Limnological studies in Connecticut lakes: The use of periphytic diatoms in the assessment of lake trophic status

The first chapter of this dissertation presents a brief introduction giving the reader a sense of the connection between the three following Chapters. ^ In the second Chapter, lake trophic status of 47 Connecticut lakes was calculated using physical/chemical variables and periphytic diatom abundance in surface lake sediments. First, lake trophic scores were calculated using environmental variables only using PCA (Principal Component Analysis) in CANOCO (Canonical Community Ordination) version 4. Second, the same trophic scores were calculated by linking environmental and biological data. For this latter analysis, DCA (Detrended Correspondence Analysis) and CCA (Canonical Correspondence Analysis) were used to assess whether trophic variables explained patterns of periphytic diatom distribution. ^ Then, an inference model for total nitrogen was calculated using WA (Weighted Averaging) in WACALIB (Weighted Averaging Calibration) version 3.3. PCA derived and trophic conditions inferred by WA were more accurate in expressing lake trophic status than single trophic variables. Additionally, inferred total nitrogen values were highly correlated with total nitrogen measured in the field indicating that periphytic diatoms do have a high predictive value. The total nitrogen inference model was then compared to scores inferred from planktonic diatom data for a similar set of Connecticut lakes. In general, periphytic diatoms seem to be better indicators of lake trophic conditions probably due to their high diversity, better adaptation to the acidic conditions of many of the studied lakes, and to the apparent stability of their environment. ^ The third and fourth Chapters deal with taxonomical issues during routine ecological analyses. In Chapter three, it is argued that light microscopy is not sufficient for identification of small diatom taxa of high ecological importance. Specific examples are used to demonstrate that scanning electron microscopy can increase accuracy in the identification of such taxa. As a result of detailed morphological analyses under the electron microscope, two new species are described, one of them placed in a genus new to science.