We analysed long-term changes in phytoplankton composition in relation to hydrological, meteorological and nutrient loading data in the large (270 km(2)) shallow (mean depth 2.8 m) Lake Vrtsjarv. Nutrient loads to the lake were heavy in the 1970s and 1980s and decreased considerably thereafter. The average nutrient concentrations for 1985-2004 (1.6 mg l(-1) of total nitrogen and 53 mu g l(-1) of total phosphorus) characterize the lake as a eutrophic water body. All four calculated taxonomic indices showed a unidirectional deterioration of the lake's ecological status, despite reduced concentrations of nutrients. We focused our analysis on the PTSI index, which revealed a stepwise change between the years 1977 and 1979 that coincided with a large increase in water level, but also with a change of investigator. After correcting input data for possible investigator-induced differences, the step change remained because it was caused by major changes in the whole phytoplankton community. The previous dominant Planktolyngbya limnetica was replaced by two species of seasonally altering Limnothrix. Among phytoplankton functional groups, there was a decrease in all groups comprising small-sized phytoplankton species, such as X1, E, F, J, N and an increase in S1 and H1, both represented by filamentous cyanobacteria. Our results suggest a non-linear response of phytoplankton to changing nutrient loadings, and that the change observed between 1977 and 1979 was a regime shift triggered by water level change. High shade tolerance of the new dominants, and their ability to create shade, obviously stabilized the new status making it resistant to restoration efforts.

Analysis of changes over 44 years in the phytoplankton of Lake Võrtsjärv (Estonia): The effect of nutrients, climate and the investigator on phytoplankton-based water quality indices / Peeter, Noges; Ute, Mischke; Reet, Laugaste; Solimini, ANGELO GIUSEPPE. - In: HYDROBIOLOGIA. - ISSN 0018-8158. - 646:(2010), pp. 33-48. (Intervento presentato al convegno 6th Shallow Lakes Congress 2008 tenutosi a Punta del Este, URUGUAY nel NOV 23-28, 2008) [10.1007/s10750-010-0178-y].

Analysis of changes over 44 years in the phytoplankton of Lake Võrtsjärv (Estonia): The effect of nutrients, climate and the investigator on phytoplankton-based water quality indices

SOLIMINI, ANGELO GIUSEPPE
2010

Abstract

We analysed long-term changes in phytoplankton composition in relation to hydrological, meteorological and nutrient loading data in the large (270 km(2)) shallow (mean depth 2.8 m) Lake Vrtsjarv. Nutrient loads to the lake were heavy in the 1970s and 1980s and decreased considerably thereafter. The average nutrient concentrations for 1985-2004 (1.6 mg l(-1) of total nitrogen and 53 mu g l(-1) of total phosphorus) characterize the lake as a eutrophic water body. All four calculated taxonomic indices showed a unidirectional deterioration of the lake's ecological status, despite reduced concentrations of nutrients. We focused our analysis on the PTSI index, which revealed a stepwise change between the years 1977 and 1979 that coincided with a large increase in water level, but also with a change of investigator. After correcting input data for possible investigator-induced differences, the step change remained because it was caused by major changes in the whole phytoplankton community. The previous dominant Planktolyngbya limnetica was replaced by two species of seasonally altering Limnothrix. Among phytoplankton functional groups, there was a decrease in all groups comprising small-sized phytoplankton species, such as X1, E, F, J, N and an increase in S1 and H1, both represented by filamentous cyanobacteria. Our results suggest a non-linear response of phytoplankton to changing nutrient loadings, and that the change observed between 1977 and 1979 was a regime shift triggered by water level change. High shade tolerance of the new dominants, and their ability to create shade, obviously stabilized the new status making it resistant to restoration efforts.
2010
trophic index; nutrient loading; phytoplankton functional groups; lake water level; regime shift
01 Pubblicazione su rivista::01a Articolo in rivista
Analysis of changes over 44 years in the phytoplankton of Lake Võrtsjärv (Estonia): The effect of nutrients, climate and the investigator on phytoplankton-based water quality indices / Peeter, Noges; Ute, Mischke; Reet, Laugaste; Solimini, ANGELO GIUSEPPE. - In: HYDROBIOLOGIA. - ISSN 0018-8158. - 646:(2010), pp. 33-48. (Intervento presentato al convegno 6th Shallow Lakes Congress 2008 tenutosi a Punta del Este, URUGUAY nel NOV 23-28, 2008) [10.1007/s10750-010-0178-y].
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11573/396502
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