Gosford City Council Historical Water Quality Review & Analysis

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RESULTS OF WATER QUALITY DATA ANALYSIS 3-17 Turbidity in Avoca Lagoon is also highly variable, with measurements up to 160 NTU. As discussed for the Koolewong site, turbidity records can be influenced by fouling of the probe, and there appears to be some evidence of this at Avoca Lagoon. Also, given its relatively shallow water, stirring of fine bed sediments during periods of lower water levels would also be a notable cause of elevated turbidity levels in Avoca Lagoon. Higher turbidity concentrations are observed during and flowing entrance breakout events, and also periods of catchment runoff (which do not result in entrance breakout). 3.2.3 Cockrone Lagoon The Cockrone Lagoon entrance also broke out 14 times during the period March 1996 to Jun 2002, which included a period of 20 months (Sept 1999 to May 2001) when no breakouts occurred. The hydrology of Cockrone Lagoon is very similar to that described for Avoca Lagoon, with sudden responses to catchment runoff, gradual evaporation effects, and small periods of tidal influence following entrance breakout. The salinity of Cockrone Lagoon is variable, falling to levels of about 6ppt when the lagoon is ‘full’, and peaking at levels well in excess of oceanic salt concentrations (i.e. Hypersaline conditions) following breakout, recharge with ocean waters, and subsequent evaporation of ocean waters from the closed waterway. Temperature within Cockrone Lagoon varied on a seasonal basis, from approximately 25 – 30 °C in the summer to about 10 – 15 °C in the winter. pH levels generally ranged between 7 and 10. Similar to Avoca Lagoon, the pH levels in Cockrone Lagoon generally followed a seasonal trend, with higher levels during the later Autumn / early Summer months, and lower levels during the Autumn / Winter months. This trend was somewhat disrupted by the predominantly dry period of 2000 / 2001, which resulted in higher than expected pH levels for the majority of the time. pH is likely to be affected by the amount of primary productivity (photosynthesis) occurring within the water. Dissolved Oxygen (DO) in Cockrone Lagoon is highly variable ranging between 16 mg/L and zero. Although not completely evident, there appears to be a trend in DO concentrations that is also seasonal. Higher DO concentrations are recorded during the late autumn / early summer period, coinciding with the increase in primary productivity (as suggested by the higher pH levels). Lower DO levels occur during mid to late summer, extending through autumn. It is possible that the higher primary production rates in early summer are unsustainable, resulting in a massive die-off of the algae colonies. The decay (reduction) of this organic matter would generate a significant oxygen demand on the water column, thus depleting DO levels. Turbidity in Cockrone Lagoon is mostly less than about 10 NTU, however, some periods of heighten hydrologic activity result in significantly elevated turbidity levels (up to 160 NTU). Higher turbidity is recorded coinciding with catchment runoff events and entrance breakouts. However, there remains a considerable amount of data with higher turbidity concentrations that cannot be explained by such mass hydrologic processes. D:\R.N0754.002.01.DOC 7/11/03 16:11
RESULTS OF WATER QUALITY DATA ANALYSIS 3-18 3.3 Historical Water Quality Results 3.3.1 Chemical Parameters Chemical parameters, such as nitrogen and phosphorus have been measured within the Gosford waters at various times in the past. John Laxton (1994, 1999) completed two different monitoring programs in the 1990s, with monitoring carried out approximately monthly. The first period was from September 1993 to October 1994. The second period was from February 1996 to December 1998. Monitoring sites for these previous programs were not the same as the most recent monitoring program by Cheng, and therefore, direct comparisons between the datasets is difficult. A summary of the water quality results for the coastal lagoons, taken from the previous Laxton datasets, is provided in Table 3.26. The most recent Cheng data is also shown in this table for comparative purposes. As can be seen in Table 3.26, the total nitrogen concentrations measured by Laxton are considerably lower than those taken by Cheng. There are a number of possible explanations for this significant different in results, including monitoring at different sites, and the use of different analytical approaches (both Laxton and Cheng use non-NATA accredited labs when determining water quality). Table 3.26 Nutrients in the Coastal Lagoons (1993 – 2002) 1993/94 Mean 1996 – 98 Mean 1999 – 2002 Mean (Cheng) Total Nitrogen (mg/L) Wamberal Lagoon 0.65 0.60 2.51 Terrigal Lagoon 0.72 0.52 2.48 Avoca Lagoon 0.80 0.70 1.60 Cockrone Lagoon 1.23 0.85 1.72 Total Phosphorus (mg/L) Wamberal Lagoon 0.058 0.060 0.062 Terrigal Lagoon 0.064 0.059 0.082 Avoca Lagoon 0.079 0.066 0.070 Cockrone Lagoon 0.052 0.054 0.046 The total phosphorus concentrations were more similar between the Laxton and Cheng results. This may indicate that similar analytical techniques were adopted for both monitoring programs. Cheng also carried out a limited water quality monitoring program in Brisbane Water between April 1993 and April 1994. Water quality at sites within Brisbane Water showed reasonably consistent results during this period, with a typical mean Total Phosphorus concentration of about 0.075 mg/L and a typical mean Total Inorganic Nitrogen concentration of about 0.135 mg/L. Cheng also noted that concentrations of phosphorus and inorganic nitrogen increased substantially following rainfall. D:\R.N0754.002.01.DOC 7/11/03 16:11
Page 1 and 2: Gosford City Council Historical Wat
Page 3 and 4: CONTENTS I CONTENTS Contents List o
Page 5 and 6: LIST OF FIGURES III 4.4 Outcomes fr
Page 7 and 8: LIST OF TABLES V Table 3.23 Water Q
Page 9 and 10: INTRODUCTION 1-2 locations in Brisb
Page 11 and 12: INTRODUCTION 1-4 aquatic ecosystems
Page 13 and 14: INTRODUCTION 1-6 Default trigger va
Page 15 and 16: GWQ: A DATA MANAGEMENT AND ASSESSME
Page 23 and 24: RESULTS OF WATER QUALITY DATA ANALY
Page 37: RESULTS OF WATER QUALITY DATA ANALY
Page 43 and 44: FUTURE DIRECTIONS FOR WATER QUALITY
Page 67 and 68: MHL DATASONDE RESULTS: AVOCA LAGOON
Page 69: MHL DATASONDE RESULTS: KOOLEWONG C-

Gosford City Council Historical Water Quality Review & Analysis

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