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<Technology Needs for Lake Management in Indonesia - Investigation of Rawa Danau and Rawa Pening, Java> L. Available Resources and the Technologies for their Use 1. Water plants as a resource These plants are often called water weeds. This is unfortunate as it has tended to conceal their real value as a useful resource. Too much effort has been dedicated in many countries to getting rid of the water plants rather than assessing their potential value. The water plants which are relevant in this case are - Water hyacinth - or enceng gondok - Eichornia crassipes. Hydrilla sp. Typha sp. There is an abundant literature which shows that water plants cannot be effectively controlled by chemical means. They may be eliminated at one time in a limited area such as a lake, but the seeds of Eichornia can remain dormant in mud for at least 7 years. Chemical control is effective in the short term but expensive. It is not economically viable in the long term, particularly in an environment such as Rawa Pening where there is no substantial direct economic value resulting from the control of the weeds. Biological control of Eichornia crassipes has been successful in some environments. Fungal infections affect the leaves and some insects will eat the leaves. Some fish will eat the roots of water hyacinth, but it is not necessarily their preferred food. It would be much preferable if the water plants could be regarded as a resource, as they represent one of the main outputs from a very productive ecosystem. Eichornia crassipes or water hyacinth is known to be able to take into its tissues large quantities of nutrients such as phosphates. It is therefore likely that much of the mobile phosphate in the Rawa Pening ecosystem is held at any one time in the Eichornia mats. Sporadic efforts are made and have been made in the past to remove some proportion of the Eichornia mat from the rawa. No sound and profitable use has so far been found for Eichornia in Java. Hydrilla has been used as feed for pigs in the past, and has proved quite successful. Nevertheless the use of the plants for this purpose has not continued. They are not used for anything at present. Typha has been shown, in other countries, to be a valuable asset in providing a cheap and effective method of water purification. The plant has the advantage that it has a strong rhizome which helps to stabilise river banks and limit erosion. The plants of Typha have a "luxury uptake" of phosphate. That is to say, the plants absorb more phosphate than they actually need for growth and store it in their tissues. Thus they act as sponges, mopping up phosphate from the environment. A species of Typha is reported to live in Rawa Pening. The presence of these three species suggests that it should be possible to establish an industry based on the use of this resource. The water in the rawa, though probably having very high values of phosphate does not appear to suffer from algal blooms, though small blooms of Cyanophyceae can be seen on some of the small creeks and land drains entering the lake. One reason may be that much of the mobile phosphate is incorporated in the tissues of the water plants at any one time. The water plants, and particularly Eichornia, therefore offer a cheap and effective means of extraction of phosphate from the rawa. It would be very desirable to continue to extract water plants from the rawa on a planned and controlled basis to establish some control over phosphate levels with the aim of ultimately reducing the phosphate levels in the water. There have been numerous attempts in the past to find an effective and economically viable use for these and similar water plants. Some uses have been found for the water plants in the lake, but none have proved to be economically attractive, or at least, none have attracted any substantial economic investment either by Government or by private industry. In a number of papers Soerjani has reported the use of water hyacinth leaves in the manufacture of specialty paper and thin cardboard. The technology for introduction of a cottage industry manufacturing these products has been demonstrated. Plants of water hyacinth could be sold to industries elsewhere in Java as a cheap and effective means of removing certain pollutants from industrial waste waters. It is unlikely that this would be economic for large quantities of water hyacinth in view of the transport costs, but could well be economic in terms of supply at intervals of new plants for an ongoing extraction process. Plants of Hydrilla have been used successfully as food for pigs, and though water hyacinth is not a preferred food for pigs they will eat it if mixed with Hydrilla. Water hyacinth is known to have been used successfully as a stock feed for cattle in Queensland when mixed with molasses from sugar processing plants, and urea. Again, the costs of transport would seem to limit this possibility to use of leaves as cattle fodder in the immediate area round the edge of the lake. Eichornia is used as green fertiliser for growing rice. During the dry season, the exposed area of mud on the lake shore is available for the cultivation of rice. Goeltenboth (1979) reports that in the period prior to his report about 1,100ha of exposed mud was converted to padi fields every year. This exposed mud was tilled and divided into fields by creation of mud walls, using water hyacinth plants as supports and as green fertiliser. He calculates that over 60ha of water hyacinth plants were used this way each year and notes that this makes a major contribution to restriction of the growth of water hyacinth on the body of the lake. The other major contribution to this limitation is the number of plants of water hyacinth which die during exposure to the sun on the mud during the dry season. Water hyacinth has been shown to be an effective mulch which is necessary at times in the dry season in this area. Investigation has shown that increases of up to 10% in production of some crops can be achieved by use of this material as a mulch. Again the costs of transport limit the area through which this use of water hyacinth would be commercially viable. The use of water hyacinth leaves to generate gas in a small scale bio-gas generator has been demonstrated at Universitas Kristen Satya Wacana. The use of such generators is only economic if the leaves can be transported or carried cheaply to the generator. Households in the immediate vicinity of the lake might benefit from such generators. The cost of manufacture is unknown. One of the most profitable potential uses for water hyacinth is in the growing of mushrooms. This has the great advantage that mushrooms are seen as a luxury crop and command a relatively high value in the market. The demand in Central Java may be met at the present time by the present level of production. The question is whether an export industry of dried or tinned mushrooms would be economically viable using the leaves of water hyacinth as a growth medium. No investigation of the economics of the mushroom industry has been undertaken. This was considered to be outside the parameters of the investigation. Already one commercial grower uses leaves of water hyacinth in mushroom production from a small factory in the Dieng Plateau. Leaves are collected periodically from Rawa Pening for this purpose. It is believed that these mushrooms are sold locally and in Jakarta. If a viable export industry were to be developed it would call for a large scale operation using similar principles. The requirements would start with a system of regular collection of good quality leaves of water hyacinth. These would be collected using boats and presumably bought from local boat owners on the lake shore at agreed points on the shore. Trucks would be necessary to transport the leaves to a processing plant. The processing facility would probably be situated on the upper slopes of one of the adjacent volcanoes. It is noteworthy that most tropical mushroom production facilities are situated on mountains or at high altitude as in the Dieng Plateau, and the Genting Highlands in Malaysia. Transport costs would therefore be substantial. There would be considerable capital cost in construction of the production factory for the mushrooms, of the growing rooms which would be kept dark and cool, of the cleaning and of the preparation facility. If the mushrooms were dried or canned for export this would require further substantial capital investment. The entire enterprise would call for a considerable work force for maintenance of the process. It would be necessary to investigate the nature of a potential market for the end product and perhaps to engage a marketing group. A guaranteed market is essential before such an enterprise is started. The level of capital investment involved would call for Government support initially or for investment by a large private corporation. This is a level of investment which is quite beyond the individual small business man. Any initiative to develop effectively an industry using water plants as a source of raw material calls for investigation by a Government which is prepared to invest in the selected enterprise. So far no Government initiative has been detected in developing any industry using the water plant resources of the lake or the human resources provided by the people living on the lake shore. Rawa Pening is one area where it would be feasible to establish large scale economic production of Eichornia crassipes, and where it would be possible to manage the plants efficiently. The capacity of these plants to take up phosphate is equalled by their release of the same phosphate when the plants or particular leaves die. So to be effective in removing phosphate from the rawa, the water hyacinth plants need to be taken from the rawa regularly (harvested) and taken some distance from the shore. They can then be burned to produce ash, incorporated in the soil as green fertiliser, fed to cattle, or fed to appropriate species of fish in fish ponds. 2 Fish populations in Rawa Pening. A summary of their biology and ecology Dominant fish species The fish species found in Rawa Pening are dominated by indigenous species characteristic of open waters in Javanese lakes. These species are very much influenced by the physics and chemistry of the water, and particularly by factors such as temperature, and dissolved oxygen. These species include plankton feeders, (microphagous species) herbivores feeding on aquatic weeds, and predators. The commonest species are plankton feeders, including Osteochilus hasselti ("nilem"); Trichogaster trichogaster, ("sepat siam", or the snake skin gourami); Trichogaster pectoralis, ("sepat rawa", or three spot gourami); Puntius javanicus ("tawes"); and Puntius binotatus, ("wader"). The commonest species of predacious fish include Ophiocephalus striatus (the snake head or "gabus"); Clarias batrachus (the catfish, or "lele"); and Monopterus albus, (the swamp eel or "belut"). The dominance of the plankton feeders in the fish community is presumably determined by the abundance of plankton in the lake. The density of both phytoplankton and zooplankton is high, and reflects the high productivity of the water in the lake. The density of the plankton varies seasonally (Goeltenboth 1979). There are no recent data detailing the distribution of the plankton in the lake and the factors affecting their abundance. The high levels of plankton in the lake do not by themselves guarantee that plankton feeding fish will be dominant in the lake and many other factors are likely to affect the abundance of particular species. It may be that conditions near the bottom of the lake and the availability of benthic food do not favour fish. There are no recent data on these factors. Other indigenous species found less commonly in the lake include Rasbora spp (or "wader andong") and Anabas testudianus (the "betik" or climbing perch). Grass Carp The Grass Carp, Ctenopharyngodon idella, has been introduced with the objective of controlling aquatic weeds. The grass carp is very efficient at consuming submerged aquatic weeds, such as Hydrilla verticillata, Ceratophyllum demersum, and Najas indica, consuming sometimes consuming as much as 125% to 150% of its weight in aquatic weeds per day. However, as regards the floating aquatic weeds such as Eichornia crassipes, the fish would normally only consume the roots and young leaves if other preferred food weres available. Grass Carp cannot breed in the open waters of Rawa Pening. If there is any desire to maintain the stock of grass carp in the lake to reduce the volume of aquatic weeds in the lake, then a fish breeding station should be established on Rawa Pening to ensure an adequate supply of fingerlings. Fingerlings could then be supplied from the fish breeding station to other lakes in Central Java with an aquatic weed problem. 3. The economics of the fishery Fish Production Fish production from Rawa Pening has decreased in the last 30 years. This may be due to a variety of causes. These include the use of herbicides to control Eichornia crassipes, the excessive use of pesticides on rice fields round the lake, or the illegal use of pesticides for fishing. The fisheries of the lake have been investigated by Carlander in a series of articles, and in particular the paper by Carlander in 1979 refers to this issue. Possible introduction It might be possible to increase the production of fish from Rawa Pening by the introduction of the species Oreochromis nilotica (or Red Nile). Much research work on fish and the potential for improved fishery in this lake was undertaken in the period prior to 1979 by research workers from Universitas Kristen Satya Wacana in Salatiga. This data should be used as the basis for further investigation of the potential for introduction of new species such as the Red Nile, to ensure that any new species introduced will not have any adverse impacts on existing species of fish in the lake or on the environment of the lake. This fish would have the ability to reproduce in Rawa Pening and the technology for breeding in aquaculture is well known. The physical and chemical parameters of the lake would support this species with a water temperature of 26.8 (±0.3) degrees Celsius in the wet season and 27.3 (±0.9) degrees Celsius, in the dry season; dissolved oxygen levels of 0.4 (±11.2) ppm, alkalinity of 40-80 ppm calcium carbonate equivalent, and pH of 7.3 to 7.4. The Red Nile is omnivorous and so could utilise food resources in the centre of the lake which are not fully utilised at present. Common Carp are not recommended for introduction Common carp (Cyprinus carpio) are normally reared in cages in rivers and lakes in many parts of Java. This form of aquaculture should not be introduced to Rawa Pening. The introduction of these fish would lead eventually to an increase in the organic content of the water. This would affect the penetration of light into the water and so reduce photosynthesis. This would lead to a reduction in productivity in the lake. Thus the productivity of several species would be affected. Also, the culture of the fish in boxes cages leads to a loss of fish food on to the bottom of the lake. There is already too much fish food reaching the bottom of the lake and this is one of the major concerns about the low oxygen levels in the water. Orientation of the Directorate of Fisheries The main concern of staff of Direktorat Perikanan appeared to be to maintain employment among fishermen, rather than to be concerned with what exactly the fishermen were catching. There may be some political overtones in this, as many of the people who go fishing on the lake are people who, for one reason or another, do not own land or have lost land for farming. They may therefore not be "popular" in the village for some reason. Fishing is often seen as a "last resort" for these people, as a source of income. Staff who are members of a Directorate of Fisheries should be acquainted with the general ecology of the lake. It would be desirable to increase the breadth of vision of the staff of Direktorat Perikanan in the future, as they have a significant role to play in the ecology of the lake. 4. Rice cultivation Extensive areas of padi fields south of Ambarawa are irrigated by canals from the lake. The amount of water used in rice cultivation and derived from Rawa Pening is unknown. Rice is also grown in smaller areas of suitable land along the shores of the lake. Certain local residents apparently hold an entitlement to cultivate rice on the land exposed on the bed of the lake during the dry season. Since the lake is relatively shallow, the area involved is considerable (over 1,000 hectares). The area of the lake at a water level of 463.9 metres during the wet season is reported to be approximately 2,770 hectares, while during the dry season the water level falls to 462.8 metres and the area is reported to be approximately 1,707 hectares. Not all of the exposed land can be cultivated by the common methods of using padi fields. Some low-yielding floating rice is grown. The advantage of floating rice is that it avoids the necessity of construction of mud walls to define individual fields and to retain water. There is no information on the economic value of the crops grown in, or with, water from Rawa Pening. Nevertheless this is a major resource which depends on Rawa Pening. The success of the rice crop is threatened by two factors, according to conversations in the area. The occurrence of floods can disrupt the harvest of rice, by flooding and swamping padi fields. Floods may occur near particular rivers, or as a result of a general rise in the level of water in the lake. A shortage of water may also threaten the economic value of the rice crop. If the availability of water declines during the dry season, the water available will not be sufficient to allow the rice to reach maturity, or optimal size, before it has to be harvested. The use of fertilisers on rice fields constitutes one of the major sources of pollutants entering the lake. These pollutants include salts of potassium, phosphorus and nitrogen, which encourage plant growth, and in particular algal growth. An excess of such nutrients in the water can lead to the production of algal blooms. The use of pesticides on rice also causes problems in the lake. Pesticides of different kinds may accumulate in the tissues of fish or they may kill the fish directly. It is possible that the use of pesticides to control insect attacks on rice crops is one reason for the decline in the fishing industry on the lake. At certain times of the year, it is possible to see scores of "back-pack" insecticide sprayers working in the fields along the shores of the lake. There is a clear case for improvement in the methods of application of pesticides to rice in such areas. Similarly there should be an examination of methods of incorporating fertilisers in waterlogged soil. No effort appears to be made in this area to restrict the loss of fertiliser in storms, when the soluble chemicals are carried into the lake either in solution or adsorbed on particles of clay. 5. Utilisation of water by PLN This has already been considered. The question, from the point of view of resources, is whether it would be better to reduce the volume of water used by PLN during the dry season, in order to ensure that rice crops had enough water to reach maturity. Similarly it would be preferable, from the point of view of the rice crop, to minimise the extent of flooding and consequential crop destruction during the wet season. The ecological objective should be to produce a system which will optimise the production of rice in relation to the needs of PLN and other users. PLN is seen as being a priority user since PLN controls the release of water from the dam. Various linear programming systems could be utilised to produce more optimal utilisation of water resources. To explore these in detail would be beyond the scope of this project.
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