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

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 ofthe blue-green Nodularia spumigena Mert., especially in HarveyEstuary. By analysis of time series data from 1977–1983,it is shown that the magnitude of the Nodularia bloom in summeris related to the minimum salinity of the estuary (and hencetotal river flow), maximum phosphate concentration and totalriverine phosphorus loading, in the previous winter. The relationshipshave a predictive capacity. It is argued that diatom bloomstrap phosphorus, which is sedimented largely as faecal pellets;the phosphorus is recycled and supports Nodularia growth underwarmer conditions, and the amount available determines Nodulariabiomass. Nodularia blooms collapse when summer salinities reach30