Stable H and O isotope-based investigation of moisture sources and their role in river and groundwater recharge in the NE Carpathian Mountains, East-Central Europe

Abstract

The region situated between the mountain area and the lowlands in NE Romania (East-Central Europe) is experiencing increased competition for water resources triggered by a growing population, intensification of agriculture, and industrial development. To better understand hydrological cycling processes in the region, a study was conducted using stable isotopes of water and atmospheric trajectory data to characterize regional precipitation and vapour sources derived from the Atlantic Ocean, Mediterranean and Black Seas, as well as recycled continental moisture, and to assess and partition these contributions to recharge of surface and groundwater. Atmospheric moisture in the lowlands is found to be predominantly delivered along easterly trajectories, while mountainous areas appear to be dominated by North Atlantic Ocean sources, with moisture transported along mid-latitude, westerly storm tracks. Large-scale circulation patterns affect moisture delivery, the North Atlantic Oscillation being particularly influential in winter and the East Atlantic pattern in summer. Winter precipitation is the main contributor to river discharge and aquifer recharge. As winter precipitation amounts are projected to decrease over the next decades, and water abstraction is expected to steadily increase, a general reduction in water availability is projected for the region.

Tracing the Relationship between Precipitation and River Water in the Northern Carpathians Base on the Evaluation of Water Isotope Data

“…The average δ 18 O lapse rate was 0.25‰/100m for the BN (380 m asl) -RA (1600 m asl) transect (western slope of the Carpathians) and 0.27‰/100m for the SV (350 m asl) -RA (1600 m asl) transect (eastern slope of the Carpathians). Similar results have been found for the eastern Carpathian transect (0.27‰/100 m) [23] and close value have been reported for the western Carpathian in Slovakia (0.21‰/100 m) [28]. Because of the short time series at the GH, CM and VD stations, data from these stations was discussed together with that from RA.…”

“…River water samples were stored and analyzed similar to precipitation ones. Full details of the sampling procedure are given in [23].…”

“…Reduced amplitudes of stable isotope values in river water compared to precipitation water variability suggest that rivers are recharged via subsurface flow, with water from individual rain events being stored in the phreatic zone before recharging the rivers [17,43]. Low d-excess in river water occurs in summer, suggesting that evaporative loss plays an important role in the hydrological balance in the region [23]. These losses are higher at the low-elevation SVr station, and reduced in Mr and BNr stations, respectively.…”

Speleothem Records from the Eastern Part of Europe and Turkey—Discussion on Stable Oxygen and Carbon Isotopes

“…SE Europe is the only region on the continent where the contribution of Mediterranean sourced moisture exceeds~20% all year-round [36]. The Black Sea acts as an important moisture source for the surrounding coastal region (as far as the eastern Carpathians [37]) and for northern Turkey [38,39].…”

Stable isotopes in cave ice suggest summer temperatures in East-Central Europe are linked to AMO variability

“…2018). Precipitation in the region is mainly delivered by weather systems carrying moisture form the Atlantic Ocean, with the Mediterranean Sea contributing moisture during autumn and winter(Nagavciuc et al, 2019). The deuterium excess (d-excess or d) in precipitation, defined as d =  2 H -8* 18 O(Dansgaard, 1964) allows for a clear separation of the two types of 10 air masses; its values being close to the global average of 10(Craig, 1961) for moisture sourced from the Atlantic Ocean, and between 12 and 17, for moisture sourced in the Mediterranean Sea (resulting from the high evaporative conditions in the Eastern Mediterranean Sea).…”