No abstract

Many countries/areas are experiencing or may soon experience water scarcity owing to rapid population growth, urbanization and/or climate change. Currently, almost one-fifth of the world's population (1.2 billion) live in areas of physical water scarcity. Water diversions have become a commonplace solution proposed by governments for alleviation of physical water scarcity. Thus far, more than 80 major projects are completed or under construction globally, including the world's largest diversion: South-to-North Water Transfer Project (SNWTP) in China. Negative effects associated with water diversions, such as habitat loss and transfer of pollutants, have been recognized. However, it has been largely overlooked that ''invasion highways'' are created when water diversions link biogeographic regions. These ''invasion highways'' can facilitate spread of an array of non-native species. Although previous experiences have provided clear warnings regarding spread of non-native invasive species through artificial waterways, these lessons have been largely ignored by governments when resolving water scarcity problems. Here we use SNWTP, which will likely facilitate spread of invasive golden mussels, as well as many known examples of non-native invasive species spread through artificial waterways in other water systems, to call on governments to formally establish policy and seek management solutions to considering spread of non-native species when planning water diversions.

Chiayi County is located in the largest alluvial plain of Taiwan with extensive aquaculture and rice farming sustained by water extracted from groundwater wells. Chiayi is a typical aquaculture area affected by land subsidence, yet such lands worldwide combine to provide nearly 90% of global aquaculture products, greatly reducing oceanic overfishing problems. This study uses precision leveling, multi-layer compaction monitoring well (MLCW) and spaceborne SAR interferometry (InSAR) to examine the cause and effect of land subsidence in Chiayi associated with groundwater extractions and changes. Heights at benchmarks in a leveling network are measured annually and soil compactions at 24-26 layers up to 300-m depths at 7 MLCWs are collected at one-month intervals. Over 2007-2011, 15 ALOS/PALSAR images are processed by the method of TCPInSAR to produce subsidence rates. All sensors show that land subsidence occur in most parts of Chiayi, with rates reaching 4.5 cm/year around its coast, a result of groundwater pumping from shallow to deep aquifers. MLCWs detect mm-accuracy seasonal soil compactions coinciding with groundwater level fluctuations and causing dynamic compactions. Compactions near Taiwan High Speed Rail may reduce the strength of the rail's supporting columns to degrade its safety. The SAR images yield subsidence rates consistent with those from leveling and compaction wells after corrections for systematic errors by the leveling result. Subsidence in Chiayi's coastal area leads to relative sea level rises at rates up to 15 times larger than the global eustatic sea level rising rate, a risk typical for world's aquaculture-rich regions. At the fish pond-covered Budai Township, InSAR identifies subsidence spots not detected by leveling, providing crucial geo-information for a sustainable land management for aquaculture industry.