Geology topics

P.J. Blanchfield

Publications and source records attributed to P.J. Blanchfield.

3 recordsLinked to original sources

USGS2009

Seasonal habitat selection by lake trout (Salvelinus namaycush) in a small Canadian shield lake: Constraints imposed by winter conditions

The need for cold, well-oxygenated waters significantly reduces the habitat available for lake trout (Salvelinus namaycush) during stratification of small temperate lakes. We examined the spatial and pelagic distribution of lake trout over two consecutive summers and winters and tested whether winter increased habitat availability and access to littoral regions in a boreal shield lake in which pelagic prey fish are absent. In winter, lake trout had a narrowly defined pelagic distribution that was skewed to the upper 3 m of the water column and spatially situated in the central region of the lake. Individual core areas of use (50% Kernel utilization distributions) in winter were much reduced (75%) and spatially non-overlapping compared to summer areas, but activity levels were similar between seasons. Winter habitat selection is in contrast to observations from the stratified season, when lake trout were consistently located in much deeper waters (>6 m) and widely distributed throughout the lake. Winter distribution of lake trout appeared to be strongly influenced by ambient light levels; snow depth and day length accounted for up to 69% of the variation in daily median fish depth. More restricted habitat use during winter than summer was in contrast to our original prediction and illustrates that a different suite of factors influence lake trout distribution between these seasons. ?? Springer Science+Business Media B.V. 2009.

Aquatic Ecology↗

USGS2009

Performance of temperature and dissolved oxygen criteria to predict habitat use by lake trout (Salvelinus namaycush)

We compared theoretical habitat volumes, determined from traditional combinations of temperature and dissolved oxygen concentration (DO) boundaries, with in situ habitat use by acoustically tagged lake trout ( Salvelinus namaycush ). The widely used criteria of 8–12 °C underestimated lake trout habitat use by 68%–80%. Instead, combined temperature (<12 or 15 °C) and DO (>4 or 6 mg·L –1 ) criteria most closely matched lake trout habitat use, had a similar seasonal trend as the tagged fish, suggested modest reductions (5% of total lake volume) in habitat during a warmer year, and performed best when the constraints of temperature and DO were most limiting. All data were collected in a small boreal shield lake (27 ha, z max = 21 m) at the Experimental Lakes Area in northwestern Ontario, Canada, during two contrasting periods of thermal stratification (2003: warmer and longer; 2004: cooler and shorter), providing an assessment of observed and theoretical habitat volumes over current environmental extremes.

Canadian Journal of Fisheries and Aquatic Sciences↗

USGS2007

Whole-ecosystem study shows rapid fish-mercury response to changes in mercury deposition

Methylmercury contamination of fisheries from centuries of industrial atmospheric emissions negatively impacts humans and wild-life worldwide. The response of fish methylmercury concentrations to changes in mercury deposition has been difficult to establish because sediments/soils contain large pools of historical contamination, and many factors in addition to deposition affect fish mercury. To test directly the response of fish contamination to changing mercury deposition, we conducted a whole-ecosystem experiment, increasing the mercury load to a lake and its watershed by the addition of enriched stable mercury isotopes. The isotopes allowed us to distinguish between experimentally applied mercury and mercury already present in the ecosystem and to examine bioaccumulation of mercury deposited to different parts of the watershed. Fish methylmercury concentrations responded rapidly to changes in mercury deposition over the first 3 years of study. Essentially all of the increase in fish methylmercury concentrations came from mercury deposited directly to the lake surface. In contrast, <1% of the mercury isotope deposited to the watershed was exported to the lake. Steady state was not reached within 3 years. Lake mercury isotope concentrations were still rising in lake biota, and watershed mercury isotope exports to the lake were increasing slowly. Therefore, we predict that mercury emissions reductions will yield rapid (years) reductions in fish methylmercury concentrations and will yield concomitant reductions in risk. However, a full response will be delayed by the gradual export of mercury stored in watersheds. The rate of response will vary among lakes depending on the relative surface areas of water and watershed.

Proceedings of the National Academy of Sciences of↗