# Presence of Cyanotoxins in a Mexican Subtropical Monometric Crater Lake
## 3 Results  
The results of this study demonstrate the presence of seven MC analogs in the algae scums of the SMO lake. The MC congeners identified were MC-WR, MC-LR, MC-LA, MC-HiIR, MC-LF, MC-YR and MC-LY (Figure 4). In a weight basis, the total MC concentrations were low when compared with other zones [36; 37] and ranged between 0.15 \(\upmu\)g/kg and 6.84 \(\upmu\)g/kg (Figure 5). The MC-WR, MC-LR and MC-LA congeners dominated the toxin profile, representing 94.5% of the total sample on a percentage concentration basis, with each of these congeners contributing 39.8%, 38.1% and 16.5%, respectively (Table  
Horizontal surface distribution showed higher total microcstin values at the northern and southern part of the lake, and most of the MC congeners were detected with this general distribution pattern (Figure 6). These toxin distribution patterns can be explained by the modeled circulation cells. According to [PERSON] et al. [38], water circulation patterns in SMO lake are forced by the valley breeze circulation and the drift of currents from two circulating rings that have opposite directions: an anticyclonical direction on the northern part of the lake and a cyclonical pattern on the southern side. Thus, this circulation pattern may accumulate MCs in both rings, as demonstrated in this work.  
HPLC fluorescence detector (HPLC-FLD) chromatograms from floating scums for PST analysis showed two peaks that have the same retention time as GTX3 and dcSTX (data not shown). However, these chromatographic peaks may correspond to other natural fluorescence co-extractives from the matrix, since reanalyses of this material by mass spectrometry confirm the absence of any considered PST analogs (data not shown). Neither MCs nor PST analogs were detected in the phytoplankton samples.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Toxin** & **Mean (\%)** & **SD** \\ \hline MC-WR & 39.9 & 7.65 \\ MC-LR & 38.2 & 4.25 \\ MC-LA & 16.5 & 4.25 \\ MC-HilR & 2.7 & 0.44 \\ MC-LF & 1.5 & 1.29 \\ MC-YR & 1.1 & 0.61 \\ MC-LY & 0.19 & 0.41 \\ \hline \hline \end{tabular}
\end{table}
Table 2: MC congener contribution (as a percentage) to the total MC concentration.  
Figure 4: Ion chromatograms obtained following UHPLC-MS/MS, showing quantitative SRM transitions for detected microcstin congeners in (**A**) the high level calibration standard and (**B**) the algal scum sample from Station 4.  
Figure 5: Total microcystn distribution (ug/kg of dry weight) in algae scums in Santa Maria del Oro lake during March 2015.  
Figure 6: _Cont._  
The bloom was confirmed to be caused by the cyanobacteria _L. robusta_ and _M. aeruginosa_, although minor quantities of _Lyngbyba_ sp. were also recorded [21]. A lower cell density of _L. robusta_ (43,139 cells/mL) and number of colonies of _M. aeruginosa_ (2.9 colonies/mL) were recorded between stations 6 and 7, whereas the highest values were found between stations 8 and 9, with values of 50,936,326 cells/mL and 5300 colonies /mL for _L. robusta_ and _M. aeruginosa_, respectively (Table 3).  
\begin{table}
\begin{tabular}{c c c} \hline
**Stations** & _L. robusta_ & _M. aeruginosa_ \\ \hline
1–2 & 4,504,067 & 550 \\
2–3 & 4,987,405 & 133 \\
3–4 & 299,032 & 18 \\
4–5 & 3,962,304 & 20 \\
5–6 & 5,428,251 & 214 \\
6–7 & 43,129 & 3 \\
7–8 & 4,206,629 & 356 \\
8–9 & 50,936,326 & 5300 \\
9–10 & 373,391 & 25 \\
10–11 & 3,691,423 & 180 \\
11–12 & 992,170 & 26 \\
12–13 & 54,601,192 & 1700 \\ \hline \end{tabular}
\end{table}
Table 3: Cyanobacteria density of _L. robusta_ (cells/mL) and _M. aeruginosa_ (colonies/mL) during sampling.  
Figure 6: Surface distribution (\(\mu\)g/kg of dry weight) of microcystin congeners in algae mats in Santa Maria del Oro lake during March 2015. (**a**) MC-WR; (**b**) MC-LR; (**c**) MC-LA; (**d**) MC-HiIR; (**e**) MC-YR; (**f**) MC-LF; and (**g**) MC-LY distributions.