Abstract
Mediterranean forests along the eastern Adriatic coast have an important ecological role. However, few studies have been conducted on nitrogen deposition so far. To improve this knowledge, the main aims of our study were: (i) to estimate nitrogen inputs and determine differences among the four Mediterranean forests, (ii) to determine the seasonal behaviour of N deposition compounds, and (iii) to discuss the results in relation to forest type and precipitation. Measurements were carried out over a two-year period on four plots in two regions: holm oak and pubescent oak in Istria, Aleppo pine and black pine in Dalmatia. Bulk open field and throughfall deposition were sampled with continuously exposed collectors. Measurements, analyses and data validation of precipitation and N compounds were carried out. The results showed that the highest average monthly precipitation was recorded in the black pine plot and the lowest in the Aleppo pine plot. Nitrate and ammonia in conifer plots in throughfall samples were lower than in bulk open field samples, indicating possible retention by the tree canopy. The results revealed a higher amount of N deposition collected in broadleaved forests than in conifer forests indicating the washing out of N compounds previously deposited and accumulated in forest canopy. The chemistry of N deposition was strongly influenced by local and anthropogenic sources as well as neighbouring countries. Our results may fill the knowledge gap in understanding the influence of precipitation and seasonality of N compounds in different Mediterranean forest types along the eastern Adriatic coast.
Highlights
The emission of air pollution in Europe has significantly increased in the course of the twentieth century
The measurements were conducted on four different Mediterranean forest ecosystems to identify the amount and differences in seasonal precipitation and N deposition
Total precipitation in the studied period at all plots was generally lower in throughfall deposition (THR), ranging between 1047 mm in Aleppo pine (AP) to 2193 mm in black pine (BP) (Table 2)
Summary
The emission of air pollution in Europe has significantly increased in the course of the twentieth century. Large amounts of nitrogen oxides (NOx) are released by human activities, mainly fossil fuel combustion in industry, power plants, heating systems and transport, while ammonia (NH3) from agriculture and farming. This increase has affected N cycling in ecosystems worldwide (Erisman et al 2013) and is considered one of the threats to Mediterranean sustainability, along with climate change and ozone (De Marco et al 2019, Jakovljević et al 2021). Atmospheric deposition and its transformation in contact with vegetation are of great importance in understanding its effects on forests It has an impact on forest ecosystems through eutrophication by nitrogen and soil acidification, altering soil properties and processes (Clark et al 2007). Critical loads for nutrient nitrogen and their exceedances were both important for defoliation (De Marco et al 2014)
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