Thermoelectric power plants interact with climate, hydrology, and aquatic ecosystems while rivers serve as "horizontal cooling towers"  — but at a cost to the environment, says a new analysis.  

90% of the electricity in the US is created by power plants that boil water and create steam that drives turbines to produce electricity. Cooling the waste heat generated during the process requires that high volumes of water be used. The thermoelectric sector is the largest user of freshwater in the U.S. - energy companies use more water than agriculture. 

Water withdrawals are either evaporated in cooling towers or returned 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. A new paper says that, of the waste heat transferred to rivers, only slightly more than 11 percent goes into the atmosphere, with the rest delivered to coastal waters and the ocean. 

The study quantified the various dynamics using a spatially distributed hydrology and water temperature model called the Framework for Aquatic Modeling in the Earth System, or FrAMES model, coupled with the Thermoelectric Power and Thermal Pollution Model developed by collaborators at City College of New York.

The combined models showed that there are roughly 4,700 river miles in the region potentially impacted by power plants. The study found that, in general, the impact to river temperatures, and thus fish habitat, is "considerable" and disruptions in river flow "minimal," in part because so many of the region's power plants are located well down river near coastal areas.

But the study also noted that in the face of changing climate and increasing energy demand, "it is essential to assess the capacity and associated environmental trade-offs of heat regulating ecosystem services that support the electricity sector."

Last summer a reactor at the Millstone nuclear power plant in Waterford, Conn. was shut down because the water in Long Island Sound was too warm to cool it—something utterly unanticipated when the plant was designed in the 1960s. And in July 2012, a nuclear plant in Illinois had to obtain special permission to continue operations because its cooling water pond reached 102 degrees in the wake of low rainfall and high air temperatures.

University of New Hampshire assistant professor Wilfred Wollheim said in their statement, "We can better understand the unintended consequences to other ecosystem services as we rely on rivers to support generation of electricity. Integrative, regional approaches will be needed to help plan as society adapts to changing climate and hydrology while demand for power continues to increase."

Published in Environmental Research Letters.