National Inventory (2)

NATIONAL INVENTORY OF THE MAJOR LAKES AND RESERVOIRS IN INDONESIA (2)

General Limnology, Revised Edition (1997)

Oleh:  Pasi Lehmusluoto in cooperation with Badruddin Machbub, Nana Terangna, Sudarmadji Rusmiputro, Firdaus Achmad, Lusia Boer, Simon S. Brahmana, Bambang Priadi, Bambang Setiadji, Oman Sayuman and Agus Margana

Sumber:
http://www.kolumbus.fi/pasi.lehmusluoto/210_expedition_indodanau_report1997
.

PART 3. SHORT DESCRIPTIONS OF INDIVIDUAL LAKES AND RESERVOIRS

In order to give some general idea of the physical and chemical properties, of phytoplankton,   when applicable, and of the state of each of the individual lakes and reservoirs, summarized results are   presented below. Table 3 shows the range of variables measured. Detailed information on regional data   comparison (Figures) and on each lake and reservoir are in separate data files (Tables and Figures), and the data are included in the data bank at RIWRD.

As the morphology and hydrology of the natural lakes and the reservoirs are generally quite   different, the summaries are presented in separate chapters. The summaries are based on the results of   Expedition Indodanau, but also on the personal observations of the principal author, since he is the only   one in the team who has visited all the lakes and reservoirs studied. The number after the name in   brackets is the project code number. The location can be found in Figure 1. The sampling dates can be   found in the data files. The general evaluation is made only for the lakes. All the conclusions shall be verified by diel, interannual and long-term observations.

3.1. NATURAL LAKES

Batur Lake (26)

Lake Batur is the largest and deepest confined lake in Bali, and its basin is a caldera. It is situated  next to the volcano Gunung Batur. The most recent eruption happened in 1963. There is some small-  scale agriculture around the lake, and an increasing number of guest houses are being built. The lake is  also used for fisheries. The volcano is a favored hiking area, and on the western shore, there is the oldest  village in Bali, Trunyan. By now, there are no major man-caused threats to the lake. A survey has been  made on the flood control regulation (DPU and Exsa International 1981). The lake was variously  stratified during the visits (RTR 8.9, 48.0 and 126.9), and there were indications that it may have had a  full circulation in July 1993 (see also Ruttner 1931, Green et al. 1994). However, Schmitz (1994) is  claiming that Batur Lake is both thermo- and chemostratified, although his studies were only to the  depth of 50 meters. It is the most saline of the studied lakes, having a conductivity of 1,750-1,800  µS/cm, and a dissolved solids concentration of 1,340-1,520 mg/l. It has also the highest alkalinity (3.60- 3.70 meq/l) and high pH (8.8), especially in the epilimnion. There was no carbon dioxide in the lake, and  iron and manganese concentrations were not elevated near the bottom. The concentrations of calcium,  chloride, potassium, sodium, magnesium and sulfate were high. Nutrient concentrations of the lake were  rather low, total nitrogen from 0.256 to 0.970 mg/l N and total phosphorus from undetectable to 0.028  mg/l P. Chlorophyll a concentrations were from 0.57 to 3.83 mg/m3. The phytoplankton composition  was rather diverse, but the diatom Synedra acus v. angustissima was dominant in September 1992. The  total biomass was 2.4 mg/l, and transparency from 3.0 to 3.2 meters. The lake is considered oligotrophic.

Evaluation: Generally good, but highly saline.

Bratan Lake (25)

Bratan is the shallowest confined lake in Bali, but yet very heavily under the pressure of  recreational activities, motor boating and other outdoor activities, hotels and restaurants. The temple of  Pura Ulun Danu (goddess of the lake) is at the lake. There are several big outboard engines for a small  (3.9 km2) and shallow (22 meters) lake, the biggest being more than 200 horsepower. Attention to this  fact has been drawn already some 18 years ago (Lehmusluoto 1977 a). Some small- scale agriculture is  maintained around the lake. The lake was weakly stratified (RTR 19.0, 41.5 and 72.6) when visited.  Schmitz (1994) claims that the lake is thermo- and chemostratified. Its water is the most dilute of the  studied lakes, conductivity being 22-27 µS/cm and alkalinity from 0.18 to 0.20 meq/l. The nutrient  concentrations were also relatively low, but total nitrogen showed some elevated values (0.310-1.310  mg/l N) compared to some earlier studies (Lehmusluoto & Badruddin 1989). Total phosphorus values  were from undetectable to 0.002 mg/l P. The chlorophyll a concentrations were from 5.59 to 7.33  mg/m3 . In September 1992 the conjugatophyte Staurastrum cf. tetracerum was a strong dominant, 97  % of the total biomass, which was 4.4 mg/l. The lake shows some signs of beginning eutrophication, which has also been observed by Green et al. (1994). Transparency is 1.8 meters.

Evaluation: Reasonable, but susceptible to eutrophication and pollution, e.g. engine oil.

Buyan Lake (24)

Lake Buyan is a confined lake surrounded by rain forests, small-scale agriculture and quite recent  vacation housing. There are some fishing activities at the lake. Its stratification was weak (RTR 2.7,  27.0 and 39.8), and it has an electrical conductivity above average, about 280 µS/cm, but close to the  bottom, it elevates to about 750 µS/cm. The total nitrogen concentrations were from 0.224 to 1.060  mg/l N and total phosphorus concentrations from undetectable to 0.004 mg/l P. The carbon dioxide  concentrations were from 3.3 to 6.6 mg/l. Chlorophyll a concentrations were 2.32-5.08 mg/m3, and total  biomass 0.76 mg/l. The conjugatophytes Cosmarium bioculatum and Staurastrum chaetoceros were the dominant species, 74 % of the total biomass. Transparency was 2.3-3.1 meters. It is oligotrophic.

Evaluation: Good, with no immediate threats.

Diatas Lake (04)

Lake Diatas is one of the larger shallow natural lakes in Indonesia. It has a river outlet through the  River Gunanti. Although the drainage area is used for extensive agriculture, it has seemingly not yet  affected the lake. It was weakly stratified (RTR 16.3 and 27.0). The oxygen conditions are favorable. As  the lake is rather shallow, 44 meters, it may circulate down to the bottom periodically. Total nitrogen  values were from 0.076 to 0.927 mg/l N and total phosphorus values from undetected to 0.040 mg/l P.  The highest carbon dioxide concentration in the hypolimnion was 5.30 mg/l, and iron concentration of  0.82 mg/l. The lake is oligotrophic, having chlorophyll concentrations of 1.43-1.71 mg/m3, biomass 0.05  mg/l and transparency of 5.5-6.5 meters. The dominant phytoplankton species in March 1992 was  similar to Cyanodictyon imperfectum, a blue-green alga, in addition to green alga Oocystis spp., but in August 1993 Oocystis sp. dominated and the diatom Aulacoseira granulata was well represented.

Evaluation: Good, but non-point loading from agricultural land shall be controlled.

Dibawah Lake (05)

Lake Dibawah has a natural outlet through the River Lembong into Lake Singkarak, being thus  part of one of the three lake chains in the studied islands. The drainage area, which is small, is used to  some extent for agriculture. Small-scale fish farming is practiced at the outlet, and mollusc shells are  collected from the shallow areas for various uses. The lake was weakly stratified (RTR 34.9) and the  oxygen depletion began at the depth of about 50-60 meters, while the maximum depth is 309 meters.  Thus, the major proportion of the lake volume is lacking oxygen. The pH was rather high, 7.7-8.5. As  the lake is deep, it is likely that mixing occurs down to the chemocline periodically. Total nitrogen values  were from 0.180 to 0.466 mg/l N and total phosphorus values from 0.015 to 0.080 mg/l P. The highest  carbon dioxide concentration was 6.5 mg/l. The chlorophyll a concentration varied from 1.16 to 1.64  mg/m3, biomass was 0.18 mg/l and transparency 2.5 meters. The lake is oligotrophic. The dominant  algae in March 1992 were coccal green algae, like genus Coenochloris, and in August 1993, the  dominant genus was conjugatophyte Spirogyra sp., and chlorophytes Didymocystis bicellularis and Oocystis cf. solitaria were abundant.

Evaluation: Good.

Kerinci Lake (07)

Kerinci lake, which origin is uncertain, has two outlets, Segara Agung and Batang Kali rivers. The  fisheries activities are intense. It had the very average chemical chraracteristics in the epilimnia in  Indonesia, but pH was rather low. The lake is governed by a large wetland area and floating vegetation.  Due to logistical hardships, no observations of the stratification could be made, and no vertical sampling  could be performed. The total nutrient concentrations of the outlet water were 0.380 mg/l N and 0.080  mg/l P, and chlorophyll a concentration was 17.17 mg/m3, and biomass 0.19 mg/l. The high chlorophyll  concentration may be due to sampling error. The dominant species was in August 1993 raphidophyte  Gonyostomum semen, and other well represented algae were dinophyte Peridinium cf. gutwinskii,  conjugatophyte Spondylosium secedens and chlorophytes Monoraphidium contortum and Crucigenia tetrapedia.

Evaluation: Good, but some threats may come from the large surrounding agricultural area.

Limboto Lake (32)

Limboto Lake is a very shallow lake in Sulawesi flowing to the Molucca Sea through the River  Limboto. It is largely covered with higher vegetation and submerged plants. It was weakly stratified.  Otherwise, the water quality is reasonable, but conductivity is some 550 µS/cm. The nutrient values are,  0.545-0.566 mg/l total N and 0.011-0.028 mg/l total P. Chlorophyll a concentration was 5.24 mg/m3, biomass 4.8 mg/l and transparency 0.4 meters. Sulfate concentrations varied from 5.5 to 9.4 mg/l. The  phytoplankton was dominated by chlorophytes (98 % of biomass), the dominant species being Oocystis  sp. in August 1993. Hartoto (1994) has made studies of the lake in 1992-1993, but the results were not available for comparison. The lake may be considered eutrophic.

Evaluation: Reasonable, but siltation and overgrowth are the problems.

Lindu Lake (33)

Not visited.

Maninjau Lake (03)

Lake Maninjau has an outlet to the west at Muko Muko through the Antukan (Sikikis) River. The  lake is the only one in Sumatra having its outlet to the west. The drainage area is used to some extent for  small-scale agriculture, and it is a popular tourist place with several lakeside hotels and guesthouses. The  temperature stratification of the lake was rather weak (RTR 45.3), oxygen was depleted near the  bottom, and conductivity was somewhat higher in the hypolimnion (200 µS/cm) than at the surface.  However, the pH is rather high at the surface. The total nitrogen concentrations were from 0.116 to  1.110 mg/l N and total phosphorus from undetected to 0.250 mg/l P. Ruttner (1931) calculated that in the deeper layers below 60 meters has accumulated 7,000 tons of NH4-N and 1,500 tons of phosphorus. These correspond approximately to concentrations of 0.875 mg/l N and 0.187 mg/l P. Chlorophyll a  concentrations were from 1.30 to 2.52 mg/m3  and biomass 0.2 mg/l. It is oligotrophic, but there are  some signs of beginning eutrophication. Transparency was 3.4 meters. The carbon dioxide concentration  was in the deepest hypolimnion 18.0 mg/l, one of the highest in the studied deep lakes, and iron  concentrations were up to 1.90 mg/l. Ruttner (1931) found during the Sunda-Expedition in 1929 about  20 mg/l CO2 near the bottom. The dominant algae in March 1992 were coccal green algae representing  genera Oocystis, Lagerheimeia, Treubaria and Scenedesmus, without any strong dominant species. In August 1993 Oocystis sp. strongly dominated.

Evaluation: Reasonable, but susceptible to eutrophication by population centers.

Matano Lake (37)

Lake Matano, the uppermost in the Matano-Mahalona-Towuti chain, is the seventh deepest lake  in the world, although some information in literature may give other information. It drains through the  Penten River to Lake Mahalona. It is the only lake in Indonesia with a 208 meter cryptodepression, e.g.   the sea level corresponds to the depth of 382 meters. The lake was weakly stratified (RTR 34.3), with  anoxic hypolimnion. According to Whitten et al. (1987 b), the lake has been homotherm, but no  mentioning was made of the chemical gradients. Is the lake permanently meromictic is an open question.  Hartoto (1994) states that the lake was unstratified and that oxygen curve was clinograde. The results  may indicate it. The water quality is good in the epilimnion, but at the depth of 150-200 meters there is a  clear gradient of most of the physical and chemical variables; alkalinity increases two fold, conductivity  from about 200 to about 300 µS/cm, ammonia increases 20 fold, total nitrogen 10 fold, calcium two  fold, magnesium three fold, iron ten fold and manganese from undetected to 0.22 mg/l, while sodium  decreases from about 3 to 1.1 mg/l. Nitrate maximum was in 50 meters, ORP minimum (-177) in 150  meters and suspended solids and turbidity maxima in 200 meters. The total nitrogen concentrations were  from 0.150 to 1.740 mg/l N and total phosphorus was undetected in the entire water column of 500  meters. Chlorophyll a concentration was only 0.15 mg/m3. The highest carbon dioxide concentration of  5.3 mg/l was found at the depth of 500 meters, as were also iron and manganese concentrations, 4.59  and 0.22 mg/l, respectively. The phytoplankton biomass was only 0.002 mg/l, and only seven algal  species were found, chlorophyte Staurastrum furcigerum dominating but also dinophyte Peridinium sp.  was prominent. The lake is clearly oligotrophic, and its transparency was 15.5 meters. Nevertheless, the  wastewaters of the small towns and the effluents of the nickel industry shall be taken care of. It would  have been interesting to compare the physical and chemical results of 1992-1993 by Hartoto (1994), but  they were not available. The rain forest surrounding the nickel industrial plants seemed to be without major disturbances, by the bare eye.

Evaluation: Good, but the nearby nickel mine and processing plants are discharging effluents into the lake. Due to its long residence time, they may have cumulative effects in the future.

Poso Lake (34)

Poso Lake is situated in Central Sulawesi close to Sulawesi “Highway”. It drains through the Poso  River to the Molucca Sea. There are also reasonable tourist facilities. Poso Lake with its over 400 meter  depth was weakly stratified (RTR 13.3). The lower hypolimnion was anoxic, but the carbon dioxide  concentrations did not exceed 5.3 mg/l. Otherwise the lake was like an “average” Indonesian lake, and  the total nitrogen concentrations were from 0.240 to 1.090 mg/l N and total phosphorus concentrations  from undetectable to 0.040 mg/l P. The chlorophyll a concentration was 0.28 mg/m3  and biomass 0.03  mg/l. The lake seems to be oligotrophic, and transparency was of 4.8 meters. It has a good stock of  silver and yellow eels and two endemic fish species, Adrianichtys kruyti and Xenopoecilus poptae  species, and the dominant algal species were Coccomyxa confluens and Kirchneriella contorta  (Hehanussa 1994), but in July 1993 the diatom, Aulacoseira sp. dominated. There are also some observations of 1992-1993 made by Hartoto (1994), but unfortunately, they were not available.

Evaluation: Good, with no actual threats.

Ranau Lake (08)

Lake Ranau has an inlet of Warkuk River at Kota Batu and an outlet at Surabaja through the  Komering River to the Bangka Strait. The drainage area is used for agriculture. Lake Ranau is in the  Indonesian conditions a high-altitude lake, and surrounded by rain forests and agricultural fields. There is  also a spa at the lakeshore. It has been observed that the western end is four centigrades warmer than  the eastern end because of the influence of hot springs (Forbes 1885), but this kind of observations were  not made in this study. It was weakly stratified (RTR 57.7 and 64.7), and it had an anoxic hypolimnion.  Oxygen concentration was zero at about the depth of 70-100 meters. At the same depth hydrogen  sulfide could already be detected, and the highest concentration near the bottom was 1.5 mg/l. The  maximum depth is 229 meters. The nutrient concentrations were; total nitrogen from 0.158 to 0.893  mg/l N and total phosphorus from 0.055 to 0.411 mg/l P. Chlorophyll a concentrations varied from 1.21  to 1.28 mg/m3. The highest carbon dioxide concentration in the deeper hypolimnion was 12.0 mg/l and  sulfate concentration 20.2 mg/l. The lake is oligotrophic, having a biomass of 0.03 mg/l and  transparency of 8.8 meters. The most abundant taxa were in March 1992 Chodatella spp. and  Planktonema lauterbornii, and in August 1993 chlorophyte Botryococcus braunii and diatom Aulacoseira granulata.

Evaluation: Good, with no immediate threats. A dam is planned to its outlet.

Rawa Pening Lake (15)

Rawa Pening Lake is a semi-natural lake, with a man-made dam at its outlet to the Tuntang River.  Large areas of rice paddies and small towns surround it. The lake is heavily used for fisheries and other  water related economic activities (bottom mud and molluscs). When visited it was stratified (RTR 71.2),  but without epilimnion. The nutrient concentrations were; total nitrogen from 0.510 to 0.520 mg/l N and  total phosphorus was undetected. Chlorophyll a concentration was 1.65 mg/m3, and biomass 2.6 mg/l.  The strongly dominant alga was dinophyte Peridinium umbonatum, but also euglenophytes were rather  well represented in August 1992. It is largely infested and overgrown with e.g. Eichhornia crassipes,  but the eradication activities did not seem to be extensive, although a mechanical harvester is at the lake. The nearby Satya Wacana Christian University in Salatiga actively studies the lake.

Evaluation: The lake needs an immediate management plan.

Segara Anak Lake (28)

Not visited.

Sentani Lake (30)

The Sentani Lake is the only one in Irian Jaya included in the program. It drains through the Jafuri  River to the Pacific Ocean. There is available a background study for the Sentani Hydro Scheme  conducted by a Canadian company. However, this did not give much information on the limnology of  the lake. The lake was stratified (RTR 51.5), with an anoxic hypolimnion. Traces of hydrogen sulfide  could be detected in the hypolimnion, and carbon dioxide concentrations were from 2.2 to 3.0 mg/l.  Total nitrogen varied from 0.234 to 0.899 mg/l N and total phosphorus from 0.013 to 0.040 mg/l P.  Chlorophyll a concentration was 2.39 mg/m3, biomass 0.24 mg/l and transparency 2.6 meters. The  dominant algal species was diatomophyte Aulacoseira granulata, which comprised of 47 % of the  biomass. In addition, cyanophytes and chlorophytes were found. The lake showed some signs of eutrophication.

Evaluation: Reasonable, but prone to eutrophication.

Sidenreng Lake (35)

Visited, but not sampled due to strong wind.

Singkarak Lake (06)

Lake Singkarak has a natural flushing system (inlet from Dibawah lake via River Sumani/outlet  through Umbilin river), and it acts as a sediment sink. The lake was stratified (RTR 55.2 and 78.8). The  hypolimnion is likely to be permanently or semipermanently stagnant, meromictic, from the depth of 45- 50 meters on. Therefore, roughly two thirds of the lake’s water volume of about 15.6 km3  is oxygen depleted. The maximum depth is 268 meters. During the last few decades, the oxygen-depleted layer has  moved closer to the surface, being now at about the depth of 50 meters (see Ruttner 1931). From that  depth down to the bottom, there is also hydrogen sulfide present in the lake. In the oxygen depleted  layer there is storage of about 60,000 tons of carbon dioxide (highest concentration 14.0 mg/l) and  18,000 tons of hydrogen sulfide (highest concentration 0.4 mg/l). To oxidize the 18,000 tons of  hydrogen sulfide some 36,000 tons of oxygen would be needed, but there is instantaneously only 70  tons available in the epilimnion. The highest iron and manganese concentrations were 0.82 and 0.36  mg/l, respectively. It seems likely that the lake has not yet developed eutrophic. The suggested  additional abstraction through the natural outlet of the River Umbilin would be several m3/s for  hydroelectric generation and for irrigation (Alpine Consultants, Switzerland). However, the effects of  the abstraction shall be carefully evaluated, if in unfavorable proportion to the present recharge. It may  affect the whole lake by reducing the volume of the epilimnion, and the vulnerability for mixing may  become evidently more possible. In addition, the wetlands around the lake may be in danger, if the water  level may be lowered. Withdrawal of hypolimnion water would be more beneficial from the  environmental point of view and for irrigation purposes because of its higher nutrient concentrations  (see Ruttner 1931). However, the smell of hydrogen sulfide may cause some local nuisance. Tundisi  (1984) has suggested the nutrient rich hypolimnia of reservoirs to be used for irrigation, too. The total  nutrient concentrations were; total nitrogen from 0.176 to 1.199 mg/l N and total phosphorus from  0.016 to 0.166 mg/l P. The chlorophyll a concentrations varied from 0.88 to 1.97 mg/m3, and biomass  was 0.1 mg/l. The lake can still be considered as oligo-mesotrophic, with transparency of 2.1-3.2 meters.  The main phytoplankton groups were Chlorococcales and desmids from the group of Conjugatophyceae  in March 1992. In August 1993, the majoring algae were conjugatophytes (Spondylosium planum and  Cosmarium punctulatum), dinophytes (Peridinium umbonatum) and chlorophytes (Tetraedron minimum).

Evaluation: Susceptible to eutrophication. The effects of the additional water abstraction shall be closely studied. The possibility of a complete overturn shall also be evaluated.

Tamblingan Lake (23)

Tamblingan is the smallest of the confined Balinese lakes. It is well sheltered from winds in the  caldera, but its stratification was not especially strong (RTR 55.2). The lake has an anoxic hypolimnion,  but is it meromictic has to verified. The total nitrogen concentrations were from 0.690 to 0.780 mg/l N  and total phosphorus concentrations from undetected to 0.002 mg/l P. The carbon dioxide  concentrations were from 4.4 to 7.7. The lake was seemingly oligotrophic, although the daytime oxygen  concentrations showed some oversaturation. The chlorophyll a concentration was 3.77 mg/m 3, biomass  0.5 mg/l and transparency 2.7 meters. In the phytoplankton dinophytes, chlorophytes and  conjugatophytes were rather evenly represented, but the dominant species was diatom Synedra acus v. angustissima.

Evaluation: Good, with no threats.

Tawar Laut Lake (01)

Not visited.

Tempe Lake (36)

Tempe is one of the floodplain lakes in Indonesia (and the only lake of which the principal author  has ever taken samples from a terrace of a house), the lowest in the Sidenreng-Tempe chain of lakes.  During the rainy season, its area is about 300 km2, but it shrinks to mere 10 km2 during the dry season, during which time its dry shore area is used for agriculture. Its economic value is great both because of  agriculture and fishery. It cannot be considered, even during the high-water season, as a real lake, since  the through-flow water velocity is quite high. Its maximum depth was during the visit 5.3 meters, and  the stratification was naturally weak (RTR 3.5). Transparency was 0.6 meters. Lake Tempe is a fertile  and productive water body, with total nitrogen values from 0.720 to 1.010 mg/l N and total phosphorus  concentrations from 0.050 to 0.060 mg/l P, in which high allochthonous organic matter concentrations   support a large and uniform fishery. The chlorophyll a concentration was 2.94 mg/m3, and biomass 0.04  mg/l. The phytoplankton composition was diverse, without any distinct dominant alga. The fish yield is  650 kg/ha/year. The carbon dioxide concentration amounted to 33.0-38.0 mg/l. Recent studies in 1992- 1993 have been made by Hartoto (1994), but the results were not available. From the limnological point  of view the lake is much affected by the allochthonous transport of organic matter and nutrients, and thus by the drainage area. However, it is important for its fisheries and for migrating birds.

Evaluation: Due to the surrounding agricultural land the lake may be prone to further  eutrophication and siltation, noted already by James Brooke in 1840 (see Whitten et al. 1987 b).  However, the flushing rate of the lake is high. It has been infested by Eichhornia crassipes. Plans affecting the fisheries and migrating birds shall be reviewed.

Tigawarna Lake (29)

Not visited.

Toba Lake (02)

The maximum depth of the southern basin is 433 meters and in the northern basin 529 meters.  Lake Toba has an outlet through the River Asahan at Porsea to the Strait of Malacca. The northern  basin may circulate down to the bottom periodically (RTR 31.1 and 61.1), but the southern basin is  likely to be more stagnant throughout the year as there is a more clear thermocline and a distinct  oxycline at the depth of 100-150 meters although its RTR was only 25.0, or it is caused by pollution.  Thomas (1995) observed that the southern basin of the lake was stratified from 140 meters to 50 meters.  Roughly, two thirds of the southern basin is oxygen depleted. The total volume of the lake is estimated to be some 240 km3  (principal author’s evaluation). During the last few decades the oxygen depleted  volume in the southern basin has slightly increased, and the depth at which oxygen gets depleted, has  moved towards the surface. It seems likely that the changes have been slight. The lake is still  ecologically very sound, but extremely vulnerable. Therefore, e.g. the dam and forest estate projects  shall be carefully restudied. The present water level fluctuations of 1.5 meters have some effects on the  whole ecosystem of the lake. The vulnerability of the lake may be enhanced. It is necessary to make a  full inventory of the drainage area, and review the development plans accordingly. In addition, an  inventory of the loading effects of e.g. the townships of Parapat, Porsea, Balige and Muara shall be  made. The total nitrogen concentrations were from 0.100 to 1.186 mg/l N and total phosphorus  concentrations from undetected to 0.061 mg/l P. According to Thomas (1995) ammonium and  phosphate phosphorus were undetectable in the southern basin. The chlorophyll a concentrations were  1.21-1.93 mg/m3, and biomass from 0.023 to 0.036 mg/l. The carbon dioxide concentrations did not  exceed 7.8 mg/l in the voluminous north and south basins. According to Ruttner, (1931) the  concentrations may be 30-40 mg/l in the small and confined Panggururan basin. Lake Toba is an  oligotrophic lake, transparency being 13.5-15.0 meters. In March 1992, the dominant alga was diatom  Denticula tenuis, which favors alkaline waters and waters with low organic matter concentrations.  Besides the diatom the lake had a rather diverse phytoplankton community with many species of coccal  green algae, some desmids, tribophytes, other diatoms, cryptophytes, dinoflagellates and even some  chrysophytes. In September 1992 was dominated by green algae, in the northern basin by  Monoraphidium and Oocystis, and in the southern basin by Monoraphidium and Lagerheimia.  Ratulanggi (1995) stressed the necessity of the comparable long-term data is stressed, because of its  paucity. An integrated Toba conservancy shall immediately be prepared. ILEC & UNEP (1994 a) included the lake in their data book, as one of the two lakes from Indonesia.

Evaluation: Very good, but vulnerable and sensitive to small additions in nitrogen and phosphorus loading.

Tondano Lake (31)

Tondano Lake is a very shallow Indonesian lake with no distinctive features. It is silting up by  some 20 cm/year (Anonymous 1979). It is draining through the River Tondano to the Molucca Sea. Its  stratification was weak (RTR 19.1). The total nitrogen values varied from 0.365 to 0.624 mg/l N, and  total phosphorus values were undetectable. Chlorophyll a concentration was 1.47 mg/m3, and biomass  0.82 mg/l. The phytoplankton was in August 1993 dominated by cyanophytes and diatoms, and the  major species was the diatom Aulacoseira granulata. The lake was mesotrophic with a transparency of  2.5 meters, which is affected also by other than phytoplankton turbidity. Hartoto (1995) studied also his lake in 1992-1993.

Evaluation: Reasonably good, but high siltation rate.

Towuti Lake (38)

Towuti Lake is one of the magnificent lakes in Indonesia, last in the chain of Matano-Mahalona-  Towuti. Its maximum depth is some 200 meters, but we found only 82 meters in the northwestern basin  because the location of the greatest depth is not well documented. It flows through the Larona and  Malili rivers to the Bone Bay. It was weakly stratified (RTR 39.8). Whitten et al. (1987 b), indicated that  the lake was homotherm. The water quality is good and the lake is oligotrophic. Total nitrogen  concentrations were from 0.360 to 0.610 mg/l N and total phosphorus concentrations were  undetectable. Chlorophyll a concentration was 0.19 mg/m3, biomass 0.016 mg/l and transparency was  20 meters. The phytoplankton consisted of only nine species, and the strongly dominating one was Peridinium cf. baliense. See also Hartoto’s studies of 1992-1993 (Hartoto 1995).

Evaluation: Very good.

3.2. RESERVOIRS

Cirata Reservoir (10)
Cirata reservoir is the second in the Saguling-Cirata-Jatiluhur chain of reservoirs in the Citarum  river basin. The stratification was sharp, RTR being 56.5 and 152.1 during the two visits. The oxycline is  as sharp as the thermocline. Anoxic conditions began at the depth of nine meters. No “exceptional”  concentrations of chemical variables were observed. The total nitrogen concentrations were from 0.050  to 1.220 mg/l N and those of total phosphorus from undetected to 0.010 mg/l P. Chlorophyll a  concentrations were from 1.98 to 2.15 mg/m3. Zinc concentrations were from 0.03 to 0.30 mg/l. The  reservoir may be considered mesotrophic. Its transparency was 1.2 meters, but it is also affected by  inorganic turbidity. The abundant species were e.g. diatomophyte Synedra acus v. angustissima and chlorophyte Oocystis sp., and iron bacterium Planktomyces bekefii occurred in the deeper layers.

Darma Reservoir (12)

Darma is a small and shallow reservoir. It was weakly stratified (RTR 41.5). Conductivity and  dissolved solids increase with depth, from 97 to 770 µS/cm and from 62 to 485 mg/l, respectively. The  reservoir can be considered mesotrophic, having total nitrogen values from 0.380 to 0.420 mg/l N and  total phosphorus level of 0.002 mg/l P. Chlorophyll a concentration was 2.14 mg/m3, biomass 0.57 mg/l  and transparency 1.5 meters. The algal population consisted outstandingly of conjugatophytes, mainly of Staurodesmus mucronatus.

Gajah Munkur Reservoir (16)

Visited, but not sampled.

Jatiluhur Reservoir (11)

Jatiluhur is the third sink in the Saguling-Cirata-Jatiluhur chain of reservoirs. The main basin was  stratified (RTR 31.2 and 103.2), and anoxic conditions began during the low-water season at the depth  of 11 meters and during the high-water season at the depth of about 20 meters. No “exceptional”  concentrations of measured variables were found. The total nitrogen concentrations varied from 0.020  to 0.680 mg/l N and total phosphorus concentrations from 0.002 to 0.006 mg/l P. The reservoir is not  turbid like the upper two in the chain, although in the seventies it had inorganic turbidity. The reservoir  is rather oligotrophic than mesotrophic with chlorophyll a concentrations from 2.25 to 0.79 mg/m3 and biomasses from 0.024 to 0.052 mg/l. Transparency was from 2.6 to 3.8 meters, depending on the  season. The major algae were dinophytes (Peridinium spp.), conjugatophytes (Spondylosium spp. and Staurastrum spp.) and chlorophytes (Tetraedron minimum).

Kedung Ombo Reservoir (17)

Reservoir Kedung Ombo was stratified (RTR 69.5 and 79.9). The anoxic conditions began at the  depth of 30 meters, and hydrogen sulfide was traced at the same depth. No “unusual” concentrations of  variables were observed. The total nitrogen concentrations were from 0.380 to 0.800 mg/l N and total  phosphorus concentrations from undetectable to 0.012 mg/l P. Calcium values were from 35.0 to 37.0  mg/l. Chlorophyll a concentration was 0.77 mg/m3  and biomass 0.2 mg/l. The reservoir was dominated  by conjugatophytes, mainly by Staurastrum spp., but also Cosmarium spp. were found. It is oligotrophic, and its transparency was 5 meters.

Lahor Reservoir (19)

Lahor is one of the upstream reservoirs in the Brantas river basin system, located within the  agricultural and industrial areas. However, this cannot clearly be seen in the water quality of the  reservoir. It was stratified (RTR 96.4) and anoxia began at the depth of 10 meters. Only the nitrogen  values, total nitrogen from 0.930 to 1.300 mg/l N was somewhat elevated. Total phosphorus  concentrations were from undetectable to 0.009 mg/l P. The reservoir is probably mesotrophic, with  signs of eutrophication, since there is oversaturation of oxygen during daytime and transparency is 1.5  meters. Chlorophyll a concentration was 2.38 mg/m3  and biomass 0.26 mg/l. Dinophytes dominated in  the reservoir in August 1992, mostly Peridinium spp., but also chlorophytes (e.g. Oocystis spp.) were  well represented. The reservoir may be prone to heavier eutrophication and pollution, if e.g. accidental spills may occur. The vulnerability to phosphorus increases shall be investigated.

Mrica Reservoir (14)

Mrica reservoir was stratified (RTR 79.9), and anoxic conditions began at the depth of 50 meters.  The measured variables did not show any “exceptional” values. Total nitrogen was from 0.560 to 1.100  mg/l N and total phosphorus from 0.002 to 0.004 mg/l P. Chlorophyll a concentrations were from 0.46  to 2.52 mg/m3, and biomass 0.45 mg/l. The dominant algae were Peridium spp. in the otherwise sparse plankton. It can probably be considered mesotrophic, having transparencies of 1.9-3.6 meters.

Palasari Reservoir (27)

Palasari is a small reservoir in Bali. It was used for small-scale fisheries. When visited its water  level was far below the utility level, and there was neither mentionable inflow to the basin nor discharge  from it. The reservoir has also the highest maximum depth:area-ratio (about 15) of all the reservoirs,  which, as a whole, is 1-3. Hypolimnetic waters were anoxic, and some hydrogen sulfide was observed at  the depth of 20 meters. The total nitrogen concentrations were rather high, from 0.810 to 1.720 mg/l N  and total phosphorus concentrations from undetected to 0.012 mg/l P. It may be considered  mesotrophic, but to be prone to eutrophication if the water level tends to be as low as it was with no  flushing. The chlorophyll a value was 2.81 mg/m3, biomass 4.2 mg/l and transparency 0.8 meters. The  reservoir was strongly dominated by dinophyte Peridiniopsis cunnigtonii, 87 % of the biomass.

Saguling Reservoir (09)

Saguling is the first reservoir in the Saguling-Cirata-Jatiluhur chain of reservoirs. In the reservoir,  there are very sharp thermoclines and oxyclines at the depth of about 5-10 meters, depending on the  season (RTR 75.5 and 96.7). In both observation days, oxygen was depleted in the hypolimnia, in  March from the depth of seven meters and in August from the depth of ten meters, and hydrogen sulfide  was present from the depth of 5-10 meters on. The total nitrogen concentrations were from 0.160 to  0.720 mg/l N and total phosphorus from 0.002 to 0.014 mg/l P. Iron concentrations were rather high at  each studied location, from 0.22 to 1.39 mg/l, but in the manganese concentrations no elevation was  observed. Zinc concentrations varied from undetectable to 0.25 mg/l. The reservoir is showing some  signs of eutrophication, especially in the shallow Bongas Bay, where oxygen was depleted in March  already at the depth of eight meters and in August at the depth of five meters, partly due to organic  matter and fish feed (see also Widjaja & Adiwilaga 1995). The nutrient concentrations were higher at  the inlet at Maroko than in the main basin. The chlorophyll a concentrations were from 0.82 to 4.99  mg/m3, and biomasses from 0.096 to 0.212 mg/l. The dominant algae were cyanophytes and  cryptophytes, and the strongly dominant species was Cryptomonas sp., 48 % of the biomass. In March  1992 the area was densely covered with Eichhornia crassipes vegetation, but in August only a few  floating plants could be seen. The loading by fish feed shall be considered as one of the reasons for the  situation in the Bongas Bay. There are occasional fish kills, generally in the beginning of the filling-up  periods, the reasons of which are not yet known. It may be the result of overturn, upwelling, nocturnal  depletion of oxygen at the surface, river water intrusion, toxic materials or excess production of  methane. The reservoir is turbid and the nutrient concentrations seem, in general, not to be alarming,  although some signs of eutrophication could be observed. Transparency was 0.5-0.6 meters. ILEC & UNEP (1994 b) have included Saguling in their data book, together with Lake Toba from Indonesia.

Selorejo Reservoir (22)

Selorejo is at the confluence of two rivers, Konto and Kwayangan Rivers, thus having a relatively  large catchment area. The inflowing waters tend to layer on the bottom near the Konto inlet, thus  improving the oxygen conditions in the hypolimnion in the eastern part of the reservoir. The reservoir  was quite strongly stratified (RTR 111.8, 132.9 and 156.2). At the Kwayangan inlet the stagnant deep  water was anoxic, and some hydrogen sulfide could be detected from the depth of 10 meters onwards.  Concentrations of chloride and calcium were somewhat elevated, from 16.0 to 27 mg/l and from 24.0 to  27.0 mg/l, respectively. The total nitrogen concentrations were from 0.250 to 1.020 mg/l N and total  phosphorus concentrations from undetectable to 0.009 mg/l P. However, the reservoir could be  considered relatively eutrophic, because of the high oversaturation of oxygen in daytime, close to 200  %. Transparency was 0.8 meters. Also the chlorophyll a concentration was one of the highest in the  reservoirs, 6.08 mg/m3, but biomass was only 0.18 mg/l. Phytoplankton was dominated by  conjugatophyte Cosmarium punctulatum and Spondylosium pygmaeum, but also diatoms were found in some degree (Achnantes sp.).

Sempor Reservoir (13)

Sempor reservoir is quite an “ordinary” mid-size reservoir with no “exceptional” characteristics.  RTR was 42.3. The Sempor Reservoir was clearly stagnant having a distinct oxycline at the depth of  12-14 meters. The maximum depth of the basin was 29 meters in August 1992. Oxygen was depleted at  the depth of 14 meters and hydrogen sulfide was found at the depth of 20 meters. At the surface pH was  8.5 and in the hypolimnion 7.3. Nitrate concentrations were in the whole water column about  0.060-0.080 mg/l N, but no phosphate was found. Total nitrogen ranged from 0.420 to 0.600 mg/l N  and total phosphorus from 0.002 to 0.003 mg/l P. Chlorophyll a concentration was 3.78 mg/m3, biomass  0.35 mg/l and transparency 1.9 meters. The strongly dominant species was conjugatophyte Cosmarium  spagnicolum, and other algae were practically non-existent. The reservoir showed some signs of eutrophication.

Sengguruh Reservoir (18)

Not visited.

Sutami Reservoir (20)

Sutami reservoir is one of the upper reservoirs in the Brantas river basin system. It was quite  strongly stratified (RTR 77.0 and 130.5), and oxygen was depleted at the depth of 20 meters. The  nitrate nitrogen concentrations were high, and total nitrogen values from 1.330 to 1.650 mg/l N. Total  phosphorus values were from 0.002 to 0.015 mg/l P. Daytime oxygen concentrations showed  oversaturation, but no other remarkable signs of eutrophication were observed. Chlorophyll a  concentration was 1.18 mg/m3, biomass 0.27 mg/l and transparency was 1.5-1.9 meters. The highly  dominant algae were diatomophytes, and the dominant species Aulacoseira granulata. In addition, chlorophytes were present, such as Tetraedron minimum and Oocystis spp.

Wlingi Reservoir (21)

Wlingi is the downstream reservoir in the Brantas river basin system. It is, after heavy siltation, a  slow motion part of the river, which may also be indicated by the rather weak stratification (RTR 7.0  and 48.5). Nitrate concentrations were high, from 1.340 to 1.560 mg/l N. Total phosphorus  concentrations were undetectable, but magnesium concentrations were highest among the reservoirs,  about 14.0 mg/l. No remarkable signs of eutrophication could be observed. Chlorophyll a value was  1.47 mg/m3, biomass 0.06 mg/l and transparency varied from 1.3 to 1.4 meters. This may be partly due  to the inorganic turbidity. The dominant algae were diatomophytes (Aulacoseira granulata, Synedra  acus v. angustissima) and chlorophytes (Tetraedrom minimum).

PART 4. LAKE AND RESERVOIR MANAGEMENT

4.1. MAJOR OBJECTIVES

One of the major objectives in the beneficial use and management of the natural lakes and  reservoirs in Indonesia will be the maintaining of the production capacity of the relatively thin epilimnetic  water layers in those lakes which do not have a complete mixing and in meromictic lakes, because fish  production in the inland waters will be of increasing importance as food source. The productive  trophogenic layers shall not be disturbed by increased loading through the activities either in the drainage  area or in the water area, and thus consequently contributing e.g. to the level of eutrophication, or by  increasing the oxygen consumption rates, which in turn may decrease the value of the vital epilimnion.  In the water areas, such harmful activities are e.g. the extensive cage cultivation of fish. The main  threats from the drainage area are silt transport, nutrients, harmful industrial effluents and agro- chemicals. The data showed that no real threats of carbon dioxide accumulation were evident in any of the lakes.

The activities in the water areas can be more easily controlled than the activities in the drainage  areas, because the population pressure is on the land areas. However, it is likely that in some water areas  the fish cultivation has gone beyond the planned figures. When only 1 % of the water surface was  originally planned in Indonesia to be allowed for the fish cultures, there are some restricted areas where  this figure has been exceeded. In addition to that, the increasing floating vegetation has taken its share of the water surface. These cannot be affecting the water quality and thus also fisheries.

The population pressure is high in Indonesia. For the livelihood of people, all the available food  sources will be needed. It is hoped that the results of the Expedition Indodanau will, in its part, help in  resolving the present state of the major lakes and reservoirs, in evaluating the future development of  their state, in sustaining their productivity and in formulating the monitoring programs and action plans also at regional and local levels.

The state of the Indonesian lakes is varying. In many lakes, hypolimnetic oxygen depletion is  common, and in some hydrogen sulfide is present. The extent of deoxygenation cannot be described by  area, as e.g. in the temperate region, but by volume. In fact, the depth at which the oxygen concentration  is zero describes the changes rather well in the natural lakes, but also a certain level of area dependent  equilibria may be reached, as may have happened in Lake Singkarak. The deoxygenated water volume is more than 60 % of the total lake volume in several lakes.

The main long-term environmental threats, especially to the natural lakes, but also to the  reservoirs, are population increase, forestry, agriculture, and all the other activities, which are directly  related to the use of the natural resources. In lake quality studies, a distinction between holistic and  reductionistic approaches is evident. Work should not only be reductionistic in the sense of seeking to  understanding phenomena by detailed study of smaller and smaller components, but also synthetic and  holistic in the sense of seeking to understand large components as functional wholes (Odum 1977). This  means good cooperation between various disciplines and organizations in order to achieve the major objectives and targets for the sustainable utilization of the lakes and reservoirs.

Industrial, and other types of pollution, are less serious in the long run, because the majority of the  harmful effluent wastes can be recycled, purified or treated, contrary to the direct interference with the  nature. This needs only more devotion and attention to the lake and reservoir resources, and political will.

4.2. RECOMMENDATIONS

Physical processes of the Indonesian equatorial lakes are largely unknown (weak Coriolis force  and prevailing winds), and chemistry is strongly affected by biological and perhaps geothermal  processes. Whether there exist geothermal inflows into the lakes shall be verified lake by lake. The  density structure is governed by small temperature gradients and relatively important gradients in total  dissolved solids. The importance of biogenically driven stratification maintained by salinity gradient has   also to be emphasized, as well as the deep thermal gradients, which may be adiabatic and stable.  Geothermal heating may exceed the adiabatic gradient. There may also be hot springs flowing into the lakes (see Goldman 1988).

Water balance is dominated by seepage, rainfall and evaporation. As the turbidity increases, the  depth of light penetration is reduced, resulting in greater surface warming and an increased evaporation  rate, causing a net loss of heat. Continuous transparency measurements may give an easy means to  follow the algal increase in the otherwise clear lakes. The nutrient profiles and budgets demonstrate also  distinct differences perhaps reflecting different rates of methanogenesis or fluvial influx. The variations in  the mixing depth caused by weather, and depth of seasonal mixing, may have impacts on the nutrient  flux into the epilimnion. Incomplete vertical mixing of lakes is highly dependent on the relative depth (or  area) and how exposed they are to wind. Indonesian limnology requires more information on the  physical and chemical phenomena of the lakes and reservoirs, to better understand and document the processes (see Melack 1995, Carranza 1995).

The productive layer may extend to four or five times the Secchi depth in the highly transparent  lakes. The phytoplankton assemblage is supported by nutrient recycling through zooplankton and fish  excretion, and unpredictable deep mixing, which may also transport viable biomass from below to the  euphotic zone. Although the annual runoff and precipitation is important in the steady accumulation of  nutrients (e.g. nitrates and phosphates) in the lakes, it is the internal loading from deep mixing that may  account for most interannual variability in production (Lewis 1995). Nitrogen loading is also derived  from fallout from the atmosphere, and phosphorus in the streamflow. Careful depth profiles of major  physical and chemical variables are a necessity. The residence time of the hypolimnetic waters shall also  be investigated by modern methods as they may represent pools of nutrients for the productivity drive,  as is also the atmospheric deposition of nitrate. Wetlands are an important buffer between the land and  lakes, and they may prove to be important mitigation means for intercepting nutrients before they reach the lakes.

Healthy plant cover surrounding the lakes on the watersheds, which recycles nutrients, is one of  the effective ways of reducing nutrient flow from the watershed areas to the lakes. Whether the food  web structures are more “bottom up” or “top down” controlled shall be demonstrated. The biological  processes may have significantly greater importance than physical processes controlling the nutrient  cycling. It is important to concentrate on various issues, such as climate and weather, physical and  chemical limnology, geochemistry and biological processes along with the real field and laboratory studies, data banks and logistical activities.

Without proper information, management of the natural lakes and reservoirs is fraught with  uncertainties and dangers. For example, the vulnerable lakes may respond to additional nitrogen or  phosphorus increases of as little as 1 µg/l. In Indonesia, the main constraint is simply the lack of  background information and daily, short-term and long-term temporal and spatial data. It is, therefore,  suggested that serious efforts shall be made to collect and evaluate all the scattered information (reports,  publications and even manuscripts) and data in Indonesia, and include them in one data bank, such as the one in RIWRD.

The management has to be based on multiple-objective planning in which non-economic  objectives shall be given considerably more weight, and benefit-cost analyses shall be important tools. It  is to be based on reduction of e.g. silt transport, runoff loading, waste generation (water-carriage  sewerage systems shall not be supported), reduction of wastes after generation and increased or better  understanding of assimilative capacity and vulnerability of receiving waters. Standards should be chosen  to suit the present dominant uses of water, potable water supply, irrigation and fishing, and reflect the  level of economic development of drainage basin. The concept of polluter pays is a prerequisite (ECAFE  1974).

As, after the baseline inventories, data beginning to accumulate, it is important to keep an open  mind and allow the actual results to answer the questions set forth. This, however, requires the most  objective interpretation of data and not to “miss the forest for the trees” (Goldman 1988). The  importance of long-term data collection cannot be overemphasized. Records shall be kept to eliminate  the possibility of uncalibrated changes in sampling procedures and analytical methods. This fact has greatly affected the value of the earlier scattered data.

It is necessary to further environmental sustainability of freshwater ecosystems. The near-term  objective shall be to promote interdisciplinary and institutional cooperation to improve the understanding  of the freshwaters in the context of environmental change. Expedition Indodanau shall necessarily need  continuation to widen the fundamental ecological understanding for the management of the natural lakes  and reservoirs in Indonesia, and that the lake and reservoir management would not any more be an  unpredictable challenge. In preserving the ecological balance of the lakes, it is essential to understand the structure, function, and coupling of terrestrial and aquatic ecosystems.

The Freshwater Imperative (see Wetzel 1995) under preparation in the United States has similar aims in four major sectors: science, information management, decision makers’ needs and education.

It is necessary to identify and prioritize;

• Information and research needs with scientific significance, sociopolitical relevance and pertinence to the requirements of decision makers,
• Promote freshwater monitoring to enable improved detection, assessment and prediction of environmental effects and freshwater quality, and
• Recommend ways by which researchers can assess the quality of lakes, classify the lakes  and reservoirs and provide their findings in a timely and appropriate form to enable responsible decision making in the areas of water policies, management and conservation.

To fulfill this strategy a broad cooperative institutional support is needed, but it would provide a  new paradigm for linking science, management and policies to social needs (see e.g. Boon 1995). In the  following Table 7, which has been produced for “administrational” purposes, a combination of  ecological factors and evaluations has been put together to give some advice in considering the lake and  reservoir management in detail, and timing of activities. Especially attention shall be given to the  likelihood of mixing (LM), relation of oxic and anoxic water masses (TC), presence of hydrogen sulfide (Zhs), trophic status (TS), and to the potentiality of a lake being hazardous (PH).

As a plausible continuation to the Expedition Indodanau preparation of a strategy, research and  action plan agenda, Indonesian Lake Basin Action Plan, to direct the freshwater research and utilization  in Indonesia, may be outlined based on the Lake Basin Atlas of Indonesia to be compiled from the  existing information and data, and which is continuously updated. The decision makers’ needs at various  levels should also be carefully reviewed for the appropriate research and data acquisition programs.

PART 5. REFERENCES AND USEFUL LITERATURE

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