The Impact of Land Use Change on Primary Stream Organic and Inorganic Carbon Export

Abstract:

Terrestrial land use may impact both the amounts of and characteristics of organic and inorganic carbon (OC and IC, respectively) entering aquatic ecosystems. Better understanding of how different land uses alter carbon characteristics and export fluxes from watersheds may lead to better management practices for retaining OC in terrestrial habitats and therefore mitigate CO₂ emissions from freshwater ecosystems where terrestrial OC may be more rapidly respired. We examined the fluxes and δ¹³C and ∆¹⁴C signatures of dissolved IC (DIC), dissolved OC (DOC), and particulate OC (POC) exported from 6 watersheds with differing land use at the North Appalachian Experimental Watershed (NAEW) in Coshocton county in northeastern Ohio to assess whether differences in land use are related to variability in the export fluxes and isotopic characteristics of OC and IC pools. We used a Bayesian mixing model (MixSIR) to determine how the relative contributions of potential carbon sources to DIC, DOC, and POC change as a function of watershed land use. Mixing model results from each season were used to approximate relative annual contributions of potential sources to DIC, DOC, and POC export fluxes from each watershed. We found that agricultural land uses (i.e., corn, under both conventional till and no-till management) experienced the greatest degree of disturbance and had the greatest carbon export fluxes. However, the relative extent to which soil OC contributed to export fluxes compared to corn biomass varied as a function of tillage practices. In addition, nonparametric multidimensional scaling (NMDS), based on the δ¹³C and ∆¹⁴C data and mixing model results for DIC, DOC and POC export fluxes, separated non-corn watersheds into 2 further classes of disturbance: moderate disturbance (pasture and mixed land use) and low disturbance (forest). These findings suggest that land use has a measurable impact on the concentration and characteristics of watershed C export fluxes.