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Oxbow Lakes (oxbow + lake)
Selected AbstractsFish assemblage changes relative to environmental factors and time in the Warta River, Poland, and its oxbow lakesJOURNAL OF FISH BIOLOGY, Issue 2 2004T. Penczak Four oxbow lakes and two neighbouring sections of their parent Warta River (Odra River system, Poland) were sampled to investigate differences in fish assemblages between habitats in 1999,2000. Additional comparisons were made with 12 other oxbow lakes in this section of the river that were sampled 30,40 years ago. Downstream of a man-made reservoir, higher species number, diversity and evenness were recorded in oxbow lakes than in the river channel. Upstream of the reservoir, differences in these variables from both habitats were insignificant. Fluvial and stagnant water samples were clearly separated in the multivariate space of a detrended correspondence analysis (DCA). For two oxbow lakes and two neighbouring sections of the Warta River, 12 abiotic and biotic environmental variables were available, and only velocity, water temperature and conductivity were significantly correlated with canonical correspondence analysis (CCA) axes. Fish assemblages of four recently investigated oxbow lakes were clearly separated in the multivariate space of DCA from other neighbouring oxbows sampled 30,40 years ago. Species previously subdominant were becoming rare. Oxbow lakes that are continuously or at least periodically connected with the channel are indispensable for maintaining high biodiversity and a sustainable fishery in the river system. [source] Geological controls on the formation of alluvial meanders and floodplain wetlands: the example of the Klip River, eastern Free State, South AfricaEARTH SURFACE PROCESSES AND LANDFORMS, Issue 8 2002S. Tooth Abstract Floodplain wetlands are common features of rivers in southern Africa, but they have been little studied from a geological or geomorphological perspective. Study of the upper Klip River, eastern Free State, South Africa, indicates strong geological controls on the formation of alluvial meanders and associated floodplain wetlands. Along this river, pronounced and abrupt changes in valley width are strongly linked to lithological variations. Where weakly cemented sandstone crops out, the Klip has laterally eroded bedrock and carved valleys up to 1500 m wide. In these valleys, the river meanders (sinuosity up to ,1·75) on moderate gradients (<0·001) within extensive floodplains marked by numerous oxbow lakes, backswamps and abandoned channels, many of which host substantial wetlands. In contrast, where highly resistant dolerite crops out, lateral erosion of bedrock is restricted, with the Klip tending instead to erode vertically along joints or fractures. Here, valleys are narrower (<200 m), channel-bed gradients are steeper (>0·003), the river follows a much straighter course (sinuosity ,1·10,1·34), and floodplains are restricted in width. Long-term landscape development in the Klip and numerous similar catchments depends on the interaction between fluvial processes in the sandstone and dolerite valleys. In the sandstone valleys, vertical erosion rates are controlled by erosion rates of the more resistant dolerites downstream. Hence, in the short- to medium-term (decades to tens of thousands of years), lateral erosion dominates over vertical erosion, with the river concomitantly planing sandstone in the channel floor and reworking floodplain sediments. The thickness of alluvial fill in the sandstone valleys is limited (<4 m), but the resultant meanders are naturally dynamic, with processes such as point bar deposition, cutoff formation and channel avulsion resulting in an assemblage of fluvial landforms. In the longer term (greater than tens of thousands of years), however, vertical erosion will occur in the sandstone valleys as the downstream dolerites are lowered by erosion, resulting in channel incision, floodplain abandonment, and desiccation of the wetlands. Identification of the geological controls on meander and wetland formation provides information vital for the design of effective management guidelines for these ecologically rich habitats, and also contributes to a better understanding of rivers that are intermediate between fully alluvial and fully bedrock. Copyright © 2002 John Wiley & Sons, Ltd. [source] Fish assemblage changes relative to environmental factors and time in the Warta River, Poland, and its oxbow lakesJOURNAL OF FISH BIOLOGY, Issue 2 2004T. Penczak Four oxbow lakes and two neighbouring sections of their parent Warta River (Odra River system, Poland) were sampled to investigate differences in fish assemblages between habitats in 1999,2000. Additional comparisons were made with 12 other oxbow lakes in this section of the river that were sampled 30,40 years ago. Downstream of a man-made reservoir, higher species number, diversity and evenness were recorded in oxbow lakes than in the river channel. Upstream of the reservoir, differences in these variables from both habitats were insignificant. Fluvial and stagnant water samples were clearly separated in the multivariate space of a detrended correspondence analysis (DCA). For two oxbow lakes and two neighbouring sections of the Warta River, 12 abiotic and biotic environmental variables were available, and only velocity, water temperature and conductivity were significantly correlated with canonical correspondence analysis (CCA) axes. Fish assemblages of four recently investigated oxbow lakes were clearly separated in the multivariate space of DCA from other neighbouring oxbows sampled 30,40 years ago. Species previously subdominant were becoming rare. Oxbow lakes that are continuously or at least periodically connected with the channel are indispensable for maintaining high biodiversity and a sustainable fishery in the river system. [source] | ||||||||||