Nutrients and horticulture
What are the potential sources of nutrients from horticultural activities?
Repeated cultivation and harvesting of the soil for crop production can increase surface runoff. Surface runoff often carries high sediment loads and nutrients, especially following heavy rain on exposed soils.
Excess nutrients from fertiliser applications can also end up in waterways when soils are cultivated to the water's edge or if they leach through the soil. Herbicides and pesticides used on crops to control weeds and insect pests (chemical contaminants) can pollute nearby waters if used too close to waterways. Nutrients, herbicides, and pesticides are less likely to contaminate waterways when riparian vegetation is maintained as a buffer between productive land and an adjacent stream, river, or estuary.
Potential impacts of high nutrients on water quality and mahinga kai
- Eutrophication - excess nutrients in lakes, estuaries, or slow-moving streams and rivers can lead to an increase in primary productivity (excessive plant and algal growth) that degrades water quality.
- Loss of species - an increase in plant growth, sometimes called an algal bloom, reduces dissolved oxygen (DO) in the water when dead plant material decomposes and can cause organisms (fish and invertebrates) to die. If this cycle happens repeatedly, species may be lost from the lake or waterway.
- Loss of habitat - eutrophication of the water can kill off plants that fish depend on for their habitat and alter the lake bed habitat for invertebrate species.
- Increased turbidity and decreased visibility - when algae increase in response to nutrients this reduces water clarity, visibility, and recreational suitability. It also reduces the ability of some fish to see prey or predators.