Abstract
Abstract. We collected soil solutions by suction lysimeters in a central European temperate forest with a history of acidification-related spruce die-back in order to interpret spatial patterns of soil nutrient partitioning, compare them with stream water chemistry and evaluate these parameters relative to concurrent loads of anions and cations in precipitation. Five lysimeter nests were installed in the 33 ha U dvou loucek (UDL) mountain catchment at different topographic positions (hilltops, slopes and valley). Following equilibration, monthly soil solution samples were interrogated over a 2-year period with regard to their SO42-, NO3-, NH4+, Na+, K+, Ca2+, Mg2+ and total dissolved Al concentrations, organic carbon (DOC) and pH. Soil pits were excavated in the vicinity of each lysimeter nest to also constrain soil chemistry. For an estimation of phosphorus (P) availability, ammonium oxalate extraction of soil samples was performed. Cation exchange capacity (CEC ≤58 meq kg−1) and base saturation (BS ≤13 %) were found to be significantly lower at UDL than in other monitored central European small catchments areas. Spatial trends and seasonality in soil solution chemistry support belowground inputs from mineral-stabilized legacy pollutants. Overall, the soil solution data suggest that the ecosystem was still chemically out of balance relative to the concurrent loads of anions and cations in precipitation, documenting incomplete recovery from acidification. Nearly 30 years after peak acidification, UDL exhibited similar soil solution concentrations of SO42, Ca2+ and Mg2+ as median values at the Pan-European International Co-operative Program (ICP) Forest sites with similar bedrock lithology and vegetation cover, yet NO3- concentrations were an order of magnitude higher. When concentrations of SO42-, NO3- and base cations in runoff are compared to soil pore waters, higher concentration in runoff points to lateral surficial leaching of pollutants and nutrients in excess than from topsoil to subsoil. With P availability being below the lowest range observed in soil plots from the Czech Republic, the managed forest ecosystem in UDL probably reflects growing inputs of C from regenerating vegetation in the N-saturated soil, which leads to P depletion in the soil. In addition, the observed spatial variability provides evidence pointing to substrate variability, C and P bioavailability, and landscape as major controls over base metal leaching toward the subsoil level in N-saturated catchments.
Highlights
During the second half of the 20th century, atmospheric deposition of reactive nitrogen (N) and sulfate (SO24−) caused persistent perturbations in temperate forest soils and watersheds across Europe (Blazkova, 1996; Alewell, 2001; Verstraeten et al, 2017)
Landscape and lithological simplicity, which facilitates discerning flow paths without variability effects introduced by differential bedrock weathering, it was possible to discuss which factors in association with soil N saturation affect the soil solution chemistries of a small mountainous catchment area reforested by Norway spruce after acidification-related spruce die-back
By combining soil solution chemical measurements and establishing comparisons with published hydrochemical data, this work provides evidence pointing to substrate variability, and C, but not P bioavailability, as major controls over the flux of base metal leached into the subsoil level and across the elevation gradient
Summary
During the second half of the 20th century, atmospheric deposition of reactive nitrogen (N) and sulfate (SO24−) caused persistent perturbations in temperate forest soils and watersheds across Europe (Blazkova, 1996; Alewell, 2001; Verstraeten et al, 2017). Atmospheric inputs of reactive N species in excess to the nutritional demands of plants and microorganisms have prevailed (Waldner et al, 2014, 2015). These have resulted in forest ecosystem perturbations consisting of a cascade of biogeochemical reactions linked to soil N saturation (Galloway et al, 2003). Despite a > 50 % reduction in atmospheric N inputs (Kopacek et al, 2015), in the Czech Republic alone the value of the total nitrogen deposition remained during the last decade in the range of 70 000–80 000 t yr−1 as a result of the production of NOx emissions from transport, industrial production and energy generation (CENIA, 2017). A detrimental effect of unmanaged soil N saturation in catchment areas is the propagation of environmental effects to nearby lacustrine ecosystems (Kopacek et al, 1995)
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