Mitigating nutrient loss from pastoral farmland in the Rotorua lakes district of New Zealand

Abstract. New Zealand’s pasture-based agricultural sectors rely upon inputs of both nitrogen (N) and phosphorus (P) to sustain economic levels of agricultural productivity. However, N and P loss from farming systems are contributing to water quality issues. N loss pathways are largely via infiltration whereas most P is initially transported from farm systems as sediment to down-stream water bodies via over-land runoff. We outline an existing ‘capping’ regulation as well as a proposed new rule from the Bay of Plenty Regional Council to reduce the current nitrogen loads to Lake Rotorua from farming by 140 t y -1 and from other activities by 270 t y -1 by 2032. Lake Rotorua is a large (area 80 km 2 ), shallow (mean depth 10 m) lake in the Central Volcanic Plateau region of North Island. As well as these regulatory provisions, we examine voluntary methods used by the farming community. We discuss how the choice, scheduling and implementation of mitigations can be managed using two New Zealand farming industry-administered Environmental Management Systems (EMS); Beef + Lamb New Zealand’s Land and Environment Plan (LEP) for sheep, beef and deer farms, and DairyNZ’s Sustainable Milk Plans (SMP) for dairy farms. Both systems function as frameworks for organising and achieving continuous reductions in nutrient losses to achieve water quality targets. Both of these industry tools are considering the adoption of a proposed ‘EMS (Environmental Management System) Dashboard’ to transfer Key Performance Indices from the voluntary industry to the regulator. There is a range of available methods to reduce nutrient loss from farmland. We use Detainment Bunds (DBs) as an example of a P mitigation tool which has been implemented in the Lake Rotorua watershed. DBs pond stormwater (overland flow) for up to three days to reduce suspended sediments and particulate P