Introduction to Ecosystem Monitoring and Metabolism

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. http://science.nasa.gov/earth-science/oceanography/ocean-earth-system/ocean-carbon-cycle/

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)

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

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.

What sensors can be used? 106 CO2 + 16 HNO3 + H3PO4 + 122 H20 ↔ C106H175O42N16P + 138 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): 615-627.

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

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

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.

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

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)?

Datasets YB1 Wind (46050) YB2 SR15

Diel signal in Dissolved Oxygen

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

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 = 130-180 g C m-2 d-1

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.

References Caffrey, J.M. 2004. Factors controlling net ecosystem metabolism in U.S. estuaries. Estuaries 27(1): 90-101. Caffrey, J.M. (2003). Production, respiration and net ecosystem metabolism in U.S. estuaries. Environmental Monitoring and Assessment 81: 207-219. 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): 615-627. 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): 102-117. Staehr et al. (2010). Lake metabolism and the diel oxygen technique: State of the science. Limnology & Oceanography: Methods 8: 628-644. Staehr et al. (2012). The metabolism of aquatic ecosystems: History, applications and future challenges. Aquatic Science 74:15-29.