Hubungan Antara Kandungan Nitrat dan Fosfat Dengan Kelimpahan Fitoplankton di Perairan Pulau Harapan, Kepulauan Seribu a.n RIFTIA ISHAB ANNISA (C5401221069)

Abstract

Abstrak: Perairan Pulau Harapan, Kepulauan Seribu, menghadapi tekanan antropogenik yang berpotensi meningkatkan konsentrasi unsur hara dan memicu eutrofikasi. Penelitian ini bertujuan menganalisis kandungan nitrat dan fosfat, mengidentifikasi jenis dan kelimpahan fitoplankton, serta mengkaji hubungan keduanya. Pengambilan data dilakukan pada Februari, Mei, Agustus, dan November 2025 di empat Stasiun. Nitrat dan fosfat dianalisis secara spektrofotometri, sedangkan fitoplankton diidentifikasi dan dihitung menggunakan Sedgwick–Rafter Counting Chamber. Konsentrasi nitrat berkisar 0,018–0,070 mg/L dan fosfat 0,010–0,023 mg/L. Nitrat melampaui baku mutu selama seluruh periode pengamatan, sedangkan fosfat mulai Mei. Fitoplankton didominasi Bacillariophyceae, dengan 7–18 taksa dan kelimpahan 1,0–9,8 × 106 sel/L. Fosfat menunjukkan hubungan lebih kuat terhadap kelimpahan fitoplankton (R² = 0,1555) dibandingkan nitrat (R² = 0,0079). Rasio Redfield menunjukkan nitrat sebagai unsur hara pembatas.

Abstract: Pulau Harapan, Kepulauan Seribu, is subject to anthropogenic pressures that may increase nutrient concentrations. This study aimed to determine nitrate and phosphate concentrations, identify phytoplankton composition and abundance, and their relationships. Data were collected in February, May, August, and November 2025 at four stations. Nitrate and phosphate were analyzed spectrophotometrically, while phytoplankton were enumerated using a Sedgwick–Rafter Counting Chamber. Nitrate ranged from 0.018–0.070 mg/L and phosphate from 0.010–0.023 mg/L. Nitrate exceeded the seawater standard throughout observations, whereas phosphate exceeded the standard from May onward. Phytoplankton were dominated by Bacillariophyceae, with 7–18 taxa and abundances of 1.0–9.8 × 106 cells/L. PCA explained 51.68% of variance. Regression showed a stronger relationship between phosphate and abundance (R² = 0.1555) than nitrate (R² = 0.0079). The N:P ratio remained below 16, indicating nitrate limitation.