How do various activities affect our stream life?
West Coast Regional Council has basic functions under the Resource Management Act (1991) to protect and monitor the life-supporting capacity and natural character of wetlands, lakes and rivers and their margins as well as significant habitats for indigenous fauna and trout and salmon. The aim of this study was to compare the diversity and abundance of macro-invertebrates and fish in farmland streams of varying habitat condition caused by various activities. The study also aimed to estimate the regional extent of stream habitat modification in farmland.
Farmland streams were selected along with some reference forest streams chosen because:
- There is relatively little existing information about fish biodiversity or the rate or extent of stream habitat modification in farmland streams on the West Coast.
- Most of the activities that modify stream habitat are represented in farmland, particularly dairy farmland.
- Various activities associated with agricultural development in other regions have been found to cause very significant declines in native fish populations which suggests that there is a risk in this region also.
- There is a large proportion of stream length potentially affected by agricultural land use.
Stream habitat was assessed using the following physical and chemical factors:
Channel and bank form, bank stability, bed substrate composition, water quality (conductivity, temperature and pH), and amount and type of riparian vegetation. On the basis of water quality measurements and knowledge of the location of point-source discharges, any polluted streams were excluded from sampling of macro-invertebrates and fish. Additional data from the National Fish Database and the West Coast Regional Council Macroinvertebrate Database were used in the analysis.
57.5 stream kilometres were assessed on 40 1st - 4th order, permanently flowing streams between August and October 2001. Periphyton percentage cover and the abundance and diversity of macro-invertebrate species were measured at all 40 streams. Fish abundance and diversity was measured at 28 sites.
For data analysis stream reaches assessed were divided into four disturbance classes (1 being the most highly modified), based on the following criteria: stream channelisation and straightening, amount of riparian vegetation that has been disturbed or removed and restriction of stock access.
Riparian vegetation associated with farmland streams approximately two thirds of the assessed streams was highly or moderately modified. Channelisation (evening of stream depth and width and battering of stream banks) was very common. Extensive straightening was only found in only two stream reaches. From observations the presence of significant trampling of the stream bed and banks appears to be highly correlated with farming type (eg. intensive dairy or extensive dry-stock farming). Rotational strip or mob-stocking seemed to give rise to the most extensive damage to the stream bed or banks. Fencing of cattle into narrow strips along the stream bank/beds was not common.
Macro-invertebrate diversity and abundance appears to be largely unaffected by stream habitat disturbance on the West Coast. This may because of recruitment by downstream drift from headwater tributaries and aerial colonisation from forested streams, which are never far from disturbed streams and/or bottom substrate is generally suitable.
Regardless of the degree of modification, most stream sites sampled sustained reasonable numbers and diversity of across all fish species. However, within a particular stream reach with disturbance class as 1, 2 or 3, there appeared to have poor communities of sensitive native fish such as Banded Kokopu, Shortjaw Kokopu, Giant Kokopu and Koaro. Trout communities appeared to be only affected by high to moderate levels of stream habitat modification. More information would be needed to determine the relationship between trout density and stream habitat modification and trout density and density of sensitive native fish.
Click here to download the Stream Habitat Assessment Report (450kb PDF)