Arch. Biol. Med. Exp. 20: 131-134 (1987) Printed in Chile Biological implications of lake management with reference to lago Chungará Consideraciones biológicas del manejo de lagos, en relación con el lago Chungará TONY E. ANDREW The Limnology Laboratory, The University of Ulster, Traad Point, Drumenagh, Magherafelt, Co. Derry, N. Ireland El lago Chungará se caracteriza por su altitud, su endorreismo, su composición y estructura de Ias comunidades biológicas representadas así como por su avifauna y bofedales asociados. Los niveles dei espejo de agua van a modificarse a medida que se extraiga el agua. Regímenes de agua fluctuantes tendrían efectos más catastróficos que la reducción del nivel dei lago. Ambas situaciones necesitan de un manejo cuidadoso para minimizar los câmbios. INTRODUCTION cally concerned with the general aspects of lake management include those of Historically, many lakes have been subject Lowe-McConnell (1966), Edwards and to a degree of management for a variety of Garrod (1972) and Ilmavirta, Jones and purposes. Such purposes include fisheries, Persson (1982). There also exists a large irrigation and flood control, water supply number of works dealing with many aspects and disposal and other functions such as of particular lakes, e.g. Neusiedlersee transport, conservation and amenity. An (Lõffler, 1979), Chilwa (Kalk, McLaughlan example of antique management for and Howar-Williams, 1979) or with catch­ irrigation and fisheries is Parakrama Sa- ments, e.g. Cruickshank and Wilcock mundra, a partially man-made lake in (1982). The observation that "In recent Sri Lanka, managed for over fifteen cen­ years we have begun to understand water turies (Schiemer, 1983). To maintain bodies as parts of larger systems and par­ several, often conflicting, activities on ticularly as parts of their respective catch­ one lake requires management based upon ments" (Blazka, Backiel and Taub, 1980) fundamental biological and hydrological still has to receive wide acceptance. Specific understanding often enshrined in legislation elements of lake ecosystems have received or traditional practices. much attention as evidenced by many Relatively recently we have seen the learned tomes e.g. fisheries (Gerkin, 1978) development of a considerable interest etc. However, it is apparent to the limno- in all aspects of limnological research logist that although lakes with common often directed towards problem solving characteristics of geography, chemistry or for management purposes. Much of the morphometry, are often grouped together international stimulation and collation of for convenience, every lake has its own information may be attributed to inter­ individual characteristics and, as such, needs national programmes such as IBP1 and a "personal" management programme. MAB2 and the activities of SIL3. A sum­ mary of the recent advances in the under­ Several schemes have been erected to standing of the biological attributes of classify lake types and these are often freshwaters is found in Le Cren and Lowe- based on simple characteristics such as the McConnell (1980). Works more specifi- mixing qualities of the water column (Hutchinson, 1957) or their geographical 1 International Biological Programme. location. Although useful, these schemes 2 Man and Biosphere. do not adequately describe more than one 3 Societas Internationalis Limnologiae. specific lake. An equally simplistic scheme 132 LAKE MANAGEMENT might be initially, to identify lakes as of the catchment, closely associated with natural, man-manipulated or man-made, the lake, consists of a permanent marsh perhaps more useful in a management (bofedal) an important part ot the system. context. Examples of each type may be Algal elements of the plankton commu­ found in most countries. Man-made lakes nity are dominated by the Chlorophyceae, are usually constructed for a specific Botryococcus sp. and Sphaerocystis spp. purpose such as hydro-electric power together with centric diatoms-indicative generation (Embalse Rapel) or water of a cold water assemblage. The presence supply (Embalse El Yeso). Other functions, of Nostóc sp. implies nitrate limitation, secondary uses are subjugated to the prime as appears to be the case from the ionic function without other uses such as ame­ composition of the water. Phosphate nity or fisheries being excluded. This is limitation is unlikely. Algal production is good management practice. At the other high (Montecino et al, 1982) and sufficient end of the scale, natural lakes (the majo­ to support high standing crops of zoo- rity of the southern lakes) are exploited plankton dominated by copepods (Sanzana only to a very limited extent, particularly & Thomann, 1984). Although population in the area of fisheries and this only to densities of cladocerans are smaller than the extent of stocking with the exotic copepod densities, the cladoceran fauna Salmo gairdneri Richardson. It is the is diverse (Dominguez, 1973). man-manipulated lakes (Laguna Negra, The littoral communities appear to be potentially L. Chungará) that require the highly developed and include areas of most stringent management as they are rooted macrophytes (Miriophyllum elati- usually natural lakes whose fundamental noides). This suggests that marginal benthic characteristics may be irrevocably altered communities are highly developed con­ by management practice. Occasionally such taining a variety of invertebrates. This lakes may be encouraged to revert to their is confirmed by the presence of fish original state after gross perturbations to populations (Orestias spp.) which are their ecology, but at great cost, for example dependent on the littoral regions for Lake Washington (Edmondson, 1972). feeding and breeding. Lago Chungará Unfortunately, not all lakes have the suports an internationally famous bird potential to accommodate such changes, fauna including, among fifteen species, particularly those with unique characte­ flamingo and tagua. Flamingoes are ristics or isolated catchments. Careful dependent on the shallow, marginal areas consideration, which can only be based of the lake for feeding, tagua require on sound limnological research, must rooted macrophytes or marshy areas to be given to such lakes. nest, both marked features of the littoral regions of the lake. Lago Chungará The potential effects of water abstraction In world terms, Lago Chungará represents The following observations are based on one of a very rare type. Distinguishing the assumption that the following premises features include the isolated geographical have been satisfied; (a) the project is location at extreme altitude, (4539 m), feasible and sustainable in hydrobiological in the Altiplano, the self-contained catch­ terms and that the abstracted water is ment with its balanced water budget and appropriate for the purposes required, a high ionic concentration with magnesium (b) that the return on investment, social sulphate of major importance. These and biological, as well as economic, have characteristics together with a well mixed been equated with the benefits that would water column and cold annual tempera­ accrue in that the Lauca region is de­ ture cycle "polymictic" (Hutchinson and signated a Biosphere Reserve. Lõffler, 1956) — combine to create a lake The principle effect of water abstraction, of considerable limnological interest. Part given the closed nature of the catchment, ANDREW 133 would be to alter the water level. Depend­ planktonic communities and benthic com­ ing upon the abstraction demand, volume munities would be significant. Many and temporal pattern, this would manifest zooplankton species have resting stages itself as either a fluctuating water level which find refuge in the littoral regions or as a permanent fall in water level. The and these would not survive, reducing major areas to be affected include the the diversity in the plankton. Insect species littoral region and the marsh. Secondary often lay their eggs at the margins and effects will occur in the plankton commu­ the developing larvae migrate into deeper nity. The exact nature of the changes waters as part of a seasonal cycle, this depend partly on the morphometry of would become precarious. Many of the the lake, particularly around the margins littoral species provide food for fish and (Fig. 1). birds and consequent effects would be manifest in those populations. Some Rooted macrophytes Zooplankton diverse lakes, particularly in tropical situations, J Submerged macrophytes are subject to natural or controlled fluc­ Benthic algae Planktonic algae tuations e.g. L. Chilwa (Kalk et al, 1979) and Parakrama Samundra (Schiemer, 1983) Diverse invertebrates Mollusca, Insecta, respectively. In these cases species diver­ Annelida, Crustacea, sity tends to be limited and shows very Nematoda Protozoa i slow recovery especially in numerical population density terms. Zooplankton, for example, tends to alter its composition in favour of smaller species with rapid Reestablished Limited zooplankton diversity generation times, — a strategy not common macrophytes Planktonic algae no marsh in cold, polymictic waters. The effect of a permanent reduction in Limited invertebratesV \ water level would also catastrophically no fish V'.. Benthos alter the community structure of the lake margins. If morphological characteristics of the lake allow, some elements of the flora and fauna might become re-esta­ blished in the new littoral and sublittoral Limited zooplankton diversity region, but at a very much reduced level. No littoral Small