Key Points

Aslan Wright-Stow, environment and catchment manager, DairyNZ.

Dr Tom Stephens, (previously DairyNZ), senior freshwater specialist, Auckland Council.

On-farm studies confirm that riparian management:

• improves water quality, by intercepting contaminants before loss from the farm to water
• can be highly effective over three- to five-metre buffers of grass or plantings (natives or willow and poplar)
• improves fish and invertebrate habitat, by stabilising banks, providing shade, cooling water and enhancing oxygenation.

Get hassle-free guidance in the Riparian Planner – dairynz.co.nz/riparian-planner

One of the goals of riparian fencing and planting is to improve water quality. Planting leads to a wide range of environmental benefits (such as improved fish and insect life habitats). However, it also makes good sense economically and from an animal welfare perspective, as it reduces the chances of stock injury or loss from cows falling into unfenced waterways.

It’s also important to remember that riparian management doesn’t replace good management practices such as effective nutrient budgeting and ensuring sufficient effluent storage for keeping contaminants out of water – rather, it complements them.

That’s why DairyNZ’s levy-funded research on improving water quality aims to help farmers understand why water quality is important, how riparian planting can help them to meet catchment limits and what the full range of benefits from it are. Our development of various riparian planting-related resources and tools also aims to make it easier for farmers to carry out riparian fencing and planting on their properties.

In this article, you’ll find out what riparian management is, and how science confirms its beneficial effects on water quality. You’ll also read about some of the tools farmers are using to include riparian management as part of their overall farm approach and planning. We’ve also provided a few tips on identifying where plantings will have the best effect and outlined where you can get information, guidance and support on establishing riparian planting on your farm.

What is riparian management?

Riparian management covers a lot more than just planting. It includes stock exclusion, vegetating excluded margins, and maintaining what you’ve planted against weeds, bankside erosion and natural events (e.g. floods). Whether you plant natives or exotics or just leave the grass to grow rank depends on the water quality issue being addressed. Using just grass filters in many farm situations is likely to deliver a cost-effective strategy for water quality but less so for biodiversity. Also, whether planting natives or exotics, it’s not necessarily the type of plant that’s the issue, it’s also about the ecosystem processes they regulate (for example, filtering, uptake, stabilisation, provision of shade) and the outcomes desired.

Effects of riparian management

Water quality

As we mentioned earlier, riparian management can improve water quality, which in turn benefits our native fish and insects, but more broadly, affects many other values such as biodiversity and on-farm aesthetics. The effects of riparian margins on contaminant loss, whether the planted areas are grass or native plantings, vary with slope, soil type, climate and setback width. However, water quality benefits for filtration and contaminant uptake tend to reduce rapidly after five to 10 metres, with most filtration or deposition occurring within the first few metres from a fence^{1, 2, 3}.

Research has demonstrated that riparian management can help reduce the amount of nutrients (phosphorus, P; and nitrogen, N), sediment and faecal pathogens (E. coli) entering the water^{4, 5, 6}. For instance, livestock exclusion on Southland dairy farms has been linked to a 20 percent reduction in (E. coli) contributions and a 40 percent reduction in P loss. Those estimates vary between farms, but they’re driven by reduced bank disturbance and stock defecation directly into water⁷.

For nutrient and sediment lost in overland runoff, rank grass can generate equivalent or better reductions in these contaminants as native planted margins^{3, 4, 8, 9}. An  international review found grass filters of five metres can reduce N, P and sediment loss by 54 to 74 percent, while a study in the Bay of Plenty reported grass filters of three metres can reduce N, P and sediment loads by 35 to 87 percent^{3, 8}.

Physical habitat, bank stability and biodiversity

Planting natives or sterile willows and poplars (available from most regional councils) is generally of greater benefit than grasses and sedges when it comes to reducing riverbank erosion or enhancing biodiversity^{10, 11}.

Other studies have shown riparian vegetation benefits water quality by stabilising banks, removing and filtering contaminants, providing shade and, therefore, cooling water temperature. Temperature is a key constraint on the in-stream oxygen available to native fish and invertebrate communities^{12, 13, 14}. Shading can also effectively prevent nuisance algal growths on small-to-moderate channels (four to five metres wide)^{4, 13}.

Be aware though, many studies caution of long timeframes needed to see improvements tied to riparian plant growth rates. That’s because of a legacy of fine sediment already in waterways from two centuries of land use. It’s also affected by the time needed to re-colonise insects and fish to healthier waterways. These waterways need to have the in-stream habitat complexity that insects and fish need to support their sensitive populations^{4, 6}.

For example, wood in a stream might be critical to biodiversity, but grass filters – that don’t survive under heavy shade – actually provide suitable spawning environments for many native Galaxiid fish^{6, 15, 16, 17, 18}. The scientific community is investing heavily to better understand how to best improve habitat and connectivity, not just the geochemistry or physical condition of water.

Wetland riparian management

Wetlands are unique environments. Their chemistry and hydrology are ideal for treating nitrogen in shallow subsurface and runoff from dairy farms^{19, 20, 21}. Wetlands sometimes contain open water but typically are smaller areas where ponding quickly occurs and remains after rainfall, where springs emerge and where soils are generally saturated. You’re likely to recognise these areas on your farm as locations that pug easily.

The vast majority of wetlands on pastoral land (90 percent) have been drained over the past 200 years²². That’s undoubtedly contributed to historic water quality degradation, but it also means many farms will have areas suitable for wetlands re-establishment.

Wetland contaminant reduction

A wetlands ’denitrification’ process involves bacterial communities converting nitrate into harmless nitrogen gas before it can reach a waterway. A recent review of scientific studies in New Zealand found that wetlands can reduced the nitrate entering them by 75 to 98 percent^{21, 23, 24, 25, 26}.

Sediment and phosphorus trapping

Wetlands are also great for trapping sediments and sedimentbound phosphorus^{5, 27, 28, 29}. Through the levy paid by dairy farmers, DairyNZ, along with the National Institute of Water and Atmospheric Research (NIWA) and regional councils, are investing in science to further refine these estimates so they can determine the potential for wetlands to be re-established on farms. Once we have this information, we can help farmers contribute to addressing the total reduction in contaminants achievable through wetlands management in New Zealand.

Using the research and tools

Dairy farmers and tools in action

The most recently published data available at the time of writing this article shows more than 98 percent of waterways more than a metre wide on dairy farms had been fenced to keep out stock³⁰. The next step involves farmers creating a farmspecific riparian plan to show council and milk processors what has been achieved, and plan fencing and planting for smaller waterways.

One of the ways you can do this is to use DairyNZ’s Riparian Planner, which has been used by 2200 dairy farmers so far with great success. The Riparian Planner allows you to map waterways and wetlands, and plan and cost additional fencing and planting³⁰.

We’ve developed this tool with regional councils and Manaaki Whenua. It includes regionalised riparian planting guides and it’s currently undergoing further development to enable user-defined data-sharing with regional councils and milk suppliers. This will simplify Farm Environment Plan reporting requirements.

Ongoing research

Further studies aim to increase riparian effectiveness, quantify the performance of constructed wetlands and buffers that specifically target overland flow runoff (critical source areas) and reward farmers for their efforts through regulatory-recognised nutrient credits. We are also working with partners including Manawatu’s regional council, Horizons, and Sustainable Wairarapa to carry out a study into grass filter effects, and investigating the potential to engineer floodplain management through two-stage channels (see our Tech Series December 2018 article and podcast) to reduce contaminants carried by flood-flows, so we’ll be keeping a close eye on the results of those, as well.

Taranaki's riparian efforts pay off

The Taranaki region has the longest history of recognising and using riparian management as a tool for mitigating the effects of land use. Established in 1993, the region’s riparian programme has seen more than 4100 kilometres (km) of streambank fenced, including more than 2300km planted.

Aquatic macroinvertebrates (insects) are often used as an indicator of water quality, because they integrate water quality and habitat conditions over time and respond to pressures in a predictable way. Out of 57 monitoring stations, none reported a statistically significant decline from 1995 to 2014 for insect health. Better yet, 30 were found to have improved significantly over this period³¹.

These changes are centred on lowland and middle catchments where land use is most intense and with its impacts likely to be greatest. Given our understanding of insect health, the reductions in sediment loss and decreasing temperatures, together with more diverse in-stream habitats and food supply reflected in these changes, can be linked to the adoption of riparian action plans on farms in those areas.

Riparian tips

Before using the Riparian Planner, assess your property next time it rains heavily. Look for overland flow across your paddocks. Consider whether this can be slowed with riparian buffers before it reaches a waterway, and whether wetlands could be re-established in low-lying areas on your farm. Aligning fences smartly to take in those ‘critical source’ areas increases the ability for rank grass or native plant communities to then filter out nutrients, sediment and faecal pathogens.

Accessing tools, guidance and support

DairyNZ’s website has plenty of information, resources and tools related to environmental sustainability, improving water quality and carrying out riparian planting. Go online to dairynz.co.nz – you’ll also find our Riparian Planner at dairynz.co.nz/riparian-planner

Talk to your local DairyNZ consulting officer (contact details at dairynz.co.nz/co) and/or your regional council for more information and guidance on water quality, riparian planting and regulatory compliance and support.

References

1. Collier, K., A. Cooper, R. Davies-Colley, K. Rutherford, C. Smith, and R. Williamson. 1995. Managing riparian zones: A contribution to protecting New Zealand’s rivers and streams. Department of Conservation, Wellington.
2. Gharabaghi, B., R. Rudra, H. Whiteley, and W. Dickinson. 2002. Development of a management tool for vegetative filter strips. Best modelling practices for urban water systems. Volume 10 of Monograph Series: 289-302.
3. McKergow, L., K. Costley, and G. Timpany. 2008. Contour grass filter strips: hydrology and water quality. NIWA Client Report: HAM2008-134. Available at: https://www.boprc.govt.nz/media/32593/NIWA-100203-Countourgrassfilterstrips.pdf
4. Parkyn, S. 2004. Review of riparian buffer zone effectiveness. MAF Technical Paper No:2004/05.
5. Quinn, J., and L. McKergow. 2007. Answers to frequently asked questions on riparian management. NIWA Client Report: HAM2007-072.
6. McKergow, L., F. Matheson, and J. Quinn. 2016. Riparian management: A restoration tool for New Zealand streams. Ecological Management and Restoration 17:218 227.
7. Goldsmith, R., D. Olsen, and G. Ryder. 2013. Environmental effects of activities within the riparian zone: Technical review. Ryder Consulting Client Report for Environment Southland.
8. Dillaha, T. A., R. B. Reneau, S. Mostaghimi, and D. Lee. 1989. Vegetative filter strips for agricultural non-point source pollution control. Transactions of the American Society of Agricultural Engineers 32: 491-496.
9. Collins, R., A. Donnison, C. Ross, and M. McLeod. 2004. Attenuation of effluent-derived faecal microbes in grass buffer strips. New Zealand Journal of Agricultural Research 47:565-574.
10. Basher, L., A. Manderson, I. McIvor, L. McKergow, and J. Reid. 2016. Evaluation of the Effectiveness of Conservation Planting and Farm Plans: A discussion document. Landcare Research Client Report for Greater Wellington Regional Council.
11. Hughes, A. 0. 2016. Riparian management and stream bank erosion in New Zealand. New Zealand Journal of Marine and Freshwater Research 50:277-290.
12. Quinn, J., A. Cooper, R. Davies-Colley, K. Rutherford, and R. Williamson. 1997. Land-use effects on habitat, periphyton and benthic invertebrates in Waikato hill country streams. New Zealand Journal of Marine and Freshwater Research 31:579-597.
13. Davies-Colley, R., and J. Quinn. 1998. Stream lighting in five regions of North Island, New Zealand: control by channel size and riparian vegetation. New Zealand Journal of Marine and Freshwater Research 32:591-605.
14. Olsen, D., L. Tremblay, J. Clapcott, and R. Holmes. 2012. Water temperature criteria for native aquatic biota. Auckland Council Technical Report 2012/036.
15. Richardson, J., and M. Taylor. 2002. A guide to restoring inanga habitat. NIWA Science and Technology Series No. 50, Wellington.
16. Parkyn, S., R. Davies-Colley, N. Halliday, K. Costley, and G. Croker. 2003. Planted riparian buffer zones in New Zealand: Do they live up to expectations. Restoration Ecology 11:436-447.
17. Quinn, J. 2009. Riparian Management Classification Reference Manual. NIWA Client Report: HAM2009-072.
18. Mahuta, R., C. van Schravendijk-Goodman, and C. Baker. 2016. Matamata - eating with our tipuna. Pages 107-117 in Te Reo o Te Repo – The Voice of the Wetland. Chapter 5.5. Y. Taura, C. van Schravendijk-Goodman, and B. Clarkson, eds. Manaaki Whenua – Landcare Research and the Waikato Raupatu River Trust.
19. Cooper, A. 1990. Nitrate depletion in the riparian zone and stream channel of a small headwater catchment. Hydrobiologia 202:13-26.
20. Burns, D., and L. Nguyen. 2002. Nitrate movement and removal along a shallow groundwater flow path in a riparian wetland within a sheep-grazed pastoral catchment: Results of a tracer study. New Zealand Journal of Marine and Freshwater Research 36:371-385.
21. McKergow, L. A., A. O. Hughes, and K. Rutherford. 2017. Seepage wetland protection review. NIWA Client Report: 2016048HN.
22. Ausseil, A., J. Dymond, and E. Weeks. 2011. Provision of natural habitat for biodiversity: quantifying recent trends in New Zealand. Pages 201-220 in Biodiversity loss in a changing planet. Chapter 9. O. Grillo, ed. InTech Open Access. ISBN: 978-953-307-707-9. Available at: http://cdn.intechopen.com/ pdfs/23610/InTech Provision_of_natural_habitat_for_biodiversity_ quantifying_ recent_trends_in_new_zealand.pdf
23. Rutherford, K., A. O. Hughes, and L. A. McKergow. 2017. Review of Nitrogen Attenuation in New Zealand Seepage Wetlands. NIWA report prepared for DairyNZ. NIWA Client Report No: 2017241HN.
24. Gilliam, J. 1994. Riparian wetlands and water quality. Journal of Environmental Quality 23:896-900.
25. Fennessy, M., and J. Cronk. 1997. The effectiveness and restoration potential of riparian ectones for the management of nonpoint source pollution, particularly nitrate. Critical Reviews in Environmental Science and Technology 27:285-317.
26. Ranalli, A., and D. Macalady. 2010. The importance of the riparian zone and instream processes in nitrate attenuation in undisturbed and agricultural watersheds – A review of the scientific literature. Journal of Hydrology 389:406-415.
27. Nguyen, L., M. Downes, M. Melhorn, and M. Stroud. 1999. Riparian wetland processing of nitrogen, phosphorus and suspended sediment inputs from a hill-country sheep-grazed catchment in New Zealand. Pages 481-486 in Proceedings of the Second Australian Stream Management Conference, Adelaide. I. Rutherfurd, and R. Bartley, eds. CRC for Catchment Hydrology, Melbourne.
28. McDowell, R., R. Biggs, A. Sharpley, and L. Nguyen. 2004. Connecting phosphorus loss from agricultural landscapes to surface water quality. Chemistry and Ecology 20:1-40.
29. Tanner, C., and J. Sukias. 2010. Nutrient capture by watercress beds, Lake Rotorua. Pages 142-151 in Farming’s Future: Minimising footprints and maximising margins. D. Currie and C. Christensen, eds. Fertilizer & Lime Research Centre, Palmerston North.
30. DairyNZ. 2017. Water Accord Three Years On. Progress report for the 2016/16 season. DairyNZ, Hamilton. Available at: https://www.dairynz.co.nz/media/5787294/water_accord_report_3_years_on_web.pdf
31. Taranaki Regional Council. 2017. Freshwater Macroinvertebrate Fauna Biological Monitoring Programme Annual State of the Environment Monitoring Report 2015-2016. Technical Report 2016-33. Stratford, Taranaki. Available at https://www.trc.govt.nz/assets/Documents/Environment/Monitoring-SOE/Freshwater-MCI/SEM-MCI16-w.pdf

This article was originally published in Technical Series April 2019