Diatom shifts in alpine lakes of the southern and central Rocky Mountains Jasmine E. Saros

University of Wisconsin-La Crosse

Collaborators

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 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 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 Lake Louise Wolfe et al. 2001 1970 1950 1900

Central Rockies-Beartooth Mountains 10 0 Beartooth Lake, W YOMING (~2590 m) Aulacoseira distans Small Fragilaria spp.

Fragilaria crotonensis Cyclotella bodanica var. lemanica 1989 1960 1905 20 30 40 0 20 20 40 relative frequencies 60 80 0 20 30 0 20 40 Saros et al. 2003

Central Rockies-Beartooth Mountains

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

% relative abundance

Colorado lakes

Relative frequencies (%)

Observations & experiments in Beartooth 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 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

Si P N

Design of resource bioassays

3 0 Level of limiting nutrient added (  M) Excess 5 10 25 150 N&P 0.05

0.10

0.25

5.0

Si&N 0.05

0.1

1.0

5.0

18 Si&P

0.8

0.6

F. crotonensis S. pinnata

0.4

T. glans

0.2

0.0

A. formosa

0 20 40 60 80 100 120 140 160

Silica (uM)

N P Si

Half-saturation constants for growth (



M)

S. pinnata F.crotonensis

A. formosa

0.003

(0.056) 0.0003

(0.005) 3.82

(1.09) 0.028

(0.063) 0.0008

(0.065) 0.78

(0.97) 0.041

(0.038) 0.0009

(0.003) 3.35

(3.38)

What are their distribution patterns in relation to 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 coefficient

Conductivity PAR C:P N:P Si:P

Fragilaria crotonensis

All lakes Beartooth 0.46

(0.0003) 0.37

(0.009) 0.078

(0.56) 0.0059

(0.97) 0.032

(0.81) 0.35

(0.10) 0.54

(0.007) 0.71

(0.0002) 0.56

(0.008) 0.71

(0.0002)

Asterionella formosa

All lakes Beartooth 0.20

(0.13) 0.24

(0.09) 0.44

(0.0005) 0.43

(0.001) 0.48

(0.0001) 0.31

(0.14) 0.44

(0.03) 0.44

(0.04) 0.51

(0.02) 0.41

(0.05)

How do these two species respond to 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

Initial nutrient conditions

Lake Beartooth Dissolved nut rients (  M) PO 4 NO 3 Si C:N C:P Seston ratios (  M) N:P Si:N Si:P 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

60 50 40 30 20 10 0 250 200 150 100 50 0

Fragilaria crotonensis

Control P N + P ANOVA p<0.0001

Tukey HSD control:N p=0.001

control:N+P p<0.0001

Control P

Asterionella formosa

N N N+P ANOVA p=0.001

Tukey HSD control:N p=0.039

control:N+P p=0.015

Experiment in Beauty Lake-2003 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

Summary

•

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 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

Acknowledgements

• 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

Overview

Speaker Bowman Allen Saros Indicator Alpine plant communities Exotic grasses in the desert Coastal sage communities Diatom communities in alpine lakes Critical N load (kg N/ha/yr) Individual plants: 4 Community: 10 Nitrate leaching: >20 5 60 1.5 (Baron 2006)