Spatial and temporal dynamics of water isotopes in the riverine‐marine mixing zone along the German Baltic Sea coast

Abstract

River estuaries are characterized by mixing processes between freshwater discharge and marine water masses. Since the first are depleted in heavier stable isotopes compared with the marine realm, estuaries often show a linear correlation between salinity and water stable isotopes (δ 18 O and δ 2 H values). In this study, we evaluated spatial and seasonal isotope dynamics along three estuarine lagoon transects, located at the northern German Baltic Sea coast. The data show strong seasonality of isotope values, even at locations located furthest from the river mouths. They further reveal a positive and linear salinity-isotope correlation in spring, but -in two of the three studied transects-hyperbolic and partially reverse correlations in summers. We conclude that additional hydrological processes partially overprint the two-phase mixing correlation during summers: aside from the isotope seasonality of the riverine inflows, the shallow inner lagoons in the studied estuaries are influenced by evaporation processes. In contrast the estuarine outflow regions are under impact of significant salinity and isotope fluctuations of the Baltic Sea. Deciphering those processes is crucial for the understanding of water isotope and salinity dynamics. This is also of relevance in context of ecological studies, for example, when interpreting oxygen and hydrogen isotope data in aquatic organisms that depend on ambient estuarine waters.

First Steps towards a near Real-Time Modelling System of Vibrio vulnificus in the Baltic Sea

“…The SSS climatology closely depicts the salinity gradient along the German Baltic coast. However, the model results indicate low salinity (nearly 0 PSU) for three narrow inlets (areas marked with hashed lines in Figure 4 ), which contradicts published salinity measurements from these areas [ 34 ]. This discrepancy may be caused by the model’s underestimation of the water exchange between the open Baltic Sea and these bays, as the narrowest inlet of all three areas is smaller than the model’s grid resolution of 200 m. Therefore, these specific bays were excluded from the subsequent analysis.…”

“…East of Usedom, the water is relatively turbid, leading to more intense heating of the water [ 76 , 77 ]. In shallow bays, such as the Greifswald Bodden, bathymetry limits the water exchange [ 34 ], thereby causing higher warming rates. The Greifswald Bodden is also the area for which Brennholt et al [ 38 ] projected the strongest increase in the V. vulnificus season length, defined as days with SST exceeding 17 °C.…”

“…Towards the east of the study area, the mean SSS decreases along with its variability to values as low as 7 PSU in the open Baltic Sea. In the inlets, estuaries, and Bodden, the influx of riverine freshwater reduces the salinity even further [ 34 ].…”

Corroborating otolith age using oxygen isotopes and comparing outcomes to scale age: Consequences for estimation of growth and reference points in northern pike (Esox lucius)

“…We attempted to sample fish from all lagoons in a 1:1 ratio of males to females across the entire length‐range, and supplemented lagoon samples with pike from tributaries to represent different environments and sexes. To assess the variability of water δ 18 O (δ 18 O Water ) and test whether cyclic variations in otolith δ 18 O (δ 18 O Otolith ) values were driven by seasonal temperature fluctuations, water samples were collected from a transect of the whole study system in June 2019, March 2020, and July 2020, and biweekly measurements at fixed locations from March 2020 until March 2021 (Figure 1) (Aichner et al, 2022).…”

“…Tributary abbreviations are NHG (Neuendorfer Hechtsgraben) and BKG (Badendycksgraben). Numbered yellow points mark sampling points of three δ 18 O Water measurement transects in June 2019, March 2020, and July 2020 (Aichner et al, 2022), blue points noted with letters B – I mark sampling points of biweekly δ 18 O Water measurements from March 2020 until March 2021. The average monthly salinity between 1 January 2008 and 1 January 2023 is shown as a color gradient.…”