Written by Victoria Rutherford

Ongoing work with LUCI-Ag to identify nutrient loss hotspots and mitigation solutions at a catchment scale is providing valuable learning opportunities for both Ravensdown and the Makarewa Headwaters Catchment Group in Southland.

Ravensdown’s LUCI-Ag is a decision support tool that investigates current on-farm phosphorus (P) and nitrogen (N) losses. Developed for Ravensdown by researchers at Victoria University of Wellington, LUCI-Ag identifies nutrient hotspots and pathways on spatially detailed maps, allowing for targeted mitigation investigation to determine the best approach for achieving advantageous instream water quality outcomes. This enables mitigations specific to the biophysical environment and catchment management to be explored and ranked according to effectiveness.

Thriving Southland: The Makarewa Headwaters Catchment Group LUCI-Ag project

The Makarewa Headwaters Catchment covers 412km2 and includes the Otapiri, Lora and Makarewa streams. The catchment outlet is located where the Makarewa River crosses SH96 between Invercargill and Gore, eventually feeding into the Oreti River.

The catchment area is predominantly sheep and beef, rounded out with dairy, cropping, deer and horticulture operations. The core catchment group is made up of 10–12 people, with a wider group of 40 who join in with events and projects.

Group chairperson and Otapiri Gorge farmer Alexis Wadworth says the strength of the community has been instrumental in the group’s ability to gain traction.

“One of our objectives was to be proud of what goes into the Makarewa, but more than that, we wanted to build real community around the objectives and projects. That’s helped define some of the direction and outcomes we wanted to achieve.

“We're fortunate that within our catchment we've got quite a few people who are heavily involved in the industry, including council and other related professions. They bring with them knowledge but also personal interest, helping build the direction of where we want to go.”

So far, they have looked at what the environmental standards for freshwater will mean from a practical and on-farm solution aspect as well as investigated the water quality in their catchment with help from water quality specialists.

“The key thing for us is sharing of knowledge. We've got lots of expertise within our group, but also its about helping ‘nudge thy neighbour’ in a positive way … providing the information that can help guide decisions," Alexis says.

Bringing in LUCI-Ag to inform decision making

Thriving Southland first approached the group with the LUCI-Ag project concept and Alexis says it presented as a good fit with the catchment group’s objectives.

“We thought LUCI-Ag was a good way to identify how our nutrient usage and farming practices are impacting our catchment water quality, and also to identify any changes or mitigations we could use to help improve that.”

In March 2021, work started with Ravensdown to create a LUCI-Ag project to identify N, P and sediment loss hotspots and pathways in their catchment and explore possible mitigations at a catchment-wide level. This was approved by the Thriving Southland funding panel in April and commenced July 2021. Six farms from across the catchment, including the Wadworth’s property Bare Hill, were recruited and team members from Ravensdown Environmental collected data on-farm to inform the study.

Alexis says the project gave them the chance to look at improving water quality from a different angle, such as good management practices and mitigations.

“We felt the modelling was a good way to identify opportunities and mitigations and whether they were worthwhile investing in – whether that’s fencing or sediment traps, or the impact of breaking in new ground.”

The LUCI-Ag reports were first generated for the six individual farms in the area, before being combined into a catchment wide report.

Alexis says the feedback from the six farmers was that the individual reports were both valuable and relevant for long-term planning.

On their own property, they looked at the development of some of their gorse and broom blocks.

“We got them to model [potential] development to see the impact that would have on our N and P loads from the property. It also allowed us to see how we could we mitigate that impact.

“For us, having that sort of information to hand is valuable. Should we ever start to proceed with this development, then we're armed with all the resources that we need to support consent, or for planning and budgeting at our end.”

Catchment wide modelling outcomes

The N, P and soil loss tools were run for the catchment with the aim of identifying areas of high N and P load, pathways of high N and P accumulation and areas of high soil loss. The report also identified areas where mitigation could be undertaken, suggesting actions and their likely impact.

Results from LUCI-Ag catchment modelling for the Makarewa Headwaters Catchment under current management indicate:

• The intensity of the farm system impacted N losses, with the highest N load areas on the free-draining brown soils (compared with the poorly draining gley soils). The less intense farm systems generated lower N loads, while the lowest N loads were generated under native/exotic forestry.
• The highest P load areas were on farmed sloped land underlain by pallic or other slower draining soils.
• Areas of highest soil loss are associated with harvested forest on steeper topography.
• It has been shown through individual farm reports (LUCI-Ag modelling) that fencing off waterways has resulted in significant reductions in N and P losses of 5-28% and 4-70% respectively. Further fencing work will improve individual stream N & P concentrations within the catchment.
• In a catchment scenario, 990ha of flat scrub land was intensified, and 990ha of steeper farmed land was retired. This reduced catchment P losses by 9%. Individual farm reports have shown that retiring land around streams can offset N and P losses of intensification of better land.

Follow the Makarewa Headwaters Catchment Group’s journey here: https://www.thrivingsouthland.co.nz/makarewa-headwaters/