Annual variations in microcystin occurrence in Upper Klamath Lake, Oregon, based on high-throughput DNA sequencing, qPCR, and environmental parameters

Figures & data

Table 1. Sample collection schedule and analyses performed 2013 and 2014.

Number of samples	Dates collected (weekly)	Analysis or data collected
2013
19	20 May–24 Sep	Water temperature, pH, dissolved oxygen, specific conductance
19	20 May–24 Sep	Nutrients and chlorophyll a
10	9 Jul–10 Sep	DNA sequencing, total bacteria
14	11 Jul–10 Sep	Microcystins
10	9 Jul–10 Sep	qPCR, total cyanobacteria, total Microcystis, and mcy+ Microcystis
2014
20	5 Jun–14 Oct	Water temperature, pH, dissolved oxygen, specific conductance
20	5 Jun–14 Oct	Nutrients and chlorophyll a
14	11 Jun–8 Sep	DNA sequencing, total bacteria
16	11 Jun–22 Sep	Microcystins
14	11 Jun–8 Sep	qPCR, total cyanobacteria, total Microcystis, and mcy+ Microcystis
16	4 Jun–5 Sep	qPCR, Aphanizomenon cpcA
9	21 Jul–15 Sep	qPCR, Microcystis cpcB

Table 2a. Median, ranges, and interannual comparisons (based on Wilcoxon or similar tests) of microcystin concentrations and qPCR-estimated abundances (as cell equivalents/mL) and ratios of total cyanobacteria, total Microcystis, and mcyE+ Microcystis measured in Upper Klamath Lake in 2013 and 2014. Aphanizomenon cpcA and Microcystis cpcB were quantified in 2014 only. Significant differences (p > 0.05) are in boldface. The “greater than” years without significant p values indicate that values were higher, but the difference between years was not statistically significant.

Parameters	2013		2014		Paired-sample t-test result, 2013 versus 2014
	Median	Range	Median	Range	Jun/Jul	p Value		Aug/Sep	p Value
Dissolved-phase microcystins (µg/L)	0.10	<0.10–0.38	0.10	<0.10–3.55	2013 ≈ 2014	1.00		2013 < 2014	0.038
Particulate-phase microcystins (µg/L)	0.13	<0.10–0.61	0.11	<0.10–51.9	2013 ≈ 2014	0.902		2013 ∼ 2014	0.251
Total cyanobacteria (16S rRNA)	6,791	843–18,044	280,143	38,905–4,197,071	2013 < 2014	0.006		2013 < 2014	0.001
Total Microcystis (16S rRNA)	185	2.55–1,079	3586	20.0–150,661	2013 ≈ 2014	0.788		2013 < 2014	0.001
Total Microcystis (cpcB)			8531	1702–101,793
Microcystis (mcyE)	16.9	3.50–379	4385	20.2–47,113	2013 ≈ 2014	0.536		2013 < 2014	0.001
Aphanizomenon (cpcA)			12,949	560–100,428

Figure 1. Changes in copy number (as cell equivalents per mL of water sample) of (A) cyanobacteria 16S rRNA in 2013; (B) cyanobacteria 16S rRNA in 2014; (C) Microcystis 16S rRNA and Microcystis-specific mcyE in 2013; and (D) Microcystis 16S rRNA, Microcystis-specific mcyE, and Aphanizomenon cpcA in 2014. Error bars represent standard deviation. The first day of each month is shown by a vertical line. Asterisk indicates no detection of Microcystis (16S rRNA); + indicates no detection of mcyE.

Table 2b. Median, ranges, and interannual comparisons (based on Wilcoxon or similar tests) of environmental parameters measured in Upper Klamath Lake in 2013 and 2014. Significant differences (p > 0.05) are in boldface.

Parameters	2013		2014		Paired-sample t-test result, 2013 versus 2014
	Median	Range	Median	Range	Jun/Jul	p Value	Aug/Sep	p Value
Water temperature (C)	19.7	13.6–23.1	18.4	14.1–23.6	2013 ≈ 2014	0.796	2013 ≈ 2014	0.500
pH	8.65	7.20–9.85	8.28	7.15–10.0	2013 ≈ 2014	0.627	2013 ≈ 2014	0.630
Dissolved oxygen (mg/L)	5.40	1.95–9.85	6.30	2.65–9.65	2013 ≈ 2014	0.863	2013 ≈ 2014	0.074
Specific conductance (µS/cm)	119	113–128	121	115–132	2013 ≈ 2014	0.164	2013 ≈ 2014	0.193
Chlorophyll a (µg/L)	88.7	6.40–478	84.9	3.50–486	2013 ≈ 2014	0.265	2013 ≈ 2014	0.151
Phycocyanin fluorescence (RFU)	4.50	0.80–44.8	5.65	0.80–20.6	2013 ≈ 2014	0.427	2013 < 2014	0.038
TN (mg/L)	1.95	0.69–6.39	1.90	0.79–5.38	2013 ≈ 2014	0.489	2013 ≈ 2014	0.963
TP (mg/L)	0.12	0.10–0.52	0.18	0.08–0.45	2013 ≈ 2014	0.723	2013 ≈ 2014	0.130
TN:TP	11.9	6.25–16.3	10.2	5.27–14.2	2013 > 2014	0.040	2013 > 2014	0.004
NH4 (µg/L)	116	7.00–745	90.5	16.0–443	2013 ≈ 2014	0.693	2013 ≈ 2014	0.060
NO2^−-NO3^− (µg/L)	14.5	<8.00–465	41.2	<8.00–395	2013 < 2014	0.046	2013 > 2014	0.011
NH4-N:NOx-N	2.61	0.13–26.4	1.97	0.14–10.39	2013 > 2014	0.044	2013 ≈ 2014	0.736
DIN (µg/L)	232	9.00–858	139	16.0–554
DIP (µg/L)	48.0	9.00–151	69.2	20.5–223	2013 ≈ 2014	0.143	2013 ≈ 2014	0.810
DIN:DIP	3.19	0.22–18.7	1.66	0.35–9.55	2013 ≈ 2014	0.489	2013 > 2014	0.001
Dissolved-phase microcystins (µg/L)	0.10	<0.10–0.38	0.10	<0.10–3.55	2013 ≈ 2014	1.00	2013 < 2014	0.038
Particulate-phase microcystins (µg/L)	0.13	<0.10–0.61	0.11	<0.10–51.9	2013 ≈ 2014	0.902	2013 ≈ 2014	0.251
Total microcystins (µg/L)	0.14	<0.10–0.91	0.14	<0.10–53.7

Figure 2. Variations in (A) chlorophyll a concentration, (B) pH, (C) water temperature, and (D) dissolved oxygen concentration in 2013 and 2014. The first day of each month is shown by a vertical line. Water temperature, dissolved oxygen, and pH are average values from the sensors positioned at 3.5 m and 10.5 m in the water column.

Figure 3. Variations in (A) TN concentration, (B) TP concentration, (C) ammonia concentration, (D) nitrite-plus-nitrate concentration, (E) DIN concentration, and (F) DIP concentration in 2013 and 2014. The first day of each month is shown by a vertical line.

Table 3. Change in total and dissolved nutrient concentrations for time periods leading up to and leading away from maxima TN concentrations in 2013 and 2014.

Dates	Direction of TN change	Change in TP (ΔTP) mg/L	Change in TN (ΔTN) mg/L	ΔTN/ΔTP	Change in DIP (ΔDIP) mg/L	Change in DIN (ΔDIN) mg/L
2013
28 May–9 Jul	Rising	+0.41	+5.70	13.9 (+)	+0.08	+0.24
9 Jul–16 Jul	Falling	−0.15	−2.66	17.7 (−)	+0.01	−0.08
16 Jul–30 Jul	Rising	+0.04	+0.69	17.3 (+)	+0.02	+0.03
30 Jul–3 Sep	Falling	−0.31	−3.01	9.70 (−)	−0.11	+0.38
2014
5 Jun–23 Jun	Rising	+0.23	+4.59	20.0 (+)	−0.06	+0.05
23 Jun–21 Jul	Falling	−0.03	−3.13	104 (−)	+0.18	+0.39
4 Aug–11 Aug	Rising	+0.12	+2.55	21.4 (+)	−0.06	+0.08
11 Aug–25 Aug	Falling	−0.32	−3.47	10.8 (−)	−0.09	+0.02
August 25–September 2	Rising	+0.09	+0.79	8.80 (+)	−0.02	−0.32
2 Sep–15 Sep	Falling	−0.11	−1.11	10.1 (−)	−0.01	−0.08

Figure 4. Variations in (A) TN:TP ratio, (B) NH₄-N:NO_x-N ratio, and (D) DIN:DIP ratio in 2013 and 2014. The first day of each month is shown by a vertical line.