The influence of bioturbation and water column oxygenation on nutrient recycling in reservoir sediments

Abstract

Sediments are sinks of nutrients in reservoirs, but may also act as temporary nutrient sources to the water column, leading to eutrophication during the warm season. Several abiotic and biotic factors at the water–sediment interface are known to influence the role of sediments as temporary nutrient sources. This study aimed at quantifying the effects of two factors (i.e., oxygenation and bioturbation) on fluxes of nutrients from the water–sediment interface of the reservoir. An experimental approach was developed in the laboratory to test three fauna conditions (no fauna, presence of tubificid worms, and chironomids larvae) and three conditions of water column oxygenation (aerobic, fluctuating, and anaerobic conditions). Chironomid larvae significantly increased concentrations of N (NH4+ + NO3−) and PO43− released from sediments by 3.7-fold and by 17-fold, whereas tubificid worms had a lesser effect (twofold for N and threefold for PO43−). Anaerobic conditions increased N by 56-fold and PO43− by 102-fold compared to the aerobic treatment. Thus, anaerobic conditions produced greater N and P fluxes than fauna. Nevertheless, fauna and anoxic conditions at the water–sediment interface should not be neglected when quantifying the role of sediments on nutrient dynamics in lakes and reservoirs.