Gosford City Council Historical Water Quality Review & Analysis

FUTURE DIRECTIONS FOR WATER QUALITY / ENVIRONMENTAL HEALTH MONITORING 4-3
4.2.1.2 Seagrass
The depth range of the seagrass Zostera capricorni is monitored twice yearly at 18 locations
throughout Moreton Bay. In the bay, the depth at which this seagrass can grow depends on water
quality, particularly light availability (refer Figure 4.2). Detection of changes to the seagrass depth
range therefore provides an indication of long term integrated water quality throughout the bay and if
it is impacting on the integrity of these critical habitats.
Figure 4.2 Seagrass depth range measures the distance between the upper tidal
limit of seagrass distribution and the lower light-limited distribution
4.2.1.3 Sewage
Sewage effluent can contribute to the eutrophication of receiving estuarine and coastal waterways. It
is important to be able to trace the source and extent of sewage effluent in receiving waters in order to
evaluate the extent of its impact on the ecosystem. The use of nitrogen stable isotopes enables the
detection and delineation of sewage-derived nitrogen from other nitrogen sources entering the
waterways and its potential influence on the ecosystem. The most abundant form of naturally
occurring nitrogen is 14 N. Sewage is generally enriched in 15 N compared to 14 N and therefore the
relative proportion of 15 N to 14 N, referred to as d 15 N, is elevated in receiving waters of sewage
treatment plants.
4.2.1.4 Report cards
Report cards are provided annually outlining the overall condition of the South-East Queensland
waterways, based on the EHMP results. An example of an EHMP report card is provided in Figure
4.3, while an example plot of the spatial representation of the Ecosystem Health Index is presented in
Figure 4.4.
The report cards provide a clear picture of the overall health of the waterways, and more importantly,
how they relate to previous years. By comparing the waterway health with past results, managers and
decision-makers can obtain quantitative feedback on the relative success of various management
measures implemented within the catchments. The report cards are released each year amid the
Annual Riverfestival, which is designed to maximise community awareness and ownership of the
waterways and their issues.
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