Linking carbon and nitrogen spiraling in streams
Stephen Plont, Brynn O'Donnell, Morgan T. Gallagher, Erin R. Hotchkiss
Abstract
Anthropogenic activities have altered biogeochemical cycles and the fate of organic carbon (OC) and nutrients in freshwater ecosystems. To investigate coupled OC and nutrient cycling and fate in streams, we compared the spiraling lengths (S) and uptake velocities (vf) of OC and nitrate (NO3−) in headwater streams (n = 72) across different land uses (i.e., agricultural, urban, natively vegetated) and regions (n = 8) in the United States. We did these comparisons with data collected for the second Lotic Intersite Nitrogen eXperiment (LINX II; Mulholland et al. 2009). OC spiraling lengths (SOC) in reference (21–4180 m) were shorter than in agricultural streams (89–37,156 m) and urban streams (104–12,605 m). OC mineralization velocities (vf−OC) and NO3− uptake velocities (vf−NO3) were weakly positively correlated across all sites (r = 0.33, p = 0.008). The strongest correlations between OC mineralization and NO3− uptake were in streams with gross primary production (GPP) similar to ecosystem respiration (ER) and human-altered streams (all agricultural streams: r = 0.56, p = 0.008, GPP∶ER = 0.6; all urban streams: r = 0.73, p < 0.001, GPP∶ER = 0.5). Additionally, the distances traveled by OC and NO3− before they were permanently removed from the stream by mineralization (SOC) or denitrification (Sw–den) were similar in magnitude, although SOC was shorter than Sw–den in most streams. This study demonstrates how OC and NO3− spiraling can be used to investigate how region and land use influence coupled OC-NO3− interactions and fate.