Factors determining the character of wetland vegetation

There are many factors that influence the development and character of vegetation, of which the nutrient loading and the pH of the water are the most important.

Nutrient loading

The amount of dissolved nutrients in the water body (particularly nitrogen, but also phosphorus and potassium) have a profound affect on both the productivity of wetland vegetation and its species composition. Water bodies with very low nutrient levels are

called oligotrophic, those with medium levels, mesotrophic, and those with high levels, eutrophic. Hypertrophic means an extremely high nutrient content. Hypertrophic conditions are often found in newly filled ponds and result in the undesirable development of murky water due to a ‘bloom’ of floating algae and dense carpets of Duckweed (Lemna minor) on the surface. In water bodies without a permanent high nutrient inflow, this situation will rectify itself in time, as bacterial denitrification releases nitrogen back into the air, dissolved phosphorus will be precipitated into the sediment and nutrients become locked up in plant tissues. However, in many natural water bodies this inflow is strong enough to cause long-term eutrophic or even hypertrophic conditions. As well as promoting algal blooms, high nutrient levels result in the vigorous growth of aggressive competitive higher plant species (both submerged and emergent), leading to low biodiversity and a requirement for continuous management to maintain open water.