Spatially Related Sampling Uncertainty in the Assessment of Labile Soil Carbon and Nitrogen in an Irish Forest Plantation

Junliang Zou,Bruce Osborne

doi:10.3390/app11052139

Abstract

The importance of labile soil carbon (C) and nitrogen (N) in soil biogeochemical processes is now well recognized. However, the quantification of labile soil C and N in soils and the assessment of their contribution to ecosystem C and N budgets is often constrained by limited information on spatial variability. To address this, we examined spatial variability in dissolved organic carbon (DOC) and dissolved total nitrogen (DTN) in a Sitka spruce forest in central Ireland. The results showed moderate variations in the concentrations of DOC and DTN based on the mean, minimum, and maximum, as well as the coefficients of variation. Residual values of DOC and DTN were shown to have moderate spatial autocorrelations, and the nugget sill ratios were 0.09% and 0.10%, respectively. Distribution maps revealed that both DOC and DTN concentrations in the study area decreased from the southeast. The variability of both DOC and DTN increased as the sampling area expanded and could be well parameterized as a power function of the sampling area. The cokriging technique performed better than the ordinary kriging for predictions of DOC and DTN, which are highly correlated. This study provides a statistically based assessment of spatial variations in DOC and DTN and identifies the sampling effort required for their accurate quantification, leading to improved assessments of forest ecosystem C and N budgets.

Highlights

Soil organic carbon (SOC) and total nitrogen (STN) play an important role in the global biogeochemical cycling of C and N within and between terrestrial ecosystems and between atmospheric and terrestrial pools [1,2,3]
Labile carbon and nitrogen originate from dissolved organic matter (DOM), which is defined as the entire pool of water-soluble organic matter that is either absorbed on soil or sediment particles or dissolved in interstitial pore water [6,7]
The variation in dissolved organic carbon (DOC) and dissolved total nitrogen (DTN) increased with the expansion of the sampling area (Figure 2)

Summary

Introduction

Soil organic carbon (SOC) and total nitrogen (STN) play an important role in the global biogeochemical cycling of C and N within and between terrestrial ecosystems and between atmospheric and terrestrial pools [1,2,3]. Whilst measurements of SOC and STN in soils are relatively straightforward, their quantification, and their significance, is often hampered by marked spatial variability [4]. This includes variability in both the vertical (soil depth) and horizontal directions [5]. Water-extractable organic matter (WEOM), extracted from soil under various laboratory conditions, is widely considered to be a substitute for in situ DOM [10,11]

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