Dissolved Organic Carbon in Headwater Streams and Riparian Soil Organic Carbon along an Altitudinal Gradient in the Wuyi Mountains, China

Wei Huang,Xiaoming Zou,Jiashe Wang,Liguang Li,Honghua Ruan,William H Mcdowell,Xiujun Wang

doi:10.1371/journal.pone.0078973

Abstract

Stream water dissolved organic carbon (DOC) correlates positively with soil organic carbon (SOC) in many biomes. Does this relationship hold in a small geographic region when variations of temperature, precipitation and vegetation are driven by a significant altitudinal gradient? We examined the spatial connectivity between concentrations of DOC in headwater stream and contents of riparian SOC and water-soluble soil organic carbon (WSOC), riparian soil C:N ratio, and temperature in four vegetation types along an altitudinal gradient in the Wuyi Mountains, China. Our analyses showed that annual mean concentrations of headwater stream DOC were lower in alpine meadow (AM) than in subtropical evergreen broadleaf forest (EBF), coniferous forest (CF), and subalpine dwarf forest (SDF). Headwater stream DOC concentrations were negatively correlated with riparian SOC as well as WSOC contents, and were unrelated to riparian soil C:N ratio. Our findings suggest that DOC concentrations in headwater streams are affected by different factors at regional and local scales. The dilution effect of higher precipitation and adsorption of soil DOC to higher soil clay plus silt content at higher elevation may play an important role in causing lower DOC concentrations in AM stream of the Wuyi Mountains. Our results suggest that upscaling and downscaling of the drivers of DOC export from forested watersheds when exploring the response of carbon flux to climatic change or other drivers must done with caution.

Highlights

Stream dissolved organic carbon (DOC) is suggested to be a major constituent of the global carbon cycle [1], [2]
DOC flux from watersheds is strongly related to soil C/N ratio [4], and similar relationships hold in some regions [5], [6]
Annual mean concentrations of stream DOC were lower in alpine meadow (AM) than in subtropical evergreen broadleaf forest (EBF), coniferous forest (CF), and subalpine dwarf forest (SDF), exhibiting a decreasing pattern with increasing altitude (Fig. 2a, Table 2)

Summary

Introduction

Stream dissolved organic carbon (DOC) is suggested to be a major constituent of the global carbon cycle [1], [2]. At region to global scales, stream DOC concentrations and flux are largely governed by the quantity and quality of soil organic carbon (SOC). Soil organic carbon storage is an important driver of spatial variation in stream DOC fluxes [3]. At a much smaller scale of investigation, Billett et al [8] showed that the spatial pattern of stream DOC concentrations was linked to changes of the SOC content in a small catchment (1.3 km). Dosskey and Bertsch [11] found that riparian soil contributed over 90% of DOC flux in a stream, even though they covered only 6% of the catchment area. Riparian SOC contents might have a first order control on stream DOC concentrations

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