Suspended particulate matter affects the nutrient budget of turbid estuaries: Modification of the LOICZ model and application to the Yangtze Estuary

This study estimates the importance of the estuarine suspended particulate matter (SPM) on the nutrient budget of the Yangtze Estuary by using extensive field data and a modified version of the LOICZ biogeochemical model that incorporates the partitioning of the nutrients between dissolved and particulate phases. The value of the nutrient partition coefficient in the Yangtze Estuary shows a similar dependence to that in European estuaries. High values of the Net Ecosystem Metabolism are found, with p-r values equal to −10.9 mmol C m-2 day−1 for the non-flood season. If nutrient partitioning was neglected this value would be −2.7 mmol C m-2 day−1, which would have been wrongly interpreted as biological decay and primary production in the turbidity maximum zone and in coastal waters, respectively. The rate of heterotrophy is thus three times higher than when the interaction of SPM with the nutrients is neglected. These results suggest that the estimates of nutrient budgets in turbid estuaries worldwide that ignore the role of SPM in sequestering nutrients, as with most estuarine biogeochemical models, may be incorrect and need to be re-calculated.