Hypolimnetic oxygenation 3: an engineered switch from eutrophic to a meso-/oligotrophic state in a California reservoir. (3rd July 2019)

• Record Type: Journal Article
• Authors: Horne, Alex J.; Beutel, Marc
• Is Part Of: Lake and reservoir management. Volume 35:Number 3(2019)
• Page Start: 338
• Page End: 353
• Publication Date: 2019-07-03
• Subjects: Aphanizomenon -- eutrophication -- nitrogen limitation -- oxygenation; Water quality management -- North America -- Periodicals; Lake restoration -- North America -- Periodicals; Lake restoration; Water quality management; North America; 628
• DOI: 10.1080/10402381.2019.1648613
• Languages: English
• ISSNs: 1040-2381

Abstract

Abstract: Horne AJ, Beutel M. 2019. Hypolimnetic oxygenation 3: an engineered switch from eutrophic to a meso-/oligotrophic state in a California reservoir. Lake Reserv Manage. 35:338–353. A long-term improvement in water quality due to a hypolimnetic oxygenation system (HOS) used without other management actions was shown for Camanche Reservoir in California (volume = 514 million m 3 ). Prior to oxygenation, the reservoir was eutrophic with low water clarity, high chlorophyll a (Chl- a ), and blooms of cyanobacteria primarily caused by internal nutrient loading from anoxic sediments. All 4 trophic state indicators showed major improvement, most pointing to a new oligotrophic state. Days after HOS startup in July 1993, hypolimnion soluble phosphate and ammonium concentrations declined and, unexpectedly, nitrate remained low. This report covers pre-HOS (1988 to mid-1993) and 12 yr of post-HOS measurements (mid-1993 to mid-2005). For surface waters during the growth season (Apr–Oct) after HOS, average Chl- a decreased 79% (14.6–3.1 μg/L) and peak Chl- a decreased sixfold (from 49 to 8 μg/L). Average Secchi depth increased 10-fold (0.47 to 4.9 m) and peak Secchi depth doubled (4.2–8 m). Cyanobacteria ( Aphanizomenon and Dolichospermum, formerly Anabaena ) decreased >95% while the previously absent Merismopedia, an indicator of clean water, appeared. The large colonial diatom Fragilaria also decreased by >90%. Zooplankton (rotifers and crustaceans) appeared unchanged. After HOS, late winter surface nutrients prior to the next spring bloom were much reduced (total phosphorus, TP, by 58%, total inorganic nitrogen, TIN, by 88%). The TIN:TP ratio dropped from 6 to 1.6. In 2004, the last full year of measurements, further declines were found for nitrate nitrogen (42–3 μg/L) and Chl- a (3.1–2.8 μg/L) while TP was unchanged (14 μg/L).