Colorado mountains
From Long-Term Data to Understanding: Toward a Predictive Ecology
2015 LTER ASM Estes Park, CO - August 30 - September 2, 2015

Inertial biogeochemical effects inhibit recovery from chronic nitrogen deposition in alpine tundra

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Poster Number: 
Presenter/Primary Author: 
William Bowman
Cliff Bueno de Mesquita
Teal Potter

The increase in the deposition of pollutant nitrogen (N) has been linked to losses of plant diversity, soil and surface water acidification, and aluminum toxicity.  The degree to which these changes are reversible if emissions and deposition of reactive N are lowered is uncertain.  Ten years of experimental N additions in dry meadow alpine tundra on Niwot Ridge led to changes in plant species abundances (but not richness), increases in net N mineralization, loss of base cations, increases in extractable aluminum, and decreases in soil pH.  To examine the potential for recovery from the effects of N deposition, treatments were stopped in one half of the plot, but continued in the other half of the plot.  Five to seven years after stopping treatments, few signs of recovery were apparent.  Soil pore water inorganic N and extractable aluminum concentrations were still elevated, plant species composition and individual species abundances were unchanged, and soil pH and base cation values remained lower, despite cessation of the N treatments.  These results indicate significant inertia in reversal of biogeochemical effects from the impact of N deposition hinders ecosystem recovery, even if the emissions of N are lowered.  Critical loads for N deposition should take this into account, using metrics such as plant diversity and abundances that occur during the early stages of ecosystem change.