Blue-green algal toxin (microcystin) levels in Minnesota lakes

Figures & data

Figure 1 Study lake locations and ecoregion map. 2006 study and 2007 National Lake Assessment Project (NLAP) sites noted.

Table 1 2006 Study lake morphometric and watershed characteristics

ID	Lake	County	Area ha	Littoral %	Z max m	Z mean m	Watershed Ha
07-0047	George	Blue Earth	57	76	8.5	1.8	162
07-0053	Duck	Blue Earth	116	82	7.6	2.4	289
07-0054	Ballantyne	Blue Earth	143	86	17.6	1.8	1405
07-0060	Eagle	Blue Earth	370	100	2.7	0.9	1472
07-0096	Loon	Blue Earth	331	100	2.1	1.5	1144
07-0044	Madison	Blue Earth	1,113	64	59	10	10,828
43-0073	Hook	McLeod	132	100	3.2	1.5	1225
43-0084	Marion	McLeod	237	99	5.5	2.0	1722
43-0085	Otter	McLeod	111	100	3.6	0.9	115,378
43-0104	Stahl's	McLeod	57	100	11.2	4.0	1032
43-0115	Cedar	McLeod	779	100	2.4	1.5	3675
43-0034	Silver	McLeod	202	100	3.2	1.5	357

Table 2 Minnesota Department of Health laboratory methods and precision estimates

			Precision
Parameter	Reporting Limit & Units	Method number	Mean difference ^1	Percent of observed ^2
Total Phosphorus	3.0 μg/L	EPA365.1	4.8 μg/L	2.7%
Total Kjeldahl N	0.1 mg/L	EPA351.2	0.05 mg/L	2.8%
Total Suspended Solids	1.0 mg/L	SM2540D	2.8 mg/L	9.6%
Total Sus. Volatile Solids	1.0 mg/L	SM2540E	—	—
Alkalinity	10.0 mg/L	SM 2320B	—	—
Chloride	1.0 mg/L	EPA 325.2
Color	5.0 Pt-Co	EPA 110.2
Chlorophyll-a		SM10200H	1.7 μg/L	7.4%
Pheophytin		SM10200H	—	—

Table 3 Summer-mean pelagic water quality 2006: McLeod County lakes. Last column represents the Western Cornbelt Plain (WCBP) ecoregion reference lake interquartile range (Heiskary and Wilson 2008)

Parameter units	Cedar	Stahl's	Hook	Otter East	Otter Main	Silver	Marion	WCBP Range
TP μg/L	85	35	121	296	351	323	82	65–150
Chl a μg/L	45	13	79	88	88	252	41	30–80
Chl-a max μg/L	55	23	150	194	153	365	52	60–140
Secchi meter	0.4	1.0	0.3	0.2	0.1	0.2	0.4	0.5–1.0
TKN mg/L	1.9	1.5	2.7	2.4	2.57	5.4	1.8	1.3–2.7
Alkalinity mg/L	172	168	116	238	246	130	142	125–165
Color Pt-Co	20	20	26	28	32	26	20	15–25
pH SU	8.8	8.5	9.5	8.6	8.5	9.5	9.2	8.2–9.0
Cl mg/L	15	14	28	26	27	60	32	13–22
Total. Sus. Solids mg/L	26	7	38	41	100	49	26	7–18
T. Sus. Volatile. mg/L	16	4	28	15	24	42	16
T. Sus. Inorganic. mg/L	10	3	10	26	76	7	10	3–9
Spec. Cond. μS/cm	280	275	234	623	519	340	340	300–650
Pheophytin ug/L	9.9	2.7	7.5	20	19.7	60.2	8.3

Table 4 Summer-mean pelagic water quality 2006: Blue Earth County lakes. Last column represents the NCHF ecoregion reference lake interquartile range (Heiskary and Wilson 2008)

Parameter units	Ballantyne	Duck	Eagle	George	Loon	Madison	NCHF Range
TP μg/L	40	70	142	105	157	81	23–50
Chl a μg/L	19.3	42	75	40	82	47	5–22
Chl-a max μg/L	24	66	104	76	102	67	7–37
Secchi meter	0.8	0.8	0.3	0.5	0.3	0.7	1.5–3.2
TKN mg/L	1.4	1.5	3.1	2.0	2.9	1.8	0.60–1.2
Alkalinity mg/L	142	154	118	91	136	144	75–150
Color Pt-Co	14	10	30	24	16	18	10–20
pH SU	8.6	8.7	9.2	9.2	8.9	8.7	8.6–8.8
Cl mg/L	19	21	19	16	24	21	4–10
Total. Sus. Solids mg/L	10	13	43	23	67	10	2–6
T. Sus. Volatile. mg/L	6	10	33	17	49	8
T. Sus. Inorganic. mg/L	4	3	10	6	18	2	1–2
Spec Cond μS/cm	286	284	231	188	246	268	300–400
Pheophytin μg/L	2.7	8.3	8.0	5.2	6.0	8.8

Figure 2a Pelagic chlorophyll-a concentration by lake and date for 2006 study. Severe nuisance bloom level (30 μg/L) noted by heavy black line for perspective. Concentrations beyond scale are noted immediately below bars and ordered by date.

Figure 2b Near-shore chlorophyll-a concentrations by lake and date for 2006 study. Severe nuisance bloom level (30 μg/L) noted by heavy black line for perspective. Concentrations beyond scale are noted immediately below bars and ordered by date.

Figure 3a Pelagic microcystin (MC) concentrations by lake and date for 2006 study.

Figure 3b Near-shore microcystin (MC) concentrations by lake and date for 2006 study. MC concentrations beyond scale noted on graph.

Figure 4 Microcystin (MC) frequency distributions for 2006. Comparisons for (a) pelagic vs. near-shore MC and (b) near-shore (MC) for scum vs. no scum.

Figure 5 Spearman Correlation Coefficients (R_s) for microcystin (MC) and various chemical, physical and biological variables. See Table 3 for complete parameter names and units.

Figure 6 Cross tabulation of microcystin (MC) relative to: (a) Chlorophyll-a (bloom intensity) (108 pairs), (b) Secchi (69 pairs) and (c) pH (91 pairs) based on 2006 data. Number of observations in each category noted.

Figure 7 Microcystin (MC) box and whisker plots by study and site location for 2006 pelagic and near-shore samples; 2007 NLAP pelagic and near-shore samples, and 2004–2007 incident-based samples.

Heiskary , S. A. and Wilson , C. B. 2008 . Minnesota's approach to lake nutrient criteria development . Lake Reserv. Manage. , 24 ( 3 ) : 282 – 297 .

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