Using 81Kr and Noble Gases to Characterize and Date Groundwater and Brines in the Baltic Artesian Basin on the One-Million-Year Timescale

Analyses for $^{81}$Kr and noble gases on groundwater from the deepest aquifer system of the Baltic Artesian Basin (BAB) were performed to determine groundwater ages and uncover the flow dynamics of the system on a timescale of several hundred thousand years. We find that the system is controlled by mixing of three distinct water masses: Interglacial or recent meteoric water (\delta^{18}\text{O} \approx -10.4\unicode{x2030}) with a poorly evolved chemical and noble gas signature, glacial meltwater (\delta^{18}\text{O} \leq -18\unicode{x2030}) with elevated noble gas concentrations, and an old, high-salinity brine component (\delta^{18}\text{O} \geq -4.5\unicode{x2030}, \geq 90 \text{g Cl}^{-}/\text{L}) with strongly depleted atmospheric noble gas concentrations. The $^{81}$Kr measurements are interpreted within this mixing framework to estimate the age of the end-members. Deconvoluted $^{81}$Kr ages range from 300 ka to 1.3 Ma for interglacial or recent meteoric water and glacial meltwater. For the brine component, ages exceed the dating range of the ATTA 3 instrument of 1.3 Ma. The radiogenic noble gas components $^{4}$He* and $^{40}$Ar* are less conclusive but also support an age of > 1 Ma for the brine. Based on the chemical and noble gas concentrations and the dating results, we conclude that the brine originates from evaporated seawater that has been modified by later water-rock interaction. As the obtained tracer ages cover several glacial cycles, we discuss the impact of the glacial cycles on flow patterns in the studied aquifer system.Comment: Accepted for publication in Geochimica et Cosmochimica Act

Noise level modelling from traffic source within project "Riga north transport corridor"

Troksnis ir nozīmīgs miega traucējumu, darbaspēju mazināšanās un stresa izraisītājs. Jo īpaši paaugstinātām trokšņu vērtībām tiek pakļauti lielpilsētu iedzīvotāji. Satiksmes radītais troksnis ir lielākais vides trokšņa avots Eiropas Savienības valstīs. Izmantojot matemātiskās modelēšanas priekšrocības tika veikta trokšņu līmeņa prognozēšana vienam no lielākajiem Rīgas infrastruktūras projektiem. Darba gaitā tika sagatavots kartogrāfiskais materiāls esošās situācijas un iespējamo izmaiņu atainošanai. Iegūtie rezultāti liecina par būtisku trokšņu līmeņa pieaugumu plānotā projekta teritorijā. Lielu ietekmi uz trokšņu nevienmērīgo izplatību noteica valdošo vēju virziens un plānotais ceļa profila augstums. Atslēgvārdi: troksnis, modelēšana, trokšņu līmenis, transportsNoise pollution cause significant impact on sleep disturbances, decreased work capacity and works as a stressor. Especially exposed to great noise levels are inhabitants in large urban areas. Traffic noise is a major source of environmental noise in European Union countries. Mathematical modelling advantages were used to predict noise levels of one of the largest infrastructure projects in Riga. Obtained cartographic material was made to portray present situation and possible changes after project is realized. Data shows that noise levels will become more significant after highway is built. Result differences were caused by influence of dominant wind direction and hight of planed road profile. Keywords: noise, modelling, noise level, traffi

Groundwater flow modelling at wellfields Baltezers and Baltezers ІІ

Maģistra darba pētījumā veikta hidroģeoloģiskā modeļa izveide Baltezers un Baltezers II ūdensgūtņu apkārtnē. Ūdensgūtņu teritorijā raksturīgi sarežģīti hidroģeoloģiskie apstākļi, kas saistīti ar pazemes ūdens ieguvi no Kvartāra ūdens kompleksa centralizētajai ūdens apgādei un gruntsūdens mākslīgo papildināšanu no virszemes ūdens objektiem. Pētījuma teritorija aptver 20 km2 lielu platību, kurā iekļauta visa aktīvā ūdens apmaiņas zona. Hidroģeoloģiskā modeļa izveidei izmantota PAIC izstrādātā datorprogramma HiFiGeo v3.5. Pētījuma rezultātā tika izveidots kalibrēts hidroģeoloģiskais modelis, kurš izmantots divu situāciju modelēšanai, pie mainīgiem ūdensgūtņu režīmiem. Balstoties uz modelētajiem rezultātiem ir veikti secinājumi par īpatnībām, kas saistītas ar gruntsūdens plūsmu modeļu izveidi. Atslēgas vārdi: pazemes ūdens, hidroģeoloģiskā modelēšana, HifiGeo, Baltezers, gruntsūdeņi, gruntsūdens plūsmas.Hydrogeological model for surrounding area of Baltezers and Baltezers II well fields was carried out during the Master’s paper study. Surrounding is estimated to have complex hydrogeological conditions, which is related to groundwater extraction from the Quaternary water complex for water supply and artificial recharge of groundwater from surface water bodies. The study covers area of 20 km2 and it covers whole active water exchange zone. The hydrogeological model was developed using computer program HiFiGeo v3.5. created by PAIC. The study resulted in a calibrated model, which was used for two situation modeling, at variable well field regimes. Resulting in conclusions of characteristics and approaches to unconfined groundwater flow modeling. Keywords: groundwater, hydrogeological modeling, HifiGeo, Baltezers, unconfined groundwater, unconfined groundwater flow

Effects of karst processes on surface water and groundwater hydrology at Skaistkalne Vicinity, Latvia

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.</jats:p

Pleistocene age paleo-groundwater inferred from water-stable isotope values in the central part of the Baltic Artesian Basin

<p>A new data set of δ²H and δ¹⁸O in the groundwater from the central part of the Baltic Artesian Basin is presented. The hydrogeological section is subdivided into stagnation, slow exchange and active exchange zones. Na–Ca–Cl brine found at the deepest part – the stagnation zone – is characterized by δ¹⁸O values above −5 ‰ and δ²H values approaching −40 ‰ with respect to Vienna Standard Mean Ocean Water. The slow exchange zone where waters of mostly intermediate salinity reside is characterized by δ¹⁸O values around −11.7 ‰ and δ²H values around −85.3 ‰. Mean δ¹⁸O and δ²H values of the fresh groundwater in the active water exchange zone are −11.1 and −79.9 ‰, respectively. Characteristically, the groundwater in the active and slow exchange zone is isotopically more depleted compared with the precipitation values observed, and the depletion increases with depth down to the level where strongly enriched brines are encountered.</p

Rescue of groundwater level time series: How to visually identify and treat errors”

Groundwater level time series are of great value for a variety of groundwater studies, particularly for those dealing with the impacts of anthropogenic and climate change. Quality control of groundwater level observations is an essential step prior to any further application, e.g., trend analysis. Often the quality control of data is limited to the removal of outliers or elimination of entire time series from a dataset, while such approaches drastically reduce the spatial coverage of initially huge datasets. Frequently studies tend to present already qualitycontrolleddata, but neglect to demonstrate how the data were selected, judged, and modified. We present a data rescue approach developed for correcting the Latvian national groundwater level database, containing 1.68 million groundwater level observations since 1959, including 0.69 million manual measurements. A web-based R-Shiny interface was developed and used for visual identification and manual correction of erroneous measurements in groundwater level time series. All data manipulations were performed programmatically. Reproducibilityand traceability were ensured by deploying separate data tables for raw observations, data repair actions and the final dataset. As a result of applied actions, 34.3% of all automatic measurements were either deleted or corrected, while only 6.5% of manual measurements were edited. Commonly found errors ingroundwater level time series were grouped into: errors in measurement and data recording; technical problems at the observation site; local anthropogenic impact and other unclassified problems. The improvement from the rescue approach was assessed by comparing the Akaike information criterion derived from fitted ARMA and ARIMA models to both original and repaired time series. The results showed that models fitted using repaired time series were better than those fitted on the original time series for the same time series sections. The presented rescue approach and results can be of great value for all studies using groundwater level time series as an input.Original artticle excluded the Delft the affiliation (second) of Willem Jan Zaadnoordijk Corrigendum DOI 10.16/j.hydrol.2022.127563Water ResourcesCivil Engineering and Geoscience