shifts of the nutrient stoichiometry in the coastal water column. Besides being a very active reaction zone little is known about the physical, chemical and biological processes in the benthic boundary layer and surface sediments, where fresh groundwater and recirculating seawater are mixing and discharging.

Three groundwater-dominated barrier islands in the German North Sea (Mellum, Norderney, and Spiekeroog) with similar geology and climate, but different anthropogenic impacts (e.g., groundwater nutrient loading and groundwater utilization), will be compared in relation to their biogeochemistry of SGD to determine whether the DOM in the STE is derived from marine or terrestrial sources. This PhD project will focus on the photochemically reactive fractions of dissolved organic matter (DOM), colored dissolved organic matter (CDOM).