Hubungan antara Nitrat dan Fosfat dengan Kelimpahan Fitoplankton di Waduk Jatibarang Semarang Correlation between Nitrate and Phospate with Abundance of Phytoplankton in Jatibarang Reservoir, Semarang

ABSTRAK Waduk Jatibarang merupakan salah satu waduk yang memiliki peran penting di Kota Semarang sehingga kualitas perairannya perlu diperhatikan. Keberadaan fitoplankton di perairan berkaitan erat dengan kesuburan dan kualitas suatu perairan dikarenakan fitoplankton berperan sebagai produsen primer. Tujuan penelitian ini untuk mengetahui kualitas perairan berdasarkan kelimpahan fitoplankton serta melihat sejauh mana korelasi nitrat dan fosfat akan mempengaruhi kelimpahan fitoplankton diperairan. Penelitian dilakukan pada tanggal 27 Maret 2019 di Waduk Jatibarang semarang. Pengambilan sampel dilakukan menggunakan metode purposive sampling di tujuh stasiun dengan tiga titik kedalaman (permukaan, tengah dan dasar perairan) dan tiga pengulangan (pagi, siang dan malam). Pengolahan data menggunakan program SPSS 25 dengan analisis regresi liner berganda. Konsentrasi nitrat yang didapatkan berkisar antara 0,45-9,64 mg/l, konsentrasi fosfat berkisar antara 1,26-4,81 mg/l, kelimpahan fitoplankton berkisar antara 1.667 – 275.833 ind/l. Hubungan antara konsentrasi nitrat dan fosfat dengan kelimpahan fitoplankton tergolong lemah dengan koefisien korelasi (r = 0,378). Nitrat dan fosfat mempengaruhi kelimpahan fitoplankton sebesar 15% dengan koefisien determinasi (r square = 0,150). Tingkat kesuburan di Waduk Jatibarang termasuk dalam kategori mesotrofik hingga eutrofik berdasarkan konsentrasi nitrat, fosfat dan kelimpahan fitoplankton. ABSTRACT Jatibarang Reservoir is one of the reservoirs that has an important role in the city of Semarang so that the quality of its waters needs to be considered. The presence of phytoplankton in waters is closely related to the fertility and quality of a waters because phytoplankton act as primary producers. The purposes of this research are to determine the quality of water based on the consentration of nitrate and phosphate, to calculate the abundance of phytoplankton and also to know the correlation of nitrates and phosphate toward the abundance of phytoplankton. The research was conducted on 27 March 2019 in Jatibarang Reservoir Semarang. Sampling was carried out at seven stations with three depth points (surface, middle and bottom) and three repetitions (morning, day and night). Data processing using SPSS 25 programme with multiple liner regression analysis. The concentration of nitrate gained ranged from 0.45 - 9.64 mg/l, phosphate concentrations ranged from 1.26 - 4.81 mg/l, the abundance of phytoplankton ranges between 1,667 – 275,833 ind/l. The relationship between nitrate and phosphate concentrations with an abundance of phytoplankton is relatively weak with a correlation coefficient (r = 0.378). Nitrates and phosphates affect the abundance of phytoplankton by 15% with coefficient of determination (r square = 0.150). Water’s trophic state in the Jatibarang reservoir belongs to the mesotrophic up to Eutrophic category.