Investigating the reasons for decreasing phosphorus concentrations in many waterways
Project Details Ngā taipitopito
Collaborators Ngā haumi
AgResearch | Ballance Agri-Nutrients | Land & Water Science | Massey University | Ministry for the Environment
Fertiliser and farm dairy effluent contain phosphorus, which can enter freshwater via runoff or leaching from agricultural land. In freshwater, phosphorus can stimulate algal growth, leading to impairment of water for swimming, fishing, drinking, and reduced biodiversity.
Algal growth in New Zealand streams and rivers is widespread due to agricultural phosphorus, but in many areas the concentration of phosphorus in our waterways is decreasing.
Phosphorus has decreased at over 40% of measured sites in streams and rivers since 1994, and 65% of sites since 2004, despite an increase in national dairy cow numbers by 26% and the expansion of dairying into areas previously used for sheep farming.
The research investigated the possible factors contributing to reductions in phosphorus concentrations at these sites. We found the 3 most probable causes for improvement were that on-farm strategies were mitigating phosphorus loss from land, industry guidelines were directing where to best use strategies (for example, in critical source areas), and phosphorus was being mentioned more in policy instruments.