Distribution and flux of microcystin congeners in lake sediments

Figures & data

Figure 1. Microcystin congener concentrations on sediment particles in the top 6.25 cm of a 40 cm sediment core from Hay Island, Lake of the Woods, Ontario. Below 6.25 cm, measurements were below the method detection limit. Interval midpoints are plotted (0.5 cm intervals from 0 to 7 cm). MC-LF and -LY were not detected in sediment. We analyzed a total of 80 half-cm intervals.

Figure 2. Individual microcystin congeners in the pore water of a 40 cm sediment core from Lake of the Woods (Hay Island) as a percentage of the congener in pore water and on sediment particles summed. Interval midpoints are plotted (0.5 cm intervals from 0 to 7 cm). Open circle (○) = LA, × = LR. RR, LW, 7dmLR, YR, and WR were not detected in pore water. MC-LF and -LY were not detected in the sediment core. We analyzed a total of 80 half-cm intervals.

Table 1. The number of sediment intervals where microcystin congeners were detected in a 40 cm core from Hay Island, Lake of the Woods, Ontario. We analyzed a total of 80 half-cm intervals.

	Intervals where	Intervals where detected
Congener	detected	in pore water
LR	13	1
LA	9	5
RR	2	0
7dmLR, YR, LW, WR	1	0
LY, LF	0	0

Table 2. Concentrations, sedimentation rates, burial rates, and sediment–water diffusive fluxes of microcystin congeners (MC-LR and -LA) at 3 sites in Lake of the Woods: Hay Island (HI), Rat Portage Bay (RP), and Bigstone Bay (BB).

		Sedimenta(ng/g dw)		Pore watera(ng/L)		Overlying water (ng/L)		Sub-surface (5 m) (ng/L)		Buriala(ng/m^2/d)		Diffusionb(ng/m^2/d)
Site (m depth)	Sedimentation (g/m^2/d)	LA	LR	LA	LR	LA	LR	LA	LR	LA	LR	LA	LR
HI (13)	0.82	39	364	1600	1230	1048	960	1590	1260	32	298	646	303
RP (23)	1.6	5	19	1731	2044	638	1545	110	280	9	32	1078	492
BB (23)	0.62	4	10	1595	1433	660	929	270	420	3	7	1050	566
Mean	1.0	16	131	1642	1569	782	1145	657	653	15	112	925	454
SD	0.54	20	202	77	424	231	347	812	530	15	162	242	136

^a Calculated using measurements made on the 0–0.5 cm interval.

^b Calculated using a microcystin diffusion coefficient of 1.4 × 10⁻⁶ cm²/s, porosity of 0.99, tortuosity of 1.02, and the concentration gradient between the pore water of sediments (0–0.5 cm) and water overlying sediment.

Figure 3. A schematic summary of the burial rates and diffusive fluxes of microcystin congeners (MC-LR and -LA; mean ± SD) in surficial sediments (0–0.5 cm) and at the sediment–water interface at 3 sites in Lake of the Woods (Hay Island, Rat Portage Bay, Bigstone Bay).