Identification of dissolved organic matter size components in freshwater and marine environments

Dissolved organic matter (DOM) in the transition zone from freshwater to marine systems was analyzed with a new approach for parameterizing the size distribution of organic compounds. We used size-exclusion chromatography for molecular size analysis and quantified colored DOM (CDOM) on samples from two coastal environments in the Baltic Sea (Roskilde Fjord, Denmark and Gulf of Gdansk, Poland). We applied a Gaussian decomposition method to identify peaks from the chromatograms, providing information beyond bulk size properties. This approach complements methods where DOM is separated into size classes with pre-defined filtering cutoffs, or methods where chromatograms are used only to infer average molecular weight. With this decomposition method, we extracted between three and five peaks from each chromatogram and clustered these into three size groups. To test the applicability of our method, we linked our decomposed peaks with salinity, a major environmental driver in the freshwater-marine continuum. Our results show that when moving from freshwater to low-salinity coastal waters, the observed steep decrease of apparent molecular weight is mostly due to loss of the high-molecular-weight fraction (HMW; >2 kDa) of CDOM. Furthermore, most of the CDOM absorbance in freshwater originates from HMW DOM, whereas the absorbing moieties are more equally distributed along the smaller size range (<2 kDa) in marine samples.Peer reviewe

The effect of pH, aluminum, and chelator manipulations on the growth of acidic and circumneutral species of Asterionella

The growth rates of two diatoms, acidophilic Asterionella ralfsii and circumneutral A. formosa , were differentially affected by varying pH, Al, and EDTA in chemically defined media. Free Al ion concentration increased as pH and EDTA concentration decreased. Free trace metal ion concentration decreased as EDTA levels increased but increased by orders of magnitude upon addition of Al. pH had an overriding species specific effect on growth rate; at low pH A. ralfsii had higher growth rates than A. formosa and vice versa at high pH. For both species higher EDTA levels depressed growth rates. Moderate additions of Al generally resulted in growth stimulation. The growth rate stimulations, especially at 200 and 400 μg L −1 Al additions, correlate to increases in free trace metal ion concentrations. The EDTA-AI interaction effects on growth rate were both pH and concentration dependent: at pH 7 both species were stimulated by addition of Al at all EDTA levels (except A. ralfsii at 5.0 mM EDTA and A. formosa at 0.5 mNM EDTA); at pH 6 Al addition either stimulated or had no effect on the growth rates of both species (except at low EDTA and high Al levels); at pH 5 A. formosa did not grow and additions of 200 μg L −1 Al stimulated growth of A. ralfsii . It is likely that the effect of pH, Al, and EDTA on speciation of essential or toxic trace metals affects growth rates of these diatoms in a species specific manner.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43905/1/11270_2004_Article_BF00282626.pd

Naturlige bakgrunnskonsentrasjoner av metaller. Kan atmosfæriske avsetninger påvirke metallkonsentrasjoner i flomsedimenter slik at de ikke reflekterer berggrunnens geokjemi?

Det var en god overensstemmelse mellom konsentrasjoner av Cr, Ni, Cu, V, Be og Co i flomsedimentenes fin-fraksjon (< 62 um) og de tilhørende innsjøsedimentene avsatt i før-industriell tid. For disse elementene var de atmosfæriske avsetningene relativt små og den antropogene andelen liten. For Pb, As, Hg og Cd, som alle hadde klare antropogene atmosfæriske avsetninger, var det derimot ingen sammenheng mellom konsentrasjonene i flomsedimentene og de tilhørende innsjøsedimentene avsatt i før-industriell tid. Årsaken var at flomsedimentene inneholdt organisk materiale som sammen med forurensningene fra atmosfæren antagelig har perkolert (sivet) ned i flomsedimentet fra humussjiktet. Kombinasjonen grunne flomsedimenter, betydelige atmosfæriske avsetninger og store nedbørmengder gjør at geokjemiske kart basert på flomsedimenter ikke reflekterer berggrunnens geokjemi på Sørlandet og Sør-Vestlandet for den sistnevnte elementgruppen. Se og Hg var positivt korrelert til organisk materiale i alle sedimenttyper inklusive de pre-industrielle referansesedimentene. Dette skyldes en kombinasjon av lave konsentrasjoner i berggrunnen og betydelige naturlige atmosfæriske avsetninger (dette er spesielt for Se og Hg). Derfor må selv uforurensede flomsedimenter være tilnærmet uorganiske hvis de skal reflektere berggrunnens innhold av Hg og Se

Trace metal concentrations in lake and overbank sediments in southern Norway

Abstract As, Be, Cd, Co, Cr, Cu, Hg, Ni, Pb, V, Se and Zn concentrations were determined and compared in lake and overbank sediments from 33 catchments without local pollution sources in southern Norway. There were no significant differences in concentrations of Be, Co, Cr, Cu, Ni, and V in overbank and pre-industrial lake sediments. In areas with shallow overburden, and significant influence from long-range atmospheric pollution, concentrations of As, Cd, Hg, Pb, Se, and Zn in overbank sediments were probably modified by vertical percolating water. In such areas, we suggest using lake sediments as a better sampling medium for mapping pre-industrial concentrations. Pre-industrial lake sediments yield natural concentrations of Hg and Se, which consist of both geogenic and natural atmospheric deposition. Important covariables like organic carbon content, Fe oxides, and fine mineral fraction were generally higher in preindustrial lake sediments as compared to overbank sediments. By adjusting for such differences overbank sediments could be used as an alternative in mapping background concentrations of trace metals in regions with few lakes