Coastal and estuarine water quality

  • Image, Coastal and estuarine water quality.

    Coastal and estuarine ecosystems are affected by changes in the levels of nutrients, oxygen, and light. An overload of nutrients can be toxic or lead to algal blooms. These blooms can kill marine life by depleting oxygen levels. Suspended sediment can smother habitats or reduce light levels, affecting photosynthesis. We report on five measures of water quality: turbidity (murkiness), dissolved oxygen, and the dissolved nutrients nitrate- and nitrite-nitrogen, ammoniacal nitrogen, and total phosphorus.

    We classified Coastal and estuarine water quality as a case study.

    Key findings

    In 2013, highly variable levels of nutrients, turbidity, and dissolved oxygen were recorded between sites in estuaries and coastal areas.

    • Some locations had very high levels (eg the maximum nitrate- and nitrite-nitrogen value of 3.4 mg/L was 170 times higher than the median value of 0.02 mg/L for estuarine sites).
    • Coastal sites had the following median water-quality values:
      • dissolved nutrients: nitrate- and nitrite-nitrogen (0.01 mg/L), ammoniacal nitrogen (0.01 mg/L), and total phosphorus (0.02 mg/L)

      • turbidity (2.63 nephelometric turbidity units – NTU)
      • dissolved oxygen (99.5 percent).
    • Estuary sites had the following median water-quality values:
      • dissolved nutrients: nitrate- and nitrite-nitrogen (0.02 mg/L), ammoniacal nitrogen (0.01 mg/L), and total phosphorus (0.03 mg/L)

      • turbidity (5.3NTU)
      • dissolved oxygen (95.9 percent).
    • Coastal locations tended to have better water quality than estuaries, with lower median dissolved nutrient and turbidity levels and higher median dissolved oxygen levels than estuarine waters.

    Figure 1

    Note: The ends of each ‘box’ are the upper and lower quartiles (top 25 percent and bottom 25 percent, respectively). The top and bottom ‘whiskers’ represent the highest and lowest observation in the series. The middle line of the box represents the median (middle) data point (half are above and half below this value).

    Apart from NH4-N in coastal waters, all the nutrients have a maximum value higher than 0.15 mg/L and are not shown on the graph. The maximum values were:

    • NNN – nitrate- plus nitrite-nitrogen: 0.79 mg/L (coastal) and 3.40 mg/L (estuarine)
    • NH4-N – ammoniacal nitrogen: 0.08 mg/L (coastal) and 4.20 mg/L (estuarine)
    • TP – total phosphorus: 0.35 mg/L (coastal) and 0.75 mg/L (estuarine).

    Data from Auckland Council; regional councils of Bay of Plenty, Waikato, Hawke's Bay, Manawatu-Wanganui, Wellington, and Canterbury; Gisborne and Marlborough district councils.

    Figure 2

    Note: Turbidity is a measure of water clarity, with increasing turbidity signalling a decrease in clarity. Turbidity is measured in nephelometric turbidity units (NTU). The ends of each ‘box’ are the upper and lower quartiles (top 25 percent and bottom 25 percent, respectively). The top and bottom ‘whiskers’ represent the highest (not shown on graph) and lowest observation in the series. The middle line of the box represents the median (middle) data point (half are above and half below this value). Data from Auckland Council; regional councils of Bay of Plenty, Waikato, Hawke's Bay, Manawatu-Wanganui, Wellington, and Canterbury; Gisborne and Marlborough district councils.

    Figure 3

     

    Note: DO – dissolved oxygen. The ends of each ‘box’ are the upper and lower quartiles (top 25 percent and bottom 25 percent, respectively). The top and bottom ‘whiskers’ represent the highest and lowest observation in the series. The middle line of the box represents the median (middle) data point (half are above and half below this value). Data from Auckland Council; regional councils of Bay of Plenty, Waikato, Hawke's Bay, Manawatu-Wanganui, Wellington, and Canterbury; Gisborne and Marlborough district councils.

    Definition and methodology

    We report on water-quality parameters for 2013 in the coastal and estuarine waters of nine regions (Auckland, Bay of Plenty, Waikato, Gisborne, Hawke's Bay, Manawatu-Wanganui, Wellington, Marlborough, and Canterbury) as a measure of ecosystem health.

    We report on dissolved nutrients – nitrates (NO3) and nitrites (NO2), ammoniacal nitrogen (NH4-N), and total phosphorus – as well as oxygen and turbidity levels. These are useful parameters because they influence marine life and water-column primary productivity and are affected by eutrophication (an excess of nutrients).

    Marine primary productivity depends on levels of nutrients, sunlight, and oxygen. Too little of any of these can inhibit plant and algal growth. High nutrient levels can cause excessive plant growth and lead to eutrophication (eg algal blooms). This can deplete oxygen levels, killing other organisms. The two main nutrients of concern are nitrogen and phosphorus.

    We report on the median and range of water-quality parameters because there are no New Zealand-specific guidelines. However, some regional councils report against water-quality indexes or guidelines, and local reporting should be consulted for more information.

    For more information about the limitations of this dataset, see data quality information.

    Data quality

     Topic Classification   Relevance Accuracy 
    Marine water and sediment quality and ocean acidity topic Case study

    relevance-partial 
    Partial

     accuracy-medium
    Medium

    See Data quality information for more detail.

    Archived pages

    See Coastal and estuarine water quality (archived October 2016).

    Updated 27 October 2016

marine-domain

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Related links

Our marine environment 2016

Environment Aotearoa 2015

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