We implemented a monitoring program developed by Crawford and White (2006), which was designed to assess the current condition of six key estuaries in NW Tasmania: Port Sorell, the Leven, Inglis, Black, Montagu and Arthur River estuaries. This study considered a range of water quality and ecological indictors commonly used to monitor estuaries. These included: salinity, temperature, dissolved oxygen, turbidity, pH, nutrients (nitrate + nitrite, dissolved reactive phosphorus and ammonia), silica molybdate reactive and chlorophyll a for the water column; chlorophyll a and macroinvertebrate community structure amongst the sediments. The data represented by this record was collected in Arthur River.
Maintenance and Update Frequency: notPlanned
Statement: This site was sampled on a bimonthly basis.
Sampling was conducted from a small boat or by wading if sites became inaccessible by boat. All sampling was conducted at low tide when estuaries are influenced to a greater extent by freshwater flows (Hirst et al., 2005).
Physico-chemical parameters measured at each site at low tide were:
· Temperature (ºC),
· Dissolved oxygen (% saturation),
· Turbidity (NTU),
· Dissolved nutrients – ammonia, nitrate + nitrite (NOx), reactive phosphorus(mg/L),
· Silica (mg/L),
Ecological parameters monitored were:
· Water column chlorophyll a and benthic chlorophyll a and
· Macroinvertebrates (sampled once only during autumn and spring).
Results obtained for benthic chlorophyll a were not presented in the report but will be made publicly available in a subsequent report.
Water quality measurements were taken mid channel. Salinity, temperature and dissolved oxygen were measured from the surface to the bottom at 1 m intervals. Where the bottom did not fall exactly on a 1 m interval the true depth was recorded. During the course of the study, salinity and temperature were recorded with a WTW
LF196 and WTW Cond 315i instruments. Dissolved oxygen was measured with a TPS WP-82Y meter. Salinity and dissolved oxygen were not recorded on occasions due to equipment failure.
Turbidity, pH, nutrients and water column chlorophyll a measurements were all sampled in surface waters (<30cm). Three turbidity readings were taken at each site using a HACH 2100P Turbidimeter and averaged. The pH meter (Hanna HI 98127) was recalibrated every month prior to field sampling. Nutrients were sampled using standard protocols set by Analytical Services Tasmania (AST) and Eriksen (2006) and
analysed by AST.
In the field, water column chlorophyll a samples were collected using a 1 L plastic container covered with alfoil to reduce photo-degradation and stored in an esky containing ice packs. Samples were filtered through Whatman GF/F 45mm diameter filter paper within a day of collection and immediately frozen.
Benthic chlorophyll a samples were collected using a 35mL syringe with the end removed and marked 3cm from the end point. At each site three mud samples were collected at the low tide mark (0m), each containing approximately 3cm of sediment.
After completing a field sampling day all benthic chlorophyll a samples were immediately frozen.
To determine the diversity and abundance of estuarine invertebrate fauna in the sediments, macroinvertebrate samples were collected at each site within each estuary during autumn and spring of 2007. All sampling was undertaken at low tide using similar methods to Hirst et al. (2005). At each site five sediment cores (diameter = 150mm, depth = 100mm) were taken along a line at 0.0, 0.1, 0.2, 0.3, and 0.5m depths. The core samples were sieved through a 1mm sieve in the field and the remaining contents were fixed in 10% formalin. In the laboratory macroinvertebrates were identified to species level where possible and counted.
Water column chlorophyll a
Chlorophyll a analyses were conducted using standard techniques at the Tasmanian Aquaculture and Fisheries Institute. The concentration of chlorophyll a was calculated using the equation
Total Chlorophyll a = 11.0(Abs665-Abs750) v/Vp
where V is the volume filtered (L), v is the volume of acetone (mL) and p is the path length (cm). The amount of phaeophytin, a natural degradation product of chlorophyll a was also calculated and found to be negligible. Therefore results for chlorophyll a are presented without a correction for phaeophytin.
Natural Resource Management (NRM) Cradle Coast
Given the economic, social and environmental importance of estuaries in NW Tasmania there is a need for baseline and ongoing assessment of estuarine condition.