Submitted to: Biogeochemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/26/2005
Publication Date: 1/15/2006
Citation: Barger, N.N., Herrick, J.E., Van Zee, J.W., Belnap, J. 2006. Impacts of biological soil crust disturbance and composition on c and n loss from water erosion. Biogeochemistry. 77:247-263. Interpretive Summary: Microbiotic crusts composed of lichens, mosses, cyanobacteria, and other microorganisms cover the soil surface in many arid environments. Some of these organisms fix nitrogen. The objective of this experiment was to determine the effect of disturbance of a soil crust has on C and N losses in runoff and soil erosion on the Colorado Plateau. We found that runoff and sediment export increased with disturbance, which suggests that downslope plant communities receive a higher flux of nutrients in water and sediments in a post-disturbance environment. Alternatively, higher runoff and sediment transport from plant interspaces may also result in higher nutrient losses from the watershed.
Technical Abstract: In a rainfall simulation experiment, we compared runoff and sediment C and N fluxes from intact dark, lichen crusts (controls) to both trampled dark crusts (trampled) and dark crusts where the top 1 cm of the soil surface was removed (scraped). In a second experiment, we compared C and N fluxes in runoff and sediments in light, cyanobacterial crusts to that of dark, lichen crusts. Dissolved organic carbon (DOC), dissolved organic nitrogen (DON), and NH4+ were significantly higher from trampled plots as compared to scraped and control plots. Sediment C and N losses were four- and fivefold higher from trampled plots relative to control plots. Ammonium loss was higher in light crusts compared to dark crusts, with no differences in DON or NO3- loss. Higher sediment loss in light crusts relative to dark crusts resulted in fivefold higher loss of sediment-bound C and N. Total C flux (sediment + dissolved) was on the order of 7.9 for light crusts and 0.9 g/m2 for dark crusts. Nitrogen export in sediments made up 98% and greater of the total flux in all treatments. Total N export from dark crusts was an order of magnitude lower than light crusts (dark = 0.06 g N/m2, light = 0.63 g/m2). Sediment N concentration in the first minutes after runoff was more than five times higher than the percent N of the top 1 cm of soil, suggesting that even short-term runoff events may have a high potential for N loss due to the movement of sediments highly enriched in N.