5/22/2016  |   15:30 - 15:45   |  302-303

GEOTHERMALLY-HEATED STREAM ECOSYSTEMS AT AN ALTITUDINAL GRADIENT IN ICELAND It is inevitable that climate driven changes are affecting freshwater ecosystems worldwide. Clear indications of rapid warming are seen in the Arctic regions. In stream ecology, our understanding and predictions on how warming may affect the ecosystem function, food-web structure and species assemblages have been limited. To study the effect of temperature on ecosystems, various approaches have been used e.g. mesocosms, heated stream channels or space-for-time substitutions. In our study we are using high-temperature geothermal fields at an altitudinal gradient (<100–1300 m a.s.l.) in Iceland, where we can find alkaline streams ranging between 5 and 43°C within confined areas. The overarching objective is to improve our understanding of possible consequences of climate warming upon stream ecosystems. The main results show that, with increasing temperature;1) algal biomass increases, which is mainly due to an increase in cyanobacteria biomass, 2) invertebrate density increases to a certain degree, 3) invertebrate taxa richness decreases and 4) a clear invertebrate taxa shift from chironomids assemblages to Gastrapoda, Oligochaeta and Acarina.

Jón S. Ólafsson (Primary Presenter/Author), Marine and Freshwater Research Institute, Iceland, jon.s.olafsson@hafogvatn.is;


Benoit Demars ( Co-Presenter/Co-Author), The James Hutton Institute, Aberdeen, Scotland, Benoit.Demars@hutton.ac.uk;


Gisli Mar Gislason ( Co-Presenter/Co-Author), University of Iceland, gmg@hi.is;


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


Eoin O'Gorman ( Co-Presenter/Co-Author), Imperial College London, UK, e.ogorman@imperial.ac.uk ;


Ragnhildur Magnusdottir ( Co-Presenter/Co-Author), The Institute of Freshwater Fisheries, Reykjavík, Iceland, ragna@veidimal.is;


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5/22/2016  |   15:45 - 16:00   |  302-303

COMPLEX DRIVERS OF ECOSYSTEM BIOMASS AND ELEMENT STORAGE ACROSS A NATURAL STREAM TEMPERATURE GRADIENT Anthropogenic activities have increased global surface air and water temperatures. While temperature is known to influence many ecosystem characteristics (e.g. primary production, respiration, organism body size), there has been less consideration about the complex, interacting physical and biological drivers that determine the size and composition of biomass pools that both drive—and result from—ecosystem processes. We quantified biomass and elemental composition of ecosystem compartments (macro producers, biofilm, CBOM, and FBOM) in 11 streams draining the same Icelandic catchment that vary in temperature (5-30 °C), stream gradient, and discharge. Mean benthic organic matter stocks varied across streams (range 6–200 g dry mass m^-2) and both biomass and element storage and stoichiometry were largely related to the presence/absence of macro-primary producers. Importantly, temperature was only one of many complex drivers of total ecosystem biomass and stoichiometry, while other factors such as species’ traits, channel morphology, and growth form played significant roles. Our study highlights the complex set of drivers that can influence biomass and element pools in streams, with implications for predicting stream responses to global change.

James Junker (Primary Presenter/Author), University of North Texas, james.junker1@gmail.com;


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


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


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


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


Gisli Mar Gislason ( Co-Presenter/Co-Author), University of Iceland, gmg@hi.is;


Daniel Nelson ( Co-Presenter/Co-Author), University of Oklahoma, dnelson12@crimson.ua.edu;


Jón Ólafson ( Co-Presenter/Co-Author), Icelandic Institute of Freshwater Fisheries, jsol@veidimal.is;


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5/22/2016  |   16:00 - 16:15   |  302-303

SYNTHESIZING THE EFFECTS OF EXPERIMENTAL WHOLE-STREAM WARMING ON COMMUNITY AND FOOD WEB STRUCTURE How freshwater communities will respond to future climate warming is an open question, partly because empirical studies at relevant spatial scales are essential for accurate prediction but challenging to execute. We experimentally warmed an entire stream reach in Iceland by approximately 3.5°C using a geothermal heat exchanger, and examined the response of invertebrate communities in the warmed stream and a nearby reference stream for 1 year prior to warming and 2 years during warming. Overall, warming altered invertebrate community structure and significantly reduced total community abundance, while total biomass and production remained unchanged. This neutral effect of warming on total community biomass and production was driven by declines in several small-bodied, cold-adapted taxa and concurrent increases in many larger, warm-adapted taxa, including newly invading species. Overall, our experimental results demonstrate that warming affects stream communities via exchange and relative success of species according to thermal physiology, and that shifts towards smaller body size are not a universal response to warming. Generalizing this result to global anthropogenic warming has important consequences for the future of aquatic communities and food webs.

Daniel Nelson (Primary Presenter/Author), University of Oklahoma, daniel.nelson79@gmail.com;


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


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


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


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


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


James Junker ( Co-Presenter/Co-Author), University of North Texas, james.junker1@gmail.com;


Gisli Mar Gislason ( Co-Presenter/Co-Author), University of Iceland, gmg@hi.is;


Jón Ólafson ( Co-Presenter/Co-Author), Icelandic Institute of Freshwater Fisheries, jsol@veidimal.is;


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5/22/2016  |   16:15 - 16:30   |  302-303

LANDSCAPE POSITION DEFINES LAKE WATER LEVEL FLUCTUATIONS IN RESPONSE TO PAST CLIMATE IN THE PACIFIC NORTHWEST Lake water levels fluctuate in response to interactions between precipitation, temperature and watershed hydrogeology, as well as being influenced by human land-use change (e.g., urbanization and agriculture). Although climate change impacts on river hydrology has been well studied, potential effects on lake hydrology are less well understood. This study aims to understand how natural and anthropogenic factors influence water level regimes in lakes (variability, magnitude, frequency of change, etc). Specifically, we explored the patterns and drivers of multi-decadal trends in water level across 60 small lakes in the Puget Sound lowlands of Washington State. We found that landscape position, defining the extent of upstream urbanization and other geomorphic factors, modulates the effects of local precipitation and temperature conditions on lake level regimes. By gaining a better understanding of how lake level fluctuations are driven by landscape position we provide insight into the vulnerability of lakes to the impacts of climate change on snowpack and air temperatures. This may call for either more active management of outlet weirs or inform new urban planning of green spaces.

Vincent Ouellet Jobin (Primary Presenter/Author), University of Washington, Seattle, vjobin@uw.edu;


Julian Olden ( Co-Presenter/Co-Author), University of Washington, olden@uw.edu;


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5/22/2016  |   16:30 - 16:45   |  302-303

IMPACTS OF THE 2014 SEVERE DROUGHT ON MICROCYSTIS BLOOMS IN SAN FRANCISCO ESTUARY A severe drought in 2014 provided the opportunity to test the impact of drought on freshwater cyanobacteria harmful algal blooms (CHABS) in San Francisco Estuary. The 2014 drought was the third driest year on record in San Francisco Estuary. Median chlorophyll a concentration increased by 13 and 9 fold over previous wet and dry years, respectively. Total microcystins toxin concentration exceeded that in previous wet and dry years by a factor of 69 and 11, respectively. The early initiation and persistence of warm water temperature near 19oC also extended the Microcystis bloom three months longer than previous blooms. The bloom was associated with extreme nutrient concentrations, including a 20 year high in soluble reactive phosphorus and low in ammonium concentration. Genetic analysis indicated cyanobacteria dominated the primary producer community, increased in diversity over previous years, and was accompanied by a suite of other bacteria.

Peggy Lehman (Primary Presenter/Author), California Department of Water Resources, Peggy.Lehman@water.ca.gov;


Tomo Kurobe ( Co-Presenter/Co-Author), University of California at Davis, tkurobe@ucdavis.edu;


Maxwell Mizel ( Co-Presenter/Co-Author), University of California at Davis, mtmizel@ucdavis.edu;


Sarah Lesmeister ( Co-Presenter/Co-Author), California Department of Water Resources, Sarah.Lesmeister@water.ca.gov;


Dolores Baxa ( Co-Presenter/Co-Author), University of California at Davis, dvbaxa@ucdavis.edu;


Alice Tung ( Co-Presenter/Co-Author), California Department of Water Resources, Alice.Tung@water.ca.gov;


Swee Teh ( Co-Presenter/Co-Author), University of California at Davis, sjteh@ucdavis.edu;


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5/22/2016  |   16:45 - 17:00   |  302-303

BENEATH THE SURFACE: CHANGES IN FULL TEMPERATURE PROFILES OF LAKES WITH WARMING SURFACE WATERS. In a recent study reported in Geophysical Research Letters, researchers analysing temperature data from 235 lakes from around the globe found that lake surface waters are warming at an average rate of 0.34°C/decade. There was a minimum of 25 years of data for all lakes in the study and the collection included seven lakes in the Boreal region of Canada near Sudbury, Ontario. Like other lakes in the study at northern latitudes, these seven lakes showed higher warming rates than the global average, with a mean warming rate of 0.43°C/decade. We examined changes in lake clarity measurements and the full temperature profile of these lakes over the same time period and discuss how these changes may be affecting fish habitat availability and the frequency and intensity of algal blooms.

John L Bailey (Primary Presenter/Author), Ontario Ministry of the Environment and Climate Change, jbailey@laurentian.ca;


Jocelyne Heneberry ( Co-Presenter/Co-Author), Ontario Ministry of the Environment and Climate Change, jheneberry @laurentian.ca;


Lisa Graham ( Co-Presenter/Co-Author), Cooperative Freshwater Ecology Unit, Laurentian University, grahaml76@gmail.com;


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