Water Quantity and Quality at the Urban–Rural Interface

Population growth and urban development dramatically alter natural watershed ecosystem structure and functions and stress water resources. We review studies on the impacts of urbanization on hydrologic and biogeochemical processes underlying stream water quantity and water quality issues, as well as water supply challenges in an urban environment. We conclude that converting forest lands to urban uses increases stormflow rates and volumes, alters baseflow dynamics, and degrades water quality by increasing impervious surface areas. Alterations of watershed water cycles are the root causes of many chain reactions of stream ecosystem degradation present in today’s urban areas. Knowledge gaps exist regarding interactions among processes of urbanization (land conversion, increasing impervious areas, new pollutants), hydrological functions (water budget change, infiltration and evapotranspiration processes), and ecological (biota change) functions at different temporal and spatial scales. Innovative implementation of watershed services is the key to mitigating impacts of urbanization on water and sustaining urban–rural ecosystems. Although human populations have lived a rural lifestyle throughout most of our history, the world’s urban population is rising rapidly and this change has caused serious problems that have impacted human welfare. For the United States, only 5% of the population could be classified as urban in 1790, but today 80% of the population lives in urban areas. Worldwide, about one-half the total population lives in urban areas, and this number is expected to grow to 60% by the year 2025. People are attracted to water, and in turn human activities have affected the quantity, quality, distribution of waters on Earth. Anthropogenic structures such as irrigation canals, wells, reservoirs for drinking water withdrawal, dams for power generation, and paved roads for transportation are just a few examples of how humans have shaped the natural landscape. In the 21st century, as human population rises, it becomes increasingly important to understand the impacts of “urban sprawl” at the urban–rural interface on ecosystem structure and functions, society, and culture (Foley et al., 2005). The most direct impact of urbanization on ecosystems is altering the hydrologic cycle that controls the ecosystem energy and matter flows (DeFries and Eshleman, 2004). Indeed, water resources in urban environments around the world are increasingly stressed due to population rise, rapid land use change (Foley et al., 2005; Piao et al., 2007), and climate G. Sun, Eastern Forest Environmental Threat Assessment Center, Southern Research Station, USDA Forest Service, Raleigh, NC 27606 (Ge_Sun@ncsu.edu); B.G. Lockaby, School of Forestry and Wildlife Sciences, Auburn University, Auburn, AL 36849 (lockabg@auburn.edu). doi:10.2136/2012.urban-rural.c3 Urban–Rural Interfaces: Linking People and Nature, David N. Laband, B. Graeme Lockaby, and Wayne Zipperer, editors Copyright © 2012. American Society of Agronomy, Soil Science Society of America, Crop Science Society of America 5585 Guilford Rd., Madison, WI 53711-5801, USA.