Long-term trends in Swiss rivers sampled continuously over 39 years reflect changes in geochemical processes and pollution

Abstract

Long-term changes of 14 water constituents measured in continuously and water discharge proportionally collected samples of four Swiss rivers over a period of 39 years are analyzed using several statistical techniques. Possible drivers and causes for the identified trends and shifts are explained by consideration of catchment characteristics and anthropogenic activities. Water temperatures increased by 0.8-1.3 °C, whereas water discharges remained largely unchanged. Concentrations of alkalinity, total hardness, Ca, and Mg regulated by dominant carbonate lithologies in catchments increased by up to 10%. We attribute this change to an increase in the partial pressure of CO in the subsurface, provoked by increasing temperatures. Re-oligotrophication processes in lakes also influence the behavior of alkalinity and silicic acid. In contrast to concentrations, most loads did not change significantly, due to their large variances. Therefore, no changes in overall weathering rates of carbonate rocks can be detected. The outgassing of CO in rivers from the place of carbonate dissolution to measurement stations amounts up to 6% (mean) of CO sequestered (mean 1.1 mol m a) by the weathering of rock minerals. Changes in alkalinity/Ca/Mg ratios indicate an increase in calcite precipitation over time. Total nitrogen concentrations and loads peaked at the end of the 1980s and then decreased up to 50%, while NO concentrations showed almost no changes. This dynamic matches the changes in the agricultural N balance. Concentrations and loads of Na and Cl increased up to 60% due to an increase in the various uses of rock salt.

Biogeochemistry of dissolved carbon, major, and trace elements during spring flood periods on the Ob River

“…In contrast, the middle course of the Ob River is not affected by industrial activity and thus unlikely to be linked to the change of sulfate regime. One has to keep in mind that in contrast to concentrations, element loads are less subjected to long‐term variations, due to their large interannual variances as it was recently shown for water constituents of Swiss rivers over a period of 39 years (Zobrist, Schoenenberger, Figura, & Hug, ).…”

Spatial variability in specific discharge and streamwater chemistry during low flows: Results from snapshot sampling campaigns in eleven Swiss catchments

“…We used FOEN gauging station data of larger basins in the three different regions and the long‐term datasets from the Swiss National Groundwater and River Monitoring Program (NADUF and ISOT) to relate the observed spatial variability in the studied headwater catchments to the temporal variability in the larger basins. The “National Long‐Term Surveillance of Swiss Rivers” (NADUF) dataset contains water quality data for 24 stations along the main Swiss rivers at two week intervals since 1972 (Jakob, Binderheim‐Bankay, & Davis, ; Zobrist, Schoenenberger, Figura, & Hug, ). The “Swiss National Network for the Observation of Isotopes in the Water Cycle” (ISOT) dataset has monthly streamwater stable isotope data (δ 18 O and δ 2 H) from 1992 onwards (Schürch, Kozel, Schotterer, & Tripet, ).…”

Anthropogenic and catchment characteristic signatures in the water quality of Swiss rivers: a quantitative assessment

“…Conversely, the dataset is especially suitable for the investigation of long-term trends, due to the length of the time series, which spans from 11 to 42 years (Table 1). Data are collected following ISO/EN conform methods for water analysis and are subsequently validated by means of an extensive quality control as described in Zobrist et al (2018). In addition, we inspected the data to take into account possible errors deriving from fixed detection limits, e.g., deleting the values below the detection thresholds (see Sect.…”

“…1c), consisting in conglomerates and sandstones of variable composition (e.g., detrital quartz, feldspars, calcite, dolomite, and gypsum) (Kilchmann et al, 2004). The relative chemical weathering of carbonate rock and of gypsum are respectively 12 and 40 times higher than the weathering rate of granite or gneiss (Meybeck, 1987), thus suggesting that it is a good proxy to consider the Swiss Plateau area as characterized mainly by a calcareous bedrock (e.g., Zobrist et al, 2018). As the maps in Fig.…”