consequences of nitrogen deposition to rocky mountain

Consequences ofNitrogen 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

NO3 NH4 NOx

NO NO2 NH3 NOx

NH3

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

High N waters

Altered plant communities

(plants, lichens,fungi)

In the West, Ecological Effects are Found Adjacent to Urban and Agricultural Areas

Fenn et al. 2003

Increased InvasiveSpecies and Altered Fire

Regime

Colorado population and emissions trendsColorado Population

0500,000

1,000,000

1,500,0002,000,0002,500,0003,000,0003,500,000

4,000,0004,500,0005,000,000

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

US Census Bureau

NOx emissions, CO and West/10

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1900

1907

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Thou

sand

s

shor

t ton

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US EPA

CO population vs emissions

y = 1E-04x - 36.305R2 = 0.9081

050

100150200250300350400450

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 separatesairsheds 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 GageSoil 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

FertilizationLoss of Soil

Buffering

Changes in Aquatic Species

LakeEutrophication

Loss of Lake ANC(acidification)

N SaturationChanges inPlant Communities

• 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 researchshows 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 significantlyfrom 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

0

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Min

eral

izat

ion

Rat

e (u

g N

/g/d

)

0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6Organic Soil %N

FC-WBR-W

BC-W WR-W

WA-W

LL-E

BP-E

MP-E

ER-E

GF-W

LV-EML-E

R2=0.62

As soils accumulate N, microbial activity increases

0

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%N Forest Floor

Nitr

ifica

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ugN

/g/dColorado Front Range

Baron et al. 2000Rueth & Baron 2001 Similar patterns in

New England, USAMcNulty et al. 1991

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 IncreasedAbruptly in east-side lakes ca. 1950-1960

Sky Pond

1950

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 disturbancespecies: Asterionella formosa and Fragilaria crotonensis. >40% of total diatoms since 1950

A. formosa and F. crotonensisare 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.

Chrysophytes

Green Algae

N Additions = Eutrophication

increased productivitychanged algal community

Dinobryon sp.

Chlamydomonas sp.

Summary of Research Results

N Deposition

FertilizationLoss of Soil

Buffering

Changes in Aquatic Species

LakeEutrophication

Loss of Lake ANC(acidification)

N SaturationChanges inPlant Communities

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

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Perc

ent c

hang

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LandTransformation

CO2Concentration

WaterUse Nitrogen

Fixation

Plant Invasion

Bird Extinction

MarineFisheries

Vitousek et al. 1997