PENGARUH PENUTUPAN MANGROVE TERHADAP PERUBAHAN GARIS PANTAI DAN INTRUSI AIR LAUT DI HILIR DAS CIASEM DAN DAS CIPUNEGARA, KABUPATEN SUBANG (Effect of Mangrove Vegetation Cover to the Shoreline Change and Seawater Intrusion at Downstream of Ciasem)

Abstract

ABSTRAK

Perubahan penggunaan lahan dari hutan ke penggunaan lainnya seringkali diikuti oleh penurunan fungsi tanah sebagai pengatur tata air. Penelitian ini bertujuan untuk mempelajari pengaruh tutupan mangrove terhadap perubahan garis pantai dan intrusi air laut pada hilir DAS. Penelitian difokuskan pada penentuan jenis penggunaan lahan pantai melalui interpretasi citra satelit dan pengecekan lapangan, analisis kondisi fisik tanah, pengamatan intrusi air laut, dan analisis perubahan garis pantai akibat abrasi atau ekresi. Hasil penelitian menunjukkan pada periode tahun 1989 hingga 2013, tambak yang ditanami mangrove di Kabupaten Subang mengalami penurunan luas dari 3402,6 ha menjadi 2384,9 ha, sebaliknya terjadi peningkatan luas tambak tanpa mangrove dari 5745 ha menjadi 8741,5 ha. Analisis perubahan garis pantai menunjukkan adanya abrasi di Ujung Pamanukan dan Teluk Ciasem mencapai 1,2 km ke arah daratan. Akresi dijumpai di Teluk Blanakan dan Muara Cipunagara mencapai 1,3 km dalam kurun waktu 1989 – 2013, sedangkan di Muara Sungai Cipunagara mencapai 1,7 km. Air tanah di Desa Muara dan Desa Legon Wetan termasuk air agak payau karena memiliki nilai DHL yang lebih besar dari 1500 µS/cm dan TDS di Legon Wetan > 1000 ppm, sedangkan di Muara TDS nya mendekati 1000 ppm. Perbandingan konsentrasi khlorida-bikarbonat di Desa Muara dan Desa Legon Wetan menunjukkan angka R > 1 sehingga tingginya kadar garam pada air tanah diakibatkan oleh intrusi air laut. Hal sebaliknya terjadi di Desa Tegalurung yang penggunaan pantainya didominasi tambak bermangrove memiliki nilai DHL dan TDS air tanah yang masuk dalam klasifikasi air tawar.

ABSTRACT

Changes in land use from forest to other uses are often followed by a decrease in soil functions as a regulator of the water system. This research aimed to study the effect of mangrove cover to a change of a coastline and sea water intrusion in the downstream watershed. The research were focused on determining the type of land use shore via satellite image interpretation and field inspections, analysis of soil physical conditions, observation of seawater intrusion, and analysis of shoreline change due to abrasion or accretion. The results showed in the period of 1989 to 2013, mangrove ponds in Subang decreased from 3402.6 ha to 2384.9 ha, whereas an increase in pond area without mangroves was from 5745 ha to 8741.5 ha. Analysis of a shoreline change showed abrasion in Ujung Pamanukan and Ciasem gulf, it reached 1.2 km inland. Accretion was found in the Blanakan gulf reached 1.3 km in the period of 1989-2013, while at the Cipunagara estuary reached 1.7 km. The ground water in the Muara and Legon Wetan village included brackish water because it had the DHL that was greater than 1500 μS/cm and TDS in Legon Wetan reached > 1000 ppm, whereas TDS in Muara village closed to 1,000. Comparison of bicarbonate-chloride concentrations in the Muara and Legon Wetan village showed R > 1 so that high levels of salt in groundwater is caused by seawater intrusion. On the other hand, there was occur in the Tegalurung village that the use of shores was dominated by mangrove ponds had DHL and TDS value groundwater that was classified as plain water.