Biodiversity Strategy - Gosford City Council - NSW Government

1. Salinity mediated processes – Salinity is considered to be the “master factor”
governing estuarine biota distributions, conditional on water quality conditions being
favourable. Salinity impacts on the instream and riparian flora, which links to loss of
shelter and foraging areas for fauna, bank instability and multi-linked water quality
reduction. Salinity is relevant to a further two processes because salinity rises are
associated with reductions in dissolved oxygen, which links with hostile water quality
at depth and anoxia-driven release of pollutants from estuary bed sediments.
2. Reductions in inflow-induced currents and vertical mixing – Reduced water
turbulence can result in changes to water quality. It can also reduce suspension time
for eggs and larvae, and their transport along the estuary. It also reduces high flow
habitats, especially in upper reaches of the estuary where tide induced currents are
minimal.
3. Reductions in connectivity associated with the loss of water depth – This is
particularly relevant to migrating fish and crustaceans. The loss of connecting flow is
also likely to result in the prevention of ecological processes in adjacent waterbodies
being activated or maintained.
4. Reductions in flushing and channel-maintenance flows – This is consistent with the
understanding that episodes of high bed shear stress are required to flush or
maintain estuary channels. It is concerned with reduced physical-habitat quality
where hard substrates are coated by sediments or organic material for prolonged
periods and water quality deterioration due to the accumulation of organic material
and subsequent high biochemical oxygen demand.
5. Reduced input of river-borne nutrients and organic material – Input of this material
stimulates phytoplankton and benthic production contributing to estuarine foodwebs
and is partly responsible for the high productivity of estuaries. This is consistent with
the understanding that organic matter and nutrients (bound to sediments) primarily
enter rivers from their catchments during major rainfall events.
6. Reduced dilution of pollutants – This process concerns the reduced dilution of
pollutants arising from agricultural, industrial or urban sources.
Eutrophication (where the water body becomes over enriched with nutrients resulting in the
excessive growth of organisms and depletion of oxygen) is another major concern for
waterways, which is directly linked with hydrological phenomena. Increases in nutrient loads can
result in serious impacts on water and sediment quality and community composition and
function, leading ultimately to anoxic conditions and loss of most taxa. In semi-rural and urban
areas nutrients such as nitrogen and phosphorus are released into the waterways via sewage
or diffuse sources such as stormwater or urban runoff.
Changes to the natural hydrology of an area can have serious repercussions for native
vegetation communities and the species that depend on them. For example, wetland
communities including swamp forest require periodic wetting and drying as part of their
ecosystem functioning. The artificial opening of Gosford's coastal lagoons prevents the
inundation of wetland forests that fringe the lagoons. Waterbirds forage in intertidal areas such
as saltmarsh and increased overland freshwater flows may impact on saltmarsh communities
leading to changes in vegetation composition and possible death of marine invertebrates.
Changes in hydrology may also be responsible for the encroachment of mangroves into
saltmarshes.
Where wetlands no longer go through typical wetting and drying cycles the cycling of nutrients is
disrupted often resulting in a build-up of nutrients and organic matter. Hydrological restrictions in
waterways due to sedimentation can also result in increasing spread of aquatic weeds, leading
to a further degradation of the habitat.
Biodiversity - Technical Report Page 162