Salinity-induced increase of the hydraulic conductivity in the hyporheic zone of coastal wetlands

Abstract

In coastal zones globally, salinization is rapidly taking place due to the combined effects of sea level rise, land subsidence, altered hydrology, and climate change. Although increased salinity levels are known to have a great impact on both biogeochemical and hydrological processes in aquatic sediments, only few studies have included both types of processes and their potential interactions. In the present paper, we used a controlled 3-year experimental mesocosm approach to test salinity induced interactions and discuss mechanisms explaining the observed hydrological changes. Surface water salinity was experimentally increased from 14 to 140 mmol Cl per L (0.9 and 9 PSU) by adding sea salt which increased pore water salinity but also increased sulfate reduction rates, leading to higher sulfide, and lower methane concentrations.By analyzing slug test data with different slug test analysis methods, we were able to show that hydraulic conductivity of the hyporheic zone increased 2.8 times by salinization. Based on our hydrological and biogeochemical measurements, we conclude that the combination of pore dilation and decreased methane production rates were major controls on the observed increase in hydraulic conductivity. The slug test analysis method comparison allowed to conclude that the adjusted Bouwer and Rice method results in the most reliable estimate of the hydraulic conductivity for hyporheic zones. Our work shows that both physical and biogeochemical processes are vital to explain and predict hydrological changes related to the salinization of hyporheic zones in coastal wetlands and provides a robust methodological approach for doing so.

Rewetting of Three Drained Peatlands Drives Congruent Compositional Changes in Pro- and Eukaryotic Soil Microbiomes through Environmental Filtering

“…In Coastwet the abundance of methanogens per gram soil was at least 10x lower than in the freshwater sites Alderwet and Percowet. Thus, this environmental filtering through salinity likely leads to lower CH4 emissions, also shown before in several studies [46,58,59].…”

High‐resolution peat volume change in a northern peatland: Spatial variability, main drivers, and impact on ecohydrology

“…Repeated slug tests (n = 3) within 1 day on the same filter (n = 7) indicate that the mean measurement error of K S is 5.4% of the mean observed value. This confirms the high precision that can be obtained with slug tests, in agreement with van Dijk et al (2017).…”

“…K S was estimated using the rate of change in the water level in the piezometer over time and piezometer flow system characteristics (Zlotnik, Goss, & Duffield, 2010). This confirms the high precision that can be obtained with slug tests, in agreement with van Dijk et al (2017). As water chemistry affects saturated hydraulic conductivity estimates (Kettridge & Binley, 2010), the slug-water (100 mL) was collected from a pool in the peatland to match local water quality.…”

“…We estimated the saturated horizontal hydraulic conductivity (K S ) of the 0.20-to 0.40-m-deep peat layer using in situ slug tests as described in van Dijk, Nijp, Metselaar, Lamers, and Smolders (2017). In slug tests, a volume of water (slug) is quickly poured into the piezometers, which generates a hydraulic head difference and induces flow from the piezometer into the peat matrix.…”

Impact of the water salinity on the hydraulic conductivity of fen peat

“…According to their findings, the process also continues during periods with no water flow. Field measurements of K s with a changing salinity have been carried out by van Dijk, Nijp, Metselaar, Lamers, and Smolders (2017), who observed an increase of 280% of K s for an increase of the EC from approx. 0.9 to 9 mS cm −1 .…”