Using MODIS reflectance products to monitor wetness and methane fluxes and concentration in a managed temperate peatland in California

Compared to northern peatlands, managed temperate peatlands have generally received little attention from the climate change community. Many studies in northern peatlands have demonstrated the importance of wetness on atmospheric efflux and concentration of methane (CH4). In managed temperate peatlands such as Sherman Island located within the Sacramento-San Joaquin Delta, California, the monitoring of wetness poses a major challenge since hydrological input includes irrigation through a complex network of ditches and canals in addition to precipitation. The objective of this study is to investigate the capability of six spectral vegetation indices (SVI) to capture the seasonal dynamics of near surface wetness within the day- and nighttime CH4 concentration footprints of the EC tower located on Sherman Island, and ultimately to investigate the capability of these SVI to capture the seasonal dynamics of CH4 concentration and fluxes at this site. In addition to routinely applied normalized difference vegetation index (NDVI) and enhanced vegetation index (EVI), we computed land surface water index (LSWI), shortwave infrared water stress index (SIWSI), and moisture stress index (MSI), all of which are related to wetness. These indices were derived from daily and 8-day composite MODIS surface reflectance products. We extracted information from the pixels that corresponded with the daytime footprint entirely located within a relatively "dry" area containing the EC tower, and for the nighttime footprint, which extends into adjacent relatively "wet" areas. For this purpose, the extents of day- and nighttime footprints were estimated with a 2-D version of an analytical footprint model. Preliminary results for the MODIS EC tower pixel show that especially the wetness-related SVIs compare favorably well with in situ near surface soil moisture measurements.