Agricultural sector plays a strategic role for economic development since it serves as a part of economic system. In fact, the agriculture is not only provides food and raw materials, but also gives employment opportunities to a very large proportion of communities either in city/urban or rural areas. Furthermore, it has also a great significance in international/global trade as well as foreign exchange resources, which in turn might increase a country’s GNP value. For instance, according to the data of the Indonesian Ministry of Agriculture (2013), the agricultural sector capable to involve about 46.5% of the total productive employment, and contribute to about 14.7% of the total GNP.
Serayu watershed is one of the biggest watersheds in Java island, Indonesia with catchment area of 4,375 km2 (coordinate: 7o24’49.9” – 7o40’42.2” S, 109o6’49.5” – 109o48’36” E), elevation of 0 – 2,500 mm above sea level, and annual precipitation of 2,500 – 4,000 mm per year. The watershed has about 11 sub-rivers, which is connected to the main river of 180 km in length (average monthly flow rate: ~ 2,800 m3/s), and covers four regencies, such as Wonosobo, Banjarnegara, Purbalingga, Banyumas, and Cilacap regency (Fig. 1). Regarding land use system, the upland agriculture including horticulture crop and shifting cultivation is largest in proportion (38.2% or 141.485,95 ha) of the total area, followed with rice field (20.2% or 74.826,29 ha), and agroforestry (12.7% or 47.085,99 ha). The remaining areas include tropical forest, and are used for housing, transport facilities, and industries.
Fig. 1. Serayu watershed covering various land use systems: highland agriculture, rice field, and coastal environment.
Serayu watershed is divided into three regions, such as upper-stream, middle-stream, and down-stream/coastal area, of which each has specific characteristics as well as problems to be solved (Fig. 2). For instance, the upper-stream area covering most highland agricultural system (at slope of 20-45 and >45%) leads to land degradation problem due to erosion (runoff: ~1,500 m3/ha/year; soil loss: > 160 ton/ha/year) and even landslide in some areas like Wonosobo, Banjarnegara, and Purblingga regency. Accordingly, such phenomena might in turn contribute to some related environmental problems at the middle-stream and downs-stream area, including sedimentation on river bad and dam/reservoir (2.5-3.5 x 106 m3/year; decrease in Mrican dam/reservoir capacity up to 2.5% per year, resulting in deficit water supply for irrigation as well as electricity power), river abrasion removing about 20-80 ha of the productive land in Banyumas, and water contamination causing low water quality used by surrounding communities (COD: ~100 mg/L; BOD: 16.5 mg/L). Furthermore, there is a trend of mangrove forest degradation problem in Cilacap’s coastal areas, which increase seawater abrasion as well as enlarge its unproductive sandy soil.
Fig. 2. Schematic diagram of the current environmental issues in Serayu watershed.
Understanding the roots of the problems of each specific region is essential and will be needed in order to solve the overall problems above. For example, the problems at upper-stream of Serayu watershed are mostly caused by the conventional farming system with intensive use of chemical fertilizer and pesticide and without sufficient land conservation method in highland agricultural areas like as Dieng Plateau (Wonosobo and Banjarnegara regency) and Serang village (Purbalingga regency), and some related location in Banyumas regency. Such conventional systems are also intensively adopted by many farmers to cultivate rice and lowland horticultural crops in the middle-stream (Banjarnegara, Pubalingga, and Banyumas regency) and down-stream/coastal area (Cilacap regency). In addition, mining sand material from Serayu river by local communities in middle-stream and near-coastal areas results in critical erosion/abrasion on its river embankment, hence increase river sedimentation and then reducing water supply to surrounding cultivated areas.
Fig. 3. An example of the prospective research topics in Serayu watershed.
The above phenomenon reflects the critical environmental problems of Serayu watershed, which has very important roles in supporting surrounding ecology and human life. The watershed also has a significant impact on regional and global climate change. Therefore, the solutions should be taken from the comprehensive considerations and researches including technical/physical, socio-anthropological and regulation aspect. Specifically, the solution should be performed based on accurate observation data through some related studies on overall watershed area, such as upper-stream (e.g., highland agriculture and deforestation, land conservation, etc.), middle- and down-stream (e.g., rice cultivation, soil bioremediation, etc.), and coastal areas (e.g., mangrove deforestation, aquaculture, etc.) (Fig. 3). In order to realize the goals, there is a need for the three-party collaborative works involving academician/university, targeted farmers/communities, and local government to pay attention on these matters toward harmonization among sufficient food supply (agricultural production), environmental conservation, and community welfare.