SFS Annual Meeting

5/20/2019  |   09:00 - 09:15   |  150 DEF

SURFACE TEMPERATURE OF ALPINE LAKES OF WASATCH AND UINTA Alpine lakes (lakes located at elevations above 2500~3000 meters) are some of the less studied ecosystems in the world. This is partially related to their location and accessibility. Therefore, the common perception is that they must be pristine (healthy) ecosystems. Recent events, however, have changed this view. Harmful Algal Blooms (HABs) which are toxic to both lake inhabitants and humans have been reported from a handful of alpine lakes. While climate change and urban/agricultural development have been accounted responsible for HAB events in lower elevation lakes, the origin of HAB events in alpine lakes remains unclear. During the summer of 2018, we established multiple pilot sites at various alpine lakes in Ashley National Forest and Uinta-Wasatch-Cache National Forest. We collected biweekly and monthly biological and physical samples from these lakes and deployed sensors for yearlong continuous measurements of water quality parameters. The long-term goal of this multiyear project is to determine the role of climate change in recent increase in frequency of HABs in alpine lakes.

Foad Yousef (Primary Presenter/Author), Westminster College, fyousef@westminstercollege.edu;


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5/20/2019  |   09:15 - 09:30   |  150 DEF

THE NET EFFECTS OF STRATIFICATION AND MIXING ON CYANOBACTERIA ACROSS THE COMPLETE LIFE CYCLE Cyanobacteria are increasing in freshwater lakes worldwide, with adverse consequences for ecosystem function. These increases are expected to continue, since cyanobacteria typically dominate phytoplankton communities in deep temperate lakes under warmer, more strongly stratified conditions. However, these forecasts ignore the fact that most bloom-forming taxa overwinter on or near the sediments, and thus must recruit into the water column to initiate new blooms. Moreover, many climate change scenarios for mesic north temperate regions predict an increase in high-intensity storms, which will increase episodic during otherwise thermally-stable summers. We have developed a simulation model to explore the net effects of stratification and mixing on cyanobacteria by considering their contrasting effects on benthic vs. pelagic life history stages. Informed by field data, the model includes adverse effects of episodic mixing on active pelagic colonies, but positive ffects of mixing on the return of benthic cyanobacteria to the water column. Results to date suggest that both benthic life stages and episodic mixing events need to be considered when forecasting how cyanobacteria will respond to global climate change, especially when recruitment is key to initiating blooms.

Kathryn Cottingham (Primary Presenter/Author), Dartmouth College, Kathryn.L.Cottingham@dartmouth.edu;


Cayelan Carey (Co-Presenter/Co-Author), Virginia Tech, cayelan@vt.edu;


Meredith Greer (Co-Presenter/Co-Author), Bates College, mgreer@bates.edu;


Holly Ewing (Co-Presenter/Co-Author), Bates College, hewing@bates.edu;


Kathleen Weathers (Co-Presenter/Co-Author), Cary Institute of Ecosystem Studies, weathersk@caryinstitute.org;


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5/20/2019  |   09:30 - 09:45   |  150 DEF

INTERACTIVE EFFECTS OF TEMPERATURE AND NUTRIENT SUPPLY ON STREAM ECOSYSTEM METABOLISM Stream ecosystem responses to climate warming must be considered in the context of other drivers of global change, such as nutrient enrichment. We quantified ecosystem metabolism during three summers (May-August) in four Icelandic streams that varied in mean temperature (8-16°C), before and after whole-stream nutrient additions (Year 1: no enrichment; Year 2: ~200 µg/L PO4-P; Year 3: ~200 µg/L NH4+-N+NO3-N). We predicted that addition of N, but not P, would modify temperature effects on the relative balance of gross primary production (GPP) and ecosystem respiration (ER; i.e., net ecosystem production, NEP). Nitrogen addition led to elevated GPP and ER, and the magnitude of response was positively related to temperature. In addition, N enrichment reduced NEP, particularly for warm streams, shifting their metabolic balance from net carbon sink to source. Addition of P had little effect on GPP but strong effects on ER, while again reducing NEP. Our results demonstrate that nutrient supply is critical in shaping metabolic responses to warming, and that ignoring temperature-nutrient interactions can lead to spurious conclusions about the effects of climate warming on streams.

Wyatt Cross (Primary Presenter/Author), Montana State University, wyatt.cross@montana.edu ;


James Hood (Co-Presenter/Co-Author), The Ohio State University, hood.211@osu.edu;


Jonathan P. Benstead (Co-Presenter/Co-Author), University of Alabama, jbenstead@ua.ed;


Alexander D. Huryn (Co-Presenter/Co-Author), The University of Alabama, huryn@ua.edu;


Kate Henderson (Co-Presenter/Co-Author), Montana State University, kahenderson121@gmail.com;


Jill Welter (Co-Presenter/Co-Author), St. Catherine University, jill.welter@gmail.com;


Philip Johnson (Co-Presenter/Co-Author), University of Alabama, Pjohnson@eng.ua.edu;


Jon Olafsson (Co-Presenter/Co-Author), Iceland Marine and Freshwater Research Institute, jon.s.olafsson@hafogvatn.is;


Gisli Gislason (Co-Presenter/Co-Author), University of Iceland, gisli@ui.is;


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5/20/2019  |   09:45 - 10:00   |  150 DEF

SHIFTING SNOWPACKS AND FOREST PHENOLOGY ALTER THE WINDOWS OF METABOLIC OPPORTUNITY FOR HUBBARD BROOK STREAM ECOSYSTEMS In streams that drain temperate deciduous forests, spring and autumn are the primary “windows of metabolic opportunity” in which small streams are both ice-free and well-lit. These windows may represent the only periods of high algal or microbial activity annually for many small, forested streams. For northeastern headwater streams, the spring window is constrained by snowmelt and canopy closure, while the fall window is constrained by litterfall and permanent snowpack. Long-term records for the Hubbard Brook Experimental Forest in NH document decreasing snowpack duration and a lengthening of the forest growing season. There is great interannual variability in both trends, leading to substantial variability in the timing of these key bookend events (litterfall, snow-on, snowmelt, leaf-on). Between 1989 and 2015, the spring window ranged from 7 to 43 days, while the autumn window (80% litterfall to snowpack >50mm) ranged from 37 to 105 days. Shifting forest growing season and snowpack duration are leading to colder, more well-lit streams during spring windows which may favor autotrophic activity. A longer autumn window will likely enhance the extent of leaf litter degradation, potentially reducing the residence time of organic matter in these streams.

Philip Savoy (Co-Presenter/Co-Author), Duke University, prs15@duke.edu;


Richard Marinos (Co-Presenter/Co-Author), University of Waterloo, rmarinos@uwaterloo.ca;


Emma Rosi (Co-Presenter/Co-Author), Cary Institute of Ecosystem Studies, rosie@caryinstitute.org;


Emily Bernhardt (Co-Presenter/Co-Author), Duke University, emily.bernhardt@duke.edu;


Audrey Thellman (Primary Presenter/Author), Univeristy of North Carolina at Chapel Hill, athellma@unc.edu;


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5/20/2019  |   10:00 - 10:15   |  150 DEF

RAPID SHIFTS IN ICE-OUT DATES IN NEW ENGLAND LAKES: CONSEQUENCES FOR OXYGEN AND TROPHIC STATE Lake ice-out dates offer an opportunity to see assess the regional impact of global climate change over 200 years of data, and shifts in the timing of this phenology may lead to both abiotic and biotic changes to lake ecosystems. Previous studies have shown lake ice-out dates in New England shifting 9 to 16 days earlier on average between 1800 and 2000. We examined how ice-out dates in 24 New England lakes have shifted over the past 15 years using a polynomial regression and logistic regressions to examine how ice-out date impacted oxygen depletion. For 16 of the lakes, the rate of shift in predicted ice-out date (velocity) increased for the 2000-2015 period. The ice-out velocity increased 39% between the two time periods (0.18 days per year 1975-2000, 0.25 days per year 2000-2015) Controlling for year, a logistic regression showed that oxygen stress was more likely to occur during years with early ice-out presumably due to a longer growing season. Analysis on phosphorus is ongoing, but anoxic conditions could lead to dissolution of previously insoluble phosphorus, thereby contributing to eutrophication.

William G. McDowell (Primary Presenter/Author), Merrimack College, wgmcdowell@gmail.com;


Alyssa Kullberg (Co-Presenter/Co-Author), EcoMinga Foundation, alyssa.kullberg@gmail.com;


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5/20/2019  |   10:15 - 10:30   |  150 DEF

EXPERIMENTAL EVIDENCE FOR STRONGER COMPETITION AT HIGHER ELEVATIONS: A MECHANISM FOR UPSLOPE RANGE MARGINS? Species’ geographic range shifts towards higher latitudes and elevations are among the most frequently reported consequences of climate change. Consequently, there has been increased interest in understanding the mechanisms that set range margins in the first place. The Species Interaction-Abiotic Stress Hypothesis (SIASH) predicts that harsh abiotic conditions should determine range margins at high elevations and latitudes. An alternative hypothesis is that species interactions can set range boundaries at high latitudes or elevations if harsh environmental conditions increase the susceptibility of organisms to predators or competitors. This results in range margins that appear to be set by abiotic constraints, a scenario we refer to as Apparent Climatic Exclusion (ACE). We used cage experiments in ponds in the Elk Mountains, CO to test whether SIASH or ACE dynamics structure the elevational range margins of an up-slope range-shifting caddisfly Limnephilus picturatus McLachlan. We found that the strength of competition between L. picturatus and a cosmopolitan resident species, Limnephilus externus Hagen, is stronger in L. picturatus’ new subalpine habitats compared to in lower montane habitats. These results support ACE and have broad implications for the role species interactions play in setting range margins.

Isaac Shepard (Primary Presenter/Author), University of Maine, isaac.shepard@maine.edu;


Scott Wissinger (Co-Presenter/Co-Author), Allegheny College, swissing@allegheny.edu;


Brad Taylor (Co-Presenter/Co-Author), North Carolina State University Dept. of Applied Ecology; Rocky Mountain Biological Laboratory, bwtaylo3@ncsu.edu ;


Hamish Greig (Co-Presenter/Co-Author), University of Maine, hamish.greig@maine.edu;


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