Technology Needs for Lake Management in Indonesia- Investigation of Rawa Danau and Rawa Pening


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<Technology Needs for Lake Management in Indonesia -
Investigation of Rawa Danau and Rawa Pening, Java>

E. Discussion of Management of Rawa Pening

Meetings were held with Government staff in Salatiga. Items discussed at meetings included an explanation of the objectives of this project in attempting to define the technological needs for the establishment of ecologically sustainable management policies for a number of lakes in Indonesia, one of which is Rawa Pening.

1. Long term management objectives

These should be based on sustainability of the ecological system in the long term, and on the stability of the related socio-economic system, not on the maximisation of economic benefit in the short term, or on financial values. Financial values have to be taken into account as part of the management system but are not to be seen as the primary guiding factors in determination of the management policy. Social objectives have to be seen as closely connected to, and dependent on, the ecological system.

2. Hydro-electric power generation

To achieve these long term management objectives, preliminary assessment showed that certain types of ecological data would be required. The question then becomes whether these data are available at present.

Total resource management requires information on the status of individual resources, such as water, in terms of sources of water and potential sources of water, uses of water, both within the catchment, the lake, and uses of water flowing out of these areas. This project is restricted (by funding limitations and time constraints) to examination of the uses of water held within the lake and in the immediate vicinity of the lake.

Similar and equivalent information is required in terms of land use and land management. Total catchment management requires information on the status of the catchment in terms of urbanisation, forest cover, quantity and speed of run-off, water quality from run-off, river inputs, and from diffuse sources of inputs.

In these terms there is a need for the development of a budget dealing with the input of water to, and output of water from Rawa Pening. This budget should form a major component of the basis for management planning aimed at sustainability in the long term of the ecological system of the lake. Similarly, there is a need for assessments of the quality and quantity of water flowing through the ecological system of which Rawa Pening is the centre.

In parallel with the budget for water resources, it would be very desirable to have similar budgets for materials such as phosphate, nitrogen, and organic matter, which affect and to a large extent determine productivity in the lake. Understanding of the productivity of the lake and how to manage it is vital for the future of Rawa Pening.

3. Types of socio-economic data required

Basic sociological statistics have to be obtained as regards the reasons why some families live near the lake shore. They may do so for historic and traditional reasons in that their families have always lived there and worked in particular occupations. Some may do so for other reasons such as having been displaced from their former homes. Such different groups will have different attitudes to the lake as a resource.

An excellent preliminary study of many of these issues was undertaken in 1979 by Prajarta et al (1979). This and other similar studies could provide a base-line for assessment of the ways in which communities on the shores of the lake have altered during the last 20 years. Such studies would also provide a basis for the assessment of population growth in the region where there has been extensive migration of people to the lake shore and to the lake catchment. Other aspects of change affecting population growth which are known to have occurred include the intensification of the agricultural systems in use on the lake shore (Wirjomihardjo and Pramonosidhi 1977a, 1977b). This process, which was related to population growth, was recognised to be occurring and was measured as far back as 1976.

It is necessary to determine which groups in the community are dependent on the lake for their income, either directly (such as fishermen), or indirectly (such as staff of hotels and restaurants on the lake shore). The relative importance of the lake to their standard of living has to be defined.

The expectations of these various groups will be quite different. Some may hope for an extensive development of tourism and its associated infrastructure. Others may hope for a continuation of their traditional way of life, in which tourism might be seen as an intrusion.

It is necessary to define those groups which live near the lake but which are not dependent on the lake for their income, either directly or indirectly.

4. Immediate requirements to achieve these objectives

There is a need to attempt some assessment of the conditions in the lake and the catchment in the period prior to 1940. Possibly some records still exist in the Netherlands which might clarify the chemical and biological conditions in the lake and the catchment in this period.

The major impacts on the ecology of the lake and on the environmental processes affecting it are likely to have started in the period of extensive economic development after 1965. These changes and the consequent environmental pressures need to be measured and their impact on the lake and its catchment assessed. It is necessary to determine whether these changes are still occurring, and if so what their eventual impact may be on the lake at specified times in the future.

The impact of environmental changes on various community groups has to be assessed and some determination made on whether these impacts are positive or negative. Decisions have to be made on management to correspond with these. Overall, an attempt must be mad to predict the consequences of particular environmental management policies on the catchment on the lake and on the people living there. This would provide a basis for decision making about the preferred management policies to be implemented.

Any long term planning by Government for new developments has to be incorporated in these assessments, and their sociological implications defined.

On the basis of these assessments one should be able to define the optimal management strategies to maximise the long term sustainability of the environment of the lake and the maintenance of a stable socio-economic system based on the lake, among the surrounding communities.

5. Hypothetical water budgets

The water budget in Rawa Pening prior to the arrival of Water Hyacinth was probably as shown below -

At present it might be better shown as -

There are some variables about which there are no data. Has river input increased as a result of clearing of forest areas on hill sides, or has it decreased as a result of much greater domestic consumption in the catchment upstream from the Rawa? Probably it has decreased and at the same time the impact of clearing has been to produce larger, faster quantities of run-off, so that flooding may actually occur more often, though the total volume of water reaching the lake each year may be substantially smaller than 40 years ago. There are no data on this at present.

6. "Concealed" inputs, outputs and processes

There are new categories of processes which are mainly a result of urbanisation and industrial development.

It is on the basis of the "black box" diagrams (see over) that a preliminary water budget could be constructed. Similar budgets could be constructed for particular chemicals such as phosphorus and nitrogen, and for particular substances such as clay.

7. General nature of processes which are likely to be occurring in the lake

This combination of factors is likely to produce increased sedimentation on the bottom of the lake. The sediment will now have a greatly increased volume of organic matter in it, following the arrival of water hyacinth plants and increased urbanisation. If the water input is decreasing while the organic matter input is increasing this will lead to increasing eutrophication. The existing data support this suggestion. In fact the phosphate data available from studies 20 years previously at Universitas Kristen Satya Wacana suggest that eutrophication was far advanced at that time.

The input of toxic chemicals will discourage the growth of green algae, but is less likely to affect the development of large populations of Cyanophyceae, or blue-green photosynthetic bacteria, which can be toxic. Cyanophyceae "blooms" can be seen on some of the small water bodies in ditches and streams leading into the Rawa.

If toxic chemicals of certain kinds such as chlorinated hydrocarbons or heavy metals, such as lead, are introduced to the lake water these will accumulate in food chains and cause problems with the fisheries. Heavy metals of various kinds are extracted from water by water plants and would cause the water plants to be unusable as a source of feed for livestock.

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