Effects of two emergency stabilization treatments on main soil properties four years after application in a severely burnt area.

In NW of the Iberian Peninsula, the incidence of anthropogenic fires is very high and, due to the climatologic and topographical conditions, burnt soils are prone to high erosion risks. In recent years several environmental management techniques (BAER: burnt area emergency response) have been applied after some wildfires, but there are still few field studies about their effects on soils (the foundations of terrestrial ecosystems) and most of them are short-term. Aiming to fill this gap of knowledge, sixteen properties useful as soil quality indices (pH, WHC, total N, δ15N, NH4+-N, NO3--N, and NH4Ac-DTPA extractable Na, K, Ca, Mg, P, Al, Fe, Mn, Cu and Zn) were studied four years after BAER application in a severely burnt area in the 0-2 and 2-5 cm depth layers of unburnt soil (US), burnt soil untreated (BS), and burnt soil treated with two BAERs techniques: rye seeding (BSS) and straw mulching (BSM). The effects of fire on soil WHC, total N, Mg, Na, P, Zn, NO3--N, Cu and K were mitigated in both BSS and BSM, but especially in the latter. The highest values for Ca and Mn were recorded in BSM. The BAER treatments affect NO3--N, Cu and K only in the top layer, but no clear effects were found for soil pH, δ15N, NH4+-N, Al and Fe. Soil samples were quite similarly grouped by the hierarchical cluster and the principal component analyses (PCA): a) 0-2 cm layers of US plots; b) 0-2 cm layers of BSM plots; c) 2-5 cm layers of US plots; d) most of top layers of BS and BSS plots; and e) most of the 2-5 cm layers of BS, BSM and BSS plots. The distribution of soil samples in the PCA showed that straw mulching and, to a lesser extent, rye seeding reduced the distance between burnt and unburnt topsoil along Factor 1, but not along Factor 2 (explaining 56% and 29% of the variance, respectively). Consequently, these BAER treatments mitigated, but not wiped out, the effects of fire on soil quality after four years.

Possible impact of environmental policies in the recovery of a Ramsar wetland from trace metal contamination.

The Umia-Grove Intertidal Complex is located within the Ria of Arousa (NW Iberian Peninsula). Out of its significance for wintering shorebirds it has been included in the Ramsar List of Wetlands of International Importance as well as in international protection networks such as the European Natura 2000 and Important Bird and Biodiversity Areas-BirdLife International. In a sediment analysis conducted in the year 1999, the wetland was found to have been contaminated by potentially toxic trace metals, to wit: Cr, Cu, Ni, and Pb. Sediment samples retrieved in 2014 to make an updated assessment of the condition of the ecosystem showed evidence of the presence of selected trace elements, namely, Cd, Co, Cr, Cu, Ni, Pb, and Zn, within or slightly above the background ranges of local, regional, and general references. In the 15-year time frame between the two samplings there has been noticeable change in the relationship between nature and society as a consequence of the entry into force of a number of regulations aimed at avoiding the emission of contaminants; among others, the ban of Pb in gasoline, the deployment of wastewater treatment plants according to the European Water Framework Directive, and the limitation of the use of Cu pesticides. With the ensuing drop of human pressure, the self-purifying capacity of the ecosystem has effectively contributed to the wetland's recovery. Nevertheless, the application of a normalized enrichment factor to the more recent set of samples suggests the presence of relict low contamination by Cd, Cu, and Ni in localized areas. The compared analysis of the wetland condition in the two years is a sign of the success of the policies and regulations for environmental protection, but further work and more effectiveness are necessary in order to preserve threatened ecosystems of such importance as the Umia-Grove wetland.

Short and medium-term effects of a wildfire and two emergency stabilization treatments on the availability of macronutrients and trace elements in topsoil.

In NW Spain, a European region with very high fire incidence and erosion risks, the effects on soils of a medium-to-high severity wildfire and two emergency stabilization techniques were studied. In burned plots (control, BS; seeded with cereal, BSS; straw mulched, BSM) and adjacent unburned plots (US), the topsoil (0-2 cm) pH and thirteen NH4Ac-DTPA extractable elements were evaluated at t = 0, 4, 8 and 12 months after the fire. Compared to US, fire increased by 0.3-0.5 units the soil pH which decrease slowly over time, but remaining significantly higher at t = 12 (BS, BSM, BSS>US). Ammonium nitrogen (N) levels were higher (p<0.05) in burned plots than in US, difference decreasing progressively from 48-fold (t = 0) to 25-fold (t = 12). Although no significant effect of fire was immediately observed, the extractable sodium (Na) and potassium (K) were higher (p<0.05) in burned plots than in US at t = 4 and t = 8, probably due to cation leaching from the overlying ash. Fire did not modify the extractable magnesium (Mg), but at t = 0 the extractable calcium (Ca) and phosphorous (P) were transiently and significantly higher in burned plots than in US. Extractable aluminum (Al), iron (Fe), copper (Cu), cobalt (Co) and zinc (Zn) were lower and manganese (Mn) was higher in burned plots than in US. Neither seeding nor mulching significantly modified the topsoil concentrations of the elements considered. The PCA revealed that BS, BSM and BSS became more similar to US over the study period due to a rapid decrease in extractable Ca and Mg and a slow decrease in extractable Mn and NH4(+)-N. At t = 12, the most notable differences between burned plots and US were in the concentrations of extractable Al and Zn. Data suggest that at least another 4-8 months will be required for full recovery of the burned plots to unburned conditions.