Water quality characteristics of regulated rivers

Abstract

Rivers are complex physical, chemical and biological systems determined by processes operating not only within the confines of the channel but also -and perhaps more importantly -on and within the hillslopes of the drainage basin.From headwaters to mouth exists a gradient of physico-chemical factors that exerts a direct control upon the biological strategies and dynamics of river systems, as encompassed in the River Continuum Concept (Vannote et al., 1980). Dams interrupt the pattern of downstream transfers producing discontinuities along the stream continuum (Ward and Stanford, 1983). For the highest level of ecological investigation, namely studies of fish productivity, water quality is only one of eight groups of factors that interact to influence the character of impounded rivers (Petts, 1984). Nevertheless, river impoundment can exert an important influence upon water quality for tens, and in some instances hundreds, of kilometres below a dam. Moreover, the effects can extend not only to the river but also to the nearshore zone.The effect of reservoirs on water quality has been an important focus of research since the late 1950s but it is only since 1979, as a result of the First International Symposium on Regulated Streams, held at Erie, USA (Ward and Stanford, 1979), that researchers have become aware of the full consequences of impoundment for the river downstream. Today, dams are being completed at a rate of two each day (Mermel, 1976), some countries are experiencing increasing dambuilding activity, notably, Argentina, Canada, Spain, India and China (Mermel, 1981), andCroome et al. (1976) have suggested that by the year 2000, about 66 per cent of the world's total streamflow will be controlled by dams. Similar physical and biological processes are operative in large and small reservoirs, although they show profound differences in limnology and management. Furthermore, the effects of an impoundment of particular dimensions will depend upon its geographical location. Reservoirs have been built on rivers in subarctic, temperate and tropical regions, and in arid areas traversed by exogenous streams, such as the River Nile. Spatial variations in water quality are conditioned, within climatic regions, by catchment characteristics, not the least important of which are geology and land use (Gower, 1980). At the global scale, Gibbs ( 1970) classified rivers into three geographical groups by reference to both climate and geology, each of them

Downstream impacts of a dam and influence of a tributary on the reproductive success of Leporinus reinhardti in São Francisco River

“…The conservation of dam-free tributaries is important as an alternative route for fish reproduction because these watercourses have not had their hydrological regime and physical and chemical conditions of the water changed (Pelicice & Agostinho 2008). The degree to which a tributary helps to minimise thermal effects imposed by a dam depends on its size and its characteristics, such as flow, sediment load and water temperature (Petts 1986).…”

Effects of the flood regime on the body condition of fish of different trophic guilds in the Upper Paraná River floodplain, Brazil

“…Although the floods and water turbidity are important in spawning and survival and development in the initial life stages of fish -especially the migrators (Gomes and Agostinho, 1997;Agostinho et al, 2007) -these events cause profound changes to the habitats, increasing the dynamics of the watercourse and affecting energy expenditure (Ortlepp and Mürle, 2003) and changing the characteristics of the substrate, thus changing the benthic communities as a result (Petts, 1986). As a further result, these events reduce the primary productivity of phytoplankton (Train and Rodrigues, 1998;Rodrigues et al, 2002) and of submerged macrophytes (Padial and Thomaz, 2008;Thomaz et al, 2009), affecting the abundance and composition of the plankton (Velho et al, 2001;Ortlepp and Mürle, 2003) and the periphyton (Bielsa et al, 2003;Murakami et al, 2009).…”

Afforestation and stream temperature in a temperate maritime environment

“…Langford, 1990) and indirectly through modification of catchment land use, in particular by impoundment of rivers (e.g. Petts, 1984Petts, , 1986 and forestry practices (e.g. Beschta, 1987;Crisp et al, 2004).…”