Chihuahuan Desert Network
The Chihuahuan Desert Vital Signs Network (CHDN) includes 6 national park units in Texas and New Mexico: Amistad National Recreation Area (NRA), Big Bend National Park (NP), Carlsbad Caverns NP, Fort Davis National Historic Site (NHS), Guadalupe Mountains NP, and White Sands National Monument (NM). CHDN includes over a thousand square miles of the Chihuahuan Desert. Ecosystems range from desert lowlands to high-elevation ponderosa pine forests with mountains to over 8,000 feet. The network also includes over 200 miles of major rivers. Because of this significant range of habitats, there are a wide variety of biotic communities.Big Bend NP, Carlsbad Caverns NP, and Guadalupe Mountains NP are Class I air quality areas, receiving the highest protection under the Clean Air Act. The other park units are Class II air quality areas and also receive protection under the Act. Air quality issues of concern in the CHDN include atmospheric deposition effects and visibility impairment from fine particle haze. Atmospheric nitrogen deposition can cause changes in soil that affect soil microorganisms, plants, and trees. Excess nitrogen can cause changes in plant community structure and diversity, with native species being replaced by invasive and exotic species. Nitrogen and sulfur deposition can also have an acidifying effect on soils and water, decreasing buffering capacity and eventually reducing pH. Research in the park has found a rapid, major decrease in soil pH in Big Bend grasslands. Studies were initiated in 2003 to assess the impacts of atmospheric nitrogen deposition and climate change on desert ecosystems in the park. Ozone is not currently a significant concern for vegetation in network park units. An ozone injury risk assessment indicates the risk of injury to vegetation is moderate in Amistad NRA; the remainder of the park units in the network have a low risk rating.
The Network map below provides information on air quality monitoring. Ozone, sulfur dioxide, dry deposition, and meteorology are collected by the Clean Air Status and Trends (CASTNet) and Gaseous Pollutant Monitoring (GPMN) networks. Ozone is also monitored with passive samplers and portable continuous analyzers. Wet Deposition is monitored through cooperation with National Atmospheric Deposition Program/National Trends Network (NADP/NTN). The Mercury Deposition Network (MDN), part of NADP, collects precipitation samples that are analyzed for mercury. Visibility is monitored as part of the Interagency Monitoring of Protected Visual Environments (IMPROVE). Additional details on these parameters are described in Air Quality Monitoring.
Air quality monitoring in or near the network is indicated on the map by symbols, with the blue line showing the approximate borders of the network. The legend shows the symbols for the type of monitoring present, with NPS park units in green. Class I areas have linkable access to ARIS information.