Tracing the sources of refractory dissolved organic matter (RDOM) in a large lake using multiple analytical tools

Transcription

1 Tracing the sources of refractory dissolved organic matter (RDOM) in a large lake using multiple analytical tools Hang Vo- Minh Nguyen * Ph.D. Candidate Jin Hur Asso. Prof. Dept. of Earth & Environmental Sciences Sejong University, Korea * nvmhang83@gmail.com

2 Contents Introduction Materials & methods Results & discussion Conclusions

3 Introduction Long term trends of RDOM using BOD and COD RDOM (Lake Paldang, Korea) increase (COD ; BOD ) RDOM in lakes: major component, precursor of trihalomethane formation RDOM sources: autochthonous + allochthonous sources Investigating RDOM sources: chemical structures, molecular sizes, spectral features of potential DOM sources.

4 Introduction UV-visible spectroscopy Fluorescence spectroscopy SEC, Resin fractionation Py-GC/MS 13 C-NMR + PCA Objectives Compare the structural & chemical characteristics of various RDOM sources Suggest the major sources of the lake RDOM using PCA

5 Materials & methods RDOM sources Algae (AG) Leaf (LT) Reed (RD) Paddy water (PW) Treated sewage(ts) Field soil (FS) Compost (CP)

6 Materials & methods Sample collection Catchment: 23,800 km 2 6% 6% RD Han river basin LT AG PD LT PW LT FS Paldang Lake RD RD TS

7 Materials & methods DOM Extraction and Preparation ALGAE Concentration Plankton net Ultrasonication (1h) Shaking FIELD SOIL COMPOST air-dried ground through 0.18-mm sieve Mixing (H 2 0) 0) Solid:solution 1:3 Concentration Rotary evaporator 30 C(for field soil)

8 Materials & methods DOM Extraction and Preparation LEAF REED air-dried Cut pieces 1cm 2 Mixing (H 2 0) 0) Solid:solution 1:20 PADDY WATER TREATED SEWAGE LAKE PALDANG Concentrate Nanofiltration NE Cation exchange resin Dowex 50WX8-100, Sigma

9 Materials & methods Preparation of RDOM based on microbial incubation experiments NH 4 NO 3 & K 2 HPO 4 C:N:P 30:10:3 Microbial innoculum (from lake Paldang) (Hur et al., 2009) (Hur et al., 2011) Extracted DOM solution sterile 5L glass container 20 C+28 days

10 Materials & methods Analytical methods DOC: Shimadzu V-CPH analyzer SUVA: (UV 254 ) Evolution 60, Thermo Scientific Synchronous fluorescence spectra: luminescence spectrometer (Perkin-Elmer LS-50B) MW: SEC (HPLC Waters model 590), UV detector (Waters 486) Py-GC/MS: gas chromatograph equipped with a 30m DB WAX fused silica capillary column 13 C NMR: Brucker Avance II 500 MHz spectrometer at 300 K, 90 pulse width of a 4.5 ls, contact time of 1.5 ms

11 HiN Materials & methods Analytical methods Resin fractionation HoA+HoN+HiA+HiB+HiN Step 1: acidify ph 2, pass through DAX8 resin Step 2: elute 0.1 M NaOH Step 3: pass through cation and anion exchange resins HiA XAD8 resin HiA+HiB+HiN AG-MP-50 cation exchange resin HiA+HiN AG-MP-1 anion exchange resin

12 Biodegraded carbon (%) Results & discussion Biodegraded carbon percentage AG LT RD CP FS PW TS PD -- Samples AG: highest value of biodegraded carbon percentage

13 Results & discussion UV-visible characteristic of different RDOM sources L/mgC-m LT CP AG RD FS PW TS PD AG LT RD CP FS PW TS PD AG, FS, PW, TS, PD RDOM: low SUVA non-aromatic C LT, RD >AG RDOM Polyphenolic compounds PD: lowest SUVA

14 Results & discussion UV-visible characteristic of different RDOM sources AG LT RD CP FS PW TS PD Low aromaticity Low MW

15 Results & discussion DOC-normalized synchronous fluorescence spectra DOC-normalized fluorescence 7 a Treated sewage Algae Leaf litter Reed Wavelength (nm) DOC-normalized fluorescence 7 b Compost Field soil Paddy water Lake Paldang Wavelength (nm) FLF, HLF >PLF PLF is vulnerable to microbial degradation

16 Results & discussion DOC-normalized synchronous fluorescence spectra

17 Results & discussion Fluorescence index (FI) From data FI of RDOM may not applied to distinguish allochthonous RDOM sources AG LT RD CP FS PW TS PD FI: ratio of emission intensity 450/500 Excitation wavelength: 370 nm (McKnight et al., 2001).

18 Results & discussion Humification index (HIX) HIX: ratio of the last/first quarter regions for a fluorescence emission spectrum (wavelengths nm) AG LT CP FS PW TS Excitation wavelength 254 nm (Zsolnay et al., 1999) RD PD High polyaromatic structures Low oxygen-containing functional groups

19 Results & discussion Comparison of the molecular weight distribution AG LT MW w RD CP FS PW TS PD Polydispersity AG 3.4 LT 2.3 RD 3.8 CP 3.2 FS 1.3 PW 1.3 TS 1.6 PD 1.6

20 Results & discussion Resin fractionation results Ho>>Hi HoA>HoN>HiN> HiA>HiB AG, PW, TS: highest HiB

21 Results & discussion Biopolymer components (%) PS, PR >PHA, AS LT, RD: High PR + PHA PD, FS: high PS>PR>AS

22 Results & discussion Relative carbon contributions (%) Aliphatic carbon>aromatic carbon RD, AG: High O-alkyl C PD: Low O-alkyl C

23 Results & discussion Identification of the primary sources using PCA

24 Results & discussion Identification of the primary sources using PCA

25 Conclusions Largely affected sources of Lake Paldang Field soil Lake Paldang Treated sewage Paddy water PCA: 77% of the variance is possibly explained by the source difference Paldang sources: low molecular weight, low UVabsorbing & non-aromatic structures

26 Acknowledgments We are thankful to The National Research Foundation of Korea Grant funded by the Korean government (No ). The Han River Watershed Management Fund. Dr. Jaewon Cho for his help for the Py-GC/MS analyses

27