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The ecosystem health of the Logan estuary
deteriorated from 2007/2008 (“D-”) to an “F” in the 2009 Report Card.
This reduction in grade was due to lower compliance with QWQ guidelines
for EHI indicators, especially Chl-a, which
dropped from 50% compliance in 2007/2008 to only 35% compliance in
2008/2009. The overall water quality remained poor with nutrients (TN
and TP) and turbidity failing to comply with water quality guidelines
throughout the reporting period.
Turbidity in the Logan estuary is typically
around 20 NTUs in the reaches below the Pacific Highway overpass
(approximately 19 km upstream). Above the overpass however, turbidity
levels sharply increase to levels ranging between 100 and 230 NTUs. This
is likely due to a combination of reasons. The shallowing of the river
just above the highway overpass leads to increased tidal movement and
more turbulence and consequently greater resuspension of sediments.
Additionally, in this reporting period high rainfall produced some of
the lowest salinities recorded in the estuary since the inception of the
EHMP and the associated runoff led to some of the highest turbidities.
The BHR for the Logan estuary was unchanged from
2007/2008 with 53% of the estuary having unmodified riparian habitat
along its banks. Much of the natural riparian habitat of the estuary
has been modified for agricultural or residential purposes.
Abbreviations glossary |
Indicators and methods
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