Holger Weiß

Sediments in urban river basins: identification of sediment sources within the Lago Paranoá catchment, Brasilia DF, Brazil - using the fingerprint approach.

The development of effective sediment management strategies is a key requirement in tropical areas with fast urban development, like Brasilia DF, Brazil, because of the limited resources available. Accurate identification and management of sediment sources areas, however, is hampered by the dearth of reliable information on the primary sources of sediment. Few studies have attempted to quantify the source of sediment within fast urbanizing, mixed used, tropical catchments. In this study, statistically verified composite fingerprints and a multivariate mixing model have been used to identify the main land use specific sources of sediment deposited in the artificial Lago Paranoá, Central Brazil. Because of the variability of urban land use types within the Lago Paranoá sub-catchments, the fingerprinting approach was additionally undertaking for the Riacho Fundo sub-catchment. The main contributions from individual source types (i.e. surface materials from residential areas, constructions sites, road deposited sediment, cultivated areas, pasture, farm tracks, woodland and natural gullies) varied between the whole catchment and the Riacho Fundo sub-catchment, reflecting the different proportions of land uses. The sediments deposited in the silting zones of the Lago Paranoá originate largely from urban sources (85 ± 4%). Areas with (semi-) natural vegetation and natural gullies contribute 10 ± 2% of the sediment yield. Agricultural sites have only a minor sediment contribution of about 5 ± 4% within the whole catchment. Within the Riacho Fundo sub-catchment there is a significant contribution from urban (53 ± 4%) source, such as residential areas with semi-detached housings (42 ± 3%) with unpaved roads (12 ± 3%) and construction sites (20 ± 3%) and agricultural areas (31 ± 2%). The relative contribution from land use specific sources to the sediment deposition in the silting zone of the Lago Paranoá demonstrated that most of the sediment is derived from sites with high anthropogenic impact.

Arsenic speciation in iron hydroxide precipitates

In this study a special sequential extraction method is proposed to discriminate between arsenic adsorbed and co-precipitated in precipitates arising mainly from iron hydroxides or bound in low solubility mineral phases. Synthetic iron hydroxide precipitates were prepared to investigate the influence of the amount of arsenate, of the manganese additionally added and of the valence state of arsenic on the remobilisation of arsenic. After preparing the precipitates with arsenate no arsenic could be detected in the supernatant solution. About 82% (w/w) of the arsenate is adsorbed to the precipitate and the remaining part can be dissolved by shaking with an oxalate buffer. A significant difference between the amount of arsenic added and the amount analysed in the two steps was not found. Consequently, compounds with a low solubility, such as scorodite, were not formed in the synthesized precipitates. The valence of the arsenic and addition of manganese influence significantly the uptake of arsenic by iron hydroxides. Natural precipitate samples from a percolate water of tin mill tailings were investigated using this method.

Challenges of an integrated water resource management for the Distrito Federal, Western Central Brazil: climate, land-use and water resources

Land-use/cover change (LUCC) and climate change are major controlling factors for water resources in the Distrito Federal in Western Central Brazil. Dynamic LUCC in the region has severe impacts on water resources, while climate changes during the last three decades is thought to have only moderate effects. LUCC affects water quantity mostly during base flow conditions. River basins with substantial expansion of agriculture since the end 1970s show a dramatic decrease of base flow discharge by 40–70%, presumably due to irrigation. In contrast, the effects of urbanization on runoff are less distinct, since factors controlling runoff generation might be more variable. For water quality, we found urban areas to have a strong influence on the parameters CSB, NH4+, and suspended solids. In addition, we assume emerging pollutants, e.g. organic (micro)pollutants, might play a major role in the future. The project IWAS-ÁGUA DF focuses on creating the scientific base to face these problems in frame of an IWRM concept for the region. Results of our study will be a contribution to an IRWM concept for the Distrito Federal and will help to maintain high standards in water supply for the region.

Using the soil gas radon as an indicator for ground contamination by non-aqueous phase-liquids

Abstract1 The ProblemOne of the major problems facing risk assessment at polluted industrial sites and military bases is subsurface contamination by non-aqueous phase-liquids (NAPLs), since tracing the extent of a NAPL plume using conventional methods (drive point profiling) is usually associated with difficulties. In an effort to trace subsurface contamination as precisely as possible, monitoring points are placed in the area that might be affected by contaminants, and groundwater and soil samples are taken to the laboratory for analysis. However, the final number of monitoring points is hardly ever sufficient for distinctive contamination mapping, and this may ultimately result in an unsuitable remediation action being taken.2 ObjectivesTo obtain a more detailed image of a subsurface NAPL plume and, hence, to facilitate remediation measures that are best suited for the site in question, a denser network of monitoring points is desirable. The aim of the investigation described in this paper was therefore to develop a new detection method for subsurface NAPL contamination, which is based on an easily accessibleindicator for NAPLs rather than on the analysis of soil and groundwater samples taken at the site. Based on the good solubility of radon in NAPLs, the idea was put forward that subsurface NAPL contamination should have an influence on the natural radon concentration of the soil gas. Provided this effect is significant, it would be possible to carry out a straightforward radon survey on an appropriate sampling grid covering the suspected site and thus enabling the NAPL contamination to be detected by the localization of anomalous low radon concentrations in the soil. The overall aim of the investigation was to assess the general suitability of the soil-gas radon concentration as an indirect tracer for NAPL contamination in the ground.3 MethodsThe partitioning coefficient KNAPL/air is one of the most influential parameters governing the decrease of the radon concentration in the soil gas in the presence of a subsurface NAPL contamination. Since NAPL mixtures such as gasoline, diesel fuel and paraffin are among the most important NAPLs regarding remediation activities, laboratory experiments were performed to determine the radon-partitioning coefficient for these three NAPL mixtures.Field experiments were carried out as well. The aim of the field experiments was to test the use of the soil-gas radon concentration as a tracer for NAPL contamination on-site. For the field experiments, each site was covered with a suitable grid of soil gas sampling points. Finally, the lateral radon distribution pattern achieved on each of the sites was compared to the respective findings of the earlier research performed by conventional means.4 Results and DiscussionThe results of the laboratory experiments clearly show a very strong affinity of radon to the NAPL mixtures examined. The partitioning coefficients achieved correspond to those published for pure NAPLs (Clever 1979) and are thus in the expected range. The results of the field experiments showed that the minimum radon concentrations detected match the respective NAPL plumes traced previously.5 ConclusionsBoth the results of the lab experiments and the on-site findings demonstrate that the soil-gas radon concentration can be used as an indicator for subsurface NAPL contamination. The investigation showed that NAPL-contaminated soil volumes give rise to anomalous low soil-gas radon concentrations in the close vicinity of the contamination. The reason for this decrease in the soil-gas radon concentration is the good solubility of radon in NAPLs, which enables the NAPLs to accumulate and ‘trap’ part of the radon available in the soil pores.6 Recommendations and OutlookFurther research is required into contamination with rather volatile NAPLs such as BTEX. Further research is also needed to examine whether it is possible to not only localize a NAPL plume, but also to obtain some quantitative information about the subsurface NAPL contamination. The authors also believe that additional investigations should be carried out to study the ability of the method to not just localize a NAPL contamination, but also to monitor on-site, clean-up measures.

Untersuchungen zum Benzininhaltstoff Methyltertiär-butylether (MTBE) in Grund- und Oberflächenwasser in Deutschland

KurzfassungIn Deutschland wird von offizieller Stelle die Meinung vertreten, dass die Verwendung von MTBE in Benzin kein akutes Risiko für die Umwelt darstelle. Im Rahmen dieser Studie wurden an fünf von zehn untersuchten Standorten mit Benzinschadensfällen MTBE-Gehalte im Grundwasser von > 20 μg/l (Geruchs- und Geschmacksschwellenwert) im unmittelbaren oder weiteren Abstrom des Schadensherdes gefunden. Die gemessenen MTBE-Konzentrationen in kontaminierten Grundwasserproben von diesen Standorten lagen zwischen 29 und 87.800 μg/l. Es ist davon auszugehen, dass an anderen Standorten in Deutschland Verunreinigungen des Untergrundes mit MTBE unentdeckt geblieben sind. Schadensfälle mit MTBE-haltigem Benzin können weitreichende Verunreinigungen des Grundwassers verursachen, da der Benzininhaltsstoff im Grundwasserleiter kaum retardiert und, wenn überhaupt, nur sehr langsam biologisch abgebaut wird. Das Auftreten von MTBE als Grundwasserkontaminant wird typischerweise zu einer deutlichen Erhöhung der Erkundungs- und Sanierungskosten führen. Die gemessenen MTBE-Gehalte in Proben aus Oberflächengewässern betrugen zwischen 18 und 199 ng/l (Nachweisgrenze: 10 ng/l). Um einen umfassenden Überblick zum tatsächlichen Ausmaß an MTBE-Kontaminationen in Deutschland zu gewinnen, sollte MTBE in die regulären Monitoringprogramme bei Benzinschadensfällen aufgenommen werden.AbstractGerman Federal authorities do not see an acute environmental risk of the use of MTBE in gasoline. Within this study, however, MTBE concentrations of > 20 μg/l (the taste and odour threshold) in groundwater downstream of gasoline spills were found at five out of ten investigated sites. The measured MTBE concentrations at these sites ranged between 29 and 87,800 μg/l. Apparently, subsurface contamination with MTBE has also remained undetected at other sites in Germany. The ether is virtually unretarded in the aquifer and only degrades slowly, if at all. Spills of MTBE-amended gasoline can therefore cause extensive groundwater contamination. The occurrence of MTBE in groundwater will typically cause a significant increase of investigation and remediation costs. The measured MTBE concentrations in surface water samples from this study ranged between 18 and 199 ng/l (detection limit: 10 ng/l). In order to gain an overview about the actual extent of MTBE-contamination in Germany, MTBE should be included into the regular monitoring programs at gasoline spill sites.

Geochemical signature and properties of sediment sources and alluvial sediments within the Lago Paranoá catchment, Brasilia DF: A study on anthropogenic introduced chemical elements in an urban river basin

One of the largest urban agglomerations in Brazil is the capital Brasilia and its surrounding area. Due to fast urban sprawl and accelerated land use changes, available water supplies are near their limits. The water supply depends largely on surface water collected in reservoirs. There are increasing concerns regarding water shortages due to sediment aggradations, and of water quality due to geochemical modification of sediments from human activities. The concentration of 18 chemical elements and five sediment properties was analyzed from different potential land-based sediment sources and deposited alluvial sediment within the Lago Paranoà catchment. The goal of this study was to assess the distribution of chemical elements and geochemical/physical properties of potential sediment sources in the Lago Paranoá catchment. Principal component analysis and hierarchical cluster analysis were used to investigate the influence of different land use types on the geochemistry of sediments. Geochemical fingerprints of anthropogenic activities were developed based on the results of the cluster analysis grouping. The anthropogenic input of land use specific geochemical elements was examined and quantified by the calculation of enrichment factors using the local geological background as reference. Through comparison of the geochemical signature of potential sediment sources and alluvial sediments of the Lago Paranoá and sub-catchments, the relative contribution of land use specific sediment sources to the sediment deposition of the main water reservoir were estimated. The existing findings suggest a strong relationship between land use and quantifiable features of sediment geochemistry and indicate that urban land use had the greatest responsibility for recent silting in the Lago Paranoá. This assessment helps to characterize the role of human activities in mixed-used watersheds on sediment properties, and provides essential information to guide management responses towards more effective source-reduction strategies.

Formation of heavy metal bearing phases at a spring affected by the weathering of ore processing residues

The Mansfeld region in Sachsen-Anhalt, Central Germany, has a long tradition of mining Kupferschiefer, a marine copper-containing black shale of Permian age. One of the residues from the processing of that low-grade copper ore is ‘Theisen Sludge’, a very fine-grained scrubber dust composed of metal sulphide particles in a matrix of highly viscous hydrocarbons. The Theisen Sludge is considered to be the main source for heavy metal releases into the local environment. The most important discharge point for contaminated water is the ‘Stadtborn Spring’. The extremely high metal and sulphate concentrations in the spring water cause the precipitation of a mineral phase exceptionally rich in heavy metals. This precipitate is the focus of the current investigation. It is shown that a gel with adsorbed metals first is formed from spring water. Then zinc-copper-aluminium hydroxides start to crystallise from the gel at an early stage, forming (Zn,Cu,Al)(O,OH) 2 brucite-type layers, which are positively charged owing to a remarkable A1 content. These precursor layers take up SO 4 2 - for charge compensation and H 2 O into interlayers and begin to form zinc-copper-aluminium hydroxide-sulphates such as Al-rich zincowoodwardite within a few weeks of aging. Further maturation of the precipitate took place in the gaseous environment of atmospheric CO 2 after part of the brook dried up several decades ago. This ‘maturation’ due to the long-term interaction of the precipitate with atmospheric CO 2 is characterised by the transformation of the zinc-copper-aluminium hydroxide-sulphates into zinc hydroxide-carbonates with a residual copper content. The resulting crystalline phase is characterised structurally as disordered hydrozincite. The results described are the first step in a study which aims to optimise the natural precipitation process observed as a part of a remediation strategy for the local surface water system. It also is noticed that the fresh precipitate may be of use as a precursor material for copper/zinc co-precipitated oxide catalysts for industrial hydrogenation processes.

Sediment characteristics and sedimentations rates of a small river in Western Central Brazil

The purpose of this study is to characterise the alluvial sediments and to quantify sedimentation rates of a small river system, the Ribeirão do Torto in Central Western Brazil. The study area provides an excellent opportunity to examine the effect of land use on sedimentation rates in the region for the first time and thus contributes to understanding sediment transport processes into water reservoirs (silting). 137Cs, 210Pb and 14C dating techniques were used to estimate natural sedimentation rates and those associated with land use development. Complementary use of physical and chemical analyses of the sediments and contained anthropogenic materials revealed that sedimentation dynamics had varied over time. Natural sedimentation rates are more than ten times lower than in the period since the mid-1950s for the alluvial system of the Ribeirão do Torto. The results indicated that human impact had accelerated the sedimentation dynamics, which resulted in higher sediment quantities and sand content and changes of sediment sources. The variation of sedimentation rates may reflect also several other factors, e.g. natural fluctuation in flow energy or geomorphologic changes within the alluvial system. However, the multiple dating techniques and supplementary interpretation employed in this study show the potential use of radionuclides and soil/sediment parameters to identify changes in sedimentation rate, stream energy and sediment characteristics in floodplains.

A web-based planning support tool for sediment management in a meso-scale river basin in Western Central Brazil

In scope of an IWRM concept for the Federal District, Western Central Brazil we developed a planning support tool, which enables non-experts to test the effects of land-use and land-cover change (LULCC) on landscape processes and landscape functions (LPF) related to sediment generation and retention. For this purpose we developed the web-based tool Letsmap do Brasil. The tool has two principal layers. The upper layer contains information on land use and its effect on LPF, i.e. sediment retention, runoff control, nitrogen loss control and agronomic value. The parameterized relation between land use and LPF is the core of the whole system. For each LPF a value specific to land use has been assigned. A second layer contains information on landscape properties and potentials (LPP), e.g. potential for sediment input in river networks and runoff potential. By linking land use and LPPs the system provides a spatially explicit assessment of effects of LULCC on landscape processes and functions (LPF). Letsmap do Brasil might have two major purposes. (1) It will support decision-making in river basin management and sediment management. By creating their own land-use/cover pattern non-expert users are enabled to test effects of LULCC on LPFs. (2) It will support and train non-experts to participate in decision processes in land-use planning. Because of its high adaptability, transparency, and simple handling Letsmap do Brasil might be used as tool in river basin management and land-use planning.

Compound Specific and Enantioselective Stable Isotope Analysis as Tools To Monitor Transformation of Hexachlorocyclohexane (HCH) in a Complex Aquifer System

Technical hexachlorocyclohexane (HCH) mixtures and Lindane (γ-HCH) have been produced in Bitterfeld-Wolfen, Germany, for about 30 years until 1982. In the vicinity of the former dump sites and production facilities, large plumes of HCHs persist within two aquifer systems. We studied the natural attenuation of HCH in these groundwater systems through a combination of enantiomeric and carbon isotope fractionation to characterize the degradation of α-HCH in the areas downstream of a former disposal and production site in Bitterfeld-Wolfen. The concentration and isotope composition of α-HCH from the Quaternary and Tertiary aquifers were analyzed. The carbon isotope compositions were compared to the source signal of waste deposits for the dumpsite and highly contaminated areas. The average value of δ13C at dumpsite was -29.7 ± 0.3 ‰ and -29.0 ± 0.1 ‰ for (-) and (+)α-HCH, respectively, while those for the β-, γ-, δ-HCH isomers were -29.0 ± 0.3 ‰, -29.5 ± 0.4 ‰, and -28.2 ± 0.2 ‰, respectively. In the plume, the enantiomer fraction shifted up to 0.35, from 0.50 at source area to 0.15 (well T1), and was found accompanied by a carbon isotope enrichment of 5 ‰ and 2.9 ‰ for (-) and (+)α-HCH, respectively. The established model for interpreting isotope and enantiomer fractionation patterns showed potential for analyzing the degradation process at a field site with a complex history with respect to contamination and fluctuating geochemical conditions.