Cleveland Bay Marine Water Quality (Turbidity and Available Light) Monitoring Plan

Transcription

1 Cleveland Bay Marine Water Quality (Turbidity and Available Light) Monitoring Plan 1 BACKGROUND Port of Townsville Limited (PoTL) administers the Port of Townsville, a general purpose cargo port in North Queensland with a land and sea jurisdiction in excess of 450 km 2. The port is located within an environmentally sensitive area of the coastline in close proximity to mangrove habitats, ecologically important seagrass beds, wetlands as well as fringing coral reefs and in close proximity to residential areas. The Port of Townsville s sea jurisdiction encompasses the Great Barrier Reef World Heritage Area, which is also a national heritage place. However, the port and its marine infrastructure are in an exclusion area from the Central region of the Commonwealth Great Barrier Reef Marine Park and the State Great Barrier Reef Coast Marine Park (Figure 1). Figure 1: Coastal Habitats in Cleveland Bay. Since November 2004, the Port of Townsville has conducted a long-term marine water monitoring program, which was implemented primarily to characterise water quality in the marine environment within and surrounding the port that may be influenced from day to day operations. These long-term water monitoring program monitoring results are used to assist with improving PoTL and Port Customer control measures where possible and environmental management in general and as a management tool for product handling activities throughout the port. Page 1 of 5

2 Dredging is regularly undertaken at the Port of Townsville and dredged material placed at the approved Dredge Material Placement Area located between Cape Cleveland and Magnetic Island (Figure 1). The long-term marine water monitoring program, mentioned above, is not designed to monitor dredging and material placement activities. A number of sensitive areas are within close proximity to both the dredge areas (Platypus Channel and/or Sea Channel) and the Dredge Material Placement Area. Dredging and Placement activities can impact turbidity levels and light availability. This monitoring plan has been established to measure turbidity and light availability at a number of sites within Cleveland Bay. The information will be used to understand the variations in turbidity and light levels within the Bay at sites known to contain sea-grasses and corals and to assist with interpreting the impact of maintenance dredging and dredge material placement by PoTL. 2 OBJECTIVE The objective of the monitoring plan is to measure turbidity and light availability at key sensitive receptor sites (coral and sea-grass communities) within Cleveland Bay. This will involve the measurement of turbidity (via optical backscatter), underwater light, along with conductivity, depth and temperature as well as timelapse underwater cameras at some sites. The data will be used to develop baseline values for key water quality parameters and light and to document changes in turbidity/light in relation to prevailing environmental conditions and dredging operations. This Plan will be subject to assessment and regular review. Further consideration of scope will be undertaken following review of the first 12 months of data. 3 SCOPE 3.1 Sediment and Turbidity in Cleveland Bay Ongoing research into turbidity and sediment movement within Cleveland Bay has been undertaken by a range of different research groups. Cleveland Bay has a number of rivers that directly feed into it, including the Ross River, which has a number of weirs to control flow, and the Alligator Creek which drains a mangrove and mud flat dominated area of coast. Both these systems have monsoonal dominated flows with very low movement during the dry season, but with high-flow events associated with summer monsoon rainfall. The Ross River drains an urban area which has some sand mining in the upper part of the catchment so, during flood events, significant amounts of fine material can be transported out into the Bay. Approximately 80 kilometres to the south of the Bay is the Burdekin River, one of the major North Queensland rivers, with a catchment of over km 2. The science of determining the impacts of the Burdekin River on Cleveland Bay is still evolving, however it is recognised the Burdekin River is the largest sediment contributor to the central Great Barrier Reef Region. The sediment with Cleveland Bay is mostly fine muds and it is estimated that the Bay is a net accumulator of sediment in non-cyclone years and that import rates are % of current export rates. Most studies of turbidity in Cleveland Bay, or the general region, indicate that for dry-season periods, most turbidity is related to re-suspension of existing material. Sediment material in deeper waters (below 20m) tends to not re-suspend, except under exceptional conditions such as storms, cyclones etc. This means that most re-suspension is a local within-bay phenomenon, whereby local in-situ sediment is put back into the water column. While there will be turbidity from processes transporting sediment through the Bay, most upper water column turbidity is via local wave and wind driven re-suspension. Page 2 of 5

3 A previous review undertaken by Orpin et al. examined historical wind records to determine how often events would occur that were strong enough to cause in-situ re-suspension. They found that at 5m, conditions favourable to in-situ sediment re-suspension occurred on average 220 days per year; while at 10m it was 110 days per year; and at 15m 40 days per year. The shallow areas of Cleveland Bay experience conditions favourable to re-suspension for a significant part of the year with in-situ sediment re-suspension a normal dry-season phenomenon. While sediment re-suspension may be the main and consistent source of turbidity in Cleveland Bay during the dry season, it is influenced by small scale localised factors and therefore not uniform across the Bay. Similar geographic, sedimentary and hydrodynamic conditions may result in different turbidity conditions. Previous analysis of the available turbidity data for Cleveland Bay has shown a 10-fold difference in the 50 percentile turbidity value for sites within the Bay, indicating a high degree of localised variability driven by infrequent, localised, high turbidly events. Increased turbidity decreases underwater light. Many organisms require light for photosynthesis including two of the main biodiversity groups in Cleveland Bay sea-grasses and corals. Changes in turbidity can result in altered light conditions, which in turn lead to a range of impacts. The amount of available light therefore is a major determinant for the health of many of the benthic communities in Cleveland Bay. 3.2 Monitoring Locations Locations have been selected in key sensitive receptor areas within the Bay with a focus on coral and seagrass communities, which have been subject to previous or ongoing monitoring by various organisations and which align with sites monitored under the Marine Monitoring Program and Sea-grass Watch. Three of the locations represent known coral and sea-grass habitats located in near-shore reefal areas along Magnetic Island, whilst two locations are located within the Bay where sea-grass beds are known to be present (Figure 2). Details of the locations are presented in Table 1. Table 1: Details of Monitoring Locations and Associated Programs. Note: (POTL = Port of Townsville Limited, MMP = Marine Monitoring Program, SW = Seagrass Watch, AIMS = Australian Institute of Marine Science, JCU = James Cook University). Page 3 of 5

4 Figure 2: Monitoring Locations in Cleveland Bay. 3.3 Equipment At each location, a shallow area 3-5m below LAT was selected to house a bottom frame (these are located close to the dominant benthic community, but in a location that provides easy access for servicing). Attached to this frame is: a small CTD (conductivity (salinity), temperature and depth) sensor, which allows quantification of any nearby fresh water runoff and associated sedimentation to be determined; a WET Labs ECO-NTU nephelometer giving readings in Nephelometric Turbidity Units (NTU), which measures turbidity by optical scatter (the instruments deployed are also used by the MMP and in other studies); a LI-COR Li-192 underwater quantum sensor giving light quanta readings in μmol s-1 m-2, which measures underwater light as Photosynthetically Active Radiation (PAR) - that is that part of the light spectrum that is available to photosynthetic organisms to utilise; and a small time-lapse camera is mounted at some sites to give a visual indication of water clarity and, via a simple distance measure, an estimate of clarity as a pseudo Secchi disk depth. The camera field of view will include the turbidity instrument so that any anomalous turbidity events can be assessed from the camera images. 3.4 Frequency and Timing of Sampling AIMS has been contacted to undertake this work. The equipment was placed in the field in September 2014, noting some locations had partial equipment deployed in September and further equipment deployed during subsequent monthly servicing events. Locations are visited every month with the equipment retrieved and serviced and the data downloaded. The equipment will be cleaned, tested, re-powered and then re-deployed. All equipment was calibrated before the start of the project and then annually or as required. Page 4 of 5

5 Water samples will be taken in conjunction with monthly servicing to be analysed for Total Suspended Solids (TSS) using the MMP protocols. These samples will be used to validate the nephelometers and to give independent measures of turbidity. The in-situ instruments will sample every 10 minutes, which corresponds to the timing of the weather data from the AIMS weather station in Cleveland Bay and aligns with sampling frequencies from other instruments. As many high turbidity events are short lived, obtaining a high temporal resolution data set over these events may help link the observations to causation parameters. Detailed QC for the water quality component of the MMP, including data QC, can be found at: In the event of a Tropical Cyclone the equipment will be removed (if safe to do so), while the cyclone is present and the re-deployed once the cyclone has passed. 4 REPORTING The data collected by this program will be an important resource in understanding conditions within Cleveland Bay; in understanding the future status of corals and sea-grasses in the region; and in understanding how other factors, such as port operations, impact or contribute to localised water quality. Reporting will be undertaken following collection of one year of data. It is anticipated that the plan design will deliver the following: 1. Measures of ambient turbidity and PAR using industry standard techniques at five sites that contain seagrass and/or coral located near dredging and dredge material placement operations. This will compliment data collected under other programs (specifically the MMP) and will add to the long term record of water conditions in the area; 2. Data to assist in the development of various trigger or environmental targets when combined with information from other related studies; 3. Provide high level data to enhance understanding of the impact of sediment derived turbidity on the coral and seagrass communities of the Bay; 4. Relationships between the three turbidity related parameters backscatter via the nephelometer, Total Suspended Solids (TSS) via water samples and light as PAR; and 5. Data to understand the relationship between environmental forcing factors, such as waves and wind, and localised turbidity. 5 RELATED DOCUMENTS / REFERENCES POT 1569 Marine Water Monitoring Plan. A. R. Orpin, P. V. Ridd, S. Thomas, K. R. N. Anthony, P. Marshall and J. Oliver, Mar. Pollut. Bull., 2004, 49, Page 5 of 5