Relationships between iron (Fe) and the carbon specific absorbance (a₄₂₀/DOC) based on all available data from Swedish lakes, streams and river mouths (panel A) and confirmed by data from Canadian lakes (panel B).

<p>In panel B we predicted a₄₂₀/DOC by using the regression equation of panel A and obtained the regression line which is shown. Note the different scales between panel A and B.</p

Prediction of absorbance (a₄₂₀) by dissolved organic carbon (DOC), iron (Fe) and particulate matter (particles) for 46787 Swedish water samples.

<p>Particulate matter was assessed by the absorbance ratio between unfiltered and filtered water (see methods). 92% of the a₄₂₀ variations could be explained by the simple standard least squares model (panel A; a₄₂₀ = e^{(0.73+0.76·ln<i>DOC</i>+0.38·ln<i>Fe</i>−0.83·ln<i>Particles</i>)}) where all three input variables made a significant contribution to the model performance, here shown by model leverage plots (panels B–D). Removing the input variable particles from the model, the model performance decreased to <i>R</i>² = 0.85, <i>P</i><0.0001, <i>n</i> = 46787. Using only DOC as input variable the model performance was <i>R</i>² = 0.73, <i>P</i><0.0001, <i>n</i> = 46787.</p

Fate of iron (Fe), dissolved organic carbon (DOC) and absorbance (a₄₂₀) along the aquatic continuum under normal wet conditions (panel A) and in a wetter climate (panel B).

<p>When water travels from headwaters to river mouths and passes lakes Fe, DOC and a₄₂₀ all decline (compare <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0088104#pone-0088104-g003" target="_blank">Fig. 3</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0088104#pone-0088104-g004" target="_blank">Fig. 4</a>). It is suggested that a concomitant Fe, DOC and a₄₂₀ decline in surface waters of lakes is a result of Fe-OC complexes that can flocculate and reach bottom waters and sediments (panel A). In a wetter climate with a consequent faster flushing of waters through lakes the settling of Fe-OC complexes towards bottom waters and sediments becomes less efficient and Fe-OC complexes reach downstream waters, where they cause strong declines in a₄₂₀ (panel B). The conceptual figure assumes that Fe-OC complexes mainly originate from soils.</p

Iron (Fe), dissolved organic carbon (DOC), absorbance (a₄₂₀), Fe/DOC and a₄₂₀/DOC ratios in relation to the percentage of lake surface area in the catchment area (% Water).

<p>For the figure, site-specific long-term median data of 5837 different lakes and streams were used. Taking the median of each of the 11% Water categories and applying a simple exponential decay along the % Water gradient we received highly significant results (<i>P</i><0.0001, <i>n</i> = 11; <i>R²</i> = 0.78 for Fe/DOC in panel A, <i>R²</i> = 0.84 for a₄₂₀/DOC in panel B, <i>R²</i> = 0.95 for Fe in panel C, <i>R²</i> = 0.89 for a₄₂₀ in panel D and <i>R²</i> = 0.88 for DOC in panel E).</p

Temporal development of dissolved organic carbon (DOC), absorbance (a₄₂₀), iron (Fe) and reactive silica (Si) in Swedish freshwaters and changes in long-term annual precipitation across Sweden since 1996.

<p>The DOC, a₄₂₀, Fe and Si data (panels A–D) are based on annual mean values from 66 lakes, streams and river mouths for which complete monthly time series were available. Thus, for each year, 66 data points have been used for the percentile calculations. For panel E, 10-year running means of data from entire Sweden have been used (see methods).</p

Decreasing iron (Fe), dissolved organic carbon (DOC) and absorbance (a₄₂₀) with increasing percentage of lake surface area in the catchment area (% Water).

<p>The figure shows the predicted values of Fe, DOC and a₄₂₀ from the simple exponential decay functions along the % Water gradient presented in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0088104#pone-0088104-g003" target="_blank">Fig. 3</a>. Fe and a₄₂₀ decline equally fast with increasing % Water. The Fe and a₄₂₀ decline is substantially faster than the decline of DOC. % Water can be seen as a proxy for water retention in the landscape (see methods).</p

Selective Chlorination of Natural Organic Matter: Identification of Previously Unknown Disinfection Byproducts

Natural organic matter (NOM) serve as precursors for disinfection byproducts (DBPs) in drinking water production making NOM removal essential in predisinfection treatment processes. We identified molecular formulas of chlorinated DBPs after chlorination and chloramination in four Swedish surface water treatment plants (WTPs) using ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). Chlorine-containing formulas were detected before and after disinfection and were therefore classified to identify DBPs. In total, 499 DBPs were detected, of which 230 have not been reported earlier. The byproducts had, as a group, significantly lower ratio of hydrogen to carbon (H/C) and significantly higher average carbon oxidation state (C_OS), double bond equivalents per carbon (DBE/C) and ratio of oxygen to carbon (O/C) compared to Cl-containing components present before disinfection and CHO formulas in samples taken both before and after disinfection. Electrophilic substitution, the proposed most significant reaction pathway for chlorination of NOM, results in carbon oxidation and decreased H/C while O/C and DBE/C is left unchanged. Because the identified DBPs had significantly higher DBE/C and O/C than the CHO formulas we concluded that chlorination of NOM during disinfection is selective toward components with relatively high double bond equivalency and number of oxygen atoms per carbon. Furthermore, choice of disinfectant, dose, and predisinfection treatment at the different WTPs resulted in distinct patterns in the occurrence of DBP formulas

Appendix A. Search strategy.

Search strategy

Appendix C. Results for lentic ecosystems.

Results for lentic ecosystems

Appendix B. Tables listing studies that observationally quantified or manipulated subsidies for testing our hypotheses.

Tables listing studies that observationally quantified or manipulated subsidies for testing our hypotheses