welsh rivers and reservoirs: management for wildlife conservation

REGULATED RIVERS: RESEARCH & MANAGEMENT, VOL. 4, 213-223 (1989)

WELSH RIVERS AND RESERVOIRS: MANAGEMENT FOR WILDLIFE CONSERVATION

RON EDWARDS*? AND RICHARD HOWELL? *School of Pure & Applied Biology, W C C , Cardifl, CFI 3XF, U . K .

tWelsh Water, Regional Rivers Divkion, St Mellons Business Park, Cardiff, CF3 OEG, U. K .

INTRODUCTION

Conservation of wildlife in all ecosystems, whether terrestrial or aquatic, depends on the maintenance of the physical and chemical habitat within prescribed limits. Where one is considering individual species in particular, the regulation of competition, disease, predation, and the various biotic factors which impinge on the viability of plant and animal populations are also important. In the U.K. several important fattors are not readily controlled by regional regulatory agencies especially water authorities, but require Governmental control and action (Figure 1); these include acid-rain and land-use policy. Others, although influenced by human action, have a major natural component and here climate and the introduction and spread of alien species serve as examples. Nevertheless, several factors affecting wildlife conservation are partially controlled by water authority policies and operations. Inevitably, where such authorities have several duties-to provide wholesome water, treat and dispose of sewage, control pollution, protect properties from flooding, provide recreational facilities, promote fisheries, and conserve wildlife-there are times when compromises must be made.

The aquatic environment of Wales is extensive and occupies about 1 per cent of the total land surface. There are about 1700 lakes, mostly in the uplands, and about 40 reservoirs in private ownership over which water authorities have no statutory conservation responsibilities. Nevertheless, the Welsh and Severn Trent Water Authorities own 94 and 3 reservoirs respectively, covering 5600 ha, within the Principality. With respect to rivers, there are 5800 km of ‘main rivers’ defined in relation to land-drainage responsibilities, but conservation and pollution control functions extend to an indeterminate length of ‘non-main’ rivers generally regarded as at least of equivalent total length.

PARTIAL CONTROL REGULATION OF PREDATORS NO OR LITTLE CONTROL PARASITES, COMPETITORS

PREDATORS ( i n c l u d i n g MAN)

WILDLIFE C I POINT-SOURCE !ONSERVATION I ACID RAIN

A 1

LAND-USE & MANAGEMENT POLLUTION

’RIVER FLOW

HUMAN DISURB MAINTENANCE OF HABITAT

~ ~ ~ _ _

Figure 1. Some factors affecting wildlife conservation in rivers and reservoirs

0886-9375/89/020213-1 lf05.50 @ 1989 by John Wiley & Sons, Ltd.

214 R. EDWARDS AND R. HOWELL

This paper will focus principally on those factors shown in Figure 1 affecting wildlife conservation in Wales over which some regulation is possible. It will also comment initially on the current procedures for biological assessment and the perceived needs of the future.

SURVEILLANCE METHODOLOGY

Establishing the conservation value of reservoirs and rivers, together with their margins-which in the case of rivers have been described as ‘corridors’-represents a major task. It is one which water authorities can only attempt in collaboration with statutory and voluntary wildlife organizations which have complementary expertise in amphibious and terrestrial organisms.

Water authorities in general have developed biological surveillance systems for rivers only and then principally to describe the impact of pollution from chronic sources. The results have been expressed as simple indices and scores, the one finding general favour in the U.K. being the BMWP score based on benthic invertebrates. These scores are derived from sampling ‘typical’ habitats, which in the predominantly erosional Welsh rivers are riffles. Furthermore, they do not depend on detailed identification of collections and some have been deliberately developed to reduce the workload of identification. There is ample evidence (Brooker, 1984) that they provide adequate integrative descriptions of the pollution status of sites for most management purposes. However, conservation values of sites are generally assessed using several attributes (Usher, 1986), some of which depend, as far as is practicable, on identification to species so that the distribution of rarities and the diversity of species can be determined.

Because of the inadequacy of these water quality indices for the assessment of conservation value, some detailed taxonomic information of macroinvertebrates in rivers, collected over many years from about loo0 sites in Wales, has been utilized in establishing their distributions (Brooker, 1983) (Figure 2).

Figure 2. Distributions of (a) Baetis bucerutus (mayfly) and (b) Diura bicauduta (stonefly) in the WWA area

WILDLIFE CONSERVATION ON WELSH RIVERS AND RESERVOIRS 215

It is hoped that the predictive methods being developed using multivariate analysis (see Moss et al., 1987; Ormerod and Edwards, 1987) will facilitate the prediction of macroinvertebrate communities from physicochemical measurements and that biological surveys will verify and refine these predictions. However, such methods need further development and testing before widespread adoption. Even then, macroinvertebrates represent only one constituent of communities.

The assessment of species diversity also depends on an exploration of all habitats at a site and not just one habitat selected for water quality assessment. In studies of the R. Teifi, Jenkins et al. (1984) showed that whilst most species are not found solely in one habitat, nevertheless where several habitats are present at a site and are sampled, then the number of taxa is increased. They also found most ‘rare’ species on tree-roots and marginal macrophytes, a finding based on the rarity with which these habitats are sampled rather than the rarity of species associated with them. Ormerod (1985), from studies in the R. Wye, concluded that the distribution of invertebrates established from collections in stream margins may be very different from those of the stream-bed. Some species, such as the nationally rare mayfly, Baetis digitatus and beetle, Stenelmis canaliculata were restricted to marginal habitats and others, such as the crustacean Gammarus pulex and the mayfly Paraleptophlebia submarginata, were inadequately described by samples from riffle habitats. Figure 3 shows the distribution of further species as indicated from collections in riffles and margins in the Wye catchment.

The problems of survellance methodology extend beyond the waterline and in recent years the importance of river corridors as avenues for wildlife distribution and as linear seminatural systems containing terrestrial, amphibious, and aquatic elements, has been recognized. Assessments of the conservation value of stretches of river corridor are routinely carried out within Welsh Water in response to proposed engineering works (principally land drainage activities). Habitat features most in need of protection are identified subjectively by skilled surveyors, based on their knowledge of factors such as speciedhabitat associations and the recreatability of habitats and communities. Whilst studies such as those of Raven (1986a, b) have helped validate such relatively quick assessments, there is a need for further work to establish that the most important features and habitats are being protected and that the working methods to protect and enhance them are achieving their desired aims. Attempts have also been made to assess wildlife values of these corridors from a gross description of their plant communities derived from dominant species but, as with the other procedures described above, such methods must be tested and validated before widespread application (Slater et al., 1987). A review of conservation evaluation in river corridors, written by Eckstein (1984), highlights the importance of developing such a national methodology. With respect to riparian birds, several surveys of major river corridors have been completed and standard procedures have been developed (Eckstein, 1984).

Perhaps because of their artificiality and strict operating regimes, it is generally considered that reservoirs will not achieve a similar conservation status as natural lakes. In consequence there is no

MARGIN

Centroptilum luteolum

E Ian Reservoirs

10 Km

Figure 3. Distributions of (a) Baetis niger and (b) Centroprilum lureolum in margins and riffles of the Wye river system


systematic collection or analysis of biological data except, in some regions, for phytoplankton, which is of direct concern in water treatment, zooplankton, which is now recognized as a major controlling factor of phytoplankton, and birds, for many species of which reservoirs are important feeding and roosting sites.

Table I shows the proportion of reservoirs and lakes in Wales for which there are reasonable descriptions of elements of the fauna and flora. Even for phytoplankton, only 35 per cent of reservoirs had been surveyed adequately. Whilst many reservoirs and lakes had not been surveyed for fish, several are stocked with brown and rainbow trout.

The substantial summer draw-down zone on many direct supply and regulatory reservoirs prevents the establishment of a diverse epilimnetic benthic fauna. Nevertheless, the colonization of this zone by plants, provides a fascinating example of succession which deserves wider study (Merry and Slater, 1978).

FACTORS WITH PARTIAL CONTROL

Point-source pollution Water quality is influenced by pollutants from several sources and is responsive to the policies of Welsh

Water Authority to varying degrees. Its own discharges of sewage effluent represent a major component of the polluting load and in 1985-6, whilst 84 per cent of the effluents sampled complied with their consent conditions, 120 effluents failed on at least one sampling occasion. Priority for capital expenditure is only available for the worst offenders.

Trade effluents discharged directly to surface waters showed a much lower compliance with consent standards, only 48 per cent complying on at least 80 per cent of sampling occasions, 30 per cent complying on less than 50 per cent of occasions.

Despite this poor compliance of trade effluents, mirrored by those discharged to sewers, the quality of rivers in general remained good with 81, 12, 6, and 1 per cent in class 1, 2, 3, and 4 respectively.

Increasingly, however, concern is not with continuous discharges of pollutants over which some control can be exerted, but with pollutant incidents which although causing significant damage to river ecology and particularly fisheries, are not as readily detected as continuous discharges when using routine sampling programmes geared to chronic pollution. Some of these pollution episodes are derived from point sources (sewer overflows, industrial, and most farm wastes) although others are diffuse, the most important being acidic waters discussed later.

In 1985-6, of the number of classified pollution incidents, 23, 44, and 33 per cent were from sewage, industry, and farming respectively, the proportion from farming increasing dramatically in recent years. These statistics may be misleading in that some incidents are of minor significance, causing little damage, and Howells and Merriman (1986) suggest that over 90 per cent of serious incidents result from silage liquor and cow slurries. In one county alone (Dyfed) in 1983, they estimate at least 110000 fish were killed by farm waste discharges. The general ecological impact of farm discharges remains to be assessed and WRC is currently studying the pattern of farm pollution and its ecological effects in the Cleddau catchment of S.W. Wales and is investigating the response of streams to experimental pulses of single ‘pollutants’ which are normally components of complex mixtures (e.g. ammonia, sulphide, low-oxygen content).

Table I. Percentage of reservoirs and lakes in Welsh Water Authority area or within SSSIs with good descriptions of major taxa

SSSI Macrophytes Phytoplankton Zooplankton Benthic Fish inverts

Reservoirs 31 4 35 8 11 12 Lakes (>5 ha) 40 18 2 2 18 7


0 .20 :

0.10 .

Several rivers, particularly in the South Wales Coalfield, have been chronically polluted with industrial wastes and sewage for more than a century and some have had no or reduced stocks of fish during most of that period. In many of these rivers, substantial improvements have recently occurred. The R. Ebbw was essentially abiotic from steel-works effluents for much of its length until the early 1970s: this river now contains a diverse flora and fauna-including nine species of fish widely distributed in the catchment. Spawning problems are still experienced by the salmonids principally because of coal particles occluding gravels (Edwards et al., 1984). The R. Taff has similarly recovered from sewage and industrial pollution, the most tangible indication being the return of migratory salmonids to the river in 1979 (Mawle ef al., 1985). This coincides with dramatic improvements in water quality which with the marginal exception of nitrite, satisfies the quality criteria of the EEC Fish Directive (Figure 4).

Predators Because of declining catches of migrating salmonoids, principally salmon, the effects of predators are

coming under close scrutiny. Not only are conventional predatory activities by man being assessed (commercial sea-fishing, poaching, sport-fishing) but natural predators are being included.

In Wales particular attention is being devoted to the goosander (Mergus merganser), principally because of its expansion in numbers over the past two decades-from very few to about 100 breeding

/\ Unloolsed Amaonla

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4

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1975 1977 1979 1981 1983

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1975 1977 '1979 1981 1983

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Figure 4. Comparison of annual minimum dissolved oxygen concentration and 95 percentiles for BOD and NH3 (-1-') in the lower Taff from 1975 to 1983 with criteria for salmonids in the EEC freshwater fish directive


pairs-and its obvious predatory habits, during a period of declining salmon catches. However, there are many other predators such as the otter, mink, heron, kingfisher, trout, pike, and several invertebrates whose impact requires urgent review before there is destructive focus on one or two of the more obvious candidates. Over Wales as a whole the goosander population probably consumes no more than 20 tonnes of fish each year, a very small fraction of the total production and one which would probably be diverted along other predatory routes in any event. Nevertheless, with the high proportion of young salmonids in their diet and their comparatively high densities on important rivers for migrating salmonids, such as the Tywi, the situation needs to be kept under surveillance.

Human disturbance The potential impact of recreation through the disturbance of wildfowl by humans has been described

by several authors. For otters, recent radio-tracking studies have suggested their tolerance of game anglers and the crucial importance of the provision of adequate bank-cover (MacDonald et al., 1978). In Wales otters are once again widely distributed on most river systems except those of the coalfield: even in this area there is recent evidence, from the presence of spraint, of otter visits to a mid-section of the R. Taff.

For wildfowl, reservoirs are particularly important, especially as roosting and feeding sites during winter migrations. However, there is pressure to extend the traditional fly-fishing season (April-October) on reservoirs and, in some instances, to allow fishing throughout the winter. Studies carried out at Llandegfedd Reservoir, an important site for overwintering wildfowl in South Wales, suggest that the distributions of certain species, such as wigeon (Anas penelope), pochard (Athya ferina), and mallard (Anasplatyrhynchos), are strongly influenced by the presence of anglers (Bell and Austin, 1985; Cryer et al. , 1987). As an example, wigeon only move from the central area of the reservoir to their preferred feeding areas around the grassy sectors of the shore when anglers have left those shore positions at the close of the fishing season. The wigeon return to the centre at the start of the fishing season. The shift in location is coupled with a change in the proportion of birds feeding. If sailing occurs when birds are only able to occupy the central area because of shore fishing, they leave the reservoir to search for another site. It is clear therefore that the extension of either fishing or sailing seasons, unless matched by zoning based on a knowledge of bird biology, threatens the value of such recreational sites for overwintering birds. At Llandegfedd Reservoir and other sites, the management plans recognise this interplay of recreational factors in the zoning of activities.

Angler litter could be regarded as an aspect of human disturbance and, although causing damage to wildlife, it has far wider consequences, particularly to amenity. The toxic effects of lead on water birds, particularly swans, through the use of lead shot have resulted in a ban on further sales, and in most areas, including Wales, the prohibition of its use. There remains a high density of lead shot in the marginal areas of intensively used coarse fisheries, up to 330 shot m-* having been recorded by Edwards and Cryer (1987). Whilst the solution rate of lead suggests that shot will remain at least for several decades, its continued accessibility to wildlife remains to be established. In that event on fishing waters where swans and other birds are threatened, the removal of surface sediment near heavily used fishing positions would be possible though tedious. Other angler litter, particularly hooks and line, are dangerous to wildlife through injestion and entanglement respectively, as autopsies and radiographs of dead birds have shown. However, such mortalities probably represent an animal welfare issue rather than a conservation one. Since evidence of damage has become available to anglers many clubs in Wales have responded by appointing conservation officers, establishing anti-litter policies and providing training for young anglers.

It has been shown that heavy groundbaiting at coarse fisheries could lead to the local deoxygenation and the destruction of benthic Fauna (Cryer and Edwards, 1987).

Engineering works The effects of engineering works, often associated with land-drainage, on the ecology of rivers and

their comdors, are now widely recognized and both the design and operation of schemes are far more sensitive to wildlife needs (Raven, 1986a,b). In Wales, both the consultation procedures and the


acceptability of schemes to conservationists support this recognition of wildlife interests. As an example, at one end of the spectrum, the potential disruptive damage to migratory salmonids caused by the construction of a road tunnel under the Conwy Estuary has been compensated by the provision of a fish pass costing about €180k, which will increase the rearing capacity of the catchment by about 40 per cent or 8OOO smolts. This is one component of a package of environmental safeguards costing about f500k.

At the other end of the spectrum, where riparian tree felling is required, individual trees which provide shelter for otters are retained wherever possible and, even when creating a threat of flooding, tree stumps are left.

The major pumped storage scheme at Dinorwic in North Wales threatened one of the few breeding populations of Arctic char (Salvelinus alpinus) in Wales, at Llyn Peris, the lake being drained intermittently. In advance of the scheme, char were transferred to a nearby lake, Ffynnon Llugwy, which provides both suitable spawning areas and zooplankton for feeding, in an attempt to establish a replacement breeding population. Initial transfers of fish occurred in 1977 and later surveys have shown that the population has become established and is breeding successfully (Jones, 1983).

FACTORS WITH LITTLE CONTROL

Acid rain and land use Acid rivers are caused primarily by acid rain (associated with both SO4 and NO,) falling on catchments

and secondarily by certain forms of land-use and management-particularly conifer afforestation. River quality is generally worse during storms when hydrological pathways are largely confined to flow through the surface horizons of the soil from which toxic aluminium may be leached.

There are large areas in Wales with rivers which are vulnerable at least to storm pulses of acid water and in more restricted areas, rivers which are likely to be acidic at most flows (Figure 5) . These areas frequently have impoverished or no fisheries (Milner and Varallo, pers. comm.) and a restricted fauna (Weatherley and Ormerod, 1987) and flora (Ormerod et al., 1987). The decline of one upland aquatic bird, the dipper (Cinclus cinclus) has been linked to this impoverishment of the macro invertebrate fauna (Ormerod et al., 1985). The situation in Welsh lakes is not so severe, in part because brief acid pulses entering such lakes during storms are diluted by resident water of higher quality. Nevertheless, a questionnaire organized by Welsh Water Authority for fishery managers and anglers of a large sample of lakes of surface area greater than 1 ha suggested that 74 per cent of lakes are vulnerable to chronically acid inflows and of those only 3 per cent had ‘good’ fisheries. In contrast, of the 26 per cent less vulnerable lakes, 35 per cent had good fisheries. The interpretation of questionnaires is fraught with problems but the substantial difference between the lake groups suggests that real damage is being caused to lake fisheries by acidification. This obviously has implications for other lake biota.

There is currently a major programme of experiments involving the change in use and management of subcatchments in the area of the reservoir Llyn Brianne, some of the influent streams being severely affected by acidity and aluminium. The long-term effects of treatments, such as liming and afforestation, cannot be assessed immediately so the experiments are complemented by hydrochemical and biological models, using data derived from several sources, which relate inputs of acidity and land-use to ecological targets. In the first instance fish and invertebrates have been selected as the targets. These models, which require further refinement and validation, suggest that fisheries and invertebrates will continue to deteriorate or remain impoverished in forestry areas even with reductions in acid deposition of 50 per cent. Moorland streams, with similar reductions would support some salmonids although recovery from their current state would not be dramatic (Ormerod et al., 1988). Figure 6 shows model predictions of the effects of differences in future atmospheric inputs of acid (100 and 50 per cent of 1984 inputs) and of alternative land uses (moorland and planting with sitka spruce in 1958-a time of major planting in the area) in terms of the LT50 (lethal time for average fish) of brown trout in one subcatchment drained by a stream containing <2 mg Cal-’. The model suggests that biological decline has continued since the mid 19th century when atmospheric pollution became significant and that afforestation in 1958 would have accelerated the decline to a situation where no fish would survive (it has


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Figure 5. Distribution of acid vulnerable rivers in the Welsh Water Authority area

been found that the demarcation between fisheries and no fisheries is around a LT50 of 10-15 days). A 50 per cent reduction in acid inputs would merely maintain the current position. If retained as moorland, a maintenance of current air pollution levels would bring about the total loss of the fishery in this catchment within the next 30 years whereas a 50 per cent reduction would prevent further deterioration at least. Whilst the models make certain assumptions which may prove unwarranted, hind casts of conditions in the 19th century are supported by historical evidence of past changes from the analysis of lake sediment.

The options for amelioration of effects of acidification on streams are few. From recent experimental treatments, the liming of moorland catchments or of the major source areas of streams shows promise. The effects of modifications to forestry practices, particularly in changing draining patterns in removing trees from stream margins, remain equivocal (Hornung and Le Grice, pers. comm.). The liming of naturally acidic uplands is likely to have a profound effect on existing vegetation which needs to be assessed before widespread liming is undertaken.

The effects of forestry are not confined to those of acidification and are reviewed by Ormerod et al. (1987). Figure 7 shows a comparison of faunal diversity for afforested and moorland streams in two major Welsh rivers: moorland streams on average have almosk twice the number of invertebrate families.

Introduction and transfers Enthusiasm for the introduction of exotic organisms has waned in recent years with the evidence of

major problems, sometimes to native species, resulting from them. The native crayfish, Austropotarno- bius pallipes, Britain's largest freshwater invertebrate, is fairly widespread but, not tolerating soft water,


20

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5

0 I 1 0 4 4 1484 2054 2;24

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Figure 6. Predicted survival of trout (in days) in a soft water moorland stream on the R. Towy from 1884 to 2124. In one prediction the catchment is afforested in 1958 (A). Dotted lines show the effect of reducing acid inputs by 50 per cent from 1984

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a, L c

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Afforested Streams

l-7 Moorland Streams U

i 5 18

Number of Families

h 24 27

Figure 7. Percentage frequency distributions of invertebrate taxon richness (from kick-samples) from moorland and afforested streams


its distribution in Wales is fairly restricted. However, substantial stocks do occur within the Wye and Usk catchments. Native stocks in some British rivers are threatened with extinction by crayfish plague (the fungus Aphunomyces asruci) which was introduced into Britain with commercial imports of the American signal crayfish (Pacifastacus lenisculus) .

The NCC considers the establishment of a sanctuary area for the native crayfish to be of the highest priority and, although having little formal control over commercial crayfish farming, Welsh Water Authority supports the protection of the Wye and Usk from American crayfish and other carriers of the plague.

The mink is another escape which has not been controlled and is now widespread in most Welsh river catchments (Birks, 1986). Although trapped and hunted it no longer seems likely that it can be effectively controlled except through natural regulation. Although the mink is sometimes regarded as a competitor of the otter, the latter is expanding its distribution in Wales despite the mink’s abundance. Whilst predating on fish, the mink is a generalist carnivorous feeder, with other animals usually providing the bulk of its diet.

With respect to plant introductions, the Japanese knotweed (Reynoutria juponicum) and Himalayan balsam (Impatiens glandulifera), have recently caused problems in Wales through their extensive spread in the riparian habitat. The Japanese knotweed has displaced blocks used in urban flood protection schemes and its form could increase the risk of flooding in some river systems through the increase in frictional resistance to water flow. Its dense and tall habit also makes river inspection difficult during the summer whilst in the winter its woody stems can block trash grills and so contribute to flooding. Trials with the herbicide Glyphosate look promising but need further development.

Since biochemical studies have shown the extent of genetic separation of fish stocks and the homing mechanism of migrating salmonids has implicated pheromones which could be race specific in their action, care has been taken to avoid undue transfers of stock between catchments. In order to maintain genetic integrity, Welsh Water has recently agreed a policy with respect to the stocking of migratory salmonids in its area that only permits the use of fish of local origin for stocking purposes, except when reestablishing extinct or non-viable stocks.

GENERAL CONCLUSIONS

With the changing patterns of pollution, the recently extended responsibilities of water authorities to conserve wildlife through the Wildlife and Countryside Act 1981, and the increasing awareness of the importance of the banks of rivers as important linear habitats, there needs to be a fundamental reappraisal of biological survellance techniques. The recent enquiry of the House of Commons Select Committee on the Environment into the pollution of rivers and estuaries stessed current inadequacies in relation to pollution monitoring (H.M.S.O., 1987) but any reappraisal of needs should be far wider in its remit and address the problem of our ignorance of the fauna and flora of many of our lakes and reservoirs.

Recreational pressures on the aquatic environment will increasingly demand compromises between access and protection of wildlife habits from disturbance and damage. Sensitive management of sites, in part through zoning in space and time, may reduce disturbance in many instances, but environmental damage through habitat modification, e.g. groundbaiting, dangerous litter, needs further evaluation and recognition in environmental protection.

Factors outside the control of regional protection agencies impinge directly on their ability to conserve aquatic ecosystems. In Wales, afforestation and acid rain have a profound effect on these ecosystems.

ACKNOWLEDGEMENTS

The authors wish to thank their many colIeagues who provided information. The views expressed are personal and not necessarily those of the Welsh Water Authority.


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welsh rivers and reservoirs: management for wildlife conservation

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