Atmospheric stilling offsets the benefits from reduced nutrient loading in a large shallow lake
Laen...
Kuupäev
2020
Kättesaadav alates
Ajakirja pealkiri
Ajakirja ISSN
Köite pealkiri
Kirjastaja
Wiley
Abstrakt
As part of a global phenomenon, a 30% decrease in average wind speed since 1996 in southern Estonia
together with more frequent easterly winds resulted in 47% decrease in bottom shear stress in the large
(270 km 2
), shallow (mean depth 2.8 m), and eutrophic Lake Võrtsjärv. Following a peak in eutrophication pres-
sure in the 1970s–80s, the concentrations of total nutrients were declining. Nonmetric Multidimensional Scal-
ing (NMDS) ordination of a 54-year phytoplankton community composition time-series (1964–2017) revealed
three distinct periods with breaking points coinciding with changes in wind and/or water level. Contrary to
expectations, we detected no decrease in optically active substances that could be related to wind stilling,
whereas phytoplankton biomass showed an increasing trend despite reduced nutrient levels. Here we show how
opening of the “light niche,” caused by declining amount of suspended sediments, was capitalized and filled by
the light-limited phytoplankton community. We suggest that wind stilling is another global factor, complemen-
tary to climate warming that counteracts eutrophication mitigation in lakes and may provide a challenge to
assessment of the lake ecological status.
Kirjeldus
Märksõnad
large shallow lake, nutrient load, articles