All results are indicated as surface and bottom means for each site within the Peel Inlet and the Harvey Estuary. The results are separated into sections for each measured parameter, physical followed by chemical. For the purposes of clarity, the terms "pre Channel years" and "post Channel years" have been used throughout this section. These terms refer only to the years documented in Table 1.
The mean water temperature of both surface and bottom waters was higher in post Channel years at all sites during winter, spring and summer (Figure 2). However, this was only significant in a small number of cases: at the two sites closest to the Channel (2 and 58) during winter; at sites 4 and 7 in the Peel Inlet during spring and summer and sites 31 and 1 in the Harvey Estuary during spring. The greatest difference between mean values was at site 2 during winter with a 1.75 oC difference between pre and post Channel data sets.
Mean salinity values were higher in surface and bottom waters post Channel at all sites during winter, spring and summer (Figure 3). During spring and summer, salinity in surface and bottom waters was significantly higher in post Channel years at all sites. During winter, however, the site closest to the Serpentine and Murray River inflows (site 4) had statistically similar salinities in pre and post Channel years in both surface and bottom water. This was also the case for the site closest to the Harvey River (site 31) and site 7 in winter surface waters.
There was a gradient of increasing mean salinity from sites closer to river flows (4 and 31) to sites adjacent to the Channel (sites 2 and 58) in winter and spring of post Channel years. This trend was reversed in summer months, where mean salinity of sites 2 and 58 after the opening of the Dawesville Channel, was lower than that of sites furthest from ocean influence. The mean salinity of sites 4 and 31 during winter was 40 ‰ during summer with a maximum of 49 ‰ recorded in the bottom water of site 4 during February 1998. Salinities of < 3 ‰ were recorded in the surface waters of these two sites during winter on a number of occasions and as low as 5 ‰ at sites close to the Dawesville Channel (Appendix 1). The maximum salinity recorded in the pre Channel years was 47 ‰ in the bottom water of site 1 during March 1988 (Appendix 1) with < 3 ‰ recorded at all sites on a number of occasions during winter.
There was no clear pattern of dissolved oxygen concentrations in pre and post Channel years (Figure 4). During winter, mean dissolved oxygen concentrations were higher in post Channel years. However, this was only statistically significant at site 4 (surface and bottom), site 31 (surface) and sites 7 and 58 (bottom).
During spring, post Channel mean dissolved oxygen concentrations were lower than pre Channel years in the surface water; significantly so at site 7 in the Peel Inlet and all sites in the Harvey Estuary. However, in the bottom waters, mean dissolved oxygen concentrations in post Channel years were higher at all sites except site 31. This was significant at site 4 in the Peel and site 1 in the Harvey.
During the summer months the surface dissolved oxygen concentrations at site 7 were significantly lower during post Channel years. In the bottom water, however, post Channel dissolved oxygen concentrations were significantly higher than pre Channel years at site 2 in the Peel Inlet and all sites in the Harvey Estuary.
There has also been a change in the occurrence of dissolved oxygen stratification, since the opening of the Dawesville Channel. Comparisons between the pre and post Channel years were difficult, due to the varied frequency in sampling. Therefore, occurrence of oxygen stratification was assessed, based on the percentage of sampling occasions in which there was a difference between surface and bottom oxygen concentrations of 1 mg L-1 and bottom dissolved oxygen concentrations of < 5 mg L-1 were recorded.
The occurrence of oxygen stratification was lower in post Channel years at all sites in winter, spring and summer, with the exception of site 1 during winter (Figure 5). The difference between pre and post Channel years was more marked at sites 2 and 58 (adjacent to the Channel) than at sites 4 and 31 which are closer to river inflows. The greatest change was during summer, when the highest occurrence of oxygen stratification was recorded in pre Channel years (site 58) and there were no incidences recorded in the post Channel data set.
Mean pH values differed slightly between pre and post Channel years, with mean
values between 7.9 and 8.6 before the Dawesville Channel opened, and between
7.9 and 8.4 after (Figure 6). During winter, mean pH
values of surface and bottom water were predominantly higher in post Channel
years, significantly so at site 7 in the Peel Inlet and 58 in the Harvey Estuary.
During spring and summer this trend was reversed, with mean post Channel values
lower than those of pre Channel years. This was significant at site 31 in the
Harvey for surface and bottom water during both seasons, and for the remaining
Harvey sites (1 and 58) in the surface water during spring.
The variability in pH was markedly different between pre and post Channel years.
Prior to the opening of Dawesville Channel, pH values ranged from 2.9 in the
bottom water at site 2 (2nd August, 1988) to 11.5 in the surface
water of the same site (5th November, 1988). There were a number
of pH values recorded in pre Channel years that were < 5 in bottom waters
and > 10 at the surface (Appendix 1). The range
for post Channel years was 7.1 in the surface water of site 4 (12th
of July, 1994) to 8.9 in the surface water of site 1 (15th November,
1996). The majority of post Channel pH values recorded were in the range of
7.9 to 8.3 (Appendix 1).
Light is shown as an attenuation coefficient, the highest value indicating maximum reduction of incident light as it passes through the water column. The highest attenuations correspond to periods of reduced light penetration when there are either high chlorophyll a concentrations, high river flow or increased wind induced mixing.
Mean light attenuation was predominantly lower during post Channel years, with the exception of site 4 during winter and summer (Figure 7). Light attenuation was significantly lower during post Channel years at sites 2 and 58 during winter, all sites during spring (with the exception of site 4) and sites 1 and 58 during summer.
Light attenuation was more variable prior to the opening of the Dawesville Channel, with attenuation coefficients ranging from 0.1 m-1 on a number of occasions, to 9.11 m-1 at site 1 (3rd December, 1985) and site 58 (26th November, 1985). Attenuation coefficients of 2 m-1 were often recorded in pre Channel years (Appendix 1). The range of attenuation coefficients recorded in post Channel years was 0.1 m-1 on a number of occasions to 3.97 m-1 at site 1 (2nd August, 1996).