Atmospheric Nitrogen Deposition and the Properties of Soils in Forests of Vologda Region

Twenty plots (20 m² each) were selected in coniferous and mixed forests of the industrial Vologda district and the Vytegra district without developed industries in Vologda region. In March, snow cores corresponding to the snow cover depth were taken on these plots. In August, soil samples from the 0- to 20-cm layer of litter-free soddy-podzolic soil (Albic Retisol (Ochric)) were taken on the same plots in August. The content of mineral nitrogen (Nₘᵢₙ), including its ammonium (NH⁺₄) and nitrate (NO⁻₃) forms, was determined in the snow (meltwater) and soil. The contents of total organic carbon, total nitrogen, and elements (Al, Ca); pH; particle size distribution; and microbiological parameters―carbon of microbial biomass (Cₘᵢc) and microbial respiration (MR)―were determined in the soil. The ratio MR/Cₘᵢc = qCO₂ (specific respiration of microbial biomass, or soil microbial metabolic quotient) was calculated. The content of Nₘᵢc in meltwater of two districts was 1.7 mg/L on the average (1.5 and 0.3 mg/L for the NH⁺₄ and NO–₃ forms, respectively). The annual atmospheric deposition was 0.6–8.9 kg Nₘᵢₙ/ha, the value of which in the Vologda district was higher than in the Vytegra district by 40%. Reliable correlations were found between atmospheric NH⁺₄ depositions and Cₘᵢc (–0.45), between NH⁺₄ and qCO₂ (0.56), between atmospheric NO⁻₃ depositions and the soil NO⁻₃ (–0.45), and between NO⁻₃ and qCO₂ (–0.58). The content of atmospheric Nₘᵢₙ depositions correlated with the ratios C/N (–0.46) and Al/Ca (–0.52) in the soil. In forests with the high input of atmospheric nitrogen (>2.0 kg NH⁺₄/(ha yr) and >6.4 kg Nₘᵢₙ/(ha yr)), a tendency of decreasing Cₘᵢc, C/N, and Al/Ca, as well as increasing qCO₂, was revealed, which could be indicative of deterioration in the functioning of microbial community and the chemical properties of the soil.