Factsheet: Monitoring estuaries

Most estuary monitoring is carried out by regional councils and unitary authorities, who are responsible for managing the sustainable use of natural resources in their region and have a duty to gather and record information on the State of the Environment (SOE).  Other agencies that undertake monitoring in estuaries include Fisheries NZ (fish and shellfish focus) and Department of Conservation (marine reserves focus), plus citizen science is conducted across the country.

Councils monitor estuaries to understand their ecological condition and how this is changing over time, especially in relation to human activities that may degrade their health. The monitoring results help us understand whether such activities are being managed effectively.

Throughout New Zealand there are various estuary types, ranging in size from a few hectares to tens of thousands. Some estuaries have been monitored for two or three years and others for over three decades. 

Three indicators of estuary health that are measured nationally by councils are presented on LAWA:

  • Mud content refers to the amount of fine silt and clay particles (collectively known as mud) that are present in the surface layers of estuary intertidal flats. It is one of the main environmental characteristics that determines where plants and animals can and cannot live within an estuary.

  • Contaminants includes the metals copper (Cu), lead (Pb), zinc (Zn), cadmium (Cd), chromium (Cr), nickel (Ni), silver (Ag), mercury (Hg), arsenic (As), and organic contaminants such as hydrocarbons and pesticides.  When concentrations of these contaminants get too high, they can have negative effects on estuary health.

  • Estuary macrofauna are small invertebrates that can be seen with the naked eye and include hundreds of species such as worms, snails, crustaceans, and shellfish like pipi and cockles. Macrofauna are good indicators of estuary health because the community of species found in an area represent relatively long-term, local conditions.

These indicators have been selected for the Estuary Health topic as they provide meaningful information about estuary condition and are monitored in a consistent way by regional and unitary councils across the country.  In some regions, other useful indicators are monitored including sediment nutrient concentrations, sediment organic matter, Chlorophyll a content, sedimentation rates and the extend of certain habitats.  Most monitoring sites are intertidal, and data are available from 2010 onwards as this constitutes the most complete and consistent national dataset (regional councils and unitary authorities may hold longer datasets for individual monitoring sites).  The Estuary Health topic will be expanded as the collection of data for these and other indicators become more uniform.