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 (TM)) that received runoff from a citrus orchard operated by the USDA in southern Florida. A pilot scale ATS (1.2 m wide x 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 gm (2) day (1) (range: 1-16 gm (2) day (1)) of periphyton (dry weight). However, the upper 60 m yielded 11 gm (2) day (1) (range: 1-26 gm (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 gm (2) day (1) of total phosphorus, and 0.18 gm (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 gm (2) day (1) of total phosphorus, and 0.49 gm (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. Published by Elsevier B.V.