Water Quality Monitoring Results for Port Arthur Area by EPA Tasmania October 2020 to March 2021 - July 2021
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Water Quality Monitoring
Results for Port Arthur
Area by EPA Tasmania
October 2020 to March
2021
July 2021
Department of Primary Industries,
P a r k s , Wa t e r a n d E n v i r o n m e n t
Publishing Information Citation: EPA Tasmania (2021) Water Quality monitoring results for Port Arthur area by EPA (Tasmania) October 2020 to March 2021, EPA Tasmania, Hobart, Tasmania. Date: July 2021 Enquiries: EPA Tasmania Department of Primary Industries, Parks, Water and Environment GPO Box 1550 Hobart, Tasmania 7001 Telephone: (03) 6165 4599 Email: Enquiries@epa.tas.gov.au Web: www.epa.tas.gov.au Copyright: © The Crown in the Right of Tasmania Disclaimer: The information provided in this document is provided in good faith. The Crown, its officers, employees and agents do not accept liability however arising, including liability for negligence, for any loss resulting from the use of or reliance upon the information in this document and/or reliance on its availability at any time.
Table of Contents
Water Quality Monitoring Program.................................................................................................................. 4
Introduction......................................................................................................................................................................... 4
Aims....................................................................................................................................................................................... 4
Description .......................................................................................................................................................................... 4
Default Guideline Values (DGVs).............................................................................................................................. 4
Monitoring sites ............................................................................................................................................................. 4
Key Parameters/Indicators of Interest ..................................................................................................................... 7
Results................................................................................................................................................................................... 9
Water Quality ................................................................................................................................................................ 9
Temperature ............................................................................................................................................................. 9
Dissolved Oxygen .................................................................................................................................................. 10
Salinity ....................................................................................................................................................................... 12
pH .............................................................................................................................................................................. 13
TAN (Total Ammoniacal Nitrogen) .................................................................................................................. 14
NOx (Nitrate and Nitrite)................................................................................................................................... 16
Nitrogen (total) ...................................................................................................................................................... 17
Phosphorus (total) ................................................................................................................................................. 18
DRP (Dissolved Reactive Phosphorus) ............................................................................................................. 19
Chlorophyll a........................................................................................................................................................... 20
Epiphytic Algal growth ............................................................................................................................................... 20
Discussion .......................................................................................................................................................................... 22
Water Quality .............................................................................................................................................................. 22
Temperature ........................................................................................................................................................... 22
Dissolved Oxygen .................................................................................................................................................. 22
Salinity ....................................................................................................................................................................... 23
pH .............................................................................................................................................................................. 23
TAN (Total Ammoniacal Nitrogen) .................................................................................................................. 23
NOx (Nitrate and Nitrite)................................................................................................................................... 24
Nitrogen (total) ...................................................................................................................................................... 24
Phosphorus (total) ................................................................................................................................................. 25
DRP (Dissolved Reactive Phosphorus) ............................................................................................................. 25
Epiphytic Algal growth ............................................................................................................................................... 26
Conclusion ......................................................................................................................................................................... 26
Appendix 1......................................................................................................................................................................... 27
Surface Water Nitrogen Compounds.................................................................................................................... 27
Bottom Water Nitrogen Compounds ................................................................................................................... 29
EPA Tasmania, July 2021 3
Water Quality Monitoring Program Introduction The Water Section of EPA Tasmania conducted water quality monitoring in the Port Arthur area from October 2020 to March 2021 to increase the understanding of water quality across the area and in particular within Long Bay. Aims • To provide water quality information to increase the understanding of water quality in the Port Arthur area and in particular Long Bay; • To collect data on key indicators for comparison against Default Guideline Values (DGVs) for aquatic ecosystems developed for the Port Arthur area; • To investigate if any departures from background conditions (DGVs) are attributable to anthropogenic or natural sources and if possible show attribution. • To provide a summer snapshot for the extent of epiphytic growth on seagrass habitat. Description The Port Arthur area is a large embayment on the Tasman Peninsula which opens directly to the Tasman Sea at its southern extent. Default Guideline Values (DGVs) Default Guideline Values (DGVs) for aquatic ecosystems have been developed for the Port Arthur area. The DGVs have been derived from site specific information in accordance with the National Water Quality Management Strategy (NWQMS). The DGVs are based on data collected from August 2013 to July 2017 from four locations (PA1, PA2, PA3 and PA4). The available data has allowed for the derivation of annual and seasonal DGVs of surface, 5 metre depth, integrated depth and bottom waters for key indicators. For dissolved oxygen, temperature and pH the 20th percentile represents the lower DGV and the 80th percentile the upper DGV, whilst for all other indicators the 80th percentile of the aforementioned data represents the DGV. When a value reported by the laboratory is below the Limit of Reporting (LoR), the reported value has been halved prior to inclusion in the dataset for DGV derivation. Information on all indicators (particularly nutrients) is not available at all depths due to being beyond the scope of the initial program requirements. The Port Arthur area DGVs provide a level of refinement over the interim Default guideline values for Coastal and Marine waters based on the IMCRA bioregion. Monitoring sites Water quality data have been collected from nine (9) sites across the Port Arthur area, which include four (4) sites monitored on a monthly basis as part of the environmental licence conditions for lease MF55 (Long Bay Port Arthur). The proximity of site PA1 to the Long Bay lease should be taken into account when interpreting monitoring results. Due to the site being adjacent to the lease and within 60 metres of stocked cages the location is unlikely to represent ambient conditions. The site is however valuable in the interpretation of ‘near field’ effects. Epiphytic growth data have been collected from seven (7) sites across the Port Arthur area. The data represents a snapshot for February 2021 at these locations. An overview of the monitoring locations is provided in Table 1 and distribution across the Port Arthur area in Map 1. EPA Tasmania, July 2021 4
Table 1: Port Arthur monitoring locations
Site ID Location Easting Northing Monitoring Distance from Lease Comment
boundary
EPA-PA1 North of Garden Point 570485 5224084 Nutrient, phytoplankton, physico-chem. ~ 20 m (near scale) Co-located with BEMP-PA1
EPA-PA2 East of Fryingpan Point 570287 5222948 Nutrient, phytoplankton, physico-chem. ~ 1.0 km (intermediate) Co-located with BEMP-PA2
EPA-PA3 South East of Suicide Point 571217 5221408 Nutrient, phytoplankton, physico-chem. ~ 2.5 km (intermediate) Co-located with BEMP-PA3
EPA-PA4 East of Dog Bark 571352 5218242 Nutrient, phytoplankton, physico-chem. ~ 5.6 km (Far field) Co-located with BEMP-PA4
EPA-PA5 Long Bay 300m off Garden Point 569987 5224610 Nutrient, phytoplankton, physico-chem. ~ 300 m (near scale)
Boat Ramp
EPA-PA6 Long Bay west of shellfish lease 569865 5225420 Nutrient, phytoplankton, physico-chem. ~ 800 m (intermediate)
EPA-PA7 Long Bay north east of shellfish lease 570240 5225825 Nutrient, phytoplankton, physico-chem. ~ 1.1 km (intermediate)
EPA-PA8 Stingaree Bay 569655 5224900 Nutrient, phytoplankton, physico-chem. ~ 600 m (intermediate)
EPA-PA9 Carnarvon Bay 569885 5221210 Nutrient, phytoplankton, physico-chem. ~ 2.8 km (intermediate)
SG_PA17 Stingaree Bay 569640 5224888 Epiphyte cover Co-located with IMAS_SG_PA17
SG_PA16 Stingaree Bay 569328 5225068 Epiphyte cover Co-located with IMAS_SG_PA16
SG_PA9 Long Bay 570128 5225741 Epiphyte cover Co-located with IMAS_SG_PA9
SG_PA4 Long Bay 570274 5226192 Epiphyte cover Co-located with IMAS_SG_PA4
SG_PA28 Stewarts Bay 569739 5223742 Epiphyte cover Co-located with IMAS_SG_PA28
SG_PA29 Stewarts Bay 569591 5223580 Epiphyte cover Co-located with IMAS_SG_PA29
SG_PA30 Stewarts Bay 569669 5223188 Epiphyte cover Co-located with IMAS_SG_PA30
EPA Tasmania, July 2021 5
Map 1: Port Arthur monitoring locations EPA Tasmania, July 2021 6
Key Parameters/Indicators of Interest
The following table outlines the key water quality indicators of interest and the type of measurement from
which the reported value is derived. The DGVs of surface and bottom waters are provided for the full year
and summer period. For those indicators with a DGV range, the most relevant value from an
environmental perspective is discussed. For temperature the upper value is reported against and for
dissolved oxygen and pH the lower limit.
Table 2: Indicators of interest, measurement type and associated DGVs
Indicator Measurement type Summer Annual Summer Annual
surface surface Bottom Bottom
Nitrogen (Total) (mg/L) Laboratory analysis (AST) 0.30 0.32 0.30 0.32
Nitrogen, Total Kjeldahl (mg/L) Laboratory analysis (AST) Nil Nil Nil Nil
TAN (NH3 and NH4+) (mg/L) Laboratory analysis (AST) 0.008 0.007 0.013 0.010
Nitrate (mg/L) Laboratory analysis (AST) 0.001 0.025 0.009 0.027
Nitrite (mg/L) Laboratory analysis (AST) Nil Nil Nil Nil
Nitrate and Nitrite (mg/L) Laboratory analysis (AST) 0.001 0.024 0.005 0.033
Phosphorus (Total) (mg/L) Laboratory analysis (AST) 0.03 0.03 0.04 0.04
Dissolve Reactive Phosphorus (mg/L) Laboratory analysis (AST) 0.006 0.008 0.008 0.009
Silica, Molybdate Reactive (mg/L) Laboratory analysis (AST) 0.1 0.2 0.1 0.2
NPOC (dissolved) (mg/L) Laboratory analysis (AST) Nil Nil Nil Nil
Chlorophyll a (µg/L) Laboratory analysis (AST) 1.0 1.5 Nil Nil
Temperature (oC) Calibrated Field Instrument 14.8 - 17.6 12.3 - 16.9 14.0 - 16.4 12.0 -16.0
Salinity (PPT) Calibrated Field Instrument 35.4 35.6 35.4 35.6
Dissolved Oxygen (mg/L) Calibrated Field Instrument 8.0 – 8.8 7.9 – 8.8 8.0 – 8.7 7.7 – 8.7
Dissolved Oxygen (% saturation) Calibrated Field Instrument 103.4 – 98.6 – 97.6 – 96.1 –
108.0 106.5 105.9 101.4
pH Calibrated Field Instrument 8.1 – 8.3 8.1 – 8.2 8.2 - 8.3 8.1 - 8.2
SpCond (µS/cm) Calibrated Field Instrument Nil Nil Nil Nil
Turbidity (NTU) Calibrated Field Instrument Nil Nil Nil Nil
Epiphyte Score Drop Camera Nil Nil Nil Nil
Integrated samples are also taken for the identification and enumeration of phytoplankton by AST.
EPA Tasmania, July 2021 7Epiphytic growth
The EPA committed to undertake strategic monitoring of the volume and extent of epiphytic algae growth
on shallow reef and seagrass habitats across the south east of Tasmania. The monitoring aims to improve
the understanding of fluxes in epiphytic algal growth in response to natural coastal processes as well as
anthropogenic interactions, in particular salmon farming activities. A key outcome of the monitoring is the
provision of a snapshot of broadscale epiphytic algal growth dynamics across the south east of Tasmania.
The following table outlines the qualitative categories for assessing epiphytic growth on shallow reef and
seagrass habitats.
Table 3: Description of scoring system used to assess epiphytic growth
Score Description
0 No epiphytic growth present.
1 Very low epiphytic growth, virtually clean plant.
2 Low, minimal epiphytic growth.
3 Medium, obvious epiphytic growth.
4 High, most of plant covered.
5 Very high, plant completely covered.
For the Port Arthur area epiphytic algal growth surveys were undertaken at seven (7) locations as outlined
in Table 1. The data was collected on 25 February 2021 and as such the survey represents a snapshot for
February 2021 at these locations.
Images were captured using a GoPro camera mounted on a quadrat and frame (drop camera). The quadrat
being 0.5mx0.5m in size and fully captured within the field of view of the camera. The quadrat is further
divided into 0.1m2 sections. At each location the camera was set at the surface to record images at
10 second intervals. Location information was recorded via the GoPro camera which is GPS enabled.
Additional GPS information was recorded on the vessel via Garmin GPS.
For each location, 5 or 6 camera drops were conducted. For each camera drop a suitable image was
selected for analysis. The selected images were scored against the qualitative categories outlined in Table 3.
A total score for the location was derived on the basis of the average value for the images analysed at the
location.
ArcGis Pro mapping software was used to spatially display the epiphytic score information.
EPA Tasmania, July 2021 8Results Water Quality Graphical representation of data for key water quality indicators against surface and bottom water annual and summer DGVs. Temperature Figure 1: Water temperature at surface and associated DGVS Figure 2: Water temperature at bottom and associated DGVS EPA Tasmania, July 2021 9
Dissolved Oxygen Figure 3: Dissolved oxygen (mg/L) levels at surface and associated DGVS Figure 4: Dissolved oxygen (mg/L) levels at bottom and associated DGVS EPA Tasmania, July 2021 10
Figure 5: Dissolved oxygen (%Sat) levels at surface and associated DGVS Figure 6: Dissolved oxygen (%Sat) levels at bottom and associated DGVS EPA Tasmania, July 2021 11
Salinity Figure 7: Salinity levels at surface and associated DGVS Figure 8: Salinity levels at bottom and associated DGVS EPA Tasmania, July 2021 12
pH Figure 9: pH levels at surface and associated DGVS Figure 10: pH levels at bottom and associated DGVS EPA Tasmania, July 2021 13
TAN (Total Ammoniacal Nitrogen) Figure 11: TAN concentrations at surface and associated DGVS Figure 12: TAN concentrations at bottom and associated DGVS EPA Tasmania, July 2021 14
NO3 (Nitrate) Figure 13: NO3 concentrations at surface and associated DGVS Figure 14: NO3 concentrations at bottom and associated DGVS EPA Tasmania, July 2021 15
NOx (Nitrate and Nitrite) Figure 15: NOx concentrations at surface and associated DGVS Figure 16: NOx concentrations at bottom and associated DGVS EPA Tasmania, July 2021 16
Nitrogen (total) Figure 17: Nitrogen (total) concentrations at surface and associated DGVS Figure 18: Nitrogen (total) concentrations at bottom and associated DGVS EPA Tasmania, July 2021 17
Phosphorus (total) Figure 19: Phosphorus (total) concentrations at surface and associated DGVS Figure 20: Phosphorus (total) concentrations at bottom and associated DGVS EPA Tasmania, July 2021 18
DRP (Dissolved Reactive Phosphorus) Figure 21: DRP concentrations at surface and associated DGVS Figure 22: DRP concentrations at bottom and associated DGVS EPA Tasmania, July 2021 19
Chlorophyll a Figure 23: Chlorophyll levels from integrated sample and associated DGVS Epiphytic Algal growth Tabulated and spatial representation of survey location epiphytic algal growth scores. Table 4: Average epiphytic algal growth score by survey location Location Score Description SG_PA17 2.20 Low, minimal epiphytic growth. SG_PA16 3.00 Medium, obvious epiphytic growth. SG_PA9 2.83 Low, minimal epiphytic growth. SG_PA4 2.17 Low, minimal epiphytic growth. SG_PA28 3.83 Medium, obvious epiphytic growth. SG_PA29 2.00 Low, minimal epiphytic growth. SG_PA30 3.40 Medium, obvious epiphytic growth. EPA Tasmania, July 2021 20
Map 2: spatial representation of epiphytic algal growth scores EPA Tasmania, July 2021 21
Discussion In this section the results for summer 2021 water quality data will be discussed in relation to the summer and annual Default Guideline Values (DGVs) for aquatic ecosystems for surface and bottom waters. It should be noted that the DGVs are based on data collected from August 2013 to July 2017 from four locations (PA1, PA2, PA3 and PA4). The resultant figures have been applied to the entire Port Arthur area. A degree of caution is required in interpreting the findings for sites in the upper reaches of Long Bay against the DGVs. However, in the absence of site specific data, the application of regional DGVs is the acceptable approach. It should also be noted that the summer DGVs are based on the data from December to February (inclusive). The results for epiphytic growth will be discussed in relation to the qualitative categories described in Table 3 and broader findings for epiphytic growth on seagrass across the South East of Tasmania. Water Quality Temperature The pattern observed for water temperature is as expected during summer where increased solar radiation increases surface water temperatures, particularly in shallow regions of waterways. The East Australian Current (EAC) transports warm water down the eastern seaboard during summer and this can also result in elevated water temperatures around Tasmania. For October and November all surface water temperature readings were below the annual and summer period DGVs. For January the surface water temperature for EPA-PA3 and EPA-PA4 were below the annual DGV whilst all other sites were equal to or greater than the annual DGV. For January all sites were above the annual DGV and only EPA-PA6 reached the summer DGV level (17.6 oC), whilst for February all sites except EPA-PA4 exceeded the summer DGV for surface waters. For March all sites were equal to or above the annual DGV and EPA-PA9 was the only site to equal the summer DGV for surface waters. This range is comparable to that of the baseline period, being 10.09 oC to 20.91 oC. For October and November all bottom water temperature readings were below the annual and summer period DGVs. For January the bottom water temperature reading exceeded the annual DGV for all sites and the shallow sites within Long Bay (EPA-PA5 to EPA-PA8) also exceeded the summer DGV. For January the shallow site within Carnarvon Bay (EPA-PA9) was equal to the summer DGV. For February all bottom water temperature readings exceeded the annual and summer period DGVs. For March all bottom water temperature readings exceeded the annual DGV and all readings were equal to (EPA-PA4) or exceeded (all other sites) the summer period DGVs. The elevated bottom water temperatures during February and March coincide with a southern extension of the EAC which extended around southern Tasmania (IMOS Ocean current). This range is comparable to that of the baseline period, being 9.44 oC to 19.15 oC. Dissolved Oxygen Given that the annual and summer DGVS for surface waters of Port Arthur for dissolved oxygen are 7.9 mg/L and 8.0 mg/L, respectively, the results will be compared to the more conservative summer DGV. For October and November all surface water dissolved oxygen readings were above the summer DGV. For January the surface water dissolved oxygen readings for EPA-PA3, EPA-PA4 and EPA-PA9 were above the summer DGV, whilst all other sites were below. For February and March, the surface water dissolved oxygen readings were below the summer DGV for all sites. With the lowest values being within Long Bay. This is not unexpected given that as water temperature increases the carrying capacity for oxygen decreases. This range is comparable to that of the baseline period, being 7.2 mg/L to 9.6 mg/L. As with the surface waters, bottom water dissolved oxygen levels shall be compared to the more conservative summer DGV. For October all bottom water dissolved oxygen readings were above the summer DGV. For November only EPA-PA5 had a bottom water dissolved oxygen reading that was below the summer DGV. For January, February and March all dissolved oxygen reading were equal to or below the summer DGV. The lowest dissolved oxygen reading was 5.0 mg/L for site EPA-PA7 in March. This is a likely indicator of localised oxygen demand resulting from the combined influence of in-situ factors (such as senescence of algae) and external factors (such as runoff from the surrounding catchment). This range is comparable to that of the baseline period, being 7.0 mg/L to 9.7 mg/L. EPA Tasmania, July 2021 22
Salinity The pattern observed for salinity indicates that the water column at all sites is dominated by water of marine origin. The values recorded were below that of the annual and summer DGVs for surface and bottom waters on all occasions. pH The pattern observed for pH indicates that the water column at all sites is dominated by water of marine origin. Of note is that the value for EPA-PA7 is markedly lower in March than the other locations. The low value in the upper section of Long Bay may indicate catchment-based inputs. This range is comparable to that of the baseline period, being 7.3 to 8.4. TAN (Total Ammoniacal Nitrogen) For the monitoring period (October 2020 to March 2021) the majority (23 of 45 readings) of surface water TAN (Total Ammoniacal Nitrogen) readings were either at or below the Limit of Reporting (LoR), being 0.005 mg/L. Of the remaining records eight were above the summer and annual DGVs, of which four were associated with EPA-PA1. This reflects the close proximity of the site to the finfish lease. On these occasions, TAN accounted for between 4.1 % to 14.6 % of total nitrogen. In January, TAN was lower than the annual and summer DGVs and represented 1.9 % of total nitrogen. One observation above the annual and summer DGVs was evident for EPA-PA3 during October. TAN represented 4.8 % of total nitrogen for the site on this occasion. The remaining observation above the annual and summer DGVs occurred during March at sites EPA-PA5 (0.009 mg/L), EPA-PA6 (0.016 mg/L), and EPA-PA7 (0.018 mg/L). These observations indicated that TAN accounted for 3.5 %, 5.9 % and, 6.2 % of total nitrogen, respectively. This range is comparable to that of the baseline period, being 0.001 mg/L to 0.031 mg/L. Interestingly, the TAN values increased the further toward the upper section of Long Bay. The elevated readings in the upper section of Long Bay may indicate catchment-based inputs. For the monitoring period (October 2020 to March 2021) around one third (14 of 45 readings) of bottom water TAN (Total Ammoniacal Nitrogen) readings were either at or below the Limit of Reporting (LoR), being 0.005 mg/L. Of the remaining readings, eleven were above the annual DGVs of 0.010 mg/L, and six of these were above the summer DGV of 0.013 mg/L. During October, TAN levels for EPA-PA3 and EPA- PA4, were 0.018 mg/L and 0.015 mg/L, respectively. This indicates the intrusion of marine water masses from outside of Port Arthur, though this accounted for less than 2.5% of total nitrogen at the sites. During January the TAN level for EPA-PA5 was 0.031 mg/L, which is the highest recorded for the period or for the baseline period (0.0025 mg/L to 0.028 mg/L). This accounted for 9.1 % of total nitrogen at the site. The remaining readings above the annual and summer DGVs occurred during March 2021 at sites EPA-PA5 (0.017 mg/L), EPA-PA6 (0.016 mg/L), and EPA-PA7 (0.017 mg/L). TAN accounted for 6.5 %, 5.7 % and 5.0 % of total nitrogen, respectively for these sites. This pattern indicates the ingress of bottom waters into Long Bay, as is typical in tidal systems. NO3 (Nitrate) For the monitoring period (October 2020 to March 2021) all surface water NO3 (nitrate) readings were either at or below the Limit of Reporting (LoR), being 0.002 mg/L. This is consistent with the summer period values used in deriving the DGVs where only a single value was above the LoR from August 2013 to July 2017. For the monitoring period (October 2020 to March 2021) all bottom water NO3 (nitrate) readings were either at or below the Limit of Reporting (LoR) for sites EPA-PA1, EPA-PA6, EPA-PA7, EPA-PA8 and EPA- PA9. EPA-PA5 was below the LoR for all months except March when a value of 0.003 mg/L was recorded. These findings indicate that for shallow sites, the NO3 levels were consistently low throughout the water column for the monitoring period. For October, of the deeper sites (EPA-PA2, EPA-PA3 and EPA-PA4) only EPA-PA4 exceeded the summer DGV for bottom waters. EPA-PA4 also exceeded the annual DGV for bottom waters. For November EPA-PA2 was below the summer and annual DGVs whilst, EPA-PA3 and EPA Tasmania, July 2021 23
EPA-PA4 exceed the summer DGV but were below the annual DGV for bottom waters. For January EPA- PA2, EPA-PA3 and EPA-PA4 were below the LoR value for bottom waters. For February EPA-PA2 and EPA-PA3 were below the LoR value and EPA-PA4 at 0.003 mg/L which is below the summer DGV. For March EPA-PA2 and EPA-PA3 are greater than the summer DGV and below the Annual DGV for bottom waters. EPA-PA4 exceeded the summer and annual DGVs for bottom waters. The maximum value recorded for NO3 during the base line period for bottom waters was 0.061 mg/L. The pattern observed in nitrate values for bottom waters at the deep water sites reflects the intrusion of marine water masses from outside of Port Arthur. The nature of the marine water is strongly influenced by eddies of the EAC, intrusion of the Zeehan current from the west and currents within the Southern Ocean and Tasman Sea. The Zeehan current is a dominant current during winter and extends down the west coast of Tasmania and then past the south east in an easterly direction. Much like the EAC which is a dominant current over summer the Zeehan current is relatively warm and low in nitrate concentration. In contrast waters brought in by currents from the Southern Ocean are of sub-antarctic origin and tend to be relatively cool with elevated nitrate concentrations. NOx (Nitrate and Nitrite) For the monitoring period (October 2020 to March 2021) all surface water NOx (nitrate and nitrite) readings were either at or below the Limit of Reporting (LoR), being 0.002 mg/L. This is consistent with the summer period values used in deriving the DGVs where only a single value was above the LoR from August 2013 to July 2017. For the monitoring period (October 2020 to March 2021) all bottom water NOx (nitrate and nitrite) readings were either at or below the Limit of Reporting (LoR) for sites EPA-PA6, EPA-PA7, EPA-PA8 and EPA-PA9, EPA-PA5 was below the LoR for all months except March when a value of 0.003 mg/L was recorded. EPA-PA1 was below or equal to the LoR for all months except November when a value of 0.003 mg/L was recorded. These findings indicate that for shallow sites, the NOx levels were consistently low throughout the water column for the monitoring period. For October, of the deeper sites (EPA-PA2, EPA-PA3 and EPA-PA4,) only EPA-PA4 was above the summer DGV for bottom waters. EPA-PA4 was also above the annual DGV for bottom waters. For November EPA-PA2, EPA-PA3 and EPA-PA4 were above the summer DGV but were below the annual DGV for bottom waters. For January EPA-PA2, EPA-PA3 and EPA-PA4 were below the LoR value for bottom waters. For February EPA-PA2 and EPA-PA3 were below the LoR value and EPA-PA4 at 0.003 mg/L which is below the summer DGV For March EPA-PA2 and EPA- PA3 are greater than the summer DGV and below the Annual DGV for bottom waters. EPA-PA4 was above the summer and annual DGVs for bottom waters, with a value of 0.42 mg/L. The maximum value recorded for NOx during the base line period for bottom waters at PA4 was 0.055 mg/L. The pattern observed in NOx values for bottom waters at the deep water sites reflects the intrusion of marine water masses from outside of Port Arthur, as described for Nitrate above. Nitrogen (total) For the monitoring period (October 2020 to March 2021) Nitrogen total readings for surface water tended to be higher within Long Bay than for all other sites. During October, EPA-PA6 recorded a reading of 0.31 mg/L, which is above the summer DGV (0.30 mg/L) but lower than the annual DGV (0.32 mg/L). All other sites recorded values lower than the summer DGV. For November and March all sites recorded values lower than the summer DGV, though values for sites within Long Bay were higher than for the other sites. For January and February the Long Bay sites (EPA-PA1, EPA-PA5, EPA-PA6, EPA-PA7, and EPA-PA8) recorded values above the summer DGV, In February, EPA-PA1 recorded a value equal to the annual DGV as did EPA-PA8 in January. Interestingly, EPA-PA7 was above the annual DGV value for January and February. The elevated readings for EPA-PA7 may indicate catchment based inputs. These values are well below the maximum recorded for the baseline period, being 0.46 mg/L for surface waters. For sites EPA-PA1, EPA-PA2, EPA-PA3 and EPA-PA9 all readings for bottom waters were below the summer DGV value of 0.30 mg/L. EPA-PA4 was above the annual DGV during October, recording a value of 0.37 mg/L. During January EPA-PA5, EPA-PA6 and EPA-PA7 recorded values above the annual DGV. EPA Tasmania, July 2021 24
During February EPA-PA7 and EPA-PA8 were above the annual DGV. These values are well below the maximum recorded for the baseline period, being 0.45 mg/L for bottom waters. For all sites, organic nitrogen represents the majority of nitrogen within surface and bottom waters. Organic nitrogen (ON) is calculated by removing the TAN component from Total Kjeldahl Nitrogen (TKN). The relative proportions of TAN, NOx and organic nitrogen for each site on a monthly basis for surface and bottom waters are presented in Appendix 1. Phosphorus (total) For the monitoring period (October 2020 to March 2021) Phosphorus total readings for surface waters tended to be equal to or above the annual and summer DGVs of 0.030 mg/L for the shallow water sites and lower for the deep water sites. EPA-PA4 (the outer most deep water site) recorded a value of 0.030 mg/L during November but was as with EPA-PA2 and EPA-PA3 consistently lower on all other occasions. Interestingly, EPA-PA9 (shallow Carnarvon Bay site) had a value below the DGVs on all occasions. EPA-PA1 was equal to the DGVs values during October and February and above the DGVs for January (0.038 mg/L) and March (0.032 mg/L), whilst below in November. This pattern is also reflected in the shallow water sites in Long Bay (EPA-PA5, EPA-PA6, EPA-PA7, and EPA-PA8). These values are well below the maximum recorded for the baseline period, being 0.07 mg/L for surface waters. Phosphorus total readings for bottom waters have a less evident trend. EPA-PA4 had a reading of 0.048 mg/L for October. This is the only occasion however that a site not within the shallow reaches of Long Bay had a reading that was above the summer and annual DGVs, being 0.040 mg/L. Only EPA-PA5 had readings above the DGVs during October and November, being 0.047 mg/L and 0.049 mg/L, respectively. During January, EPA-PA5, EPA-PA6, EPA-PA7, and EPA-PA8 had bottom water readings above the DGVs (ranging from 0.044 mg/L to 0.049 mg/L). During February, EPA-PA8 returned a reading of 0.042 mg/L as did EPA-PA7 during March 2021. These were the only two sites for the last two months of the survey period to have bottom water values above the DGVs. These values are well below the maximum recorded for the baseline period, being 0.07 mg/L for bottom waters. The elevated reading for EPA-PA7 during March 2021 may indicate catchment based inputs. DRP (Dissolved Reactive Phosphorus) For October to February all surface water DRP (Dissolved Reactive Phosphorus) readings were either at or below the summer DGV, except for EPA-PA7 during January. For January, EPA-PA7 had a reading of 0.007 mg/L , which is higher than the summer DGV (0.006 mg/L) but lower than the annual DGV (0.008 mg/L). For March, the deep water sites (EPA-PA2, EPA-PA3 and EPA-PA4) were lower than annual and summer DGVs. The shallow water sites in Long Bay, were equal to the summer DGV (EPA-PA5 and EPA-PA8) or lower than the annual DGV value (EPA-PA1 and EPA-PA6). The only exception was EPA-PA7 that had a value of 0.011 mg/L. Interestingly, EPA-PA9 (shallow Carnarvon Bay site) had a value of 0.005 mg/L, which is the same as that for the outer deep site (EPA-PA4). The elevated readings in the upper section of Long Bay may indicate catchment based inputs. Stream gauge information from Allens Rivulet indicates that a high rainfall event occurred within the catchment causing discharge to rise over a two day period (24 March to 26 March) from 1.2 ML/day to over 275.0 ML/day. Long Bay Creek which shares headwaters with Allens Rivulet would have shown a similar discharge pattern. The increase at EPA- PA7 and associated decrease in pH may reflect runoff associated with the onset of the rain event. For the monitoring period bottom water DRP (Dissolved Reactive Phosphorus) readings were lower than the summer or annual DGVs on all but 4 occasions. EPA-PA4 recorded a value of 0.01 mg/L during October and of 0.009 mg/L during March. The latter value being equivalent to the annual DGV for bottom waters. EPA-PA5 recorded a value of 0.016 mg/L during November and EPA-PA7 of 0.013 mg/L in March. The elevated reading for EPA-PA7 may indicate catchment based inputs. EPA Tasmania, July 2021 25
Chlorophyll a For all months EPA-PA1, EPA-PA2, EPA-PA5, EPA-PA6 and EPA-PA8 chlorophyll a values were above the annual and summer DGVs for chlorophyll a. EPA-PA7 was above the summer DGV for all months and the annual DGV for all months except October. Interestingly, EPA-PA9 (shallow Carnarvon Bay site) had a value lower than the summer and annual DGVs for October 2021, had a value that lies between the summer DGV and annual DGV from November to February and was above both DGVs during March. EPA-PA3 was above the summer DGV for all months but below the annual DGV for November and February. EPA-PA4 was above the summer DGV and annual DGV for November to January and equal or lower than both DGVs for February and March. It is not uncommon that chlorophyll a concentration is higher in shallow areas where light is not limited, and nutrients are available. The higher chlorophyll a levels for the shallow Long Bay sites (EPA-PA5, EPA- PA6, EPA-PA7, and EPA-PA8) indicate a higher level of nutrient availability compared to the shallow Carnarvon Bay site (EAP-PA9) which is of similar depth and water clarity. Epiphytic Algal growth Overall the February 2021 snapshot indicated that epiphytic growth was of the Low (minimal) to Medium (obvious) range for seagrass within Port Arthur. These findings are in line with those for the South East of Tasmania, where 45% (22 of 49 locations) and 35% (17 of 49 locations) were of the Low (minimal) to Medium (obvious) range, respectively. Other areas with sea grass habitat with epiphytic algal growth that is comparable for the February 2021 snapshot include Blackman Bay, the D’Entrecasteaux Channel, Recherche Bay, Frederick Henry Bay, Norfolk Bay and the Mercury Passage. Conclusion The data reviewed in this document indicates that the water quality of the Port Arthur is akin to that of the baseline period on which the DGVs were derived. For most parameters the levels have remained within the overall range of the baseline dataset even when lower or greater than the DGVs. Water within the Port Arthur area is chiefly of marine origin and nature. The upper section of Long Bay is at times subject to catchment runoff following rainfall events. Some elevation in TAN and Nitrogen (total) is discernible within waters near the finfish lease. These elevations are not persistent over the period surveyed and seem to be limited to the surface water in the immediate vicinity of the lease. The increased nutrient availability from these sources contributes to the elevated chlorophyll a levels noted within Long Bay. The level of epiphytic growth noted was comparable to that for other sea grass habitats across the South East of Tasmania for the February snapshot. EPA Tasmania, July 2021 26
Appendix 1 Surface Water Nitrogen Compounds Figure 24: October 2020 surface water nitrogen compounds and budget for Port Arthur. Figure 25: November 2020 surface water nitrogen compounds and budget for Port Arthur. EPA Tasmania, July 2021 27
Figure 26: January 2021 surface water nitrogen compounds and budget for Port Arthur. Figure 27: February 2021 surface water nitrogen compounds and budget for Port Arthur. EPA Tasmania, July 2021 28
Figure 28: March 2021 surface water nitrogen compounds and budget for Port Arthur. Bottom Water Nitrogen Compounds Figure 29: October 2020 bottom water nitrogen compounds and budget for Port Arthur. EPA Tasmania, July 2021 29
Figure 30: November 2020 bottom water nitrogen compounds and budget for Port Arthur. Figure 31: January 2021 bottom water nitrogen compounds and budget for Port Arthur. EPA Tasmania, July 2021 30
Figure 32: February 2021 bottom water nitrogen compounds and budget for Port Arthur. Figure 33: March 2021 bottom water nitrogen compounds and budget for Port Arthur. EPA Tasmania, July 2021 31
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