Ground Water and Surface Water Interaction

Ground water-surface water (GW-SW) exchange links aquifers to above-ground aquatic ecosystems via bidirectional fluxes that influence physical, chemical, and biological conditions in both subsurface and surface environments. This article reviews GW-SW exchange and emphasizes how it influences the structure and function of aquatic ecosystems. It first addresses the multiple spatial and temporal scales of exchange and illustrates how geomorphic and biological structure influences the direction of GW-SW interaction. A general framework for how GW-SW exchange has the potential to alter hydrologic, biogeochemical, and biological conditions within and among aquatic ecosystems is then provided. Next the article addresses the basic methods and approaches employed to quantify GW-SW interaction including: (1) direct measures of exchange; (2) heat tracer methods; (3) use of Darcy's law; and (4) mass-balance approaches. A topological approach then addresses GW-SW exchange and its ecological implications for streams, including the concepts of the hyporheic zone and transient storage, the occurrence of underflow and baseflow interactions in larger rivers, differences among hydrologically-mounded, throughflow, and terminal ground water-discharge lakes, and ground water influences on wetlands. Finally, it addresses how human activities may interact with GW-SW to influence hydrologic and ecological aspects of GW-SW exchange including a brief description of future research needs.