Location: Warmwater Aquaculture Research UnitTitle: Use of vegetated drainage ditches and low-grade weirs for aquaculture effluent mitigation: I. Nutrients) Author
Submitted to: Journal of Aquaculture Engineering
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/25/2014
Publication Date: 5/1/2014
Citation: Flora, C.L., Kroger, R. 2014. Use of vegetated drainage ditches and low-grade weirs for aquaculture effluent mitigation: I. Nutrients. Journal of Aquaculture Engineering. 60:56-62. Interpretive Summary: This article describes the first use of vegetated drainage ditches and low-grade weirs as best management practices for mitigating nutrients in aquaculture effluent. Often management of effluent occurs in pond where management can apply volume reduction techniques to reduce amount of water leaving the pond. Vegetated drainage ditches and low-grade weirs offer a water quality improvement service to farmers by creating conditions conducive for nutrient removal. The ubiquitous drainage ditch, if left vegetated, removes nutrients as a result of wetland like conditions created. This study documented significant reductions in nutrients of total P and total ammonia nitrogen. When low-grade weirs were added to the ditch system, further nutrient concentrations and loads of nitrogen and phosphorus were removed. Results highlight that utilizing a ubiquitous landscape feature such as a vegetated drainage ditch with installed low-grade weirs can be added as a promising effluent management strategy of nutrients for aquaculture.
Technical Abstract: Implementation of water management practices could be a strategy for reducing mass discharge from aquaculture production. Of greatest concern is the delivery via discharge of excess loads of nitrogen and phosphorus to downstream systems and their effects on ecological impairments. This study assessed effects of consecutive low-grade weirs on chemical retention of aquaculture pond effluent in a single, vegetated drainage ditch. Two control (without weirs) and nine treatment (with weirs) discharges were conducted September to October 2012 at the Mississippi State University South Farm Aquaculture Facility. From discharge to drainage ditch outlet, control discharges had a 154% increase in soluble reactive phosphorus (SRP) load, whereas total phosphorus (TP), total ammonia nitrogen (TAN), and nitrate (NO3--N) loads decreased (47%, 43%, and 63%, respectively). Additionally, concentrations of TP (F = 4.59, P = 0.02) and TAN (F = 6.70, P <0.001) in control discharges were significantly decreased. In treatment discharges, nutrient mass loads decreased across all analytes (80% SRP, 86% TP, 89% TAN, 89% NO3--N). Treatment discharges’ concentrations of TP, nitrite, and NO3--N (F=4.95, P=0.01; F=2.91, P=0.06; F=5.18, P=0.01, respectively), were significantly reduced while SRP concentrations increased significantly (F=12.60, P<0.001). Changes in concentration were further analyzed with additional fixed effects of distance to weir 1, number of discharges prior, initial effluent concentration, and flow rate; initial effluent concentrations were shown to have a significant negative effect on TP (F = 4.28, P < 0.001) and NO3--N (F = 2.41, P = 0.02) concentration decrease. Results of this study indicate utilizing a ubiquitous landscape feature such as a vegetated drainage ditch with installed low-grade weirs has the potential to reduce nutrient mass loads moving downstream and can be added as a promising effluent mitigation strategy for aquaculture.