Running two computer models in tandem（协力地）, scientists from the University of New Hampshire have detailed for the first time how thermoelectric（热电的） power plants interact with climate, hydrology（水文学）, and aquatic ecosystems throughout the northeastern U.S. and show how rivers serve as "horizontal cooling towers" that provide an important ecosystem service to the regional electricity sector -- but at a cost to the environment. The analysis, done in collaboration with colleagues from the City College of New York (CCNY) and published online in the current journal Environmental Research Letters, highlights the interactions among electricity production, cooling technologies, hydrologic conditions, aquatic impacts and ecosystem services, and can be used to assess the full costs and tradeoffs（权衡，折衷） of electricity production at regional scales and under changing climate conditions.

Lead authors of the study are Robert Stewart of the UNH Institute for the Study of Earth, Oceans, and Space (EOS) and Wilfred Wollheim of the department of natural resources and environment and EOS.

Thermoelectric power plants boil water to create steam that in turn drives turbines to produce electricity. They provide 90 percent of the electricity consumed nationwide and an even a greater percentage in the Northeast -- a region with a high density of power plants.

Cooling the waste heat generated during the process requires that prodigious volumes of water be withdrawn and makes the thermoelectric sector the largest user of freshwater in the U.S. -- withdrawing more than the entire, combined agricultural sector. Water withdrawals are either evaporated in cooling towers or returned to the river at elevated temperatures. Rivers can help mitigate these added heat loads through the ecosystem services of conveyance, dilution, and attenuation -- essentially acting as horizontal cooling towers as water flows downstream.

Says Stewart, a research scientist in the EOS Earth Systems Research Center, "Our modeling shows that, of the waste heat produced during the production of electricity, roughly half is directed to vertical, evaporative（蒸发的） cooling towers while the other half is transferred to rivers."

The study also shows that, of the waste heat transferred to rivers, only slightly more than 11 percent wafts into the atmosphere with the rest delivered to coastal waters and the ocean.

"We were surprised to find that relatively little of the heat to rivers is exchanged back to the atmosphere," notes Wollheim, an assistant professor and co-director of the Water Systems Analysis Group at EOS. Wollheim adds, "Reliance on riverine ecosystem services to dispense waste heat alters temperature regimes, which impacts fish habitat and other aquatic ecosystem services."