Mann-Whitney Rank Sum, p<0.001). Wet season PO 4 in Zone 1 was significantly higher in the 
historical data set compared to recent, while in Zone 2 there was no difference between recent and 
historic PO 4 levels (Table 6.2; Mann-Whitney Rank Sum, p>0.05). 
There were no significant trends in NO3 + NCf within Zones 1 or 2 during either season 
(Figures 6.1 and 6.2; determined using the Seasonal Kendall and Mann Kendall tests). In Zone 1, there 
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was a significant increasing trend in PO4 during the dry season (Figure 6.3a) and a significant 
decreasing trend in PO 4 during the wet season (Figure 6.4a), while in Zone 2 there were not 
significant trends during either the wet or dry season (Figures 6.3b and 6.4b). Due to the opposing 
seasonal trends in Zone 1, there was not a significant trend in PO4 using the Seasonal Kendall test. 
Caution needs to be used in interpreting the trends and the differences in historic and recent 
3 - . 
median NO 3 + NO 2 and PO 4 levels (Tables 6 .1 and 6.2) due to differences in sampling frequencies. 
There are considerably more recent data (more stations and higher sampling frequency) than historic 
data, particularly in Zone 1 during the dry season (Table 6.1 and Table 6.2). Nutrient (NO 3 + NO 2 and 
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PO4 ) inputs associated with oceanic sources are highly variable depending upon the wind forcing and 
respond rapidly to changes in wind forcing. In addition, there is considerable interannual variability in 
oceanic input to estuaries (Brown and Ozretich, in review) associated with variability in upwelling 
(Corwith and Wheeler, 2002; Wheeler et al., 2003). During the dry season, the recent nutrient data 
3 - 
(NO3 + NO2 and PO4 ) are consistently higher than the historic data in Zone 1 (Tables 6 .1 and 6.2), 
possibly reflecting either differences in ocean conditions or better characterization of ocean input due 
to increased sampling frequency in recent data. In contrast, the historic nutrient (NO3 + NO2 and 
3 - 
PO4 ) median levels are higher than recent data in Zone 2 (Tables 6.1 and 6.2). Since the pattern in 
Zone 2 is opposite to that in Zone 1, this suggests that differences in ocean input are not driving this 
difference in Zone 2. Caution is needed in interpreting these differences since the trend analysis 
3 - 
revealed that there were no significant trends in nutrients (NO3 + NO2 and PO4 ) in Zone 2. The 
differences in water column nutrients during the last 30-40 years, although some are statistically 
significant, do not indicate a major change in nutrient loading (as inferred by nutrient concentrations) 
as experienced in other estuarine and coastal systems (e.g., Cloem 2001; Soetaert et al., 2006). 
44 
