Nutrient levels and the development of diatom and blue-green algal blooms in a shallow Australian estuary

Abstract

In the Peel-Harvey estuary system, Western Australia, some 90% of riverflow and nutrient loading occurs in three winter months. Diatom blooms follow riverflow, but are replaced by blooms of the blue-green Nodularia spumigena Mert., especially in Harvey Estuary. By analysis of time series data from 1977–1983, it is shown that the magnitude of the Nodularia bloom in summer is related to the minimum salinity of the estuary (and hence total river flow), maximum phosphate concentration and total riverine phosphorus loading, in the previous winter. The relationships have a predictive capacity. It is argued that diatom blooms trap phosphorus, which is sedimented largely as faecal pellets; the phosphorus is recycled and supports Nodularia growth under warmer conditions, and the amount available determines Nodularia biomass. Nodularia blooms collapse when summer salinities reach 30‰