Solute transport in Sphagnum dominates bogs. The ecophysiological effects of mixing by convective flow

PhD ceremony: Mr. W. Patberg, 11.00 uur, Aula Academiegebouw, Broerstraat 5, Groningen

Dissertation: Solute transport in Sphagnum dominates bogs. The ecophysiological effects of mixing by convective flow

Promotor(s): prof. J.T.M. Elzenga, prof. A.P. Grootjans

Faculty: Mathematics and Natural Sciences

Wouter Patberg has concluded in his thesis that buoyancy flow is a quantitative important transport mechanism for nitrogen in a water-saturated bog. Nutrients enter Sphagnum bogs mainly by atmospheric deposition. However, the most important nutrient source for Sphagnum is the mineralization of organic material in lower peat layers. In contrast, the highest metabolic activity and the uptake of nutrients take place in the upper part of the Sphagnum mosses, the capitula, which reside in the top of bogs. This separation between the actively growing capitula and the site of mineralization, requires an efficient nutrient transport system. Diffusion and internal transport were the known transport mechanisms in a water-saturated Sphagnum habitat. Complementary to these mechanism, buoyancy-driven water flow was proposed as an external nutrient transport mechanism. Buoyancy flow is the vertical flow of water, driven by differences in density between water layers as a consequence of the temperature difference between day and night.

In his thesis Patberg has shown that buoyancy flow is a worldwide occurring phenomenon and that solutes are transported more rapid and in larger quantities by buoyancy flow than by diffusion and internal transport. As a consequence, a stepwise nutrient increase in the surroundings of the capitula can be induced. The uptake kinetics of ammonium by Sphagnum was determined by him and indicates that Sphagnum is able to benefit very well from a stepwise increase in ammonium availability. Therefore, Patberg concludes that buoyancy flow is a quantitative important transport mechanism for nitrogen in a water-saturated bog. Next to nitrogen, other solutes like CO₂ and O₂ will be redistributed by buoyancy flow, which presumably plays an important role in ecosystem functioning.