title: Phytoplankton community responses in a shallow lake following lanthanum-bentonite application.
abstract: The release of phosphorus (P) from bed sediments to the overlying water can delay the recovery of lakes for decades following reductions in catchment contributions, preventing water quality targets being met within timeframes set out by environmental legislation (e.g. EU Water Framework Directive: WFD). Therefore supplementary solutions for restoring lakes have been explored, including the capping of sediment P sources using a lanthanum (La)-modified bentonite clay to reduce internal P loading and enhance the recovery process. Here we present results from Loch Flemington where the first long-term field trial documenting responses of phytoplankton community structure and abundance, and the UK WFD phytoplankton metric to a La-bentonite application was performed. A Before-After-Control-Impact (BACI) analysis was used to distinguish natural variability from treatment effect and confirmed significant reductions in the magnitude of summer cyanobacterial blooms in Loch Flemington, relative to the control site, following La-bentonite application. However this initial cyanobacterial response was not sustained beyond two years after application, which implied that the reduction in internal P loading was short-lived; several possible explanations for this are discussed. One reason is that this ecological quality indicator is sensitive to inter-annual variability in weather patterns, particularly summer rainfall and water temperature. Over the monitoring period, the phytoplankton community structure of Loch Flemington became less dominated by cyanobacteria and more functionally diverse. This resulted in continual improvements in the phytoplankton compositional and abundance metrics, which were not observed at the control site, and may suggest an ecological response to the sustained reduction in filterable reactive phosphorus (FRP) concentration following La-bentonite application. Overall, phytoplankton classification indicated that the lake moved from poor to moderate ecological status but did not reach the proxy water quality target (i.e. WFD Good Ecological Status) within four years of the application. As for many other shallow lakes, the effective control of internal P loading in Loch Flemington will require further implementation of both in-lake and catchment-based measures. Our work emphasizes the need for appropriate experimental design and long-term monitoring programmes, to ascertain the efficacy of intervention measures in delivering environmental improvements at the field scale.
authors.affiliation: Ecology Assessment Unit, Scottish Environment Protection Agency, 6 Parklands Avenue, Maxim Business Park, Eurocentral, North Lanarkshire ML1 4WQ, Scotland, UK. Electronic address: pauline.lang@sepa.org.uk.
authors.forename: P
authors.initials: P
authors.lastname: Lang
authors.affiliation: Freshwater Ecology Group, Centre for Ecology & Hydrology, Bush Estate, Penicuik, Midlothian EH26 0QB, Scotland, UK.
authors.forename: S
authors.initials: S
authors.lastname: Meis
authors.affiliation: Department of Ecology, Faculty of Science, Charles University in Prague, Viničná 7, CZ-128 44 Prague, Czech Republic.
authors.forename: L
authors.initials: L
authors.lastname: Procházková
authors.affiliation: Freshwater Ecology Group, Centre for Ecology & Hydrology, Bush Estate, Penicuik, Midlothian EH26 0QB, Scotland, UK.
authors.forename: L
authors.initials: L
authors.lastname: Carvalho
authors.affiliation: Lake Ecosystems Group, Centre for Ecology & Hydrology, Lancaster Environment Centre, Library Avenue, Bailrigg, Lancaster LA1 4AP, England, UK.
authors.forename: E B
authors.initials: EB
authors.lastname: Mackay
authors.affiliation: Freshwater Ecology Group, Centre for Ecology & Hydrology, Bush Estate, Penicuik, Midlothian EH26 0QB, Scotland, UK.
authors.forename: H J
authors.initials: HJ
authors.lastname: Woods
authors.affiliation: Broombank, Loch Flemington, Inverness IV2 7QR, Scotland, UK.
authors.forename: J
authors.initials: J
authors.lastname: Pottie
authors.affiliation: Ecology Partnership Development Unit, Scottish Environment Protection Agency, Graesser House, Fodderty Way, Dingwall Business Park, Dingwall IV15 9XB, Scotland, UK.
authors.forename: I
authors.initials: I
authors.lastname: Milne
authors.affiliation: Ecology Assessment Unit, Scottish Environment Protection Agency, 6 Parklands Avenue, Maxim Business Park, Eurocentral, North Lanarkshire ML1 4WQ, Scotland, UK.
authors.forename: C
authors.initials: C
authors.lastname: Taylor
authors.affiliation: Lake Ecosystems Group, Centre for Ecology & Hydrology, Lancaster Environment Centre, Library Avenue, Bailrigg, Lancaster LA1 4AP, England, UK.
authors.forename: S C
authors.initials: SC
authors.lastname: Maberly
authors.affiliation: Freshwater Ecology Group, Centre for Ecology & Hydrology, Bush Estate, Penicuik, Midlothian EH26 0QB, Scotland, UK.
authors.forename: B M
authors.initials: BM
authors.lastname: Spears
mesh_terms: D001546:Bentonite / Q000737:chemistry; D005068:Eutrophication; D060106:Lakes / Q000737:chemistry*; D007811:Lanthanum / Q000737:chemistry; D010758:Phosphorus; D010839:Phytoplankton
chemical_list: D001546:Bentonite; D010758:Phosphorus; D007811:Lanthanum
keywords: Cyanobacteria; Eutrophication; Lake restoration; Lanthanum-modified bentonite; Recovery