The impact of human activities

on water resources.

"Today's water crisis is the logical consequence of the "waste/water" illusion. Where water is a waste vehicle and anything can be a waste, no water resource is safe. Our culture is permeated with this "waste/water" illusion. It is instilled in one of the earliest and strongest lessons in childhood - toilet training. It is reflected in the design and operation of every conventional home, city, business, factory and farm."

Pat Costner. We All Live Downstream. A Kamo High School student project.

Contamination of water supplies

Most year-round rivers are sites of urban, peri-urban and agricultural activities. Their water catchments are subject to intense pressure from agricultural and housing activities. Consequently, most of the larger rivers experience a variety of pollution problems. Smaller rivers adjacent to bush farming, mining and forestry activities are also subjected to heavy sediment loading from erosion and chemical pollution.

Water contamination is an old and serious problem in New Zealand. Although many waterways still have water contamination problems, there have been significant advancements made since the last century. Typhoid and cholera are no longer the pervasive threat that they were and a great deal of effort is now being turned towards restoring water quality in streams and rivers.

Everybody, including the plants and animals, needs safe drinking water. Living creatures are molecular filters, removing protozoans, bacteria, viruses, and even individual atomic elements from the water as it passes through us. Our bodies are able to get rid of most undesirable elements through an elaborate system of defence mechanisms. But some of the contaminants defeat our biological capabilities and accumulate in our bodies.

Kinds of contaminants

Many of New Zealand's rivers, creeks and lakes are contaminated by the deliberate or accidental discharge of sediment, chemicals or sewage. Various kinds of pollutants do different things to the people and creatures that depend on or live in the rivers and lakes.

The amount of damage depends on the concentration and duration of the pollutant. In some instances, very high concentrations of a poison might pass through a river in a short time, but kill off a wide variety of important species. Contamination of this sort is often from industry and urban discharges. Because the discharges enter the water from pipes, they are called "point source pollution." Rapid, highly toxic discharges might include cleaning milk vats with lime or metal plating vats with acids. The residues being cleaned and the cleaning solvents are often highly toxic. Of course this is illegal, but if it is done quickly and at night it is often difficult to find out who did it. Today, new monitoring and testing techniques can "fingerprint" chemical solutions and trace a pollutant back to its source.

In other cases, small amounts of pollution entering a river over a long time can cause extensive damage to the balance of life or reproductive abilities of the creatures. For example, agricultural run-off and fall out from atmospheric pollution is diffuse and is called "non-point source pollution." The effects of chronic and diffuse pollution are difficult to assess and as many people are often involved, correcting the problem is not easy.

Some of the more important pollutants in New Zealand and their impact on rivers are:

A survey of the New Zealand Regional council officials, responsible for water quality, resulted in a prioritised list of sources of water quality pollution. Agriculture was the most significant source of pollution. The local severity of the problem depended on the particular river, lake, or ground water system examined, and who examined it.

Sources of Impacts on Water Quality, ranked by New Zealand regional council officials. From Statistics New Zealand 1993. 0 = No damage and 10 = Severe damage:


4.9 Primary agriculture
4.8 Human sewage
3.9 Urban storm run off
3.8 Industry
3.7 Agricultural processing
2.6 Mining
2.6 Forestry
0.7 Other

Chemical pollution

Pollutants of fresh water that are especially hazardous to both human and natural life systems include heavy metals, such as lead, mercury, chromium, plutonium and arsenic. These are very difficult for living systems to deal with and the build up in tissues and pass from one organism to another. Once ingested, they remain in the body until death (or unless special chealating agents are used to remove them). If people eat creatures - such as fish or molluscs - containing heavy metals, the metals become even more concentrated in them.

Highly Toxic Wastes that contaminate fresh water (Statistics New Zealand 1993) include:

Heavy metals make humans, stock and wildlife extremely sick. At low doses, they impair the nervous system causing depression and fatigue. As they accumulate, this becomes worse and co-ordination begins to fail. In times of stress or starvation, the heavy metals are released back into the blood as fat is burned. The high levels then disrupt all normal body functions and the liver and kidneys fail causing death.

Pesticides containing chlorine are also very difficult to get rid of. Once ingested, they pass into fat and bone tissues. Some of the fat tissue surrounds nerves and reproductive organs. As the poisons accumulate, they begin to interfere with normal metabolic processes. The rate of damage depends on how contaminated the water is and the age of the person drinking it. Young (of people and wildlife) are more easily poisoned by these chemicals than adults. The health problems that result can lower spirits and productivity. Over time, the poisons can become so concentrated they destroy the ability to have normal children. In sufficient doses, the contaminants may cause cancers or death by poisoning. As with heavy metals, stress or starvation will release the poisons from fat tissues and cause acute poisoning symptoms.

Extensive sampling of rivers and streams on the Southland Central Plain of New Zealand revealed serious deterioration of key indicator species in the streams and a possible correlation with the absence of these organisms and pesticide use. Nitrate levels in agricultural wells exceeded the WHO guidelines of 10gms/m3 for drinking waters. Pesticides were found in 11% of wells in agricultural areas. Chemicals associated with timber treatment practices forced the recent closure of a children's camp in the small South Island town of Hanmer Springs. Routine water testing near the town found that timber treatment chemicals had leached into the water course. (Statistics New Zealand 1993).

Eight percent of public water supplies in New Zealand fail to meet microbiological standards. Twenty six percent of chlorinated supplies failed to meet standards for disinfection by-products. Three quarters of water supplies that used aluminum in the water treatment process exceed the WHO guidelines for aluminum.

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