Characterization of Dissolved Organic Matter in Cache Slough Complex

1. Characterization of dissolved organic matter in the Cache Slough ComplexMurage Ngatia (mngatia@water.ca.gov)DES/Municipal Water Quality Program/QA • Introduction • Natural organic matter (NOM) are decaying aquatic materials of biological origin comprised of many poorly understood compounds. • Dissolved organic matter (DOM) are the portions of NOM that pass through a specified filter size: 0.45µ in drinking water, 0.2µ in oceanography. • Dissolved organic carbon (DOC) is often used as a surrogate for DOM. DOC provides quantity but not quality of DOM. • Some DOM absorbs light in the UV/Vis range and is called colored or Chromophoric Dissolved Organic Matter (CDOM) which absorbs at ~355 nm. Absorbance at a certain wavelength (e.g. 254 nm) divided by DOC is referred as specific absorbance (this case SUVA254). Methods We use the principles of absorption & fluorescence spectroscopy to characterize DOM utilizing the light spectrum as follows: Results (cont’d) • Fluorescence Index (FI) values of 1.4 or less suggest allochthonous (terrestrial) and ~1.8 autochthonous (bacterial) DOM, (Cory et al. 2010). All stations in this study suggested that DOM was of autochthonous origin, Table 1. • Humification Index (HIX) is also a relative ratio with values <5 suggesting new DOM (Birdwell and Valsaraj 2010). Therefore the limited HIX indices suggested all the stations had ‘new’ (fresh) DOM. Fig 2. The light spectrum Fluorescence Absorbance Top 5 reasons to study DOM in water: It reacts with disinfectants in drinking water (e.g. chlorine) to form carcinogenic byproducts (DBPs): trihalomethanes and haloacetic acids. It complexes with metals like Pb & Cu affecting their toxicities in water It affects the fate and transport of pesticides in water. It shields aquatic organisms from harmful UV radiation. It is energy for bacteria & other microorganisms in aquatic food webs. ... Table1. DOC and related fluorescence indices • Discussion • DOC quantity and CDOM quality are similar at stations near BPP (Fig 4a, b) but are not influenced by Lindsey Sl. It might be expected that DOM as food quality for microorganisms would be different which could lead to different populations in habitat restoration projects near BPP compared to Lindsey Sl. • Since all the sloughs near the Pumping Plant have high DOM concentrations, water quality cannot be improved by modifying flows. Moving the Pumping Plant (as proposed) is the only feasible option. • Although FI and HIX indicate DOM at all stations are autochthonous and relatively new on a humification scale, there are too few data points to make definitive observations and more data are needed. S3 Fig 3a. Shined light (lo) passes through a sample & emerges attenuated light (l) due to absorbance . Io – I is a measure of concentration & composition of the sample. Fig 3b. Molecule absorbs a photon. Electron goes from ground (So) to excited state (S3). Electron then drops down emitting energy as fluorescence. S1 • Objectives • Barker Sl Pumping Plant (BPP) delivers water into North Bay Aqueduct (NBA) which provides water to over 500K residents in Solano Co. BPP has the worst drinking water quality in the SWP with high levels of DOM & turbidity (DWR 1996). This study was initiated in 1998 to characterize sources of organic matter in the BPP watershed with the goals of determining: • the amount of DOC in the tributaries adjacent to BPP. • Potential contribution of algae to the DOC pool near BPP. • quality of DOM near BPP in relation to disinfection byproducts (DBPs). Energy Fluorescence So Absorption coefficients Specific absorption coefficients Spectral slope ratios Spectral slope coefficients Fluorescence Index (FI): f470/f520 Humification Index: HIX (Zsolnay et al. 1999) (f is fluorescence at a certain wavelength) Excitation/Emission Matrices (EEM). • Results • DOC: Lindsey was significantly lower (*p=0.000, n=12-15) from all the other stations. Other stations had similar to each other. Fig 4a. • SUVA254 results were mixed. Lindsey was different from Pumping Plant and Calhoun but similar to Cook Rd (*p=0.000, n=12-15). Pumping Plant and Calhoun were different from Lindsey, Fig 4b. • CDOM: Lindsey was significantly different from all the other stations (*p=0.000, n=12-15), Fig 4c • Spectral slope ratios (Helms et al. 2008) and E2/E3 ratios (absorbance at 250 nm divided by 365 nm) )were not significantly different (not shown). Conclusions Historically, other studies have shown that BPP has high quantities of DOM. This study provides additional information that DOM in the sloughs adjacent to BPP is of different quality than downstream at Lindsey Sl. • Materials • Grab samples were collected weekly in 1998 during high algal growth period (March-June 1998). • Additional samples were collected in July and September 2010, and September 2011. Study Area Literature Cited Birdwell JE, Valsaraj KT. 2010. Characterization of dissolved organic matter in fogwater by excitation-emission matrix fluorescence spectroscopy. Atmospheric Environment 44: 3246-3253. Cory RM, Miller MP, McKnight DM, Guerard JJ, Miller PL. 2010. Effect of instrument- specific response on the analysis of fulvic acid fluorescence spectra. Limnology and Oceanography: Methods 8: 67-78. DWR. 1996. The Sanitary Survey update of the State Water Project. Pages 397. Sacramento: DWR. Helms JR, Stubbins A, Ritchie JD, Minor EC, Kieber DJ, Kenneth M. 2008. Absorption spectral slopes and slope ratios as indicators of molecular weight, source, and photobleaching of chromophoric dissolved organic matter. Limnology and Oceanography 53: 955–969. Zsolnay A, Baigar E, Jimenez M, Steinweg B, Saccomandi F. 1999. Differentiating with fluorescence spectroscopy the sources of dissolved organic matter in soils subjected to drying. Chemosphere 38: 45-50. SUVA254 DOC CDOM (c) (a) (b) Acknowledgements Thanks to the QA Program for supporting this study. Thanks to the MWQI Field Support Unit for sampling and Bryte Lab for chemical analyses. Fig 4. *Kruskal-Wallis multiple comparison tests between stations. These are paired comparisons between all stations. If round station symbol is outside the dotted red line, the station on the left column is significantly different from those on the right hand column.