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Mechanisms of nutrient turnover in the soil compartment of forests: phase III of the CORE project


The principal aim of CORE Project is to determine the response of biogeochemical processes in coniferous forest soils to changes in the amount and composition of atmospheric pollutants and climate.

A novel approach is employed for manipulating ionic inputs to soils in which lysimeters containing undisturbed soil columns are reciprocally exchanged within a network of locations in Europe with different pollution environments. In order to achieve this it has been essential that each group used identical materials, following the same protocol for establishmend and subsequent monitoring of the field installations. The German group prepared the materials for the filed centrally, and performed the initial extraction of soil cores by travelling to the different sites. Seven soil columns were reciprocally exchanged between the six sites plus a further seven cores from the Exeter site, which were designated for "control" treatments. Leachates concentrations of majors anions and cations were determined in the laboratories of each group, with "round-robin" calibration checks being overseen by the Chemistry Section at Grange over Sands.

Individual, more detailed studies of the effects of N and S inputs on the soil biota, decomposition progress, N- mineralisation and denitrification are also in progress at the different laboratories, according to their specialisation.

Traditionally, biogeochemical research has concentrated on single sites to understand and describe the development of soil processes under existing conditions. The concept behind the current study is to use the different physical and chemical climates across Europe to investigate the development and change of forest soil processes when exposed to changing conditions. Therefore, different sites along a transect of increasing acid deposition from Ireland to Germany were chosen. Each of the six forest sites represents a specific pollution situation.

From these previous Phases of the project a rule-based model has been constructed which appears to describe one of the major underlying mechanisms in the causation of forest die-back.

The feedback mechanisms which may lead to forest decline on certain soil types and under conditions of N saturation have been outlined. In Phase III the objective is to validate the key interactions in this model through laboratory and field experimentation. The main objective is to verify this process model which describes the turnover of nitrogen in forest soils and the responses to changes in pollutant inputs and climate.

The expected achievements from the project are :

(i) to identify which forest may be at risk form N induced dieback;
(ii) to quantify the role of denitrification in "shedding" excess N;
(iii) evaluation of the importance of tree N status and root uptake in soil solution chemistry;
(iv) a piratical assay for the determination of N saturation status of forest ecosystems.

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Natural Environment Research Council
Windermere road
LA11 6JU Grange-over-sands - cumbria
Vereinigtes Königreich

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