Recovery of aquaculture treatment constructed wetlands function after prolonged flood inundation events in South Texas

Abstract

Constructed wetlands have been evaluated for many years as a means of low cost water treatment; however studies of performance evaluation and recovery after system upsets are not often reported. The Loma Alta Shrimp Aquaculture Facility (LASAF), located on the El Sauz Ranch in South Texas employs an innovative re-circulating aquaculture-wetland system where pond effluent is filtered through a constructed wetland and then re-circulated back into the shrimp production ponds. The goals of this study were to evaluate the relative water quality treatment ability for several wetland areas and evaluate the recovery of nutrient removal activity after major flooding damage and inundation in 2002. The practical implications of these results were incorporated into the design of a new constructed wetland that treats pond effluent in a sequential manner based on water depth. Despite variable loadings from aquaculture pond discharges, a steady state operation developed prior to harvest operations can be used to evaluate the nutrient removal performance of the wetlands, which can be determined through a change point statistical technique. The flooding events caused by storms and operator management requirements in 2002 resulted in diminished vegetation and wetland performance which was able to be restored in 2003, with the growth of primarily submerged vegetation. The smaller (8 ha) Phase III sequential basin design appeared to be able to effectively treat aquaculture effluent as well as the larger (19 ha) dual system Phase I and II wetlands. Close attention to water depth and recirculation rate management suggest a linkage to optimal performance for water treatment targets. It is suggested that techniques such as change-point analysis can help confirm as to when the retention time significantly changes in a dynamic wetland system as a result of changing water depth and provide insight as to the nature of its hydraulic efficiency.