Assessment of exploitable groundwater resources of Denmark by use of ensemble resource indicators and a numerical groundwater–surface water model
ABSTRACT The trend towards construction of comprehensive dynamical numerical groundwater–surface water models to facilitate the examination of the quantitative status of groundwater resources by means of indicators is growing. A typical resource indicator is the assumption that the maximum abstraction should not exceed the groundwater recharge to an aquifer. From an aquatic, ecological point of view, the recommendation is only to exploit a small fraction of the recharge, in order to allow a significant fraction to supply wetlands and river systems. The paper proposes a set of four resource indicators for translating qualitative policy considerations on sustainable groundwater developments into quantitative criteria that can be evaluated by use of comprehensive hydrological models: (1) Indicator 1 is equal to a maximum abstraction of 35% of the pre-abstraction recharge; (2) Indicator 2 assumes a maximum 30% utilisation of current recharge; (3) Indicator 3 is identified as the abstraction at which mean river runoff is reduced by a maximum 10%, compared to pre-abstraction runoff; and (4) Indicator 4 is the abstraction at which baseflow is reduced by a maximum 5%, 10%, 15%, 25% and 50% aggregated for the reaches with the same environmental goal (e.g. a maximum 10% reduction of baseflow for salmonid spawning and nursery waters compared to pre-abstraction baseflow). The methodology for the design of the four ensemble resource indicators is described and the results of applying those indicators are demonstrated for assessment of the regional and national exploitable groundwater resources of Denmark.
- SourceAvailable from: Jes Jessen Rasmussen[show abstract] [hide abstract]
ABSTRACT: The release of chemicals such as chlorinated solvents, pesticides and other xenobiotic organic compounds to streams, either from contaminated sites, accidental or direct application/release, is a significant threat to water resources. In this paper, different methods for evaluating the impacts of chemical stressors on stream ecosystems are evaluated for a stream in Denmark where the effects of major physical habitat degradation can be disregarded. The methods are: (i) the Danish Stream Fauna Index, (ii) Toxic Units (TU), (iii) SPEAR indices, (iv) Hazard Quotient (HQ) index and (v) AQUATOX, an ecological model. The results showed that the hydromorphology, nutrients, biological oxygen demand and contaminants (pesticides and trichloroethylene from a contaminated site) originating from groundwater do not affect the good ecological status in the stream. In contrast, the evaluation by the novel SPEAR(pesticides) index and TU indicated that the site is far from obtaining good ecological status - a direct contradiction to the ecological index currently in use in Denmark today - most likely due to stream sediment-bound pesticides arising from the spring spraying season. In order to generalise the findings of this case study, the HQ index and AQUATOX were extended for additional compounds, not only partly to identify potential compounds of concern, but also to determine thresholds where ecological impacts could be expected to occur. The results demonstrate that some commonly used methods for the assessment of ecological impact are not sufficient for capturing - and ideally separating - the effects of all anthropogenic stressors affecting ecosystems. Predictive modelling techniques can be especially useful in supporting early decisions on prioritising hot spots, serving to identify knowledge gaps and thereby direct future data collection. This case study presents a strong argument for combining bioassessment and modelling techniques to multi-stressor field sites, especially before cost-intensive studies are conducted.Science of The Total Environment 05/2012; 427-428:319-31. · 3.26 Impact Factor
Dataset: McKnight et al., 2010
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ABSTRACT: We evaluate links between climate and simulated river bank erosion for one of the world's largest rivers, the Mekong. We employ a process-based model to reconstruct multidecadal time series of bank erosion at study sites within the Mekong's two main hydrological response zones, defining a new parameter, accumulated excess runoff (AER), pertinent to bank erosion. We employ a hydrological model to isolate how snowmelt, tropical storms and monsoon precipitation each contribute to AER and thus modeled bank erosion. Our results show that melt (23.9% at the upstream study site, declining to 11.1% downstream) and tropical cyclones (17.5% and 26.4% at the upstream and downstream sites, respectively) both force significant fractions of bank erosion on the Mekong. We also show (i) small, but significant, declines in AER and hence assumed bank erosion during the 20th century, and; (ii) that significant correlations exist between AER and the Indian Ocean Dipole (IOD) and El Niño Southern Oscillation (ENSO). Of these modes of climate variability, we find that IOD events exert a greater control on simulated bank erosion than ENSO events; but the influences of both ENSO and IOD when averaged over several decades are found to be relatively weak. However, importantly, relationships between ENSO, IOD, and AER and hence inferred river bank erosion are not time invariant. Specifically, we show that there is an intense and prolonged epoch of strong coherence between ENSO and AER from the early 1980s to present, such that in recent decades derived Mekong River bank erosion has been more strongly affected by ENSO.Water Resources Research 04/2013; 49(4):2146-2163. · 3.15 Impact Factor