NUTRIENTS, TROPHIC STATE, AND

ECOSYSTEM HEALTH:

perspectives from ecosystem ecology

Michelle Baker

Organisms are part of a physical, chemical and biological system inwhich energy flow andmaterial cycles are important functions.

Chapin et al. 2004

APPROACHES IN ECOSYSTEM ECOLOGY

Observations

N2O

(µg

l-1)

0

600

1200

0 1530 60 90 120

Time (min)

0.14 µg N l-1 s-1

Baker and Jeffs published in Hall et al. 2009, L+O

APPROACHES IN ECOSYSTEM ECOLOGY

Experiments

Hochhalter et al. in prep, Ecol. Mon.

APPROACHES IN ECOSYSTEM ECOLOGY

Models

DIN

sequestrationas PON

algal uptake

PON burial

DIN

denitrification

N fixation

DINDONPON

Littoraluptake

DONPON

regeneration

GW inputs

GW inputs

Long nutrient spiralsShort nutrient spirals

INFLOW LAKE OUTFLOW

DIN plungetemperature dependent

PON, DON

NUTRIENTS: THE UNDERBELLY OF GLOBAL CHANGE

Nir Elias/Reuters

Work in the Baker lab focuseson nutrient cycling processesin streams and rivers.

These processes affect water quality for use by humansand other organisms.

Bioavailable nutrients are increasing globally, threatening water quality and the life that depends on it.

• Nutrients required for all life

• Reactive nutrients increasing globally

• Cycling is complex; impairment can occur below toxic levels

• Sources (and thus management options) extend beyond watershed boundaries

• Opportunities to foster interdisciplinary research – we measure attributes of stream health!

NUTRIENTS: THE UNDERBELLY OF GLOBAL CHANGE

Chemical elements/compounds needed by organisms to survive, grow, and reproduce.

Nitrogen• 1-5% dry weight

• found in proteins

• nitrate (NO3-)

• ammonium (NH4

+)

• natural fixation

• decomposition

Phosphorus• 0.1-1% dry weight

• found in lipids, DNA

• phosphate (PO4

3-)

• mineral weathering

• decomposition

Carbon• 25-40% dry weight

• found in everything

• natural fixation

• decomposition

Measured ratio of C:N:P can indicate physiological needs

WHAT ARE NUTRIENTS?

AtmosphereLithosphereSoilsOcean (dissolved)Terrestrial biomassOcean biomass

79.6%20.4%0.006%0.002%0.00007%0.00001%

0.000005%7.3%61.1%30.5%0.032%0.99%

Key point: Most are NOT biologically available

data from Schlesinger 1997

Nitrogen Phosphorus

WHERE ARE MOST OF THE NUTRIENTS?

Nitrogen : natural fixation, lightening, decomposition,

combustion, Haber-Bosch, legume crops

Phosphorus: chemical weathering, decomposition, mining

HOW DO NUTRIENTS BECOME BIOLOGICALLY AVAILABLE?

Human activity has morethan doubled the amountof “reactive” nitrogencycling globally.

• Haber-Bosch process• N-fixing crops• N oxide formation from combustion

HUMANS INCREASE NUTRIENT AVAILABILITY

Falkowski et al. 2000 Nature

Human activity has quadrupled the amount of “reactive” phosphoruscycling globally.

Phosphate mining production

HUMANS INCREASE NUTRIENT AVAILABILITY

Nationally N or P enrichment occurs in ca. 1/3 of stream miles (over 200,000 miles of wadeable streams have too much N and/or P).

EPA, 2006 Wadeable Streams Assessment

NUTRIENTS: THE UNDERBELLY OF GLOBAL CHANGE

AquaticLife

DO

pH

Habitat

Food

Plant/Algal Growth

MicrobialGrowth

Nutrients

LightFlow

Temperature Substrate

Water ChemistryHerbivory

Competition

Recreation

PathogensDrinking

Credit: Mike Paul, Tetra Tech

Linkages among nutrients, biota, and designated uses

Trophic State

OH WHAT A TANGLED WEB…

TROPHIC STATE

Associated Press (2008)

Autotroph (self-feeder)

Heterotroph (other-feeder)

TROPHIC STATE

Wayne Wurtsbaugh 2000

Oligotrophic

Eutrophic

• Trophic state often characterized by chlorophyll; but production depends on biomass AND activity.

• Heterotrophic state not often considered. Driven by organic matter supply.

• Both autotrophic and heterotrophic states affected by temperature AND nutrients.

TROPHIC STATE IN STREAMS

Nutrients (N,P)

Light

Removal (grazing/floods)

Biomass specificrates

Biomass(chlorophyll)

Ecosystem primaryproduction rate

Nutrients (N,P)

Removal (grazing/floods)

Organic matter

Biomass specificrates

Biomass(all organisms)

Ecosystem respirationrate

from Dodds 2007 TREE

Autotrophic State

Heterotrophic State

TROPHIC STATE IN STREAMS

THINGS WE MEASURE THAT ARE INDICATORS OF STREAM HEALTH IN THE CONTEXT OF NUTRIENTS AND TROPHIC STATE THAT ARE IMPORTANT FOR SUSTAINABILITY OF WATER RESOURCES…

nutrients

C, N, P

ECOSYSTEM METABOLISM

Time of day

Dis

solv

ed O

2 (

mg/

L)

2

4

6

8

10

12

14

16

00:00 10:00 20:00 06:00

photo sources: National Geographic, NABS, Microbe zoo

Dissolved oxygen record

time of day

Small increases in nutrients stimulateprimary production, respiration.

Elapsed time (h)

0 20 40 60 80

Dis

solv

ed

Oxy

gen

(%

sa

tura

tion)

40

60

80

100

120

140

160

2100 SCudahy Lane

Jordan River data, August 2006, courtesy of E. Duffindata plotted after Dodds 2007 TREE

net photosynthetic

respiration

2100 S is net autotrophicP>R

Cudahy Lane is netheterotrophic P<R

Either Cudahy Lane hasless autotrophic activity,more heterotrophic activityor both.

ECOSYSTEM METABOLISM

BIOCHEMICAL OXYGEN DEMAND (BOD)

N-BOD•nitrogenous

oxygen demand

•autotrophic bacteria

•heterotrophs can outcompete nitrifyers for NH4

+ C-BOD•carbonaceous

oxygen demand

BOD5

•biochemical oxygen demand in a bottle incubated at 25 C in dark for 5 days

• includes organic matter oxidation AND inorganic matter oxidation

Nutrient treatment

NO3 NH4 SRP N+P

BO

D a

s %

co

ntr

ol (

me

an

+ S

D)

0

100

200

300

400

500

600

Logan RLittle Bear RCutler ResBear Lake

BIOCHEMICAL OXYGEN DEMAND (BOD)

Nutrients can stimulateoxygen consumption.

Reed and Baker, 2010 (unpublished)

NDS deployed in East Canyon Creek

NDS after incubation in East Canyon Creek showing algal growth on glass disks

4 treatmentscontrol+ N (as NO3

-)+ P (as PO4

3-)+ N+P

5 replicates of each treatmentincubated ca. 3 weeksand analyzed for chlorophyll a

NUTRIENT LIMITATION ASSAYS

Re

lativ

e r

esp

on

se (

tre

atm

en

t/co

ntr

ol)

0

1

2

3

4

5

above below

N P N+P

Periphyton growth in East Canyon Creek respondsto N and N+P addition.

NUTRIENT LIMITATION ASSAYS

Baker et al. 2008

NUTRIENT SPIRALLINGTracer tests with addedBr, PO4-P, NH4-N or NO3-N

Uptake = loss of P or Nrelative to Br

Endpoint evaluatedusing Michaelis-Mentenkinetics

Sw

Vf

NUTRIENT SPIRALLING

Sw, NH4 – 833 mVf, NH4 – 28 mm/min

Sw, NO3 - 2062 mVf, NO3 – 11 mm/min

1680 m

3360 m

5880 m 8040 m

Baker et al. 2010, unpublished

NUTRIENT SPIRALLING

Covino et al. 2010

Slug allows evaluationof Michaelis-Mentenkinetics. Km = 48.7-13.9 ppb

Covino et al. 2010

NUTRIENT SPIRALLING

We use a combination of tools and ideas from ecology, biogeochemistry, hydrology, and microbiology to understand processes that control nutrients in streams and rivers.

These processes describe stream functioning (health).

Lab GroupC. Arp, K. Goodman, S. Hochhalter, A. Myers, S. Vallaire, C. Crenshaw, I. Washbourne, A. Benedetto, J. Crawford, E. Lytle, B. Ombach, J. Reed

Other CollaboratorsM. Gooseff, R. Haggerty, R. Hall, B. McGlynn, E. Rosi-Marshall, J. Tank, W. Wurtsbaugh

FundingNSF EAR 04-09534, NSF DEB 01-32983, 05-19327,09-22153, UT DWQ

ACKNOWLEDGEMENTS