Spatial and temporal patterns in microcystin toxins in Lake of the Woods surface waters

Figures & data

Figure 1. Map of Lake of the Woods (Canada and US) with each of the six ECCC-designated lake zones identified. Dots represent sampling locations offshore in 2006 (brown), 2008–2010 (orange), and 2014–2015 (orange) and nearshore in 2006 (yellow) and 2009 (green).

Table 1. Summary statistics for surface water (1 m depth) particulate MCs (2006, 2008–2010, and 2014–2015) and total MCs (MC) (2010 only) in LOW in combined sites in each ECCC zone measured using ELISA (or PPIA if noted).

Zone	Measure	Mean	Std Dev	Max	Min
	Particulate MC/Chl-a (µg/µg)	0.016	0.026	0.076	0.000
1	Particulate MC(PPIA)/Chl-a (µg/µg)	0.014	0.013	0.039	0.001
	Total MC (µg/L)	0.546	0.128	0.707	0.402
	Particulate MC (µg/L)	0.100	0.129	0.389	0.017
	Particulate MC/Chl-a (µg/µg)	0.008	0.010	0.025	0.001
2	Particulate MC(PPIA)/Chl-a (µg/µg)	0.005	0.005	0.016	0.001
	Total MC (µg/L)	0.140	0.190	0.274	0.005
	Particulate MC (µg/L)	0.114	0.150	0.418	0.015
	Particulate MC/Chl-a (µg/µg)	0.007	0.010	0.028	0.001
3	Particulate MC(PPIA)/Chl-a (µg/µg)	0.012	0.010	0.027	0.002
	Total MC (µg/L)	0.122	0.166	0.357	0.005
	Particulate MC (µg/L)	0.062	0.069	0.227	0.012
	Particulate MC/Chl-a (µg/µg)	0.029	0.037	0.083	0.004
4	Particulate MC(PPIA)/Chl-a (µg/µg)	0.057	0.094	0.197	0.004
	Total MC (µg/L)	0.005	0.000	0.005	0.005
	Particulate MC (µg/L)	0.059	0.052	0.133	0.022
	Particulate MC/Chl-a (µg/µg)	0.020	0.021	0.066	0.002
5	Particulate MC(PPIA)/Chl-a (µg/µg)	0.025	0.025	0.079	0.001
	Total MC (µg/L)	0.235	0.236	0.602	0.005
	Particulate MC (µg/L)	0.082	0.076	0.237	0.017
	Particulate MC/Chl-a (µg/µg)	0.013	0.013	0.033	0.003
6	Particulate MC(PPIA)/Chl-a (µg/µg)	0.033	0.031	0.079	0.003
	Total MC (µg/L)	0.005	0.000	0.005	0.005
	Particulate MC (µg/L)	0.047	0.045	0.118	0.009

Figure 2. Box and whisker plots of total microcystin (MC) (top; 2010) and particulate MC (bottom; 2008–2009) in 1 m grab samples offshore among ECCC lake zones as measured by ELISA.

Figure 3. Comparison of Chl-a-normalised total microcystin (MC) analysed using ELISA (top) and PPIA (bottom) across ECCC lake zones, 2008–2009.

Figure 4. Particulate microcystin (MC) from collective data sources, 2006–2009 with a comparison among years (top) and comparison among ECCC zones (bottom).

Table 2. Particulate MC measured in net tows, LOW September 2009.

			Distance from	Particulate MC
Station	Zone	Date	shore (m)	(µg /g dwt)
710	1	23-Sep-09	144	9.6
411	2	23-Sep-09	738	16.5
510	2	23-Sep-09	2076	189.7
530	2	22-Sep-09	294	1.6
Duck Bay Dock	2	23-Sep-09	20	13.4
Turtle Bay	2	23-Sep-09		34.4
W. Hanson Bay	2	23-Sep-09		8.1
210	3	22-Sep-09	302	39.1
211	3	22-Sep-09		117.7
220	3	18-Sep-09	271	11.9
310	4	21-Sep-09	439	13.1
French Portage	4	22-Sep-09		90.9
Whylie Point	4	6-Sep-09		7.4
110	5	16-Sep-09	297	25.7
111	5	20-Sep-09	83	36.1
120	5	1-Sep-09	243	182.9
140	5	15-Sep-09	99	101.6
181	5	9-Sep-09	149	10.3
182	5	19-Sep-09		17.0
910	6	23-Sep-09	123	54.1

Table 3. Mean, median and range of surface water (1 m) MC concentrations in Lake of the Woods in 2009. Concentrations are reported as µg MC-LR equivalents/L.

Location	# samples	Mean	Median	Range
Clearwater Bay	9	< 0.10	< 0.10	< 0.10 to 0.17
Lobstick Bay	4	0.16	< 0.10	< 0.10 to 0.49
Town Island	4	2.20	2.50	< 0.10 to 3.73
Channel Island	2	4.26	4.26	3.16 to 5.36
Frenchman's Rock Road	4	9.05	5.96	0.87 to 45.57
Pine Portage Bay	4	17.31	4.69	0.16 to 59.69
Sunbath Island	4	47.32	39.03	5.73 to 105.37
Nestor Falls	4	40.35	7.31	0.21 to 146.55
Bigstone Bay	4	264.33	231.58	48.42 to 545.71

Figure 5. Concentration of microcystin (MC) along a shoreline near Frenchman's Rock Road (September 24, 2009). Sampling sites were located 5 m apart and collected within 30 sec. of each other. World Health Organization recreational risk categories: <10 µg MC-LR equivalents/L – Low risk, 10–20 µg MC-LR equivalents/L – Moderate Risk, >20 µg MC-LR equivalents/L – High risk.

Table 4. Correlation analysis between cyanobacterial species abundance and MC concentration in shoreline samples (n = 24).

Species	Correlation Coefficient (r)	P value
Microcystis ichthyoblabe	0.69	< 0.001
Microcystis (all species combined)	0.78	< 0.001
Dolichospermum flos-aquae	0.88	< 0.001
Dolichospermum circinale	0.61	0.001
Dolichospermum (all species combined)	0.87	< 0.001

Table 5. Percent of shoreline samples with MC concentration in excess of 20 µg MC-LR equivalents/L and which cyanobacterial species are either dominant (i.e. >50% of the total cyanobacterial biomass in the sample) or co-dominant (i.e. 25–49% of the total cyanobacterial biomass in the sample).

	% of samples where species is
Species	dominant or co-dominant
Microcystis (all species combined)	72
Microcystis ichthyoblabe	45
Microcystis sp.	36
Microcystis aeruginosa	27
Microcystis flos-aquae	18
Microcystis smithii	9
Dolichospermum (all species combined)	81
Dolichospermum flos-aquae	72
Dolichospermum mendotae	63
Dolichospermum lemmermannii	36
Dolichospermum crassum	18
Dolichospermum planktonicum	9
Dolichospermum circinale	9
Pseudanabaena sp.	9
Woronichinia sp.	9
Aphanizomenon (all species combined)	72
Aphanizomenon flos-aquae complex	55