Integrated Catchment Management Research
The Motueka River catchment is about 2,200 sq.km that extend from sea level to 1600m and is the source of most of the fresh water going to Tasman Bay. Annual rainfall is around 1400mm. Mountainous areas in the catchment are mostly native bush reserve, rolling to steep hill country is grazed or in plantation forest, and the fertile alluvial plains support diverse horticulture operations. The river itself is a significant brown trout fishery but over the past 20 years the numbers of adult trout have reduced by two-thirds.
Tasman Bay is also a significant scallop, cockle and oyster fishery, and there is a rapidly expanding mussel aquaculture industry.
The catchment is sparsely populated with the biggest town, Motueka, containing around 12,000 people. Maori have a strong interest in the management of the catchment and Tasman Bay, and have a marae in Motueka township.
Dr Andrew Fenemor is involved in an Integrated Catchment Management Research programme in the Motueka catchment. It is is aimed at answering questions like: how does local land use affect the availability and quality of ground and surface water over the whole catchment, how has it changed, and how should it be managed? What is the source and effect of sediment on trout and native species, and how can that be mitigated? How do land activities affect marine farming production? And importantly, how do people assimilate and use scientific knowledge to make management decisions, how can scientists, resource managers, iwi and the general community interact better, what lessons can be learned from iwi about the environment, and how do they all work together for win-win sustainable management solutions?
The goal of the Integrated Catchment Management programme in general is to improve the management of land, freshwater, and near-coastal environments in catchments that have potentially conflicting land and water uses. The strategy is to involve scientists, local authority staff, farmers, foresters, horticulturists, marine farmers and iwi and other stakeholders in owning the problems and finding ways to improve the management of the area.
This combined approach is designed specifically to improve interactions between scientists and the community, to publicise the findings and facilitate the adoption of new tools and technology.
The Motueka programme has been going for nearly seven years and some of its activities have been reported on Rural Delivery, such as the Sherry River project, that has seen substantial improvements to stream and river water quality through stock bridges over waterways, and riparian fencing and planting. More recently a move towards developing an environmental plan for individual farms, identifying ways in which farming practices can be improved to reduce the impact on water quality in the river system.
Initially, research focused on water availability and sediment generation. Work is being done on nutrient and pollutant dynamics, the values and opportunities for riparian management and restoration, the impacts of gravel extraction, and the development of new models of land-river-coastal interactions.
The intention long term is to develop a catchment perspective that includes cultural, economic, and political as well as scientific considerations and base management strategies on that.
Dr Paul Gillespie is a marine scientist in the Coastal and Freshwater Group at the Cawthron Institute in Nelson. He has been involved in studies of the Motueka River and its impact on the bay that show the river plume affects 50 square kilometres of seabed and a variable but much larger area of seawater conditions. As well, three aquaculture management areas are within the area influenced by the river plume. Shellfish production is increased by nutrients in runoff. Sediment loads can have a negative effect on aquatic life. Sediment can contain high concentrations of unexpected contaminants from natural sources, particularly Nickel (Ni) and Chromium (Cr).
A 50-year flood in 2005 brought down a load of sediment from a mineral belt in the upper catchment, and now the area where it settled to the seabed contains high levels of Ni and Cr.
"There has been a decrease in the number of animal species and their densities within the plume environment, but we don't know whether that is due to the metals or to suspended sediment or something else. The metals aren't readily taken up into shellfish so there is no concern for humans consuming shellfish from the region, which is the good news, but they could be having an effect on the types of animals that live there naturally.
"We have to consider the river plume as an integral part of the catchment in order to develop a river plume concept for managing coastal environments found throughout New Zealand, and improve the management of these areas by considering the input from the land.
"Dredging and trawling have an effect too, and they need to be considered in the same way we would consider catchment land uses like horticulture or forestry or dairying.
"Bacterial loads are going to be periodically higher depending on rainfall, and at present we can't trace bacterial contamination back to the source. However, we are working on developing a procedure called Microbial Source Tracking that will allow us to identify the source of bacterial contaminants in shellfish as humans, animals such as cattle or sheep, or birds. This is an important issue because harvesting days are reduced dramatically in Golden Bay because of faecal bacterial levels in the water."
Barney Thomas belongs to a very active iwi group from local tribes that is carrying out cultural health monitoring for the river, bringing their own lens to bear at different places in the river system and in some cases coming up with a different perspective to the physical monitoring of western science.
Iwi have identified some of the occupation sites, harvesting sites along the river, and are concerned with the mauri or carrying capacity of the river, the life in and around it, and the potential for harvest. They have developed their own GIS system and now measure the rivers health at various sites using a cultural river health index developed by Ngai Tahu.
This view takes into account the bush surroundings of the river, overhanging trees giving shade, what water was being taken from it and what discharged to it, and birds, insect and fish species living in and around the river. They assess various aspects at a dozen sites, scoring them on a 1 to 5 scale. The result is an integrated and holistic assessment that can accurately predict the results of laboratory testing.
Iwi also believe that people who take from the river should give something back, for example, if they take water, perhaps they should plant native species along river margins, and so see themselves having a guardian role.