June 5, 2023: Stu Weiss – Smog Effects on Downwind Ecosystems

Join us via Zoom (info below) on June 5, 2023 at 7:30 PM (chat begins at 7:15) when we hear from Dr. Stu Weiss.

Succinct Abstract

Smog is nitrogen fertilizer. Emissions of nitrogen oxides and ammonia from vehicles, combustion, fertilizers, livestock, and other sources deposit onto downwind ecosystems over years and decades. The scientific community recognizes atmospheric nitrogen (N) deposition as a major threat to biodiversity, but N threats have largely flown under the radar and mitigation is not routinely sought. N-deposition should be routinely incorporated into environmental review, conservation planning, and mitigation.

Extended Abstract

The rich flora of California, including more than 225 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. N-deposition stimulates growth of introduced annual grasses that crowd out native wildflowers and enhance fire cycles; annual grasses are consistently raised as a major stewardship issue. Exposure of imperiled flora is quantified by overlaying NADP Total Deposition maps onto plant taxa in the CNDDB. More than 60% of listed taxa, and 44% of more than 1,400 rare but unlisted taxa, are exposed to significantly increased N per year, and many occupy sensitive habitats such as serpentine, other nutrient-poor soils, vernal pools, coastal sage scrub, deserts, and grasslands.

The direct impacts of this are easy to measure in thousands of acres burned in wildfires, particularly in areas where one wouldn’t have expected vast fires such as the desert.  Reporter Judith Lewis brought this home to LA in her article, “What’s Killing Joshua Tree National Park?” in the July 8, 2004, LA Weekly: The problem begins with nitrogen, which along with sulfur dioxide and ground-level ozone, is one of the components of air pollution produced by internal-combustion engines in the form of nitric oxide (NO) and the greenhouse gas nitrous oxide (NO2). Having blown in through the mountains, NO and NO2 bind to airborne dust particles and settle on the naturally nitrogen-poor desert floor.

“It’s called ‘fertilizing the desert,’” … Plants that belong in the desert don’t need nitrogen, but non-native grasses, such as red brome and cheatgrass, thrive like backyard tomato plants on it, even in the absence of water. The grass grows tall and spreads in the winter, dries out in the spring, and efficiently conducts fire from plant to plant in the summer and fall.  https://www.laweekly.com/whats-killing-joshua-tree-national-park/

Total N-deposition has decreased since 2002, primarily driven by strict regulation of NOx emissions. But ammonia emissions, which are not regulated, have increased, especially in urban areas where catalytic converters on vehicles produce large quantities of ammonia. Excessive N-deposition will continue into future decades. N-deposition should be routinely incorporated into environmental review, conservation planning, and mitigation. Project specific mitigations in several counties, and a regional HCP/NCCP in Santa Clara County provide models for addressing N-deposition impacts, especially maintaining moderate grazing regimes to crop excessive grass growth.


Stu Weiss

Stuart Bryan Weiss, Ph.D., is the Founder and Chief Scientist at Creekside Center for Earth Observation, LLC.  Stu has wide-ranging research experience in conservation and population biology, microclimate characterization, and statistical analysis.  He worked for over fifteen years at the Center for Conservation Biology at Stanford University, has authored more than 25 scientific publications, and has served as principal investigator for more than 50 grants and contracts.  He has researched the Bay checkerspot butterfly and serpentine grasslands since 1979 and has authored numerous scientific papers concerning climate/microclimate, population dynamics, nitrogen deposition, and conservation ecology.

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