Coastal and estaurine water quality, state, 2016-2020

Adapted by The Ministry for the Environment and Statistics NZ to provide for environmental reporting transparency. Dataset used to develop the "Coastal and estuarine water quality" indicator (available at https://www.stats.govt.nz/indicators/coastal-and-estuarine-water-quality).

This indicator reports on state for 15 coastal and estuarine water quality measures, grouped below by type, monitored at sites across Aotearoa New Zealand between 2016 and 2020:
• nutrient – ammoniacal nitrogen, nitrate-nitrite nitrogen, total nitrogen (unfiltered), dissolved reactive phosphorus, and total phosphorus (unfiltered)
• microbiological – faecal coliforms, Enterococci, and chlorophyll-a
• optical – visual clarity, turbidity, and suspended solids (inorganic and organic)
• physico-chemical – dissolved oxygen, pH, salinity, and temperature.
Coastal and estuarine ecosystems are affected by changes in water quality.

Nutrients
The two main nutrients of concern in coastal and estuarine ecosystems are nitrogen and, to a lesser degree, phosphorus. An overload of nutrients (eutrophication) can lead to algal blooms that can kill marine life by depleting oxygen levels. Some bloom-forming algal species also contain toxins that can harm marine life, and can pass through food chains to humans (for example, via shellfish poisoning).

Microbiological
Abundant Enterococci and faecal coliform bacteria indicate the possible presence of human faecal pathogens in coastal waters and represent the risk of infectious disease. Chlorophyll-a is a measure of phytoplankton biomass and is a primary indicator of eutrophication.

Optical
High suspended sediment concentrations are associated with estuarine and coastal sedimentation, reduced light levels in benthic (seabed) environments, and reduced feeding rates and health of estuarine and coastal animals (Lowe et al., 2015). Visual clarity and turbidity are monitored because light affects primary production, plant and animal distributions and ecological health, aesthetic quality, and recreational values (Davies-Colley et al., 2003).

Physico-chemical
Dissolved oxygen is fundamental to supporting marine life. Low levels of dissolved oxygen can have adverse effects on aquatic fauna, from reduced growth rates to death from lack of oxygen (Tomasetti & Gobler, 2020). Decreased pH results from the absorption of CO2 from the atmosphere by seawater but can also reflect local processes caused by eutrophication (Cai et al., 2011; Fraser et al., 2021). Changes in the pH of seawater can have harmful effects on marine life, impacting chemical communication, reproduction, and growth. The building of skeletons in marine organisms is particularly sensitive to acidity, so acidification (lower pH) of sea waters can be harmful for organisms such as shellfish and corals (Fabry et al., 2008). Salinity provides information on the freshwater content of coastal waters. Water temperature is important as it controls biochemical processes and affects the balance of parameters such as dissolved oxygen levels. As a result, seawater temperature determines distributions of many marine plants and animals (Kleisner et al., 2017).

More information on this dataset and how it relates to our environmental reporting indicators and topics can be found in the attached data quality pdf.