Comment on “Towards ecologically relevant targets for river pollutant loads to the Great Barrier Reef” by F.J. Kroon

Abstract

[Extract] Kroon (2012) makes first-order estimations of the reduction in sediment and nitrogen loads from north Queensland rivers to the coastal waters of the Great Barrier Reef lagoon (GBRL) that would be required to reduce the concentrations of sediment (TSS) and dissolved inorganic nitrogen (DIN) in coastal waters to values less than water quality targets outlined in the Great Barrier Reef Water Quality Action Plan (Reef Water Quality Protection Plan Secretariat, 2009). Kroon (2012) makes the explicit assumption that TSS and Chl a values measured within the coastal waters are directly proportional to the river loads of TSS and DIN respectively. The modeling approach of Kroon (2012) assumes that rivers are the primary source of sediment and nutrients to the water column within the lagoon. In this comment we suggest that (a) the references cited by Kroon (2012) to support the assumptions in the model give scant justification, and are in some respects contradictory, and that (b) Kroon (2012) has ignored a large body of literature on both sediment and nitrogen fluxes and storage, which indicate that river discharge is not the sole contribution into sediment and nutrient budgets for the GBRL.