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Human Perturbations of Large River Ecosystems 247 Table 9.5. Various anthropogenic perturbations in a river-floodplain ecosystem 'Main channel Fragmentation of riverine habitat by high- and low-head dams Conversion of reaches from lotic to lentic environments Regulated streamflow (disruption of daily and seasonal patterns) Channelization Changes in hydrograph (e.g., water quantity with time) Changes in natural water temperature regime Reduced water quality (pollution through wastewater discharge; increased contaminant levels) Disruption of natural sediment transport Disruption of natural nutrient cycling (Le., continuum concept) Loss of diverse lotic habitats Replacement of native fish with nonnative fish species Predation and competition by nonnative fishes on native species Potential for introduction of fish diseases and parasites Alteration of natural food webs Floodplain Disruption of natural river-floodplain connectivity Disruption of natural nutrient cycling (Le., flood pulse concept) Loss of diverse wetland habitats Loss of fish nursery habitats Floodplain loss places endangered species in jeopardy of extinction Decreases the integrity and diversity of faunal and floral communities that occupy floodplain habitats Increases potential for contaminant accumulation Increases potential for flooding downstream Riparian zone Replacement of native riparian vegetation with nonnative species Reduced riparian corridor along main channel Reduced riparian area in floodplain Loss of integrity and diversity of faunal and floral communities that occupy natural floodplain habitats Upland areas Agriculture (depletion in natural water regime and increased erosion disrupting natural sedimentation processes) Logging (increases surface water runoff and decreases groundwater supplies, increased erosion, reduced forest canopy) Mining (increased erosion, increases leaching of minerals, increase potential for introducing contaminants into aquatic environments) Recreation (increased erosion and runoff from road construction, potential for increased pollution of aquatic environments through discharge of wastes and contaminants) the Amazon River in Brazil, South America, but even this mighty river has been adversely affected by indiscrete logging on upland and flood- plain forests (Obeng, 1981; Sparks, 1995). Humans will continue to have a dominating influence on watersheds and floodplains of river ecosystems, altering their natural integrity, productivity, biodiversity, and heterogene- ity (Frissell et aI., 1993; Stanford et al., 1996). Human perturbations involving stream regulation adversely affected na- tive plants in various countries - e.g., Sweden (Nilsson and Jansson, 1995), France (Decamps et aI., 1995), and the United States (Graf, 1978) _ while allowing introduced plants to become established, increase in abundance,