Many of our rivers and streams have changed dramatically since European settlement. Waste and runoff discharge, water diversions for irrigation, construction of dams, livestock grazing, and invasive plants have all contributed to these waterway changes.
The land draining into these rivers (their catchment area) has been cleared for agriculture, forestry and urban development. This all leads to an increase in the amount of run-off entering rivers and streams which affects the quality of the water. Many of our rivers and streams are probably in better condition now than they were half a century ago due to increasing awareness of land and water management practices. However, they continue to be affected by pollution from a variety of sources, including:
The greatest potential effect from forestry is fine sediment discharge into streams and coasts which becomes a ongoing issue for years post-harvesting. An additional effect is the reduced water yield (less flow in streams), particularly in summer, due to the increased rate of evaporation and transpiration from pine trees. Harvesting large catchments within a short time period can also lead to extensive bank erosion and stream habitat disturbance due to flooding.
In general, there has been a significant improvement in sediment and erosion control by larger forest management companies in Tasman in the last 20 years. Despite this, several rainfall-induced events have caught these companies out and large sediment discharges into streams have resulted.
Studies in Separation Point granite areas (Land Disturbance Area 1) have shown that harvesting in larger catchments increased sediment yields by 7-10 times the pre-harvest rates. Harvesting in Graham Creek near Kikiwa, produced very little effect on water quality during base flows, or fine sediment bedload, compared to the neighbouring Moutere Gravel catchments.
In order to reduce the potential negative environmental impacts of forestry, most of the larger forestry companies operate other environmental protection systems, such as the ISO14000 quality system in addition to the rules in the Tasman Resource Management Plan. Under this system, any identified environmental issue caused by the company requires an investigation involving agencies such as Council. Several of these companies now have Forest Stewardship Council certification that has strict environmental performance standards that also must be adhered to.
Intensively-farmed land has a high potential to produce high levels of disease-causing organisms, fine sediment and in some cases, nutrients, in downstream waterways. Cows in creeks, mobs of stock crossing creeks, effluent discharges, and pasture run-off are the biggest sources of these contaminants.
In general, this poor water quality exists in catchments where land is dominated by intensive farming practices, e.g. Motupipi, Sherry, and Mackay catchments. Our flood-flow monitoring has shown 10-100 times greater concentrations of disease-causing organisms from farm run-off.
Since 2005, when the 'Dairying and Clean Streams Accord' was signed in Tasman, very steady progress has been demonstrated by the dairy farming industry towards fencing streams, bridging stock crossings, and upgrading effluent treatment systems. Upgrades in these areas can lead to promising changes. For example, E.coli concentrations in the Sherry River having halved since the installation of bridges and fencing in 2004.
More information regarding the application of fertiliser and pesticide products while following council regulations can be found below:
Sewage discharges from town sewage treatment plants (STPs) or household septic tanks can cause elevated levels of disease-causing organisms and toxic ammonia in streams and the coast. The timeframe of highest risk in much of Tasman is from late December to February when there are the greatest numbers of holiday-makers present in the district.
Resource consent monitoring of STPs generally show a high level of compliance. Several small townships without a community STP, such as Tasman, experience contaminated groundwater or waterways, particularly during periods with high groundwater levels.
Most of the district's townships have had significant upgrades to their STPs and the effects of the discharges are controlled. Raw sewage overflows from sewerage pipelines such as from Pōhara to Tākaka are much less frequent than in the past.
The Motueka STP located near the mouth of the Motueka River is one of the last to receive such an upgrade and it is scheduled to take place in 2023, which will help improve issues with discharges.
Department of Conservation have installed STPs at most of the popular huts and campgrounds in Abel Tasman National Park.
Runoff from roads, roofs, and areas popular for dog-walking appear to be the biggest water quality issues in Richmond. However, there are many other contaminants that get tipped down drains in urban areas that have had noticeable effects. From domestic households these include:
Stream life can also be adversely affected by a high number of sealed surfaces in urban catchments causing changes in flow regime. This causes increased bed and bank disturbance during and after rain, and reduced flows in dry periods.
Levels of zinc, copper and chromium are generally the most concerning contaminants in Richmond's waterways. Council engages in on-going education activities with households and industry on this issue as well as actively monitoring facilities storing or using hazardous substances.
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