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Abstract Wetland protection and recovery needs scientific foundations for a better understanding of wetland floods, since the flooding existence and its dynamics are the key aspects in the formation and evolution of wetland ecosystems. The Honghe National Natural Reserve (HNNR) in the Northeast China has been listed in the Ramsar Convention on Wetlands since 2002. The specific dates for determining of an average inundation boundary caused by a regular flooding were firstly fixed from multiple rainfall events by a hydro-meteorological analysis based on the long-term rainfall data. The flood inundation areas in the HNNR marshes were mapped according to the correlation between hydro-geomorphology and regular flood progress. The mapping of the flood inundation areas were supported technically from the application of remote sensing images, combining the hydro-geomorphologic analysis with meteorological statistical data. The final map with the spatial-temporal content of an inundation created by hydro-geomorphological analysis and remote sensing data was validated by the long-term rainfall, soil moisture and surface water level data in the HNNR. The results indicated that the flood inundation areas were mainly distributed in large patches along the two main river courses of Nongjiang River and its branch of Woyalan River in the northern and central HNNR. The flood inundation patches were scattered as seasonal marshes and permanent ponds in the southern and eastern HNNR. The extracted flood inundation area accounted for more than a quarter of the total area of HNNR. The flood inundation area of Nongjiang was much larger than that of Wuyalan. [ABSTRACT FROM AUTHOR]

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.

This article describes a unique flood hazard, produced by the dramatic expansion of wetlands in Nelson County, located within the North American Prairie Pothole Region of North Dakota, USA. There has been an unprecedented increase in the number, average size, and permanence of prairie wetlands, and a significant increase in the size of a closed lake (Stump Lake) due to a decade-long wet spell that began in 1993 following a prolonged drying trend. Base-line land cover information from the 1992 USGS National Land Cover Characterization dataset, and a Landsat TM scene acquired 9 July 2001 are used to assess the growth of the closed lake and wetland pond surface areas, and to analyze the type and area of various land cover classes inundated between 1992 and 2001. The open water profile in Nelson County changed from one marked by relatively comparable coverage of closed lake and wetland pond areas in 1992, to one in which wetland open water accounted for the vast majority of total open water in 2001. The bulk of the wetland pond area expansion occurred by displacing existing wetland vegetation and agricultural cropland. Producers responded to the flood hazard by filing Federal Crop Insurance Corporation (FCIC) claims and enrolling cropland in the Conservation Reserve Program (CRP), a federal land retirement program. Land taken out of agricultural production has had an enormous impact upon the agricultural sector that forms the economic base of the rural economy. In 2001 the land taken out of production due to CRP enrollment and preventive planting claims represented nearly 42% of Nelson County’s 205.2 K ha base agricultural land. The patterns obtained from this detailed study of Nelson County are likely to be the representative of the more publicized flood disaster occurring within the Devils Lake Basin of North Dakota. [ABSTRACT FROM AUTHOR]

Methane emissions were measured from a bog and lake in the Experimental Lakes Area in Northern Ontario in 1992 and 1993, prior to and following flooding. Bog fluxes were small in 1992 (0.27 mg m-2 d-1) but increased 5-fold in 1993 after flooding. Over the bog, there was a diel cycle of nighttime emission and daytime uptake in 1992 in contrast to constant emission in 1993. Lake emissions decreased after flooding but were much greater than bog emissions in both years (average = 7.3 mg m-2 d-1). Seasonally, the bog flux was correlated with ground temperatures after flooding. In 1992, lake fluxes were correlated with air temperature on a daily basis. In contrast, seasonal lake fluxes were correlated with water and sediment temperatures in 1992, but only with sediment temperatures in 1993. These results are explained with respect to the effects of flooding on lake and bog dynamics. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Four approaches were used to assess the effect of inundation on methane emissions from floodplain wetlands in Victoria, Australia: (i) field observations following natural rainfall events; (ii) experimentalmanipulation of water levels in small floodplain depressions; (iii) experimental manipulation of water levels in replicated mesocosms; and (iv) in vitro incubation of floodplain sediment under laboratory conditions. Raftery's Swamp, a large (150 ha) wetland on the floodplainof the Goulburn River, became inundated in June 1993 following autumn-winter rainfall. Methane emissions peaked (1.7 ~ 0.05 mmol m-2 h-1) some six months later, and the methane contentof sediment gas bubbles reached 59% v/v, even though the positive sediment redox potentials (176 to 243 mV) indicated that sediments wereonly moderately reducing. Three small (< 1 ha) depressions on the floodplains of the River Murray and Kiewa River were inundated either naturally (by rain and/or overflow from nearby rivers) or artificiallyby flooding at specific times of year; emissions from these sites were usually negligible after flooding in autumn or winter. In contrast, the onset of methane emission was very rapid (within 3 to 6 days) after the depressions had been flooded in summer, and the methane content of sediment gas bubbles could then reach 36% v/v. At their peak, emissions from the ephemeral wetlands were similar to peak emissions from permanent wetlands in south-eastern Australia. Emissions from replicated wetland mesocosms (4.5 m diameter, 0.9 m deep) were always very small (< 0.2 mmol m-2 h-1), regardless of time of flooding, water depths, or season. In vitro incubation of wetland sediment under anaerobic conditions indicated a progressive decrease in benthic methanogenesis with sediment desiccation and exposure to air. Ephemerally inundated floodplain wetlands may be sites of significant methane emission, especially over the summer months. Moreover, th [ABSTRACT FROM AUTHOR]