Modelling Contrasting Responses Of Wetland Productivity To Changes In Water Table Depth

  • Sites: US-Los
  • Publication Type: JOUR
  • Authors: Grant, R.F.; Desai, A.R.; ¬†Sulman, B.N.

  • Responses of wetland productivity to changes in water table depth (WTD)
    are controlled by complex interactions among several soil and plant
    processes, and hence are site-specific rather than general in nature.
    Hydrological controls on wetland productivity were studied by
    representing these interactions in connected hummock and hollow sites in
    the ecosystem model ecosys, and by testing CO2 and energy
    fluxes from the model with those measured by eddy covariance (EC) during
    years with contrasting WTD in a shrub fen at Lost Creek, WI. Modelled
    interactions among coupled processes for O2 transfer,
    O2 uptake, C oxidation, N mineralization, N uptake and C
    fixation by diverse microbial, root and mycorrhizal populations enabled
    the model to simulate complex responses of CO2 exchange to
    changes in WTD that depended on the WTD at which change was occurring.
    At the site scale, greater WTD caused the model to simulate greater
    CO2 influxes and effluxes over hummocks vs. hollows, as has
    been found at field sites. At the landscape scale, greater WTD caused
    the model to simulate greater diurnal CO2 influxes and
    effluxes under cooler weather when water tables were shallow, but also
    smaller diurnal CO2 influxes and effluxes under warmer
    weather when water tables were deeper, as was also apparent in the EC
    flux measurements. At an annual time scale, these diurnal responses to
    WTD in the model caused lower net primary productivity (NPP) and
    heterotrophic respiration (Rh), but higher net ecosystem
    productivity (NEP = NPP – Rh), to be simulated in a cooler
    year with a shallower water table than in a warmer year with a deeper
    one. This difference in NEP was consistent with those estimated from
    gap-filled EC fluxes in years with different water tables at Lost Creek
    and at similar boreal fens elsewhere. In sensitivity tests of the model,
    annual NEP declined with increasing WTD in a year with a shallow water
    table, but rose in a year with a deeper one. The model thus provided an
    integrated set of hypotheses for explaining site-specific and sometimes
    contrasting responses of wetland productivity to changes in WTD as found
    in different field experiments.


  • Journal: Biogeosciences
  • Funding Agency: —
  • Citation Information:
  • Volume: 9
  • No: 11
  • Pages: 4215-4231
  • Publication Year: 2012
  • DOI: 10.5194/bg-9-4215-2012