Variation of Microcystis and microcystins coupling nitrogen and phosphorus nutrients in Lake Erhai, a drinking-water source in Southwest Plateau, China

Abstract

Lake Erhai is the second largest lake of Southwest China and an important drinking water source. The lake is currently defined as the preliminary stage of eutrophic states, but facing a serious threat with transfer into intensive eutrophication. The present study examined the dynamics of Microcystis blooms and toxic Microcystis in Lake Erhai during 2010, based on quantitative real-time PCR method using 16S rRNA gene specific for Microcystis and microcystin systhesis gene (mcy), and chemical analysis on microcystin (MC) concentrations. Total Microcystis cell abundance at 16 sampling sites were shown as an average of 1.7×10 7 cells l −1 (1.3×10 2 -3.8×10 9 cells l −1 ). Microcystin LR (MC-LR) and microcystin RR (MC-RR) were the main variants. The strong southwesterly winds, anticlockwise circular flows and geographical characteristics of lake and phytoplankton community succession impacted the distribution patterns of Chl a and MC in the lake. The concentration of Chl a and MC and abundances of total Microsytis and MC-producing Microsystis (MCM) were shown to be positively correlated with pH, DO and TP, negatively correlated with SD, NO 3 -N, TN/Chl a and TN/TP, and not correlated with NH 4 -N, TN, dissolved total nitrogen (DTN) and water temperatures. When TN/TP decrease, Microcystis tended to dominate and MC concentrations tended to increase, suggesting that the "TN/TP rule" can be partially applied to explain the correlation between the cyanobacterial blooms and nutrients N and P only within a certain nutrient level. It is speculated that N and P nutrients and the associated genes (e.g., mcy) may jointly drive MC concentration and toxigenicity of Microcystis in Lake Erhai.

Dynamics and polyphasic characterization of odor-producing cyanobacterium Tychonema bourrellyi from Lake Erhai, China

“…However, compared with the cell abundance of Tychonema at the same time during 2010, total Microcystis from the same sites of Lake Erhai have higher cell abundance with an average of 1.7 × 10 7 cells L −1 (Yu et al 2014). The nutrient T. bornetii var.…”

“…Water samples were collected monthly from 12 sites in Lake Erhai from January 2009 to August 2010 (see Yu et al 2014, Fig. 1).…”

“…The cell numbers of Tychonema were calculated from the mean cycle threshold (Ct) value of three replicates according to the standard curve. Standard curves between cell concentration and Ct were created similar to the description of Yu et al (2014). The Tychonema culture under the logarithmic phase was subpackaged as six concentration gradients.…”

“…The toxigenicity of the strains was examined by the HPLC method and mcy gene (both mcyA and mcyB) approach (Yu et al 2014). However, it was shown that no T. bourrellyi strains had neither mcyA nor mcyB product, and no microcystins were detected by the HPLC method in any strains of T. bourrellyi.…”

Biomanipulation in mesocosms using silver carp in two Chinese lakes with distinct trophic states

“…The mean and maximum depths of Lake Erhai are approximately 10.7 m and 22 m, respectively. Lake Erhai has suffered continual nutrient loading and is regarded as a mesotrophic lake with TN values ranging from 0.39-0.60 mg L − 1 and TP values ranging from 0.004-0.028 mg L −1 (Yu et al, 2014).…”