Carbon metabolism in marine ecosystems

1
Carbon metabolism in marine ecosystems

• C.M. Duarte and S. Agusti (1998)
• J.-P. Gattuso, M. Frankignoulle and S.V. Smith
  (1999)
• J.-P.Gattuso, M. Frankignoulle and R. Wollast
  (1998)
• P.A. Raymond, J.E. Bauer and J.J. Cole (2000)

2
Overview

• Introduction
• Estuaries
• Macrophyte-based ecosystems
• Mangroves
• Coral reefs

3
Introduction main processes

• Primary prod CO2 H2O light CH2O O2
• Respiration CH2O O2 CO2 H2O
• Calcification Ca2 2HCO3- CaCO3 CO2 H2O
• RgtGPP Heterotrophic source of CO2
• GPPgtR Autotrophic sink of CO2
• RR RP2/3 in aquatic ecosystems

4
Introduction coastal zone

• lt 200 m, 7 of total ocean
• Great diversity of primary producers
• Contributes for
• 14-30 to oceanic pp
• 80 to OM burial
• 90 to sedimentary mineralization
• 75-90 to oceanic sink of suspended river load
• 50 to deposition of CaCO3

5
Marine ecosystem Estuaries

• 0.38 of total ocean
• Nutrient input ? eutrophication ? anoxic parts
• Nutrient input ? turbidity rises ? light
  limitation
• Benthic contribution to RT 25-50

6
Marine ecosystem Estuaries

• CO2 exchange
• Flux k(CO2water CO2air)
• k is based on wind speed
• Fluxes DIC
• Input flux (mmol s-1) Q(Cs Co)
• Co concentration at zero salinity
• Cs concentration at seawater end-member

7
Marine ecosystem Macrophyte-based ecosystems

• Macrophyten sea grasses and macro algae
• 0.56 of total ocean
• Biomass of Macrophyten 400x higher than
  phytoplankton
• Mostly appear in nutrient-poor and non-turbid
  areas
• Seasonal variation
• CNP ratio is 274241
• Human activities are damaging the sea grasses

8
Marine ecosystem Macrophyte-based ecosystems

• Decomposition within the system is an important
  process (gt40 of Pn)
• Herbivore pressure is significant for macro algae
• Export is an important process (24-43)
• Storage in the sediment is only significant for
  seagrasses (gt15)

9
Marine ecosystem Mangroves

• Intertidal forests which cover 0.06 of total
  ocean
• Environmental forcing and forest type causes
  variation in metabolism
• Benthic heterotroph use C from litter fall and
  deposited phytoplankton
• Benthic micro-algae production is low, but
  benthic bacterial productivity is high
• Nowadays 50 is destroyed by human

10
Marine ecosystem Coral reefs

• Carbonate structures located near sea level
• 0.17 of total ocean
• Dominated by benthic processes
• Algal dominated RCorg ? RCalcification? (compared
  to coral/algae dominated reef flats)
• CNP ratio is 550301

11
GPP vs R in different coastal ecosystems
12
P/R Ratios of different systems