Groundwater pollution by agrochemicals such as nitrogen fertilizers can cause complex biogeochemical transformations to take place in groundwater-dependent ecosystems. To explore the interaction between nitrogen load and groundwater-dependent, spring-fed ecosystems, a study was conducted in Latvia in an area of suspected high nitrate (NO₃⁻) vulnerability due to its geological settings. A map of NO₃⁻vulnerability along the margins of the carbonate aquifer in Latvia is presented. The map is based on a conceptual model that was developed during an extensive case study involving hydrological, hydrochemical, and habitat investigation of springs discharging from a karst aquifer and spring-fed ecosystems. Areas that should be prime targets for restricting fertilizer application are highlighted on the map. Although the case study revealed increased nitrogen pollution (up to 51 mg L⁻¹, standard deviation of 9 mg L⁻¹, in the springs discharging from the karst aquifer), no clear evidence of adverse effects due to NO₃⁻pollution on the groundwater-dependent ecosystems using biotic indicators was found, highlighting the resilience of spring-fed ecosystems against high nitrogen inputs. In the case study, downstream groundwater-dependent ecosystems retained 70% of the reactive nitrogen during the vegetation season, but only a small proportion during the cold season. Thus, NO₃⁻pollution can be partly mitigated by restoring wetlands along valley slopes where natural groundwater discharge takes place. The conceptual model developed for groundwater NO₃⁻vulnerability is applicable to other areas in the Baltic region and other places with similar climatic and geological conditions.

Landfill leachate is regarded as a significant point source of pollutants that may pose a hazard to the environment, particularly to surface and ground waters. Leachates are highly variable and heterogeneous. Our study was focused on the characterization of landfill leachates derived from young (YDS) and matured (MDS) dumpsites in terms of the abundance of micropollutants, antimicrobial resistance genes (ARG), and microbial community structure. The concentrations of poly- and perfluoroalkyl substances (PFASs) were found to be higher in MDS compared to YDS, i.e., 13.19 and 7.16 μg/L, respectively. Among pharmaceutical compounds, ibuprofen was detected at the highest concentrations, i.e., 12.54, 12.81, and 13.13 μg/L, in the leachates derived from MDS, YDS, and ponds. The distribution of bacteria, archaea, eukaryotes, and viruses in the three leachate samples was as follows: 85.15 ÷ 88.04%, 9.13 ÷ 12.29%, 2.20 ÷ 2.68%, and 0.12 ÷ 0.15%, respectively. In total, 31 distinct families of ARGs were identified, comprising a total of 80 ARGs. Incubation of P. putida MSCL650 in sterile leachate from the pond resulted in decreasing the minimum inhibitory concentrations for six antibiotics as compared to cells incubated in nutrient broth. Hydrological processes, i.e., runoff and infiltration, can increase the dissemination of ARGs.

The Skaistkalne area in Latvia is one of the places where karst processes in gypsum strata occurs. The Iecava and Memele rivers border the area with extensive surface karst features such as sinkholes and karst lakes. Earlier investigations suggested a hydraulic connection between the Iecava and Memele rivers exists via the karst conduits due to the water level (WL) difference in the rivers. A set of methods was performed to study the possible connection: dye tracer was applied in the Iecava river and its occurrence was visually observed at the karst lakes and Memele river; the current velocity was measured and discharge of rivers calculated at several profiles; surface water and groundwater composition was studied involving in situ measurements of water pH and electrical conductivity, water sampling and chemical analysis of the water samples on the content of sulphates, calcium and magnesium ions. A numerical finite element 3D groundwater flow model was developed to assess the impact of WL changes in rivers to groundwater flow. The study showed that there is direct hydraulic connection between the rivers – water from the Iecava river flows to the Memele river. The groundwater discharge to the Memele river varies seasonally, and more intensive groundwater discharge is observed during the high season.

The importance of CO₂ removal from the atmosphere has long been an essential topic due to climate change. In this paper, the authors aim to demonstrate the suitability of the underground reservoirs for CO₂ storage based on their geological characteristics. The research addressed the potential of geological formations for fossil CO₂ storage in the Baltic States to support the goal of achieving carbon neutrality in the region. The geological, technical, and economic feasibility for CO₂ storage has been assessed in terms of carbon sequestration in geological structures and the legal framework for safe geological storage of fossil CO₂. Results indicate that prospective structural traps in the Baltic States, with reasonable capacity for CO₂ storage, occur only in Southwestern Latvia (onshore) and in the Baltic Sea (offshore), whilst other regions in the Baltics either do not meet basic geological requirements, or have no economically feasible capacity for CO₂ storage. Based on the examination of geological characteristics, the most fitting is the middle Cambrian reservoir in the Baltic sedimentary basin, and one of the most prospective structural traps is the geological structure of Dobele, with an estimated storage capacity of 150 Mt CO₂. This study revealed that the storage capacity of the middle Cambrian reservoir (up to 1000 Mt CO₂) within the borders of Southwestern Latvia is sufficient for carbon capture and safe storage for the whole Baltic region, and that geological structures in Latvia have the capacity to store all fossil CO₂ emissions produced by stationary sources in the Baltic States for several decades.

Benzalkonium chloride (BAC) is one of the most commonly used quaternary ammonium compounds in the pharmaceutical, cosmetic, and food industries. The aim of our study was to compare the physiological responses of Escherichia coli MSCL 332, Pseudomonas putida MCCL 650, and Staphylococcus epidermidis MSCL 333 on 50 mg/L BAC in rich and poor medium (100% and 5% tryptone soya broth (TSB)) in the temperature range from 8 °C to 37 °C, under static and shaking conditions. A high-throughput, 96-well microplate method was used to compare a broad range of cultivation conditions. The effect of BAC on growth, biofilm formation activity, and dehydrogenase and fluorescein diacetate hydrolysis activity was evaluated. Addition of BAC to 100% TSB inhibited biofilm formation at 37 °C by 2.4, 1.8, and 1.6 times for E. coli, P. putida, and S. epidermidis, respectively. In turn, BAC stimulated biofilm formation in E. coli in 5% TSB at 37 °C and 100% TSB at 8 °C, i.e., 1.4 and 1.3 times, respectively. Statistical optimization of broth composition with emphasis on biofilm formation and further testing under experimental conditions was performed with P. putida.