The use of diatom records to establish reference conditions for UK lakes subject to eutrophication

Abstract

A knowledge of pre-disturbance conditions is important for setting realistic restoration targets for lakes. For European waters this is now a requirement of the European Council Water Framework Directive (WFD) where ecological status must be assessed based on the degree to which present day conditions deviate from reference conditions. Here, we employ palaeolimnological techniques, principally inferences of total phosphorus from diatom assemblages (DI-TP) and classification of diatom composition data from the time slice in sediment cores dated to ~1850 AD, to define chemical and ecological reference conditions, respectively, for a range of UK lake types. The DI-TP results from 169 sites indicate that reference TP values for low alkalinity lakes are typically < 10 µg L -1 and in many cases < 5 µg L -1 , whilst those for medium and high alkalinity lakes are in the range 10-30 µg L -1 and 20-40 µg L -1 , respectively. Within the latter two alkalinity types, the deeper waters (> 3 m mean depth) generally had lower reference TP concentrations than the shallow sites. A small group of shallow marl lakes had concentrations of ~30 µg L -1 . Cluster analysis of diatom composition data from 106 lakes where the key pressure of interest was eutrophication identified three clusters, each associated with particular lake types, suggesting that the typology has ecological relevance, although poor cross matching of the diatom groups and the lake typology at type boundaries highlights the value of a site-specific approach to defining reference conditions. Finally the floristic difference between the reference and present day (surface sample) diatom assemblages of each site was estimated using the squared chord distance dissimilarity coefficient.Only 25 of the 106 lakes experienced insignificant change and the findings indicate that eutrophication has impacted all lake types with > 50% of sites exhibiting significant floristic change.The study illustrates the role of the sediment record in determining both chemical and ecological reference conditions, and assessing deviation from the latter. Whilst restoration targets may require modification in the future to account for climate induced alterations, the long temporal perspective offered by palaeolimnology ensures that such changes are assessed against a sound baseline.3

Composition and distribution of diatom assemblages from core and surface sediments of a water supply reservoir in Southeastern Brazil

“…Among the biological groups preserved in the sediments, diatoms have been widely used because of their taxonomic distinction, abundance, good preservation in sediments and their rapid response to environmental changes (Reid 2005, Bennion & Simpson 2011. The use of diatoms as indicators of environmental changes require high taxonomic precision (Birks 1994), since misidentifications can modify the interpretation in obtaining reliable data on modern diatom biodiversity (Buczkó & Magyari 2007, Wetzel & Ector 2014.…”

Diatomáceas planctônicas e de sedimento superficial em represas de abastecimento da Região Metropolitana de São Paulo, SP, Sudeste do Brasil

“…A eutrofização é uma das maiores ameaças à qualidade ecológica de lagos e represas, sendo principalmente causada pelo aporte de fósforo e nitrogênio oriundos de atividades humanas (Smith et al 2006, Bennion & Simpson 2011. A Região Metropolitana de São Paulo (RMSP) é a segunda megalópole em grau de precariedade de recurso hídrico devido a sua localização geográfica nas cabeceiras do Rio Tietê e aos intensos impactos antropogênicos que recebe (Beyruth 2000, Whately & Diniz 2009.…”

“…Para o gerenciamento efetivo dos ecossistemas aquáticos é necessário estabelecer metas de mitigação de impactos e, neste sentido, é fundamental reunir informações sobre as condições ambientais antes dos distúrbios antropogênicos (Sayer & Roberts 2001, Bennion & Simpson 2011. Diante das mudanças ambientais atuais e considerando a escassez de informações em condição pré-impacto, é urgente o conhecimento de ambientes protegidos como o Sistema Produtor Alto Cotia, considerado como referência para o abastecimento da RMSP e exemplo de conservação ambiental.…”

Disentangling natural and anthropogenic drivers of changes in a shallow lake using palaeolimnology and historical archives

“…Therefore, it appears that these feedbacks maintained high water transparency despite increased trophic status (Scheffer & Nes, 2007). The presence of C. radiosa and N. radiosa in DAZ-1 but not DAZ-2, suggests lower nutrient conditions and lower, intermediate alkalinity in the earlier zone relative to the subsequent period (Bennion & Simpson, 2011). Due to the short history of human impact in the catchment the lake started to deviate from 'reference conditions' in the 19 th century, which is relatively late compared to other parts of Europe (e.g.…”

“…However, such catchment modification changed groundwater discharge, lowering calcium carbonate supply. Therefore, alkaliphilous Staurosira construens and Staurosira pinnata declined in zone DAZ-3 and were replaced more generalist taxa such as A. minutissimum (Bennion & Simpson, 2011). At the same time, increased precipitation may have enhanced external nutrient loading (Jeppesen et al, 2015), depicted in rising content of humic substances and phosphorus.…”