icolls - Sustainable Tourism CRC

ECOLOGY, THREATS AND MANAGEMENT OPTIONS FOR SMALL ESTUARIES AND ICOLLS
a more brackish type estuary for about seven months of the year at present. This drastic change in the salinity
regime represents a major change in habitat for the biota. The degraded present state was also caused by other
anthropogenic influences such as a road across the salt marshes, seepage of saline water from mining activities
and human disturbance of birds. It was therefore not possible to improve the health of the system through river
flow adjustments alone. The Orange River Mouth was designated Ramsar status in 1991, but it was placed on the
Montreux Record in 1995 due to its severely degraded state. The study concluded that it was critical to improve
the current health status of the estuary through: •Managing the river flow so that it resembles the natural
conditions more by eliminating the winter release to facilitate mouth closure during the low flow period and
elevating the flows in autumn/summer to facilitate a more river dominated system. Mitigating actions to reverse
modifications caused by the non-flow related activities and developments in the estuary by the responsible
authorities.
Title of paper: Wilson Inlet – A case example of seasonally closed estuaries in the SW of WA
Author: Malcolm Robb
Author's email: malcolm.robb@environment.wa.gov.au
Abstract: Many of the estuaries along the south coast of WA are showing the symptoms of eutrophication
ranging from annual phytoplankton blooms to choking growths of macroalgae. Estuaries in the high rainfall area
are either permanently open or open seasonally from winter rainfall whereas those in the lower rainfall areas to
the east open irregularly often in response to summer rainfall events. Wilson Inlet lies in the medium rainfall
area and is artificially opened each year to manage water levels in the estuary. Over the last 10 years a range of
studies has elucidated the key eutrophication processes linking catchment influences, sediment accumulations
and the effect of marine exchange often in the context of vigorous community debate centred around the annual
opening of the bar. Wilson Inlet is remarkably resilient to nutrient accumulations partly due to its size (45km2)
and vigorous wind mixing. Denitrification efficiencies and phosphorus retention capacities are high and the
extensive Ruppia megacarpa growth at the mouths of the influent rivers acts to absorb and attenuate the nutrient
signal in the estuary. The transfer of process understanding from Wilson Inlet across the across the other
estuaries of the south coast provides managers with guidance to estuarine response to eutrophication and
suggests direction for management intervention. Ocean connectivity, timing of rainfall events and relative size of
estuary are key drivers of estuarine response. The similarity and differences of these estuaries may throw light on
the behaviour of ICOLLs elsewhere
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