Importance of marine inputs to the sediment and nutrient loads of coastal plain estuaries: a case study of Pumicestone Passage, south east Queensland, Australia

Sediment and nutrient exchange between Deception Bay and Pumicestone Passage was studied to test the hypothesis that marine input of sediment and associated particulate nutrients may dominate the nutrient loading of coastal-plain estuaries. Estimates suggest that Deception Bay contributes 110–111 x 10³ t of sediment and 68–74 t of phosphorus annually to Pumicestone Passage. These yearly transports were 10 times the sediment and two times the phosphorus contributed from the catchment. In contrast, Deception Bay contributed only 100–220 t of nitrogen annually to Pumicestone Passage, or 12–25% of the nitrogen contributed by the catchment as a result of leaching from agricultural and horticultural areas and/or from groundwater. However, caution is required when extrapolating these findings to other coastal-plain estuaries since some features may be unique to Pumicestone Passage. In particular, the sediment and phosphorus inputs were dominated by a net northerly flow through the passage and high concentrations of suspended sediment and phosphorus in adjacent coastal waters (Deception Bay).