A Generalized Model of Hourly Net Ecosystem Exchange (NEE) for Florida Everglades Freshwater Wetlands

Abstract

A generalized model is presented to estimate the diurnal cycle of hourly net ecosystem exchange (NEE) based on a corresponding single reference-time observation from the Florida Everglades freshwater wetlands. The year-round diurnal cycles of NEE for two different (short vs. long hydroperiod) marsh sites were normalized by the corresponding day- and site-specific reference observations of NEE to obtain a common dimensionless cycle. An extended stochastic harmonic analysis (ESHA) was utilized to calibrate and validate the model with hourly eddy-covariance observations of NEE during 2008–13. The model involved five parameters, which exhibited spatiotemporal robustness by collapsing into narrow ranges among different days, years and sites. The daily estimates were averaged over all calibration days to calculate the site-specific ensemble parameter sets. The site-specific ensemble parameters were further averaged over four mid-day reference times (11 A.M. to 2 P.M.) across sites to obtain a generalized ensemble parameter set. Estimated hourly NEE using the site-specific and the generalized parameter sets indicated a good performance of the model (e.g., Nash-Sutcliffe Efficiency, NSE = 0.66–0.89). The model is represented in three standalone formats, including an Excel spreadsheet, to simulate the hourly NEE for the desired Julian days and years from the respective single reference observations.