Preece EP, Moore BC, Skinner MM, Child A, Dent S. A review of the biological and chemical effects of hypolimnetic oxygenation. Lake Reserv Manage. XX:XX–XX. The technology of hypolimnetic oxygenation (HO) as a management tool continues to mature; at least 30 HO systems have been deployed worldwide in lakes and reservoirs to combat water quality issues that can flow from hypolimnetic hypoxia/anoxia. HO has been shown to decrease internal nutrient loading, decrease soluble metals (i.e., manganese, iron and mercury), reduce cyanobacteria blooms, and increase cold-water fish and zooplankton habitat. In this article, we review available case studies to examine how HO affects the biological and chemical components of lakes and reservoirs. Because HO is typically implemented with other restoration activities it is difficult to discern the exact impacts of HO in many waterbodies. Nevertheless, evidence from the reviewed case studies suggests that HO can be an important tool for restoring water quality when used properly.

Since the mid-20th century, oxygen status at the sediment–water interface (SWI) has been implicated in regulating lake internal phosphorus loading. In deeper lakes, summer hypolimnetic oxygen depletion may thus play a critical role in phosphorus cycling and lake trophic status. Hypolimnetic aeration (HA) has been utilized for more than 4 decades to prevent development of anoxia, decrease internal phosphorus load, and enhance fisheries. Most recently, interest has shifted to hypolimnetic oxygenation (HO) for potential performance and economic advantages. In Newman Lake, hypolimnetic oxygenation was initiated in 1992 when the first lake application of downflow contact bubble oxygenation (Speece Cone technology) was installed. Oxygenation at Newman has reduced growing season Nürnberg Anoxic Factors (AF) from a range of about 30–60 d to <10 d. We propose that differences in predicted versus observed AF based on phosphorus may be utilized to assess lake restoration performance. Newman Lake has demonstrated the importance of operating the system at full capacity, as lower oxygen delivery rates do not produce proportional hypolimnetic oxygen concentrations, as well as other insights into HO system sizing and design.

In 2013, the U.S. Environmental Protection Agency (USEPA) updated its national recommended water quality criteria for the protection of aquatic life from the toxic effects of ammonia in freshwaters. From its updated national dataset, USEPA determined freshwater mussels in the family Unionidae were the most sensitive taxa to ammonia. Thus, it has become necessary to determine whether freshwater mussels exist in waterbodies near discharge locations from Publically Owned Treatment Works (POTWs), to ensure that POTWs are regulated appropriately with regard to ammonia levels in their treated effluent. However, because mussels are notoriously difficult to detect using traditional survey methodologies, most POTWs have not determined whether freshwater mussels exist in their receiving waters. Environmental DNA (eDNA) presents a promising methodology to survey for freshwater mussels in POTW receiving waters. We developed and validated a quantitative polymerase chain reaction (qPCR) assay for the three freshwater mussel taxa that are currently known to exist in California's Central Valley. We then placed a cage with 20 Gonidea angulata into a riverine environment and collected water samples at evenly spaced downstream intervals to determine how habitat type and distance from the caged mussels affected eDNA detection. Using two‐stage occupancy modeling, we determined higher detection probabilities occur in riffle habitats compared to pool or run habitats. We also found surface samples work well for collecting freshwater mussel eDNA in riffle habitats, but are less likely to capture mussel eDNA in pools or runs. The maximum downstream distance at which the eDNA from the 20 placed G. angulata mussels was detected was 8 km. Our study demonstrates that eDNA is a reliable tool for determining freshwater mussel presence in riverine systems, but that sampling should consider habitat type, distance between sampling locations, and time of year for the most effective results.

Presence of the cyanobacterial hepatotoxin microcystin was detected by liquid chromatography-mass spectrometry in mussels (Mytilus trossulus) from Puget Sound, Washington. Microcystin was found in all but one mussel exposed to inflows from a lake, with maximum concentrations of 52.4 ppb. This is the first known report of marine bivalves in Puget Sound, Washington, accumulating microcystin from freshwater sources.

Cyanobacterial harmful algal blooms (CHABs) have become a persistent seasonal problem in the upper San Francisco Estuary, California also known as the Sacramento-San Joaquin Delta (Delta). The Delta is comprised of a complex network of open water bodies, channels, and sloughs. The terminus of the Stockton Channel is an area identified as a CHAB "hotspot." As CHABs increase in severity, there is an urgent need to better understand CHAB drivers to identify and implement mitigation measures that can be used in an estuarine complex like the Delta. We investigated water quality conditions and nutrient dynamics in the Stockton Channel by measuring nutrients in the water column, sediments, and pore waters. In situ nutrient addition bioassay experiments were used to assess the effects of nutrient enrichment on total algal/cyanobacterial growth and pigment concentrations. In both June and September, relative to unamended controls, total chlorophyll and cyanobacterial pigment concentrations were unaffected by nutrient additions; hence, the study area showed signs of classical hypereutrophication, with ambient nitrogen and phosphorus present in excess of algal growth requirements. A cyanobacterial bloom, dominated by Microcystis spp. was present throughout the study area but was most severe and persistent at the shallowest site at the channel terminus. At this site, Microcystis spp. created water quality conditions that allowed for a prolonged bloom from June through September. While targeted nutrient reductions are recommended for long term mitigation, on a shorter timescale, our findings suggest that physical/mechanical controls are the more promising alternative approaches to reduce the severity of CHABs in the terminus of the Stockton Channel.