Relationships between hydrology, hydrochemistry and vegetation patterning on Scottish fens

Abstract

Fens are increasingly recognised as important habitats in terms of biodiversity, and this has been formalised in recent legislation (EC Habitats Directive, 92/43/EEC). The influence of groundwater and surface water inputs on the fen habitat increases its vulnerability to water pollution, particularly from nutrients. Despite the conservation importance and potential vulnerability of the habitat, fens have not been widely studied in Scotland, in terms of extent, location, sensitivity to increased nutrient inputs, or in comparison to similar European sites. This study found that fens were widespread throughout mainland Scotland, and that basin fens were the most commonly occurring fen type, representing 43% of the 355 sites assessed. A survey of 18 basin fens found that 72% were potentially vulnerable to elevated nutrient inputs, being surrounded by improved/modified land. Despite this, only four sites showed greater nutrient concentrations in sub-surface water samples or water inputs. There was, however, a significant amount of variation in hydrochemistry between the sites. Detailed studies further assessed spatial and temporal variations in hydrochemistry, and associated hydrologic regimes on two similar basin fens, one in an agricultural catchment, the other surrounded by unimproved grassland. Spatial patterning of vegetation was associated with both base-richness and nutrient concentrations of subsurface water, and the frequency of water inundation. General relationships between the six fen vegetation types and the observed hydrological and hydrochemical variation were presented.