Temporal and geographical variation in lake trophic status in the English Lake District: evidence from (sub)fossil diatoms and aquatic macrophytes

Abstract

1. A sediment core (representing 250–300 years) was taken from each of three lakes of conservation interest and contrasting trophic status in the English Lake District: Wastwater, Bassenthwaite Lake and Esthwaite Water. Lithostratigraphic analyses, radiometric dating and analysis of fossil diatoms were carried out. 2. Transfer functions, based on the diatoms, were used to reconstruct total phosphorus (TP) and, thus, eutrophication at the study lakes. In Wastwater, changes in lake pH were also reconstructed. 3. The lakes were also classified according to their present macrophyte flora, the latter being compared with previous records. 4. The fossil diatoms of Wastwater were continuously dominated by taxa typical of oligotrophic, circumneutral waters, indicating that the lake has not been enriched or acidified in the last 250 years. The aquatic macrophyte flora has probably remained unchanged since before the Industrial Revolution. 5. The diatom assemblages of both Bassenthwaite Lake and Esthwaite Water began to change in the mid‐1800s. Further change occurred from the 1960s, at the onset of a recent period of eutrophication. These two lakes have experienced continued nutrient enrichment throughout the 1970s, 80s and 90s, largely associated with increasing phosphorus inputs from sewage effluent. There is no evidence of any recovery in response to recent reductions in external nutrient loads. 6. Only in Esthwaite Water has the change in aquatic macrophytes been pronounced. 7. Palaeolimnological reconstruction is useful in determining background conditions and natural variation in lake ecosystems.

Contribution of sediment focussing to heterogeneity of organic carbon and phosphorus burial in small lakes

“…Both organic content (measured as LOI) and total phosphorus concentrations in Esthwaite Water (Table 2) were comparable to those found in other lakes such as Bassenthwaite Lake, Wastwater (15% and 25% organic content as LOI, respectively) (Bennion, Monteith & Appleby, 2000), Lake Rotoiti, New Zealand (3460 mg P kg -1 ) (Trolle et al, 2008) and Loch Leven, Scotland (2288 mg P kg -1 ) (Spears et al, 2006).…”

Assessment of ecological status in UK lakes using benthic diatoms

“…the Cumbrian lakes included in the validation study, are not in their former oligotrophic state and have experienced enrichment (Bennion et al 2000). However, this impact is not reflected in the epilithic diatom assemblage.…”

Combining limnology and palaeolimnology to investigate recent regime shifts in a shallow, eutrophic lake

“…As the diatom community changed, diversity, recorded by Hill's N2 diversity index, declined, indicating a less diverse diatom community post-1978. This, too, could be an indication of the slow eutrophication of the lake (Bennion et al 1996(Bennion et al , 2000.…”