Presentation on theme: "Dissolved organic matter (DOM) is an important property of lake ecosystems, resulting from the decomposition of organic matter stored in soils and of plankton."— Presentation transcript:
Dissolved organic matter (DOM) is an important property of lake ecosystems, resulting from the decomposition of organic matter stored in soils and of plankton in the water column. Colored dissolved organic matter (CDOM), the fraction that absorbs ultraviolet (UV) and visible light, is the controlling factor for the optical properties of many surface waters. Little is known about the mechanisms by which DOM and CDOM evolve in lakes formed during glacial retreat. As part of a larger study of the ecosystems in glacial lakes, the present project examined the quality of DOM and CDOM in lakes in SW Greenland. Nine lakes in Kangerlussuaq, Greenland were studied. The specific ultraviolet absorbance (SUVA) of a water sample at 254 nm (SUVA 254 ), computed by normalizing absorption (a 254 ) to dissolved organic carbon (DOC) concentration, is related to the aromatic carbon content of DOM. The ratio of the slope of CDOM absorption at 275-295 nm to the slope of CDOM absorption at 350-400 nm (S R ) is another method of characterizing the quality of OM. a 254, SUVA 254, DOC, and S R values were studied to analyze DOM quality in these lakes. In addition, DOM was fractionated into different sizes to examine trends in organic matter quality in Greenland lakes. The aim of this project was to compare the aromatic content in lakes (for which SUVA 254 is an index) among the size fractions and between young lakes near the glacial meltwater and “adolescent” lakes located approximately 38 kilometers away. Results and Discussion As the SUVA 254 values increase, so do the sizes of OM (Figure 2). The larger the size fraction, the larger the humic substances; Weishaar et al (2003) showed a correlation between aromatic carbon and aromaticity. The SUVA 254 values from this study fall in the 6-12% aromatic carbon range. These sites have very little vegetation. The sites from the Weishaar et al. 2003 study that are in the same 6-12% aromatic carbon range, and have similar SUVA 254 values, are also from lakes with very little organic material (Table 1). Sites with higher SUVA 254 values in the Weishaar study have as much as 35% aromaticity. These sites are from regions that are more forested and therefore contain more organic material with a higher aromaticity. The higher the SUVA 254 value, the higher the aromaticity, the more vegetation and the more autochthonous they are. The SUVA 254 value increases with increasing molecular weight. Lakes SS1381 and SS1590 are in Kellyville, Greenland and are further from the glacier. Their SUVA 254 values are higher, possibly due to the arctic tundra vegetation. Lakes SS901, SS903, SS904, and SS906 are closer to the glacier and lighter because of the glacial flower which is powdered rock from the expanding and contracting of that accumulates after the glacier retreats and advances. The lakes become darker and larger over time due to precipitation. As lakes mature, they have decided changes in organic matter quality which is important for understanding lake ecosystems over time. An increase in absorbance, or concentration of aromatic rings, is an indicator of an increase in humic substances. a 254 is the concentration of aromatic rings. If the number of aromatic rings increases, that will increase the conjugation and therefore larger molecules will generate absorbance at larger wavelengths. The older a lake is in its watershed, the longer time it has for soil development and opportunity for organic matter to develop. The slope is how fast absorbance changes over a wavelength. Acknowledgements NC DENR 319 NPS Program Grant #4443, Wake Technical Community College MEAS Program, UNC-IMS MODMON Program References Weishaar, J. L., Aiken, G. R., Bergamaschi, B. A., Fram, M. S., Fujii, R., & Mopper, K. (2003). Evaluation of specific ultraviolet absorbance as an indicator of the chemical composition and reactivity of dissolved organic carbon. Environmental Science & Technology, 37(20), 4702-4708. Anderson, N. J., and Stedmon, C. A. (2007) The effect of evapoconcentration on dissolved organic carbon concentration and quality in lakes of SW Greenland. Freshwater Biology 52.2 280-289. Print. Findlay, S. (2003) Aquatic ecosystems interactivity of dissolved organic matter. Amsterdam: Academic Press. Print. Williamson, C. E., Morris, D. P., Pace, M. L., and Olson, O. G. (1999) "Dissolved organic carbon and nutrients as regulators of lake ecosystems: Resurrection of a more integrated paradigm." Limnology and Oceanography 44.3_part_2 795-803. Print. Findings In each graph from Figure 3, there are three separate groupings, each with a negative trend. In the first group, lakes SS901, SS903, SS904, and SS906 are closer to the glacier. In the second group, lakes SS1381, SS1590, and SS2 are further away from the glacier. The third group is comprised of lakes SS8 and SS85. Further research is needed to understand this separation, since the second and third groups are essentially in the same area. Study Sites Figure 1. Sampling Sites consist of various lakes in Kangerlussuaq, Greenland (Source: Google Earth) Methods Water samples were collected from 9 sampling sites. Absorption was measured for each filtered sample on Varian Cary 300 spectrophotometer. Once absorption data was obtained, the samples were preserved with an 85% solution of phosphoric acid (H 3 PO 4 ). DOC was measured for each acidified sample using an Aurora 1030 TOC analyzer. Appropriate instrument corrections were applied where necessary SUVA254 values were obtained using the following equation: Sample Site SUVA 254 (Lm ⁻ ¹mgC ⁻ ¹) Source SS9030.5This Study SS9060.7This Study SS13810.7This Study SS850.9This Study SS9010.9This Study SS20.9This Study SS9041.1This Study SS15901.2This Study SS81.6This Study Pony Lake FAa1.7Weishaar et al. 2003 Lake Fryxell HPOA1.8Weishaar et al. 2003 Upper Shingobee HPOA2.9Weishaar et al. 2003 Suwannee River FA3.2Weishaar et al. 2003 Ogeechee River FA3.8Weishaar et al. 2003 Ogeechee River HA5.3Weishaar et al. 2003 Sample Sites Table 1. SUVA 254 values from this study and Weishaar et al. 2003, by sample site. Figure 2. Standard Deviation of SUVA 254 Values by Size Fraction A C Figure 3. a 254 vs. (A) Slope by Lake, (B) Slope by Size fraction, and (C) DOC. Abstract Methods References Acknowledgements Results and Discussion Findings
Your consent to our cookies if you continue to use this website.