Limestone wetland mesocosm for recycling saline wastewater in coastal Yucatan, Mexico

To understand wetland self-organization and to prevent pollution of groundwater and coral reef on the calcareous east coast of Yucatan, Mexico, a wetland mesocosm system was developed for treatment and recycle of saline, septic-tank wastewater. High diversity wetland ecosystems were developed in two concrete-lined chambers, using subsurface flow through limestone gravel, arranged in series with discharge to backbeach mangroves.; Evapotranspiration in the wetlands averaged 35% of design influent during summer months and 20% during winter months. Tall wetland vegetation developed with 66 plant species in 131 m2. Shannon diversity of vegetation was 5.01 (logarithm base 2), far greater than that of the mangrove wetland (1.49), but less than the inland Yucatan forest (5.35). Leaf area index increased over 13 months from 3.96 +/- 0.28 to 6.05 +/- 0.49. In wastewater passing through the systems, biochemical oxygen demand was reduced 85%, suspended solids 40%, phosphorus 78% and nitrogen 75%. Coliform bacteria were reduced 99.8+%. Limestone gravel in the treatment system removed 5.75 +/- 1.68 mg/kg phosphorus per year. Nutrients in mangrove water and soil sediments increased 5--10% from discharge of treated wastewater. Water budgets in treatment system and mangrove were studied with simulation model.; On a per-capita basis, the wetland systems for 40 people cost approximately {dollar}160 per person to construct, vs. over {dollar}400 for alternative treatment technologies. Operation and maintenance costs were 10% that of conventional treatment. Emergy in purchased inputs for construction were less than 1/3 of free environmental inputs; empower density was 2.5 E19 sej/ha/yr (one third that of conventional treatment).; The potential for economic development using the new treatment systems was evaluated. Treatment systems would require 0.3% of the annual monetary flow (vs. 1.1% for conventional sewage treatment) and 2.4% of total emergy while contributing 71,000 emdollars (the monetary equivalent of useful work contributed by nature and by humans). The new systems conserve mangroves, reduce eutrophication, prevent pollution of groundwater, protect marine resources, and contribute aesthetic values.; Research results indicate high biodiversity can be achieved in sewage treatment wetlands, use of limestone gravel augments phosphorus uptake and such systems can be integrated into the larger environmental setting.