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Nitrogen Saturation Studies

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Summer program student taking a soil sampleAnthropogenic emissions of reactive nitrogen to the atmosphere (primarily due to fertilizer production and fossil fuel combustion) and the subsequent deposition to Earth's surface have increased nearly 200% since the beginning of the industrial revolution and are projected to double yet again by 2050. Nitrogen deposition rates over large regions of the world now exceed 10 kg N ha-1 yr-1, more than an order of magnitude higher than natural background levels.This fertilization of historically nitrogen-limited ecosystems has the potential to saturate biotic demand for nitrogen thereby producing a cascade of negative impacts on ecosystem processes.

Following more than two decades of research on the nitrogen saturation phenomenon, known effects of atmospheric nitrogen deposition on temperate ecosystems include:

  • increased nitrate leaching to groundwater,
  • enhanced trace gas (i.e., nitrous and nitric oxide) emissions to the atmosphere,
  • altered ecosystem carbon storage,
  •  nutrient imbalances (e.g., declines in tree Ca:Al and Mg:N ratios),
  • and shifts in plant and microbial communities. Ecosystem responses to simulated nitrogen deposition will continue to be studied and compared to data from similar experiments in the region and globally. 

We are also comparing the effects of soil nitrogen enrichment to other global change factors (e.g., warming and biotic invasions).

This project is supported by the Harvard Forest Long-Term Ecological Research Program.