Nutrient partitioning in the upper Canning River, Western Australia, and implications for the control of cyanobacterial blooms using salinity

Abstract

The partitioning of N and P is examined between the submerged macrophytes, sediment and phytoplankton in a eutrophic freshwater impoundment on the Canning River, Western Australia. The importance of the macrophytes as a nutrient sink, and the effect of salinity increase on their growth were assessed. Summer cyanobacterial blooms in this system have led to a proposal to increase the salinity of this system to curtail or prevent the blooms. Uptake of N and P by Potamogeton crispus accounted for the major portion of the observed loss from the sediments. Luxury uptake of P, and N limitation, were indicated by tissue N:P ratios, with high biomass and tissue N and P concentrations indicating the capacity of this macrophyte to act as a nutrient sink in midsummer. Water column dissolved inorganic N (DIN) and filterable reactive phosphorous (FRP) was also reduced in midsummer. P. crispus showed significant reduction in growth at 8 ppt salinity, and Hydrilla verticillata at 6 ppt. Therefore, use of increased salinity to control freshwater cyanobacterial blooms is likely to reduce nutrient uptake by macrophytes, and may cause a change to phytoplankton dominance.