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Bioaccumulation, Contaminants and our Waterways Sarah Silverstar Water – the lifeblood of our planet. Life depends on water. Water forms the basis of our planet, combining with sunlight to create diversity and richness. However, water is largely taken for granted. It is assumed to be consistently available in a clean, plentiful supply. It is not usually until water is restricted, contaminated, or recreation is affected, that the significance of water is considered. Streams open to livestock become polluted Many everyday activities and actions have detrimental impacts on our water. Nature exists in a state of flexible balance - if one aspect of a natural system is altered, either naturally or otherwise, then other parts of that system will also experience an upheaval. The significance depends on the initial cause and the cumulative effects of the disturbance over time. When conditions are not natural and are persistent then we encounter problems that require mitigation, and frequently ongoing management. Waterways in New Zealand are subjected to a variety of inputs from the urban and rural environment, many of which add contaminants to the water. A local stream may receive runoff from roads, construction, seepage from sewage and septic tanks, and stormwater. Light industry may also discharge into the same stream. Bioaccumulation and the food web Regionally the food web is affected by the supply and influence of certain key minerals, in particular nitrogen (N) and phosphorus (P). (see diagrams) This web is also influenced by the impacts of bioaccumulation (see diagram). This occurs when chemical contaminants (e.g.: heavy metals from roads and industrial runoff, plastics and their derivatives e.g. PCB, and organochlorines) enter waterways. These poisons pass upwards through the food chain and because they are hydrophobic, accumulate in the fatty tissue of mammals at the apex of the chain. Substances that begin at low chemical concentrations in sediments and plants become concentrated as they are ingested by successive species of the food chain, adversely affecting animals, fish and birds. Many substances since found to be highly toxic such as DDT have been banned, however the debate continues as to whether certain chemicals are acceptable to be released into the environment, provided they are under a certain dosage/limit. In the lab, chemicals including pesticides and household chemicals are measured by lethal dose (LD), which is the dose of chemical sufficient to kill an adult rat in one application. Previous scientific policy concluded that any dose below the LD was acceptable in the environment and for humans. It is now more widely recognised that miniscule doses of chemicals can have harmful effects, especially when we consider bioaccumulation, and the fact that our modern life has released hundreds of thousands of chemicals into the ecosystem. The majority of which react to environmental factors (e.g. sunlight), and with each other, forming new chemical compounds – none of which have ever been known or assimilated by natural systems, including ourselves. This raises the question - how are correct limits set for acceptable levels of environmental discharge when we are currently unaware of the full impacts? Currently guideline levels of contamination are based on the assumption that unless a contaminant is proven to be detrimental to the ecosystem, low to moderate levels are acceptable. Effects of chemical overload, such as feminisation of fish and birds, falling fertility rates and evidence of endocrine disruption are not currently accounted for in regional policy. We need to remain aware that these insidious chemicals are present in all ecosystems on earth, the ‘barely detectable’ levels of chemicals are not to be dismissed, as they have unknown effects and impacts on all future generations. What are the main issues affecting water quality in New Zealand? Environment Canterbury water quality monitoring states three main concerns as: Sedimentation; Nutrients; & Bacterial Counts. Sedimentation is a result of building and development (subdivisions, roads etc), including the clearance of farmland. 98% of New Zealands wetlands have been cleared for farmland and development. Wetlands act as water purifiers, and the natural filtration offered by wetlands has been lost, making areas prone to flooding, nutrient loss and erosion. Any sediment run off ends up in waterways, smothering streambeds and suffocating the invertebrate life that forms the backbone of an aquatic ecosystem. Bacteria in the water are usually a result of overflowing stormwater septic tanks and sewage pipes. With multiple stormwater outlets and seepage to any one stream or river, many local beaches have high fecal coliform counts, and are unsuitable for swimming, fishing and gathering shellfish as a result. Nature bites back Nutrient loads are pivotal to waterbody equilibrium. Research has found that nitrogen is the limiting factor in a water ecosystem, so when fertilizer use and deforestation occurs, this added load is highly detrimental to an aquatic community. This process is known as Eutrophication. When extra nutrients such as N and P from fertilizers and effluent are consistently added from streams, algae growth is fuelled within the lake; growth explodes as algae decomposes, using up the valuable oxygen available to a stream community, creating an anoxic (oxygen depleted) habitat. If the problem becomes severe enough, waterways can become ‘dead’ to all micro invertebrates and fish. Hot weather exaggerates these blooms, impairing aquatic communities including recreation and amenity values. Lake Rotoiti, Lake Omatere and Lake Forsyth are ongoing examples of severe eutrophication. Unfortunately many of New Zealands lakes are affected. There are 10 lakes in the Bay of Plenty alone, which are currently listed as damaged, at risk or deteriorating in quality and their vulnerability to algae blooms. Phytoplankton (microscopic organisms which feed on plant material) which form the blooms produce a toxin as a by-product of their metabolism making affected waters unsuitable for any purpose, even contact with these waters can be harmful or even fatal to humans and animals. How is water quality managed? All regional councils set water management guidelines using regional policy statements and regional plans. The Resource Management Act (RMA) requires councils request a resource consent for the direct discharge of contaminants (defined as ‘any substance, energy or heat that when discharged into water, or onto land, or into air, changes the physical, chemical, or biological condition of that water, land or air’). Contaminants and sediments can be approved under the rules of a regional plan or as a condition of resource consent. Diffuse discharges (‘any general discharge or seepage, either over or under ground, of water borne material, which is not from any readily identifiable point – a.k.a. non-point source discharge’) are more difficult to monitor and as a result are likely to provide multiple sources of contamination. Resource consents consider the potential environmental effects of a proposed water use, including any effect on water permit holders. Additional sources of contaminated runoff are farming and agriculture. These have impact on waterbodies in multiple ways: · Runoff from pesticides · Runoff from fertilisers · Stock effluent seepage and dispersal · Sedimentation from land clearance/erosion These effects are interlinked and can compound upon one another, placing stress on a waterbody and degrading it. Pesticides bio-accumulate in the food web, resulting in a disrupted ecosystem. Fertilisers applied to the land increase the N & P levels of waterways which, along with land clearance, also contribute to sedimentation. Effluent adds again to the nutrient levels of a stream/lake, contributing to sedimentation and bottom smothering of a waterway. The need for robust monitoring and mitigation strategies becomes clear when these cumulative effects are considered. However reliable scientific data is expensive and time consuming to obtain, making implementation and management of policy and rules challenging and prone to debate. What are some solutions to these issues? Successful restoration projects seek to re-create natural stream processes. In nature a system of pools and 'wiffles' in a stream oxygenates water and provides a steady flow of debris for micro invertebrates to feed on. A steady current inhibits weed growth and sediment build up. As a result of development and infilling, many local streams become stagnant and clogged, reducing habitats for the many creatures that depend on them, and creating an eyesore. Providing the source/s of contamination are identified and mitigated, a stream can make a rapid recovery if assisted. Natural systems are adaptable and what work best - a stream bank replanted, with wetlands restored has the ability to process any additional contaminants which may affect it. Many successful waterway restoration projects exist around the country on a large and small scale. In the Northern Hemisphere entire river systems have been rehabilitated, reducing the contaminant inflow, and allowing natural systems to re-establish has restored systems. In NZ water conservation orders can be placed on a waterway deemed to demonstrate 'outstanding amenity or intrinsic values'. Frequently restoration occurs on a small-scale local level. Farm and property owners seeking advice and assistance can contact their local council, community groups and native plant nurseries to begin and maintain a water way restoration. Regional councils have funds available for restoration; funds may also be obtained from MfE sustainable management grant, charity community and environmental grants. Because so many Lakes and streams suffer from eutrophication, projects are under way in an attempt to restore water quality. These projects are often joint efforts spanning years of research between city councils, iwi, educational institutions and government agencies. Rotorua city council is using an adapted nutrient stripping sewage system to decrease nutrients released into the lake. While a new fertiliser 'n-care' is now available to farmers, which reduces the amount of N leached into soil, and nitrous oxide (a green house gas released as a by-product of N fertilisers). Along with Lake Forsyth (which is being studied and monitored by ECan), Lake Ellesmere suffers frequent blooms, and impaired quality. Last year a joint management plan with Ngai Tahu and DoC was released to restore the lakes values as a habitat, iwi food source and recreation destination. Research is underway at Waikato University in conjunction with Environment BoP, to assist the lakes to recover, and to provide ongoing solutions. There is currently a 5 year trial to inject low doses of aluminum sulfate (aluminum binds to P, creating a stable compound, reducing the available nutrients) into Lake Okaro. Adding chemical compounds, however, can have unforeseen long-term effects: Prevention through enforcement of strong environmental policy is the best option. Lake Tarawera is currently one lake in the area to remain unaffected (it is also a lake in an undeveloped area, surrounded by forest) by nutrient overload - it's ecosystem is being studied to assist with understanding the processes which lead to quality decline. Not that difficult to determine – again, perhaps more difficult to enforce the changes required. Along with Lake Forsyth, Lake Ellesmere suffers frequent blooms, and impaired quality. Last year a joint management plan with Ngai Tahu and DoC was released to restore the lakes values as a habitat, iwi food source and recreation destination. Keeping NZ waterways and lowlands clean and green is a difficult task, but one we have to embrace for the future of our water sources, our food sources and the farming community. The health and happiness of all New Zealanders and our visitors depend on it. It is our lifeblood.
SIDEBAR DIAGRAM INFO: Phosphorus (P) - This does not have an atmospheric component, and cycles locally. Rates of P vary depending on the localised system - the mineral composition of the rocks for that area. Losses from leaching (via soil and water) are balanced by rock weathering. Most P is cycled through plants and the food web. eg; P fixed by plants is then fixed in the soil by decomposers (fungi/microorganisms) and animals (worms), some returns to plant, whicle the rest remains in the soil and some is leached into waterways, were it settles as sediment and eventually is uplifted to form new rocks, recycling the process again.
Nitrogen Cycle (N) - Plants are responsible for most N fixation. Certian plants such as legumes fix N via root nudules and make it available for grazing animals, thus providing an added source of N via dung. N is also found in the atmosphere, where is is absorbed by plants. Decomposing animals are broken down and provide a further source for the soil. Nitrogen fixing soil bacteria further break down material - denitrification releases N back into the atmosphere, while nitrification is the process of converting N to ammonia where it is used as an energy source by the soil bacteria.
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