3.0 RESULTS AND DISCUSSION 3.1 WATER MONITORING Raw water monitoring data are displayed in Table I. Table I: Water monitoring data for 4 sites on Shorewell Creek Because of the size of the Images the table has been broken up into two parts, Part a) consists of Site 1 & 2, and Part b) consists of Sites 3 & 4. Click to view the files Table Part 1 a) Table Part 1 b) 3.1.1 pH pH data is displayed in Fig. 7. The graph shows most results were either on or below the lower limit of 6.5 recommended by ANZECC (1992). This may, in part, be due to the local geology. High concentrations of hydrogen ions are released as basalt rock is weathered to clays and this may lower pH (Holmes, 1965). Lower values at Site 1 may be caused by the microbial decay of bank vegetation as the water level rises. The variation at Site 2 suggests that inputs from nearby stormwater outlets may be impacting on pH. Fig. 7: pH of 4 sites on Shorewell Creek. 3.1.2 Alkalinity Figs. 8a-d show that the alkalinity at all sites is generally lower than the 100 mg/L CaCO3 proposed by GLOBE Program (1997) as being the minimum for adequate buffering of pH changes in streamwater. Site 3 shows the greatest variation in alkalinity and this may be due to material leaching into the pipeline under the disused tip. Sites 1,3 and 4 registered a significant decrease in alkalinity on one occasion (14/9/98) with a corresponding decrease in pH. Although no explanation was found for the decreased alkalinity, this set of results clearly demonstrates the strong correlation between low alkalinity levels and a reduced buffering capacity in streamwater. Fig.8a: pH v.Alkalinity at SiteW1 on Shorewell Creek. Fig.8b: pH v.Alkalinity at SiteW2 on Shorewell Creek. Fig.8c: pH v.Alkalinity at SiteW3 on Shorewell Creek. Fig.8d: pH v.Alkalinity at SiteW4 on Shorewell Creek. 3.1.3 Temperature Water temperatures ranged from between 10.5°C and 15.0°C (see Fig. 9), with the upward trend probably the result of seasonal patterns. Higher temperatures recorded at site 1 can probably be attributed to the absence of overhanging vegetation and the reduced mixing in the the dam. Although there is quite a significant variation in temperature, both through time and space, studies of other Engaeus spp. by Suter and Richardson (1977) have shown that variations in stream temperature have a negligible effect on water temperature in burrows. However, it should be noted that fluctuating water temperature may alter the structure of aquatic macroinvertebrate communites which may affect the food source available to E. yabbimunna. Fig.9: Stream temperature at 4 sites on Shorewell Creek. 3.1.4 Turbidity Turbidity levels were observed in the field to be quite closely correlated with rainfall events. The fact that this is not shown in Fig. 10 can be explained by the size of the catchment. The level of water in the stream rose quite quickly following rain with a subsequent increase in turbidity to, in several cases higher levels than the 25 NTU recommended by Jolly, et. al. (1996). However, because of the small catchment area (» 5 km2) runoff soon ceased and was quickly followed by a corresponding decrease in turbidity. Fig.10: Turbidity v. Rainfall at 4 sites on Shorewell Creek. 3.1.5 Dissolved Oxygen Monitoring showed that DO was generally at acceptable concentrations, although one result was recorded from Site W1 which was lower than the 6 mg/L recommended by ANZECC (1992). A decrease in DO concentration at site W3 was also recorded at the same time. Fine weather and light winds in the period prior to sampling may have resulted in low water turbulence and increased microbial activity at these sites (Allaby, 1983; Lake & Marchant, 1990). This occurred during a period of fine weather and light winds and may have resulted from low diffusion rates in the dam water coupled with an increase bacterial activity. Relatively high DO concentrations at Site W3 may result from the rocky substrate increasing water turbulence along this section of stream. The DO remained high at Site W4 throughout the monitoring period. This can be attributed to the waterfall immediately upstream aerating the water. In additon, the rocky stream bottom at this site adds to stream turbulence, which helps to maintain relatively high DO concentrations. Fig.11: Dissolved Oxygen at 4 sites on Shorewell Creek. 3.1.6 Coliform Bacteria Coliform counts showed an increasing downstream trend (see Table I). The absence of cattle from the pasture surrounding Site W1 may have explained the fact that no coliforms were recorded at site W1. On the other hand, stock had access to the stream immediately upstream from Site W2 and this may be reflected in higher bacterial counts at this site. In addition, it is possible that urban stormwater runoff entering the stream at this site may have contained faeces from domestic animals such as dogs and cats, further contributing to the higher readings. The factors that may have been contributing to the presence of coliforms at Site W3 are not immediately clear. However, Shafron, et. al. (1990) point out that not all coliforms are the result of faecal contamination and that some are naturally found living in soil and on vegetation. It may therefore be that some coliforms were present in tip leachate. The relatively high numbers of coliforms recorded from Site W4 are probably the result of faecal contamination from the duck pond located about 1 km upstream from this site. 3.1.7 Macroinvertebrates Results of macroinvertebrate sampling are displayed in Table II and show an interesting change in macroinvertebrate community structure along the length of the stream. 3.1.7a Site W1 Site W1 showed quite a diverse macroinvertebrate community. Species which are sensitive to poor water quality such as stonefly (Insect Order: Plecoptera) and mayfly (Insect Order: Ephemoptera) nymphs co-existed with more tolerant species such as flatworms (Class: Turbellaria) and segmented worms (Class: Oligochaeta). All of these organisms were typical of what could be expected in a water reservoir where there is an absence of bankside vegetation (Williams, 1980). Water fleas (Class: Crustacea) were the most abundant species at Site W1. These small crustaceans typically occur in still or slow flowing streams (Williams, 1980) and the large numbers which were found here may have been due to seasonal influences. A water quality ranking of "fair-good" was obtained from the the Tolerance Ranking Index outlined in Appendix 1. This was probably a reasonable assessment of water quality when compared to the physicochemical parameters for this site. 3.1.7b Site W2 The aquatic macroinvertebrate community at this site reflected changes in water quality compared to Site W1. The species which were found here (e.g. Caddisfly larvae; Insect Order: Trichoptera and Oligochaete worms) are representative of those found in relatively turbid waters with increasing DO concentrations (Cranston, et. al, 1996). The loss of very sensitive species and the overall fewer number of species collected from this site may indicate an increased pollution load. This is supported by the poor-fair water quality rating assigned by the Tolerance Ranking Index. 3.1.7c Site W3 Although not obvious from the physicochemical parameters, a decline in water quallity at this site was indicated by a significant decline in species diversity and the domination of tolerant chironomid larvae. As a result, a water quality ranking of "poor" was assigned to the site. An interesting feature of the macroinvertebrate community here was the presence of freshwater crabs. 3.1.7d Site W4 Black fly larvae (Insect Order: Diptera) was the only species present at this site. The lack of species diversity is probably due in part to the artificial channel through which the water flows at this point. The water quality at this site was assessed as "fair" which corresponds to the physicochemical data. 3.2 Vegetation Mapping The results of the mapping program are shown in Fig. 12. Four distinct categories of vegetation were identified: mainly native species - composed of Blackwoods, Eucalypts and occasionaly Tea Tree, with an understory of Manferns. This association is probably similar to the original vegetaion in the area as described by de Gryse & Hepper. (1994). mainly introduced species - this association was composed mainly of Willows (Salix spp.) and Blackberries (Rubus spp.) with some Manferns, a few eucalypts and an assortment of weed species and garden ornamentals. grasses - this category contained a mixture of introduced grass species. marsh plants - this grouping was composed mainly of the introduced Cumbungi (Thypha spp.) together with other aquatic plants. As can be seen from Figs. 12a,12b, most of the vegetation along Shorewell Creek consists of introduced species. Some of this vegetation is quite badly degraded (see Fig. 13). There are only two locations where native species dominanted the vegetation. These areas were quite small and are both contained within Burnie City Council Reserves. Figures 12a, and 12b Figure 13 3.3 Burrow Mapping 3.3.1 Burrow Distributions As can be seen from Fig. 14, Engaeus spp. construct quite obvious mud chimneys as they excavate their burrows. Figure 14 The locations of all sites where mud chimneys were observed are shown in Fig. 12 and it is quite obvious from this data that Engaeus spp. have a disjunct distribution on Shorewell Creek. This must be considered a significant threat to the survival of burrowing crayfish in this area. Habitat assessments were performed at all sites where burrows were located (see Table III). A rating was obtained for each site based on the type and extent of vegetation present, the type of instream habitat present, evidence of pollution and other environmental trauma and land use activities near the site (as outlined in Appendix 2). Almost half of the sites rated as having only "poor" or "fair" habitat Litter and oil slicks were present at some sites (e.g. B7 and B9). Several of the sites with a "good" rating were vulnerable to degradation. For example, at Site B6 there was some evidence of vandalism. In addition, the presence of a large population of ducks probably posed a threat to crayfish populations in the area (as well as downstream water quality). Although Site 10 had a "good" habitat rating, cattle in the area had unrestricted access to the stream, which must threaten environmental integrity at this site. The one factor which was common to all sites where burrows were located was the presence of Manferns. Even where the habitat quality was quite poor and the vegetation consisted predominantly of introduced species, burrows could be located, provided there were also at least a few Manferns. 3.3.2 Trapping Program As mentioned previously both E. yabbimunna and E. fosser have been found on Shorewell Creek. The trapping program was unsuccessful in locating any specimens of E. yabbimunna. This was not unexpected as the species is known to be quite elusive (J. Nelson, pers. comm). Pellets inside the trap indicated that specimens entered the Norrocky traps on at least two occasions at Site B9. However, these pellets prevented the flap from closing and the animals returned to their burrows before the traps could be cleared. One specimen of E. fosser (identified by J. Nelson) was captured by excavating a burrow at Site B9. E. yabbimunna was located by Doran & Richards (1996) at our Sites B1,B3 B6 B9 and B10. It was suspected that the burrows at Site B5 were also constructed by E. yabbimunna (B. Mesibov, pers. comm.). The presence or absence of the species at the other 6 sites could not be determined from our study. However, it is intended that work continue with the "Norrocky" trap in the hope it may be eventually possible to identify Engaeus spp. on the basis of burrow morphology.