Threats to water sustainability in the Columbia Basin
Water sustainability is one of the grand challenges facing our society in the 21st century. With ongoing land development driven by population growth and expected climate change, many regions of the world are facing the issues of water scarcity and water pollution, threatening the long-term sustainability of water resources. Climate, land use, and water management systems are considered the three major controls on hydrological regimes and water resources. Inputs of precipitation, temperature, evaporative demand (i.e., climate aspect), vegetation and land cover characteristics (i.e., land aspect), and spatial and temporal allocation of water resources (i.e., water management aspect) are all important for assessing current water system vulnerability, and they need to be considered in integrated water resource management under various environmental change scenarios.
Climate variability and change affects the water system through the hydrologic cycle by modifying water supply, water demand, and water quality. High climate variability often contributes to regional water resource vulnerability by increasing the frequency of extreme hydrologic events such as floods and droughts. A rise in air temperature is also associated with increasing irrigation and municipal water demand (House-Peters and Chang 2011), while increasing wind speed could lower summer water demand due to evaporative cooling (Praskievicz and Chang 2009). Water quality typically degrades after a prolonged dry period, increasing nitrate concentrations substantially (Saunders et al. 2004). Changes in the timing and amount of rainfall and temperature increases are associated with changes in seasonal water supply. Additionally, changes in the intensity and frequency of rainfall and snowpack result in frequent regional droughts or floods (Jung and Chang 2011). Rising air temperature is related to increases in water temperature and reduction in dissolved oxygen, thus affecting instream biogeochemical cycles. Changes in hydrological regimes driven by different rainfall characteristics affect sediment transport and deposition (Lane 2011).
Land cover changes from forested lands to impervious agricultural or urban lands also affect various aspects of water resource vulnerability. First, increased impervious surface area resulting from urban and industrial development will make surface runoff flashier by lowering rates of soil-water infiltration and groundwater recharge. In a typical urban environment, wet-season flow becomes higher, while dry season flow becomes lower (Chang 2007). Second, urban and agricultural land development will also increase water demand to sustain development (Franczyk and Chang 2009). It has been well-known that different spatial patterns of urban development are highly correlated to different water consumption patterns (House-Peters and Chang 2011 b; Shandas and Parandvash 2010).
Third, together with point source pollution, increases in storm runoff will deliver more urban and agricultural non-point source pollutants, such as thermal or nutrient pollution to water bodies, yet the concentration of constituents is likely to remain high during low-flow season (Sonoda and Yeakley 2007). As a result, highly developed watersheds tend to have more impaired water quality and thus have increased vulnerability while less developed watersheds may be more resilient. Increased sediment loads in surface water have been repeatedly linked to land use change (Trimble and Lund 1982, Tang et al. 2011). In fact, the sediment budget approach to modeling sediment flux in a watershed is based largely on land use (Reid and Dunne 2003). Given the high degree of correlation between land use types and water quality (Snyder et al., 2007), population pressure will increase water quality vulnerability and drive the need for innovative water quality management to be integrated within land use management.
This map, courtesy of Dan Wise of the USGS, shows estimated total nitrogen yields for the Pacific Northwest. Heightened levels of nitrogen due to non-point source pollution are major water quality challenge.
The consequences of nutrient pollution could be significant, resulting in increased phytoplankton and benthic algal biomass, often in the form of toxic or bloom-forming species, decreased clarity and reduced esthetic value, taste and odor problems, oxygen depletion, and fish kills (Smith 1998). In addition to environmental effects, increased nutrient concentrations can lead to human health effects, such as nitrogen toxicity, which has been linked to methemoglobinemia in infants, certain types of cancer, and birth defects (Carpenter et al. 1998, Camargo and Alonso 2006), as well as health effects on livestock. Indirect effects of high nutrient loads on human health can result from increased production of toxic algae, including cyanobacteria (neurotoxins and hepatotoxins: Hitzfeld et al. 2000), dinoflagellates in estuaries and coastal waters (paralytic and neurotoxic shellfish poisoning associated with red tides: Van Dolah 2000, Van Dolah et al. 2001), and marine diatoms (amnesic shellfish poisoning: Van Dolah 2000).