Metal and nutrient cycling and its impact on food-web dynamics in Darwin Harbour in comparison to the Van Diemen Gulf

 Aim

To understand the effect of increased metals and nutrient loading on sediments, meiofauna and phytoplankton population dynamics and species diversity in Darwin Harbour and its catchment, in comparison to the semi-enclosed basin of Van Diemen Gulf.

Background

Recent ecosystem research reports on Darwin Harbour and its catchment have forecast increases in metals and nutrient loadings based on escalated urban and port development. Northern Territory Government Report released in 2009, noted that nitrogen and phosphorus levels had increased 3 and 12 fold when comparing urban and rural locations, metals including Lead, Copper and Zinc using the same comparison have increased by 10, 7 and 3 fold respectively, with sediments coefficients now registering 8 fold increases (Skinner et al., 2009), indicating that urban development is having a disproportional effect on the nutrient and metal loads within the Harbour and catchment based on land mass usage of 11%, however urban development is projected to increase in the future. Ascertaining the effects of contaminants on the benthic marine food-web is key to understanding the effects on the marine ecosystem, particularly due to the primary producers and the lower trophic level organisms being directly affected by contaminants. Increased rates of turbidity within the Harbour based on elevated total suspended solids (TSS) values (ERG, 2007) will undoubtedly enhance bacterial growth and potentially decrease phytoplankton diversity, possibly leading to ecosystem shifts and species dynamics. A recent report on water quality in Darwin Harbour concluded that seasonal changes have a greater impact on the Harbour water quality dynamics than tidal effects (French, 2010).  Recommendations have concluded that one of the major gaps in knowledge on Darwin Harbour include comprehensive monitoring of organic pollutants entering the water column as a consequence of anthropogenic and industrial waste (French, 2010).