5/19/2015  |   13:30 - 13:45   |  101B

VARIATIONS IN COMPOSITION AND SIZE OF DISSOLVED ORGANIC MATTER ACROSS THE RIVER-LAKE INTERFACE IN SOUTHWEST LAKE MICHIGAN Water samples along a river-lake transect from the Milwaukee River (MR) to open Lake Michigan (LM) were collected between July-2012 and May-2014 and characterized for DOC abundance, UV-absorbance, fluorescence EEM and colloidal size spectra using FFF techniques. DOC and a254 decreased from the MR to LM, showing a strong terrestrial influence on the bulk DOM. Colloidal (>1kDa) DOM comprised 52-70% of the bulk DOM, decreasing from the MR to harbor and open LM. PARAFAC modeling identified three humic-like (C1, C3, C4) and one protein-like (C2) DOM components, with increasing C2/C1 and in-situ production from river to the lake. Colloidal chromophoric and humic-like DOM showed major (>70%) size partitioning at the 0.5-4 nm size range, while protein-like DOM had additional peaks at the 4-8nm and >30nm size ranges. Ratio of protein-like DOM between the 4-8nm and 0.5-4nm size ranges increased from river to lake, similar to the ratio between the >30nm and 0.5-4nm size ranges, suggesting more protein-like DOM with higher molecular weight in open lake waters. Variations in DOM characteristics were closely linked to sources and biogeochemical processes.

Zhengzhen Zhou (Primary Presenter/Author), School of Freshwater Sciences, University of Wisconsin-Milwaukee, zhengzhen.zhou.eagles@gmail.com;


Laodong Guo (Co-Presenter/Co-Author), School of Freshwater Sciences, University of Wisconsin-Milwaukee, guol@uwm.edu;

5/19/2015  |   13:45 - 14:00   |  101B

CHARACTERIZATION OF BULK AND CHROMOPHORIC DISSOLVED ORGANIC MATTER IN GREEN BAY, LAKE MICHIGAN Bulk dissolved organic carbon (DOC) analysis, UV-vis absorption, and fluorescence excitation-emission matrices (EEMs) coupled with parallel factor (PARAFAC) were used to quantify abundance, spatial distribution, composition, and sources of dissolved organic matter (DOM) in Green Bay, Lake Michigan in June 2014. DOC concentrations ranged from 202 – 571 µM-C with an average of 361 ± 73 µM-C. A significant south-to-north DOC gradient was evident, with the highest concentration in the Fox River, followed by stations near Sturgeon Bay. Absorption coefficient (a254) ranged from 12.4 – 58.5 m^-1 with an average of 30.5 ± 8.9 m^-1 and was significantly correlated to both DOC concentration and specific conductivity, attesting a significant terrestrial DOM source from the Fox River with higher molecular weight and aromatic components. Non-chromophoric DOM comprised ~32% of the bulk DOC, suggesting potential importance of photochemical processes. EEMs-PARAFAC modeling identified four major fluorescent DOM components, including two terrestrial humic-like, one aquagenic humic-like, and one protein-like component. The abundance and distribution of the terrestrial components buttress the dominance of riverine DOM and support a physicochemical control in southern Green Bay.

Stephen DeVilbiss (Primary Presenter/Author), University of Wisconsin-Milwaukee - School of Frehswater Sciences, devilbi3@uwm.edu;


Zhengzhen Zhou (Co-Presenter/Co-Author), School of Freshwater Sciences, University of Wisconsin-Milwaukee, zhengzhen.zhou.eagles@gmail.com;


Val Klump (Co-Presenter/Co-Author), School of Freshwater Sciences, University of Wisconsin-Milwaukee, vklump@uwm.edu;


Laodong Guo (Co-Presenter/Co-Author), School of Freshwater Sciences, University of Wisconsin-Milwaukee, guol@uwm.edu;

5/19/2015  |   14:00 - 14:15   |  101B

CHARACTERIZATION OF RIVERINE ORGANIC MATTER IN AN URBAN LANDSCAPE Dynamics of allochthonous and autochthonous organic matter (OM) in aquatic systems have been studied for decades, but urban studies have revealed additional, less studied, OM sources such as storm water, lawn clippings and wastewater effluent. We used the natural abundance of carbon, nitrogen and hydrogen isotopes to determine the sources of coarse particulate organic matter (CPOM), fine particulate organic matter (FPOM), and dissolved organic matter (DOM). Organic matter was sampled at 32 sites, in 4 watersheds that encompass a range of urban, suburban, range, and agricultural land uses in north east Utah. The proportional contribution of each source was estimated using the Stable Isotope Analyses in R package. CPOM was dominated by terrestrial sources (mean = 52%, range 35-61%), and FPOM by autochthonous sources (mean = 54%, range 38-68%). DOM carbon and hydrogen isotope signatures indicate primarily terrestrial DOM (d13C mean = -25.9 ‰ ± 0.5‰ and d2H = -98 ‰, ± 15.4‰). DOM spectroscopy indices including the Fluorescence Index, and SUVA254, were variable across all sites suggesting a mixture of microbial and terrestrially DOM regardless of land use.

Julie Kelso (Primary Presenter/Author), ORISE Environmental Protection Agency, julia.kelso@gmail.com;


Dave Epstein (Co-Presenter/Co-Author), Utah State University, davepstein@gmail.com;


Michelle Baker (Co-Presenter/Co-Author), Utah State University, michelle.baker@usu.edu;

5/19/2015  |   14:15 - 14:30   |  101B

CHARACTERIZATION OF DISSOLVED ORGANIC MATTER IN THE LAURENTIAN GREAT LAKES USING FLUORESCENCE EEM AND PARAFAC TECHNIQUES Chromophoric and fluorescent-DOM was characterized for surface waters in all Laurentian Great Lakes including Lake Superior (LS), Michigan (LM), Huron (LH), Saint Clair (LSC), Erie (LE), and Ontario (LO). DOC-concentrations, a254 and SUVA254 increased from LS to LE and LO, reflecting a change of DOM sources and reworking processes along the water transport pathway. DOM humification index was the highest in LE while the biological index (BIX) was the highest in open lake waters. Higher DOC abundance in LE, LO, and north LM was accompanied by higher aromaticity, molecular weight, and humification degree, but lower spectral slope (S275-295), and BIX values, suggesting sources of terrestrially-derived DOM from surrounding catchments. PARAFAC analysis on EEM data revealed four major fluorescent DOM components in the Great Lakes, including three terrestrial humic-like DOM components and one protein-like DOM component. The ratio of protein-like/humic-like DOM was the highest in open LH, but lowest in LE and LO. Changes in DOM composition along the water transport pathway in the Great Lakes indicate varying impacts from terrestrial inputs and human activities in the different lake systems.

Laodong Guo (Primary Presenter/Author), School of Freshwater Sciences, University of Wisconsin-Milwaukee, guol@uwm.edu;


Zhengzhen Zhou (Co-Presenter/Co-Author), School of Freshwater Sciences, University of Wisconsin-Milwaukee, zhengzhen.zhou.eagles@gmail.com;


Elizabeth Minor (Co-Presenter/Co-Author), University of Minnesota Duluth, eminor@d.umn.edu;

5/19/2015  |   14:30 - 14:45   |  101B

SPATIAL VARIABILITY IN A EUTROPHIC LAKE DURING FALL TURNOVER Assessments of spatial variability in lakes are often limited and extrapolations from a small number of sampling points increase uncertainty with respect to elemental budgets, and the underlying drivers of important processes such as primary production. We mapped surface water chlorophyll and CO2 on Lake Mendota, WI in Oct-Nov 2014 during fall turnover using a high-resolution sensor platform (> 35,000 spatially-distributed measurements). Surface water concentrations of chlorophyll and CO2 increased during lake turnover suggesting that the hypolimnion released stored nutrients and dissolved gas. Turnover increased lake-wide primary production and carbon dioxide efflux. Spatial patterns of chlorophyll and CO2 revealed strong contrasts across the lake’s surface. Littoral zones and river mouths had higher concentrations of chlorophyll and lower CO2 than pelagic zones. Spatial variability in these parameters was greatest in the nearshore areas, as complex sediment-surface water interactions lead to large variations in surface water conditions. While using single point observations in the middle of lakes may accurately represent metabolic and efflux rates across pelagic zones, such datasets are not representative of processes in littoral and riverine transition zones.

Luke Loken (Primary Presenter/Author), University of Wisconsin-Madison, lloken@wisc.edu;


John Crawford (Co-Presenter/Co-Author), U.S. Geological Survey, jtcrawford@usgs.gov;


Nora Casson (Co-Presenter/Co-Author), University of Winnipeg, n.casson@uwinnipeg.ca;


Vincent Butitta (Co-Presenter/Co-Author), Center for Limnology, vincent.butitta@wisc.edu;


Emily Stanley (Co-Presenter/Co-Author), University of Wisconsin - Madison, ehstanley@wisc.edu;

5/19/2015  |   14:45 - 15:00   |  101B

INFLUENCES OF DOC ON NITRATE UPTAKE IN SUBURBAN STREAMS DOC strongly influences N processing in streams but the underlying mechanisms driving the coupled interaction of organic matter quantity and uptake of inorganic nitrogen forms are not well understood. A series of NO3 additions was conducted in four sites within the Lamprey River Watershed (LRW) with a wide range in background DOC (1 - 8 mg C/L) and NO3 (2 – 1160 ug N/L) concentrations from spring through fall in 2013 and 2014. Across all sites and experimental dates, ambient and dynamic uptake velocities (Vf) correlated negatively with NO3 concentrations and positively with increasing DOC concentrations and DOC:NO3 ratios. Individual sites varied in their uptake kinetics, with data suggesting that saturation and efficiency loss models, hysteresis, undetectable uptake, and an increase in Vf with higher NO3 concentrations can all occur. Sites with high DOC and DOC:NO3 were the most efficient at removing NO3 from the water column but demonstrated saturation kinetics; those with high NO3 concentrations were less efficient but did not saturate. NO3 uptake dynamics in the LRW seem to be most influenced by DOC rather than NO3 concentrations.

Bianca Rodriguez-Cardona (Primary Presenter/Author), University of New Hampshire, bianca.rodz.pr@gmail.com;


William H McDowell (Co-Presenter/Co-Author), University of New Hampshire, bill.mcdowell@unh.edu;