Effects of Agricultural Carbon Sources On Water Quality and Phytoplankton Community Composition in Flocponic System

Abstract

Carbon products promote aggregate floc-rich plankton, with diverse roles in flocponic production. Availability, low-cost, and chemical composition of agricultural by-products make them ideal substrates for phytoplankton production. Phytoplankton maintains water quality by reducing toxic substances, but it is problematic under some conditions. Therefore, the study evaluates how agricultural carbon sources affect flocponic phytoplankton community composition and water quality. Five treatments (wheat-bran, Rhodes-hay, maize-cob, maize-stables, and lucerne-hay) and a control (no byproduct) were employed in a complete randomized design, each in triplicate for nine weeks. Each treatment and control had Nile tilapia (0.155 ± 0.01 g) and rice (seeds) densities of 98 m-3 and 250 m-2 , respectively. Temperature, pH, dissolved oxygen, and salinity levels did not differ significantly between treatments and control. However, TDS, soluble reactive phosphorus (SRP), ammonia, nitrite, and nitrate showed significant differences (p<0.05) between treatments and control. Lucerne-hay exhibited the highest nitrate levels (0.9 ± 0.06 mg L-1 ), SRP (0.6 ± 0.05 mg L-1 ), and the lowest ammonia and nitrite levels compared to other treatments and control. Lucerne-hay had the highest phytoplankton diversity (2.48), while the control (1.37) had the least. Further, there were significant differences in phytoplankton abundance, with lucernehay having the highest Charophyta (1.45 ± 0.02 indsL-1 ), Chlorophyta (1.60 ± 0.02 indsL-1 ), and Ochrophyta (1.64 ± 0.03 indsL-1 ) abundance, while the control had the least. The result of the study revealed that carbon sources influence flocponic water quality and phytoplankton. The composition and solubility of lucerne-hay and wheat-bran may have improved water quality and phytoplankton. The study suggests that lucerne-hay and wheat-bran are the best flocponic carbon sources for phytoplankton and water quality.