Dynamic emergy accounting for assessing the environmental benefits of subtropical wetland stormwater management systems

An eco-hydrological model of a subtropical urbanizing watershed in south Florida, USA was developed to simulate solar emergy using H.T. Odum's energy systems language as programmed in an iconographic simulation software (i.e., Extend®) to provide dynamic valuation of a wetland stormwater management system (WSMS). The solar emergy (i.e., ultimate amount of solar energy required to produce another form of energy) and emdollar (EM$, value an energy flow contributes to an economy based on its proportion of total emergy flow) values of watershed transpiration (a measure of productivity), surface discharge and change in landscape water storage were quantified for various ratios of wetland to upland areas, valuing wetlands in EM$ ha−1 y−1. Simulation results indicated that integrating a WSMS into the watershed increased landscape productivity, decreased surface discharge and increased surface water storage. The eco-hydrological value of watershed productivity was 367 EM$ ha−1 y−1 when 10% of the watershed was wetland, which was an increase of 65 EM$ ha−1 y−1 (based on Florida's emergy-to-dollar ratio in 1985, 2 × 1012 sej $−1). The annual contribution of this extra ecological productivity to public welfare was 12 million EM$, which was estimated from the product of eco-hydrological value and local emergy investment ratio of south Dade County (18:1). Average emdollar value of water saved per unit of wetland was 343 EM$ ha−1 y−1. Dynamic emergy accounting provided distributions of solar transformities of hydrologic variables as opposed to more commonly used point estimates. Our work advances the temporal dynamic principles of emergy accounting by demonstrating how solar emergy may be continuously tracked through an ecosystem to estimate the value of nature's life-support services.