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Our Freshwater State of the Environment report 2012 | Our freshwater Surface water quality OUR Northland has an extensive network of rivers flowing and muddy because the land is FRESHWATER and streams. None of them are considered dominated by deeply weathered geology and major on a national scale as Northland's fine clay soils. narrow land mass means most rivers are relatively short with small catchments. Most of Northland also has a large number of small, the major rivers flow into harbours, rather than shallow lakes and associated wetlands. Most discharging directly to the open coast which of these have been formed between stabilised means contaminants tend to take longer to sand dunes on the west coast. These dune disperse from these sheltered environments. lakes are grouped on the Aupōuri, Karikari and Poutō peninsulas. Most are between five and The Northern Wairoa River is Northland's 35 hectares in area and are generally less than largest river, draining a catchment area of 15 metres deep. However, Lake Taharoa of the 3650 square kilometres, or 29 percent of Kai Iwi group near Dargaville is one of the Northland's land area. largest and deepest dune lakes in New Zealand. It covers an area of 237ha and is 37m Flows in rivers vary considerably with rainfall deep. There are also a few volcanic and man- and high intensity storms causing flash floods, made lakes. Northland’s largest lake is Lake while prolonged dry spells lead to very low Ōmāpere, which is 1160ha in area and located flows in many smaller catchments. Northland’s to the north of Kaikohe. rivers are generally characterised as being slow Northern Wairoa River – Northland’s largest river 52 152 152 15 State of the Environment report 2012 | What do we want for water quality in Northland? The operative Regional Policy Statement for The operative Regional Policy Statement also Northland details existing council and states anticipated environmental results as a community objectives for each natural and consequence of implementing the policies and physical resource in our region. The objectives methods for achieving the water quality OUR FRESHWATER relating to water quality are: objectives: · The maintenance or enhancement of the · Water quality is suitable for desired water quality of natural water bodies and purpose. coastal waters to be suitable, in the long- · Contaminants in water bodies are reduced. term, and after reasonable mixing of any · The adverse effects of contaminants in contaminant with the receiving water bodies and coastal waters are environment and disregarding the effects avoided, remedied or mitigated. of any natural events for aquatic · That all existing discharges of organic ecosystems, contact recreation, water contaminants be via the best practicable supplies, and aesthetic and cultural option for treatment and disposal by the purposes. year 2004. · The reduction and minimisation of the · That all new discharges of organic quantities of contaminants entering water contaminants be via the best practicable bodies and coastal waters in particular option for treatment and disposal. those that are potentially toxic, persistent, · Improved aquatic habitat. or bio-accumulative. · Avoid, remedy or mitigate the adverse Note: the operative Regional Policy Statement effects of discharges of contaminants on is currently being reviewed. The proposed the traditional, cultural and spiritual values Regional Policy Statement (2013) is available at of water held by tangata whenua. www.nrc.govt.nz/newRPS What are the issues affecting freshwater quality in Northland? Like the rest of New Zealand, Northland’s · Diffuse surface runoff – the discharge of water quality varies greatly. In general terms, contaminants via water running directly off water is pristine in native forested headlands the land, which can be either urban or rural. and then becomes increasingly contaminated The three main water contaminants of greatest as it flows through modified lowland concern in Northland are faecal pathogens, catchments. These contaminants can enter the sediment, and nutrients. Pathogens are river in two ways: disease-causing organisms and obviously deserve being labelled contaminants however · Point source discharges – the discharge of contaminants from a single facility at a sediment and nutrients are only water known location (for example, a wastewater contaminants by virtue of being in the wrong treatment plant) ; or place; they belong on the land, not in the waterways. 153 State of the Environment report 2012 | While sediment and nutrients occur naturally however pathogens can still be washed into in water, when too much soil and sediment the water if the storage pond overflows, the washes off the land it becomes destructive in effluent irrigator breaks down, or the receiving water. Nutrients, specifically phosphorus and land is too wet for the effluent to soak in. nitrogen, should also stay on the land helping plants to grow there rather than in water. We The bulk of livestock manure is deposited want fertile land not fertile water. directly onto pasture. Whenever it rains, some manure gets washed off the land into streams, OUR FRESHWATER Pathogens rivers, and lakes. Additional sources of When pathogens get into water they can make pathogens, such as Canada geese, dogs, and people and livestock sick. Salmonella, a well- ducks, are insignificant nationally known cause of food poisoning in humans, is (Parliamentary Commissioner: 2012), but can also an emerging problem for livestock. be important in Northland (Northland Regional Council: 2011), particularly in small Recent outbreaks in New Zealand have caused diarrhoea, loss of milk production, miscarriage, streams and ponded water. and deaths (Teague: 2011). The main sources of pathogens in freshwater are human sewage and animal manure. While human waste in Northland is treated by wastewater treatment systems before being discharged to land or water, the extent and effectiveness of treatment varies. Storm overflows, broken sewer pipes, and poorly located and maintained septic tanks mean some sewage gets into water with little or no treatment. Animal effluent and stream bank erosion When livestock manure gets into water, create bacteria, water clarity, and nutrient pathogens also get into water. Some manure problems in freshwater is deposited directly into water where livestock have access to it. According to one study, Sediment dairy cows are over 50 times more likely to Sediment makes clear water murky (or turbid), defecate straight into water rather than land, smothers aquatic life, and sediment build-up when given the opportunity (Parliamentary alters water flows and exacerbates flooding. Commissioner: 2012). Sediment is made up of particles of soil and rock eroded from the land and washed or Around 15% of dairy cow effluent is deposited blown into rivers and lakes. Sediment is in the shed during milking. Traditionally in probably the most widespread and serious Northland, this effluent was run through two- contaminant of water in Northland. pond treatment systems and eventually discharged into water. These systems Erosion itself is a natural process – even the removed most of the solids, but pathogens Waipoua River (one of Northland’s pristine often survived the process. Today, many dairy rivers) turns brown when it’s in flood, and farmers irrigate shed effluent back onto land native ecosystems are adapted to such 54 154 15 State of the Environment report 2012 | conditions. The problem is that land use Other land uses can also produce large activities that disturb soil accelerate erosion amounts of sediment in waterways. Losses of and increase the amount of sediment soil from plantation forests are lower than discharged to water. The loss of most of the from pasture for most of the forest rotation region’s wetlands and original forest cover has but when the trees are harvested and exposed soil to accelerated erosion. replanted, erosion rates go up 10-100 fold. Opencast mining, market gardening, urban development, and road building can all put OUR FRESHWATER sediment into water (Parliamentary Commissioner: 2012). Nutrients Plants and algae require nitrogen and phosphorus to grow, which are found naturally in water bodies. However, too much nutrient can cause algal blooms and other unwanted plant growth that impact on aquatic ecosystems. Sediment in the Kaihū River after a storm Both nutrients occur in different chemical event forms. The two common forms of nitrogen in water are nitrate and ammonia, whereas Sediment ranges in size from fine particles of phosphorus mainly exists as phosphate. Both clay to boulders. Smaller particles of silt and common forms of nitrogen – nitrate and clay tend to float in the water as ‘suspended ammonia – are highly soluble in water whereas sediment’. In calm water, they gradually settle phosphorus – in the form of phosphate – to the bottom forming soft layers of usually clings to soil and sediment. ‘deposited sediment’. Waves, winds, and floods can stir up deposited sediment, filling Man-made sources of nitrogen include the water with suspended sediment again. fertiliser runoff, urine from farm animals, and treated wastewater discharges. Phosphate Sediment is also a major source of phosphorus usually gets into waterways via erosion, as because phosphate clings to the surface of soil sediment, because it clings to soil particles. particles carried into water. Phosphorus is one Much of the phosphorus in freshwater today is of the two problem nutrients discussed in this a legacy of erosion caused by land clearance report. and fertilising for sheep farming. Pasture produces two to five times more Sewage and animal effluent are rich in both sediment than an equivalent area of forest nitrogen and phosphorus. Many smaller (Blaschke, P. et al.: 2008.). Animals can break wastewater treatment plants have limited down banks, putting soil directly into streams. treatment capability, leaving behind much of Overgrazing pastures leaves soil exposed and the nitrogen and phosphorus. Some sewers sheep tracks along hillsides create channels for overflow at times and septic tanks can be water to carry away soil into rivers, lakes, poorly located and maintained.
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