Effects of summer drought on peat soil solution chemistry in an acid gully mire

In a field experiment to investigate potential impacts of climatic change, a small area of flush wetland in Wales was subjected to three successive years of simulated summer drought/rewetting (autumn-spring) cycles (1992?94). Drought was simulated achieved by diverting stream water around the experimental wetland during the summer, so that the wetland received only precipitation inputs during that time. The effects on peat-water chemistry in the rhizosphere were monitored at regular intervals until spring 1996, and comparisons made with a control. Simulated summer drought decreased, significantly, the natural summer peaks in dissolved organic carbon (DOC) and iron, whilst subsequently increasing the natural autumn-winter peaks in sulphate concentrations and acidity in the peat water. The effects of simulated drought on SO₄ concentrations in the peat water compared favourably with subsequent events monitored following a natural summer drought in 1995. Autumn-winter peaks in SO₄ concentrations in the control wetland following the natural drought were of similar magnitude to those induced by the drought simulated in the experimental wetland in the previous three years.