Showing papers by "Christoph Schüth published in 2013"

Suitability of temperature, hydraulic heads, and acesulfame to quantify wastewater-related fluxes in the hyporheic and riparian zone

Abstract: [1] Groundwater and surface water are in many cases closely linked components of the water cycle with respect to both quantity and quality. Bank filtrates may eventually be impacted by the infiltration of wastewater-derived micropollutants from surface waters. Artificial sweeteners such as acesulfame have recently been reported as a novel class of potentially valuable tracers to study the fate of wastewater-derived substances in groundwater and, in particular, to determine the (bio)degradability of micropollutants. In this paper, a model-based analysis of a field experiment within the hyporheic and riparian zone of a highly polluted German stream was performed to assess the physical and chemical behavior of the artificial sweetener acesulfame. In the first part of this study, a reliable flow and transport model was established by jointly using hydraulic heads, temperatures, and acesulfame concentrations as inverse model calibration constraints. The analysis confirmed the conservative behavior of acesulfame and, therefore, its usability as an indicator of sewage flux provenance. However, a comparison of the appropriateness of hydraulic head, temperature, and acesulfame concentrations revealed that the characterization of the surface water-groundwater flux data indicated diurnal temperature fluctuations are the best indicator in terms of characterizing the flow and transport behavior in the groundwater system.

Occurrence and distribution of organic trace substances in waters from the Three Gorges Reservoir, China

Abstract: This study deals with the evaluation of water quality of the Three Gorges Reservoir (TGR) in order to assess its suitability as a raw water source for drinking water production. Therefore, water samples from (1) surface water, (2) tap water, and (3) wastewater treatment plant effluents were taken randomly by 2011-2012 in the area of the TGR and were analyzed for seven different organic contaminant groups (207 substances in total), applying nine different analytical methods. In the three sampled water sources, typical contaminant patterns were found, i.e., pesticides and polycyclic aromatic hydrocarbons (PAH) in surface water with concentrations of 0.020-3.5 μg/L and 0.004-0.12 μg/L, disinfection by-products in tap water with concentrations of 0.050-79 μg/L, and pharmaceuticals in wastewater treatment plant effluents with concentrations of 0.020-0.76 μg/L, respectively. The most frequently detected organic compounds in surface water (45 positives out of 57 samples) were the pyridine pesticides clopyralid and picloram. The concentrations might indicate that they are used on a regular basis and in conjunction in the area of the TGR. Three- and four-ring PAH were ubiquitously distributed, while the poorly soluble five- and six-ring members, perfluorinated compounds, polychlorinated biphenyls, and polybrominated diphenyl ethers, were below the detection limit. In general, the detected concentrations in TGR are in the same range or even lower compared to surface waters in western industrialized countries, although contaminant loads can still be high due to a high discharge. With the exception of the two pesticides, clopyralid and picloram, concentrations of the investigated organic pollutants in TGR meet the limits of the Chinese Standards for Drinking Water Quality GB 5749 (Ministry of Health of China and Standardization Administration of China 2006) and the European Union (EU) Council Directive 98/83/EC on the quality of water intended for human consumption (The Council of the European Union 1998), or rather, the EU Directive on environmental quality standards in the field of water policy (The European Parliament and The Council of the European Union 2008). Therefore, the suggested use of surface water from TGR for drinking water purposes is a valid option. Current treatment methods, however, do not seem to be efficient since organic pollutants were detected in significant concentrations in purified tap water.

Methods to Countermeasure the Intrusion of Seawater into Coastal Aquifer Systems

Abstract: Seawater intrusion is a widely occurring environmental problem, which concerns the majority of the coastal aquifers in the world, having large negative impacts – from an economic, developmental, environmental as well as social point of view – on the coastal local communities. The fact that almost 40% of the world’s population lives within a distance of 80 km from the coastline gives rise to the significance of the aforementioned problem and emphasises the necessity for its prevention. This chapter analyses the engineering, managerial as well as techno-economical aspects with respect to the prevention of seawater encroachment into freshwater coastal aquifers and presents some state-of-the-art methods that are currently applied worldwide. It provides a critical review of the application of different type of coastal barriers (either by hydraulic, biological or construction means), management of aquifer recharge (through the application of underground or surface artificial recharge techniques), control of groundwater abstraction and exploitation scheme (by means of suggesting the optimal allocation of abstraction areas for minimising the risk of further intrusion) and other methods of prevention. Finally, this chapter investigates the current enacted legislation as well as adopted policy – mainly developed at a European level – with respect to the prevention of seawater intrusion, together with all the observed gaps and problems which create difficulties for its enforcement.

Surface and subsurface conceptual model of an arid environment with respect to mid- and late Holocene climate changes

Abstract: The water demand in arid regions is commonly covered by groundwater resources that date back to more humid periods of the Pleistocene and Holocene. Within the investigated arid part of SE Saudi-Arabia information about climate, groundwater levels, and pumping rates are only available for regions where groundwater extractions occur at present-day. For the prediction of the impact of long-term climate changes on groundwater resources an understanding of the hydrogeological and hydrological past and the development of the aquifers is necessary. Therefore, all available information about hydrology and hydrogeology for the past 10,000 years BP were collected and compiled to a conceptual model of the aquifer development on the Arabian Peninsula since the last Ice-Age. The climatic history was displayed by changes in precipitation, temperature and recharge during the mid-S and late Holocene. The hydrogeological development is described by groundwater ages, sea level fluctuations, movement of the coastline, and the development of sabkhas. The most sensitive parameter to describe the development of aquifer system is recharge. Present-day recharge was calculated with the hydrological model system HEC-HMS accounting for current precipitation, temperature, wind, soil types, and geomorphology. With respect to changes in precipitation and temperature over the past 10,000 years the temporal and spatial variability of groundwater recharge was calculated using empirical equations valid for semi-arid and arid settings. Further inflow into the groundwater system results from surface water infiltration in wadi beds, while natural outflow from the groundwater system occurs by discharge to the Gulf, evaporation from sabkhas, and spring discharge. Backward predictions can be verified by sedimentological observations of palaeo-river systems and lakes indicating that groundwater levels reached temporarily the surface under wetter climate conditions and 14C groundwater ages displaying groundwater residence times.

Impact of Preboreal to Subatlantic shifts in climate on groundwater resources on the Arabian Peninsula

Abstract: A large-scale numerical flow and transport model was developed for the central-eastern arid part of the Arabian Peninsula. The model was applied to a region with freshwater resources dating back to more humid periods of the past, which are faced with overexploitation today. Model inflow was based on infiltration around wadi beds and groundwater recharge. Inflow was balanced by natural outflows, such as evaporation from sabkhas, spring discharge, and discharge to the sea. Two models were developed: (1) a short-term present-day model to estimate effective model parameters, and (2) a long-term model to study the development of the groundwater resources during the Mid- and Late Holocene and the natural response of the groundwater system to changes in climate. Hydraulic model parameters (hydraulic conductivity and specific storage) were assigned with respect to geological structures. Hydraulic parameters were estimated with an inverse PEST model by calibrating against observed depression cones cause by groundwater abstraction. Sensitivity analysis demonstrated that estimated model parameters were associated with a high uncertainty at a certain distance from agricultural areas when calibration data were lacking. A long-term model starting 10,000 years BP was calibrated by spring discharge and palaeo-groundwater levels and validated using measured 14C groundwater ages. The long-model predicted that groundwater levels adapted in response to changes in precipitation. During the Mid-Holocene, which was characterized by an intensification of the monsoon season, groundwater levels increased by 10 m on the mainland within the shallow aquifers and adapted quickly to higher recharge rates. The deeper aquifers were less affected by changes in climate. Along the present-day coastline, the groundwater level rose by about 25 m due to the declined sea level in the Mid-Holocene. During this period, surface run-off was possible as groundwater levels temporarily reached the ground surface. The natural groundwater budget reacted sensitively to changes in climate. Between 10 and 3 ka, groundwater storage occurred. During the Late Holocene, at 3 ka, natural depletion of the groundwater system began, which still prevails today.

Untersuchungen zur Sorptionsreversibilität von organischen Schadstoffen in Aktivkohle, Holzkohle und Zeolith Y-200

Abstract: In einer Vielzahl von Untersuchungen wurde gezeigt, dass die Sorption von organischen Schadstoffen in Boden insbesondere vom organischen Kohlenstoffgehalt (C org) bestimmt wird. Kontrovers wird jedoch die Frage diskutiert, inwieweit Sorptionsprozesse vollstandig reversibel sind oder ob eine irreversibel sorbierte Schadstofffraktion in den Sorbenten verbleibt. Dieser Effekt ist etwa bei der Beurteilung von Sanierungsmasnahmen oder bei der Festlegung von Sanierungszielen von groser Bedeutung. In mehrstufigen Sorptions- und Desorptions-Batch-Versuchen mit TCE und PCE bzw. ortho-Xylol und para-Xylol und den Sorbenten Aktivkohle, Holzkohle sowie einem hydrophobem Zeolith Y-200 wurde diese Fragestellung untersucht. Es konnte gezeigt werden, dass der strukturelle Aufbau des Sorbenten von entscheidender Bedeutung fur das Auftreten einer desorptionsresistenten Schadstofffraktion ist. Wahrend fur den mikroporosen Zeolith Y-200 mit starrem Porensystem Sorption weitestgehend reversibel ist, wurde fur die Holzkohle und die Aktivkohle eine signifikante irreversibel sorbierte, oder zumindest sehr langsam desorbierende Schadstofffraktion ermittelt. Diese Schadstofffraktion kann jedoch bei einem folgenden weiteren Sorptionsschritt durch konkurrierende Sorptionseffekte mobilisiert und freigesetzt werden.