Vincent Post’s research while affiliated with Bundesanstalt für Geowissenschaften und Rohstoffe and other places

In high-energy beach aquifers fresh groundwater mixes with recirculating saltwater and biogeochemical reactions modify the composition of groundwater discharging to the sea. Changing beach morphology, hydrodynamic forces, and hydrogeological properties control density-driven groundwater flow and transport processes that affect the distribution of chemical reactants. In the present study, density-driven flow and transport modelling of a generic 2-D cross-shore transect was conducted. Boundary conditions and aquifer parameters were varied in a systematic manner in a suite of 24 cases. The objective was to investigate the individual effects of boundary conditions and hydrogeological parameters on flow regime, salt distribution, and potential for mixing-controlled chemical reactions in a system with a temporally variable beach morphology. Our results show that a changing beach morphology causes the migration of infiltration and exfiltration locations along the beach transect, leading to transient flow and salt transport patterns in the subsurface, thereby enhancing mixing-controlled reactions. The shape and extent of the zone where mixing-controlled reactions potentially take place, as well as the spatiotemporal variability of the freshwater–saltwater interfaces, are most sensitive to variable beach morphology, storm floods, hydraulic conductivity, and dispersivity. The present study advances the understanding of subsurface flow, transport, and mixing processes that are dynamic beneath high-energy beaches. These processes control biogeochemical reactions that regulate nutrient fluxes to coastal ecosystems.

In high-energy beach aquifers fresh groundwater mixes with recirculating saltwater and biogeochemical reactions modify the composition of groundwater discharging to the sea. Changing beach morphology, hydrodynamic forces as well as hydrogeological properties control density-driven groundwater flow and transport processes that affect the distribution of chemical reactants. In the present study, density-driven flow and transport modelling of a generic 2-D cross-shore transect was conducted. Boundary conditions and aquifer parameters were varied in a systematic manner in a suite of twenty-four cases. The objective was to investigate their individual effects on flow regime, salt distribution, and potential for mixing controlled chemical reactions in a system with a temporally-variable beach morphology. Our results show that a changing beach morphology causes the migration of infiltration and exfiltration locations along the beach transect that lead to transient flow and salt transport patterns in the subsurface, thereby enhancing mixing controlled reactions. The shape and extent of the zone where mixing controlled reactions potentially take place as well as the spatio-temporal variability of the freshwater-saltwater interfaces are most sensitive to variable beach morphology, storm floods, hydraulic conductivity and dispersivity.

The new isotope module in HYDRUS‐1D can be used to infer the origin of root water uptake (RWU), a suitable dynamic indicator for agriculture and forest water management. However, evidence shows that the equilibrium fractionation between liquid water and water vapor within the soil is affected not only by soil temperature but also by soil tension. How soil tension affects isotope transport modeling and interpretations of the RWU origin is still unknown. In this study, we evaluated three fractionation scenarios on model performance for a field dataset from Langeoog Island: i ) no fractionation (Non_Frac), ii ) the soil temperature control on equilibrium fractionation as described by the standard Craig‐Gordon equation (CG_Frac), and iii ) CG_Frac plus the soil tension control on equilibrium fractionation (CGT_Frac). The model simulations showed that CGT_Frac led to more depleted surface isotopic compositions than CG_Frac. The vertical origin of RWU was estimated using the water balance calculations (WB) and the Bayesian mixing model (SIAR). While the former directly used water flow outputs, the latter used as input simulated isotopic compositions (using different fractionation scenarios) of RWU and soil water. Both methods provided similar variation trends with time and depth in different soil layers’ contributions to RWU. The contributions of all soil layers interpreted by the CGT_Frac scenario were always between Non_Frac and CG_Frac. The temporal origin of RWU was deduced from particle tracking (PT, releasing one hypothetical particle for individual precipitation event and tracking its movement based on the water balance between particles) and a virtual tracer experiment (VTE, assigning a known isotope composition to individual precipitation event and tracking its movement based on the cumulative isotope flux). Both methods revealed similar variation trends with time in drainage and root zone (RZ) travel times. The interpreted drainage and RZ travel times were generally ranked as Non_Frac > CGT_Frac > CG_Frac. Overall, the factors considered in the standard CG equation dominated isotope fractionation, transport, and interpretations of the RWU origin. Isotope transport‐based methods (SIAR, VTE) were more computationally demanding than water flow‐based methods (WB, PT). This article is protected by copyright. All rights reserved.

voorziet in Noord-Holland circa 70% van de inwoners in haar voorzie-ningsgebied van drinkwater gemaakt uit IJsselmeerwater. In recente droge jaren is het IJsselmeer enkele malen verzilt, wat gevolgen had voor de drink-waterproductie. Dit riep voor PWN de vraag op: 'kunnen we de kwaliteit van IJsselmeerwater bij het innamepunt in Andijk simuleren en voorspellen, en zo ja, met hoeveel dagen vooruit?' Om dit te onderzoeken is een model ontwikkeld dat is gekoppeld aan beschikbare actuele data en prognoses. Hiermee is een verwachting te maken van enkele dagen tot weken vooruit. De betrouwbaar-heid van de prognoses zal de komende tijd onderzocht worden. De analyse bracht al wel aan het licht dat lang niet alle benodigde data goed ontsloten zijn, wat een obstakel vormt bij de doorontwikkeling. Het ontwikkelde model is tevens gebruikt om de effectiviteit van een vergroot spaarbekken (de zogenaamde 'klimaatbuffer') te onderzoeken. Uit dit onderzoek blijkt dat de 'klimaatbuffer' een effectief middel is om de effecten van periodieke verzilting van het IJsselmeer op de drinkwaterproductie te mitigeren. In de zomers van 2017, 2018 en 2022 werd zichtbaar wat de consequenties van langdurige droogte in het Rijnstroomgebied kunnen zijn voor het IJsselmeer. Door het watertekort op het IJsselmeer kon minder water worden gespuid dan in gemiddelde jaren waardoor zoutwater dat bij de schutsluizen in de Afsluitdijk binnenkomt verder het IJsselmeer op kon migreren. Verzilte, windgedreven 'zoutwaterbellen' op het IJsselmeer zorgden ervoor dat IJsselmeerwater bij PWN's innamepunt in Andijk niet meer geschikt was voor productie van drink-water. Hierdoor werd in een aanzienlijk deel van Noord-Holland de jaargemid-delde norm voor chloride van 150 mg/l in drinkwater overschreden. Ook in 2022 leidde verzilting tot 19 preventieve innamestops bij Andijk, al werd de jaargemiddelde chloridenorm niet overschreden. Voor PWN is meer grip op deze innamebron noodzakelijk. Immers, 70% van de klanten van PWN wordt voorzien van drinkwater geproduceerd uit IJsselmeerwa-ter. Het is dus van belang te weten wat er van deze bron te verwachten valt, zowel morgen als de komende weken, maanden, jaren en zelfs decennia. Die wens/am-bitie ligt er voor meerdere parameters, maar gezien de recente jaren heeft zout de prioriteit. Opgemerkt moet worden dat waar hier over zout gesproken wordt, het specifiek over chloride gaat. Dit leidde tot de vraag of verzilting in een sys-teem als het IJsselmeer in voldoende mate te voorspellen is en in hoeverre deze voorspelling te gebruiken is voor operationele en strategische beslissingen?

We have better maps of the surfaces of Venus, Mars, and the Moon than of the Earth’s seafloor. There is even less information available about the geologic structure below the seafloor. In particular, the transition zone deep beneath and crossing the coastline is a very poorly studied frontier resulting from limitations of technology and logistical barriers. Here, we point out the significance of this region for understanding fundamental geologic processes, geohazards, and especially coastal aquifers. One prominent example is the increasing awareness of the importance of groundwater exchange between land and sea. This Perspective defines the region beneath the coastal transition zone, or coastal white ribbon as an underexplored frontier, and highlights the need for characterization of this critical region to depths of tens of km. We discuss available geophysical methods and their limitations with coastal groundwater used as the primary illustration. Advances in geophysical and drilling technology, coupled with numerical modeling, are needed to enable better accounting of this poorly understood component of the geosphere.