Accurate and updated finer resolution maps of rubber plantations and stand ages are needed to understand and assess the impacts of rubber plantations on regional ecosystem processes. This study presented a simple method for mapping rubber plantation areas and their stand ages by integration of PALSAR 50-m mosaic images and multi-temporal Landsat TM/ETM+ images. The L-band PALSAR 50-m mosaic images were used to map forests (including both natural forests and rubber trees) and non-forests. For those PALSAR-based forest pixels, we analyzed the multi-temporal Landsat TM/ETM+ images from 2000 to 2009. We first studied phenological signatures of deciduous rubber plantations (defoliation and foliation) and natural forests through analysis of surface reflectance, Normal Difference OPEN ACCESSRemote Sens. 2015, 7 1049Vegetation Index (NDVI), Enhanced Vegetation Index (EVI), and Land Surface Water Index (LSWI) and generated a map of rubber plantations in 2009. We then analyzed phenological signatures of rubber plantations with different stand ages and generated a map, in 2009, of rubber plantation stand ages (≤5, 6-10, >10 years-old) based on multi-temporal Landsat images. The resultant maps clearly illustrated how rubber plantations have expanded into the mountains in the study area over the years. The results in this study demonstrate the potential of integrating microwave (e.g., PALSAR) and optical remote sensing in the characterization of rubber plantations and their expansion over time.

The sources, transport, and transformation of terrestrial dissolved organic matter (DOM) in large river systems are of great interest due to their importance in the regional and global carbon cycles. However, knowledge of these factors is limited, especially for different DOM compositions coupling with hydrodynamics at the basin scale. To investigate the dynamics of different DOM compositions in a large river system, we characterized the dissolved organic carbon (DOC), chromophoric DOM (CDOM), and dissolved lignin at both moderate (September–October 2009) and high (August 2012) discharges in the Changjiang River basin. We found that extensive soil erosion resulted in the increased DOC concentration in the middle to lower reaches in 2012. In 2009, the transformation of DOM was dominated by flocculation and photo degradation due to the low flow velocity and depressed particle suspension. In 2012, the degradation of CDOM and dissolved lignin was coupled and dominated by microbial degradation and photo degradation. In 2012, CDOM (absorbance and fluorescence) and dissolved lignin concentrations were positively correlated, demonstrating the potential of using CDOM to quantitatively estimate dissolved lignin. Mass balance estimations of the DOM fluxes further confirmed that 17.0% (6.1%) of DOC, 24.2% (32.3%) of dissolved lignin, and 14.5% (0.8%) of CDOM were degraded at high (moderate) discharge. This study reveals contrasting transformation processes of DOM compositions with different sources and reactivities along the Changjiang River under different hydrological conditions, and it provides new insights into the linkage between the chemical and optical properties of DOM in large river systems.

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