Sediment Quality Sampling Design for Darwin Harbour
Brinkman, Richard; Logan, Murray; Northern Territory. Department of Environment and Natural Resources; Australian Institute of Marine Science
E-Publications; E-Books; PublicationNT; Report Number 44/2019
In the context of increasing development and associated pressures, this project aims to inform the development of a first systematic, long-term, sediment monitoring program for Darwin Harbour which takes into consideration the physicochemical nature of Darwin Harbour sediment and the oceanographic processes which will influence the movement of contaminated sediment in the Harbour. The rationale for the program is that seabed and estuarine sediments are both an extensive habitat and the ultimate repository for many contaminants that enter waterways. In addition, monitoring of contaminants in sediment may facilitate the identification of increasing contaminant loads in the Harbour which may not be detected by water monitoring programs due to the high flushing rate within Darwin Harbour and infrequent water sample collection.
Made available by via Publications (Legal Deposit) Act 2004 (NT).
1. Executive summary -- 2. Introduction -- 3. Methods -- 3.1 Overview of methodology -- 3.2 Tidal Hydrodynamics -- 3.3 Wave Dynamics -- 3.4 Sediment Modelling -- 3.5 Sediment sampling design analysis -- 4. Results -- 4.1 Tidal and wave driven hydrodynamic processes -- 4.2 Sediment transport modelling -- 4.3 Sediment characteristics from previous sampling programs -- 4.4 Sediment sampling design analysis -- 4.4.1 Existing chemical sediment data, Outer Harbour sediment monitoring data, and designated sampling sites -- 4.4.2 Hydrodynamic modelling layers -- 4.4.3 Exclusion zone masks -- 4.5 Spatial Model fitting -- 4.5.1 Background on statistical techniques for designing sediment sampling program -- 4.5.2 Results from statistically derived sampling design - East Arm -- 4.5.3 Results from statistically derived sampling design - Outer Harbour -- 4.5.4 Representation of sampling sites mapped with hydrodynamic and sediment modelling parameters -- 4.6 Harbour Sediment Zonation, and conceptual representation: -- 5 Conclusions -- 6 References -- 7 Appendix 1
Sediment quality; Tidal hydrodynamics; sediment sampling; design analysis
Northern Territory Government
Report Number 44/2019
43, 74 pages : colour maps ; 30 cm
Attribution International 4.0 (CC BY 4.0)
Northern Territory Government
31 Figure 18 Comparison of the mean Error conditional on sample size and sampling method for the Outer Harbour On the basis of Figure 18 we could conclude that a sample size of 100 within Outer Harbour is a sound choice, although it is likely that as few as 50 could still potentially yield similar overall patterns particularly if the sediment sampling site selection is based on cLHS. If the purpose of the sampling design is to provide an unbiased representative sample of the general conditions across the spatial domain, then it could be argued that the 2D spatially balanced design is most appropriate for the Outer Harbour - particularly if there is any doubt in the assumptions below. Therefore, the spatial representation of the two dimensional spatially balanced sampling configuration for the Outer Harbour (100 samples) is shown in Figure 19. The sample size of 100 also accommodates a buffer against sample loss. Nevertheless, this entire simulation process is contingent on a number of unverifiable assumptions: 1. that the Outer Harbour sediment sampling data are representative of the typical conditions and spatial patterns. 2. all Outer Harbour sediment chemicals are equally useful and informative 3. the INLA models are able to fully represent the true metal(loid) and nutrient concentrations in sediment in the area of interest 4. the costs and logistics of sampling are equal irrespective of location With the 2D spatially balanced design most of sediment sampling sites are in Shoal Bay (Figure 19), the underrepresentation of sites closer to Darwin city may decreases the power of the monitoring to detect changes associated with development of Darwin city. The exclusion of sites closer to Darwin city is controlled by the application of spatial masks of areas of high hydrodynamic energy.