Gosford City Council Historical Water Quality Review & Analysis

RESULTS OF WATER QUALITY DATA ANALYSIS 3-9
3.1.2.2 Oxidised Nitrogen
Annual median concentrations of oxidised nitrogen (i.e. nitrates and nitrites) in the Gosford waters is
shown in Table 3.14, while the quarterly averages of oxidised nitrogen for the past 15 months is
shown in Table 3.15. The annual results show that the sites located at the creek entrances (i.e.
Narara, Erina, Kincumber and Woy Woy Creeks) all have relatively elevated concentrations of
oxidised nitrogen.
The quarterly results show variable concentrations throughout the 15 month period, which may be a
function of the amount of catchment runoff during preceding weeks or months. Highest
concentrations were recorded during the last quarter (Apr – Jun 2002) following extensive rainfall
during the February to April 2002 period. Oxidised nitrogen is generated through the nitrification of
ammonia, and so its presence in the environment can be delayed somewhat due to the time taken for
such chemical processes to occur.
Table 3.14 Annual Medians for Oxidised Nitrogen
Oxidised Nitrogen (mg/L)
Site No. and Location 2001/ 2002 2000/ 2001 1999/ 2000
n=11 n=12 n=9 Trend
Site : 77 - Booker Bay 0.021 0.017 0.021
Site : 78 - Narara Creek Entrance 0.049 0.048 0.036
Site : 79 - Erina Creek Entrance 0.052 0.048 0.042
Site : 80 - Kincumber Creek Entrance 0.049 0.049 0.040
Site : 81 - Cockle Creek 0.036 0.032 0.020
Site : 82 - Woy Woy Creek 0.040 0.051 0.036
Site : 83 - Wamberal Lagoon 0.027 0.031 0.042
Site : 84 - Terrigal Lagoon 0.036 0.038 0.046
Site : 85 - Avoca Lagoon 0.041 0.031 0.032
Site : 86 - Cockrone Lagoon 0.031 0.020 0.020
Average Rainfall at Gosford 1248mm 1038mm 1228mm
Table 3.15 Quarterly Means for Oxidised Nitrogen
Oxidised Nitrogen (mg/L)
Site No. and Location
Apr - Jun Jan - Mar Oct - Dec Jul - Sep Apr - Jun
2002 2002 2001 2001 2001
n=4 n=1 n=3 n=3 n=3 Trend
Site : 77 - Booker Bay 0.034 0.022 0.018 0.017 0.023 Variable
Site : 78 - Narara Creek Entrance 0.145 0.034 0.049 0.042 0.057 Variable
Site : 79 - Erina Creek Entrance 0.091 0.024 0.049 0.031 0.047 Variable
Site : 80 - Kincumber Creek Entrance 0.135 0.045 0.059 0.042 0.056 Variable
Site : 81 - Cockle Creek 0.072 0.036 0.043 0.026 0.035 Variable
Site : 82 - Woy Woy Creek 0.082 0.040 0.041 0.024 0.039 Variable
Site : 83 - Wamberal Lagoon 0.049 0.028 0.025 0.025 0.040 Variable
Site : 84 - Terrigal Lagoon 0.082 0.026 0.026 0.033 0.056 Variable
Site : 85 - Avoca Lagoon 0.079 0.066 0.029 0.034 0.052 Variable
Site : 86 - Cockrone Lagoon 0.069 0.070 0.025 0.026 0.032 Variable
Average Rainfall at Gosford 150mm 735mm 189mm 174mm 445mm
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