Physico-chemical characterisation of protected lake habitats: A matter of dystrophy

Abstract

Oligotrophic waters containing very few minerals of sandy plains (code 3110) and Natural dystrophic lakes and ponds (code 3160) are widespread freshwater lake habitats within Atlantic blanket bog habitats. Despite being protected under Annex I of the European Union (EU) Habitats Directive, the conservation conditions of these lake habitats is considered bad and inadequate respectively. A lack of field data (including physico-chemical, algal, macrophytes and invertebrates) is preventing appropriate conservation condition assessments, and recommendations to maintain / restore favourable conservation condition. This research aims to characterise these lake habitats with water chemistry data from favourable conservation condition sites and determine their natural state, and to consider seasonal and regional variability to evaluate whether two lake habitats exist. Several water chemistry parameters were monitored in 24 waterbodies monthly for 12 months. Lake habitat 3110 were characterised by higher levels of pH, alkalinity, silica and dissolved oxygen, whereas, contrary to previous reports, levels of true colour and dissolved organic matter (DOM) were lower in lake habitat 3160. However, all 24 sites were acidic with low alkalinity and slightly coloured, hence exhibiting dystrophic conditions. Principal Component Analysis highlighted a strong regional influence separating larger, coloured sites from smaller acidic and altitudinal sites. Differences in true colour were due to strong positive relationships between DOM and catchment area confirming their influence on a regional scale. This research highlights an urgent need to gather physico-chemical field data from a wider range of protected lake habitats 3110 and 3160, and from across the EU to discern whether a gradient of dystrophy exists along which both habitats occur. Outcomes of such research would have implications on the reporting and conservation assessment of these lake habitats by Member States and help harmonise monitoring methods and provide more accurate assessment tools for their reporting under the EU Habitats Directive.