Cecchini G*, Andreetta A, Carnicelli C
Contatto: Stefano Carnicelli (firstname.lastname@example.org)
Abstract: Monitoring of soil solution composition, within the forest monitoring program CONCECOFOR, the Italian branch of the ICP-Forest program, started in 1996 in the permanent monitoring site ABR1, in Collelongo, Abruzzo. Monitoring soil solution composition is a potentially very useful tool in the study of forest ecosystems, as it can allow to describe ongoing processes of acidification, nutrient flow, pollution and so on, but there are two basic shortcomings. First of all, the high variability, in time, of solution composition only allows to draw some conclusions after several years of continuous monitoring. Second, solution composition does not actually quantify element flow through the soil; to achieve this data, it is necessary to quantify the actual flow of water. This last objective requires a completely different and independent set of technical capabilities and skills, and it has been undertaken only in recent years, within the ICP-Forests network, during the FutMon programme. Anyway, it by now certainly possible to draw some conclusions from the extended monitoring, especially for the two permanent sites for which duration of monitoring has been longer, namely ABR1 and LAZ1, in Monte Rufeno (VT). The first series of significant considerations concerns the acidification mechanisms operating in these two, both acid, soils. It is not surprising that this kind of conclusions are being obtained; it should be kept in mind that the original focus issue of the ICP-Forest network was represented by acid rains, so that all protocols and investigations are set up with a special eye on acidification mechanisms. In the years, two main acidification mechanisms have been discussed for forest soils. The more classical, and “natural” one could be described as an imbalance between supply and demand. Accordingly, the model focuses uptake of buffering cations like K, Mg and Ca, which are essential plant nutrients, from a large soil volume, with sequestration of such elements within the living biomass of the forest, plus eventually in the forest floor. The resulting net depletion of the mineral soil would, in the long term, cause its acidification. The second conceptual model stresses, instead, the role of external, or semi-external, loads. Originally, such loads were, of course, represented by the sulfate and nitrate anions typically present in acid rains but, with the progress of studies, nitrate, which can have different sources, has taken pre-eminence, also thanks to successful steps taken to reduce sulfate emissions. In these years, it has been possible to ascertain that the first mechanism is predominant in the LAZ1 site. Here, nitrate inputs from any of possible sources are, at best, half the value of the inputs in ABR1. Yet, the soil is definitely more acid, and within-profile buffering appears weak. In ABR 1 site, instead, nitrate loading is significant, though not all external inputs are “acid”, some of them coming already well buffered. Clear and strong acidification “pulses” are produced in the surface horizons, but these are generally well buffered. The main reason appears to be the presence of a relatively thin A horizon, which is rich in both organic matter and buffering cations. This last basic difference between the two sites (LAZ1 has a bleached E horizon under the forest floor) suggests that one of the factors steering this process is the activity of soil fauna, and consequently the lesser or greater incorporation of organic matter into the soil.
Parole chiave: Soil, Acidification, Nitrate, Soil Solution
Citazione: Cecchini G, Andreetta A, Carnicelli C (2011). The first fifteen years of soil solution monitoring in Italian forest soils – what has been learned . 8° Congresso Nazionale SISEF, Rende (CS), 04 – 07 Ott 2011, Contributo no. #c8.10.17