Diatom shifts in alpine lakes of the southern and Diatom shifts in alpine lakes of the southern and central Rocky Mountainscentral Rocky Mountains

Jasmine E. SarosJasmine E. SarosUniversity of Wisconsin-La CrosseUniversity of Wisconsin-La Crosse

CollaboratorsCollaborators

Alexander P. Wolfe, University of Alberta, Canada

Sebastian J. Interlandi, Drexel University

Tamara Blett, National Park Service

Jill Baron, Colorado State University

Craig Williamson, Miami University

Lisa Graumlich, Montana State University

Jeffrey Stone, University of Nebraska

Sensitivity of diatomsSensitivity of diatoms

• Often the first aquatic organisms to respond to environmental changes

• Change in species assemblages, chemical composition

• Changes are well-documented in response to nutrients, pH, climate

Beartooths

Front Range

Enhanced atmospheric N depositionEnhanced atmospheric N deposition

• Major effects of nitrogen deposition on aquatic systems:– Fertilization: adding biologically-available nitrogen – Acidification: one component of acid precipitation

• Alpine lakes may be more sensitive than temperate lakes to nitrogen deposition– The growth of algae in these lakes is often limited by nitrogen– These lakes have low buffering capacities

• Spatial variation in rate of nitrogen deposition across the Rockies

Southern Rockies-Colorado Front Range

19701950

1900

Lake Louise

Wolfe et al. 2001

Fragilariacrotonensis

Cyclotella bodanicavar. lemanica

Aulacoseiradistans

Small Fragilariaspp.

Beartooth Lake, WYOMING (~2590 m)

0

10

20

30

40

depth (cm)

20 80 30 40relative frequencies

198919601905

Central Rockies-Beartooth Mountains

0 40 6020 200 200

Saros et al. 2003

Emerald Lake, Wyoming (2970 m. a.s.l.)

% relative abundance

Central Rockies-Beartooth Mountains

Colorado lakesRelative frequencies (%)

Observations & experiments in Observations & experiments in Beartooth Mountain lakesBeartooth Mountain lakes

1) Resource physiology for N, P, and Si

2) Vertical profiling in multiple lakes

3) Nutrient enrichment experiments

What are the resource requirements of these What are the resource requirements of these two diatom taxa?two diatom taxa?

Resource physiology experiments

• Determined requirements for N,

P, and Si• Used lake water from

Beartooths with low initial nutrient concentrations

• Collected cells from lakes in the area

• Incubated in Beauty Lake

Design of resource bioassaysDesign of resource bioassays

Level of limiting nutrient added (M) Excess

Si 3 5 10 25 150 N&P

P 0 0.05 0.10 0.25 5.0 Si&N

N 0.05 0.1 1.0 5.0 18 Si&P

Silica (uM)

0 20 40 60 80 100 120 140 1600.0

0.2

0.4

0.6

0.8

(d

ay-1

)

F. crotonensis

S. pinnata

A. formosa

T. glans

Half-saturation constants for growth (Half-saturation constants for growth (M) M)

S. pinnata F.crotonensis A. formosa

N 0.003(0.056)

0.028(0.063)

0.041(0.038)

P 0.0003(0.005)

0.0008(0.065)

0.0009(0.003)

Si 3.82(1.09)

0.78(0.97)

3.35(3.38)

What are their distribution patterns in relation to What are their distribution patterns in relation to physicochemical parameters?physicochemical parameters?

Vertical profiles

• Sampled 7 lakes • Every 3 m:

– Temperature, pH, conductivity, PAR, SRP, nitrate, silica, seston ratios (C:N, C:P, N:P, Si:P, Si:N), chlorophyll

– Species composition

Spearman’s rank correlation coefficientSpearman’s rank correlation coefficient

Fragilaria crotonensis Asterionella formosa

All lakes Beartooth All lakes Beartooth

Conductivity 0.46(0.0003)

0.35(0.10)

0.20(0.13)

0.31(0.14)

PAR 0.37(0.009)

0.54(0.007)

0.24(0.09)

0.44(0.03)

C:P 0.078(0.56)

0.71(0.0002)

0.44(0.0005)

0.44(0.04)

N:P 0.0059(0.97)

0.56(0.008)

0.43(0.001)

0.51(0.02)

Si:P 0.032(0.81)

0.71(0.0002)

0.48(0.0001)

0.41(0.05)

How do these two species respond to How do these two species respond to

nutrient additions?nutrient additions?

Nutrient enrichment experiments

• Beartooth Lake- July 2002– Control, P, N, N+P

• Beauty Lake- July 2003– Control, high N:P, low N:P, high Si:P, low Si:P

• Lake water was filtered through 150 m mesh and incubated at 3 m

• When added: N=18 M, P=5 M, Si=100 M

Dissolved nutrients(M)

Se stonratios(M)

Lake PO4 NO3 Si C:N C:P N:P Si:N Si:P

Beartooth 0.04 1.34 36.0 9.9 197 19.9 0.88 17.5

Beauty <0.015 1.43 29.7 10.8 323 30.0

Initial nutrient conditionsInitial nutrient conditions

ANOVA p<0.0001

Tukey HSD

control:N p=0.001

control:N+P p<0.0001

ANOVA p=0.001

Tukey HSD

control:N p=0.039

control:N+P p=0.015

Fragilaria crotonensis

Control

N + P

N

P

0

50

100

150

200

250

Cells/ml

Asterionella formosa

Control

P

N N+P

0

10

20

30

40

50

60

Cells/ml

Asterionella formosa

control

high N:P

low N:P

high Si:Plow Si:P

0

5

10

15

20

25

30

35

40

45

ANOVA p<0.0001

Tukey HSD

control:high N:P p<0.0001

control:low N:P p=0.039

high to low N:P p=0.10

Experiment in Beauty Lake-2003

SummarySummary

• Both species of diatoms have moderate N and very low P requirements

• The recent increases in these two species across the western U.S. can be attributed to enhanced rates of N deposition

• Future work should include:– Sediment cores from additional areas that vary in rates of N

deposition– Culturing work to quantify the minimum N level at which

phytoplankton communities shift

Critical N load determination from diatomsCritical N load determination from diatoms

• Current work: development of a critical N load model based on existing diatom records plus those of additional parks:

• Sequoia • Glacier• Northern Cascades

• Baron (2006) used diatom records to test her model

• Determined a critical load of 1.5 kg N/ha/yr

• Funding:– National Science Foundation (DEB 0089600)– UW-L Faculty Research Grant– River Studies Center

• Students:– David Dean, Shaina Doyle, Lisa Poser, Rita Seston, Courtney

Smith, LeeAnne Thorson, Courtney Wigdahl, Kate Wroblewski

• Assistance in the field and lab:– Misa Saros, Barbara Interlandi

AcknowledgementsAcknowledgements

OverviewOverview

Speaker Indicator Critical N load

(kg N/ha/yr)

Bowman Alpine plant communities Individual plants: 4

Community: 10

Nitrate leaching: >20

Allen Exotic grasses in the desert

Coastal sage communities

5

60

Saros Diatom communities in alpine lakes

1.5 (Baron 2006)