icolls - Sustainable Tourism CRC

ECOLOGY, THREATS AND MANAGEMENT OPTIONS FOR SMALL ESTUARIES AND ICOLLS
northern mouth remained open as ever. The annual mean salinity of the lagoon, prior and after the damming of
the upstream is 27 and 37 psu respectively, thus the normal estuary turned into a perennial hypersaline estuary
after the damming. However, after the closer of the southern mouth, the salinity is below the oceanic during the
Northeast Monsoon, otherwise it remain as a hypersaline estuary with a week horizontal salinity gradient. In the
inner end, the salinity increases far beyond the oceanic, some times to 55 or 60 because of evaporation whereas
the rain periods may lower the salinities to between 20 and 30. Stronger exchange is observed during periods of
slack water and neap tide. The periods of weak or non-existent horizontal gradients are coincided with poor
exchange. The salinity is in constant raise and the water exchange is poor even during the periods of stronger
evaporation, possibly due to the convectional mixing, which may hinder inverse estuarine circulation from being
established. The residence times of the lagoon during the wet and dry seasons are between 40 -100 days but even
longer during the transition between normal to hypersaline estuary. Thus, the frequent shifts from normal to
hypersaline condition bring down the long-term water exchange. Thus, the tropical shallow lagoons being more
sensitive to human impact, the ad hoc regulation of freshwater input into the shallow tropical lagoon may result
in large salinity variation and poor water exchange than in a normal estuary.
Title of paper: The importance of volume correction when investigating plankton dynamics in intermittently
opening and closing lagoons
Author: David Rissik and Iain Suthers
Author's email: dave.rissik@dipnr.nsw.gov.au
Abstract: Increased volume of a closed ICOLL can dilute incoming nutrients, potentially reducing their
influence. Comparing data before and after rainfall events can be difficult because of the associated changes in
volume that may occur. A study in Dee Why lagoon on Sydney’s northern beaches investigated the effects of
volume on plankton responses. To accurately determine volume the bathymetry of the lagoon was determined
and water level data were collected at regular intervals throughout a three-month study during summer, 1999.
Three sampling events were conducted before a rainfall event and six during and after rainfall. Following
rainfall, the volume of the lagoon increased by more than 50%. Plankton data from throughout the study were
transformed to a standard lake volume (the volume on the final sampling event) to enable the real influence of
rainfall to be determined. Accounting for volume made little difference to the trends in plankton responses but
made a difference to the magnitude and hence the significance of the responses. Phytoplankton biomass grew 10
fold within a week after initial rainfall and declined to near initial levels 2 weeks later. Zooplankton responded
within a day with two fold increase in the adult stages of the calanoid copepod Oithona sp., followed a week
later by nauplii and adult Acartia bispinosa. The nutrients from run off, growth and the influx of new
zooplankton into the water column resulted in a depleted 13C and 15N stable isotope signature of A. bispinosa
by 2-4 ppt within 1-2 weeks, consistent with diatom growth and the terrestrial supply of depleted nutrients. D34S
of A. bispinosa was enriched by 2 ppt for 1-2 weeks after rainfall, but unlike C and N, returned to pre-rainfall
levels, indicating the different trophic pathways of C, N and S.
Title of paper: Developing a framework to identify condition, values and management priorities for estuaries in
Australia
Author: Andrew Moss, David Rissik, Dianne Rose
Author's email: andrew.moss@epa.qld.gov.au
Abstract: This paper describes linked projects that are being undertaken by environmental management
agencies in Queensland, New South Wales and Victoria and the Cooperative Research Centre for Coastal Zone,
Estuary and Waterway Management. The aims of all these projects are broadly similar, to set up a framework for
reporting on the condition and values of estuaries and how these interact with each other. Ultimately, the
reporting framework will be used to identify management priorities. The proposed framework will be based on a
Pressure/Condition/Impact (social and economic)/Response model. Indicators for pressure, condition and impact
will be developed through a logical sequence comprising identification of the key pressures â identification of
related pressure indicators â identification of related condition indicators â identification of related social and
economic impact indicators. By following this process we will ensure that there are direct linkages between the
pressures, condition and impact. The project will also seek to quantify these linkages as far as possible. The
qualitative and quantitative links will be important in identifying and prioritising management responses. The
framework will be holistic in that it will seek to cover all aspects of estuary condition including not only
traditional water quality but also biological health, habitat extent and aesthetic condition. The framework will be
designed to allow indicators to be rolled up into composite indices for reporting at a high level while at the same
time it will be possible to report in more detail on individual issues. The project has a number of stakeholders in
Queensland, New South Wales and Victoria. These groups will be used to assess draft frameworks in terms of
their usefulness to local government, community groups and industry.
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