Yields and Characterization of Dissolved Organic Matter From Different Aged Soils in Northern Alaska. Issue 7 (7th July 2018)

• Record Type: Journal Article
• Authors: Gao, Lei; Zhou, Zhengzhen; Reyes, Alberto V.; Guo, Laodong
• Is Part Of: Journal of geophysical research. Volume 123:Issue 7(2018)
• Page Start: 2035
• Page End: 2052
• Publication Date: 2018-07-07
• Subjects: soil dissolved organic matter -- DOM yield -- nutrients -- permafrost -- northern Alaska; Geobiology -- Periodicals; Biogeochemistry -- Periodicals; Biotic communities -- Periodicals; Geophysics -- Periodicals; 577.14
• DOI: 10.1029/2018JG004408
• Languages: English
• ISSNs: 2169-8953

Abstract

Abstract: Soil organic matter (SOM) in northern high‐latitude regions is a major component of the global carbon cycle. However, the yield of soil‐dissolved organic matter (DOM) during soil‐water interactions and its chemical characteristics and reactivities remain poorly understood. We report here elemental composition and isotopic signatures of bulk‐SOM from northern Alaska, and yields of water‐leachable soil‐DOM, including dissolved organic carbon, dissolved organic nitrogen, and dissolved organic phosphorus, and nutrients (dissolved inorganic nitrogen and phosphate). The bulk‐SOM contained 5, 400–373, 900 μg‐C/g‐soil, 500–12, 610 μg‐N/g‐soil, and 38.6–384 μg‐P/g‐soil, with a C/N ratio of 13–37 and a C/P ratio of 80–3, 911. The water‐extractable dissolved organic carbon, dissolved organic nitrogen, and dissolved organic phosphorus only accounted for 0.58–2.5%, 0.91–3.4%, and 1.2–3.0% of their corresponding total soil‐OC, N, and OP, respectively. While SOM‐δ 13 C was less variable (−27.08‰ to −26.49‰) showing the same overall C source, 14 C‐ages varied widely from 1, 170 ± 20 to 16, 200 ± 55 years before present, indicating different deposition‐conditions and subsequent‐processes among the soil samples. The specific‐UV‐absorbance at 254 nm (or aromaticity) of soil‐DOM differed considerably and was negatively correlated to spectral slope values. A humic‐like (C1), a low‐molecular‐weight fulvic‐like (C2), and a protein‐like component (C3) were identified as the major fluorescent‐DOM components. The C3/C2 and C3/C1 ratios generally increased with SOM‐ 14 C‐age, suggesting a preferential degradation/transformation of humic‐like and fulvic‐like components or a transformation/production of protein‐like components within permafrost. Both biological and humification indices increased with 14 C‐age, excluding the oldest soil, which pointed to a preferential preservation or transformation/production of protein‐like DOM within permafrost, implying that soil‐DOM derived from old permafrost can be highly vulnerable and readily decomposed upon permafrost thaw. Plain Language Summary: The yields of soil dissolved organic matter (DOM) and nutrients (N and P) from different aged soils in northern Alaska were quantified in the laboratory mimicking soil‐water interactions upon permafrost thaw. The overall fluxes of soil‐DOM and nutrients can significantly influence carbon and nutrient cycle and the ecosystem as a whole in Arctic waterways and coastal environment although the yields were generally within 4% of their corresponding total mass in the bulk soil. Humic‐like substances with high optical reactivity were the major organic components preserved in permafrost, but the relative percentage of protein‐like components having high biological activity increased with increasing soil C‐14 age. This implies that soil‐DOM released from old‐permafrost thaw can be highly vulnerable and readily decomposed, causing a positive feedback to climate change. Key Points: Soil organic matter samples with different 14 C ages were characterized for elemental composition and isotopic signatures Yields of soil‐DOM and nutrients were quantified using soil leaching experiments mimicking permafrost‐water interactions Soil‐DOM was further characterized for C/N/P ratio, optical properties, and molecular size distribution to evaluate its potential reactivity