Lake of the Woods phyto- and picoplankton: spatiotemporal patterns in blooms, community composition, and nutrient status

Figures & data

Figure 1. Map of Lake of the Woods showing major hydrologic zones (1–6) and sampling sites, 2008–2010.

Figure 2. Top left: Seasonal (Jun–Sep) average total phosphorus (TP) vs. chlorophyll (chl) plotted for north temperate lakes dataset (NTLk) and collective data from Lake of the Woods (LOW); top right: LOW data plotted on a smaller scale to show relationship within this lake. Bottom left: Seasonal (Jun–Sep) average TP vs. total algal biomass and (bottom right) total cyanobacteria biomass, plotted for large among-lakes dataset (Watson et al. 1997, light blue symbols) and LOW, using collective data from this and other LOW studies (see text).

Table 1. Summary results of multivariate analysis for nonlinear models of (log) Chl-a vs. log total phosphorus (LTP) across each LOW zone using backward selection (α = 0.05); only significant relationships reported.

LOW zone	N	Model	F	Pr > F
All data	143	−0.198 + 0.096 [LTP]^2	141.5	<0.0001
1	23	−0.324 + 0.102 [LTP]^2	17.9	0.0004
2	21	−0.692 + 0.144 [LTP]^2	13.7	0.0015
3	28	−0.123 +.0876 [LTP]^2	14.8	0.0007
4	12	−0.676 + 0.171 [LTP]^2	12.6	0.0053
5	40	9.908 −11.00 [LTP]	12.0	<0.0001
		+ 4.007[LTP]^2 − 0.454 [LTP]^3
6	19	−1.482 + 0.747 [LTP]	14.9	0.0013

Figure 3. Box and whisker plot of total phytoplankton biomass in LOW from subsurface samples (1 m) at the six in-lake EC zones. Data from 1998 to 2010 (see text).

Table 2. Summary statistics of biomass for total phytoplankton (TB), cyanobacteria (CYAN), N-fixers (Nfix), Dolichospermum spp. (Dol), Aphanizomenon spp. (Aph), and levels of total microcystin toxins (MC) in LOW, 1998–2010; all units in µg/L.

Zone	Variable	Mean	Std Dev	Median	N
1	TBCYANNfixMCAphDol	8358807899560.2159820136	12,24812,08315,6600.28815,676152	2460223018600.0801560108	333333
2	TBCYANNfixMCAphDol	9386739964420.1956209234	6315413445540.1254316249	9145827464300.1856320110	665455
3	TBCYANNfixMCAphDol	3808341525260.111246759	3290325025220.0562482105	3937373621480.12221452.9	991031010
4	TBCYANNfixMCAphDol	13859488180.029648171	10599709760.035958218	10346135020.01015650	888588
5	TBCYANNfixMCAphDol	2986369610810.235105624	433163191374—137737	8495093350.2353314	23247177
6	TBCYANNfixMCAphDol	239520546890.02393596	452746087550.01683749	11606744100.02065305	171714131414

Figure 4. Cyanobacteria biomass (top) and percent contribution to total phytoplankton biomass (bottom) from subsurface samples (1 m) averaged across sites within in each of the six LOW hydrologic zones, 1998–2010.

Figure 5. Left: biomass of the two dominant N₂-fixing cyanobacteria taxa (Dolichospermum and Aphanizomenon) and percent contribution of Aphanizomenon to N₂-fixing biomass averaged from sites within the six zones in LOW.

Figure 6. Late-summer biomass of major taxonomic groups in samples from LOW at all LOW zones, Sep 2010. Top: all taxa; bottom: same plot with cyanobacteria removed.

Figure 7. Abundance of heterocysts associated with the two major N₂-fixing cyanobacteria taxa in LOW, Dolichospermum (gray series) and Aphanizomenon (black series), across the six hydrologic zones, Sep 2010.

Table 3. Average abundances of picoplankton (<2 µm) fractions across LOW zones, 2008–2010 (1-m samples) measured using flow cytometry. See text for abbreviations; APP/HPP = [PC + PE + Pk]/BAC.

		Abundance (cells/mL)				Abundance (cells/mL)
EC Zone	Pico fraction	Mean	Std Dev	N	Pico fraction	Mean	Std Dev	N
1	PC	9.93E + 03	9.22E + 03	19	PE	3.34E + 02	1.24E + 02	19
2	PC	3.64E + 04	4.86E + 04	18	PE	2.39E + 03	5.11E + 03	18
3	PC	2.18E + 04	3.56E + 04	22	PE	1.35E + 03	3.50E + 03	22
4	PC	8.34E + 03	1.22E + 04	9	PE	1.64E + 04	2.18E + 04	9
5	PC	1.80E + 04	1.81E + 04	28	PE	1.13E + 04	1.53E + 04	28
6	PC	9.26E + 03	1.33E + 04	16	PE	3.44E + 04	4.10E + 04	16
1	PK	1.50E + 04	8.54E + 03	19	BAC	1.79E + 06	1.21E + 06	19
2	PK	2.81E + 04	2.26E + 04	18	BAC	2.02E + 06	1.34E + 06	18
3	PK	1.51E + 04	1.24E + 04	22	BAC	1.32E + 06	7.87E + 05	22
4	PK	7.20E + 03	6.76E + 03	9	BAC	8.60E + 05	5.38E + 05	9
5	PK	1.03E + 04	5.47E + 03	28	BAC	1.47E + 06	6.49E + 05	28
6	PK	8.58E + 03	7.65E + 03	16	BAC	1.39E + 06	8.29E + 05	16
		Ratio
1	APP/HPP	0.0296	0.0356	19
2	APP/HPP	0.0424	0.0377	18
3	APP/HPP	0.0351	0.0333	22
4	APP/HPP	0.0301	0.0120	9
5	APP/HPP	0.0216	0.0151	28
6	APP/HPP	0.0422	0.0381	16

Figure 8. Spring biomass of major taxonomic groups in LOW from EC zones 1, 4, and 5, Jun 2010.

Figure 9. Phytoplankton biomass in surface (1 m) and mixed-depth integrated (0–7 m) samples at collected at station 710 (southern basin), Sep 2010. Left: all major taxa present in the samples; right: plot of all major groups with cyanobacteria removed to illustrate the changes in these less abundant taxa.

Figure 10. Phycocyanin-rich picoplankton (PC; top left), phycoerythrin-rich picoplankton (PE; top right), eukaryotic picoplankton (Pk; bottom left), and bacteria (BAC; bottom right) across zones 1–6, 2008–2010 (1-m samples).

Figure 11. Phycoerythrin-rich picoplankton (PE; cells < 2 µm) vs. total dissolved P (top) and secchi depth (bottom); black symbols: southern zones 1–3; gray symbols: northern zones 4–6.

Table 4. Summary results of multivariate analysis for picoplankton groups (cells/mL) against major physico-chemical parameters (all P, N, and C fractions; Zmax, Zmix, Secchi, ashed dry mass [ADM], ash-free dry mass [AFDM}), DO at [bottom-2 m] depth, temperature of the mixed layer, Tzm) using backward selection (α = 0.05); only significant relationships reported.

PICO fraction	Variable	Parameterestimate	F	Pr > F
Log PE	TDP	−0.081	62.2	<0.0001
	DIN	−0.005	27.1	<0.0001
	P × N	0.0002	40.9	<0.0001
	TP × TN	−0.000006	7.9	0.0050
	Secchi	0.475	226.42	<0.0001
	ADM	−0.238	35.92	<0.0001
Log PC	DOC	0.14992	17.98	<0.0001
	TDP	−0.03553	4.51	0.0365
	DOmin	−0.06324	6.92	0.0100
	Zmix	−0.03059	9.09	0.0033
Log Pk	Secchi	−0.123	20.14	<0.0001
	DOC	0.018	15.03	0.0002
Log BAC	Tzm	0.03228	18.08	<0.0001

Table 5. Summary statistics, bacterial abundance (cells/mL), all sites, 2008–2010.

	cells/mL
Sample	Mean	Std Dev	N
1 m	1.82E + 06	9.81E + 05	28
Depth integrated	1.81E + 06	1.00E + 06	21
Bottom-1 m	1.37E + 06	8.98E + 05	26

Table 6. Summary statistics for nutrient deficiency indicators, all data (1 m); bold font indicative of deficiency according to criterion levels (shown in brackets) from Healey and Hendzel (1980). Stoichiometric ratios measured as moles, N-debt as µmN/Chl-a/day.

	P deficiency				N deficiency
Zone	Metric	Mean	Std Dev	N	Metric	Mean	Std Dev	N
1	C:P(129–258)	154.9	43.1	22	C:N (molar)(8.3–14.6)	8.3	1.9	22
2		143.1	80.6	21		7	0.6	21
3		175.7	77.9	26		6.9	1.1	27
4		147.4	50.9	12		7.6	1	12
5		163.4	73	36		6.8	0.8	36
6		152.1	39.9	19		7.6	1.3	19
1	N:P(>22)	19.4	6.9	22	N-Debt>0.015	0.168	0.373	23
2		20.9	12.6	21		0.149	0.247	21
3		26.2	12.2	26		0.819	2.157	31
4		19.6	7.1	12		0.207	0.498	12
5		24.1	10.6	36		0.485	1.31	40
6		20.3	5.5	19		1.336	2.296	19

Table 7. Results of multivariate analysis for general deficiency indicators against major physico-chemical and class variables (TDP, DIN, Si, Zmix/Zmax, Secchi) using backward selection (α = 0.05). Only significant relationships shown.

IndicatorVariable	Parameterestimate	F	Pr > F
C:Chl-a Si	−2.81328	15.90	0.0002
Chl-a/PP Si	0.08214	6.93	0.01

Watson S, McCauley E, Downing JA. 1997. Patterns in phytoplankton taxonomic composition across temperate lakes of differing nutrient status. Limnol Oceanogr. 42:487–495.

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Healey FP, Hendzel LL. 1980. Physiological indicators of nutrient deficiency in lake phytoplankton. Can J Fish Aquat Sci. 37:442–453.

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