atmospheric deposition: acidity and nutrients

Atmospheric Deposition: Acidity and Nutrients - Updated 3/2016

Environmental Trends Report, NJDEP, Division of Science, Research, and Environmental Health http://www.nj.gov/dep/dsr/trends/

reduc ons in nutrient levels as well as the release of aluminum, which can block nutrient uptake by vegeta on. Acid fogs and rains also have been found to leach calcium directly from spruce needles, damaging the trees. 8

Trends New Jersey has two sites that are part of the Na onal Atmospheric Deposi on Program/Na onal Trends Network (NADP/NTN), a na onwide network of precipita on monitoring sites, where acid precipita on and nutrients are measured. The network is a coopera ve effort between many different groups, including state agricultural experiment sta ons, U.S. Geological Survey, U.S. Department of Agriculture, and numerous other governmental and private en es, including DEP. The purpose of the network is to collect data on the chemistry of precipita on for monitoring of geographical and temporal long‐term trends. The precipita on at each sta on is collected weekly and then analyzed at a central laboratory. 9

Long me series of data on acidity and nutrients in precipita on in the vicinity of the New Jersey area are available for the NADP/NTN sites at Washington’s Crossing, NJ, the Edwin B. Forsythe Na onal Wildlife Refuge in Brigan ne, NJ, and Milford, PA (just west of northern NJ) (See the Figures 1‐3, below). In these charts, parameters that show sta s cally significant trends are indicated with linear fit lines.

Background Atmospheric deposi on refers to substances that are deposited on land or water surfaces from the air. These substances can be carried in precipita on, also called wet deposi on, or they can reach the earth’s surface via dry deposi on, which includes both the se ling out of par cles and the adsorp on by soil, trees, water or other surfaces of gaseous substances.

An important category of atmospheric deposi on is acidity. In precipita on, most acidity is contributed by sulfuric acid (H2SO4) and nitric acid (HNO3). Deposi on of associated nutrients, especially nitrate (NO3

‐) and sulfate (SO4‐ ‐), has important

impacts on the environment. Nitrate deposi on especially can cause eutrophica on of coastal and other water bodies and damage to terrestrial ecosystems. Terrestrial ecosystems encompass ground‐based ecosystems such as forests. Nitrate is harmful to terrestrial ecosystems because it can harm beneficial fungi1 and may encourage the growth of invasive species.2,3,4 Sulfate can combine with calcium and other nutrients necessary for plant growth, causing them to leach more quickly from the soil.

Sulfuric and nitric acids are present in unpolluted precipita on at low levels. Rainfall, unless buffered by ca ons in airborne par cles, tends to be naturally acidic, with a pH of about 5.6. However, in much of the eastern U.S., due to anthropogenic emissions of SO2 and NOx, the concentra ons of these acids in precipita on are so high that the pH of rain is o en in the 3.5 to 5.0 range.5 Most of the SO2 comes from coal‐burning power plants, whereas NOx comes from a variety of combus on sources including power plants, other industrial facili es, area sources (including commercial and residen al buildings) and motor vehicles.

Acid precipita on has damaged wildlife and ecosystems in many areas around the world. Regions where the soils and water bodies have limited buffering capacity, or the ability to neutralize the deposited acids, have been affected the most. The buffering capacity of most soils is sufficient to neutralize naturally occurring acids, but over me the capacity can be overwhelmed by high inputs of acid deposi on. A drama c effect of the acidifica on of some water bodies is loss of fish species, which has happened in areas such as the Adirondack region of New York State.6,7

Ecosystem effects of acid rain are widespread. Studies at Hubbard Brook Experimental Forest in New Hampshire have revealed that concentra ons of the nutrients calcium and magnesium (which neutralize acidity, but are leached from soils in the process) have been lowered and vegeta ve growth has slowed as a result of decades of acidic precipita on. Studies at other sites in the Northeast also show

Atmospheric Deposition: Acidity and Nutrients

Figure 1: Washington’s Crossing, NJ: pH & nutrients



For Washington’s Crossing, the data show a significant decline in deposi on of sulfate, a significant decline in deposi on of nitrate, and a significant increase in pH over me (Kendall Tau rank correla on coefficient p values < 0.001). Brigan ne and Milford show similar trends. At Brigan ne, the data show a significant decline in deposi on of sulfate (p value <0.001), a significant decline in deposi on of nitrate (p value = 0.026), and a significant increase in pH (p value <0.001). The data from Milford also show a significant decline in deposi on of sulfate, a significant decline in the deposi on of nitrate and a significant increase in pH (p values < 0.001). Despite this improvement, the average pH of precipita on in the region remains in the range of 4.85 to 5.0 which is more acidic than expected for unpolluted rain in the Northeast. There are no significant declines in the concentra on of the sum of calcium (Ca), magnesium (Mg), potassium (K), and sodium (Na) ions at any site during the periods sampled.

Figure 2: Brigan ne, NJ; pH & nutrients

Figure 3: Milford, PA; pH & nutrients

Photo Credit: h p://www.public‐domain‐image.com/free‐images/nature‐landscapes/sky/sky‐sunset‐and‐clouds



Reduc ons of sulfate in precipita on may be related to lower sulfate concentra ons observed in some surface waters. A good example is the Pequannock River, near West Milford, NJ. The Pequannock River, upstream of this loca on, is rela vely undisturbed with 92 percent of the land cover in the watershed as forests, wetlands, or water. Figure 4 shows a significant decline in sulfate concentra on over me in that river. The exact por on of the reduc on in sulfate due to reduced emissions of SO2 and NOx to the air and resul ng decreases in acidic deposi on cannot be determined as reduc ons in river concentra on may be related in part to changing agricultural prac ces or other watershed inputs.

Outlook & Implications Rules are in place at both the federal and state level to reduce emissions of SO2 and NOx from sources such as industrial facili es.10 Some of these rules have been in effect for more than two decades and have reduced U.S. emissions of SO2 by about 40 percent.11,12 Studies have shown a virtually universal reduc on in deposi on of sulfates because of a decrease in SO2 emissions, but there has not been a decrease in overall acidity in many regions.13 For the sites reported

Figure 4: Pequannock River Sulfate Concentra on

Photo Credit: h p://www.public‐domain‐image.com/free‐images/nature‐landscapes/wetlands‐and‐swamps/sun‐se ng‐behind‐trees‐in‐wetland‐with‐water‐plants

here, however, there have been significant declines in acidity (i.e., increases in pH). At Washington Crossing and Milford, pH has risen from approximately 4.3 in the early 1980s to greater than 5.0 in 2014. Brigan ne has shown a similar degree of improvement. Because pH is a logarithmic scale, these changes represent a reduc on of over 77 percent in the concentra on of hydrogen ions. Despite a general decline in acid deposi on in both Europe and North America, some areas show significant delay in aqua c recovery from acidifica on, and minimal biologi‐cal recovery in waters or soils.14 This delay probably is due to a deple on of neu‐tralizing substances in soils and water bodies due to years of impact from acidic deposi on. New, more stringent controls on NOx emissions recently have been implemented at the federal level and in New Jersey,15 and these reduc ons are expected to have a posi ve impact on acidic deposi on and nitrate deposi on. Whether these addi onal reduc ons will be sufficient to offset long‐term impacts on some ecosystems s ll is unclear. In some affected areas, it is es mated that an addi onal 80 percent reduc on in emissions of SO2 and NOx will be required to permit soils to regenerate the base ca on levels needed for healthy trees.16

More Information See the DEP Bureau of Air Monitoring Web site, h p://www.njaqinow.net/Default.aspx and the EPA acid rain program Web site, h p://www.epa.gov/airmarkets/progsregs/arp/index.html.

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References 1Dighton, J., Tuininga, A.R., Gray, Huskins, R.E. and T.J. Belton. 2004. Impacts of Atmospheric Deposi on on New Jersey Pine Barrens Forest Soils and Communi es of Ectomycorrihizae (Fungi), Journal of Forest Ecology and Management, 201, pp. 131‐144. 2Pelley, J. 1998. Is Coastal Eutrophica on Out of Control? Environmental Science and Technology, 462A‐466A. 3Seitzinger, Sybil, M. Mazurek, R. Styles, and R. Lauck. 2000. Atmospheric Deposi on of Nitrogen to Coastal Ecosystems, presenta on to NJDEP by Seitzinger, Sybil, et al., Ins tute of Marine & Coastal Sciences, Rutgers University. 4Castro, Mark and Charles Driscoll, 2002, Atmospheric nitrogen deposi on to estuaries in the Mid‐Atlan c and Northeastern U.S., Environmental Science and Technology 36:3242‐3249. 5The pH is the an log of the concentra on of hydrogen ions, H+, in moles per liter. Thus a sample with a pH of 5.0 has 1 x 10‐5 moles of H+ per liter. Rainfall, unless buffered by ca ons in airborne par cles, tends to be naturally acidic, with a pH of about 5.6. This is due to the presence in the air of carbon dioxide, which dissolves in water producing carbonic acid. 6Baker, J.P., et al. 1996. Episodic acidifica on of small streams in the Northeastern United States: effects on fish popula ons. Ecological Applica ons 6:422‐437. 7Baldigo, B. P., et al. 2007. Persistent mortality of brook trout in episodically acidified streams of the Southwestern Adirondack Mountains, New York. Transac ons of the American Fisheries Society, 136: 121‐134. 8Spiro & S gliani, 2003, p. 301. 9See the Na onal Atmospheric Deposi on Program web site at h p://nadp.sws.uiuc.edu/. 10For relevant NJ rules, see h p://www.state.nj.us/dep/aqm/rules.html#27. Also see the USEPA acid rain program web site at h p://www.epa.gov/airmarkets/arp/. 11Spiro & S gliani. 2003. p. 303. 12Rules are in place in Europe as well, although they are not based on a cap and trade program as in the U.S. The European rules have led to a similar, perhaps even rela vely larger, reduc on in emissions.

13Yoon, Carol K. 1999. Report on acid rain finds good news and bad news: sulfate levels drop, but acidity con nues, NY Times, October 7, 1999. 14Alewell, C., B. Manderscheid, H. Meesenburg, and J. Bi ersohl. 2000. Is acidifica on s ll an ecological threat? Nature 407:856‐857. 15Title IV of the Clean Air Act set a goal of reducing annual SO2 emissions by 10 million tons below 1980 levels. This was to be achieved in two phases. Emissions data indicate that 1995 SO2 emissions at regulated units na onwide were reduced by almost 40% below their required level. Phase II, which began in the year 2000, ghtened the annual emissions limits imposed on these large, higher emi ng plants and also set restric ons on smaller, cleaner plants fired by coal, oil, and gas, encompassing over 2,000 units in all. The Act also called for a 2 million ton reduc on in NOx emissions by the year 2000. A significant por on of this reduc on has been achieved by coal‐fired u lity boilers that will be required to install low NOx burner technologies and to meet new emissions standards. See the USEPA acid rain program web site at h p://www.epa.gov/airmarkets/arp/overview.html#phases and also the NJDEP Air Quality Permi ng Pro‐gram web site at h p://www.nj.gov/dep/aqpp/ 16Spiro & S gliani. 2003. p. 303.

Photo Credit: Terri Tucker, NJDEP, Division of Science, Research, and Environmental Health

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atmospheric deposition: acidity and nutrients

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