Is bacterioplankton production in the Ria de Aveiro influenced by salt marshes and bed sediment

Abstract

The contribution of potential export of materials from bottom sedimentsand salt marshes into the water column of a shallow estuarine system of Ria deAveiro to the observed high bacterial productivity in the mid section of thisestuary was evaluated. Vertical profiles of physical, chemical and bacterialvariables were studied in the marine and brackish water zones, and oftransversal profiles in the brackish zone only. Although the concentrations ofseston (17–241 mg l−1), particulate organiccarbon (3–15.5 mg l−1) and chlorophyll(1.2–7.0 μg l−1) varied widely, thevertical and transversal profiles were without much variation. Total bacterialnumber (0.2–8.5 × 109 cellsl−1) and the number of particle-attached bacteria(0.02–2.50 × 109 cellsl−1)along vertical and transversal profiles did not differ much, but the rate ofbacterial production (0.05–14.2 μg C l−1h−1) and dissolved organic carbon concentration(6.0–69.2 mg l−1) were frequently highernear the salt marsh margin at the brackish water transect. The increase inproductivity could not be associated with runoff of particulate matter butcoincided with the inputs of dissolved organic carbon. The results of verticaland transversal profiles point to a minor role of particulate matter additionsfrom the salt marsh area or from bed sediments.