The paper “Responses of stream macroinvertebrates and ecosystem function to conventional, integrated and organic farming” has just been published in the British Ecological Society’s prestigious Journal of Applied Ecology, providing the results of the first known study to investigate and compare the effects of these three farming practices on streams.
The paper shows that conventional farm streams demonstrated the strongest negative responses while, unexpectedly, the conditions of organic and integrated farm streams were similar to each other.
An integrated management system aims to reduce or eliminate the use of pesticides, increase beneficial pest predators, and encourage environmentally responsible soil, water and energy management.
Zoology PhD student Francis Magbanua and two of his supervisors, Research Fellow Dr Christoph Matthaei and Professor Colin Townsend, collaborated on the paper with Dr Grant Blackwell of both the University’s Centre for the Study of Agriculture, Food and Environment and the Agricultural Research Group on Sustainability*, and Dr Ngaire Phillips of the National Institute of Water and Atmospheric Research.
“The common assumption is that organic farming practices have the least impact on streams,” says Dr Matthaei. “But we found integrated farm management has a similar effect on stream health.”
The research focused on 15 streams (five each subject to conventional, integrated and organic practices) within farms near the South Island towns of Amberley, Akaroa, Outram, Gore and Owaka. All were in agricultural land dedicated to the relatively non-intensive farming of sheep and beef cattle on pasture.
Information was gathered on riparian management (fencing, stock access, stock presence, presence of regenerating woody vegetation) and bank vegetation (percentage of bare ground, pasture, tussock, scrub and trees).
Mr Magbanua measured the impacts of the different farm management styles on stream ecosystem functioning, water quality, biodiversity, and the abundance and diversity of pollution-sensitive macroinvertebrate species, i.e. mayflies, stoneflies and caddis flies. He also calculated the Macroinvertebrate Community Index or MCI, which weighs the presence or absence of invertebrate species according to their tolerance to pollution.
Dr Matthaei says, “The diversity of macroinvertebrates is a key indicator of stream health, and the MCI results revealed that, while all these streams are polluted to some extent, conventional farming was most damaging, and the integrated and organic farms were very similar in their effect.”
The paper notes, “Integrated and conventional farms received similar fertilizer and pesticide inputs but nutrient and pesticide concentrations in integrated farm streams were generally low and more similar to organic than conventional farm streams. This may reflect greater care taken over the timing of inputs by farmers who follow integrated farming prescriptions.”
The paper goes on to state, “Because they combine the effects of a multitude of stressors arising from agricultural activity in their catchments, stream ecosystems can play an important role as landscape-scale indicators of the ecological effects of farming practices.”
But not all is well in streams running through integrated and organic farms. In spite of their positive assessment of these farming practices compared to conventional farming, the research team also recommends that, “as the MCI index showed streams in all categories to be ‘moderately polluted’, increased attention to fencing, riparian management and stream habitat is also needed to achieve a ‘best practice’ regime.”
*Agricultural Research Group on Sustainability (ARGOS) is an unincorporated joint venture between the Agribusiness Group, Lincoln University, and the University of Otago.
For more information contact
Francis Magbanua (currently overseas)
Dr Christoph Matthaei
Department of Zoology
University of Otago
Tel 64 3 479 5863