Water quality monitoring system - Darwin Harbour, Northern Territory

Darwin Harbour is a tropical estuarine system with a distinct wet and dry season and is one of Australia's largest deep water harbours (Russell and Hewitt 2000). The annual rainfall of Darwin averages 1714 mm, with 64% of this falling between January and March. The harbour is macro-tidal, with a maximum tidal range of 7.8 m and strong currents of up to 2 m/s that transport sediment within the harbour. Nine sites were sampled throughout the harbour on a quarterly basis at the neap tides between December 2002 and December 2004. Sites ranged in depth from 5 m (river sites) to 30 m (outer harbour sites). Highly seasonal rainfall in this region greatly affects the water quality throughout Darwin Harbour, with the results from this study showing that seasonal aspects, rather than spatial or tidal, are more important in causing significant differences in water quality. However, while nutrient, suspended solid and chlorophyll a concentrations differed between locations within the harbour, rainfall appears to have the greatest impact on these parameters. Darwin Harbour is a well mixed, though not a well-flushed system, with a huge tidal range that causes large volumes of water to move into and out of the harbour. This in turn leads to considerable differences in water mixing between different areas within the harbour and so one would expect that the concentrations of nutrients, chlorophyll a and suspended solids would be greatly influenced by this. Interestingly, our observations did not detect significant variations during the tidal studies, but did detect significant differences between wet and dry seasons. Darwin Harbour water quality, as observed during this study, was not significantly different to that observed by Padovan (1997) 12 years prior to this study. This is despite the considerable alterations and developments in the harbour and the surrounding catchment during this period.
This study was undertaken to expand the existing monitoring work in the harbour carried out by the Northern Territory Department of Natural Resources, Environment and The Arts (NRETA) and to provide additional baseline information of water quality.
Parameters measured: temperature, salinity, turbidity, nutrients, chlorophyll a, particulate nitrogen, particulate phosphorus and suspended solids concentrations.

达尔文港（Darwin Harbour）是澳大利亚规模最大的深水港之一（Russell与Hewitt，2000），属于热带河口湾系统，具有鲜明的干湿两季特征。达尔文市年平均降雨量为1714毫米，其中64%的降水集中于1月至3月。该港湾为大潮差型（macro-tidal）水域，最大潮差可达7.8米，且存在流速高达2 m/s的强劲海流，在港湾内部输送沉积物。2002年12月至2004年12月期间，研究团队在全港湾内布设9个采样点位，于小潮期按季度开展采样工作。采样点水深范围为5米（河道点位）至30米（外港湾点位）。

该区域季节性极强的降雨对达尔文港的整体水质影响显著，本研究结果表明，相较于空间差异与潮汐变化，季节因素是导致水质出现显著差异的更关键因素。尽管港湾内不同点位的营养盐、悬浮固体与叶绿素a（chlorophyll a）浓度存在空间分异，但降雨似乎对这些参数的影响最为显著。

达尔文港属于混合充分但水体交换能力欠佳的系统，巨大的潮差使得巨量水体在港湾内往复吞吐，这进而导致港湾内不同区域的水体混合程度存在显著差异，因此理论上营养盐、叶绿素a与悬浮固体的浓度会受到这一过程的强烈影响。值得注意的是，本研究的潮汐观测未发现显著的浓度变化，但确实检测到干湿两季之间存在显著差异。

本研究观测到的达尔文港水质，与12年前Padovan（1997）的观测结果无显著差异，尽管在此期间该港湾及其周边流域已发生大量开发与环境变更。

本研究旨在拓展北领地自然资源、环境与艺术部（NRETA）此前在该港湾开展的监测工作，并提供补充性的水质基准数据。

本次测定的参数包括：水温、盐度、浊度、营养盐、叶绿素a、颗粒态氮、颗粒态磷及悬浮固体浓度。