Monitoring the impact of urban development on estuary ecosystems.
The problem
Estuaries are highly valuable systems that provide enormous economic and cultural benefits to all kinds of people. However, expanding human populations and urban development around estuaries is increasing contaminant loads, with metals and polycyclic aromatic hydrocarbons (PAHs) accumulating in sediments.
Although New Zealand’s urban estuaries are relatively clean by international standards, projected population increases and land use development patterns suggest that development needs to be managed wisely to ensure that estuaries continue to provide goods and services for future generations.
The solution
The work in this project is aimed at understanding how sediment-dwelling macroinvertebrate communities, species populations, individual organisms, and their tissues respond to contamination from urban sources.
We are developing indices at various levels of biological organisation to more accurately rate the condition and responsiveness of estuarine biota to sub-lethal contaminant exposures. We have sampled and performed ecological experiments at numerous sandflat sites in Waitemata and Manukau Harbours that are influenced to varying degrees by Auckland City urban development. The integration of sophisticated contaminant assays and field-based ecological experiments is a major focus of the programme.
The result
- There are significant, measurable shifts in macroinvertebrate community structure with increasing metal contamination (even after removing effect of other confounding environmental variables).
- Community data is very sensitive, with tangible impacts at metal contaminant levels well below existing sediment effect level guidelines
- Species accumulation curves suggest rare species are the ones disappearing from macroinvertebrate communities, however…
- common and functionally important “key” species (such as cockles and large macrofauna) are also affected: reduced densities with increased contaminants
- Cockles from contaminated sites had high metallothionein concentrations in their tissues and exhibited greater amounts of genetic damage. Other biomarkers and physiological assays (anti-oxidant enzymes, adductor muscle strength, shell thickness) also showed trends along contaminant gradients.
- Effects on cockles do not appear to be having major impacts on sandflat functioning yet (nutrient fluxes, net primary productivity, organic matter processing), but experimental results suggest that continued losses of macrofauna would likely reduce ecosystem functioning.
