[1] Dissolved organic matter (DOM) originating from the extensive Arctic tundra is an important source of organic material to the Arctic Ocean. Chemical characteristics of whole water dissolved organic matter (DOM) and the fulvic acid fraction of DOM were studied from nine surface waters in the Arctic region of Alaska to gain insight into the extent of microbial and photochemical transformation of this DOM. All the fulvic acids had a strong terrestrial/higher plant signature, with uniformly depleted d 13C values of À28%, and low fluorescence indices around 1.3. Several of the measured chemical characteristics of the Arctic fulvic acids were related to water residence time, a measure of environmental exposure to sunlight and microbial activity. For example, fulvic acids from Arctic streams had higher aromatic contents, higher specific absorbance values, lower nitrogen content, lower amino acid-like fluorescence and were more depleted in d 15 N relative to fulvic acids isolated from lake and coastal surface waters. The differences in the nitrogen signature between the lake and coastal fulvic acids compared to the stream fulvic acids indicated that microbial contributions to the fulvic acid pool increased with increasing water residence time. The photo-lability of the fulvic acids was positively correlated with water residence time, suggesting that the fulvic acids isolated from source waters with larger water residence times (i.e., lakes and coastal waters) have experienced greater photochemical degradation than the stream fulvic acids. In addition, many of the initial differences in fulvic acid chemical characteristics across the gradient of water residence times were consistent with changes observed in fulvic acid photolysis experiments. Taken together, results from this study suggest that photochemical processes predominantly control the chemical character of fulvic acids in Arctic surface waters. Our findings show that hydrologic transport in addition to biogeochemical alteration of the organic matter must be considered in order to predict the ultimate fate of Arctic DOM.

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39) Leighton, D.; Acrivos, A. Chem. Eng. Sci. 1986, 41, (40) Bhatty, J. I.; Reid, K. J.; Dollimore, D.; Shah, T. H.; Davies, L.; Gamlin, G. A.; Tamini, A. Sep. Sci. Technol. 1989,24, 157-185. (44) Adham, S. A.; Snoeyink, V. L.; Clark, M. M.; Bersillon, J.-L. J.-Am. Water Works Assoc. 1991,83, 81-91. (45) Wiesner, M. R.; Clark, M. M.; Mallevialle, J. J . Environ. Eng. 1989,115, 20-40. (46) Bhatty, J. I.; Reid, K. J.; Dollimore, D.; Shah, T. H.; Gamlen, G. A.; Tamini, A.Fluorescence quenching was used to measure the binding of pyrene and phenanthrene to marine interstitial water organic colloids from Boston Harbor, MA. Both pyrene and phenanthrene were sorbed by porewater colloids (Koc colloid -105.0 and 104.3, respectively) from a heavily contaminated nearshore site. Pyrene had a significantly lower affinity toward colloids from a cleaner location (Kmmuoid N 104.5). Sediments from the former site were also observed to be especially effective sorbents for these compounds relative to expectations based on the literature. The high sorption coefficients may be due to the high lipid content of these sediments and colloids. Alternatively, they may be due to a very substantial nonpolar character of the natural organic matter there.

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Materials and MethodsSurface water samples were collected in pre-combusted (450 °C, 6 hr) glass jars, filtered through pre-combusted (550 °C, 5.5 hr) glass fiber filters (0.7 m, Millipore) on site, and stored on ice for transport. Upon arrival in the laboratory, the samples were 0.22 m filtered (mixed cellulose esters, Millipore) and stored at 4 °C. The porewaters were collected by centrifugation 1 and were then 0.2 m filtered (PTFE, Pall Life Sciences). Sulfate and other anions were measured via ion chromatography (Dionex ICS 2000 with an AS19 4 mm column).Liquid state 1 H NMR spectra were obtained on a 400 MHz Bruker Biospin Avance III NMR equipped with a broadband inverse probe using a water suppression pulse program (optimized WATERGATE pulse sequence from Lam and Simpson 2 ) with a 2 sec recycle delay, a time domain of 16k, and 2000 co-added scans (approximately 3 hour run time). This sequence

Prairie pothole lakes (PPLs) are critical hydrological and ecological components of central North America and represent one of the largest inland wetland systems on Earth. These lakes are located within an agricultural region, and many of them are subject to nonpoint-source pesticide pollution. Limited attention, however, has been paid to understanding the impact of PPL water chemistry on the fate and persistence of pesticides. In this study, the abiotic reductive transformation of seven dinitroaniline pesticides was investigated in PPL sediment porewaters containing naturally abundant levels of reduced sulfur species (i.e., bisulfide (HS(-)) and polysulfides (S(n)(2-))) and dissolved organic matter (DOM). Target dinitroanilines underwent rapid degradation in PPL porewaters and were transformed into corresponding amine products. While the largest fraction of the transformation could be attributed to reduced sulfur species, experimental evidence suggested that other reactive entities in PPL porewaters, such as DOM and mineral phases, might also affect the reaction rates of dinitroanilines. Results from this study highlight the importance of reductive transformation as an abiotic natural attenuation pathway for pesticides entering the PPL sedimentary environment.

Prairie pothole lakes (PPLs) are located within the extensively farmed Great Plains region of North America, and many are negatively impacted by nonpoint source pesticide pollution. To date, the environmental fate of pesticides in these lakes remains largely unknown. In this study, two PPLs in the Cottonwood Lake area of North Dakota were sampled, and transformations of four chloroacetanilide pesticides in sediment porewaters were examined. The reduced sulfur species in the porewaters, such as bisulfide (HS(-)) and polysulfides (S(n)(2-)), readily transformed the target pesticides into sulfur-substituted products. Although HS(-) and S(n)(2-) played a dominant role, other reactive constituents in PPL porewaters also contributed to the transformation. Results from this study revealed that abiotic reactions with reduced sulfur species could represent an important removal pathway for pesticides entering PPLs.

Sediment pore-water dissolved organic matter (DOM) in two North Dakota prairie pothole lakes was quantified by dissolved organic carbon analysis (DOC) and its composition was characterized as a function of sediment depth for molecular weight distribution (MWD), molar absorptivity at 280 nm (e280), and fluorescence properties. Fluorescence excitation emission matrices were further analyzed by creating a Parallel Factor Analysis (PARAFAC) model specific to sedimentary pore-water DOM. The range of absolute pore-water DOC concentrations (, 26-183 mg C L 21 ) greatly exceeded abundances reported for other wetlands and generally increased with depth. Significant changes occurred in e280 and fluorescence seasonally. Prairie pothole pore-water DOM is primarily allochthonous in nature and three 'humic-like' components explained , 90% of total sample fluorescence, while a single 'non-humic' component was responsible for the remaining 10%. The contribution of the non-humic component, however, was more significant in the top 7 cm of sediment in samples collected in early autumn and is presumably derived from algal precursor material produced by primary production in the water column over the summer. The PARAFAC results corroborate e280 and MWD changes in pore-water DOM composition over the growing season. This dynamic process could affect the type of DOM available for biogeochemical processes seasonally.The majority of the upper Midwest and Northern Great Plains regions of the north-central United States and southcentral Canada are a glaciated prairie containing an abundance of freshwater, saline, and hypersaline depressional wetlands, known as prairie pothole lakes (PPLs), in relatively flat outwash plains and hummocky moraines (Winter and Rosenberry 1998). PPLs were formed glacially during the late Pleistocene Epoch and cover an area of , 700,000 km 2 of the United States and Canada, known as the prairie pothole region (PPR; van der Valk 2005). They are an important lacustrine and hydrologic feature in this part of North America.Dissolved organic matter (DOM) plays an integral role in a variety of biogeochemical processes in wetland and lacustrine ecosystems and influences ecosystem function in a variety of ways. DOM also plays a vital role in the overall global carbon cycle (Lam et al. 2007), in oxidationreduction reactions (Hakala et al. 2009), and has been shown to serve as an electron acceptor for microbial respiration (Lovely et al. 1996). Further, organic contaminants can be transformed in the presence of natural DOM in anoxic environments (Hakala et al. 2009;Zeng et al. 2011Zeng et al. , 2012.One well-studied wetland complex in the PPR is the Cottonwood Lakes Study Area (CWLA) in Stutsman County, North Dakota. Eighteen small pothole lake basins comprise the wetland complex. The CWLA has been investigated extensively since the 1960s (Winter and Rosenberry 1998;Euliss et al. 2004;Holloway et al. 2011) with respect to its hydrologic, chemical, and biologic attributes. To date, however, little is known about th...