Kesesuaian Makroinvertebrata untuk Bioassessment Kualitas Air Sungai Brantas Bagian Hilir

Sungai Brantas bagian hilir memiliki banyak permasalahan akibat pengaruh antropogenik yang dapat dikenali dari pola tutupan lahan. Dampak negatif yang dihasilkan berupa penurunan kualitas air yang mempengaruhi komunitas dari makroinvertebrata. Berbagai penilaian penurunan kualitas air melalui indek makroinvertebrata banyak diaplikasikan dan dikembangkan, baik dalam kajian habitat maupun kualitas air sungai. Namun, beberapa studi mengenai hubungan indeks biotik dengan kondisi kualitas air sungai banyak dikorelasikan negatif. Maka perlu adanya studi mengenai kesesuaian penilaian kualitas perairan melalui berbagai indeks. Sehingga pada studi kali ini memiliki tujuan untuk meninjau kesesuaian indeks biotik sebagai penilaian kualitas air melalui bioassessment, melalui makroinvertebrata dengan ditunjang oleh parameter lingkungan dan tutupan lahan sub-DAS Brantas bagian hilir. Penelitian ini dilakukan pada bulan September-Oktober 2018. Area studi difokuskan pada sub-DAS Brantas bagian hilir yang terbagi menjadi 2 (dua) aliran yaitu Sungai Porong dan Sungai Surabaya. Lokasi pengambilan sampel dilakukan pada 9 stasiun sampling; 2 pada aliran S. Brantas sisi Mojokerto, 4 pada aliran S. Porong, dan 5 titik pada aliran S. Surabaya. Pemilihan lokasi tersebut diambil berdasarkan potensi pengaruh antropogenik terhadap aliran sungai. Parameter yang akan dikaji berupa kondisi makroinvertebrata melalui nilai keanekaragaman Shannon-Wiener (H’) dan indeks biotik (Hilsenhoff Family Index, BMWPThai dan Sing Score); parameter perairan (suhu, kekeruhan, kecepatan arus, TSS, salinitas, pH, DO, BOD, TOC, ammonium, nitrat, konduktivitas dan fosfat) dan tutupan lahan pada masing-masing sub-DAS. Beberapa parameter perairan dikaji dengan indeks LISEC Score. Data yang didapatkan dianalisis menggunakan ANOVA one-way dan CANOCO untuk melihat pengaruh dan kecenderungannya. Kemudian ditinjau kesesuaian masing-masing indeks biotik melalui korelasi Pearson’s terhadap parameter fisik-kimia perairan dan faktor tutupan lahan. Hasil penelitian menunjukkan komunitas makroinvertebrata dan kualitas fisik-kimia perairan memiliki perbedaan di ketiga bagian sungai. Kualitas air Sungai Brantas di segmen Mojokerto memiliki nilai tertinggi dengan kategori “tercemar ringan” berdasarkan indeks keanekaragaman Shannon-Wiener dan BMWPThai, dan kualitas fisik-kimia perairan “baik” menurut LISEC Score. Hal ini disebabkan daerah aliran sungai tersebut didominasi oleh tutupan lahan berupa perkebunan dan lahan pertanian. Menuju Sungai Porong dan Sungai Surabaya, terjadi perubahan tutupan lahan menjadi kawasan pertanian dan urban. Kedua sungai tersebut memiliki indek keanekaragaman Shannon-Wiener dan BMWPThai “tercemar ringan”, dengan kategori kualitas fisik-kimia berdasarkan LISEC Score “tercemar sedang”. Kondisi ini berbeda setelah melewati aliran pembuangan lumpur Lapindo, berdasarkan indeks keanekaragaman Shannon-Wiener, BMWPThai, dan LISEC Score termasuk dalam kategori “tercemar”. Hasil korelasi antara kualitas air fisik-kimia terhadap masing-masing indeks, menunjukkan hanya BMWPThai yang memiliki nilai korelasi signifikan. Namun demikian, penggunaan indeks yang sesuai untuk daerah studi masih memerlukan modifikasi dan adaptasi, dengan penambahan taksa lokal yang belum tercantum pada matrik indeks. ================================================================================================ The lower Brantas condition has been influenced by various natural and anthropogenic factors, which cause adverse impacts to water quality and macroinvertebrates. Many water quality bioassessment methods using macroinvertebrates have been used and developed in Indonesia. However, the results were not satisfying. Therefore, a study concerning the suitability of biotic index for assessing river water quality is necessary. This study aims to assess the suitability of bioassessement methods using macroinvertebrates for assessing water quality, by putting into consideration physical-chemical water quality parameters and land cover of the lower Brantas river zone. Macroinvertebrate and water samples were collected two times from September to October 2018 at 11 sampling sites. Two of the sites were located at the Brantas river, four of which were at Porong river, and five others at Surabaya river. Collection of the macroinvertebrates was done using a standard hand net. Macroinvertebrate samples of each site were analyzed according to Shannon Wiener diversity index (H’), Hilsenhoff Family Index, Biological Monitoring Working Party (BMWP) of Thailand (BMWPThai) and Singapore (SingScore). The measured physical and chemical water quality parameters were: temperature, turbidity, current and Total Dissolved Solids (TDS), pH, DO, BOD, TOC, ammonium, nitrate, conductivity, and phosphate. Four parameter data, namely DO, BOD, ammonium, and phosphate were used for calculating LISEC Score. Land coverage from satellite imagery in the Brantas watershed was analyzed using Kappa method. Suitability of each biotic index method was examined using Pearson’s correlation to physical and chemical water quality parameters and the land cover factor. Results of this study showed that the three parts of the lower Brantas River had different characteristics. The Brantas river segment in Mojokerto was “lightly polluted” according to the Shannon Wiener diversity index. However, the physical and chemical quality of this river part based on the LISEC Score was of “good condition”. This river segment was surrounded by land cover, which comprised plantations and rice fields. Towards to the Porong and Surabaya Rivers, the land cover changed to agriculture and built in environment. Consequently, the biotic index and physical-chemical water quality in these rivers worsened to “lightly polluted” according to Shannon-Wiener diversity index and BMWPThai, “moderately polluted” according to LISEC Score. Based on the LISEC Score, the water quality in the lower part of the discharge point of Lapindo mud volcano was of “polluted” category. Based on the Shannon-Wiener diversity index, the BMWPThai and the LISEC Score, this point was classified as “polluted”. Correlation between the biotic indices and the LISEC Score showed that only the BMWPThai had a significant correlation. However, the BMWPThai has to be modified and adapted, by including the local taxa in the matrix index