National Atmospheric Deposition Program 2006 Annual Summary

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Nitrogen in the Nation's Rain

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Total Deposition 2015 Annual Map Summary

In October 2011, the National Atmospheric Deposition Program (NADP) Executive Committee formed the Total Deposition (TDEP) Science Committee. The mission of TDEP is to improve estimates of atmos-pheric deposition by advancing the science of measuring and modeling atmospheric wet, dry, and total deposition of species such as sulfur, nitrogen, and mercury by providing a forum for the exchange of information on current and emerging issues within a broad multi-organization context including atmos-pheric scientists, ecosystem scientists, resource managers, and policy makers.published or submitted for publicationis peer reviewedOpe

Nitrogen from the Atmosphere

Nitrogen surrounds us. Nitrogen (N) is required by all life on earth. N is also the most abundant gas in our atmosphere, existing primarily as N2, a form of N that almost all plants and animals cannot use. It is therefore termed non-reactive nitrogen (Nn-r). Reactive forms of nitrogen (Nr), nitrogen that can be used by organisms, is a small fraction of what’s naturally found in the atmosphere. However, humans learned in the early 1900s to change N2 into reactive forms of N to create N-based fertilizers to increase plant growth. Humans also began to burn fossil fuels, changing Nn-r to Nr. This Nr is the N that is most important to us. Reactive nitrogen causes a cascade of effects. Nr can enter ecosystems from the air or through fertilizer application to soils, having unintended effects. Nr cycles through many other forms that can move from the soil into water resources or to and from the atmosphere. For example, too much Nr in streams can cause overgrowth of algae that chokes out fish. Too much Nr in soils can damage non-crop plants, such as trees, and change soil chemistry. Nr that goes back to the air contributes to air pollution such as acid rain, ozone, and visibility problems. Nitrogen can then fall back to land and water in wet deposition (rain or snow), or as dry deposition of Nr particles and gases.published or submitted for publicationis peer reviewedOpe

2015 Summary of Critical Load Maps

This summary is a collection of critical load maps for the U.S., developed by CLAD members using critical load data that are publically available as part of the NADP CLAD National Critical Load Database (NLCD).published or submitted for publicationis peer reviewedOpe

2017 Summary of Critical Load Maps

The critical load maps provided here represent a compilation of empirical and calculated critical load values from a variety of regional- and national-scale projects. The intended uses of these maps are for scientific, policy-related, or educational purposes. These maps illustrate critical loads in the National Critical Load Database v3.0 (NCLD) and help to identify spatial gaps in information, as well as additional research needs.published or submitted for publicationis peer reviewedOpe

Long-term nutrient enrichment, mowing, and ditch drainage interact in the dynamics of a wetland plant community.

This work was supported by NSF grants to Carol Goodwillie (DUE 126824 and DEB 1049291) and Ariane Peralta (DEB 1845845). This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.Fertilization studies have elucidated basic principles of the role of nutrients in shaping plant communities and demonstrated the potential effects of anthropogenic nutrient deposition. Yet less is known about how these effects are mediated by interacting ecological factors, particularly in nutrient-poor wetland habitats. In a long-term experiment in a coastal plain wetland, we examined how fertilization and mowing affected the diversity and composition of a plant community as it reestablished after major disturbance. A drainage ditch in proximity to the experimental plots allowed us also to consider the influence of hydrology and its interactions with nutrient addition. Fertilization decreased species richness, with wetland specialist species showing especially great losses, and several lines of evidence suggest that the effect was mediated by competition for light. Altered hydrology via ditch drainage had effects that were similar to fertilization, with more rapidly draining plots showing lower diversity and decreased abundance of wetland species. Plant community diversity and dynamics were influenced by complex interactions between fertilization, disturbance, and hydrology. The negative effect of fertilization on species richness was initially mitigated by mowing, but in later years was more evident in mowed than in unmowed plots. In the absence of disturbance, nutrient addition increased the rate of transition to primarily woody communities. Similarly, drained plots experienced increased rates of succession compared to wetter plots. Our results suggest that these interactions need to be considered to understand the potential effects of anthropogenic nutrient addition and hydrologic alterations to wetland ecosystems.ECU Open Access Publishing Support Fun

Effects of experimentally added salmon subsidies on resident fishes via direct and indirect pathways

Artificial additions of nutrients of differing forms such as salmon carcasses and analog pellets (i.e. pasteurized fishmeal) have been proposed as a means of stimulating aquatic productivity and enhancing populations of anadromous and resident fishes. Nutrient mitigation to enhance fish production in stream ecosystems assumes that the central pathway by which effects occur is bottom-up, through aquatic primary and secondary production, with little consideration of reciprocal aquatic-terrestrial pathways. The net outcome (i.e. bottom-up vs. top-down) of adding salmon-derived materials to streams depend on whether or not these subsidies indirectly intensify predation on in situ prey via increases in a shared predator or alleviate such predation pressure. We conducted a 3-year experiment across nine tributaries of the N. Fork Boise River, Idaho, USA, consisting of 500-m stream reaches treated with salmon carcasses (n = 3), salmon carcass analog (n = 3), and untreated control reaches (n = 3). We observed 2–8 fold increases in streambed biofilms in the 2–6 weeks following additions of both salmon subsidy treatments in years 1 and 2 and a 1.5-fold increase in standing crop biomass of aquatic invertebrates to carcass additions in the second year of our experiment. The consumption of benthic invertebrates by stream fishes increased 110–140% and 44–66% in carcass and analog streams in the same time frame, which may have masked invertebrate standing crop responses in years 3 and 4. Resident trout directly consumed 10.0–24.0 g·m-2·yr-1 of salmon carcass and \u3c1–11.0 g·m-2·yr-1 of analog material, which resulted in 1.2–2.9 g·m-2·yr-1 and 0.03–1.4 g·m-2·yr-1 of tissue produced. In addition, a feedback flux of terrestrial maggots to streams contributed 0.0–2.0 g·m-2·yr-1 to trout production. Overall, treatments increased annual trout production by 2–3 fold, though density and biomass were unaffected. Our results indicate the strength of bottom-up and top-down responses to subsidy additions was asymmetrical, with top-down forces masking bottom-up effects that required multiple years to manifest. The findings also highlight the need for nutrient mitigation programs to consider multiple pathways of energy and nutrient flow to account for the complex effects of salmon subsidies in stream-riparian ecosystems

Mercury flux to sediments of Lake Tahoe, California-Nevada

Author Posting. © The Author(s), 2009. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Water, Air, & Soil Pollution 210 (2010): 399-407, doi:10.1007/s11270-009-0262-y.We report estimates of mercury (Hg) flux to the sediments of Lake Tahoe, California-Nevada: 2 and 15-20 µg/m2/yr in preindustrial and modern sediments, respectively. These values result in a modern to preindustrial flux ratio of 7.5-10, which is similar to flux ratios recently reported for other alpine lakes in California, and greater than the value of 3 typically seen worldwide. We offer plausible hypotheses to explain the high flux ratios, including (1) proportionally less photoreduction and evasion of Hg with the onset of cultural eutrophication and (2) a combination of enhanced regional oxidation of gaseous elemental Hg and transport of the resulting reactive gaseous Hg to the surface with nightly downslope flows of air. If either of these mechanisms is correct, it could lead to local/regional solutions to lessen the impact of globally increasing anthropogenic emissions of Hg on Lake Tahoe and other alpine ecosystems.Funding was provided by Miami University, EPA-STAR, the Postdoctoral Scholar Program at Woods Hole Oceanographic Institution, and the USGS

National Atmospheric Deposition Program 1999 Annual Summary

published or submitted for publicationis peer reviewe