Gosford City Council Historical Water Quality Review & Analysis

RESULTS OF WATER QUALITY DATA ANALYSIS 3-11
3.1.2.4 Orthophosphate
Annual median orthophosphate concentrations for sites located in the Gosford waterways are
presented in Table 3.18, while quarterly mean concentrations for the last 15 months of monitoring are
presented in Table 3.19. Annual data suggests that there has been no distinguishable overall trend in
phosphate concentrations over the last 3 years of monitoring, with all concentrations generally quite
low (and probably limiting primary productivity in most circumstances).
The quarterly analysis shows appreciably higher phosphate concentrations following periods of
significant rainfall (and runoff), with elevated concentrations at all sites during the April to June 2002
quarter (when over 800mm of rain fell between February and April) and also the April to June 2001
quarter (when 770mm of rain fell between February and May). Inorganic phosphorus (or
orthophosphate) is a typical urban pollutant, generated by numerous anthropogenic activities
including domestic gardening (i.e. fertilising).
Table 3.18 Annual Medians for Orthophosphate
Orthophosphate (mg/L)
Site No. and Location 2001/ 2002 2000/ 2001 1999/ 2000
n=11 n=12 n=9 Trend
Site : 77 - Booker Bay 0.009 0.012 0.002
Site : 78 - Narara Creek Entrance 0.009 0.017 0.010
Site : 79 - Erina Creek Entrance 0.011 0.014 0.013
Site : 80 - Kincumber Creek Entrance 0.013 0.014 0.006
Site : 81 - Cockle Creek 0.010 0.015 0.005
Site : 82 - Woy Woy Creek 0.012 0.017 0.017
Site : 83 - Wamberal Lagoon 0.006 0.009 0.005
Site : 84 - Terrigal Lagoon 0.006 0.011 0.007
Site : 85 - Avoca Lagoon 0.006 0.010 0.005
Site : 86 - Cockrone Lagoon 0.005 0.010 0.004
Average Rainfall at Gosford 1248mm 1038mm 1228mm
Table 3.19 Quarterly Means for Orthophosphate
Orthophosphate (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 0.010 0.002 0.011 0.011 0.011 Variable
Site : 78 - Narara Creek Entrance 0.023 0.007 0.007 0.013 0.015 Rain dep.
Site : 79 - Erina Creek Entrance 0.030 0.009 0.009 0.011 0.021 Rain dep.
Site : 80 - Kincumber Creek Entrance 0.032 0.007 0.010 0.024 0.020 Rain dep.
Site : 81 - Cockle Creek 0.027 0.006 0.007 0.013 0.019 Rain dep.
Site : 82 - Woy Woy Creek 0.031 0.004 0.016 0.017 0.024 Rain dep.
Site : 83 - Wamberal Lagoon 0.015 0.002 0.006 0.004 0.012 Rain dep.
Site : 84 - Terrigal Lagoon 0.038 0.010 0.006 0.006 0.014 Rain dep.
Site : 85 - Avoca Lagoon 0.020 0.003 0.006 0.004 0.014 Rain dep.
Site : 86 - Cockrone Lagoon 0.018 0.004 0.005 0.004 0.010 Rain dep.
Average Rainfall at Gosford 150mm 735mm 189mm 174mm 445mm
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