How healthy are our estuaries?
Our precious estuaries
An estuary is a semi-enclosed coastal waterbody where inflowing freshwater meets—and mixes with—seawater. Environment Waikato operates a modest monitoring programme to determine the condition or state of the water in the region’s estuaries. Over the past 10 years, water quality has been studied in a total of five of the region’s estuaries: Whangamata (1999–2001), Raglan (2002–03), Whangapoua (2006–07), Southern Firth of Thames (2006–07) and, most recently, Kawhia (2008–09).
What affects estuary health?
Water quality usually varies in time and space. In an estuary the most important factors contributing to this variability are (1) the season, (2) the weather, (3) the state of the tide, (4) the distance from the coast and (5) the extent to which inflowing freshwater is diluted with clean seawater. Water quality at a given location can also vary with depth, but this is usually only minor in the shallow, well-mixed estuaries found in this region. Our field surveys therefore need to allow for these sources of variability.
How we measure estuary health
Based on past experience, Environment Waikato has developed an estuarine monitoring programme based on (1) a one-year study of each estuary, based on bimonthly visits (i.e. six visits in a 12-month period), (2) two additional visits following periods of heavy rainfall, (3) four monitoring sites, located in the low-tide channels of the estuary at varying distances from the coast and (4) samples collected within an hour of the time of mid-tide, on an outgoing tide. Monitoring sites are visited using a boat, from which field measurements are made and water samples are collected for subsequent laboratory analysis. A number of standard water quality variables are measured: salinity, temperature, dissolved oxygen, pH, water clarity, ammonia, various forms of nitrogen and phosphorus, algal biomass and various types of faecal bacteria.
Check out Environment Waikato's indicator of estuarine water quality.
Use our map which indicates and links to the estuarine sites we are monitoring.