Ecological Perspectives on Critical Loads - Linkages between Emissions, Deposition and Biogeochemical Cycles J. N. Galloway Multi-Agency Critical Loads Workshop University of Virginia, May 2006

The sulfur story –Biogeochemical cycle –Emissions and deposition –Sulfur cascade The nitrogen story –Biogeochemical cycle –Emissions and deposition –Nitrogen cascade Future considerations Concluding thoughts Topics

Global Atmospheric S Budget, Tg S yr -1 5 Deposition 185 Fossil fuel smelters LandCoastOcean Natural Gases 10 Natural Particulate 20 Natural Gases 145 Natural Gases 25 Natural Particulate Globally and in the USA, most of gaseous sulfur emitted is anthropogenic Even with large scale reductions in SO 2 emissions, deposition will still be elevated over natural conditions--i.e., enhanced S deposition is here to stay. Mackenzie, 2003

USA SO 2 Emissions (million short tons/year) Natural emissions USA SO 2 emissions have dropped from peak of 32 tons in 1973, to 15 tons in The same as in This value is still 10 times greater than the natural rate. EPA, various sources

Wet Deposition: SO 4 = Decreases in SO 2 emissions have resulted in decreases in S deposition. Again, current deposition is substantially greater than the natural rate. NADP, 2006

Total S Deposition, (kg S ha -1 yr -1 ) Both wet and dry S deposition are important Large uncertainties in dry deposition. Natural background, 0.4 to 0.8 kg S ha -1 yr -1 EPA, NADP, CASTNeT

Atmosphere Terrestrial Ecosystems Aquatic Ecosystems Human Activities - increases acidity of surface waters - causes loss of alkalinity and biodiversity Energy Production - increases regional haze, changes radiation balance - increases atmospheric removal rates of numerous species SO x People, Industry The Sulfur Cascade - stores sulfate; delays surface water acidification - H + & Al n + acidify soil and decrease forest productivity - Ca + +, Mg + +, K + losses decrease forest productivity

The sulfur story –Biogeochemical cycle –Emissions and deposition –Sulfur cascade The nitrogen story –Biogeochemical cycle –Emissions and deposition –Nitrogen cascade Future considerations Concluding thoughts Topics

Grain Production Meat Production Energy Production Nitrogen Drivers in 1860 & 1995

Nitrogen Deposition Past and Present mg N/m 2 /yr Galloway and Cowling, 2002; Galloway et al., 2002b Next, the North American Nitrogen Budget

North American N Budget, mid 1990s (Tg N yr -1 ) N2N2 c-BNF, 6 fert.prod., 18 North America import, 5 fossil fuel, 7 BNF, Tg N was introduced into North America, mostly as new Nr Total Input ~48 Tg NO y

North American N Budget, mid 1990s (Tg N yr -1 ) N2N2 NO y NH x c-BNF, 6 fert.prod., 18 North America import, 5 fossil fuel, 7 BNF, Tg N was introduced into North America, mostly as new Nr 9 Tg N of NOx was emitted to atmosphere, 5 re-deposited to continent 4 Tg N of NH 3 was emitted to atmosphere, 3 re-deposited to continent Total Input ~48 Tg

North American N Budget, mid 1990s (Tg N yr -1 ) N2N2 NO y NH x c-BNF, 6 fert.prod., 18 North America import, 5 export, 8 river, 7 atm. trans., 4 atm. trans., 1 fossil fuel, 7 BNF, Tg N was introduced into North America, mostly as new Nr 9 Tg N of NOx was emitted to atmosphere, 4.7 redeposited to continent 4 Tg N of NH 3 was emitted to atmosphere, 3.0 redeposited to continent 20 Tg N in measured output; balance is either stored or denitrified. Total Input ~48 TgTotal Output ~20 Tg

USA NO x Emissions, (million short tons/year) Natural emissions USA NO x emissions have dropped from peak of 25 tons in 1993, to 21 tons in The same as in This value is still 10 times greater than the natural rate. EPA, various sources

NADP, Wet Deposition: NO What about that other N gas? NADP, 2006

USA NH 3 Emissions, (million short tons/year) USA NH 3 emissions are poorly known. These data show a drop from 5 tons to 4 tons from 1994 to EPA, various sources

NADP, Wet Deposition: NH Wet deposition data tell a different story. Let’s look at balance between wet and dry deposition for N species. NADP, 2006

Total N Deposition, (kg N ha -1 yr -1 ) Both wet and dry N deposition are important Large uncertainties in dry deposition. Cloud N, Organic N and NH 3 are missing! Natural background, 0.8 to 1.6 kg N ha -1 yr -1 EPA, NADP, CASTNeT

There are significant effects of Nr accumulation within the atmosphere, geosphere and biosphere Increases in: - tropospheric O 3, N 2 O & PM2.5 - soil acidity and N concentrations - coastal water N concentrations Decreases in: - stratospheric O 3 Lead to: - loss of biodiversity in terrestrial and aquatic ecosystems - human health effects - changes in earth’s radiation balance These effects can be sequential, such that a single atom of nitrogen could contribute to them all, over time and space.

Atmosphere But denitrification also produces N 2 O. Galloway et al., 2003

NH x Atmosphere Forests Head waters Coastal waters Nr Nitrogen Biogeochemical Interactions Atmosphere to Forests to Headwaters to Rivers to Coastal Waters NO y - increases forest productivity; sequesters C in biomass - H + & Al n + acidify soil and decrease forest productivity - increases tropospheric O 3 & GWP; decreases in stratospheric O 3 Rivers Nr Consequences - increases regional haze, changes radiation balance and impacts human health - increases in tropospheric O 3 & GWP; decreases in stratospheric O 3 - increases/decreases GWP and decreases forest productivity - increase in acidity of surface waters; loss of alkalinity and biodiversity - increase in tropospheric O 3 & GWP; decreases in stratospheric O 3 - increases in tropospheric O 3 & GWP; decreases in stratospheric O 3 - increase in HAB, loss of biodiversity, etc - increase in tropospheric O 3 & GWP; decreases in stratospheric O 3 Transfers Galloway et al., 2003

The sulfur story –Biogeochemical cycle –Emissions and deposition –Sulfur cascade The nitrogen story –Biogeochemical cycle –Emissions and deposition –Nitrogen cascade Future considerations Concluding thoughts Topics

Nitrogen Deposition Present and Future mg N/m 2 /yr Galloway et al., 2004 USA Relevance: New sources to west and south!

Nitrogen Deposition Present and Future mg N/m 2 /yr Galloway et al., 2004 USA Relevance: New sources to west and south!

Nr Creation Relative to NO x +NH 3 Atmospheric Emissions In 1860, 140 Tg N entered global terrestrial ecosystems; 20% was emitted to atmosphere. By 2050, almost 3 times as much N will be introduced, 50% of which will be emitted. The atmosphere is a growing transport medium for reactive nitrogen. In USA, changes in agricultural mix might increase NH 3 emissions. Galloway et al., 2004

SO 2 and NO x emissions have decreased –The former is at the 1905 level. –Both are still 10-fold greater than natural rates. –Bottom line--S and N deposition are still an issue in some regions of USA. S and N deposition is projected to increase over the next few decades –trans-boundary transport, SW and W Limits to knowledge –NH 3 emissions –Dry deposition rates –Fate of deposited N (stored or denitrified?) –Sequential impacts of N Concluding Thoughts