Campbell
John L.
Campbell
John L.
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ArticleThe disappearing cryosphere : impacts and ecosystem responses to rapid cryosphere loss(American Institute of Biological Sciences, 2012-04) Fountain, Andrew G. ; Campbell, John L. ; Schuur, Edward A. G. ; Stammerjohn, Sharon E. ; Williams, Mark W. ; Ducklow, Hugh W.The cryosphere—the portion of the Earth's surface where water is in solid form for at least one month of the year—has been shrinking in response to climate warming. The extents of sea ice, snow, and glaciers, for example, have been decreasing. In response, the ecosystems within the cryosphere and those that depend on the cryosphere have been changing. We identify two principal aspects of ecosystem-level responses to cryosphere loss: (1) trophodynamic alterations resulting from the loss of habitat and species loss or replacement and (2) changes in the rates and mechanisms of biogeochemical storage and cycling of carbon and nutrients, caused by changes in physical forcings or ecological community functioning. These changes affect biota in positive or negative ways, depending on how they interact with the cryosphere. The important outcome, however, is the change and the response the human social system (infrastructure, food, water, recreation) will have to that change.
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ArticleClimate change decreases nitrogen pools and mineralization rates in northern hardwood forests(John Wiley & Sons, 2016-03-22) Durán, Jorge ; Morse, Jennifer L. ; Groffman, Peter M. ; Campbell, John L. ; Christenson, Lynn M. ; Driscoll, Charles T. ; Fahey, Timothy J. ; Fisk, Melany C. ; Likens, Gene E. ; Melillo, Jerry M. ; Mitchell, Myron J. ; Templer, Pamela H. ; Vadeboncoeur, Matthew A.Nitrogen (N) supply often limits the productivity of temperate forests and is regulated by a complex mix of biological and climatic drivers. In excess, N is linked to a variety of soil, water, and air pollution issues. Here, we use results from an elevation gradient study and historical data from the long-term Hubbard Brook Ecosystem Study (New Hampshire, USA) to examine relationships between changes in climate, especially during winter, and N supply to northern hardwood forest ecosystems. Low elevation plots with less snow, more soil freezing, and more freeze/thaw cycles supported lower rates of N mineralization than high elevation plots, despite having higher soil temperatures and no consistent differences in soil moisture during the growing season. These results are consistent with historical analyses showing decreases in rates of soil N mineralization and inorganic N concentrations since 1973 that are correlated with long-term increases in mean annual temperature, decreases in annual snow accumulation, and a increases in the number of winter thawing degree days. This evidence suggests that changing climate may be driving decreases in the availability of a key nutrient in northern hardwood forests, which could decrease ecosystem production but have positive effects on environmental consequences of excess N.