Effects of spates of different magnitudes on a Phragmites japonica population on a sandbar of a frequently disturbed river

Abstract

In flow-regulated rivers, natural flow patterns and related sedimentation processes are disturbed, thus interrupting the magnitude and duration of spates. We hypothesized that this in turn might alter the impact of spates on plant communities inhabiting sandbars along the river channel. In order to test this hypothesis, the effects of spates of different magnitudes and durations on spatial variation and composition of a Phragmites japonica Steud. community on a sandbar during a 2-year period were investigated. The flow variation of the river was continuously monitored, and the spates were categorized as small, medium or large, based on the magnitude (depth). Growth parameters (shoot length and shoot density), above-and belowground biomass of the plant community and the quantity of litter retained within selected quadrats, and ash-free dry weight (AFDW) of the soil were observed at seven different locations: two each at the extreme upstream, middle and extreme downstream and one location in the downstream reaches of the sandbar. Our results showed that the aboveground biomass declined due to large-scale spates; however, these spates triggered the formation of secondary shoots if sediments were accumulated as a result of the spates. Conversely, the aboveground biomass did not recover if the substrate was eroded. Accumulated litter beneath shoots was easily washed away due to spates, positively affecting shoot re-growth. The effects of spates on the P. japonica plant community depended highly on the location of the plants on the sandbar and the magnitude and duration of the spates. The different erosion-sedimentation processes, depending on the local river channel morphology and spate types, significantly affected the growth and morphological characteristics of P. japonica population.

Spatial and temporal tree colonization in a midstream sediment bar and the mechanisms governing tree mortality during a flood event

“…Riverine landscapes that have been subject to a moderate duration of inundation accumulate fine sediment, even at low-inundation depths (Steiger et al, 1998;Gurnell and Petts, 2002;Richards et al, 2002;Asaeda and Rajapakse, 2008), but this accumulation may be highly affected by local morphology (Gurnell and Petts, 2002;Gilvear and Willby, 2006;Asaeda and Rajapakse, 2008). The accumulated sediment contains high levels of moisture and nutrients, making these areas more conducive to plant colonization.…”

Tree colonization trends on a sediment bar after a major flood

“…Most of R. pseudoacacia seemed to be intact in the area higher than 3 m in the 1999 flood, although, in the September 2007 flood, a significant fraction of R. pseudoacacia was washed away with 0.5 m of erosion (Asaeda et al, 2009a). It should be noted that even though the flood level did not differ much, the erosion was significant only in the September 2007 flood but not in the August 1999 flood (Asaeda and Rajapakse, 2008).…”

“…Floods represent major disturbances that influence the riparian plant communities (Nilsson, 1987;Giller and Malmqvist, 1998) by washing away herbs (Asaeda and Rajapakse, 2008) and trees (Asaeda et al, 2009a).…”

Assessment of hydrological regimes for vegetation on riparian wetlands in Han River Basin, Korea

“…Otherwise, Erigeron Canadensis L. is common in grasslands and in most disturbed sites, including riparian and wetland areas, but it does not belong to macrophytes species and is vulnerable to submersion. Therefore, all of them except hydrophilic vegetation are highly dependent on the frequency, depth and duration of inundation (Asaeda and Rajapakse 2008), and plant communities are also vulnerable when the IEP goes under the P = 0.08 IEP district, or seems to be transit to hydrophilic vegetation, such as Phragmites japonica Steud. Since the right bank of the study area has the probability that can be disrupted by flooding and submersion (Dauer et al 2007), the area needs further monitoring and investigation in order to understand continuous plant succession.…”