Isotopes for improved management of nitrate pollution in aqueous resources: review of surface water field studies.

Background: Environmental agencies have to take measures to either reduce discharges and emissions of nitrate or to remediate nitrate-polluted water bodies where the nitrate concentrations exceed threshold values. Isotope data can support the identification of nitrate pollution sources and natural attenuation processes of nitrate.

Review: This review article gives an overview of the information available to date regarding nitrate source apportionment in surface waters with the ambition to help improving future studies.

Present limitations and future prospects of stable isotope methods for nitrate source identification in surface- and groundwater.

Nitrate (NO3(-)) contamination of surface- and groundwater is an environmental problem in many regions of the world with intensive agriculture and high population densities. Knowledge of the sources of NO3(-) contamination in water is important for better management of water quality. Stable nitrogen (delta15N) and oxygen (delta18O) isotope data of NO3(-) have been frequently used to identify NO3(-) sources in water.

Methods to reduce interference effects in thermal conversion elemental analyzer/continuous flow isotope ratio mass spectrometry delta18O measurements of nitrogen-containing compounds.

On-line determination of the oxygen isotopic composition (delta(18)O value) in organic and inorganic samples is commonly performed using a thermal conversion elemental analyzer (TC-EA) linked to a continuous flow isotope ratio mass spectrometry (IRMS) system. Accurate delta(18)O analysis of N-containing compounds (like nitrates) by TC-EA-IRMS may be complicated because of interference of the N(2) peak on the m/z 30 signal of the CO peak. In this study we evaluated the effectiveness of two methods to overcome this interference which do not require any hardware modifications of standard TC-EA-IRMS systems.

Relationship between soil organic C degradability and the evolution of the delta13C signature in profiles under permanent grassland.

The main objective of this research was to investigate to what extent the potential C dynamics of soil organic matter (SOM) are related to the degree of 13C enrichment with increasing depth in soil profiles under permanent grassland. The evolution of the C content and the 13C natural abundance (delta13C value) of SOM were investigated in three soil profiles (0-40 cm depth) under permanent grassland of varying texture (a loamy sand, a loam and a clay loam soil). The delta13C value of the SOM showed a gradual increase with increasing depth and decreasing C content in the profiles, ranging from 1.

Evolution of the delta13C signature related to total carbon contents and carbon decomposition rate constants in a soil profile under grassland.

Evolution of the total carbon (C) content and the (13)C enrichment (delta(13)C signature) of soil organic matter (SOM) with increasing depth in a soil profile under permanent grassland (C(3) vegetation) were investigated. The relationship between the total C content and the delta(13)C signature at different depths in the upper 30 cm of the soil profile could be well fitted by the Rayleigh equation (y = -29.8 - 2.

Characterization of soil organic matter fractions from grassland and cultivated soils via C content and delta13C signature.

Variations in (13)C natural abundance and distribution of total C among five size and density fractions of soil organic matter, water soluble organic C (WSOC) and microbial biomass C (MBC) were investigated in the upper layer (0-20 cm) of a continuous grassland soil (CG, C(3) vegetation), a C(3)-humus soil converted to continuous maize cultivation (CM, C(4) vegetation) and a C(3)-humus soil converted to a rotation of maize cultivation and grassland (R). The amounts of WSOC and MBC were both significantly larger in the CG than in the CM and the R. In the three soils, WSOC was depleted while MBC was enriched in (13)C as compared with whole soil C.