Photomineralization and photomethanification of dissolved organic matter in Saguenay River surface water

doi:10.5194/bg-12-6823-2015

	Photomineralization and photomethanification of dissolved organic matter in Saguenay River surface water
	Zhang, Y; Xie, H; Xie, H (reprint author), Univ Quebec, Inst Sci Mer Rimouski, Rimouski, PQ G5L 3A1, Canada. [email protected]
发表期刊	BIOGEOSCIENCES
ISSN	1726-4170
	2015
卷号	12 期号:22 页码:6823-6836
DOI	10.5194/bg-12-6823-2015
产权排序	[Zhang, Y.] Chinese Acad Sci, Yantai Inst Coastal Zone Res, Key Lab Coastal Environm Proc & Ecol Remediat, Yantai 264003, Shandong, Peoples R China; [Zhang, Y.; Xie, H.] Univ Quebec, Inst Sci Mer Rimouski, Rimouski, PQ G5L 3A1, Canada
作者部门	中科院海岸带环境过程与生态修复重点实验室
英文摘要	Rates and apparent quantum yields of photomineralization (AQYDOC) and photomethanification (AQY(CH4)) of chromophoric dissolved organic matter (CDOM) in Saguenay River surface water were determined at three widely differing dissolved oxygen concentrations ([O-2]) (suboxic, air saturation, and oxygenated) using simulated-solar radiation. Photomineralization increased linearly with CDOM absorbance photobleaching for all three O-2 treatments. Whereas the rate of photochemical dissolved organic carbon (DOC) loss increased with increasing [O-2], the ratio of fractional DOC loss to fractional absorbance loss showed an inverse trend. CDOM photodegradation led to a higher degree of mineralization under suboxic conditions than under oxic conditions. AQYDOC determined under oxygenated, suboxic, and air-saturated conditions increased, decreased, and remained largely constant with photobleaching, respectively; AQYDOC obtained under air saturation with short-term irradiations could thus be applied to longer exposures. AQYDOC decreased successively from ultraviolet B (UVB) to ultraviolet A (UVA) to visible (VIS), which, alongside the solar irradiance spectrum, points to VIS and UVA being the primary drivers for photomineralization in the water column. The photomineralization rate in the Saguenay River was estimated to be 2.31 x 108 mol Cyr(-1), accounting for only 1% of the annual DOC input into this system. Photoproduction of CH4 occurred under both suboxic and oxic conditions and increased with decreasing [O-2], with the rate under suboxic conditions similar to 7-8 times that under oxic conditions. Photoproduction of CH4 under oxic conditions increased linearly with photomineralization and photobleaching. Under air saturation, 0.00057% of the photo-chemical DOC loss was diverted to CH4, giving a photochemical CH4 production rate of 4.36 x 10(6) mol m(-2) yr(-1) in the Saguenay River and, by extrapolation, of (1.9-8.1) x 10(8) mol yr(-1) in the global ocean. AQYCH(4) changed little with photobleaching under air saturation but increased exponentially under suboxic conditions. Spectrally, AQYCH(4) decreased sequentially from UVB to UVA to VIS, with UVB being more efficient under suboxic conditions than under oxic conditions. On a depth-integrated basis, VIS prevailed over UVB in controlling CH4 photoproduction under air saturation while the opposite held true under O-2-deficiency. An addition of micromolar levels of dissolved dimethyl sulfide (DMS) substantially increased CH4 photoproduction, particularly under O-2-deficiency; DMS at nanomolar ambient concentrations in surface oceans is, however, unlikely a significant CH4 precursor. Results from this study suggest that CDOM-based CH4 photoproduction only marginally contributes to the CH4 supersaturation in modern surface oceans and to both the modern and Archean atmospheric CH4 budgets, but that the photochemical term can be comparable to microbial CH4 oxidation in modern oxic oceans. Our results also suggest that anoxic microniches in particulate organic matter and phytoplankton cells containing elevated concentrations of precursors of the methyl radical such as DMS may provide potential hotspots for CH4 photoproduction.
文章类型	Article
资助机构	NSERC ; National Natural Science Foundation of China (NSFC)(41006040) ; Shandong International Exchange Association
收录类别	SCI
语种	英语
关键词[WOS]	APPARENT QUANTUM YIELD ; CARBON-MONOXIDE PHOTOPRODUCTION ; SOUTHEASTERN UNITED-STATES ; LAWRENCE ESTUARINE SYSTEM ; DIMETHYL SULFIDE ; PHOTOCHEMICAL PRODUCTION ; NATURAL-WATERS ; ABSORPTION-COEFFICIENTS ; NITRATE-PHOTOLYSIS ; METHANE PRODUCTION
研究领域[WOS]	Environmental Sciences & Ecology ; Geology
WOS记录号	WOS:000365442600018
引用统计	被引频次：35[WOS] [WOS记录] [WOS相关记录]
文献类型	期刊论文
条目标识符	http://ir.yic.ac.cn/handle/133337/9423
专题	中国科学院海岸带环境过程与生态修复重点实验室中国科学院海岸带环境过程与生态修复重点实验室_海岸带环境过程实验室
通讯作者	Xie, H (reprint author), Univ Quebec, Inst Sci Mer Rimouski, Rimouski, PQ G5L 3A1, Canada. [email protected]
推荐引用方式 GB/T 7714	Zhang, Y,Xie, H,Xie, H . Photomineralization and photomethanification of dissolved organic matter in Saguenay River surface water[J]. BIOGEOSCIENCES,2015,12(22):6823-6836.
APA	Zhang, Y,Xie, H,&Xie, H .(2015).Photomineralization and photomethanification of dissolved organic matter in Saguenay River surface water.BIOGEOSCIENCES,12(22),6823-6836.
MLA	Zhang, Y,et al."Photomineralization and photomethanification of dissolved organic matter in Saguenay River surface water".BIOGEOSCIENCES 12.22(2015):6823-6836.

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