Effects of research diving on a stratified Antarctic lake

Results are presented from a study into the effects of scuba diving on water column structure in perennially ice-covered Lake Fryxell, Antarctica. General theoretical predictions are compared with results, which assess potential impacts from diving activities on water quality parameters related to disruptions to water column stability and dissolved gas concentrations. Potential mechanisms of water column disturbance are considered including: (1) mixing due to diver motion, (2) mixing by diver-exhaled bubble plumes and (3) changes of water column gas concentrations due to dissolution of diver-exhaled gases. Data (temperature, dissolved oxygen, specific conductance, pH, dissolved organic carbon, salinity) were collected from two control holes and one dive hole immediately before and 2.5 d after dive activities. Variability in measured parameters did not differ significantly between sampling sites either before or after diving; and differences between control holes and dive hole observations, on a depth-by-depth basis, were within the range of expected statistical fluctuations. Pre- and post-dive virus-like particle, bacterial, ciliate, photo- and heterotrophic flagellate densities also did not differ significantly. An apparent lack of long-term trends indicative of water column destabilization over the past 18 ys of diving is discussed, along with recent evidence for deep mixing in this lake. Although all potentially affected parameters have not been considered, theoretical model results and an analysis of field data suggest that diving impacts on physicochemical properties and microbial distributions in a closed-basin, ice-covered lake occur at spatiotemporal scales other than those considered in this study.