Geomorphology and environmental management of the Yellow River source zone

Abstract

628 Geologic, climatic and anthropogenic factors have fashioned the distinctive landscapes and ecosystems of the Yellow River source zone (Brierley and Huang 2013; Figure 1). Located at the north-east corner of the Qinghai-Tibetan Plateau (QTP), at elevations between 2500 and 4500 m, this area has an arid/semi-arid climate. Many of these landscapes retain a significant imprint from Quaternary environmental changes. This mix of factors has induced marked variability in vegetation patterns and land use potential across this vast area, where land use practices have maintained grazing adapted ecosystems for several thousand years (Miehe et al. 2009). Despite the low population density, development pressures and climate change present significant threats to ecosystem values (e.g. Liu et al. 2012; Shapiro 2012). In recent decades, grassland and wetland degradation, alongside desertification, have placed significant stress upon land and water resources and biodiversity (including various iconic and endemic species, many of which are threatened or endangered). A sustainability focus recognizes that the costs of prevention of environmental degradation are significantly less than the costs of repair (if indeed repair is realistically achievable). Effective approaches to environmental protection and rehabilitation of rivers, wetlands and grasslands build upon a landscape platform, recognizing inherent links between geodiversity and biodiversity (Blue et al. 2013; Li et al. 2012). The Yellow River originates from the Bayankala Mountains atop the Qinghai–Tibetan Plateau of Qinghai Province, from which it flows through eight provinces and autonomous regions before emptying into the Bohai Sea north of the Shandong Peninsula. With a length of over 5400 km, it is the second longest river in China and the tenth longest in the world. The basin contains approximately 9 % of China’s population and 17 % of its agricultural area (Pietz and Giordano 2009). From its source at an elevation of around 4600 m, the upper Yellow River flows through a series of deep gorges and basins atop the QTP (Nicoll et al. 2013). Alluvial reaches in wide and shallow valleys with gentle valley slopes are characterized by a wide range of river types, including anabranching, anastomosing, braided and meandering reaches (see Figure 1; Blue et al. 2013; Li et al. 2013; Yu et al. 2013). Upstream from Hekouzhen in Inner Mongolia, the upper Yellow River contributes around 200 × 108 m3 per year (about 56 % of the total annual runoff of the basin). However, the upper Yellow River has a low sediment yield, generating about 1 × 108 t suspended sediment per year (less than 10 % of the annual suspended sediment load of the whole river basin) (Wang et al. 2007). Hence, while the source zone generates the largest portion of the total flow of the Yellow River, the majority of sediment is generated from the Loess Plateau in the middle reaches of its basin. Unlike the middle and lower reaches, which are Geomorphology and Environmental Management of the Yellow River Source Zone