Microcystin in Missouri reservoirs

Figures & data

Table 1 Provincial medians (med) and ranges of landscape, morphological, and limnological variables.

	Ozark Highlands			Ozark Border			Osage Plains			Glacial Plains
Variable	n	Med	Range	n	Med	Range	n	Med	Range	n	med	Range
Landscape
Watershed area (Ha)	29	5,309	155–1,544,940	25	502	50–38,632	20	2,611	253–4,631,671	103	677	25–1,503,965
% Urban cover	29	0	0–6	25	0	0–47	20	2	0–77	103	2	0–32
% Forest cover	29	66	28–94	25	40	0–82	20	10	0–31	103	12	0–84
% Crop cover	29	2	0–11	25	10	0–52	20	24	7–59	103	28	0–70
% Grass cover	29	24	1–59	25	34	0–74	20	46	9–73	103	39	1–78
Morphological
Mean depth (m)	29	3.7	1.8–12.3	25	3.4	1.4–9.8	20	3.2	1.0–9.6	103	2.7	1.1–8.5
Reservoir area (Ha)	29	96	6–51,334	25	46	7–379	20	109	14–53,814	103	40	5–18,524
Reservoir volume (Ha m)	29	1,900	80–2,020,000	25	796	60–13,782	20	1,400	57–1,202,700	103	450	10–500,040
Flushing rate (Yrs)	29	1.75	0.23–87	25	0.66	0.22–42	20	1.5	0.43–6.0	103	0.73	0.03–7.0
Limnological
Temperature (°C)	245	26.6	16.3–33.5	127	27.6	16.8–33.5	140	26.3	19.5–32.3	890	26.2	14.2–34.3
Dissolved oxygen (mg/L)	245	6.0	2.7–11.5	127	6.0	1.5–11.6	140	5.3	1.8–9.7	890	6.9	2.1–15.3
Secchi (m)	245	2.1	0.4–7.9	127	1.1	0.2–4.8	140	0.8	0.09–2.5	890	1.0	0.01–7.1
Total nitrogen (mg/L)	245	380	40–1,050	127	640	270–2,230	140	870	380–1,810	890	840	240–3,120
Total phosphorus (μg/L)	245	14	3–67	127	36	5–257	140	49	20–237	890	41	6–346
TN:TP	245	25.6	5.7–180	127	18.7	5.0–78.3	140	17.4	4.8–35.6	890	19.8	4.5–66.2
Chlorophyll (μg/L)	245	6	1–70	127	15	2–265	140	27	4–185	890	18	1–342
Chl:TP	245	0.4	0.08–1.16	127	0.4	0.02–2.0	140	0.5	0.03–1.4	890	0.4	0.01–2.2
Nonvolatile solids (mg/L)	245	1.1	0.07–9.6	127	1.9	0–14.3	140	3.6	0.6–22.0	890	3.0	0–42.8
Volatile solids (mg/L)	245	1.4	0.3–9.8	127	2.6	0.3–21.6	140	4.3	1.0–17.0	890	3.5	0.2–37.6
Total solids (mg/L)	245	2.7	0.6–14.6	127	4.7	0.9–28.8	140	8.4	2.1–38.0	890	7.1	0.3–51.2
Conductivity (μS)	245	168	25–368	127	118	16–489	140	193	67–401	890	186	24–613
Turbidity (NTU)	245	2.1	0.5–19.4	127	3.9	0.8–36.3	140	6.3	1.9–80.2	890	5.2	0.5–126
Dissolved organic carbon (mg/L)	245	3.5	1.0–7.0	127	5.5	3.0–11.9	140	5.4	3.3–7.8	890	6.6	3.9–12.4
Note: For landscape and morphological variables n indicates the number reservoirs; for limnological variables n indicates the number of measurements.

Table 2 Regional means, medians, and maxima of total microcystin values. Summary statistics are based on samples collected in each region.

			Total microcystin (μg/L)
Region	Reservoir n	% Detection	n	% Detection	Mean	Median	Maximum
Ozark Highlands	29	52	245	11	< 0.1	< 0.1	1.2
Ozark Border	25	44	127	20	0.15	< 0.1	3.1
Osage Plains	20	80	140	34	0.19	< 0.1	4.9
Glacial Plains	103	58	890	25	0.32	< 0.1	21
Note: Reservoir n indicates the number of reservoirs in each region. n indicates the number of samples collected in each region.

Figure 1 Physiographic location of reservoirs sampled in Missouri and total microcystin occurrence and concentration.

Figure 2 Occurrence and concentration of total microcystin in Missouri reservoirs. The World Health Organization (WHO) microcystin guidelines for finished drinking water and full-body contact recreation are 1 and 20 μg/L, respectively. (A) Occurrence and concentration among samples (n = 1402), (B) occurrence and concentration among reservoirs (n = 177).

Table 3 Monthly means, medians, and maxima of total microcystin values. Summary statistics are based on samples collected during each month.

			Total microcystin (μg/L)
Month	Reservoir n	% Detection	n	% Detection	Mean	Median	Maximum
May	153	18	281	12	0.14	< 0.1	13
June	176	40	464	24	0.33	< 0.1	21
July	177	35	464	20	0.28	< 0.1	11
August	148	35	381	22	0.18	< 0.1	4.6
Note: Reservoir n indicates the number of reservoirs sampled each month. n indicates the number of samples collected during each month.

Table 4 Annual means, medians, and maxima of total microcystin values. Summary statistics are based on samples collected during each year.

			Total microcystin (μg/L)
Year	Reservoir n	% Detection	n	% Detection	Mean	Median	Maximum
2004	76	42	514	23	0.34	< 0.1	21
2005	95	52	380	26	0.25	< 0.1	11
2006	127	46	508	20	0.16	< 0.1	4.9
Note: Reservoir n indicates the number of reservoirs sampled each year. n indicates the number of samples collected during each year.

Table 5 Trophic class means, medians, and maxima of total microcystin values. Summary statistics are based on samples collected in each trophic class.

			Total microcystin (μg/L)
Trophic class	Reservoir n	% Detection	n	% Detection	Mean	Median	Maximum
Oligotrophic	12	33	94	5	< 0.1	< 0.1	0.33
Mesotrophic	40	45	374	10	< 0.1	< 0.1	3.1
Eutrophic	100	60	776	27	0.30	< 0.1	21
Hypereutrophic	25	80	158	42	0.51	< 0.1	10
Note: Reservoir n indicates the number of reservoirs sampled in each trophic class. n indicates the number of samples collected in each trophic class.

Table 6 Comparison of environmental variables among three microcystin concentration categories: no detectable microcystin (nd), total microcystin concentrations between 0.1–1 μg/L (0.1–1), and total microcystin concentrations greater than 1 (> 1). Significant differences between means were determined using one-way ANOVA and Tukey's pairwise comparisons.

Variable	n	Mean	Range	F-value	p-value
Landscape
% Forest cover
nd	1,071	22 ^a	0–94	24.13	< 0.01
0.1–1	270	12 ^b	0–92
> 1	49	8 ^b	1–56
% Crop cover
nd	1,071	10 ^a	0–78	35.27	< 0.01
0.1–1	270	23 ^b	0–78
> 1	49	28 ^b	17–78
% Grass cover
nd	1,071	35 ^a	1–78	7.26	< 0.01
0.1–1	270	39 ^b	2–78
> 1	49	44 ^b	17–78
Morphological
Mean depth (m)
nd	1,070	3.4 ^a	1.1–12.3	5.73	< 0.01
0.1–1	266	3.2 ^a	1.1–12.3
> 1	46	2.6 ^b	1.6–4.2
Limnological
Secchi (m)
nd	1,080	1.2 ^a	0.01–7.9	26.93	< 0.01
0.1–1	271	0.9 ^b	0.2–6.8
> 1	49	0.7 ^c	0.2–3.5
Total nitrogen (μg/L)
nd	1,082	646 ^a	40–3070	77.05	< 0.01
0.1–1	271	891 ^b	140–3120
> 1	49	1170 ^c	450–2230
Total phosphorus (μg/L)
nd	1,082	32 ^a	3–251	51.33	< 0.01
0.1–1	271	47 ^b	6–346
> 1	49	76 ^c	14–237
TN:TP
nd	1,082	20 ^a	4.5–180	9.48	< 0.01
0.1–1	271	19 ^a	5.5–67
> 1	49	15 ^b	5.6–44
Chlorophyll (μg/L)
nd	1,082	11 ^a	1–342	94.34	< 0.01
0.1–1	271	26 ^b	1–306
> 1	49	46 ^c	3–140
Chlorophyll: Total phosphorus
nd	1,082	0.4 ^a	0.01–2.2	70.99	< 0.01
0.1–1	271	0.6 ^b	0.06–1.6
> 1	49	0.6 ^b	0.2–1.4
Volatile suspended solids (mg/L)
nd	1,073	2.6 ^a	0.2–25	84.86	< 0.01
0.1–1	267	4.4 ^b	0.2–38
> 1	49	7.6 ^c	0.6–19
Total suspended solids (mg/L)
nd	1,072	5.4 ^a	0.3–51	37.35	< 0.01
0.1–1	267	7.2 ^b	0.7–51
> 1	49	11.5 ^c	1.0–39
Turbidity (NTU)
nd	1081	4.0 ^a	0.5–126	56.53	< 0.01
0.1–1	271	5.7 ^b	0.7–44
> 1	49	11.5 ^c	1–48
Dissolved organic carbon (mg/L)
nd	1082	5.4 ^a	1.0–11.9	44.40	< 0.01
0.1–1	271	6.4 ^b	1.4–12.4
> 1	49	7.6 ^c	3.8–11.4

Figure 3 Total microcystin (MC), total nitrogen (TN), total phosphorus (TP) and Secchi bivariate relations. Data shown as grouped into intervals for interval-maxima regression (IMR). Curves were estimated using IMR. Black points indicate the data used for IMR analysis (n = 8–16) and gray points indicate all other data. Bar graphs represent frequency distributions of MC detection within each interval used for IMR. Hash marks on the x-axes indicate oligotrophic/mesotrophic, mesotrophic/eutrophic and eutrophic/hypereutrophic cutpoints for Missouri reservoirs as defined by Jones et al. 2008a. (A) MC–TN relation (r² = 0.87, p < 0.01, values for line fitted to black points only), (B) MC–TP relation (r² = 0.75, p < 0.01), (C) MC–Secchi relation (r² = 0.93, p < 0.01). All n = 1402.