Abstract
In the Netherlands, the area of raised bogs has been virtually lost during two millennia of human impact. Much effort has been invested in rewetting these cut-over bogs, but the recovery of Sphagnum-dominated vegetation often failed. The work presented includes research on the role of hydrochemistry in rewetting cut-over bogs and on the effects of high atmospheric N deposition on the composition of bog vegetation. Development of floating peat on inundated locations appeared to provide suitable growing conditions for Sphagnum mosses. The buoyancy of floating peat is caused by methane bubbles accumulating in the peat. High methane production rates are determined by both chemical and physical peat characteristics. Buoyant peat has a low bulk density, a relatively high pH and low lignin-to-nutrient ratios. Where these peat characteristics prevail, buoyancy of the residual peat after rewetting is very likely, providing favourable starting conditions for bog restoration. In inundated peat remnants where the amount of this poorly humified peat is insufficient, the introduction of (limed) substrates might be a valuable method to stimulate floating peat formation. The invasion of Dutch bogs by atypical species such as Molinia caerulea and Betula trees is probably triggered by the high atmospheric nitrogen loads. The imbalance between nitrogen availability and nitrogen uptake by Sphagnum mosses results in increased availability of nitrogen in the rhizosphere. Betula and Molinia are able to profit from the extra nitrogen. Whether invasion by Molinia and Betula actually takes place depends on the availability of not only nitrogen but also other nutrients, especially phosphorus. The combined high availability of nitrogen and phosphorus, together with the often sub-optimal growing conditions for Sphagnum mosses, results in the invasion of Dutch bogs by Molinia and Betula. Is the revival of Dutch Sphagnum bogs a reasonable perspective? Suitable rewetting measures and further reduction of nitrogen deposition rates provide a reasonable perspective for Dutch Sphagnum bogs!
