Remote Sensing of Wetland Flooding at a Sub-Pixel Scale Based on Random Forests and Spatial Attraction Models

Wetland flooding is significant for the flora and fauna of wetlands. High temporal resolution remote sensing images are widely used for the timely mapping of wetland flooding but have a limitation of their relatively low spatial resolutions. In this study, a novel method based on random forests and spatial attraction models (RFSAM) was proposed to improve the accuracy of sub-pixel mapping of wetland flooding (SMWF) using remote sensing images. A random forests-based SMWF algorithm (RM-SMWF) was developed firstly, and a comprehensive complexity index of a mixed pixel was formulated. Then the RFSAM-SMWF method was developed. Landsat 8 Operational Land Imager (OLI) images of two wetlands of international importance included in the Ramsar List were used to evaluate RFSAM-SMWF against three other SMWF methods, and it consistently achieved more accurate sub-pixel mapping results in terms of visual and quantitative assessments in the two wetlands. The effects of the number of trees in random forests and the complexity threshold on the mapping accuracy of RFSAM-SMWF were also discussed. The results of this study improve the mapping accuracy of wetland flooding from medium-low spatial resolution remote sensing images and therefore benefit the environmental studies of wetlands.

Limnological studies of waterfowl habitat in south-western New South Wales. II. Aquatic macrophyte productivity

Aquatic macrophyte productivity and soil organic matter were measured in two impermanent wetlands in south-western New South Wales. Macrophyte biomasses (≤463 g dry wt m-2) were similar to or higher than those in submerged communities elsewhere. Macrophyte productivities in both wetlands were greatest in the year following reflooding. But even in that year, macrophyte productivity in Lake Merrimajeel (the only wetland for which data are available) was considerably less than soil organic reserves before reflooding. It is suggested that these soil organic reserves directly contribute to the relationship between wetland flooding and waterfowl breeding, while macrophytes contribute indirectly by providing detritus for invertebrates. It is recommended that wetlands managed for waterfowl breeding should periodically dry out and reflood.