Wetlands as energy-dissipating systems

Abstract

Since wetlands are ecosystems that have an ample supply of water, they play an important role in the energy budgets of their respective landscapes due to their capacity to shift energy fluxes in favor of latent heat. Rates of evapotranspiration in wetlands are commonly as high as 6–15 mm day⁻¹, testifying to the large amount of energy that is dissipated through this process. Emergent or semi-emergent wetland macrophytes substantially influence the solar energy distribution due to their high capacity for transpiration. Wetland ecosystems in eutrophic habitats show a high primary production of biomass because of the highly efficient use of solar energy in photosynthesis. In wetlands associated with the slow decomposition of dead organic matter, such as oligotrophic marshes or fens and bogs, the accumulation of biomass is also high, in spite of the rather low primary production of biomass. Most of the energy exchange in water-saturated wetlands is, however, linked with heat balance, whereby the largest proportion of the incoming energy is dissipated during the process of evapotranspiration. An example is shown of energy fluxes during the course of a day in the wetland ecosystem of Mokré Louky (Wet Meadows) near Třeboň. The negative consequences of the loss of wetlands for the local and regional climate are discussed.

Appendix

According to materials from the IPCC, the radiative forcing due to the enhanced concentrations of greenhouse gases in the atmosphere has risen by 1–3 W m⁻² since the start of the Industrial Revolution. According to models of climate change derived by the IPCC, the radiative forcing will increase by 0.2 W m⁻² in 10 years, i.e., by 1 W m⁻² in 50 years. These increases are within the range of parts per ten thousand of the solar constant, so they cannot be measured and have only been predicted by a model.

Returning water to the landscape and restoring permanent vegetation results in more effective solar energy dissipation in primary production processes (units of W m⁻²), reduces air pressure and temperature differences (hundreds of W m⁻²), slows down the rate of decomposition and thus reduces the heat released by them (units to tens of W m⁻²), and increases energy uptake and fixation by ecosystems and the use and dissipation of this energy by various ecosystem processes.