EVALUATION OF IMPACT OF FERTILIZATION ON SOIL SOLUTION CHEMISTRY IN DOMINATED FOREST SITE TYPES IN LATVIA

Enhanced forest growth may respond to the increasing demand for wood resources. Moreover, the forest is considered to be carbon storage, thus contributing to climate change mitigation. The forest soil fertilization, as well as forest drainage, thinning and regeneration may be an effective measure in increasing harvest rates. In the context of bio-economy, wood ash needs to be managed and can be utilized as an equivalent to potassium and phosphorus containing fertilizer. Ammonium nitrate can be used as fertilizer in forests on mineral soil since nitrogen is considered to be a tree growth limiting element in boreal forests. However, environmental aspects like leaching of the fertilizer should be taken into account. The aim of this research is to evaluate the impact of wood ash, ammonium nitrate and combined wood ash and nitrogen fertilizer impact on the chemical properties of soil water in dominated forest site types in Latvia. The trials were conducted in total in 16 forest stands. The fertilizers were spread in treatment plots, but the control plots were left untreated. The soil water samples were collected for two seasons. The pH, potassium, calcium, magnesium, phosphate and total nitrogen were determined in the soil water samples. Ammonium nitrate had an impact on the elevated concentration of total nitrogen in all experimental objects; although the significant differences between the control plot and treated plot were detected only in a part of experimental objects. The elevated concentrations of total nitrogen decreased after two months and remained above the control level. Interestingly, we observed a trend of both – increased and decreased concentrations of potassium, calcium, magnesium and phosphate. Nevertheless, only a part of the differences was statistically significant. The impact of wood ash on chemical properties of soil water was less pronounced in comparison to ammonium nitrate

The Influence of the Degree of Forest Management on Methylmercury and the Composition of Microbial Communities in the Sediments of Boreal Drainage Ditches

Inorganic mercury (Hg) can be methylated to the highly toxic and bioavailable methylmercury (MeHg) by microorganisms in anaerobic environments. The Hg methylation rate may be affected by forest management activities, which can influence the catchment soils, water, and sediments. Here, we investigate the influence of forest management in the form of ditch cleaning and beaver dam removal, as well as the seasonal variations, on sediment chemistry and microbiota. The relationships between MeHg concentrations in sediment samples and archaeal and bacterial communities assessed by 16S rRNA gene amplicon sequencing were investigated to determine the microbial conditions that facilitated the formation of MeHg. Concentrations of MeHg were highest in undisturbed catchments compared to disturbed or slightly disturbed sites. The undisturbed sites also had the highest microbial diversity, which may have facilitated the formation of MeHg. Low MeHg concentrations and microbial diversity were observed in disturbed sites, which may be due to the removal of organic sediment layers during ditch cleaning and beaver dam removal, resulting in more homogenous, mineral-rich environments with less microbial activity. MeHg concentrations were higher in summer and autumn compared to winter and spring, but the temporal variation in the composition and diversity of the microbial community was less than the spatial variation between sites. Beta diversity was more affected by the environment than alpha diversity. The MeHg concentrations in the sediment were positively correlated to several taxa, including Cyanobacteria, Proteobacteria, Desulfobacterota, Chloroflexi, and Bacteroidota, which could represent either Hg-methylating microbes or the growth substrates of Hg-methylating microbes

Evaluation of impact of fertilization on soil solution chemistry in dominated forest site types in Latvia

Enhanced forest growth may respond to the increasing demand for wood resources. Moreover, the forest is considered to be carbon storage, thus contributing to climate change mitigation. The forest soil fertilization, as well as forest drainage, thinning and regeneration may be an effective measure in increasing harvest rates. In the context of bio-economy, wood ash needs to be managed and can be utilized as an equivalent to potassium and phosphorus containing fertilizer. Ammonium nitrate can be used as fertilizer in forests on mineral soil since nitrogen is considered to be a tree growth limiting element in boreal forests. However, environmental aspects like leaching of the fertilizer should be taken into account. The aim of this research is to evaluate the impact of wood ash, ammonium nitrate and combined wood ash and nitrogen fertilizer impact on the chemical properties of soil water in dominated forest site types in Latvia. The trials were conducted in total in 16 forest stands. The fertilizers were spread in treatment plots, but the control plots were left untreated. The soil water samples were collected for two seasons. The pH, potassium, calcium, magnesium, phosphate and total nitrogen were determined in the soil water samples. Ammonium nitrate had an impact on the elevated concentration of total nitrogen in all experimental objects; although the significant differences between the control plot and treated plot were detected only in a part of experimental objects. The elevated concentrations of total nitrogen decreased after two months and remained above the control level. Interestingly, we observed a trend of both – increased and decreased concentrations of potassium, calcium, magnesium and phosphate. Nevertheless, only a part of the differences was statistically significant. The impact of wood ash on chemical properties of soil water was less pronounced in comparison to ammonium nitrate