New Zealand has many water bodies with good water quality, but these tend to be in areas of native forest or areas with little impact from human activities. The human occupation of New Zealand has resulted in the spread of urbanisation and agricultural activities, including the move to high-intensity agriculture over recent decades. Some changes in land use are associated with compromised water quality in some rivers, lakes, and groundwater.
Efforts to improve water quality in the 1950s and 1960s focussed on managing and reducing point source discharges, particularly wastewater discharges and treatment plants (Campbell et al, 2004). While reducing point-source discharges was beneficial, diffuse discharges of sediment, nutrients, and other contaminants are still degrading water quality. Using land for agriculture is the greatest contributor of diffuse discharges globally; however, since diffuse discharges are hard to measure and trace, it is difficult to establish cause-and-effect relationships between land use and water quality (Campbell et al, 2004).
New Zealand’s population and agriculture-based economy are growing, and it is expected that high-intensity agriculture and urbanisation will continue to expand to new areas, potentially affecting water quality in more water bodies. Climate change is also predicted to put additional pressure on the quality of our fresh water, including increased water temperatures in some areas, which may reduce levels of dissolved oxygen and potentially increase the occurrence of algal blooms (Reisinger et al, 2014). Although substantial effort was directed at monitoring and reducing diffuse sources of contaminants with some success (eg McDowell et al, 2013), the legacy of contaminants from past land uses remain, meaning we may still see the impact of previous land uses on our water bodies in the future (Morgenstern et al, 2015).