An inventory of the status and origin of New Zealand estuarine systems.

Estuaries are vulnerable, unstable areas sensitive to the impact of man, because they are at the interface of two contrasting environments in which the results of environmental changes induced by man are focused. This study presents data on the extent, character, status and on the number of surveys of New Zealand estuaries. The widest possible interpretation of the term estuary has been used so as to produce the most comprehensive list.
Detailed study of topographic maps and information from questionnaires indicate that there are 301 estuaries widely distributed around the coast with an average of 1 per 32 km of coastline. Some data on the status of 54% of these is available. These estuaries range in size from a few ha to over 15000 ha but over ninety percent are less than 1700 ha, and 68% are less than 500 ha in area. Most estuaries are associated with human population concentrations of less than 500 persons. Overall there is approximately 0.03 ha of estuarine area per person. Bar-built and lagoonal estuaries predominate in both the North and South Islands.
Questionnaire results suggest that the water of most estuaries is well-mixed and clean or slightly polluted. Significantly more North Island estuaries are seriously polluted. The status of more than two-thirds of the estuaries has remained unchanged over the last 10 years. The balance among those which have changed is towards an overall deterioration and this has been more pronounced in the South Island. Research and surveys of estuaries are not very well developed and only 19% have been the subject of one or more reports. Very few have received satisfactory, detailed, simultaneous study of both their physical and biological characteristics over any length of time. In view of the many uses to which they are put, the frequent proximity of urban population concentrations, and the channelling of the effects of many different, widely dispersed human activities through them, estuaries should be the subject of a great deal more research. The use of systems modelling techniques as an aid to research and management is advocated.