Water resources and horticulture
How do horticultural activities potentially influence water flows?
Freshwater is a valuable renewable resource that is used for irrigation in vineyards and market gardens, and on arable and horticultural crops. Water can be pumped or diverted (via ditches, drains, and pipes) from waterways. In some parts of the country, crops cannot be grown without irrigation. In others, irrigation is used to enhance crop yield (growth).
Water take (abstraction) should be limited by minimum flow restrictions to protect mahinga kai habitats. However, changes to supply and demand may put pressure on existing resources if sustainable practices are not incorporated. Water quantity varies seasonally with, for example, variable amounts of ice melt from glaciers, rainfall, and groundwater recharge, while growers typically require a constant or increasing amount of irrigation water to maintain productivity.
Impacts of water take (abstraction) on water quality and mahinga kai
- Changes in flow - change in water levels and flow variability alters available mahinga kai habitat and the invertebrates they feed on.
- Reduction in habitat - a decrease in water levels reduces habitat for fish and can impact feeding and spawning success.
- Reduction in specialist habitats - a decrease in water levels reduces flow to riparian wetlands, backwaters, and intermittent streams.
- Decreases in species abundance and diversity - aquatic species have developed life history strategies in direct response to natural flows; for example, diadromous fish species migrate up and down waterways at various times of the year and rely on preferred velocities and depths.
- Changes in sediment accumulation - flow reduction affects movement and deposition of sediments in streams and rivers.
- Changes in water quality parameters - for example, turbidity and temperature levels can increase with reduced flows in rivers.
- Increases in algae accumulation - algae respond to changes in temperature and nutrients, which are likely to increase with reduction of flow, especially during summer months.
Applying water to land (irrigation) to improve production can result in:
- Changes to the type of crop that can be carried by the land, i.e., allow crops that need large quantities of water to be grown in arid areas with potential effects on erosion or water quality.
- Increases in effluent discharge - some irrigation practices can produce significant surface water runoff and increase the contaminant loads that reach waterways.
- Increases in nutrients reaching waterways from higher fertiliser application rates.