Effect of nutrient loading on biogeochemical processes in tropical tidal creeks

Brief description

The effect of increased nutrient loads on biogeochemical processes in macrotidal, mangrove-lined creeks was studied in tropical Darwin Harbour, Australia. Water quality and sediment composition, benthic and pelagic metabolism and benthic nutrient and gas fluxes were studied during three field surveys to compare nutrient transformation and retention processes in three tidal creeks receiving different loads of sewage discharge. There were marked differences in process rates between Buffalo Creek (hypertrophic), which receives the largest sewage loads; Myrmidon Creek (oligotrophic-mesotrophic) which receives smaller sewage inputs; and Reference Creek (oligotrophic) which is comparatively pristine. Net benthic nutrient fluxes in Buffalo Creek were more than an order of magnitude higher than in Myrmidon and Reference Creeks, which have similar and low benthic fluxes during the wet and dry seasons. Similarly, net pelagic primary production rates were much higher in Buffalo Creek and respiration exceeded primary production resulting in severe drawdown of O2 concentrations at night. In Buffalo Creek, anoxic sediments released oxide-bound phosphorus and inhibited coupled nitrification-denitrification, enhancing benthic nitrogen and phosphorus fluxes. Light limitation of primary production resulted in build-up of excess nutrients in the water column, further stimulating primary production. Poor water quality in Buffalo Creek was exacerbated by poor tidal flushing imposed by a narrow meandering channel and sandbar across the mouth. In contrast to Buffalo Creek, the effect of the sewage load in Myrmidon Creek was confined to the water column, and the impact was temporary and highly localized. This study has identified pelagic primary production, benthic nutrient fluxes and denitrification efficiency as the biogeochemical processes most affected by nutrient loading in tidal creek systems. The serious deterioration of water quality impacts on the functioning of the whole ecosystem, with potential for detrimental effects on higher trophic levels.

Lineage

Maintenance and Update Frequency: unknown

Statement: Unknown