Wolfgang Nestler

Factors affecting denitrification during infiltration of river water into a sand and gravel aquifer in Saxony, Germany

Abstract River infiltration into a sand and gravel aquifer was investigated to assess the importance of denitrification in maintaining low-NO − 3 groundwater supplies. Samples from the River Elbe and groundwater sampling points along a section of the aquifer were analysed for dissolved organic carbon, major ions and the 15 N 14 N isotopic ratio of dissolved NO − 3 . Input of NO − 3 to the aquifer is influenced by seasonal, temperature-dependent denitrification in the river bed sediments. Along an upper flowpath in the aquifer from the River Elbe to a sampling point at a distance of 55 m, the median NO − 3 concentration decreased by 4.8 mg litre −1 and the δ 15 N composition increased by +9.0‰, consistent with denitrification. Similar isotopic enrichment was demonstrated in a laboratory column experiment with a reduction in NO − 3 of 10.5 mg litre −1 for an increase in δ 15 N of +9.8‰, yielding an isotopic enrichment factor of −14.6‰. A mass balance for denitrification shows that oxidizable organic carbon required for denitrification is derived from both the infiltrating river water and solid organic matter fixed in the river bed sediments and aquifer material.

Sampling and measurement of radon-222 in water

Abstract The radon-222 content of water especially is of interest considering aspects of radiation protection or techniques to investigate hydrologie characteristics of aquifers using radon-222 as a natural tracer. Sampling and measurement of radon in groundwater are complicated by the high volatility of the gas. A method including sampling techniques (pumping, flushing time, filling arrangement and sample transportation) and rapid analysis of radon with high reproducibility was investigated and tested. The measurement is based on extraction concentration of radon-222 and liquid scintillation spectrometry. The detection limit of this method is about 0.05 Bql−1. By means of α/β discrimination it can be confirmed that radon-222 is the origin of the measured radioactivity.

The Suitability and Usage of 18O and Chloride as Natural Tracers for Bank Filtrate at the Middle River Elbe

Abstract Flow times and infiltration behaviour are very important for water extraction from riverbank filtration. Both the chloride content and the isotopic composition of oxygen (δ18O) were found to be suitable indicators for the conditions encountered in the middle course of the River Elbe near Torgau. The ranges for Elbe water were measured to be 20–43 mg Cl/l (1995-97) and -11 to -8.5‰ δ18O (1993-97). Both methods permitted flow-time spectra at two adjacent sampling profiles incorporating river and production wells to be obtained, indicating the preferred flow paths and the vertical extension of the riverbank filtrate plume in the aquifer. However, since the differences between the mean values for river water and regional groundwater were too small the percentage of river water abstracted from production wells could not be calculated.

Determination of hydraulic boundary conditions for the interaction between surface water and groundwater

Abstract The main determinants of the interaction between surface water and groundwater are the distribution of areas with different infiltration rates, the thickness of sediment layers and the hydraulic head gradient. These conditions determine the volume and velocity of infiltrating water which, together with the direction of water flow, are required to model the interaction processes. Due to difficulties with measurement, only the direction of water flow is usually determined and boundary conditions are estimated from simplified assumptions. Field techniques have now been developed that help characterize surface water-groundwater interaction. Results from field experiments using a percussion probe and a large-scale laboratory column experiment set up to simulate infiltration processes are presented. Measurements of the 222Rn distribution in the column are used to determine infiltration velocities.

Ultrafiltration: a technique for determining the molecular-mass distribution of group parameters of organic pollutants in natural waters

Abstract The heterogeneity of dissolved organic matter of natural waters and its different interactions cause particular analytical problems. As a result, a less specific parameter such as dissolved organic carbon (DOC) is often used to describe the sources and fate of organics in aquatic systems. The ion-paired organic-bounded sulfur (IOS) is a new parameter, and presently includes an important group of sulfur-containing components such as organic sulfonic acids. Natural waters have been characterised using ultrafiltration in combination with the determination of DOC and IOS concentrations. The determination of group parameters for different mass fractions (> 10 000, 10 000– 1000,

Messung der Infiltrationsgeschwindigkeit von Flußwasser mit dem Isotop Radon-222

Kenntnisse uber Infiltrationsgeschwindigkeiten von Fluswasser und Aufenthaltszeiten von Uferfiltrat sind wegen der daraus ableitbaren Aussagen zum Stofftransport ein wichtiger Baustein bei der Beschreibung des Okosystems Flusaue. Im einzelnen sind sie notwendig fur die Festlegung des Standortes von Grundwassermesstellen, die Planung von Grundwasserprobennahmen und die Interpretation von Mesergebnissen zur Beschaffenheit des Uferfiltrats. Fur die Kalibrierung geohydraulischer Modelle zur Simulation von Stromung, Stofftransport und Stoffumwandlung sind Infiltrationsraten des Fluswassers, die aus Infiltrationsgeschwindigkeiten abgeleitet werden konnen, eine wesentliche Randbedingung. Aufgrund des haufigen Wechsels von In- und Exfiltrationen in Auen ist die Entwicklung von Mesverfahren zur kontinuierlichen Beobachtung dieser Vorgange besonders wichtig.