Recent histories of six productive lakes in the Irish Ecoregion based on multiproxy palaeolimnological evidence

Abstract

Palaeolimnological data from six mesotrophic, eutrophic and hypertrophic lakes in the Irish Ecoregion, in the form of microfossil (cladocera, diatoms and pollen) and sediment chemistry data from radiometrically dated sediment cores, were used to reconstruct past variations in lake water quality and catchment conditions. Basal sediments from sediment cores from the six sites ranged in age from the late 18th century to the early 20th century. A weighted averaging partial least squares regression model was developed to reconstruct past epilimnetic total phosphorus concentrations. The results indicate that all but one of the study sites currently are in a far more productive state compared with the beginning of the sediment core record and that those same five lakes have experienced accelerated enrichment post c. 1980. Two of the sites demonstrated long-term enrichment, in one case beginning in the late 19th century, while both eutrophication and oligotrophication have occurred at three sites. The results highlight the difficulties in applying a general temporal end-point for reference conditions and demonstrate that productive lakes in the Irish Ecoregion have complex, locally specific and often long histories of enrichment. These may not be responsive to reduced external loadings of phosphorus and, as a result, restoration could prove particularly challenging. The results also provide evidence of the ways in which palaeolimnological techniques can assist implementation of the EU Water Framework Directive.

The Role of Palaeolimnology in Implementing the Water Framework Directive in Ireland

“…On the basis of analyses of three short cores of sediment (31, 39 and 40cm), Crans Lough has experienced varying human-induced stresses since at least the early nineteenth century . The preliminary palaeolimnological reconstructions initially presented in Taylor et al (2006) were signifi cantly added to by Erdil (2008) and Erdil and Taylor (submitted), who were able to work on a longer core of sediment (57cm), collected in June 2008. Palaeolimnological results from this longer core of sediment from Crans Lough are summarised in Fig.…”

Cladocera assemblages from the surface sediments of south-central Ontario (Canada) lakes and their relationships to measured environmental variables

“…Korhola et al, 2005;Guilizzoni et al, 2006;Heegaard et al, 2006;Sarmaja-Korjonen et al, 2006;Sweetman & Smol, 2006). Cladocera are excellent paleoindicators because they are influenced by changes in lake water chemistry, such as pH (Sprules, 1975;Roff & Kwiatkowski, 1977), nutrients (Jeppesen et al, 2003;Taylor et al, 2006), lake water temperatures (Korhola, 1999), calcium (Ca; Hessen et al, 1995;Waervågen et al, 2002), lake colour (Wissel et al, 2003), climate (Gyllström et al, 2005) and depth (Keller & Conlon, 1994;Hofmann, 1998). In addition, cladocerans inhabit a wide range of habitats and are sensitive indicators of lake trophic status (Jeppesen et al, 1996) as well as fish, copepod and macroinvertebrate predation (e.g.…”

Drivers of long-term trends and seasonal changes in total phosphorus loads to a mesotrophic lake in the west of Ireland

“…(Foy et al 1995;Irvine et al 2001;Taylor et al 2006). Although the most recent report on water quality in Ireland concluded that 81% of lakes were of satisfactory quality (McGarrigle et al 2010), the report also noted a decline of more than 4% in lakes in this category since the previous reporting period and reported that almost 42% of lakes surveyed were not compliant with the national target of a mean annual TP concentration of ,20 mg TP L…”