Exergy as an ecological application used in the recovery process of benthic communities

Exergy,the thermodynamic function that represents the distance of an open system from equilibrium,is proposed as an ecological indicator for summarizing the complex dynamics occurring in a disturbed community during its recovery processes.These complex dynamics can be difficult to capture by using classical indices.In this study,we sampled macrobenthos using the BACI scheme(before versus after;control versus impact)in tidal wetlands of west Chongming Island,China,an area that has been disturbed by ecological engineering measures.Exergy storage is estimated for benthic communities.The control area is proposed as dynamic reference for estimating local exergy storage of the benthic community.Three different methods were used for estimating exergy on the basis of coefficients:(a)taken for taxa groups;(b)estimated from coding genes given for broad taxonomic groups;and(c)estimated from genome size taken as close as possible to the taxonomic level of the species,providing a basis for inferring similarities.We found a decrease of local exergy content in the disturbed area 9 days after the disturbance.Subsequently,the reference exergy of the benthic community increased(i.e.in the surrounding control area)in accordance with the proposed hypothesis regarding the dynamics of exergy storage during a system’s development.Estimates of local exergy arrived at using the three methods provided comparable results.Based on this,we then discuss the feasibility of using the more readily available genome size data for estimating exergy.This result may have important implications for broader application of this indicator to biological systems.Moreover,the adjacent control samples seem to represent an appropriate dynamic reference for estimating the local exergy of disturbed communities.We found that exergy was a useful indicator that integrates the processes underlying the recovery of the benthic community after disturbance.