Geology topics

L.H. Pardo

Publications and source records attributed to L.H. Pardo.

4 recordsLinked to original sources

USGS2011

Effects of nitrogen deposition and empirical nitrogen critical loads for ecoregions of the United States

Human activity in the last century has led to a significant increase in nitrogen (N) emissions and atmospheric deposition. This N deposition has reached a level that has caused or is likely to cause alterations to the structure and function of many ecosystems across the United States. One approach for quantifying the deposition of pollution that would be harmful to ecosystems is the determination of critical loads. A critical load is defined as the input of a pollutant below which no detrimental ecological effects occur over the long-term according to present knowledge. The objectives of this project were to synthesize current research relating atmospheric N deposition to effects on terrestrial and freshwater ecosystems in the United States, and to estimate associated empirical N critical loads. The receptors considered included freshwater diatoms, mycorrhizal fungi, lichens, bryophytes, herbaceous plants, shrubs, and trees. Ecosystem impacts included: (1) biogeochemical responses and (2) individual species, population, and community responses. Biogeochemical responses included increased N mineralization and nitrification (and N availability for plant and microbial uptake), increased gaseous N losses (ammonia volatilization, nitric and nitrous oxide from nitrification and denitrification), and increased N leaching. Individual species, population, and community responses included increased tissue N, physiological and nutrient imbalances, increased growth, altered root : shoot ratios, increased susceptibility to secondary stresses, altered fire regime, shifts in competitive interactions and community composition, changes in species richness and other measures of biodiversity, and increases in invasive species. The range of critical loads for nutrient N reported for U.S. ecoregions, inland surface waters, and freshwater wetlands is 1-39 kg N.ha -1.yr -1, spanning the range of N deposition observed over most of the country. The empirical critical loads for N tend to increase in the following sequence for different life forms: diatoms, lichens and bryophytes, mycorrhizal fungi, herbaceous plants and shrubs, and trees. The critical load approach is an ecosystem assessment tool with great potential to simplify complex scientific information and communicate effectively with the policy community and the public. This synthesis represents the first comprehensive assessment of empirical critical loads of N for major ecoregions across the United States. ?? 2011 by the Ecological Society of America.

Ecological Applications↗

USGS2011

Setting limits: Using air pollution thresholds to protect and restore U.S. ecosystems

More than four decades of research provide unequivocal evidence that sulfur, nitrogen, and mercury pollution have altered, and will continue to alter, our nation's lands and waters. The emission and deposition of air pollutants harm native plants and animals, degrade water quality, affect forest productivity, and are damaging to human health. Many air quality policies limit emissions at the source but these control measures do not always consider ecosystem impacts. Air pollution thresholds at which ecological effects are observed, such as critical loads, are effective tools for assessing the impacts of air pollution on essential ecosystem services and for informing public policy. U.S. ecosystems can be more effectively protected and restored by using a combination of emissions-based approaches and science-based thresholds of ecosystem damage. Based on the results of a comprehensive review of air pollution thresholds, we conclude: ??? Ecosystem services such as air and water purification, decomposition and detoxification of waste materials, climate regulation, regeneration of soil fertility, production and biodiversity maintenance, as well as crop, timber and fish supplies are impacted by deposition of nitrogen, sulfur, mercury and other pollutants. The consequences of these changes may be difficult or impossible to reverse as impacts cascade throughout affected ecosystems. ??? The effects of too much nitrogen are common across the U.S. and include altered plant and lichen communities, enhanced growth of invasive species, eutrophication and acidification of lands and waters, and habitat deterioration for native species, including endangered species. ??? Lake, stream and soil acidification is widespread across the eastern United States. Up to 65% of lakes within sensitive areas receive acid deposition that exceeds critical loads. ??? Mercury contamination adversely affects fish in many inland and coastal waters. Fish consumption advisories for mercury exist in all 50 states and on many tribal lands. High concentrations of mercury in wildlife are also widespread and have multiple adverse effects. ??? Air quality programs, such as those stemming from the 1990 Clean Air Act Amendments, have helped decrease air pollution even as population and energy demand have increased. Yet, they do not adequately protect ecosystems from long-term damage. Moreover they do not address ammonia emissions. ??? A stronger ecosystem basis for air pollutant policies could be established through adoption of science-based thresholds. Existing monitoring programs track vital information needed to measure the response to policies, and could be expanded to include appropriate chemical and biological indicators for terrestrial and aquatic ecosystems and establishment of a national ecosystem monitoring network for mercury. The development and use of air pollution thresholds for ecosystem protection and management is increasing in the United States, yet threshold approaches remain underutilized. Ecological thresholds for air pollution, such as critical loads for nitrogen and sulfur deposition, are not currently included in the formal regulatory process for emissions controls in the United States, although they are now considered in local management decisions by the National Park Service and U.S. Forest Service. Ecological thresholds offer a scientifically sound approach to protecting and restoring U.S. ecosystems and an important tool for natural resource management and policy. ?? The Ecological Society of America.

Issues in Ecology↗

USGS2011

Synthesis: Chapter 19

Human activity in the last century has led to a substantial increase in nitrogen (N) emissions and deposition (Galloway et al. 2003). Because of past, and, in some regions, continuing increases in emissions (Lehmann et al. 2005, Nilles and Conley 2001), this N deposition has reached a level that has caused or is likely to cause alterations and damage in many ecosystems across the United States. In some ecoregions, the impact of N deposition has been severe and has changed the biotic community structure and composition of ecosystems. In the Mediterranean California ecoregion, for example (see Chapter 13), replacement of native by exotic invasive vegetation is accelerated because exotic species are often more productive under elevated N deposition than native species in some California grasslands, coastal sage scrub, and desert scrub (Fenn et al. 2010, Rao and Allen 2010, Rao et al. 2010, Weiss 1999, Yoshida and Allen 2004). Such shifts in plant community composition and species richness can have consequences beyond changes in ecosystem structure: shifts may lead to overall losses in biodiversity and further impair particular threatened or endangered species (Stevens et al. 2004). Th e extirpation of the endangered checkerspot butterfl y (Euphydryas editha bayensis), because the host plant for the larval stage disappears in N-enriched ecosystems (Fenn et al. 2010, Weiss 1999), is just one example of the detrimental impacts of elevated N deposition.

General Technical Report↗

USGS1996

Climatic control of nitrate loss from forested watersheds in the northeast United States

Increased losses of nitrate from watersheds may accelerate the depletion of nutrient cations and affect the acidification and trophic status of surface waters. Patterns of nitrate concentrations and losses were evaluated in four forested watersheds (East Bear Brook Watershed, Lead Mountain, ME; Watershed 6, Hubbard Brook Experimental Forest, White Mountains, NH; Arbutus Watershed, Huntington Forest, Adirondack Mountains, NY; Biscuit Brook, Catskill Mountains, NY) located across the northeastern United States. A synchronous pattern was observed in nitrate concentrations of drainage waters from these four sites from 1983 through 1993. Most notably, high concentrations and high drainage water losses followed an anomalous cold period (mean daily temperature -11.4 to -16 ??C in December 1989) for all four sites. After high nitrate losses during the snowmelt of 1990, nitrate concentrations and fluxes decreased at all sites. These results suggest that climatic variation can have a major effect on nitrogen flux and cycling and may influence temporal patterns of nitrate loss in a region.

Environmental Science & Technology↗