To determine temporal and spatial patterns in arctic stream biogeochemistry we conducted three synoptic surveys of streams throughout a 48km2 watershed near Toolik Lake, AK in spring (early-June), summer (mid-July), and fall (mid-September) 2011. During each synoptic survey, we sampled 52 sites within a period of four days to minimize the effect of temporal hydrologic variability. At each site we measured stream temperature, pH, and conductivity and sampled water for solute analysis.
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To determine temporal and spatial patterns in arctic stream biogeochemistry we conducted three synoptic surveys of streams throughout a 48km2 watershed near Toolik Lake, AK in spring (early-June), summer (mid-July), and fall (mid-September) 2011. During each synoptic survey, we sampled 52 sites within a period of four days to minimize the effect of temporal hydrologic variability. At each site we measured stream temperature, pH, and conductivity and sampled water for solute analysis. For measuring dissolved solutes, we filtered water samples in the field through ashed Whatman GF/F glass fiber filters. We froze water samples for nitrate, ammonium, phosphate, sulfate, chloride, total dissolved nitrogen (TDN), and dissolved organic carbon (DOC) concentration analysis. We also collected water from a subset of sites for measuring particulate carbon, nitrogen, and phosphorus. For particulates, we filtered water through ashed Whatman GF/F filters and retained the filter for analysis. Finally, we took a water sample at each site that we field filtered through ashed Whatman GF/F glass fiber filters and refrigerated to measure indices of DOC quality (Fluorescence Index (FI), Specific UV Absorbance (SUVA), and Excitation Emission Matrices (EEMs)).
Analysis of dissolved and particulate solutes in water samples from synoptic sampling sites was completed in the Water Quality Analysis Lab at the University of New Hampshire. Nitrate, sulfate, and chloride were measured on a Dionex ICS-1100 Ion Chromatograph using EPA method #300.1 for determination of inorganic ions. Ammonium and phosphate were measured colorometrically on a SmartChem 200 Discrete Analyzer using EPA methods #350.1 and #365, respectively. TDN and DOC were measured on a Shimadzu TOC-V CSH with TNM-1 using high temperature catalytic oxidation (EPA #415.1) for DOC and followed by chemiluminescent detection for TDN. We calculated dissolved organic nitrogen (DON) concentrations as TDN less nitrate and ammonium. Filters for particulate carbon and nitrogen were analyzed using combustion on a PerkinElmer 2400 Series II CHN Elemental Analyzer.
DOC quality samples were refrigerated and analyzed for specific UV absorbance (SUVA), fluorescence index (FI), and fluorescence excitation-emission matrices (EEMs). SUVA is the ratio of UV-absorbing to non-UV absorbing DOC with higher values indicating more aromatic compounds which are usually, but not always, more recalcitrant (Kalbitz et al., 2003; Weishaar et al., 2003; McDowell et al., 2006). In contrast, lower FI typically indicates a greater proportion of aromatic compounds in DOC with values near 1.3 typically indicating terrestrially derived DOC while values near 2.0 typically indicate microbially derived DOC (McKnight et al., 2001; Balcarczyk et al., 2009). Along with FI, other indexes of DOC source and quality can be calculated from EEMs, including the integrated excitation-emission peaks at 250-450 nm (Peak A), at 350-450nm (Peak C) and at 275-340nm (Peak T). In general Peak A and Peak C are indicative of more terrestrial and humic sources of DOC while Peak T is associated with more protein like sources of DOC (ref). SUVA (L mg C-1 m-1) of synoptic samples was calculated as absorbance at 254nm (measured on an Ocean Optics USB 4000) divided by path length (m) and DOC concentration (mg C L-1). The slope ratio of absorbance (unitless), inversely correlated with molecular weight of DOC, was calculated as absorbance between 275and 295 nm divided by the absorbance between 350 and 400 nm (Helms et al 2008). We measured fluorescence excitation-emission spectra on a Horiba Fluoromax-4. Fluorescence Index was calculated as the ratio of emission intensities at 470/520 nm after correction using the method of Cory et al (2010). We calculated the integrated excitation-emission peaks according to Cory et al. (2010).
No more updates. Project completed in 2012.
Organized and Prepared by K. Whittinghill: Dec. 2013
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