RUI: The Role of Dissolved Organic Material in Regulating Primary Production in Prairie Saline Lakes

Grasslands and converted grasslands (i.e. agricultural land) cover extensive areas in semi-arid regions of the world. Lakes situated in grasslands are usually saline and have high concentrations of dissolved organic matter (DOM). We hypothesize that DOM plays a critical role in regulating algal production in prairie saline lakes by binding nutrients and making them less available to algae. To explore this hypothesis, we will survey a suite of chemical and biological parameters in lakes from three areas in the central and northern Great Plains (ND, SD, NE). A series of experiments will be conducted in Years 2 and 3 to further explore patterns observed in the field surveys. This research will provide training for one graduate and six undergraduate students. A greater understanding of the controls on algal production may improve management practices in prairie saline lakes and ensure the quality of these habitats for migrating waterfowl

Collaborative Research: The Response of Lakes to Disturbance and Climate Change: Calibrating Sedimentary Records to Test the Landscape Position Concept

Landscape disturbance and climate change affect lakes in proportion to their contact with ground water, sometimes resulting in different responses in neighboring lakes. This project develops methods for reconstructing past water chemistry and food webs of lakes. The biological and chemical deposits in surface sediment samples will be compared with the water in 62 modern lakes. The resulting relationships will be tested by comparing sediment cores with 24 years of observations from the North Temperate Lakes Long Term Ecological Research (NTL-LTER) site. The methods will then be used to reconstruct 150 years of history for several lakes, adding perspective to the long-term observations of the NTL-LTER and testing the prediction that lakes high in the local landscape had more severe and longer-lasting effects of 19th century logging than low lakes that are more influenced by groundwater. This research will also help to understand the response of lakes to severe droughts that last decades to centuries by identifying periods of low lake levels during the last 10,000 years. Understanding the variability of the responses of lakes to climate change and disturbance is essential to predicting the responses of particular lakes to future changes in land use and climate. This project will bring together expertise from several strong programs at the University of Wisconsin (the Center for Limnology, Botany, the Center for Climatic Research, NTL-LTER, and UW-LaCrosse), with the Limnological Research Center and LacCORE National Lacustrine Core Repository at the University of Minnesota and the United States Geologic Survey Water, Energy, and Biogeochemical Budgets (WEBB) project. Cores collected in this project will be archived at LacCORE and made available to future researchers, forging important new links between the LTER network, the paleoecology and paleoclimate communities, and groundwater scientists at the USGS. Two graduate students and at least 10 undergraduates will participate, and the project will contribute to the Limnology Explorers program, an interdisciplinary educational experience for middle school students coordinated by the NTL-LTER and the UW Center for Biology Education as part of the SchoolYard LTER initiative

Climate-Induced Shifts in Alpine Diatom Communities: Linking Neoecological and Paleoecological Approaches to Incorporate Responses to Trophic Forcing

Diatoms are a class of microscopic algae that are sensitive to environmental changes. Diatom fossils from lake sediments in the central and northern Rocky Mountains indicate that various Cyclotella species have increased during the 20th century. This increase is often attributed to climate change, but the mechanisms involved have not yet been tested. To decipher the mechanisms by which climate change has altered diatom community structure, paleoecological analyses will be coupled with experimental approaches. Fossil records from lake sediments will be used along with tree rings to provide information on climate trends over the last 2000 years. A series of laboratory and field experiments will be used to assess the mechanisms by which climate-related parameters drive changes in these diatoms. The broader impacts of the proposed work include a greater understanding of the response of alpine lakes to climate change; many of these lakes are located in national parks and forests and have high aesthetic and recreational value. This research will address several research needs identified by Glacier National Park, hence it will potentially provide critical information to park managers. Saros will speak at Glacier National Park\u27s 2009 Science & History Conference, which is attended by the public. The investigators will also develop a Resource Bulletin on the results as part of the park\u27s series on climate change. This research will also provide training for two graduate and nine undergraduate students

The Freshwater Copepod Limnocalanus macrurus in the Canadian Arctic Archipelago: Numbers, Weights, and Respiration Observed from September 1961 – July 1962

Numbers, weights, and oxygen consumption of the copepod Limnocalanus macrurus were measured through the winter 1961 – 62 under the ice of Immerk Lake on Devon Island, Arctic Canada. Maximum abundance was 2361 animals per m3 found under ice in mid June, average adult wet weight was 65 μg, and hourly oxygen consumption per adult ranged from 0.26 μg in late summer to 0.03 μg in early winter. The results are compared with results from Char Lake and Resolute Lake on Cornwallis Island, Arctic Canada. The Immerk population was more stable than those at the other lakes, and weights and oxygen consumption appear to be comparable. The seasonal breeding cycle at Immerk Lake was different from that at Char Lake and similar to that at Resolute Lake. A comparison of Immerk Lake data from 1961 – 62 and 1972 – 73 showed almost identical levels of total oxygen metabolism. Immerk Lake copepod oxygen consumption was 6.5% of the total lake metabolism, while that at Char Lake was 6%. These data may assist in future assessment of climate or anthropogenic changes.Le nombre, le poids et la consommation d’oxygène du copépode Limnocalanus macrurus ont été prélevés au cours de l’hiver 1961-1962 sous la glace du lac Immerk, sur l’île Devond, dans l’Arctique canadien. L’abondance maximale se dénombrait à 2 361 animaux par m3 sous la glace au milieu de juin, tandis que le poids humide moyen d’un copépode adulte s’élevait à 65 μg, et que la consommation horaire d’oxygène par adulte variait entre 0,26 μg en fin d’été et 0,03 μg en début d’hiver. Les résultats ont été comparés aux résultats obtenus au lac Char et au lac Resolute sur l’île Cornwallis, dans l’Arctique canadien. La population du lac Immerk était plus stable que celle des autres lacs, tandis que le poids et la consom­mation d’oxygène de cette population semblaient comparables. Au lac Immerk, le cycle de reproduction saisonnier différait de celui du lac Char, mais il s’apparentait à celui du lac Resolute. La comparaison des données recueillies au lac Immerk en 1961-1962 ainsi qu’en 1972-1973 a affiché des taux quasi identiques sur le plan du métabolisme de l’oxygène total. La consom­mation d’oxygène chez le copépode du lac Immerk correspondait à 6,5 % du métabolisme total du lac, tandis qu’au lac Char, ce taux s’élevait à 6 %. Ces données pourraient aider à évaluer le climat à l’avenir ou à déterminer les changements de nature anthropique

Integrating neo-and paleolimnological approaches to refine interpretations of environmental change

Abstract With the development of quantitative transfer functions to relate community structure to physicochemical variables, reconstructions of past environmental conditions have been possible and have enhanced our understanding of various ecosystem processes. There are cases, however, in which this approach is not applicable, or does not provide enough information for the questions being asked. In these cases, some alternatives are to conduct experiments or to examine the distribution of species at a finer spatial resolution. These two approaches have been used as alternatives to or in conjunction with the development of transfer functions. In this review, I discuss the ways in which these two approaches are now being used in paleolimnological studies to enhance our understanding of the ecology of the species found in sediment records and thus refine interpretations of environmental change. My focus is primarily on studies that deal with establishing clearer relationships between environmental variables and the growth or distribution of organisms. I present examples of how these approaches have been integrated in a variety of studies, including those designed to: (1) refine and enhance reconstructions that are based on transfer functions; (2) develop new paleolimnological tools to reconstruct environmental change; (3) explore mechanistic links in the relationships between organisms and commonly reconstructed environmental variables; and (4) pose and test hypotheses based on patterns in the sediment record. These cases demonstrate that the use of these approaches was essential to clarify species-environment relationships as well as lake responses to disturbance. As in all disciplines, however, there are many challenges in this area of research. In particular, the quantitative integration of these approaches with the sediment record is a major challenge, due to disparate spatial and temporal scales. This research can also be quite labor-intensive, and provides information on fewer taxa than in the calibration set approach. It also requires interdisciplinary training and/or collaboration in fields that have historically been less integrated, hence they may require greater effort. These issues may hinder the use of these approaches because of the perceived difficulty. I discuss these challenges and address possible solutions

The Influence of Fetch on the Holocene Thermal Structure of Hidden Lake, Glacier National Park

We use three-dimensional modeling of the basin of Hidden Lake, Montana, to assess the influence of effective fetch on diatom-inferred changes in mixing depths throughout the Holocene. The basin of Hidden Lake is characterized by a complex morphometry; for example, three-dimensional modeling of the lake basin indicates that a decrease in lake level of 2 m would result in complete isolation of the deepest part of the lake basin from the rest of the lake. Our model suggests that small changes in the lake surface elevation at Hidden Lake would produce threshold-like responses in effective fetch, which in turn would have a profound influence on average lake mixing depth. The present-day planktic diatom community of Hidden Lake is comprised of three species. Neo-ecological experiments revealed the effect of mixing depth and nutrient levels on growth rates of these species. A sediment core collected from the deepest part of the lake basin and spanning the last 8,640 years was analyzed for diatoms. Here we show how changes in fetch through the Holocene explain changes in the dominant planktic diatom species by modification of the thermal structure of Hidden Lake. Additionally, the timing of diatominferred changes in effective moisture and thermal structure from Hidden Lake were compared to late Holocene patterns reconstructed from other regional lake records. Between 8.64 – 7.61 ka the diatom record from Hidden Lake suggests that the lake was deep and fresh, although somewhat lower than the modern lake. After 7.61 ka, water levels rose, expanding the available benthic diatom habitat. Between 6.18 and 4.13 ka, lake level declined and seasonal stratification was enhanced. After 1.4 ka, the lake became deeper and less stratified in response to the effects of enhanced fetch. We argue that changes in effective fetch may play an important, and underexplored, role in planktic diatom community structure over longer time scales and should be more broadly considered in paleolimnological studies

Patterns of seasonal phytoplankton distribution in prairie saline lakes of the northern Great Plains (U.S.A.)

Seasonal changes in freshwater phytoplankton communities have been extensively studied, but key drivers of phytoplankton in saline lakes are currently not well understood. Comparative lake studies of 19 prairie saline lakes in the northern Great Plains (USA) were conducted in spring and summer of 2004, with data gathered for a suite of limnological parameters. Nutrient enrichment assays for natural phytoplankton assemblages were also performed in spring and summer of 2006. Canonical correspondence analysis of 2004 data showed salinity (logCl), nitrogen, and phosphorus (N:P ratios) to be the main drivers of phytoplankton distribution in the spring, and phosphorus (C:P ratios), iron (logTFe), and nitrogen (logTN) as important factors in the summer. Despite major differences in nutrient limitation patterns (P-limitation in freshwater systems, N-limitation in saline systems), seasonal patterns of phytoplankton phyla changes in these saline lakes were similar to those of freshwater systems. Dominance shifted from diatoms in the spring to cyanobacteria in the summer. Nutrient enrichment assays (control, +Fe, +N, +P, +N+P) in 2006 indicated that nutrient limitation is generally more consistent within lakes than for individual taxa across systems, with widespread nitrogen and secondary phosphorus limitation. Understanding phytoplankton community structure provides insight into the overall ecology of saline lakes, and will assist in the future conservation and management of these valuable and climatically-sensitive systems

The Influence of Fetch on the Holocene Thermal Structure of Hidden Lake, Glacier National Park

We use three-dimensional modeling of the basin of Hidden Lake, Montana, to assess the influence of effective fetch on diatom-inferred changes in mixing depths throughout the Holocene. The basin of Hidden Lake is characterized by a complex morphometry; for example, three-dimensional modeling of the lake basin indicates that a decrease in lake level of 2 m would result in complete isolation of the deepest part of the lake basin from the rest of the lake. Our model suggests that small changes in the lake surface elevation at Hidden Lake would produce threshold-like responses in effective fetch, which in turn would have a profound influence on average lake mixing depth. The present-day planktic diatom community of Hidden Lake is comprised of three species. Neo-ecological experiments revealed the effect of mixing depth and nutrient levels on growth rates of these species. A sediment core collected from the deepest part of the lake basin and spanning the last 8,640 years was analyzed for diatoms. Here we show how changes in fetch through the Holocene explain changes in the dominant planktic diatom species by modification of the thermal structure of Hidden Lake. Additionally, the timing of diatom-inferred changes in effective moisture and thermal structure from Hidden Lake were compared to late Holocene patterns reconstructed from other regional lake records. Between 8.64 – 7.61 ka the diatom record from Hidden Lake suggests that the lake was deep and fresh, although somewhat lower than the modern lake. After 7.61 ka, water levels rose, expanding the available benthic diatom habitat. Between 6.18 and 4.13 ka, lake level declined and seasonal stratification was enhanced. After 1.4 ka, the lake became deeper and less stratified in response to the effects of enhanced fetch. We argue that changes in effective fetch may play an important, and underexplored, role in planktic diatom community structure over longer time scales and should be more broadly considered in paleolimnological studies

Response of boreal lakes to changing wind strength: coherent physical changes across two large lakes but varying effects on primary producers over the 20th century

Near‐surface wind speeds have changed over recent decades, raising questions about the extent to which these changes are altering the vertical thermal structure of lakes and affecting lake food webs. Neo‐ and paleolimnological techniques were used to assess wind‐driven changes in lake thermal habitat and resulting effects on primary producers in two lakes in Isle Royale National Park, an island archipelago located in Lake Superior, where wind speed has increased in recent decades. Responses in Siskiwit Lake, a large (16 km2 surface area), deep (Zmax = 49 m), oligotrophic lake, were compared to those of Lake Desor, a moderately large (4.3 km2) but shallower (Zmax = 13 m), mesotrophic lake. High‐frequency sensor data suggested that changes in wind speed affected epilimnion thickness in both lakes synchronously (ρ = 0.7, p [less than] 0.001). Diatom‐inferred mixing depths suggested a coherent shift in both lakes to deeper mixing (an increase of 3 and 6 m) since 1920 (ρ = 0.8), which was correlated with an increase in regional wind speed during the 20th century at the decadal‐scale in Lake Desor and Siskiwit Lake (ρ = 0.6 and 0.4, respectively). In Lake Desor, algal biomass declined as mixing deepened from 1920 to 1980, and then cyanobacteria and cryptophyte pigments increased from 1980 to present, a period of inferred stable and deep mixing. Algal pigment concentrations in Siskiwit Lake were unchanged as mixing depth deepened. Although changes in wind speed altered lake physical structure similarly, the ecological consequences of these changes differed between lakes and were most likely influenced by lake‐specific variability in nutrient and light availability

Melting Alpine Glaciers Enrich High-Elevation Lakes with Reactive Nitrogen

Alpine glaciers have receded substantially over the last century in many regions of the world. Resulting changes in glacial runoff not only affect the hydrological cycle, but can also alter the physical (i.e., turbidity from glacial flour) and biogeochemical properties of downstream ecosystems. Here we compare nutrient concentrations, transparency gradients, algal biomass, and fossil diatom species richness in two sets of high-elevation lakes: those fed by snowpack melt alone (SF lakes) and those fed by both glacial and snowpack meltwaters (GSF lakes). We found that nitrate (NO3-) concentrations in the GSF lakes were 1-2 orders of magnitude higher than in SF lakes. Although nitrogen (N) limitation is common in alpine lakes, algal biomass was lower in highly N-enriched GSF lakes than in the N-poor SF lakes. Contrary to expectations, GSF lakes were more transparent than SF lakes to ultraviolet and equally transparent to photosynthetically active radiation.Sediment diatom assemblages had lower taxonomic richness in the GSF lakes, a feature that has persisted over the last century. Our results demonstrate that the presence of glaciers on alpine watersheds more strongly influences NO3- concentrations in high-elevation lake ecosystems than any other geomorphic or biogeographic characteristic