State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China; School of Freshwater Sciences, University of Wisconsin-Milwaukee, 600 E Greenfield Ave., Milwaukee, WI 53204, USA.
Green Bay Metropolitan Sewerage District, Green Bay, WI 54302, USA.
Sci Total Environ. 2018 Feb 15;615:931-941. doi: 10.1016/j.scitotenv.2017.10.019. Epub 2017 Oct 7.
Dynamic variations in chemical composition and size distribution of dissolved organic matter (DOM) along the river-lake interface in the Fox River plume were investigated using ultrafiltration, flow field-flow fractionation, UV-Vis and fluorescence spectroscopy and parallel factor analysis. On average, ~67% of bulk dissolved organic carbon (DOC) were partitioned in the <1kDa (actual cutoff 2.5kDa) low molecular weight fraction, and the other 33% were in the 1kDa-0.7μm colloidal phase. Concentrations of DOC and chromophoric DOM in the bulk and size-fractionated samples decreased monotonously with decreasing conductivity from river to bay waters, demonstrating a dominant terrestrial source and quasi conservative mixing behavior. However, the percentages of colloidal fluorescent-DOM increased while those of carbohydrates decreased from river to bay waters, showing different mixing behavior in the river plume. Colloidal chromophores and humic-like fluorophores were mainly partitioned in the size range of 1-6nm, but a bimodal distribution (with peaks at 1-6 and 35-45nm) was observed for colloidal protein-like DOM. Along the river-lake transect, the peak locations of chromophores, humic-like and small-sized protein-like colloids remained almost constant, while the larger-sized protein-like colloids exhibited a slight peak shift from 38.3 to 40.4nm, showing a molecular size enhancement from high to low conductivity waters, with physical mixing, photochemical/microbial degradation, and disaggregation/repartitioning being the important processes affecting the variations of DOM size and composition. New results herein should enhance our understanding of the heterogeneity of DOM in size and composition and its fate, transport and transformation at the river-lake interface and along the aquatic continuum as a whole.
采用超滤、流场分级、紫外-可见和荧光光谱及平行因子分析等方法，研究了福克斯河羽状流沿河湖界面的溶解有机物（DOM）化学组成和粒径分布的动态变化。平均而言，约 67%的总溶解有机碳（DOC）分配在<1kDa（实际截止值 2.5kDa）的低分子量部分，其余 33%分配在 1kDa-0.7μm 的胶体相中。在 bulk 和分级样品中，DOC 和发色 DOM 的浓度随电导率从河流到海湾的降低而单调下降，表明主要为陆地源且具有准保守混合行为。然而，从河流到海湾，胶体荧光 DOM 的百分比增加，而碳水化合物的百分比减少，表明在河羽状流中具有不同的混合行为。胶体色团和类腐殖质荧光团主要分配在 1-6nm 的粒径范围内，但胶体蛋白样 DOM 呈现双峰分布（峰值在 1-6nm 和 35-45nm）。沿河湖断面，色团、类腐殖质和小尺寸蛋白样胶体的峰位置基本保持不变，而较大尺寸蛋白样胶体的峰位置略有从 38.3nm 到 40.4nm 的偏移，表明从高电导率到低电导率水体的分子尺寸增大，物理混合、光化学/微生物降解以及解团聚/再分配是影响 DOM 粒径和组成变化的重要过程。本研究的新结果应增强我们对河湖界面和整个水连续体中 DOM 大小和组成异质性及其归宿、输运和转化的认识。
