Collapse of a Planktothrix agardhii perennial bloom and microcystin dynamics in response to reduced phosphate concentrations in a temperate lake

Abstract

Planktothrix agardhii dynamics, microcystin concentration and limnological variables were monitored every 2 weeks for 2 years (2004-2006) in a shallow hypereutrophic artificial lake (BNV, Viry-Châtillon, France). Time-series analysis identified two components in the P. agardhii biomass dynamics: (1) a significant decreasing trend in P. agardhii biomass (65% of the overall variance) and (2) a residual component without significant seasonal periodicity. A path-analysis model was built to determine the main factors controlling the P. agardhii dynamics over the period studied. The model explained 66% of P. agardhii biomass changes. The decreasing trend in P. agardhii biomass was significantly related to a decrease in the PO4(3-) concentration resulting from an improved treatment of the incoming watershed surface water. The residual component was related to zooplankton dynamics (cyclopoid abundances), supporting the hypothesis of a top-down control of P. agardhii, but only when the biomass was low. Forty-nine percent of the variability in the microcystin (MC) concentration (min:<0.1 microg equivalent MC-LR L(-1); max: 7.4 microg equivalent MC-LR L(-1)) could be explained by changes in the P. agardhii biomass. The highest toxin content was observed when P. agardhii biomass was the lowest, which suggests changes in the proportion of microcystin-producing and -nonproducing subpopulations and/or the physiological status of cells.

Do stormwater source control policies deliver the right hydrologic outcomes?

“…The outlet is equipped, since 2003, with a settling unit to protect the lakes from suspended solids and eutrophication (Catherine et al, 2008).…”

Spatiotemporal changes in the genetic diversity of a bloom-forming Microcystis aeruginosa (cyanobacteria) population

“…In attempts to find out what governs cyanobacterial proliferations, over the past 10 years an increasing number of papers have dealt with the relative importance of biological, physicochemical and weather (for example Wiedner et al, 2002;Jacquet et al, 2005;Catherine et al, 2008). Furthermore, several publications have recently investigated the genetic diversity of some bloom-forming cyanobacterial populations, to assess their population structure (for example Barker et al, 2000;Wilson et al, 2005;Tanabe et al, 2007) or to find out whether biogeographic differentiation occurs between these populations at different spatial scales (for example Bittencourt-Oliveira et al, 2001;Hayes et al, 2002;Laamanen et al, 2002;Gugger et al, 2005).…”

Rapid regulation of phosphate uptake in freshwater cyanobacterial blooms

“…The rapid adaptive behaviour may explain the predominance of bloom-forming cyanobacteria in freshwaters under apparently suboptimal conditions. As shown here and in other studies, Planktothrix agardhii is able to endure several months with phosphate concentrations below detection limits (Catherine et al 2008). The predominance of bloom forming cyanobacteria must be maintained by phosphate fluctuations that are invisible to lake monitoring programs due to their short timescales (Glibert et al 2008) and low cyanobacterial threshold values.…”

“…Cyanobacterial blooms are frequently stable and resilient in lakes (Scheffer et al 1997, Bonilla et al 2012, even after dissolved nutrient depletion (Catherine et al 2008). Cyanobacterial dominance is generally explained by competitive advantages in ex ploiting low phosphate concentrations, including high affinity and maximum velocity of cellular uptake systems, and by high nutrient storage capacity (Istvánovics et al 2000, Moutin et al 2002, Antenucci et al 2005, Burford & O'Donohue 2006, Casey et al 2009, Posselt et al 2009).…”