Many of our rivers and streams have changed dramatically since European settlement. They have been dammed, had water pumped out for irrigation, been diverted, waste discharged into them, had discharges from land run-off, intensive stock grazing in and around the waterways and invasive plants have been introduced.
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:
The greatest potential effect from forestry is fine sediment discharges to streams and the coast from roading and for two years after harvesting. An additional effect is the reduced water yield (reduced flow in streams), particularly in summer, due to the increased rate of evaporation and transpiration from pine trees. Harvesting large catchments within a short duration 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, there have been several rainfall-induced events that have caught these companies out and large sediment discharges to streams has resulted.
Studies in the late 1990's in Separation Point granite areas (Land Disturbance Area 1) showed 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 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 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, such poor water quality exists in catchments whose land area is dominated by intensive farming eg Motupipi, Sherry, and Mackay. Flood-flow monitoring shows typically 10-100 times greater concentrations of disease-causing organisms from farm run-off.
In the Aorere River, an improvement in water quality is evident and mussel farmers operating in the sea a few kilometers off the mouth of the river have experienced far fewer closures as a result of these organisms.
E.coli concentrations in the Sherry River have halved since installing bridges and fencing since 2004.
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.
The very few farmers who have ignored the rules regarding effluent discharges have been forced by the environment court to upgrade in order to improve water quality.
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 highest risk in much of Tasman is in late December to February when there are the greatest numbers of holiday-makers present in the district.
Resource consent monitoring of STPs generally shows 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 Takaka 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 hoped that these discharges can be improved in the near future.
Department of Conservation have installed new STPs at most of the popular huts and 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 washings of cement, vehicles, paint, petroleum products and pesticides. Stream life can also be adversely affected by the altered flow regime in streams due to the high percentage of impervious surface in urban catchments. 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.