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A new analysis of streams in the western United States withlong-term monitoring programs has found that despite a generalincrease in air temperatures over the past several decades, streamsare not necessarily warming at the same rate. Several factors may influence the discrepancy, researchers say,including snowmelt, interaction with groundwater, flow anddischarge rates, solar radiation, wind and humidity. But even afterfactoring out those elements, the scientists were surprised by thecooler-than-expected maximum, mean and minimum temperatures of thestreams. Results of the research, which was supported by the U.S. GeologicalSurvey, the U.S. Forest Service and Oregon State University, havebeen published online in Geophysical Research Letters. "Individually, you can find streams that seem to be getting warmerand others that are getting cooler," said Ivan Arismendi, apost-doctoral researcher at Oregon State University and lead authoron the study. "Some streams show little effect at all. But thebottom line is that recent trends in overall stream temperature donot parallel climate-related trends." The researchers caution that the findings don't mean that climatechange will not have an impact on stream temperature, which is afundamental driver of ecosystem processes in streams. However, therelationship between air temperatures and stream temperatures maybe more complex than previously realized and require additionalmonitoring. Alternatively, there may be a time lag between air temperature andstream temperature, they say. "One surprise was how few stream gauging stations have thenecessary long-term records for evaluating climate-related trendsin water temperatures," said coauthor Jason Dunham, an aquaticecologist with the U.S. Geological Survey. "Most of them arelocated in streams with high human influence, which makes itdifficult to separate climate effects from local human impacts." "In those areas where human impact was minimal, the variability intrends was impressive," added Dunham, who has a courtesyappointment in OSU's Department of Fisheries and Wildlife. "Itsuggests to us that a variety of local influences may stronglyaffect how stream temperatures respond to climate." Arismendi and his colleagues considered more than 600 gaugingstations for the study but only 20 of the stations had asufficiently lengthy period of monitoring - and lacked humaninfluence. These long-term monitoring sites are operated primarilyby the U.S. Geological Survey and U.S. Forest Service, and werelocated in Oregon, Washington, Idaho, California, Nevada andAlaska. Coauthor Roy Haggerty, a professor in OSU's College of Earth,Ocean, and Atmospheric Sciences, said warming temperatures cancreate more rapid or earlier snowmelt and affect streamtemperatures in some locations. Another explanation for the lack ofwarming in many streams can be a time lag that can occur betweenprecipitation entering underground aquifers and entering thestream. "Groundwater can influence stream temperatures as well asstreamflow and in some cases, it can take many years for thatgroundwater to make it to the stream," noted Haggerty, the HollisM. Dole Professor of Environmental Geology at OSU. "This and the other physics processes of a stream need to beconsidered when analyzing its heat budget - from the geology andstream bed, to the amount of shading in the riparian zone." Sherri Johnson, a research ecologist with the U.S. Forest Serviceand coauthor on the study, said stream temperatures can beimportant for a variety of reasons. "Temperature is a key indicator of water quality and many streamsthroughout the Northwest have increased stream temperaturesassociated with human activity," Johnson said. "Generally speaking,cooler stream temperatures are beneficial, and are a crucial factorin maintaining healthy ecosystems and populations of salmon,steelhead, trout and other cold-water species." Arismendi, who did his doctoral work at the Universidad Austral deChile before coming to OSU, said the study points out the value oflong-term data from streams that have had minimal human impacts. "The fact that stream temperatures don't correlate to climatetrends in a predicable way indicates we need to study therelationship further to better appreciate the complexity,"Arismendi said. "Our knowledge of what influences stream temperatures is limited bythe lack of long-term monitoring sites, and previous lumping ofresults among streams with relatively low and high levels of humanimpacts. "Local variability is really important in driving climatesensitivity of streams," he added. We are high quality suppliers, our products such as Flat Tempered Glass , Technical Data for oversee buyer. To know more, please visits Toughened Safety Glass.
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