Phosphorus release from a tropical estuary sediment: a laboratory study of Lake Maracaibo (Venezuela)

The release of phosphorus (P) from bottom sediments is an important source of nutrient enrichment in many lakes. Reductive dissolution of P and iron (Fe) has been regarded as a mechanism responsible for the P mobilization in sediments. In this work, sedimentary P fluxes in the central portion of Lake Maracaibo were studied, considering the influences of dissolved oxygen, redox potential, pH, and Fe in the overlying water. Experiments were performed to laboratory scale in a batch system under anaerobic conditions in 1976, 1983, 1998 and 2009. For 2023, predictive models were applied. The estimated contribution of sediment to the P content in Lake Maracaibo ranged from 4.84 to 8.14x106 kgP/year, and the P release rate ranged from 1.66 to 10.30 mgP/m2.d. On the last day of the experiment, the P concentration of the sediment was 0.251 mgP/g and of the sediments from the lake (hypolimnetic cone) was 0.253 mgP/g. Fe and the redox potential account for approximately 57% of the variability in total P in overlying water. The annual contribution of sedimentary P to the P content of the lake ranged from 11.13% in 1976 to 27.25% in 2023 (52.72% in 2009).