National Atmospheric Deposition Program 2006 Annual Summary

published or submitted for publicationis peer reviewe

Nitrogen in the Nation's Rain

Ope

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

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

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

Estimation of the atmospheric flux of nutrients and trace metals to the Eastern Tropical North Atlantic Ocean

Atmospheric deposition contributes potentially significant amounts of the nutrients iron, nitrogen and phosphorus (via mineral dust and anthropogenic aerosols) to the oligotrophic tropical North Atlantic Ocean. Transport pathways, deposition processes and source strengths contributing to this atmospheric flux are all highly variable in space and time. Atmospheric sampling was conducted during 28 research cruises through the Eastern Tropical North Atlantic (ETNA) over a 12 year period and a substantial dataset of measured concentrations of nutrients and trace metals in aerosol and rainfall over the region was acquired. This database was used to quantify (on a spatial- and seasonal-basis) the atmospheric input of ammonium, nitrate, soluble phosphorus and soluble and total iron, aluminium and manganese to the ETNA. The magnitude of atmospheric input varies strongly across the region, with high rainfall rates associated with the Inter-tropical Convergence Zone contributing to high wet deposition fluxes in the south, particularly for soluble species. Dry deposition fluxes of species associated with mineral dust exhibited strong seasonality, with highest fluxes associated with winter-time low-level transport of Saharan dust. Overall (wet plus dry) atmospheric inputs of soluble and total trace metals were used to estimate their soluble fractions. These also varied with season and were generally lower in the dry north than in the wet south. The ratio of ammonium plus nitrate to soluble iron in deposition to the ETNA was lower than the N:Fe requirement for algal growth in all cases, indicating the importance of the atmosphere as a source of excess iron

An overview of atmospheric deposition chemistry over the Alps: present status and long-term trends

Several research programs monitoring atmospheric deposition have been launched in the Alpine countries in the last few decades. This paper uses data from previous and ongoing projects to: (i) investigate geographical variability in wet deposition chemistry over the Alps; (ii) assess temporal trends of the major chemical variables in response to changes in the atmospheric emission of pollutants; (iii) discuss the potential relationship between the status of atmospheric deposition and its effects on forest ecosystems in the alpine and subalpine area, focusing particularly on nitrogen input. We also present results of studies performed at a local level on specific topics such as long-term changes in lead deposition and the role of occult deposition in total nitrogen input. The analysis performed here highlights the marked geographical variability of atmospheric deposition in the Alpine region. Apart from some evidence of geographically limited effects, due to local sources, no obvious gradients were identified in the major ion deposition. The highest ionic loads were recorded in areas in the foothills of the Alps, such as the pre-alpine area in North-Western Italy and the area of Canton Ticino, Switzerland. Trend analysis shows a widespread decrease in the acidity of precipitation in the last 15–20 years as a consequence of the reduced emission of S compounds. On the other hand, nitrate concentrations in rain have not changed so much, and ammonium has decreased significantly only at the Austrian sampling sites. The deposition of N is still well above the estimated critical loads of nutrient N at some forest sites in the alpine and subalpine areas, thus confirming the critical situation of both terrestrial and aquatic ecosystems regarding N inputs. Existing data highlights the importance of continuously monitoring atmospheric deposition chemistry in the Alpine area, taking account of acidifying elements, nutrients and other pollutants such as heavy metals and organic compounds. There is also a need for unifying sampling and analytical methods in order to obtain comparable data from the different regions of the Alps