Evaluation of Dissolved Organic Carbon as a Soil Quality Indicator in National Monitoring Schemes

David L Jones,Bridget A Emmett,Robert T E Mills,Paul W Hill,Paul Simfukwe,Dafeng Hui

doi:10.1371/journal.pone.0090882

Abstract

BackgroundMonitoring the properties of dissolved organic carbon (DOC) in soil water is frequently used to evaluate changes in soil quality and to explain shifts in freshwater ecosystem functioning.MethodsUsing >700 individual soils (0–15 cm) collected from a 209,331 km2 area we evaluated the relationship between soil classification (7 major soil types) or vegetation cover (8 dominant classes, e.g. cropland, grassland, forest) and the absorbance properties (254 and 400 nm), DOC quantity and quality (SUVA, total soluble phenolics) of soil water.ResultsOverall, a good correlation (r 2 = 0.58) was apparent between soil water absorbance and DOC concentration across the diverse range of soil types tested. In contrast, both DOC and the absorbance properties of soil water provided a poor predictor of SUVA or soluble phenolics which we used as a measure of humic substance concentration. Significant overlap in the measured ranges for UV absorbance, DOC, phenolic content and especially SUVA of soil water were apparent between the 8 vegetation and 7 soil classes. A number of significant differences, however, were apparent within these populations with total soluble phenolics giving the greatest statistical separation between both soil and vegetation groups.ConclusionsWe conclude that the quality of DOC rather than its quantity provides a more useful measure of soil quality in large scale surveys.

Highlights

Measurement of dissolved organic matter (DOM) concentrations have provided a sensitive indicator for assessing large scale geographical and temporal changes in water quality [1]
We aimed to evaluate whether different soil classes and vegetation cover types possessed unique DOM signatures in terms of both quantity and quality and whether these might be useful for explaining changes in DOM occurring at a national scale
A strong positive correlation was observed between the dissolved organic carbon (DOC) concentration in soil water and both absorbance at 254 nm (r2 = 0.58; P,0.001; Fig. 1) and 400 nm (r2 = 0.47; P,0.001)

Summary

Introduction

Measurement of dissolved organic matter (DOM) concentrations have provided a sensitive indicator for assessing large scale geographical and temporal (e.g. decadal) changes in water quality [1]. Whilst differences in the quality and quantity of DOC are frequently reported for contrasting soil and vegetation types, whether these dissimilarities remain valid over large geographical scales remains uncertain. In this context, we undertook a national large scale survey of the quality and quantity of DOM across Great Britain to evaluate its potential for evaluating changes to soil quality in national soil quality monitoring programmes.

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