In this research, the recycling of nutrients was studied in two, five-year period stages and in two young radiata pine forests (the first stage) and in two oak woods (the second). To this end, weekly samples of rain, transcolation (fraction of the precipitation that passes through the forest canopy), and litterfall (vegetable material fallen from trees: leaves, twigs, fruit, and so on), the first 25 cm of mineral soil and green foliage were taken and analysed chemically, according to standard protocols. The location of parcels was carried out as a function of their distance from different foci of emission of contaminants. A flow equilibrium model for the canopy was drawn up together with a generalised micrometeorological model in order to estimate the total deposition of atmospheric constituents. Also, a model for foliar growth and abscision was designed using proportions of the various cohorts of the samples of green branches and litterfall.
The total nitrogen deposition was greater that that deemed to be the admissible critical load in European forest ecosystems so that the nitrogen saturation of the ecosystems studied is, or shortly will be, a fact. The canopy of the forests was able to neutralise the atmospheric deposition in an effective manner although the potential acidity was greater in those areas near emission foci. The uptake of acidifying ions and nitrogen caused an acceleration of the return of nutrients (amount of nutrients that the vegetation gives back to the soil together with the litterfall and foliar excretion) and a drop in their retranslocation (reabsorption of nutritive elements). Thus, the efficiency in the use of cations was affected by the atmospheric deposition of contaminants. Magnesium deficiency was observed in all the adult formations studied. The acceleration of the return of nutrients and the drop in the efficiency of their use is proposed as an explanation of this disorder.
Thanks to this investigation, it was concluded that the atmospheric deposition of contaminants produces damage in the forest masses of Bizkaia and may be aggravated in the future.
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