Abstract
Abstract. Despite the importance of mangrove ecosystems in the global carbon budget, the relationships between environmental drivers and carbon dynamics in these forests remain poorly understood. This limited understanding is partly a result of the challenges associated with in situ flux studies. Tower-based CO2 eddy covariance (EC) systems are installed in only a few mangrove forests worldwide, and the longest EC record from the Florida Everglades contains less than 9 years of observations. A primary goal of the present study was to develop a methodology to estimate canopy-scale photosynthetic light use efficiency in this forest. These tower-based observations represent a basis for associating CO2 fluxes with canopy light use properties, and thus provide the means for utilizing satellite-based reflectance data for larger scale investigations. We present a model for mangrove canopy light use efficiency utilizing the enhanced green vegetation index (EVI) derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) that is capable of predicting changes in mangrove forest CO2 fluxes caused by a hurricane disturbance and changes in regional environmental conditions, including temperature and salinity. Model parameters are solved for in a Bayesian framework. The model structure requires estimates of ecosystem respiration (RE), and we present the first ever tower-based estimates of mangrove forest RE derived from nighttime CO2 fluxes. Our investigation is also the first to show the effects of salinity on mangrove forest CO2 uptake, which declines 5% per each 10 parts per thousand (ppt) increase in salinity. Light use efficiency in this forest declines with increasing daily photosynthetic active radiation, which is an important departure from the assumption of constant light use efficiency typically applied in satellite-driven models. The model developed here provides a framework for estimating CO2 uptake by these forests from reflectance data and information about environmental conditions.
Highlights
Ocean ScienceMangrove forests have received significant attention recently due to an increased recognition of the role these systems play in global carbon (C) cycles (Donato et al, 2011)
Systems
The objectives of this study are the following: (1) to calculate RE and GPP in a tidal mangrove forest using a novel application of ECbased estimates of NEE, (2) to parameterize and test a model of daily canopy GPP and LUE driven by satellite reflectance data, and (3) to compare these GPP estimates to the Moderate Resolution Imaging Spectroradiometer (MODIS) GPP product for this location
Summary
Ocean ScienceMangrove forests have received significant attention recently due to an increased recognition of the role these systems play in global carbon (C) cycles (Donato et al, 2011). Using these EC data to calculate canopy-level light use efficiency (LUE, defined as GPP divided by incoming photosynthetic active radiation (PAR)) will improve our understanding of. Barr et al.: Modeling light use efficiency in a subtropical mangrove forest relation to PAR and ground-based scalars in turn provides a first step towards using satellite reflectance data to define the larger role these forests play in both regional and global C budgets. Typical LUE models developed for terrestrial systems do not account for the unique factors that influence C dynamics in tidal forests, and new approaches are needed
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