Fluxes and Stable Isotopic Composition of Particulate Organic Matter in the Six Largest Rivers Draining the Pan-Arctic Watershed: Insights from Seasonally-Explicit Sampling Efforts
Abstract
Six large rivers, including the Yukon and Mackenzie in North America and the Yenisey, Ob, Lena, and Kolyma in Eurasia, drain roughly two thirds of the pan-arctic watershed. Seasonally-explicit sampling programs were initiated at downstream locations on these rivers during the early 2000s in order to 1) improve estimates of fluvial export to the Arctic Ocean and 2) establish benchmarks for tracking watershed-scale changes associated with global warming. Founded as the Pan-Arctic River Transport of Nutrients, Organic Matter, and Suspended Sediments (PARTNERS) project and later continued as the Arctic Great Rivers Observatory (Arctic-GRO), this effort has led to significant revision of dissolved organic matter (DOM) export estimates as well as new insights about the quality of DOM delivered to coastal waters. Particulate organic matter (POM) data from PARTNERS and Arctic-GRO have been given less attention, yet these data are also leading to new insights. As observed for DOM, POM shows major seasonal variations with respect to carbon and nitrogen concentrations. These variations are tightly coupled with seasonal variations in runoff, exhibiting higher concentrations during periods of higher river flow. Accounting for these variations is critical for computing accurate annual fluxes. Stable isotope data demonstrate that the composition of POM in the major arctic rivers also varies widely with runoff patterns, showing strong evidence of autochthonous sources under low flow conditions and a dominance of soil-derived organic matter under high flow conditions. One of the key differences between POM and DOM in the major arctic rivers is that the C:N ratios of POM are roughly 5 fold lower than those of the DOM. This has important implications with respect to the relative roles of particulate versus dissolved organic matter as a nitrogen source to arctic coastal ecosystems. Another key finding is that although the North American rivers have much higher total suspended solid (TSS) yields than the Eurasian rivers, differences in POM yields are less pronounced. This is primarily due to lower percentages of C and N relative to TSS during peak discharge in the North American rivers.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFM.B33D0480M
- Keywords:
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- 0428 BIOGEOSCIENCES / Carbon cycling;
- 0438 BIOGEOSCIENCES / Diel;
- seasonal;
- and annual cycles;
- 0469 BIOGEOSCIENCES / Nitrogen cycling;
- 1804 HYDROLOGY / Catchment