2.7.5 'Coastal lakes and estuaries' landscape group

Summary

Qualitative models were developed for subtidal benthos and intertidal wetlands (‘Seagrass’, ‘Lakes’, ‘Lagoons’ and ‘Saline wetlands’ landscape classes). Together the two models represent the continuum of ecosystems from the shoreline to lake depths of about 2 m, and could be joined via their common seagrass nodes.

The qualitative model for intertidal wetlands includes an interaction between groundwater and saltmarsh, whereby groundwater extraction leads to micro-scale (mm) subsidence. The process is so local in scale that development of a quantitative model to evaluate potential impacts on intertidal wetlands from the additional coal resource development was not considered warranted.

The qualitative model for subtidal benthos indicates that seagrass is sensitive to subsidence resulting from underground mining, due to lowering of the lake bed, hence increasing depth of water above the seagrasses, and hence reduced light penetration. Experts did not consider groundwater drawdown a risk to seagrasses, as lake levels are maintained by seawater level and the degree of groundwater dependence for seagrass could not be determined. Changes in stream inflows to these coastal lake systems were also not expected to impact seagrasses. For these reasons, a quantitative model for subtidal benthos was not developed.