LINKING THE MOUN CONSERVING NEW ZEALAND'S RIVERS TAINS TO THE SEA

Forest and Bird, Issue 266, 1 November 1992, Page 26

LINKING THE MOUN CONSERVING NEW ZEALAND'S RIVERS

TAINS TO THE SEA

a waterfall. And one of nature’s sharpest contrasts must be the same river at low flow meandering peacefully through pools and rifles. But, as KEVIN COLLIER explains, intact and unmodified river systems are becoming increasingly rare. : ae ae. One of natures most awe-inspiring spectacles N pining sp = Boh must be a river in full flow cascading through a gorge or down O | ©

LEAN, FRESH WATER flowing from seepage to stream to lake and river and finally into the sea not only evokes emotions of awe and tranquillity, it also gives life to many species of native aquatic plants and animals. The well-being of this native life, however, is often in conflict with the way in which we regulate and use rivers. Rivers are seen as convenient sources of water and electricity, as drains for the disposal of waste, and as natural hazards that need to be controlled. The role of rivers as habitat for native communities of plants and animals, and as part of the natural landscape of New Zealand, is one of the least recognised of their values. IVERS FUNCTION like huge trees, but instead of climbing towards the sun, they grow in size as they approach the sea. Small streams feed the main stem of the river like fibrous roots providing energy and

life. As with the fine root hairs of trees, wetlands and seepages keep the small streams alive. The intact sequence of wetland or seepage, stream, river and estuary is vital for the natural functioning of river ecosystems. The existence of these intact linkages between different parts of a river is particularly important for many native fish. These are the fish which spend some of their lives in the sea and require access up and down rivers to complete their natural life-cycles (see page 30). Too often, humans do things that affect one part of a river or catchment without examining how this will influence life in other parts of the system. Dioxin and PCPs have leached into groundwaters in the Rotorua area, for example, and the insecticide dieldrin into Southland streams. Close links with the land mean that the ecological health of rivers is greatly dependent on the state of the catchment and vegetation on the banks. The natural shape of river systems means that they have very long boundaries relative to the actual area of water. Consequently, there

is much greater scope for damage to rivers compared with forest blocks which have similar areas but shorter boundaries. Activities in the catchment such as mining, subdivision and farming can cause sediment, nutrients and toxic effluents to enter waterways. On the West Coast, for example, there have been recent problems with the discharge by mining companies of settling pond effluent into Inangahua River and Fletcher Creek. The ability of rivers to dilute waste and transport it downstream has often been seen as a solution to pollution. This can create problems, however, because the pollutants move with the water and their effects on aquatic life can spread over long distances downstream. The Manawatu Ruver has long suffered from the incremental effects of catchment erosion, industrial waste and sewage, farm runoff and the dewatering of tributaries. The result is that the lower section of the river is severely degraded, although a management plan to clean it up is now being developed by the regional council. Native vegetation on the banks of rivers can help stabilise soil and prevent erosion, reduce nutrient runoff, and keep water temperatures down by providing shade. Many of our native aquatic plants are adapted to shaded conditions and have disappeared from streams where riverside forest has been removed. Plants alongside rivers also provide shelter for the adults of many aquatic insects, cover for native fishes and food in the form of leaves and terrestrial invertebrates that fall into the water. At least 14 native species of plants living on river banks are considered endangered, vulnerable or rare.

*RIVER CONSERVATION *

ECAUSE RIVERS are contained within their watersheds and many freshwater species do not disperse easily over land, the distributions of some animals can be very localised. In a recent analysis, I identified 178 species of freshwater and groundwater aquatic invertebrates which are presently known from three or fewer ecological regions in New Zealand. Aquatic habitats on Banks Peninsula, for example, are home to five invertebrate species that are found nowhere else in the world. Then there are at least 37 species of aquatic invertebrates which are known only from off-shore islands. The native plants and animals living in our fresh waters make an important contribution to the biodiversity of New Zealand. E ALL KNOW that introduced species can modify habitats and adversely influence the native communities of plants and animals. There are many species of introduced aquatic and riverside plants in New Zealand; the algal water net Hydrodictyon is one that has recently been causing major problems in some North Island waters. Several invertebrates have also been introduced to our freshwaters, either accidentally from fish tanks or intentionally as trout food. One species o! introduced snail is believed to be forcing a native snail, Glytophysa variabilis, out of many lowland rivers and lakes. In addition, 20 species of introduced fishes — almost as many species as native fish — are now found in New Zealand waterways. Fortunately, most of these introduced fish still have localised distributions. The most widespread are brown and rainbow trout which are the basis of an important

sports fishery. In terms of their recreational value, trout can be thought of as the freshwater cousins of deer in native forests. And like the deer in our forests, the presence of trout in our rivers is not without ecological consequences. An increasing body of evidence indicates that trout adversely affect many native fishes and some invertebrates through predation and competition. There is a strong case for stopping any further spread of trout and other introduced sports fishes into relatively unmodified catchments.

T IS ESTIMATED that two-thirds of world river flow will be regulated by the year 2000. In New Zealand over 62 hydroelectric schemes are our contribution to this loss of wild fresh water. Hydroelectricity should not be seen as a low-impact form of energy. The construction of dams and subsequent altered river flows, sediment levels and water temperatures can have significant effects on native plants and animals and natural river processes. The recent power crisis has shown us just how much energy

| What has been lost?

factors contributing to the degradation of freshwater habitats in New Zealand «me 85% of lowland forest cleared «e« 90% of wetlands drained «e« almost half the length of larger North Island rivers in catchments with modified vegetation cover «m« more than 62 hydroelectric projects «e« at least 200 introduced wetland plants «e 5 species of introduced freshwater snails «m 3 species of introduced frogs «e« 20 species of introduced freshwater fishes

can be saved through conservation measures, a much better alternative to the construction of more dams. With such an abundance of rivers and lakes, most people would never believe that New Zealand could become short of water. However, increasing demands from agriculture, industry and urban communities mean that some areas of the country like the east coast of the South Island, parts of Otago, the Waimea Plain in Nelson, and the eastern side of the North Island ranges may face long-term water supply problems. Over-allocation of water to orchards in the Moutere catchment near Nelson means that many streams dry up over summer and water quality in the main river is very poor. New Zealand households use 210 billion litres of water every year, and probably over one third of this could be saved by implementing water conservation measures. The solution to potential water shortages is not to abstract more from rivers or to build more reservoirs, but to use what we have in a more efficient way. Because of the degradation, small native-forested streams and seepages draining the lowlands or coastal hill country are now difficult to find in most parts of New Zealand. Furthermore, there are no large river systems in the North Island or on the east of the South Island with catchments that are wholly unmodified from their headwaters to the sea. We have to go to north-west Nelson, Westland, Fiordland and Stewart Island to find large river systems in unmodified catchments, and even then their plant and animal communities can contain introduced species. Introduced fishes are not known in the rivers of Stewart Island and they may also be absent from other areas of the country such as parts of north-west Nelson. These areas are, therefore, particularly important for river conservation. EW ZEALAND has well over 186,000 kilometres of rivers (see table). So far, only eight rivers, representing less than one percent of the total river length, have been protected by Water Conservation Orders, although several other orders are pending or under appeal. But the importance of natural value has played only a secondary role in river conservation to date. Of the 23 Water Conservation Orders applied for between 1982 and 1991, 18 came from Acclimatisation Societies (now Fish and Game Councils) primarily to protect the introduced sports fisheries. Although protection of trout and salmon habitat can also be beneficial to native species, greater importance needs to be placed on the

Lengths of major rivers in different regions of New Zealand showing the proportion of the total length currently protected by Water Conservation Orders (WCOs). This does not include the smaller river channels that were indiscernible from 1:250,000 maps. Lengths of multiple channels on braided sections of river are included.

natural values of rivers, especially those where there are no introduced animals. Many other rivers are protected indirectly because they drain land that is in a park or reserve. This does not necessarily protect their flow or the quality of their water, however, nor does it protect the lower parts of rivers because most of our parks encompass inland, mountainous areas. It is on the lowlands where the major river conservation problems lie. The lengths of rivers can make conservation a very complicated process because they cross the land of many different property owners on their way to the sea. HERE ARE MANY different types of rivers in this country, and examples of all types should be represented in our network of parks and reserves, where possible from their source to the sea. For instance, rivers in Northland kauri forests have different combinations of species than rivers flowing through South Island beech forest. Rivers emanating from lowland springs are different from mountain-fed rivers, and single-channeled rivers with bouldery substrates are different from rivers with braided channels and gravel beds. The conservation challenge is to identify and protect the most representative and least modified examples of the different river types around the country, to manage these so that their natural value is not diminished, and where appropriate to restore the channel and riverside environments. Protection will require commitment from politicians, local bodies and landowners, and research will be needed to devise and evaluate effective restoration techniques. There has been considerable recent progress Overseas 1n river restoration, and this has been aimed mainly at linking up degraded sections of river to sections of high natural value in order to restore their overall functioning. This work has included the re-planting of natural riverside vegetation, the restoration of channel meanders where these have been removed by river straightening, and the introduction of suitable riverbed materials for aquatic life where sedimentation has occurred. In some countries, passage for migratory fish and natural river processes have been restored through the removal of outmoded dams or through the construction of effective fish passes. New Zealand should ensure that development projects on rivers build in restoration options and costs at the planning stage so that the problems are not left for future generations. Most river systems are longer than mountains are high. However, because

region km of river | approximate % protected by WCOs NORTH ISLAND Northland 6,341 0 Auckland 3,013 0) Waikato 15,374 0 Bay of Plenty 8,244 0.7 Gisborne 6,448 0.8 Hawke’s Bay 11,397 0 Taranaki 6,094 0.4 Manawatu/ Wanganui 21S 0.9 Wellington 6,327 0 North Island total 80,453 0.4 SOUTH ISLAND Nelson/Marlborough 15,471 0 Canterbury 21,123 25 Westland 19,392 0 Otago 22,914 0.5 Southland 20,394 0) South Island total 105,894 0.8 NEW ZEALAND TOTAL 186,347 0.6