Empirical and Simulated Critical Loads for N Deposition in ... · High leaching rates with...

Empirical and Simulated Critical Loads for N Deposition in California Mixed Conifer

Forests

Mark FennMark Fenn

USDA Forest Service, Pacific Southwest Research USDA Forest Service, Pacific Southwest Research Station, Riverside, CaliforniaStation, Riverside, California

Collaborators: Linda Geiser, Sarah Jovan, Fengming Collaborators: Linda Geiser, Sarah Jovan, Fengming Yuan, Tom Meixner, Benjamin GimenoYuan, Tom Meixner, Benjamin Gimeno

Study Sites in California, USA

Mixed Conifer Forest: Summer-Dry Mediterranean Climate

CL Methods and Approaches Used

�� Empirical: Epiphytic lichen indicator groups; lichen Empirical: Epiphytic lichen indicator groups; lichen chemistry; NOchemistry; NO33 leaching; PP fine root biomassleaching; PP fine root biomass

�� Simulated: DayCent biogeochemical model; NOSimulated: DayCent biogeochemical model; NO33leaching and trace gas emissions from soilleaching and trace gas emissions from soil

�� Critical values indicative of CL exceedance: Litter Critical values indicative of CL exceedance: Litter C:N; foliar N; N concentration in the lichen C:N; foliar N; N concentration in the lichen Letharia Letharia vulpinavulpina

Ion Exchange Resin Throughfall Collector

Fenn & Poth, 2004JEQ 33:2007-2014

Letharia vulpina; wolf lichen;In the Sierra Nevada of California concentrations of N in L. vulpina arecorrelated with N deposition and adverse changes in lichen communitycomposition.

Lichen-Based CL

0.00.2

0.4

0.6

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1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

2.6

2.8

% N

itrog

en in

Let

haria

vul

pina

25 50 75 100Count

Clean Site Threshold Determination for N concentrations in Letharia vulpina

Based on data from 535 samples at urban, rural and remote sites east of the Cascade Crest in Oregon and Washington states. 1.0% N was selected as the upper limit for the expected background range.

Throughfall N vs. N in L. vulpina

Threshold N concentration = 1.0% N in L. vulpina; Corresponds with a CL of 3.1 kg N ha-1 yr-1 in theSierra Nevada Mountains of California.

Lichen Indicator Groups

�� Acidophytes:Acidophytes: sensitive to even small increases in N; will disappear under continued N loading.

�� Neutrophytes:Neutrophytes: are either tolerant to or enhanced by N deposition, but do not become ‘weedy’.

�� Nitrophytes:Nitrophytes: fast growing species associated with NH3deposition and substrates with relatively high pH such as many hardwoods.

CL for lichen indicator groups: Acidophyte abundance (A & D) and acidophyte dominance (C); Acidophyte dominance shifts to neutrophyte dominance at 5.2 kg N ha-1 yr-1 (C).Neutrophyte abundance (B);

Ecological Importance of AcidophytesEcological Importance of Acidophytes

� Acidophyte dominance is the natural state in these forests

� Healthy acidophyte populations are an integral part of food webs; used as nesting material and habitat for insects, mollusks, birds and animals in the Sierra Nevada

� Reduced abundance of acidophytes has direct ecological consequences Bryoria fremontii, known as the bearded

lichen; an example of an acidophyte.Serves as forage for many species (e.g.,squirrels, deer and a variety ofinvertebrates).

Platismatia glauca: A common acidophyte

Lichen Based Critical Loads: Lichen Based Critical Loads: SummarySummary

� Enhanced N in L. vulpina: 3.1 kg ha-1 yr-1

� Our data suggest that acidophyte depression begins at even lower levels (< 2 kg ha-1 yr-1)

� Relative abundance of acidophytes decreased by 50% at 4.1 kg ha-1 yr-1

� Acidophyte dominance shift to neutrophyte dominance at 5.2 kg ha-1 yr-1

� Complete extirpation of acidophytes at 10.2 kg ha-1 yr-1

� Lichens can be used as early warning indicators of other possible biological effects from N deposition

Nitrate Leaching or Runoff: Cardinal Indicator of N Saturation or N Excess

Nitrogen Deposition Elevated NO3 in surface runoff and in groundwater

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1

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14

SGW6SGW7SGW8SGW9SGW10SGW11SGW12

SGW Northern Sites

Pre

cipi

tatio

n (m

m)

020406080

100120

Pre

cipi

tatio

n (m

m)

020406080

100120

0

50

100

150

360

380

SGW1SGW2SGW3SGW4SGW5

SGW Southern Sites

Nitr

ate

Con

cent

ratio

n ( µµ µµ

mol

L-1

)N

itrat

e C

once

ntra

tion

( µµ µµm

ol L

-1)

If peak NO3 concentrationsare regularly > 14.5 µM or0.2 mg L-1 the CL has beenexceeded by definition.

Critical Value for Peak Runoff NO3 Concentration Used for Estimating the Empirical CL:

Empirical Throughfall CL for Mixed Conifer Forests: 17 kg N ha-1 yr-1

(Based on UNECE acceptable leaching value of 0.2 mg L-1 or 14.3 µeq L-1)

y = 8.69 + 0.58x r2= 0.98

Streamwater Nitrate (ueq/L)

0 10 20 30 40 50 60 70 80 90 100 110

Thro

ughf

all N

Dep

ositi

on (k

g/ha

/yr)

0

10

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70

CL for stream NO3 of 10 µeq/L = 14.5 kg N ha-1 yr-1

Empirical Bulk Deposition CL for Mixed Conifer Forests: 4.7 kg N ha-1 yr-1

0 10 20 30 40 50 60 70 80 90 100 110

Bul

k N

Dep

ositi

on (k

g ha

-1 y

r-1)

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5

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8

9

Streamwater Nitrate (ueq/L)

y = 4.65 + 0.04x r2= 0.81

CL for stream NO3 of 10 µeq/L = 4.7 kg N ha-1 yr-1

Throughfall N Deposition in the San Bernardino Mountains

White bars represent the CL (14.5 kg N ha-1 yr-1) for acceptable NO3 in runoff (10 µeq L-1)

Preliminary evidence for a biological effect of N deposition in ponderosa pine: Fine root biomass

Throughfall N deposition

0 10 20 30 40 50 60 70 80

Fine

Roo

t Bio

mas

s ( P

. pon

dero

sa)

-0.2

0.0

0.2

0.4

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0.8

1.0

g of fine roots in top 20 cm of 20 x 20 cm soil pits(Grulke et al., 1998; Env. Poll. 103:63-73)

An estimated 26% reduction in fine root biomass at N deposition of 17 kg ha-1 yr-1.

Litter C:N

24 26 28 30 32 34 36 38 40

Nitr

ogen

Dep

ositi

on (k

g/ha

/yr)

0

10

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30

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60

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80

y = 148.08 - 3.81x r2 = 0.79

Litter C:N vs. N deposition. Critical value of 34.1 associated with CL for elevated NO3 leaching.

Daycent simulated peak NO3 concentrations in seepagewater with increasing N deposition. Simulated CL

similar to empirical CL in western SBM.

0 10 20 30 40 50 60 70 800

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3

Yea

rly

peak

N c

once

ntra

tion

in s

trea

m fl

ows

(mgN

L -1

)

0.20 mgN L -1

Year 90 ~ 120Year 60 ~ 90Year 30 ~ 60Year <30

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3

0.20 mgN L -1


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N deposition rates (kg N ha-1 yr-1)

0.20 mgN L -1


(b) BF (normal)

(c) CP (under reduced PPT)

(d) BF (under increased PPT)

(a) CP (normal)

Fig. 6

1900 1920 1940 1960 1980 2000 2020 20400

1

2

3

4

Year

Yea

rly p

eak

N c

once

ntra

tion

in s

tream

flo

ws

(mgN

L

-1)

1900 1920 1940 1960 1980 2000 2020 20400

0.2

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1

Ndep starting year

0.20 mgN L-1

normal precipitation

reduced precipitation

Ndep starting year

0.20 mgN L-1



1900 1920 1940 1960 1980 2000 2020 20400

0.2

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0.6

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1

Ndep starting year

0.20 mgN L-1


increased precipitation

1900 1920 1940 1960 1980 2000 2020 20400

0.2

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0.6

0.8

1

Year

Ndep starting year

0.20 mgN L-1



(a) Empirical CL (a) Empirical CL (a) Empirical CL (a) Empirical CL (CP) (CP) (CP) (CP)

(c) Empirical CL (c) Empirical CL (c) Empirical CL (c) Empirical CL (BF) (BF) (BF) (BF)

(b) Historical N deposition scenario(b) Historical N deposition scenario(b) Historical N deposition scenario(b) Historical N deposition scenario (CP) (CP) (CP) (CP)

(d) Historical N deposition scenario(d) Historical N deposition scenario(d) Historical N deposition scenario(d) Historical N deposition scenario (BF) (BF) (BF) (BF)

Daycent simulated peak NO3 concentrations in seepage water.First exceedance in 1956 under historical deposition scenario.

Daycent simulated annual NO3 export in seepage water. Highleaching rates with historical deposition began after 1960.

1900 1920 1940 1960 1980 2000 2020 20400

0.5

1.0

1.5

2.0

2.5

3.0

Ann

ual N

stre

am fl

ow (k

gN h

a -1

yr -

1 )

Ndep starting year



1900 1920 1940 1960 1980 2000 2020 20400

5

10

15

20

Year

Ndep starting year

normal precipitationreduced precipitation

1900 1920 1940 1960 1980 2000 2020 20400

0.5

1.0

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2.0

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3.0

Ndep starting year



1900 1920 1940 1960 1980 2000 2020 20400

0.5

1.0

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3.0

Year

Ndep starting year







Bark beetle injury in Ponderosa pine: Dendroctonusbrevicomis

Ideally, critical loads should include pests and multiple stress effects.

Bark Beetle Mortality in 2003 in Ponderosa Pine in the San Bernardino

Mountains

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5

10

15

20

0 50 150

BFCP

Nitrogen Additions (kg ha-1 yr-1)

Mor

talit

y %

Eatough Jones et al. 2004;For. Ecol. Mgt. 200:67-76

Forest stand with high mortality in the San Bernardino Mountains

Biodiversity; InvasiveSpecies

Camp Paivika

2003

2006 post-fire

Deep litter, dominance ofGalium aparine

Breezy Pointexotic annual grass, bracken fern

Galium aparine withnative forbs

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Summary

� Empirical and simulated CL were similar for NO3 leaching (17 kg ha-1 yr-1)

� CL ranged from < 3 to 17 kg ha-1 yr-1

� Lichen CL ranged from <3 to 10.2 kg ha-1 yr-1

� Critical value for litter C:N was 34.1, higher than for mesic temperate forests (typically C:N of 25)

� Preliminary data suggests that fine root biomass is highly sensitive to N and may be suitable for CL setting

� Nitrogen also affecting forest susceptibility to insect pests, exotic invasions and biodiversity; but insufficient data to set a CL for these effects

� Future work looking at effects of ozone, fire, Mediterranean characteristics, and management practices on CL

Simple Mass Balance Estimates of N as a Nutrient CL for the San Bernardino Mountains

4.84.80.30.3Acceptable N Acceptable N leaching (leaching (NNle(accle(acc))))

8.88.81.41.4CLCLnutnut(N(N))

0.10.10.10.1Denitrification (Denitrification (ffdede))

3.53.51.01.0N immobilization (NN immobilization (Nii))

RevisedRevisedMapping Mapping ManualManual

ParameterParameter

Loss Rate (kg haLoss Rate (kg ha--11 yryr--11))

From: Breiner, Gimeno & Fenn, 2007

The Principal Factors Affecting Forest Sustainability in the San Bernardino Mountains

�� Summer drought; more particularly successive years of severe Summer drought; more particularly successive years of severe droughtdrought

�� Ozone injuryOzone injury�� Chronic N deposition Chronic N deposition �� Stand densification y fuel accumulation, exacerbated by long terStand densification y fuel accumulation, exacerbated by long term m

fire suppression and N depositionfire suppression and N deposition�� Insect outbreaksInsect outbreaks�� Mortality caused by the above multiple stress factorsMortality caused by the above multiple stress factors�� Severe stand replacement firesSevere stand replacement fires�� Soil acidification: unknown effects on forest health as base satSoil acidification: unknown effects on forest health as base saturation uration

is still relatively high compared to more heavily leached soilsis still relatively high compared to more heavily leached soils�� Climate change?Climate change?

In N saturated chaparral catchments fire was not sufficient to return the system to a conservative state of N cycling:

“We drink what we “We drink what we drive.” (Mark Poth)drive.” (Mark Poth)

Barton Flats with Incense cedar encroachment, highest understory richness

Changes in understory species richness, 1973 to 2003, at selected locations across an atmospheric pollution gradient, highest rates of deposition to lowest, in the San Bernardino National Forest, CA.

Location % of plant species number of species % changesame 2003* 1973* 2003 1973

Camp Paivika 53 10 37 19 27 -30

Breezy Point 36 14 50 21 36 -42

Dogwood 49 16 35 33 43 -23

Tunnel Two 42 18 40 27 37 -27

Camp Angeles 40 20 40 21 28 -33

Barton Flats 35 29 26 46 38 21

*Percent present only in 2003 or only in 1973

Simulated N Deposition in S. Cal. (from Gail Tonnesen, Center for Environmental Research and Technology, UCR)

4 km zoom in LA, Orange and western Riverside counties (s. California)

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Figure 8

1900 1920 1940 1960 1980 2000 2020 20400

2

4

6

8

10

Ann

ual N

gas

eous

em

issi

on (k

gN h

a -1

yr -

1 )

Ndep starting year


1900 1920 1940 1960 1980 2000 2020 20400

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20

30

40

Year

Ndep starting year


1900 1920 1940 1960 1980 2000 2020 20400

2

4

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8

10

Ndep starting year



1900 1920 1940 1960 1980 2000 2020 20400

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10

Year

Ndep starting year







Figure 10

0 10 20 30 40 50 60 70 800

1

2

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5

Ann

ual N

loss

es in

str

eam

flow

s (k

gN h

a -1

yr -

1 )

Year 90 ~ 120

Year 60 ~ 90Year 30 ~ 60

Year <30

0 10 20 30 40 50 60 70 800

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10

15

Year 90 ~ 120

Year 60 ~ 90

Year 30 ~ 60

Year <30

0 10 20 30 40 50 60 70 800

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Year 90 ~ 120

Year 60 ~ 90

Year 30 ~ 60

Year <30

0 10 20 30 40 50 60 70 800

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10

15


Year 90 ~ 120

Year 60 ~ 90

Year 30 ~ 60

Year < 30

(a) CP (mean)

(b) BF (mean)

(c) CP (maximum)

(d) BF (maximum)

Figure 11

0 10 20 30 40 50 60 70 800

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Ann

ual N

gas

eous

em

issi

on (

kgN

ha

-1 y

r -1 )


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Year 90 ~ 120Year 60 ~ 90Year 30 ~ 60Year < 30

(a) CP (mean)

(b) BF (mean)

(c) CP (maximum)

(d) BF (maximum)

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