Vegetation structure and dynamics of a floodplain wetland along a subtropical regulated river

Abstract

This paper documents vegetation changes in a floodplain area lying next to a newly constructed reservoir on the River Yamuna (near Delhi), about a kilometre downstream of an older, silted-up reservoir. The study site was a rectangular depression bounded by dykes on three sides and agricultural fields on the fourth. The composition and abundance of species in the plant community were observed over a ten year period (1986)(1987)(1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996) and changes in water level both at the study site and in the reservoir were followed. Site hydrology was governed by water level changes caused by reservoir operation with effect from 1990, when it was first filled to capacity and water began to seep through the dyke. The study area experienced increasing depth, duration and frequency of flooding. Species richness peaked in 1992, and the plant community developed four distinct zones closely associated with the hydrological gradient. Patchiness also increased though Typha angustata patches merged over time to form a continuous expanse. The microtopography of the study site, and hydrological and plant-induced changes were largely responsible for community changes. Dyke compaction over time resulted in cessation of seepage and the study site gradually dried up by 1998, with a consequent loss of plant species. The study concludes that the hydrological regime, rather than physical connectivity with the river, may play the dominant role in developing and maintaining plant community structure in floodplain wetlands.

Responses to water depth and clipping of twenty-three plant species in an Indian monsoonal wetland

“…Rainfall may be less predictable in this region because of atmospheric warming in recent decades (Mani et al, 2009). Perhaps a more important factor in water supply for the Keoladeo National Park is that demands for water have been increasing in north-central India (Chauhan and Gopal, 2005), so that discharge into Park has been decreasing ( Fig. 2).…”

“…1; Middleton et al, 1991). The climate is semi-arid and characterized by three seasons including a dry summer from March-June (mean maximum to minimum temperatures: 41-28 • C), monsoon from July-September, and winter from October-February with low temperatures above 0 • C (mean maximum to low minimum temperatures: 19-6 • C; Chauhan and Gopal, 2005). Before 1990, Park wetlands filled with water depending on the amount of monsoon rain and river water discharge (Fig.…”

“…Cattle grazing and harvesting of grasses were common in the Keoladeo National Park during the 1980s (Middleton et al, 1991), and in other wetlands in north-central India (Chauhan and Gopal, 2005;Middleton, 2013). Water discharge to the Keoladeo National Park ( Fig.…”

“…Along the Brahmaputra-Ganges-Meghna and Indus River in India, floodplain wetlands receive less water as impoundments store water upstream for human usage. These activities may increase with climate change (Chauhan and Gopal, 2005), which has been linked to increased variability in monsoon precipitation, i.e., both longer droughts and larger floods (Mani et al, 2009). In addition, anthropogenic changes to river floodplains could alter their seasonal water-level fluctuations by impounding wetlands during the dry season, drying them during the wet season, or altering inter-annual patterns of drought (Bond et al, 2008).…”

O papel das Macrófitas aquáticas emersas no ciclo do fósforo em lagos rasos

“…em ambientes que sofrem constantes alterações de profundidade pela alteração do nível d'água, a manutenção de estandes de macrófitas emersas pode ser comprometida. Dentre estes ambientes podemos citar as planícies de inundação (Chauhan & Gopal 2005), lagos e rios que sofreram a influência da construção de represas (Cogels et al 1997) (Glenn et al 1995). estas restrições podem variar dependendo da espécie, mas em geral o crescimento e a produtividade primária destes vegetais apresentam uma diminuição até em situações de pequenos aumentos de salinidade, como em águas com apenas 1,5ppt (Macek & Rejmankova 2007).…”