Has the role of estuaries as sources or sinks of dissolved inorganic phosphorus changed over time? Results of a Kd study

There are literature reports suggesting that some estuaries are sinks for dissolved inorganic phosphorus (DIP) whilst other estuaries appear to be sources of DIP. Here a simple Kd model is presented that is able to rationalize these disparate patterns of behaviour. This model suggests that riverine DIP levels are an important regulator of DIP behaviour in estuaries. DIP concentrations have increased in many rivers over the last 50 years as a result of human activity. The model results presented suggest that increases in riverine DIP concentrations from < 1 to > 5 μM, consistent with documented changes in some systems over the last 50 years, can change estuaries from being sources to sinks for DIP. The model results demonstrate that suspended solid concentrations in estuaries (based on simulations over the range 100–2000 mg 1−1) are also an important regulator of DIP behaviour and hence the modification of suspended solids via dredging and land reclamation activities in estuaries can alter their DIP removal capacity.