Managing cyanobacteria with a water quality control curtain in Iron Gate Reservoir, California

Figures & data

Table 1. Data collected in 2015–2021 used to determine curtain condition and to test curtain effectiveness.

Parameter	Collection Method and Location	Data Collection depths (m)	Data Collection Dates	Analysis method	Use
Water temperature, C	Onset V2 loggers, 15 minute data, UC	0.1, 0.5, 1.0, 1.5, 2.0, 3.0, 4.0, 5.0, 6.0, 8.0, 10, 15, 20	15 Jun 2016–2 Nov 2021	N/A	Determine curtain condition (calculate Wn and h)
Water temperature, C	YSI EXO2 sonde, 7-8 vertical profiles per day, UC	Approximate 1 m increments from approximately 0.2 to12.0 m	7 Jul 2015–6 Oct 2015	N/A	Determine curtain condition (calculate Wn and h)
Wind speed, m/s	15 minute averages, Iron Gate Dam weather station	N/A	2015–2021^a	N/A	Determine curtain condition (calculate Wn and h)
Air temperature, C	15 minute data, Iron Gate Dam weather station	N/A	2015–2021^b	N/A	Determine curtain condition (calculate Wn and h)
Total chlorophyll a, µg/L	Peristaltic pump grab samples,^c UC and DC	0.5, 1.5, 3.0, 6.0, 9.0, and 12 m	26 grab sample dates from 13 Jul 2015–2 Sep 2020^c^,^d	fluorescence detection	Test curtain effectiveness
Total cyanobacteria 16S rRNA gene concentration (gene copies/mL)	Peristaltic pump grab samples,^c UC and DC	0.5, 1.5, 3.0, 6.0, 9.0, and 12 m	16 grab sample dates from 28 Jun 2016–2 Sep 2020^c^,^e	real-time quantitative polymerase chain reaction (qPCR)	Test curtain effectiveness
Total Microcystis spp. 16S rRNA gene concentration (gene copies/mL)	Peristaltic pump grab samples,^c UC and DC	0.5, 1.5, 3.0, 6.0, 9.0, and 12 m	16 grab sample dates from 28 Jun 2016–2 Sep 2020^c^,^e	real-time quantitative polymerase chain reaction (qPCR)	Test curtain effectiveness
Total microcystin, µg/L	Peristaltic pump grab samples,^c UC and DC	0.5, 1.5, 3.0, 6.0, 9.0, and 12 m	25 grab sample dates from 13 Jul 2015–2 Sep 2020^c^,^f	Enzyme-linked immunosorbent assay (ELISA)	Test curtain effectiveness

UC, upstream of curtain; DC, downstream of curtain; N/A, not applicable; Wn, Wedderburn number; h, mixed layer depth.

^a Iron Gate Dam wind speed data were not available from 29 Sep 2019 through 2021 (equipment malfunction); a relationship was created between Iron Gate Dam wind speeds and Montague Siskiyou County Airport (KSIY) wind speeds and data during this period were filled using adjusted KSIY data.

^b Iron Gate Dam air temperature data were not available in 2021 (equipment replacement); air temperature data during 2021 were filled using KSIY air temperature data.

^c Autosamplers were also utilized at 0.5 m and collected samples at 4 h intervals on 24 Jul 2017, 25 Jul 2017, 26 Jul 2017, and 27 Jul 2017.

^d Vertical profile grab sample dates, not including autosampler dates, included 13 Jul 2015, 21 Jul7 2015, 27 Jul 2015, 11 Aug 2015, 25 Aug 2015, 31 Aug 2015, 7 Sep 2015, 22 Sep 2015, 20 Oct 2015, 28 Jun 6 2016, 29 Aug 2016, 20 Sep 2016, 24 Jul 2017, 27 Jul 2017, 3 Aug 2017, 5 Jul 2018, 23 Jul 2018, 26 Jul 2018, 2 Aug 2018, 29 Jul 2019, 7 Aug 2019, 14 Aug 2019, 25 Sep 2019, 28 Jul 2020, 18 Aug 2020, and 2 Sep 2020.

^e Same dates as chlorophyll a, excluding 7 Aug 2019 (samples lost in mail) and all 2015 dates.

^f Same dates as chlorophyll a, excluding 7 Aug 2019 (samples lost in mail).

Figure 1. Klamath River from Upper Klamath Lake to the Pacific Ocean, and the dams of the Lower Klamath Hydroelectric Project including Iron Gate Dam.

Figure 2. Iron Gate Reservoir (left), project area (right), approximate fetch used in Wedderburn number calculations (gray dashed dotted line), and sampling locations.

Figure 3. Iron Gate Reservoir upstream and downstream of the intake barrier curtain during deployment on 27 Jul 2017 (left) and Google Earth satellite image of Iron Gate Reservoir with intake barrier curtain deployment and downstream Klamath River on 23 Aug 2019 (right).

Figure 4. Basic thermal structure of water column with epilimnetic stratification in vicinity of the curtain and Wedderburn number (Wn) within the epilimnion. Red represents warmer and blue cooler temperatures in the continous temperature scale

Figure 5. Same thermal conditions and different curtain depths (Z₁, Z₂, and Z₃), with curtain conditions (C1, C2, and C3) based on curtain depth in relation to mixed layer depth (h). Curtain effectiveness at reducing cyanobacteria and toxins is expected to be highest during conditions present in the left panel, and to be reduced from left to right panels. Red represents warmer and blue cooler temperatures in the continous temperature scale.

Figure 6. Different thermal conditions, same curtain depth (Z₁) in relation to the mixed layer depth (h). Curtain effectiveness at reducing cyanobacteria and toxins is expected to be highest during conditions present in the left panel, and less effective during conditions present in the right panel. Red represents warmer and blue cooler temperatures in the continous temperature scale.

Table 2. Curtain condition based on curtain deployment depth (z_c) and mixed layer depth (h), and sample depth subcategory based on sample depth (z_s) in relation to h.

Curtain condition	Curtain depth (zc)	Sample depth (zs)	Curtain condition and sample depth subcategory
Deployed, condition 1 (C1)	zc > 1.5 m, zc > h	zs at least 0.5 m < zc, zs ≤ h	C1a
		zs at least 0.5 m < zc, zs > h	C1b
Deployed, condition 2 (C2)	zc > 1.5 m, zc ≈ h*	zs at least 0.5 m < zc	C2a
Deployed, condition 3 (C3)	zc > 1.5 m, zc < h	zs at least 0.5 m < zc	C3a
Deployed, all zs ≈ zc	zc > 1.5 m	zs ≈ zc	C1, C2, or C3
Deployed, all zs = 1.3 to 1.4 m > zc	zc > 1.5 m	zs > zc	C1, C2, or C3
Not deployed (ND)	zc = 1.5 m	All	NDall

* h < z_c < h₂.

Figure 7. Daily average mixed layer depths (h and h₂, based on Wedderburn number [Wn] and secondary Wn upstream of the curtain, respectively), curtain depths, and grab sample collection dates during (A) 2015, (B) 2016, (C) 2017, (D) 2018, (E) 2019, (F) 2020, and (G) 2021. The curtain was installed on 26 Jun 2015. No grab samples were collected in 2021.

Figure 8. Hourly and daily average mixed layer depths (h and h₂, based on Wn and secondary Wn upstream of the curtain, respectively) and deployed curtain (light gray shading) during (A) the first week of Jun 2018, (B) the first week of Aug 2018, and (C) the first week of Oct 2018.

Figure 9. (a) Total chlorophyll a concentrations (µg/L) for 42 sample pairs collected upstream and downstream of the curtain at different depths and periods during curtain condition and sample depth subcategory C1a (curtain deeper than the mixed layer depth and sample depth shallower than or at the mixed layer depth) and (b) corresponding sample depths by date. Vertical lines with icon at 4 m denote pooled mixed layer sample from 0 to 4 m.

Figure 10. (a) Total chlorophyll a concentrations (µg/L) for 15 sample pairs collected upstream and downstream of the curtain at different depths during curtain condition and sample depth subcategory C1b (curtain deployed deeper than the mixed layer depth and sample depth deeper than the mixed layer depth) and (b) corresponding sample depths by date.

Figure 11. (a) Total chlorophyll a concentrations (µg/L) for 9 sample pairs collected upstream and downstream of the curtain at different depths during curtain condition and sample depth subcategory C2a (curtain deployed at approximately the mixed layer depth and sample depth shallower than or at the mixed layer depth) and (b) corresponding sample depths by date. Vertical line with icon at 4 m denotes pooled mixed layer sample from 0 to 4 m.

Figure 12. (a) Total chlorophyll a concentrations (µg/L) for 3 sample pairs collected upstream and downstream of the curtain at different depths during curtain condition and sample depth subcategory C3a (curtain deployed to a depth shallower than the mixed layer depth and sample depth shallower than or at the mixed layer depth) and (b) corresponding sample depths by date.

Figure 13. (a) Total chlorophyll a concentrations (µg/L) for 31 sample pairs collected upstream and downstream of the curtain while the curtain was not deployed and all sample depths (NDall), and (b) corresponding sample depths by date.

Table 3. Sign and Wilcoxon signed-rank test results for each curtain condition and sample depth subcategory for total chlorophyll a (µg/L) sample pairs (n).

Constituent	Curtain condition and sample depth subcategory	n	Sign test results (P value)	Wilcoxon signed-rank test results (P value)	Mean bias (mean Δ from UC to DC, µg/L)	Mean change (percent)
Total chlorophyll a, µg/L	Deployed, C1a	42	0.000	0.000	−67.2	−87
	Deployed, C1b	15	0.000	0.003	−9.7	−40
	Deployed, C2a	9	0.001	<0.050**	−30.7	−52
	Deployed, C3a	3	*	*	−9.7	5
	Deployed, all zs ≈ zc	5	0.013	<0.050**	−9.7	−53
	Deployed, all zs = 1.3 to 1.4 m > zc	12	0.282	0.218
	Not deployed, NDall	31	0.557	0.268

UC, upstream of curtain; DC, downstream of curtain.

P values indicate results to the hypothesis: upstream curtain concentrations are greater than downstream curtain concentrations. Results are shown in bold if the P value is ≤0.05.

Sample sizes listed (n) include all sample pairs, including those with differences equal to zero. Both the sign test and Wilcoxon signed-rank test discard sample pairs with differences equal to zero, reducing the number of sample pairs analyzed by the test when this occurs.

* n is not large enough to test.

** n minus the number of sample pairs with differences equal to zero is less than 10, which is not large enough for the distribution of the Wilcoxon W statistic to form a normal distribution. Therefore, a table of critical values for small samples sizes is used and to determine significance at the 0.050 level and accurate P values are not available.

Mean bias and mean percent reduction are displayed for subcategories with significant results or sample sizes too small to test.

Table 4. Sign and Wilcoxon signed-rank test results, mean bias, and mean percent reduction for each curtain condition and sample depth subcategory for total cyanobacteria (copies/mL), total Microcystis spp. (copies/mL), and total microcystin (µg/L) sample pairs (n).

Constituent	Curtain condition and sample depth subcategory	n	Sign test results (P value)	Wilcoxon signed-rank test results (P value)	Mean bias (mean Δ from UC to DC)	Mean change (percent)
Total cyanobacteria, copies/mL	Deployed, C1a	32	0.000	0.000	−110,457,689	−90
	Deployed, C1b	12	0.042	0.012	−11,374,228	−47
	Deployed, C2a	6	0.007	<0.050**	−25,367,271	−53
	Deployed, C3a	2	*	*	58,694,657	424
	Deployed, all, zs ≈ zc	4	*	*	8,842,191	115
	Deployed, all zs = 1.3 to 1.4 m > zc	8	0.240***	>0.050**
	Not deployed, NDall	25	0.274***	0.472
Total Microcystis spp., copies/mL	Deployed, C1a	32	0.000	0.000	−924,198	−78
	Deployed, C1b	12	0.124	0.058
	Deployed, C2a	6	0.007	<0.050**	−1,080,703	−53
	Deployed, C3a	2	*	*	542,225	65
	Deployed, all, zs ≈ zc	4	*	*	127,688	40
	Deployed, all zs = 1.3 to 1.4 m > zc	8	0.240***	>0.050**
	Not deployed, NDall	25	0.159	0.138
Total microcystin, µg/L	Deployed, C1a	40	0.000	0.000	−1.77	−64
	Deployed, C1b	13	0.048	<0.050**	−2.87	−29
	Deployed, C2a	7	0.353	>0.050**
	Deployed, C3a	3	*	*	0.64	208
	Deployed, all, zs ≈ zc	4	*	*	−0.67	−28
	Deployed, all zs = 1.3 to 1.4 m > zc	12	0.353	>0.050**
	Not deployed, NDall	25	0.013	0.016	−0.54	−6

UC, upstream of curtain; DC, downstream of curtain.

P values indicate results to the hypothesis: upstream curtain concentrations are greater than downstream curtain concentrations.

Results are shown in bold if the P value is ≤0.05.

Sample sizes listed (n) include all sample pairs, including those with differences equal to zero. Both the sign test and Wilcoxon signed-rank test discard sample pairs with differences equal to zero, reducing the number of sample pairs analyzed by the test when this occurs.

* n is not large enough to test.

** n minus the number of sample pairs with differences equal to zero is less than 10, which is not large enough for the distribution of the Wilcoxon W statistic to form a normal distribution. Therefore, a table of critical values for small samples sizes is used and to determine significance at the 0.050 level and accurate P values are not available.

*** P value indicates results to the hypothesis: downstream curtain concentrations are greater than upstream curtain concentrations.

Mean bias and mean percent reduction are displayed for subcategories with significant results or sample sizes too small to test.