Export 2 results:
Sort by: Author Title Type [ Year  (Desc)]
Ekdahl, EJ, Teranes JL, Wittkop CA, Stoermer EF, Reavie ED, Smol JP.  2007.  Diatom assemblage response to Iroquoian and Euro-Canadian eutrophication of Crawford Lake, Ontario, Canada. Journal of Paleolimnology. 37:233-246.   10.1007/s10933-006-9016-7   AbstractWebsite

Diatom and geochemical data from Crawford Lake, Ontario, have been used to document limnological responses to periods of cultural disturbance resulting from native Iroquoian occupation of the watershed (1268-1486 AD) and Euro-Canadian agriculture and deforestation (1867 AD-present). Here, we further develop the high-resolution nature of the Crawford Lake sediment record to examine the physical, chemical and biological aspects of limnological response to human disturbances in the lake catchment area with exceptional detail. We report detailed diatom abundance and flux data for individual taxa from Crawford Lake, and further describe the relationship between assemblage composition and environmental conditions using canonical correspondence analysis (CCA). Diatom assemblage data are used to calculate diatom inferred-total phosphorus (DI-TP) concentrations for the past similar to 1,000 years. We also examine the diatom community response during and after periods of disturbance by Iroquoian and Euro-Canadian populations, and compare this response to existing geochemical proxies of lake production and new elemental geochemical indicators of catchment area erosion. In particular, we explore the differing limnological response to the two distinct periods of cultural eutrophication and examine the limnological processes that occurred during the period of low (or no) human activity (1487-1866 AD), when geochemical indicators of lake production recovered to pre-disturbance conditions, but diatom assemblages notably did not. Our results illustrate the highly susceptible nature of diatom communities to periods of anthropogenic disturbance, and emphasize that ecological indicators (such as diatom assemblages) should be included with other proxies (such as nutrient concentrations and physical characteristics) when assessing disturbance and recovery in lake systems.

Lotter, AF, Sturm M, Teranes JL, Wehrli B.  1997.  Varve formation since 1885 and high-resolution varve analyses in hypertrophic Baldeggersee (Switzerland). Aquatic Sciences. 59:304-325.   10.1007/bf02522361   AbstractWebsite

According to their microstratigraphical composition the laminated sediments of Baldeggersee are true varves. Two varve time-series from freeze cores taken in the deepest part (66 m) of Baldeggersee have been analysed for annual and seasonal layers. The varve time-series covers the period of 1885 to 1993. The two freeze-cores from Baldeggersee can be accurately correlated by means of distinct lay ers (e.g. marker varves, turbidites), lithological units, and varve measurements. The Baldeggersee varve chronology has been checked by independent high-resolution Cs-137 dating. Mobility of cesium has not been detected in Baldeggersee. A highly positive correlation between phosphorus concentration in the lake water and median grain size of calcite crystals has been observed and allows, together with the results of geochemical analyses, to hindcast the trophic state in Baldeggersee for periods where no limnological data are available. The main features of the Baldeggersee varve time-series can be summarized as follows: before 1885 there are packets of 5-10 varves interrupted by massive, homogeneous marl beds, indicating oscillating hypolimnetic oxygen levels until the lake ultimately became anoxic in 1885. Between 1885 and 1905 varves are thin, with a high carbonate content. Between 1905 and 1910 the thickness of varves increased steadily, and an increase in calcite grain size suggests a major step in eutrophication. Median grain size values increase again at the end of the 1940s, whereas the thickness of the seasonal lavers decreased between the early 1940s and the early 1960s. At the onset of the 1960s, during the time of highest epilimnetic phosphorus concentrations in Baldeggersee, the total phosphorus concentrations in the sediments as well as the varve thickness and the total accumulation rates all increased. At the beginning of the 1980s the median grain size decreased substantially as a result of lower phosphorus concentrations in Baldeggersee.