Consequences of Nitrogen Deposition to Rocky Mountain National Park Jill S. Baron, US Geological Survey M.Hartman, D.S.Ojima, K. Nydick, H.M. Rueth B.Moraska Lafrancois, A.P. Wolfe, J. Botte, W.D. Bowman
Life is Short Have Conclusions First! Nitrogen deposition is higher on the EAST side of Rocky Mountain National Park On the east side of the Front Range we have observed: Changes in alpine tundra vegetation Increased uptake of N by trees Faster rates of soil nitrogen cycling High year-round lake and stream N concentrations Large changes in algal composition, beginning ca. 50 years ago
Context: why care about nitrogen? Long-term research in and around Rocky Mountain National Park: how we know what we know The cascade of nitrogen deposition effects Research results
Why care about nitrogen? Nitrogen is necessary for life Most N on Earth is in a form unusable by living organisms The Green Revolution occurred largely due to synthetic N fertilizers Humans depend on fossil fuels for transportation and energy Thus, to sustain human life, we convert unusable N to reactive forms.
Nitrogen in the environment All of the reactive N created by fossil fuel combustion enters the environment. Ammonia from agriculture, especially animal feedlots, enters the environment Nitrogen is accumulating in the environment
NO 3 NH 4 NO x NO NO 2 NH 3 NOx NH 3
More nitrogen is now fixed by human activities than by natural processes Vitousek et al.
Nitrogen accumulation contributes to: Acid deposition Coastal dead zones Lake and river eutrophication Unnatural rates of forest growth Loss of biodiversity Smog Greenhouse effect Stratospheric ozone depletion
In the West, Ecological Effects are Found Adjacent to Urban and Agricultural Areas Altered plant communities (plants, lichens, fungi) Increased Invasive Species and Altered Fire Regime High N waters Fenn et al. 2003
Colorado population and emissions trends Colorado Population 5,000,000 4,500,000 NOx emissions, CO and West/10 4,000,000 3,500,000 3,000,000 2,500,000 2,000,000 1,500,000 short tons Thousands 500 400 300 200 1,000,000 500,000 0 100 0 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 1900 1907 1914 1921 1928 1935 1942 1949 1956 1963 1970 1977 1984 1990 1997 US Census Bureau US EPA 450 400 350 300 250 200 150 100 50 0 CO population vs emissions y = 1E-04x - 36.305 R 2 = 0.9081 0 1,000,000 2,000,000 3,000,000 4,000,000 5,000,000 Nitrogen oxide emissions are very tightly related to population.
The Continental Divide separates airsheds in Rocky Mountain National Park Spring/summer upslope winds move Front Range air to mountains
Context: why care about nitrogen? Long-term research: how we know what we know The cascade of nitrogen deposition effects Research results
Foundations 23+ years of long-term monitoring in Loch Vale Watershed Experiments in field and lab to test cause and effect Modeling of ecosystem processes and what-if scenarios Spatial comparisons in Colorado and across western US
Long-term Program Objectives To understand and differentiate natural processes from unnatural, human-caused drivers of change To understand and quantify the effects of atmospheric deposition on high elevation ecosystems To share knowledge with managers so they are better informed
Our equipment is sturdy and Park Service Brown Rain Gages NADP Buckets Stream Gage Soil Lysimeter
Loch Vale Research has been widely reviewed and published 78 Journal Papers 26 Graduate Degrees 1 Loch Vale Book 1 Special Journal Section 9 Methods and QA Reports 154 Total Publications
Context: why care about nitrogen? Long-term research: how we know what we know The cascade of nitrogen deposition effects Research results
Pathways and Effects of Excess Nitrogen Deposition N Deposition Changes in Plant Communities Fertilization N Saturation Loss of Soil Buffering Lake Eutrophication Changes in Aquatic Species Loss of Lake ANC (acidification)
Context: why care about nitrogen? Long-term research: how we know what we know The cascade of nitrogen deposition effects Research results
In the alpine nitrogen favors sedges and grasses over flowering plants Niwot Ridge research shows sedges and grasses grow better with N than flowering plants in both experiments and surveys (Korb and Ranker 2001; Bowman et al. in review)
East-side forests are closer to N saturation Six pairs of sites were similar in all characteristics except for N deposition amount East side stands differed significantly from west side forests: - higher needle and soil N, - lower C:N ratios, - higher soil N cycling rates
Experimental Fertilization of Small Forest Plots Effects - nitrate leached from soils => symptom of saturation - base cations leached from soils => depletes soil buffering capacity and fertility Rueth et al. 2001, Geick et al. in prep
As soils accumulate N, microbial activity increases Mineralization Rate (ug N/g/d) 6 5 R 2 =0.62 LV-E ML-E 4 MP-E 3 ER-E LL-E 2 BP-E 1 BR-W BC-W WR-W GF-W FC-W WA-W 0 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 Organic Soil %N 1.6 Colorado Front Range Baron et al. 2000 Rueth & Baron 2001 Similar patterns in New England, USA McNulty et al. 1991 Nitrification ugn/g/d 1.2 0.8 0.4 0 1 1.5 2 2.5 %N Forest Floor
East-side lakes have higher N concentrations Means (ueq/l) East 10.5 (5.0) West 6.6 (4.3) n=44, p = 0.02 Baron et al. 2000
Lake Sediments serve as Proxies for Past Environmental Change Wolfe et al., 2001, 2003, Baron et al. 1986
Diatoms are good indicators of environmental change Diatoms are algae: single-celled aquatic plants Species are very sensitive to water chemistry Glass (silica) cell walls do not decompose Each species has unique cell walls
Diatom Indicators of Disturbance Increased Abruptly in east-side lakes ca. 1950-1960 1950 Sky Pond Asterionella formosa Fragillaria crotonensis Aulacoseira spp.
Lakes Have Changed More Since 1950 than Previous 14,000 Yrs The rate of change in diatoms post- 1950 is an order of magnitude greater than any change since Pleistocene. The abundance of diatoms is 8-25x greater post-1950. Caused by dominance of 2 disturbance species: Asterionella formosa and Fragilaria crotonensis. >40% of total diatoms since 1950 A. formosa and F. crotonensis are indicators of nutrient-rich waters
Experiments with Bioassays (Bottles), Mesocosms (Hula Hoops), and Lakes Lafrancois et al. 2003, 2004, Nydick et al. 2003, 2004a, b
Experiments: Productivity increased with added N and N+P. Communities changed to nutrient-loving algae. Green Algae Chlamydomonas sp. Chrysophytes Dinobryon sp. N Additions = Eutrophication increased productivity changed algal community
Summary of Research Results N Deposition Changes in Plant Communities Fertilization N Saturation Loss of Soil Buffering Lake Eutrophication Changes in Aquatic Species Loss of Lake ANC (acidification)
Phew! We made it! Conclusions Nitrogen deposition is higher on the EAST side of Rocky Mountain National Park On the east side of the Front Range we have observed: Changes in alpine tundra vegetation Increased uptake of N by trees Faster rates of soil nitrogen cycling High year-round lake and stream N concentrations Large changes in algal composition, beginning ca. 50 years ago Acidification has not yet occurred
http://www.nrel.colostate.edu/projects/lvws/
Human Dominance of Earth System 100 80 Percent change 60 40 20 0 Land Water Plant Marine Transformation Use Invasion Fisheries CO 2 Nitrogen Bird Concentration Fixation Extinction Vitousek et al. 1997