Hypolimnetic oxygenation 3: an engineered switch from eutrophic to a meso-/oligotrophic state in a California reservoir

Figures & data

Table 1. Chemical and biological limnology of eutrophic Camanche Reservoir and trophic state indicators in 1990–1992 prior to HOS

Parameters, location	Annual means in growth season (annual ranges)	Eutrophic–mesotrophic border
Epilimnion surface
TP (μg/L)	29 (10–120)	29
Nitrate as N (μg/L)	17 (1–105)	150?
Ammonium as N (μg/L)	8	50?
TIN (μg/L)	25	200?
TIN:TP ratio	0.86	6.9?
Chl-a (μg/L)	14.6 (2–49)	9
Secchi depth (m)	0.47 (0.09–3.5)	2.0
Hypolimnion bottom
Soluble phosphate as P (μg/L)	36 (3–200)	29
TP (μg/L)	79 (1–540)	29
Ammonium as N (μg/L)	260 (5–1700)	50
Nitrate as N (μg/L)	110 (1–390)	150
Oxygen minimum (mg/L)	0 (decay rate 0.1 mg/L/d)	5?
Hydrogen sulfide	Detected via odor	Any present

Figure 1. The Camanche Reservoir Speece cone. (a) Diagram of the cone, side view (from Brown and Caldwell, 1995). (b) Cone assembly by the dam (Pan Marine Construction). Cone is the large, 7 m high, white structure on right; large inlet and pump pipes to top of cone are dark. Outlet manifold (not shown) attaches to bottom left of cone. (c) Final location of the submerged Speece cone is marked by a buoy (inside triangle) 180 m from dam for which the rock face is at bottom. A 3.5 m long fishing boat (circle) just outside line of small marker buoys shows scale. Photo shows the first 5 km of the reservoir, which holds most of the reservoir volume.

Figure 2. (a) Chlorophyll a and (b) water transparency in Camanche Reservoir during the growth season before and after HOS, which began July 1993. Secchi depth correlation coefficient is based on a third-order polynomial but the R² for linear regression was similar.

Table 2. Summary of declines in chlorophyll a after HOS for the entire growth season and the key recreational months of July–September.

Time	Chl-a (µg/L)		Secchi depth (m)
	Growth season	Jul–Sep	Growth season	Jul–Sep
Before HOS (1990–Jun 1993)	14.6	22.1	0.47	0.35
After HOS (Jul 1993–2004)	3.1	3.7	4.9	4.5
After 11 yr HOS (2004)	2.8	2.7	5.6	6.7

Table 3. Declines in soluble phosphate (as µg P/L) in the bottom hypolimnion water (2 m above sediment near the dam) before and immediately following HOS in late July 1993

Month	Bottom soluble phosphate as P (μg/L)
	1992 before HOS	1993 after HOS
Aug	39	18
Sep	35	40
Oct	123	38
Mean Aug–Oct	66	32
Std. dev.	50	10
CV %	76%	31%

Table 4. Summary of long-term changes in major nutrients (μg/L) in the deep hypolimnion and surface waters of Camanche Reservoir before and after HOS

	1990–1992	1994–1997	2004
Years	Before	4 yr after	11 yr after
Hypolimnion water in October (std. dev.)
Soluble phosphate as P (μg/L)	95 (55)	15 (15)	18 (18)
TP (μg/L)	201 (127)	25 (2)	28 (5)
Ammonium as N (μg/L)	706 (523)	28 (25)	14 (8)
Nitrate as N (μg/L)	40 (92)	65 (59)	50 (18)
TIN (NH4 + NO3) as N (μg/L)	746	93	64
TIN:TP ratio	3.7	3.7	2.9
	Surface water in Feb–Mar (range)
	1990–1992	1995–1999	2004
Soluble phosphate as P (μg/L)	21 (10–31)	7.8	9
TP (μg/L)	33 (20–46)	14.2	14
Ammonium as N (μg/L)	8.0	12.9	17
Nitrate as N (μg/L)	190 (180–200)	42	3
TIN (NH4 + NO3) as N (μg/L)	198	54.9	23
TIN:TP ratio	6.0	4.0	1.6

Figure 3. Phosphorus species in Camanche Reservoir before and after HOS, which began July 1993. (a) Bottom water-soluble phosphate. (b) Surface TP. Aberrant peaks after HOS were due to minimal, late-season only use of HOS (1995) and an electrical problem (1997) when brief anoxia occurred.

Figure 4. Ammonium in Camanche Reservoir before and after HOS, which began July 1993: (a) bottom water and (b) surface water.

Figure 5. Nitrate in surface water for Camanche Reservoir before and after HOS, which began July 1993.

Table 5. Changes in dominant phytoplankton and zooplankton including colonial cyanobacteria before and after HOS which began in late July 1993.

Years after HOS	Average cells/L (algae)
	Aphanizomenon	Dolichospermum	Fragilaria	Rotifers (annual mean)	Crustaceans (annual mean)
Before: 1988–1992	3,681,000	148,354^a	400,000^a	29	9.4
After +1–2	363^b	2015^b	138,000^b	100	11
+5	84,483		179,000^d	36	13
+6	0.8	50		19	10
+11 (2005)	70	7270	26,690	30	12

^aAug 1988–May 1989.

^bAug 1994–May 1995.

^c1998–2000.

^dAug 1988–May 1998.

Figure 6. Zooplankton in near-surface water of Camanche Reservoir before (1988–1992) and after (1994–2004) HOS, which began in July 1993. Grand annual means were rotifers 29/L (before) and 50/L (after); crustaceans 9/L (before) and 12/L (after) HOS. Incomplete or no data are available for 1994 and 1996–1998.

Table 6. Delineation of trophic state based on 4 commonly measured variables, 2 direct (algae and water clarity) and 2 indirect (nutrients). The table is based on literature surveys summarized in Horne (1996) and Cooke and Welch (2008)

Trophic state	Direct measures growth season surface (Apr–Oct)		Indirect measures late winter surface (Feb–Mar)
	Chl-a (µg/L)	Secchi depth (m)	TP (µg/L)	TIN (µg/L)
Hypereutrophic	>25	<1	>100	>1000
Eutrophic	8.1–25	1–2	30–100	300–1000
Mesotrophic	3.2–8	2.1–3.8	9–29	90–290
Oligotrophic	<3.1	>3.9	<8	<80
Hyperoligotrophic	<1	>8	<2	<10

Brown & Caldwell Inc. 1995. Camanche Reservoir oxygenation demonstration system: report on operation 1993/94. Oakland (CA): Brown & Caldwell, Alex Horne Assoc. & Biosystems Analysis Inc. for EBMUD.

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Horne AJ. 1996. Defining the eutrophic and mesotrophic states for Standley Lake. Report to City of Westminster, CO.

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Cooke JD, Welch EB. 2008. Eutrophication of Tenkiller Reservoir, Oklahoma, and effects on water quality and fisheries. Oklahoma City (OK): Expert Report for State of Oklahoma. Case No. 05-CU-329-GKF-SAJ.

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