Hydrochemical data of karst springs provide valuable insights into the internal hydrodynamical functioning of karst systems and support model structure identification. However, the collection of high-frequency time series of major solute species is limited by analysis costs. In this study, we develop a method to retrieve the individual solute concentration time series and their uncertainty at high temporal resolution for karst springs by using continuous observations of electrical conductivity ((Figure presented.)) and low-frequency ionic measurements. Due to the large ion content and non-negligible concentrations of aqueous complexes in karst systems, the concentration of each solute species occurring as free ion and as part of aqueous complexes are computed separately. The concentration of species occurring as free ions are computed considering their contributions to the total (Figure presented.), whereas the concentration of the species as part of complexes are obtained from speciation calculations. The pivotal role of the complexation processes for the reconstruction of solute concentration time series starting from the (Figure presented.) signal is investigated in two karstic catchments with different geologies and temporal resolution of the available hydrochemical datasets, that is the Kerschbaum dolostone system in Austria and the Baget limestone system in France. The results show that complexation processes are significant and should be considered for the estimation of the total solute concentration in case of SO₄, Ca, Mg and HCO₃. The (Figure presented.) signal of a karst spring can be used to interpolate and quantify the dynamics of those solutes characterized by large contribution (approximately >6%) to the total (Figure presented.) and low relative variability, that is HCO₃, Ca and Mg. Moreover, the presented method can be used to estimate concentrations of solutes when applied to karst systems with stationary and hydrogeochemical homogeneous contributing area. On the contrary, the method is affected by large uncertainty in case of dynamic systems characterized by varying contributions of water from different geological areas. This study aims to contribute to the problem of hydrogeochemical data availability and to support future works on karst systems conceptualization.

Awareness of design risks is essential for preparing integrated design and construction tenders as decisions in this phase can have serious consequences once the project is awarded. The practice of multi-criteria decision analysis (MCDA) promises to support contractors in dealing with risks in the decision-making process. However, due to limited time and resources in a tender, risks involved in design alternatives are often overlooked and the selection of alternatives is mainly based on the decision-makers’ knowledge and experience. This raises the question how decision makers can become aware of the risks in the tender phase of projects. Following a design science research approach three interventions to raise risk awareness are identified and validated in the context of an infrastructure tender in the Netherlands. These interventions are (1) a general list of defined criteria to identify those criteria that correspond with the characteristics of the tender; (2) mapping identified project risks on criteria and assign a bandwidth score; (3) evaluation of the quality of the decision process by scoring elements of decision quality. Based on these interventions three design rules are proposed to increase the transparency of decision problems and the understanding of choices and, by doing so, create awareness for risks involved in design alternatives.

Process management literature is skeptical about creating legitimacy and a sense of partnership when implementing concessional Public-Private Partnerships. Within such organizational arrangements, managerial interaction often resembles zero-sum games. To explore the possibility to (re)create a sense of partnership in concessional PPPs, we developed the “3P challenge” serious game. Two gaming sessions with a mixed group of practitioners and a team of public project managers showed that the game cycle recreates adversarial situations where players can enact contractual obligations with higher or lower levels of subjectivity. When reflecting on the gaming experience, practitioners point out that PPP contracts can be creatively enacted by managers who act as brokers of diverse interests. While becoming aware of each other stakes they can blend contractual dispositions or place brackets around some contractual clauses for reaching agreement. By doing so, they can (re)create a sense of partnership, clarity, and fairness of the PPP contract.

Design decision-making in infrastructure tenders is a challenging task for contractors due to limited time and resources. Multi-criteria decision analysis (MCDA) promises to support contractors in dealing with this challenge. However, the ability of MCDA to ensure decision quality in the specific context of infrastructure tenders has gained little attention. By undertaking a longitudinal case study on early design decisions in a tender for a design-build project in the Netherlands the relationship between MCDA and decision quality is investigated. The case results show that in the early tender phase the decision making very much relies on the experience and knowledge of engineers. If MCDA is inappropriately used in such a context it can create impressions of soundly underpinned evaluations of design options while neglecting uncertainties and leading to low-quality decision. Although MCDA defines the “what” is required for structuring the decision problem, it does not support decision-makers in the “how” to do it. The explicit consideration of decision quality elements in MCDA can support the “how” and can create awareness for decision makers concerning importance, scope and uncertainty of criteria.

The time that water takes to travel through the terrestrial hydrological cycle and the critical zone is of great interest in Earth system sciences with broad implications for water quality and quantity. Most water age studies to date have focused on individual compartments (or subdisciplines) of the hydrological cycle such as the unsaturated or saturated zone, vegetation, atmosphere, or rivers. However, recent studies have shown that processes at the interfaces between the hydrological compartments (e.g., soil-atmosphere or soil-groundwater) govern the age distribution of the water fluxes between these compartments and thus can greatly affect water travel times. The broad variation from complete to nearly absent mixing of water at these interfaces affects the water ages in the compartments. This is especially the case for the highly heterogeneous critical zone between the top of the vegetation and the bottom of the groundwater storage. Here, we review a wide variety of studies about water ages in the critical zone and provide (1) an overview of new prospects and challenges in the use of hydrological tracers to study water ages, (2) a discussion of the limiting assumptions linked to our lack of process understanding and methodological transfer of water age estimations to individual disciplines or compartments, and (3) a vision for how to improve future interdisciplinary efforts to better understand the feedbacks between the atmosphere, vegetation, soil, groundwater, and surface water that control water ages in the critical zone.