Gosford City Council Historical Water Quality Review & Analysis

RESULTS OF WATER QUALITY DATA ANALYSIS 3-20
Cockle Ck 9 212 0
Woy Woy Ck 9 10760 29
Brisbane Water 9 4532 9
Booker Bay 7 6055 7
Wamberal Lagoon 14 803 0
Terrigal Lagoon 11 320 0
Avoca Lagoon 7 1679 2
Cockrone Lagoon 12 500000+ 9
Of particular interest are the results for Cockrone Lagoon. As reported in Ecoscience Technology
(2002), Cockrone Lagoon was opened and drained in February 2002 (refer Appendix A for MHL
gauging of water levels in Cockrone Lagoon). Following drainage of the lagoon, filamentous bluegreen
alga Oscillatoria (and other related species) grew rapidly on the exposed lagoon sediments.
The algae remained in high numbers for a week or so until the water level increased following heavy
rainfall. Comparisons with the MHL data indicate that dissolved oxygen in the lagoon (or at least at
the datasonde location) was very low during the algal bloom (< 2 mg/L), while turbidity levels were
high (up to 160 NTU), due to the fragmentation and resuspension of the benthic algae into the water
column.
Cheng indicates that the entrance openings of the coastal lagoons seem to cause a number of
ecological problems, such as massive algal growth (and reduced dissolved oxygen levels), and that
the lagoons need to be actively management and monitored to prevent degradation. In particular,
Cheng points to better management of entrance openings, to be more sympathetic to lagoon ecology,
as a means of minimising future degradation of the coastal lagoons.
Further details on biological monitoring of the Gosford Waters are available in Ecoscience
Technology (2000, 2002).
3.3.3.2 Chlorophyll-a
Chlorophyll-a can be considered as an indicator of algal growth, as it is a measure of the amount of
green pigment within the water. Recent research by the University of Newcastle suggests that
chlorophyll-a is a good surrogate of the amount of primary productivity within an estuarine waterway
(pers comm. Dr A Redden, Uni. of Newcastle).
Chlorophyll-a has been monitored within the Gosford waters as part of Laxton’s previous water
quality monitoring programs (1993/94, 1996 – 1998). A summary of Laxton’s chlorophyll-a results
for the latter of these two programs is shown in Table 3.29.
D:\R.N0754.002.01.DOC 7/11/03 16:11