Contributed Session.

Lead Organizer: Sandra Clinton, University of North Carolina Charlotte (sandra.clinton@charlotte.edu)

Presentations

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09:00 AM

NATURAL AND HUMAN DRIVERS OF SPECIFIC CONDUCTANCE AND MAJOR ION COMPOSITION IN UNITED STATES LAKES (8916)

Primary Presenter: Xinyu Sun, Michigan State University (16xs6@queensu.ca)

Specific conductance (SC) and major ion composition are important for understanding and predicting lake water quality and ecosystem responses to global changes and disturbances. However, little is known about SC and ionic composition for populations of lakes at the continental scale, nor their relationships with natural and human factors operating at multiple spatial scales. We examined the spatial patterns in SC (N=9,784 lakes) and major anion and cation concentrations (N=1,218 lakes) across the conterminous United States, and quantified their relationships with a wide range of multi-scaled natural and human factors. We found substantial spatial variation in ion composition and that lakes with similar SC values can have very different ion composition. Most lakes had relatively low SC (median=206μS/cm), with high-SC lakes mainly located in the Plains, Desert Southwest, and Florida. Calcium and bicarbonate were the most common ions in 61% of the study lakes, with the remaining lakes dominated by the cations magnesium or sodium and the anions sulfate or chloride. Lake SC was associated with natural factors including elevation, watershed soils, and hydrology and was influenced by land uses. Ion composition was associated with similar natural factors along with surface connectivity and precipitation, but also strongly affected by road density and urban development. Our results suggest that while geological, hydrological, and climate processes control the ion inputs from natural sources, human disturbances can cause SC and major ions to deviate from their background levels.

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09:15 AM

RAZOR CLAM RESILIENCE IN A CHANGING OCEAN: VARIATION IN SHELL THICKNESS AND STRENGTH ACROSS A MOSAIC OF OCEANOGRAPHIC CONDITIONS (8985)

Primary Presenter: Amelia Ritger, University of California Santa Barbara (aritger@ucsb.edu)

Coastal communities face increasing threats from climate change-induced stressors such as ocean acidification and heatwaves. Shellfish fisheries of the Pacific Northwest U.S. exemplify this vulnerability as this region is particularly susceptible to ocean acidification, which presents a considerable risk to shellfish survival and growth. The Pacific razor clam (Siliqua patula) fishery is one of the most popular recreational fisheries in Washington state and also provides significant cultural value to coastal tribal communities. In recent years, some tribal harvesters have observed more breakage in razor clam shells during harvest. To investigate biogeographic patterns in razor clam shell traits and their relationship with local oceanographic conditions, we collected razor clams from 13 sites spanning over 700 km of coastline from Oregon, U.S. to British Columbia, Canada. We measured shell size, thickness, and strength and analyzed their correlation with environmental factors such as ocean pH, temperature, and oxygen. By comparing modern shells to historical specimens, we identified temporal trends in these relationships. For example, our findings reveal significant differences in shell length:thickness ratios between locations which may support existing evidence of biogeographic variation in species vulnerability to climate change. Our findings provide valuable information for resource managers to identify at-risk populations and effectively manage the risks and impacts on a calcifying marine species that provides important economic, recreational, and cultural benefits.

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09:30 AM

Ecosystems in transition: Exploring limnological conditions in lakes spanning the Canadian prairie to Montane Cordillera ecotone (9562)

Primary Presenter: Paola Ayala-Borda, University of Lethbridge (p.ayalaborda@gmail.com)

Environmental characteristics shift predictably with altitude, generating gradients of temperature, hydrology, and vegetation. However, how such environmental gradients transmit an effect on the ecology of freshwater ecosystems is not well understood in ecotones. To test this, we sampled 11 lakes spanning a 600m elevation gradient along the ecotone between the Canadian Prairies and Montane Cordillera. We hypothesized that shifting lake elevation and climatic and catchment features would alter the quality and quantity of allochthonous inputs, thus determining lake chemical composition and metabolic rates. We analyzed catchment variables, water chemistry, lake metabolic rates, and dissolved organic matter (DOM) composition. Surprisingly, the differences in catchment composition and water temperature along the elevation gradient were not clearly linked to DOM content nor composition. DOM composition was dominated by autochthonous sources, and most lakes were net autotrophic. Yet, primary production and respiration rates were linked to elevation indirectly through changes in water temperature. While production and respiration both scaled with DOM content, net ecosystem production was unrelated to elevation and peaked at intermediate DOM levels. Overall, while environmental features shift predictably along the ecotone, they transmit inconsistent effects to the limnology of regional lakes. We attribute the limited influence of elevation (i.e., position in the ecotone) to the region's overall low precipitation regime and lakes' low hydrological connectivity with their catchments

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