1. Introduction to Ecosystem Monitoring and Metabolism

2. What is ecosystem metabolism?
Net ecosystem metabolism is the difference between primary production and respiration within an ecosystem.
Why do we want to quantify it?
To assess ecosystem health.
Biogeochemical fluxes of carbon, oxygen and nutrients.
Integrative measure of system response to perturbations.
Can use it to examine drivers which are influencing system metabolism;
Means to link physical, biological and chemical.

3. NEM = O2 Produced from Photosynthesis – O2 utilized in Aerobic Respiration
NEM > 0: Internal production of organic matter dominates (Autotrophic)
NEM < 0: Ecosystem fueled by external sources of organic matter (Heterotrophic)

4. This is for a lake; probably should create on for shelf/estuary
Staehr et al. (2010)

5. Comparison of Methods Method Temporal Scale Advantages Disadvantages
Diel Open water Method
Daily
Seasonal
Annual
Measures all system components.
Uses remote data collection.
High frequency rates.
Physics may obscure biology
Difficult to quantify air-water flux
Horizontal and vertical heterogeneity
Incubations/
Chambers
Hourly
Direct process measurement.
Highly controlled.
Can separate ecosystem components.
Container artifacts
Labor intensive
Difficult to scale up to ecosystem.
Ecosystem budgets
Staehr et al (2012), Aquatic Science 74:15-29.

6. What sensors can be used?
106 CO HNO3 + H3PO H20 ↔ C106H175O42N16P O2
pCO2 O2 Nutrient (NO3, PO4) pH
Johnson (2010) Simultaneous measurements of nitrate, oxygen, and carbon dioxide on oceanographic moorings: Observing the Redfield ratio in real time. L&O 55(2):

7. Other useful variables: In situ fluorescence
Parameter
Advantages
Disadvantages
pCO2
Direct product of respiration.
Provides more comprehensive measure of ecosystem respiration (includes anaerobic).
NO3
Loss indicator of production.
Don’t have to account for air-water gas transfer.
Complicated by nitrogen fixation and denitrification.
Other nutrient substrates may be determining primary productivity.
PO4
Typically low concentrations O2
Simplest to measure
Widely available
Need to account for air-water gas transfer
Won’t work if productivity low, due to low signal: noise pH
Other useful variables:
In situ fluorescence
Temperature Salinity & wind stress

8. If you were to follow a parcel of water, measuring dissolved oxygen.
Time of Day (hours) 12 24 O2
Light
Production
Respiration
Animation
Air –
Sea
Flux

9. Diel Open Water Method O2 /  t = GPP – R – F – A
First used by Odum (1956)
Assumed to be negligible.
O2 /  t = GPP – R – F – A
GPP = Gross primary production
R = Aerobic respiration
F = Exchange of O2 with atmosphere
A =  other processes (including horizontal or vertical advection and non-aerobic respiration.)
Estimated as concentration gradient and/or function of wind speed.
 Assuming respiration constant, GPP estimated from daytime changes in O2.
Estimated from night time changes in O2
Assume GPP = 0 at night; therefore R estimated from night time changes in O2.
Assuming respiration at night = respiration during day; then GPP estimated from day time changes in O2.

10. NEM Calculation
Perform QA check on DO data (biofouling/spikes).
Check data to ensure that changes in O2 are due to biology not physics (i.e., mixing of water masses with different O2 levels).
Fundamental assumption is that all measurements come from a water mass that has same recent history, which allows point measurements from one location over time to be compared.
Water residence time should be sufficiently long that the same water mass is sampled over a 24 hour period.
Calculate air-sea exchange of O2 (FO2) for each time step.
If necessary, filter the O2 data to remove variability occurring at frequencies longer than diel.
Calculate Biological Oxygen Change for each time step.
BDOt = (DOt – DOt-1) * depth - FO2
Calculate Net Ecosystem Metabolism by summing BDOt over 24 hrs.
Calculate Net Ecosystem Production , Respiration and Gross Primary Production (GPP).
NEP =  BDOt during daylight hours
Respiration Rate (hourly) =  BDOt / ( number of night hours)
GPP = NEP + (daylight hours * hourly respiration rate)
Ideally first step should be analysis of water mass variability

11. Questions
What is the role of the coastal ocean on oxygen dynamics within the estuary?
What are the factors which are influencing oxygen levels and how are they varying between YB1 and YB2?
What implications does this have for NEM calculations (for examples, are the assumptions valid at each station)?

12. Datasets
YB1
Wind
(46050)
YB2
SR15

19. Diel signal in Dissolved Oxygen

21. Date
NEM
Daily Respiration
NEP
GPP
Hourly Respiration
g O2 m-2 d-1
g C m-2 d-1
g O2 m-2 h-1
8/16/07
-2.5
-4.0
-0.9
1.5
0.4
-0.2
8/17/07
-2.4
-4.2
-0.8
1.7
0.5
8/18/07
-2.2
-3.7
1.4

22. Primary Productivity Measurements from Yaquina Estuary
Water Column GPP = 0.25 – 3 g C m-2 d-1
Macroalgae NPP = 46 g C m-2 d-1
Benthic Microalgae NPP = 0.3 g C m-2 d-1
Seagrass NPP = g C m-2 d-1

24. Conclusions
NEM calculations provide a means to integrate in situ biological, physical and chemical data and gain insights into biogeochemical cycling and ecosystem drivers.
The calculation isn’t new. What has changed is the availability of high temporal resolution time series through the development of instrumentation.
Provide insights into natural and anthropogenic drivers on biogeochemical cycling.
Gliders and drifters with DO, pH, pCO2, Nutrient and Chl a sensors will lead to advances in understanding.

25. References
Caffrey, J.M Factors controlling net ecosystem metabolism in U.S. estuaries. Estuaries 27(1): Caffrey, J.M. (2003). Production, respiration and net ecosystem metabolism in U.S. estuaries. Environmental Monitoring and Assessment 81: Johnson, K.S. (2010). Simultaneous measurements of nitrate, oxygen, and carbon dioxide on oceanographic moorings: Observing the Redfield ratio in real time. Limnology & Oceanography 55(2): Needoba et al. (2012). Method for quantification of aquatic primary production and net ecosystem metabolism using in situ dissolved oxygen sensors. In: Molecular Biological Technologies for Ocean Sensing, Springer, New York. Odum, H.T. (1956). Primary production in flowing waters. Limnology & Oceanography 1(2): Staehr et al. (2010). Lake metabolism and the diel oxygen technique: State of the science. Limnology & Oceanography: Methods 8: Staehr et al. (2012). The metabolism of aquatic ecosystems: History, applications and future challenges. Aquatic Science 74:15-29.