Multi-year succession of cyanobacteria blooms in a highland reservoir with changing nutrient status, Guizhou Province, China

Abstract

Over the last 22 years significant phytoplankton changes in Hongfeng lake reservoir have been observed with multiple years of harmful cyanobacteria blooms (cHABs). Fish farming and other anthropogenic activities from 1994-2001 triggered the harmful blooms. Nine years after the cessation of aquaculture, a conversion from problematic species (Microcystis spp, Aphanizomenon flos-aquae) to the less problematic species P. limnetica and other associated non-cyanobacteria taxa was recorded. Through this period of change, trophic factors (bottom-up) were re-examined, and correlations between cHABs and selected environmental variables were observed. Higher temperatures, nutrients [total nitrogen (TN), total phosphorus (TP)] and available light significantly favored the development of Microcystis spp blooms. With declining nutrient loads, and a decline in TP relative to TN there was a competitive shift from Microcystis summer blooms to the growth of Pseudanabaena limnetica and other non-cyanobacteria. Pseudanabaena limnetica was favored over Microcystis spp when temperatures were <20°C and TP was <0.03 mg L -1 . The apparent species succession to P. limnetica was enhanced by a competitive advantage under varied light conditions. Multiple environmental and biotic conditions (not always nutrients) were driving cHABs. Although only a selected number of environmental variables were examined, the CCA analysis supports observations that temperature and nutrients were associated with the species shift. The replacement of cHABs with the growth of less toxic cyanobacteria like P. limnetica, and other algae creates an interesting scenario (new community condition) for the removal of problematic taxa in reservoir systems. Diverting or controlling blooms will have direct implications on water quality and economic remediation initiatives in reservoir and lake management.

Unusual massive phytoplankton bloom in the oligotrophic Lake Tanganyika

“…Microcystis spp. blooms for instance are favoured by higher temperatures, higher nutrient (TN, TP) contents, and reasonable light (Pick 2016;Long et al 2018), while Pseudanabaena limnetica is favoured by lower temperature (< 20°C) as observed during a monitoring in the Hongfeng Lake reservoir (Guizhou Province, China) (Long et al 2018). Moreover, Microcystis spp.…”

“…Strong SE trade winds in 2018 most likely induced a strong tilting of the thermocline and the Dolichospermum flosaquae bloom observed in September, just after the dry season winds, is likely the consequence of an upward movement of hypolimnion nutrient-rich water at this moment of the year as water layers oscillate to recover initial depths (Mortimer 1974;Plisnier et al 1999). Nutrient loading of anthropogenic impact or erosion are in this case not responsible for the Cocquyt et al, Phytoplankton bloom in Lake Tanganyika cyanobacteria bloom as often observed in aquatic ecosystems (Paerl & Huisman 2009;Long et al 2018). Rivers flowing into Lake Tanganyika are colder than the surface water of the lake and quickly sink into the hypolimnion (Capart 1949;Pierre-Denis Plisnier, pers.…”

“…Species switches in cyanobacterial blooms are well known and documented (Long et al 2018). Microcystis spp.…”

“…An increase of cyanobacterial blooms in freshwater ecosystems has been reported during the last decades (e.g. Paerl & Huisman 2009;Long et al 2018). Anthropogenic nutrient loading and global warming with its impact on the vertical stratification in lakes and reservoirs seem to play an important role in this increase.…”

How Accurate Is an Unmanned Aerial Vehicle Data-Based Model Applied on Satellite Imagery for Chlorophyll-a Estimation in Freshwater Bodies?

“…Dinoflagellates-based or diatoms blooms are not as harmful to citizens as cyanobacteriabased blooms, but their massive growth is as degrading to the freshwater quality and to the entire aquatic ecosystem as cyanobacteria blooms [3]. Additionally, Long et al [4] have reported a positive relationship between the biomass of phytoplankton as well as the concentration of their main pigment, Chlorophyll-a (chl_a), and the biomass of cyanobacteria. For these reasons, the World Health Organization (WHO) has listed chl_a as a mandatory parameter to measure in freshwater guidance level for cyanobacteriarelated risk (https://www.who.int/water_sanitation_health/bathing/srwe1-chap8.pdf, accessed on 4 February 2021).…”