Hypolimnetic oxygenation 4. Effects on turbidity in Camanche Reservoir and its downstream fish hatchery

Abstract

Horne AJ. 2019b. Hypolimnetic oxygenation 4. Effects on turbidity in Camanche Reservoir and its downstream fish hatchery. Lake and Reserve Manage. 36:360–375. Turbidity is a major concern for reservoir, river, and hatchery managers, partially because sediments smother fish eggs. The oxygenated plume of the Camanche Reservoir hypolimnetic oxygenation system (HOS) is close enough to the sediments to suppress releases of nutrients, hydrogen sulfide, and methylmercury. Experiments and models predicted little sediment resuspension from the plume. On/off in-reservoir tests in the initial year of HOS operation (1993) showed a small (x = 1.4 NTU) and not statistically significant increase in average turbidity that extended over 300 m, was minimal at 1.5 km (0.3 NTU), and was not apparent in the next year (1994). Increased turbidity was attributed to tiny (<2 μm) calcite particles caused by lake whitening during intense periods of photosynthesis during cyanobacterial blooms prior to HOS. Turbidity in the fish hatchery declined substantially (4 to 2 NTU, summer 1991 vs. 1994) and averaged 2.5 NTU in 1999 and 2009. This decline is likely due to the 79% HOS-induced decrease in chlorophyll, because bottom turbidity was related to algae blooms (R2 = 0.57) if lagged by 4 weeks to allow the algae to sink. The result would be less planktonic remains and fewer lake whitening particles sinking to deep water. Microscopic examination, size spectrum analysis, and chemical fingerprinting of particles showed that egg tray sediments (mostly inorganic silica diatom frustules and aeolian dust with an even size spectrum from 0 to 200 μm) were not like those in the reservoir bottom water outflow (mostly organic and <2-μm calcite particles).