Composition and Size Distribution of Colored Dissolved Organic Matter in River Waters as Characterized Using Fluorescence EEM and Flow Field-Flow Fractionation Techniques

Author(s): Zhou, Z. ;  Stolpe, B.;  Guo, L.

Colored dissolved organic matter (CDOM) is an active organic component in natural waters, and can have an effect on environmental and water quality in aquatic systems. In order to examine the composition and size-distribution of CDOM in the Mississippi and Pearl rivers and the effect of flooding, monthly water samples and flood samples were collected from the lower Mississippi River at Baton Rouge and the Pearl River at Stennis Space Center, followed by size fractionation using ultrafiltration and flow field-flow fractionation (FlFFF) and measurements of dissolved organic carbon (DOC), specific UV absorbance (SUVA) and fluorescence excitation emission matrix (EEM). Concentration of DOC varied from 2.8 to 3.9 mg-C/L in the Mississippi River, but was much higher in the Pearl River, ranging from 3.9 mg-C/L in Mar-2009 to 13.6 mg-C/L during the Apr-2009 flood event. Average value of SUVA (254 nm) was 0.035±0.003 L/mg-C/cm in the Mississippi River and 0.045±0.006 in the Pearl River. In the Mississippi River the SUVA254 was fairly constant, indicating similar DOM sources between seasons, while the SUVA254 in the Pearl River varied with DOC concentration and discharge, indicating variable DOM composition. Colloidal organic matter (1-450 nm) from the Pearl River had a SUVA254 value of 0.889 compared to 0.0029 for the <1 nm dissolved fraction, showing that CDOM is mostly present in the colloidal fraction and enriched in microbially-derived humic substances (SUVA at 370 nm). The colloidal size spectra of CDOM determined by FlFF with UV absorbance detection show that the majority of CDOM is found in a population of small (1-4 nm hydrodynamic diameter) colloids in both rivers although the relative proportions of CDOM in the range of 1- 4 nm, 4-20 nm, and >20 nm varied between samples. Fluorescence index (FI), which is the ratio of the emission intensity at 450 nm to that at 500 nm under excitation of 370 nm, shows a more terrestrially derived CDOM in the Pearl River (1.29-1.36), but more microbially derived CDOM in the Mississippi River (1.47-1.49). Based on the integration of fluorescence intensity in the FlFFF fractograms, the ratio of DOC-normalized protein-type fluorophores (Ex/Em 276/340 nm) (proFL/DOC) and humic-type fluorophores (Ex/Em 350/450 nm) (humFL/DOC) exhibits more amino-acids and humic-substance components of CDOM in the Pearl River (7.7-16 and 1.0-3.6) than in the Mississippi River (6.5-9.4 and 0.2-1.3). Moreover, the humFL/DOC value during flooding in the Pearl River was three times higher than normal sample values, suggesting more humic substances during the flooding event. In the EEM measurements, the Ex/Em wavelength at maximum fluorescence intensity shifted from 330/445 nm in normal samples to 338/451nm in flood samples, suggesting an increased input of humic substances that are less transformed by photochemical or microbial processes during the flooding event in the Pearl River. The SUVA and fluorescence EEM coupled with FlFFF and ultrafiltration can be used to effectively investigate the source and composition of CDOM in natural waters.


Technical Presentations

  • Delta Water Quality
  • Delta Water and Agriculture
  • Wetlands
  • Water Quality
  • Sediments
  • Non-Point
  • Management and Sustainability
  • Wood Treatment
  • Modeling
  • Soil and Water Treatment


Responsible Site Design: Implementing Innovative Stormwater Management Strategies

The primary goal of the workshop is to create a dynamic learning experience that examines the role of stormwater management in the built environment. The workshop will focus on integrating ecologically sound water management approaches into site design. After the workshop, attendees will be familiar with the following concepts and technical issues:

  • Knowledge of the stormwater treatment chain
  • Knowledge of the impact of land use codes on stormwater management
  • Application of a design process that mitigates the effects of stormwater on-site
  • Knowledge of the relationship between land use codes and design for innovative stormwater management


For information contact:
Jessie Schmidt
Box 9680
Mississippi State, MS 39762