International Journal of Applied Earth Observation and Geoinformation
Landscape change and hydrologic alteration associated with dam construction
Highlights
► The downstream landscape became more fragmented and complex after dam construction. ► The degree of hydrologic alteration increased from the upstream to downstream areas. ► The hydrologic alternation is remarkable when the dam exists. ► There was strong relationship between landscape change and hydrologic alternation.
Introduction
Excessive anthropogenic activities such as agricultural land reclamation, industrial development, road network expansion, and dam construction play important roles in landscape change and hydrologic alteration (Xu et al., 2007, Liu et al., 2008, Yang et al., 2010, Bergerot et al., 2011). Dams, which are constructed for seasonal flood control, navigation, and generation of hydroelectric power, are often cited as the most significant impact on rivers around the world, reducing the connectivity of rivers, fragmenting watersheds, causing changes to hydrological processes, and resulting in downstream river channel erosion (Tiemann et al., 2004, Hu et al., 2008). Therefore, concerns about the effects of dam construction on the environment have increased with the increasing number of dams in recent years (Jansson et al., 2000, Chovanec et al., 2002, Tockner and Stanford, 2002, Dudgeon, 2005). Early studies show that dam construction can affect a variety of processes in both inner (Ellery et al., 2003, Hu et al., 2008, Walters et al., 2009, Zeilhofer and De Moura, 2009) and outer river areas (Dudgeon, 2005, Zeilhofer and De Moura, 2009, Ouyang et al., 2010).
In the outer river area, landscape changes associated with land use and land cover change are the most obvious impacts of dam construction (Ouyang et al., 2010), and have a fundamental reciprocal relationship with ecological processes (Turner, 1989). Therefore, the investigation and quantification of landscape changes caused by dam construction in the outer area are the domain of landscape ecology and the basis for sustainable environmental management. A number of metrics have been developed to measure the influences of human activities on landscape structure (Theobald, 2010), such as the total land area and individual land use type areas, patch density, edge density, perimeter-to-area ratio, landscape diversity, and so on (Palmer, 2004, Morgan et al., 2010). Usually, researchers select metrics for quantification of landscape changes based on specific categories (e.g., fragmentation, shape and diversity) to avoid linearity and redundancy between metrics.
Dam construction can affect the hydrologic regime in the inner river area more immediately than the landscape in the outer river area (Nilsson and Berggren, 2000, Walter and Merritts, 2008). Dam construction can block the continuity of hydrology, disrupt sediment transport and fish migration by modifying the seasonality of flows, and alter surface and subsurface water levels, changing the magnitude, duration, frequency, timing, predictability, and variability of flow events (Nilsson and Berggren, 2000, Ouyang et al., 2011). These impacts may lead to a loss of biological diversity and decrease the ecological functions in an aquatic ecosystem (Postel, 1998, Isik et al., 2008, El-Shafie et al., 2009). Accordingly, it is essential to understand the impact of dam construction on aquatic systems in the inner river area. Recently, the majority of researchers in China and abroad have explored the impacts of building dams with a focus on hydrological changes in the inner river area (Richter et al., 1998, Wang et al., 2005, Lajoie et al., 2007, Ouyang et al., 2011). These studies demonstrate that the hydrologic alterations and related environmental impacts of dam construction have become a main concern in hydrological development plans (Richter et al., 1998, Lajoie et al., 2007, Ouyang et al., 2011). Regarding hydrologic alteration, many indicators have been developed from the hydrological monitoring data to quantify flow characteristics that are sensitive to human perturbations (Yang et al., 2008, Chen et al., 2010). Although over 170 hydrologic indicators have been developed to describe different components of flow regimes, which hydrologic indicators to use to summarize flow properties analogous to the use of the widely accepted metrics is still unclear (Gao et al., 2009). Comparatively, the Indicators of Hydrologic Alteration (IHA) comprising 32 parameters developed by Richter et al. (1996) are more commonly used worldwide (Shiau and Wu, 2006, Magilligan and Nislow, 2005, Hu et al., 2008, Chen et al., 2010). Further, Richter et al. (1996) introduced a useful approach referred to as the Range of Variability Approach (RVA) based on the 32 Indicators of Hydrologic Alteration (IHA) to quantitatively evaluate the degree of hydrologic alteration (DHA) induced by human disturbance. This method has been shown to be a practical, and effective way to assess the DHA caused by dam construction and other human activities (Maingi and Marsh, 2002, Magilligan and Nislow, 2005, Kummu and Varis, 2007, Yang et al., 2008, Zeilhofer and De Moura, 2009, Chen et al., 2010).
In general, dam construction has great impacts on landscape and hydrology, so it is of scientific importance to investigate and evaluate the landscape changes and hydrologic alterations induced by dam construction. Nevertheless, many previous researchers focused on quantifying land use change or hydrological alterations without investigating the interrelation between landscape changes and hydrological alterations under the influence of dam construction. However, it is inevitable that land use changes such as conversion of forest to cropland will directly influence the regional hydrologic characteristics and processes (Zacharias et al., 2004, Verbunt et al., 2005, Ouyang et al., 2011). Therefore, the objectives of this study are to (1) appraise the magnitude of the influence that dam construction imposes on local landscape and hydrology, and (2) reveal the relationships between landscape change and hydrological alteration in the Lancang River in Yunnan Province (internationally known as the Mekong River) where large dams are being constructed or have already been completed.
Section snippets
Study area
As the largest international river in Asia, the Lancang River passes through seven climatic zones, crosses different geographic environments and connects different cultural, social, and economic communities (Liu et al., 2008, Hu et al., 2009). The average rainfall in the Lancang River basin is about 500 mm in the southeast and 250 mm in the northwest parts of the river. The Lancang River exhibits strong seasonality of runoff, with 70% of the overall annual water flow normally occurring in August
Landscape fragmentation metric change
The change in the landscape fragmentation metrics at the landscape level is shown in Fig. 2. In the overall study area, PD first decreased from 1980 to 1990 and then increased from 1990 to 2000 with values of 0.222, 0.167, and 0.222, respectively. The MPS and LPI show the opposite changes with values of 451.5 ha and 54.4% in 1980, and 600.2 ha and 63.8% in 1990, 451.2 ha and 53.7% in 2000, respectively. In the upstream, midstream, and downstream areas, and landscape fragmentation metrics show the
Landscape metrics for assessing the impact of dam construction on landscape patterns
In this study, we examined landscape pattern metrics using regional land use data interpreted from Landsat MSS and TM images. Similar to previous research, the landscape metrics selected to describe variability in the landscape structure were based on categorical classifications (Ouyang et al., 2009, Morgan et al., 2010, Theobald, 2010), implying that there are problems associated with the classification scheme such as number of classes, arbitrary classification schemes, classification
Acknowledgements
This research was funded by the National Natural Sciences Foundation of China (Nos. 50939001, 40871237), the Nonprofit Environment Protection Specific Project of China (No. 201209029), and the Fundamental Research Funds for the Central Universities.
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