Page 46: of Marine Technology Magazine (November 2018)

Tech Notes

Rob Bowen with Jay Rastogi (Swan

Lake and Christmas Hill Nature

Sanctuary site manager) and AZFP.

Inset: Underwater drop-down cam- era view of abundant suspended

Aphanizomenon ? os-aquae. Image taken approximately 0.75 m below surface. Filaments are typically about 1 cm in length.

Photo credit: Matt Stone

New Application of Acoustic

Zooplankton Fish Pro? ler Used to

Examine the Onset of Hypoxia

Urban freshwater environments are often being exposed to summer leading to hypoxia and ? sh kills. Using a drop-down nutrient loading through groundwater movement and runoff camera, pre-hypoxic conditions have shown an abundance of potent fertilizers. These nutrients impose imbalances that of Aphanizomenon ? os-aquae throughout the water column. in? uence biological and chemical processes. The impacts Once hypoxia is established, Aphanizomenon ? os-aquae die are generally negative, causing onsets of algal blooms and and drop to the bottom of the lake. In this study, an ASL En- widespread ? uctuations in oxygen levels. Through an ongo- vironmental Sciences’ Acoustic Zooplankton Fish Pro? ler ing monitoring program, Rob Bowen of Diversi? ed Scienti? c (AZFP) will be deployed over the late summer to collect data

Solutions has been conducting surveys of dissolved oxygen, during this transitional period. There are a growing number pH, oxidation-reduction potential, temperature, nitrogen and of successful ocean deployments for this instrument to detect phosphorous at Swan Lake, in Victoria, B.C. Cyanobacteria zooplankton and ? sh presence and abundance. Because Apha- play a key role in the oxygen production in this system as nizomenon ? os-aquae are relatively large acoustic targets, it there is an abundance of the species Aphanizomenon ? os- is hopeful that this new application of the AZFP will provide aquae. Over the last three years, it has been observed that the valuable insights into the dynamics of this freshwater system.

lake experiences a dramatic collapse of oxygen in the late www.aslenv.com

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