Globally, agricultural mineral soils can be either sources or sinks of carbon (C) depending on the land use, environmental conditions and management activities. In Latvia, land use change in cropland and grassland categories, including afforestation and deforestation, are the key sources of greenhouse gas (GHG) emissions. It is requested by the guidelines of the Intergovernmental Panel on Climate Change (IPCC) to use verified scientific methodology and scientifically proven emission factors and data sources in National GHG emission inventory reporting for they key source categories. The scope of the study is to evaluate organic carbon (C org ) stock in mineral soil in cropland and grassland in Latvia, where no land use changes were observed for at least 20 years. Remote sensing methods were applied to identify the National Forest Inventory (NFI) plots in grassland and cropland, where no land use changes have taken place since 1990. Vegetation index was used as criteria to validate land use. In total 120 plots on cropland and 120 plots on grassland were randomly selected for soil sampling, and the data on C org stock in mineral soil from 218 plots were used in the calculation. Soil samples for physical and chemical analysis from 0-10, 10-20, 20-40 and 40-80 cm depths were collected in 2014 and 2015. The most widespread soil groups in the studied plots in cropland are Retisols (21.2%), Luvisols (20.8%) and Stagnosols (18.6%), but in grassland -Stagnosols (22.8%), Umbrisols (22.8%) and Retisols (20.6%). The mean C org stock in soil at 0-40 cm depth in cropland is 83.0 t ha -1 , in grassland -88.6 t ha -1 , but the mean C org stock in agricultural soils at 0-40 cm depth -85.6 t ha -1 . Statistically significant difference between C org stock in cropland and grassland was not detected.

We determined the magnitude of instantaneous greenhouse gas (GHG) emissions from drainage ditches in hemiboreal peatlands in Latvia during the frost-free period of 2021 and evaluated the main affecting factors. In total, 10 research sites were established in drained peatlands in Latvia, including active and abandoned peat extraction sites and peatland forests. Results demonstrated that in terms of global warming potential, the contribution of CO2 emissions to the total budget of GHG emissions from drainage ditches can exceed the CH4 contribution. The average CO2 and N2O emissions from drainage ditches in peatland forests were significantly higher than those from ditches in peat extraction sites, while there was no difference in average CH4 emissions from ditches between peatland forests and peat extraction sites. Emissions from ditches of all GHGs increased with increasing temperature. In addition, CO2 and N2O emissions from drainage ditches increased with decreasing groundwater (GW) level. They were also negatively correlated with water level in ditches, but positively with potassium (K) and total nitrogen (TN) concentrations in water. By contrast, CH4 emissions from drainage ditches increased with increasing GW level and water level in ditches but were negatively correlated with K and TN concentrations in water.

We assessed total mercury (THg) concentrations and greenhouse gas (GHG) emissions in pristine and managed hemiboreal peatlands in Latvia, aiming to identify environmental factors that potentially affect their variation. The THg concentrations in soil ranged from <1 µg kg−1 to 194.4 µg kg−1. No significant differences between THg concentrations in disturbed and undisturbed peatlands were found, however, the upper soil layer in the disturbed sites had significantly higher THg concentration. During May–August, the mean CO2 emissions (autotrophic and heterotrophic respiration) from the soil ranged from 20.1 ± 5.0 to 104.6 ± 22.7 mg CO2-C m−2 h−1, N2O emissions ranged from −0.97 to 13.4 ± 11.6 µg N2O-N m−2 h−1, but the highest spatial variation was found for mean CH4 emissions—ranging from 30.8 ± 0.7 to 3448.9 ± 1087.8 µg CH4-C m−2 h−1. No significant differences in CO2 and N2O emissions between disturbed and undisturbed peatlands were observed, but CH4 emissions from undisturbed peatlands were significantly higher. Complex impacts of environmental factors on the variation of THg concentrations and GHG emissions were identified, important for peatland management to minimize the adverse effects of changes in the biogeochemical cycle of the biophilic elements of soil organic matter and contaminants, such as Hg.

This study was designed to estimate the variation in non-volatile carbon (C) content in different above- and belowground tree parts (stem, living branches, dead branches, stumps, coarse roots and small roots) and to develop country-specific weighted mean C content values for the major tree species in hemiboreal forests in Latvia: Norway spruce (Picea abies (L.) H. Karst.), Scots pine (Pinus sylvestris L.), birch spp. (Betula spp.) and European aspen (Populus tremula L.). In total, 372 sample trees from 124 forest stands were selected and destructively sampled. As the tree samples were pre-treated by oven-drying before elemental analysis, the results of this study represent the non-volatile C fraction. Our findings indicate a significant variation in C content among the tree parts and studied species with a range of 504.6 ± 3.4 g·kg−1 (European aspen, coarse roots) to 550.6 ± 2.4 g·kg−1 (Scots pine, dead branches). The weighted mean C content values for whole trees ranged from 509.0 ± 1.6 g·kg−1 for European aspen to 533.2 ± 1.6 g·kg−1 for Scots pine. Only in Norway spruce was the whole tree C content significantly influenced by tree age and size. Our analysis revealed that the use of the Intergovernmental Panel on Climate Change (IPCC) default C content values recommended for temperate and boreal ecological zones leads to a 5.1% underestimation of C stock in living tree biomass in Latvia’s forests. Thus, the country-specific weighted mean C content values for major tree species we provide may improve the accuracy of National Greenhouse Gas Inventory estimates.