The main purpose of WP1 is to determine the optimal tide-based sampling conditions for long-term surface water quality monitoring, and thereby improve the capacity of the monitoring program to detect changes in water quality stressor and response parameters that are caused by anthropogenic pressures.
This includes testing the suitability of the existing monitoring protocol used by the DENR WQMP, which
assumes that monitoring over a 3-hour window centred on dry season high neap tide (<3 m) is an
effective approach for collecting consistent long-term data sets for detection of long-term change in
water quality in Darwin Harbour.
A project-specific field campaign was developed to collect surface water quality data during three
discrete periods coinciding with neap tides in the 2017 dry season months (June, August and
September), at four monitoring sites, along the natural estuarine gradient in the area of East Arm and the
Elizabeth River estuary. The data were collected over six hours at time intervals between 1 to 30
minutes. A total of 20 parameters were collected at each site and on three discrete dates. The collected
data sets included physico-chemical parameters, nutrients and parameters representing algal biomass.
Detailed parameter-specific assessments of neap tide surface water quality were undertaken using
project-specific data analysis methodology. Data analyses focused on the effects of intra-seasonal
variability and tidal range, spatial variability, monitoring window size and tidal flows (flood/ebb) on water
quality variability.1 Summary -- 2 Introduction -- 2.1 Background -- 2.1.1 Darwin Harbour: physical characteristics -- 2.1.2 Water quality in Darwin Harbour -- 2.1.3 DENR WQMP -- 2.2 Study Objectives -- 3 Method -- 3.1 General approach -- 3.2 Field stations and neap tide dates -- 3.2.1 Measured parameters -- 3.3 Tidal range -- 3.4 Field techniques -- 3.4.1 .In-situ field measurements -- 3.4.2 Sample collection and analysis -- 3.5 Data analysis and visualisation -- 3.5.1 Monitoring windows -- 3.5.2 Data visualising techniques -- 3.5.3 Statistical parameters -- 3.5.3.1 Coefficient of variation and mean -- 3.5.3.2 Standard errors -- 3.5.4 Hypothesis testing -- 3.5.4.1 Wilcoxon rank sum test -- 3.5.4.2 Ansari-Bradley test -- 3.5.4.3 Analysis of variance -- 3.5.5 Principal component analysis -- 3.5.6 Generalised linear mixed modelling -- 4 Results and discussion -- 4.1 Explanatory parameters -- 4.1.1 Depth -- 4.1.2 Current speed -- 4.2 Physico-chemical results -- 4.2.1 Summary statistics -- 4.2.2 Surface water temperature -- 4.2.2.1 Intra-seasonal variability -- 4.2.2.2 Spatial trend -- 4.2.2.3 Monitoring window assessment -- 4.2.2.3.1 Tidal (flood/ebb) variability -- 4.2.3 Salinity and electrical conductivity -- 4.2.3.1 Intra-seasonal variability -- 4.2.3.2 Spatial trend -- 4.2.3.3 Monitoring window assessment -- 4.2.3.3.1 Tidal (flood/ebb) variability -- 4.2.4 pH -- 4.2.4.1 Intra-seasonal variability -- 4.2.4.2 Spatial trend -- 4.2.4.3 Monitoring window assessment -- 4.2.4.3.1 Tidal (flood/ebb) variability -- 4.2.5 Turbidity -- 4.2.5.1 Intra-seasonal variability -- 4.2.5.2 Spatial trend -- 4.2.5.3 Monitoring window assessment -- 4.2.5.3.1 Tidal (flood/ebb) variability -- 4.2.6 Dissolved oxygen -- 4.2.6.1 Intra-seasonal variability -- 4.2.6.2 Spatial trend -- 4.2.6.3 Monitoring window assessment -- 4.2.6.3.1 Tidal (flood/ebb) variability -- 4.3 Nutrients ? Nitrogen and Phosphorus -- 4.3.1 Anthropogenic sources of nutrients in the study area -- 4.3.2 Summary statistics -- 4.3.3 Ammonia -- 4.3.3.1 Intra-seasonal variability -- 4.3.3.2 Spatial trend -- 4.3.3.3 Monitoring window assessment -- 4.3.3.3.1Tidal (flood/ebb) variability -- 4.3.4 Oxides of nitrogen -- 4.3.4.1 Intra-seasonal variability -- 4.3.4.2 Spatial trend -- 4.3.4.3 Monitoring window assessment -- 4.3.4.3.1 Tidal (flood/ebb) variability -- 4.3.5 Total filterable (dissolved) nitrogen -- 4.3.5.1 Intra-seasonal variability -- 4.3.5.2 Spatial trend -- 4.3.5.3 Monitoring window assessment -- 4.3.5.3.1 Tidal (flood/ebb) variability -- 4.3.6 Total nitrogen -- 4.3.6.1 Intra-seasonal variability -- 4.3.6.2 Spatial trend -- 4.3.6.3 Monitoring window assessment -- 4.3.6.3.1 Tidal (flood/ebb) variability -- 4.3.7 Soluble reactive phosphorus as P -- 4.3.7.1 Intra-seasonal variability -- 4.3.7.2 Spatial trend -- 4.3.7.3 Monitoring window assessment -- 4.3.7.3.1 Tidal (flood/ebb) variability -- 4.3.8 Total filterable (dissolved) phosphorus -- 4.3.8.1 Intra-seasonal variability -- 4.3.8.2 Spatial trend -- 4.3.8.3 Monitoring window assessment -- 4.3.8.3.1. Tidal (flood/ebb) variability -- 4.3.9 Total phosphorus -- 4.3.9.1 Intra-seasonal variability -- 4.3.9.2 Spatial trend -- 4.3.9.3 Monitoring window assessment -- 4.3.9.3.1 Tidal (flood/ebb) variability -- 4.4 Phytoplankton biomass -- 4.4.1 Summary statistics -- 4.4.2 Chlorophyll -- 4.4.2.1 Intra-seasonal variability -- 4.4.2.2 Spatial trend -- 4.4.2.3 Monitoring window assessment -- 4.4.2.3.1 Tidal (flood/ebb) variability -- 4.4.3 Euphotic depth -- 4.4.3.1 Intra-seasonal variability -- 4.4.3.2 Spatial trend -- 4.4.3.3 Monitoring window assessment -- 4.4.3.3.1 Tidal (flood/ebb) variability -- 5 Summary of results -- 5.1 Coefficient of variation -- 5.2 Variability trends -- 5.2.1 Physico-chemical parameters -- 5.2.2 Nutrients -- 5.2.3 Algal biomass -- 5.3 Principal component analysis -- 5.3.1 Intra-seasonal variability -- 5.3.2 Spatial variability -- 5.3.3 Windows -- 5.3.4 Windows-tides -- 5.4 Study limitations -- 6 Conclusions and recommendations -- 7 References -- 8 Acknowledgement -- 9 Appendix A: Current speed analyses for nutrients -- 9.1 Ammonia -- 9.2 Oxides of nitrogen -- 9.3 Total dissolved (filterable) nitrogen -- 9.4 Total nitrogen -- 9.5 Soluble reactive phosphorus -- 9.6 Total dissolved (filterable) phosphorus -- 9.7 Total phosphorus -- 10 Appendix B: Generalised linear mixed model results for nutrients -- 10.1 Ammonia -- 10.2 Oxides of nitrogen -- 10.3 Total dissolved (filterable) nitrogen -- 10.4 Total nitrogen -- 10.5 Soluble reactive phosphorus -- 10.6 Total dissolved (filterable) phosphorus -- 10.7 Total phosphate -- 11 Appendix C: Dry season 2017 -- 12 Appendix D: Elizabeth river stream discharge dataMade available by the Library & Archives NT via the Publications (Legal Deposit) Act 2004 (NT)
