NOAA/WDS Paleoclimatology - Walker et al. 2003 Canada Chironomid Data

To ascertain the extent of recent impacts, and to develop realistic goals for water quality improvement, a palaeolimnological assessment of human impact on Wood Lake, British Columbia, Canada was initiated in 1992. Geochemical and microfossil analyses on a series of short cores provided a detailed record of human impact since European settlement.

Early post-settlement sediments consisted of clastic materials rich in Mg, Al, Fe, P and associated metals. An abrupt increase in marl deposition occurred about 1940, perhaps in response to diversion of inflowing water for irrigation and/or an increase in algal productivity. Mo analyses provided a record of increasing hypolimnetic anoxia with eutrophication. Hg concentrations were highest in sediments deposited during the past decade.

Microfossil analyses (chironomids, diatoms, chrysophytes) depicted the lake's progressive eutrophication, and the disappearance of the profundal bottom fauna. Water quality improvements have been reported since 1975, but benthic invertebrate communities have recovered only slightly. The diatoms may indicate a modest water quality improvement over the last 20 years.

Wood Lake was formerly an oligo-mesotrophic lake with a well-developed profundal fauna. Appropriate mitigative programmes could substantially improve water quality, perhaps allowing re-establishment of the natural oligo-mesotrophic condition.