Algal turf scrubbers: Periphyton production and nutrient recovery on a South Florida citrus farm

There is a strong need to develop strategies that reduce nutrient loading to Florida's waters. The purpose of this study was to investigate the nutrient-removing ability and growth rate of periphyton, grown on an Algal Turf Scrubber (ATS™) that received runoff from a citrus orchard operated by the USDA in southern Florida. A pilot scale ATS (1.2 m wide × 234 m long; 0.5% declining grade) was constructed and received a continuous flow (227 L min−1) of water pumped from the orchard's drainage canal. Over an 18-month period, PO4-P, NO3-N, NO2-N and NH4+ removal averaged 16%, 49%, 19% and 41%, respectively. On average, the entire flow-way yielded 5.5 g m−2 day−1 (range: 1-16 g m−2 day−1) of periphyton (dry weight). However, the upper 60 m yielded 11 g m−2 day−1 (range: 1-26 g m−2 day−1). Over 54% of total production occurred in the upper 26% of the flow-way and growth rate over the entire flow-way, increased 195% during the summer months (June-Aug.) when compared to winter months (Jan.-Mar.). Harvested periphyton contained an average of 24.1% C, 3.8% N, 0.38% P, and 0.003% Si. The harvesting of periphyton from the entire flow-way removed a mean of 0.02 g m−2 day−1 of total phosphorus, and 0.18 g m−2 day−1 of total nitrogen. However, the highly productive upstream (1-30 m) section of the flow-way removed a mean of 0.05 g m−2 day−1 of total phosphorus, and 0.49 g m−2 day−1 of total nitrogen. During colonization, diatom chains (Aulocoseira spp.) along with various pennate diatoms dominated. However, the community was dominated by filamentous Chlorophyta for most of the study. Although this is a preliminary study to provide foundational information necessary for future optimization experiments, nutrient removal observed suggests a potential for the use of ATSs as an effective means of treating agricultural runoff from citrus and other fruit tree orchards while yielding periphyton.