Unintended consequences of urbanization for aquatic ecosystems: A case study from the Arizona desert

Many changes wrought during the construction of designer ecosystems arc intended to ensure-and often succeed in ensuring-that a city call provide ecosystem goods and services; but other changes have unintended impacts oil the ecology of the city, impairing its ability to provide these critical functions. Indian Bend Wash, all urbanizing watershed in the Central Arizona-Phoenix (CAP) ecosystem, provides all excellent case study of how human alteration of land cover, streamchannel structure, and hydrology affect ecosystem processes, both intentionally and unintentionally The construction of canals created new flowpaths that cut across historic stream channels, and the creation of artificial lakes produced sinks for fine sediments and hotspots for nitrogen processing. Further hydrologic manipulations, such as groundwater pumping, linked surface flows to the aquifer and replaced ephemeral washes with perennial waters. These alterations of hydrologic structure are typical by-products of urban growth in and and semiarid regions and create distinct spatial and temporal patterns Of nitrogen availability.