KONSENTRASI NITRAT DAN ORTOFOSFAT DI MUARA SUNGAI BANJIR KANAL BARAT DAN KAITANNYA DENGAN KELIMPAHAN FITOPLANKTON Harmful Alga Blooms (HABs) Concentration of Nitrate and Orthophosphate at Banjir Kanal Barat Estuary and their Relationship with the Abundance of Harmful Algae Blooms

Abstract

Perkembangan industri dan aktivitas rumah tangga di sepanjang aliran Sungai Banjir Kanal Barat Semarang diduga memberikan pengaruh terhadap kualitas perairan berupa buangan limbah yang mengandung nutrien (nitrat dan ortofosfat). Kedua nutrien tersebut dalam konsentrasi yang tinggi dapat mengakibatkan pengkayaan unsur hara (eutrofikasi) dan memicu ledakan populasi fitoplankton (blooming fitoplankton). Kondisi blooming ini diperburuk dengan adanya beberapa spesies fitoplankton yang mengandung racun dalam tubuhnya yang dikenal sebagai Harmful Alga Blooms (HABs). Penelitian dilakukan pada bulan Desember 2015 – Januari 2016 di Muara Sungai Banjir Kanal Barat, dengan tujuan untuk mengetahui konsentrasi nutrien (nitrat dan ortofosfat), jenis dan kelimpahan fitoplankton HABs, serta hubungan dan pengaruh antara konsentrasi nutrien (nitrat dan ortofosfat) terhadap kelimpahan fitoplankton HABs. Metode penelitian yang digunakan adalah metode survey dengan teknik purposive sampling. Hasil penelitian menunjukkan bahwa konsentrasi nitrat di lokasi penelitian berada dalam kisaran 0,6-2,2 mg/l, sedangkan konsentrasi ortofosfat dalam kisaran 0,04-1,3 mg/l. Fitoplankton HABs yang teridentifikasi berjumlah 5 genera diantaranya Trichodesmium sp., Ceratium sp., Noctiluca sp., Pseudonitzschia sp. dan Gonyaulax sp.. Persentase fitoplankton HABs dari total kelimpahan fitoplankton yang teridentifikasi sebesar 40,89% di stasiun I, 20,10% di stasiun II dan 11,49% di stasiun III. Berdasarkan analisis regresi berganda, sebesar 44,2% nutrien nitrat dan ortofosfat mempengaruhi kelimpahan fitoplankton HABs dengan persentase pengaruh nitrat dan ortofosfat masing-masing sebesar 36,6% dan 7,6%.

Industrial and households activity along Banjir Kanal Barat river flow in Semarang allegedly give an impact to the water quality which form the sewage contain nutrients (nitrate and orthophosphate). Both of the nutrients, in high concentration can cause nutrient enrichment (eutrophication) and trigger phytoplankton overpopulation (phytoplankton bloom). Blooming in this condition can be worse because of several toxic phytoplankton, this phenomenon known as Harmful Alga Blooms (HABs). The research was conducted on December 2015 – January 2016 at Banjir Kanal Barat estuary which aimed to knowing the nutrient concentration (nitrate and orthophosphate), find out the abundance of HABs phytoplankton, analyzing the relation of nutrients (nitrate and orthophosphate), and relation between chemical-physics water parameters and the abundance of HABs phytoplankton. The method of this research was used survey by purposive sampling technique. The results of the research showed that nitrate concentrations were in the range of 0.6 to 2.2 mg/l, while orthophosphate concentrations were of 0.04 to 1,3 mg/l. There were 5 generas identified as Phytoplanktons HABs, including Trichodesmium sp., Ceratium sp., Noctiluca sp., Pseudonitzschia sp. and Gonyaulax sp. The phytoplankton HABs percentage from the total abundance of identified phytoplankton was diferent within sampling stations that was 40,89% at the station I, 20,10% at the station II and 11,49% at the station III. Both nitrate and ortophosphate concentration may affected HABs phytoplankton 44,2%  (corelatoin analysis), with the influence of nitrate and orthophosphate were 36,6% and 7,6%.