250 years of climate-mediated ecological change in Santa Fe Lake, NM

Includes bibliographical references.2022 Fall.Mountain lakes are sensitive indicators of anthropogenically driven global change. Lake sediment records in the western United States have documented increased percent carbon and nitrogen and heightened primary productivity indicative of eutrophication in mountain lakes. Recent paleolimnological studies suggest atmospheric nutrient deposition and warming underlie these changes. We analyzed a short sediment core from Santa Fe Lake, NM, the southernmost subalpine lake in the Rocky Mountain Range to investigate patterns in lake biogeochemical and algal biomarkers since 1747. Lake sediments were dated using 210Pb activities and analyzed for percent C and N, δ13C, δ15N, and algal pigments representative of total biomass, chlorophytes, cryptophytes, diatoms, and other primary producers from Santa Fe Lake. Throughout the 250-year sediment record from Santa Fe Lake, we observed changes in algal community composition alongside biogeochemical alterations. During the cold dry conditions of the Little Ice Age, there were greater proportions of cyanobacteria, diatoms, and sulfur bacteria. Total algal biomass increased under increased warming and climate variability with significant increases in chlorophytes and cryptophytes. Significant rates of change occurred concurrently with increases in regional N deposition in the mid-20th century. C, N, δ13C, δ15N remained relatively stable throughout the record, until the mid-20th century when C and N increased exponentially alongside depletions in δ13C, δ15N. Our results suggest climate-driven algal assemblage changes throughout the record with regional N deposition contributing to contemporary productivity increases. The timing and magnitude of these changes differ from other studied lakes. Our findings highlight the heterogeneity of lakes' responses to changing environmental conditions in the Anthropocene and call attention to the role of climate-induced ecological change in the absence of critical N deposition

The Effect of Beaver Dams on Macroinvertebrate Communities

Impacts of habitat alterations caused by beaver presence on the composition and disturbance tolerance of local macroinvertebrate communities were studied. Beavers act as ecosystem engineers by altering water flow, temperature, nutrient, organic carbon and groundwater storage, and by increasing the overall geomorphic complexity of river systems through dam construction. Macroinvertebrates are widespread across freshwater habitats, they act as primary processers of organic materials serve as a food source for various freshwater species. Samples of macroinvertebrate communities were collected in the streams within the Methow River Watershed in North-Central Washington. Streams with known beaver presence (n= 4) and without beaver activity (n=4) were included in the study. On beaver impacted streams collections were taken above (n=3) and below (n=6) the beaver dams. Additionally, aquatic and terrestrial plants and macroinvertebrates were collected from all streams for stable isotope analysis. Macroinvertebrate species known to be sensitive to water quality were more abundant (lower HBI score) below beaver dams than above dams across all streams. One measure of community diversity (lower Percent Dominance) was greater below beaver dams than above dams. Furthermore, highly pollutant tolerant taxa (Diptera) were less abundant below beaver dams than above dams. These results demonstrate a relationship between beaver dams and a greater diversity of local macroinvertebrate communities as well as an improvement in overall stream health

An animal model of late pulmonary responses to Alternaria challenge.

The pathogenesis of the late asthmatic response to allergen inhalation is unknown; IgE as well as IgE- and IgG-dependent mechanisms have been proposed. This study was undertaken to determine whether rabbits immunized to produce only IgE to Alternaria tenius would develop immediate and late phase pulmonary responses to Alternaria aerosol challenge, and to compare this response in IgE only rabbits with the response in rabbits producing multiple antibody isotypes to the allergen. Neonatal rabbits immunized with Alternaria tenius extract produced only IgE to that allergen, whereas rabbits first immunized at 7 days of age made multiple antibody isotypes. After aerosol challenge, the rabbits with only IgE antibody to the Alternaria developed biphasic change in lung function, as assessed by changes in pulmonary resistance and dynamic compliance, whereas rabbits with anti-Alternaria IgG as well as IgE had blunted biphasic pulmonary responses. Intravenously administered isoproterenol did not reverse the late phase response. Transfusion with serum containing anti-Alternaria IgG into IgE only rabbits reduced both the early and late phase changes in pulmonary mechanics. Transfusion of plasma containing anti-Alternaria IgE into nonimmunized control rabbits produced, upon challenge, both early and late phase responses in pulmonary mechanics, which were lost in retesting 4 wk later. We conclude that in this system IgE-allergen interaction can result in both the immediate and late pulmonary responses, that the presence of IgG results in blunting rather than in enhancing of this responsiveness, and that the response can be seen in the absence of cellular immune mechanisms

Climatic variability as a principal driver of primary production in the southernmost subalpine Rocky Mountain lake

ABSTRACTMountain lakes are sensitive indicators of anthropogenically driven global change, with lake sediment records documenting increased primary production during the twentieth century. Atmospheric nutrient deposition and warming have been attributed to changes in other Western mountain lakes, however, the intensity of these drivers varies. We analyzed a sediment core representing a 270-year record from Santa Fe Lake, New Mexico, to constrain the southern margin of Rocky Mountain lakes and quantify patterns of change in lake biogeochemistry, production, and diatoms since 1750. Lake sediments were dated using 210Pb and analyzed for carbon (C), nitrogen (N), stable isotopes (δ13C, δ15N), diatoms, and phototrophic pigments. The abundance of cyanobacteria, purple sulfur-reducing bacteria, and diatom pigments were elevated during the stable conditions of the Little Ice Age; these phototrophic groups declined in the late 1800s and reached a minimum by 1950. From 1950 to 2020, sediments recorded an increased abundance of cryptophyte, diatom, and chlorophyte groups. The C and N (percentage dry mass) increased after 1950, whereas δ15N and δ13C values declined. Changes since the mid-twentieth century are contemporaneous with warming trends in the Southwest and modest deposition of atmospheric N. Our findings highlight the geographic variability of mountain lake responses to changing environmental conditions