Atmospheric Nitrogen Deposition is an Acute, but Underappreciated Threat to Imperiled California Flora
Abstract
The scientific community recognizes that atmospheric nitrogen deposition is a major threat to biodiversity, but the extent of that threat is not widely appreciated in the greater conservation community. The rich flora of California, including 226 taxa listed as Threatened or Endangered, is at risk from many factors including habitat conversion, fragmentation, and climate change. But N-deposition threats have largely flown under the conservation radar. Terrestrial eutrophication from N-deposition stimulates growth of introduced annual grasses that crowd out native wildflowers and enhance fire cycles. Much of California downwind of pollution sources exceeds critical loads. We document the scale of N-deposition exposure by overlaying NADP Total Deposition maps onto the plant taxa in the California Natural Diversity Data Base (CNDDB). Extracted statistics include mean, max, min, and oxidized versus reduced-N, as well as the trends since 2002. 138/226 (62%) of listed taxa are exposed to >5kg-N ha-1 yr-1, and many occupy sensitive habitats such as serpentine and other nutrient-poor soils, vernal pools, coastal sage scrub, deserts, and grasslands. 623/1407 (44%) of rare, but unlisted, taxa are exposed to >5kg-N ha-1 yr-1; a closer look is warranted for many plants. While exposure to total N-deposition has decreased since 2002, primarily driven by reductions in NOx emissions, reduced N has generally increased and excessive N-deposition will continue for decades into the future. Mitigation has been implemented for several power plant projects, and at a regional scale with the Santa Clara Valley Habitat Plan. This analysis demonstrates that a large fraction of imperiled plants in California are potentially at risk and that N-deposition should be routinely incorporated into environmental review and conservation planning.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.B13N2523W
- Keywords:
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- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCES;
- 0426 Biosphere/atmosphere interactions;
- BIOGEOSCIENCES;
- 0469 Nitrogen cycling;
- BIOGEOSCIENCES;
- 0478 Pollution: urban;
- regional and global;
- BIOGEOSCIENCES