The effect of freezing and drying on leaching of DOM from above ground vascular plant material from the Alaskan Arctic
Thursday, 18 December 2014
Our understanding of the seasonal dynamics of fluvial dissolved organic matter (DOM) concentrations and fluxes in Arctic catchments has increased substantially during recent years, especially during the spring, which historically has been an under-sampled time period. While a number of studies have observed peaks in both DOM concentrations and fluxes during the spring snowmelt, our knowledge of the mechanisms that control these observations are still lacking. During the initial snowmelt period, frozen ground and the snow matrix act to constrain melt-water to the soil surface. We hypothesize that restriction of flow during this time facilitates leaching of DOM from senescent above ground vegetation and detritus contributing to the high DOM concentrations observed during the spring melt. This study focuses on the effect of freezing and drying on the leaching of dissolved organic carbon and nitrogen (DOC and DON) from above ground vascular plant material. Specifically, we examined the treatment effects of freezing, drying, and freeze-drying on three genera of common Alaskan Arctic vascular plants; Eriophorum (spp.), Carex (spp.), and Salix (spp.). Frozen and freeze-dried plant material released more DOC over the experimental 96 hour leaching period compared to plant material that was only dried. Qualitatively, these patterns were similar among the different plant types, while quantitatively Salix leached more DOC than either Eriophorum or Carex in all treatments. Similar patterns were also seen for DON between the different treatments and among the different plant types. Compositionally, DOM that was leached from frozen and freeze-dried material had higher C:N ratios than material that was only dried. Comparatively, DOM leached from Salix had much higher C:N ratios than either Eriophorum or Carex. During the first 24 hours of leaching, C:N ratios tended to increase followed by a subsequent leveling or decrease, suggesting that the composition of leached DOM varied during the 96 hour time period. Our findings suggest that the seasonal timing of freezing and drying conditions experienced by senesced plant material during the late summer, fall, and winter may impact DOM leaching dynamics on that same plant material the following spring during snowmelt.