An ecological and economic overview of wetland wastewater assimilation in coastal Louisiana

We review wetland wastewater assimilation studies in the Louisiana coastal zone. Insufficient sedimentation, coupled with high rates of relative sea level rise (RSLR), are two important factors contributing to wetland loss in coastal Louisiana. We hypothesized that adding nutrient rich treated wastewater effluent to selected coastal wetlands results in four benefits: (1) improved effluent water quality; (2) increased accretion rates to help offset subsidence; (3) increased productivity of vegetation; and (4) financial savings of capital not invested in conventional tertiary treatment systems. To test these hypotheses, we are currently monitoring several wetlands that are receiving secondarily treated wastewater. At one site, rates of accretion increased significantly after wastewater application began (from 7.8 to 11.4 mm yr(-1)), and approached the estimated rate of regional RSLR (12.0 mm yr(-1)). Surface water nutrient reduction ranged from 100% for NO3-N to 66% for total P. At a site that has been receiving wastewater effluent for 40 years, dendrochronological analysis revealed significantly increased cypress stem growth in the treatment site. Results of avoided costs analyses between wetlands treatment and conventional treatment indicate cost savings of $500,000 - $1.5 million.