Defining a Precipitation Stable Isotope Framework in the Wider Carpathian Region

Abstract

The eastern part of Europe is very poorly represented in the Global Network for Isotopes in Precipitation (GNIP) database, mainly because the monitoring of the stable isotopes in precipitation started only recently compared with other regions. In this respect, the main objective of this article is to fill the gap in the GNIP database over the eastern part of Europe and show the temporal variability and potential drivers of an extended network of δ18O values in precipitation collected from 27 locations in Romania and the Republic of Moldova. We also present the first high-resolution map of the spatio-temporal distribution of δ18O values in precipitation in Romania and the Republic of Moldova, according to an observational dataset. According to our results, the stations from western and northern Romania tend to have LMWLS with higher values than those from southwestern Romania. The monthly variation of the δ18O and δ2H showed a clearly interannual variation, with distinct seasonal differences, following the seasonal temperatures. The analysis of the spatial distribution of stable isotopes in precipitation water was made on the basis of both observational data and modeled data. This allowed us to study the origin of the air moisture and the interaction with regional and local patterns and to analyze the link between the spatial δ18O variations and the large-scale circulation patterns on a seasonal scale.

Stable Isotope Hydrology of Karst Groundwaters in Romania

“…These contributions result in the overall stable isotope composition of precipitation water with low values in the Carpathian Mountains and high values in western, southern and southeastern Romania. Under the influence of northerly cold air outbreaks, in northern Romania the δ 18 O and δ 2 H values in precipitation are lower, especially in winter [7]. This pattern is also discernible in the distribution of  18 O in groundwater presented in Figure 5, with the lowest values occurring in the high Southern Carpathian Mountains (with peaks above 2500 m a.s.l.…”

“…In 2017, the maximum values occurred in the late spring, which was anomalously warm in SE Europe [15]. In Figure 4, the data are plotted in a  18 O- 2 H diagram against the Local Meteoric Water Line (LMWL, modified from [7]) from the central Apuseni Mountains. For the nonkarst groundwater, we have plotted only the data from the Apuseni Mountains.…”

“…The Carpathian Mountains (maximum altitude 2544 m a.s.l.) act as an orographic barrier, blocking atmospheric moisture derived from the Atlantic Ocean, the Mediterranean Sea and the Black Sea [7,8]. Precipitation in Romania has a dual (Atlantic and Mediterranean) source on the western and southern flanks of the Carpathians [16,17], while Atlantic air masses and eastern (continental) sources dominate on their eastern flanks.…”

“…Additionally, we used a data set of stable isotope dynamics in groundwater published by [8]. Precipitation was collected monthly using Palmex rain samplers and the data were previously published by our group [7,14]. All water samples were collected directly from the main flow of the spring/rivers in high-density polyethylene (HDPE) bottles.…”

“…In Romania (Eastern Europe), the Carpathian Mountains act as a large water tower, with virtually all surface and shallow groundwater being derived from "captured" precipitation. Previous studies have shown a large variability in the stable isotopic composition of both precipitation [7] and groundwater [8], resulting from a strong interplay between moisture sources, atmospheric circulation patterns and orography. However, the groundwater study was restricted to a small area in the northern Carpathian Mountains, and it did not include karstified areas.…”