RESUMEN
Shallow coastal aquifers are vulnerable hydrosystems controlled by many factors, related to climate, seawater-freshwater interactions and human activity. Given on-going climate change, sea level rise and increasing human impact, it is especially true for groundwater resources situated in sandbars. We developed numerical models of unsaturated zone water flow for two sandbars in northern Poland: the Vistula Spit and the Hel Spit using HYDRUS-1D. The simulations were performed for three types of land use: pine forest, grass cover and bare soil, for 2024-2100 based on weather data and sea level rise forecasts for two emissions scenarios (RCP 4.5 and RCP 8.5). The results present prognosis of groundwater recharge, water table level and water content changeability in near-term (2023-2040), mid-term (2041-2060), and long-term period (2081-2100). Expected sea level rise and decreasing hydraulic gradient of the sandbar aquifers will probably cause in-land movement of the freshwater-saltwater interface, leading to significant decrease or complete salinization of groundwater resources. The study shows that holistic monitoring including groundwater level and salinization, sea level rise, and metheorological data (precipitation amount and variability, temperature) is crucial for sustainable management of vulnerable aquifers located in sandbars.
RESUMEN
In this study, we investigated the effects of soil organic carbon (SOC) distribution and water uptake by plant roots on PFAS movement in the vadose zone with a deep groundwater table under temperate, humid climate conditions. Two series of numerical simulations were performed with the HYDRUS computer code, representing the leaching of historical PFOS contamination and the infiltration of water contaminated with PFOA, respectively. We considered soil profiles with three distributions of SOC (no SOC, realistic SOC distribution decreasing with depth, and uniform SOC equal to the content measured in topsoil), three root distributions (bare soil, grassland, and forest), and three soil textures (sand, sandy loam, and loam). The SOC distribution had a profound impact on the velocity of PFOS movement. The apparent retardation factor for realistic SOC distribution was twice as large as for the scenario with no SOC and more than three times smaller than for the scenario with uniformly high SOC content. We also showed that the root distribution in soil profoundly impacts the simulations of PFAS migration through soil. Including the root zone significantly slows down the movement of PFAS, primarily due to increased evapotranspiration and reduced downward water flux. Another effect of water uptake by plant roots is an increase of PFAS concentrations in soil water (evapo-concentration). The evapo-concentration and the slowdown of PFAS movement due to root water uptake are more significant in fine-textured soils than in sand.
RESUMEN
We investigated the influence of climate change in the period 1951-2020 on shallow aquifers in the Brda and Wda outwash plains (Pomeranian Region, Northern Poland). There was a significant temperature rise (0.3 °C/10 years), which accelerated after 1980 (0.66 °C/10 years). Precipitation became increasingly irregular - extremely rainy years occurred right after or before extremely dry years, and intensive rainfall events became more frequent after 2000. The groundwater level decreased over the last 20 years, even though the average annual precipitation was higher than in the previous 50 years. We carried out numerical simulations of water flow in representative soil profiles for the years 1970-2020 using the HYDRUS-1D model, developed and calibrated during our earlier work at an experimental site in the Brda outwash plain (Gumula-Kawecka et al., 2022). We used a relationship between the water head and flux at the bottom of the soil profiles (the third-type boundary condition) to reproduce groundwater table fluctuations caused by recharge variability in time. The calculated daily recharge showed a decreasing linear trend for the last 20 years (0.05-0.06 mm d-1/10 years), and dropping trends in water table level and soil water content in the entire profile of vadose zone. Field tracer experiments were performed to estimate impact of extremely rain events on water flux in vadose zone. The results suggest that tracer travel times are strongly determined by water content in the unsaturated zone which is determined by precipitation amount in span of weeks, rather than extremely high precipitation events.