Nutrients and wood processing
What are the potential sources of nutrients from wood processing activities?
Wastewater from sawmills is generated by runoff from storage areas - log yards and log ponds - containing wood products like lignin, bark, and wood chips. Contaminated stormwater runoff from log yards is generated when rain comes into contact with wood, woody debris, and equipment at outdoor wood sorting, processing, and storage facilities. More runoff can also be generated when water is used to control dust or fire. Waste products are collected by water on site, which then becomes part of the runoff that can end up being washed or flushed into a waterway. These waste products produce large quantities of nutrients (nitrogen and phosphorus). An increase in nutrients will deteriorate a waterway by enhancing nuisance plant growth and algal blooms.
Similarly, wastewater effluent from pulp and paper mills contains large quantities of nutrients and chemical contaminants that need to be properly treated before discharging to any waterway. Mills incorporate secondary biological treatment that breaks down wood and plant material by forced aeration. The impact and efficiency of any wastewater treatment will depend on management practices and the level of treatment employed by the processing mills.
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.
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