Two 10-cm-diameter sampling holes are drilled through the ice by auger at the deepest site of each lake and then melted out to a diameter of ~30 cm. One hole is used for water column PAR profiles and the primary productivity incubation; the other hole is used for discrete water sampling (Van Dorn or Niskin bottles) and CTD deployment and is protected with an opaque cover.

 

Discrete water samples are collected at specific depths relative to the water level in the borehole in each lake to capture important vertical characteristics. Appendix 6.1 in the Limnology Methods Manual lists the target depths at which samples are collected. However, due to environmental conditions (ice thickness, bottom depth in area of sample hole caused by lake level variation), the samples immediately beneath the ice and nearest to the bottom cannot always be replicated. Consequently, the top sample is collected ~0.5 m below the bottom of the ice cover, and the bottom sample as close to the bottom of the lake as possible without disturbing the sediment.