Geochemistry of Solutes in Soil Water under two Exotic Tree Species Plantations in South-Eastern Ethiopia

Y. Ashagrie and W. Zech, Institute of Soil Science and Soil Geography, University of Bayreuth, D-95440 Bayreuth, Germany, Tel: ++49-921-55-21-46 Fax: ++49-921-55-22-46, Email: yeshanew@hotmail.com

In Ethiopia, the increase in population and decline of native forests have led to the establishment of large scale fast growing exotic tree species plantations. The development of sustainable management practices for tropical plantations will depend largely on improved understanding of the relationship between the biotic (plantation) and the abiotic (soil and water) components of the systems. The dynamics of solutes in water passing through the mineral soils under two exotic tree species plantations (Cupressus lusitanica and Eucalyptus globulus) and an adjacent Podocarpus falcatus dominated natural forest are being monitored since 2001 at Munesa, south-eastern Ethiopia. The soil solutions collected from the different stands were dominated by Ca, NO₃–N, Cl and Na. The vertical patterns in solute concentrations showed a decreasing trend for most of the solutes under the natural forest and Eucalyptus plantation. The concentrations of Cl and Na in all forest types, and Ca, Mg and NO₃–N below Cupressus increased with increasing soil depth. The concentrations of Ca,  Mg and NO₃–N below Cupressus were 7, 3.4 and 17 times higher than under the natural forest  and 2, 2.4 and 4 times higher under Eucalyptus, suggesting that these nutrients under Cupressus are in excess of tree and microbial requirements. These variations among stands were mainly due to large differences in the subsoil (1 m soil depth) concentrations. The concentrations of Ca, Mg and NO₃–N at 1 m soil depth under the natural forest were 8, 7 and 23 times lower than under Cupressus. The corresponding figures under Eucalyptus were 3, 4 and 81 times lower than under Cupressus. These results suggest relatively tight nutrient cycling in the natural forest and Eucalyptus plantation. Overall, ecosystem-specific patterns of vegetation composition and associated demand for nutrients appear to control nutrient concentrations and rates of nutrient leaching in the forest ecosystems under study.  

Determining the Influence of Cranberry Bog Flooding on Plume Migration

Jason Dalrymple, CH2M HILL, 318C East Inner Road, Otis ANG Base, MA 02542-5028 , Tel: 508-968-4670 x 3010, Fax: 508-968-4490, Email: Jason.Dalrymple@ch2m.com
Jon Davis, P.E., Air Force Center for Environmental Excellence, 322 East Inner Road, Otis ANG Base, MA 02542-5028, Tel: 508-968-4670 x 4952, Fax: 508-968-4476, Email: jon.davis@brooks.af.mil
John Glass, PhD., P.E., CH2M HILL, 1321 Park Center Road, Suite 600, Herndon, VA 20171, Tel: 703-471-1441, Fax: 703-471-1508, Email: John.Glass@ch2m.com
Nigel Tindall, P.G., CH2M HILL, 318D East Inner Road, Otis ANG Base, MA 02542-5028, Tel:  508-968-4670 x 5620, Fax: 508-968-4916, Email: Nigel.Tindall@ch2m.com

A study was performed to determine the influence of cranberry bog flooding on groundwater plume migration at the Massachusetts Military Reservation.  These cranberry bogs are flooded to facilitate the harvesting of the berries in the fall and for frost protection in the winter.  This flooding changes the bog water levels by up to three feet, either continuously or intermittently, from October through March.  Hydrologic changes of this magnitude can produce changes in the groundwater flow field near the bogs.  Since the annual flooding lasts for five or six months, these changes have the potential to modify plume migration and contaminant discharge near the bogs.  The purpose of this study was to identify the effects of bog flooding on plume migration and discharge, and evaluate the differences between model-simulated plume migration under transient flow conditions and migration simulated under traditional steady-state flow.

The data collection effort focused on two areas; understanding the bog flooding practices, and measuring the hydraulic response in the aquifer due to the flooding.  A yearly record of bog flooding practices was divided into multiple characteristic periods that mimic the actual sequence of water-level variations.  To record the hydraulic response in the aquifer, continuous water level measurements were collected at numerous multi-screen wells and staff gauges in and around the bogs.

The field data were used in concert with the model to evaluate the magnitude and extent of the hydraulic differences between the flooded and non-flooded conditions.  The need for focused adjustments to the model aquifer parameters was evaluated.  The model was then used to evaluate the differences in simulated plume migration between runs using the average steady-state flow fields and the transient flow fields that reflect the effects of seasonal bog flooding.

Contamination of Soil and Groundwater by Leaking Sewers

J. Hua, P. An, C. Gallert, J. Winter, Institut für Ingenieurbiologie und Biotechnologie des Abwassers, Universität Karlsruhe, Am Fasanengarten, D-76128 Karlsruhe

At least half of the sewers in Germany or most European countries are more than 50 years old. Leaks lead to losses of sewage as high as 20 % of the total amount. However, the German soil protection law, based on EU regulations, does not allow to pollute soil and the underground with any anthropogenic substances, including sewage. We investigated the fate of sewage, that trickles from leaky sewers into the unsaturated soil and from there into the groundwater.

Normally, sewers are layed in more than 3 m depth below the surface and there is not much oxygen available for aerobic respiration of sewage compounds. Under mainly anaerobic conditions, between 75 and 85 % of the COD of sewage is degraded during passage of sewage through the unsaturated underground (dry weather conditions, low groundwater level) or the saturated underground (rain weather conditions, high groundwater level). Even if enough oxygen would be available all the time, degradation of COD would not excede the 92 – 94 % COD-removal, that are obtained in sewage treatment plants, although most of the biodegradable compounds are degraded in the first 25 cm trickling stretch of sewage already. In soil columns in the laboratory nitrogen compounds are leaving the columns after 1.25 cm trickling stretch as ammonia and little nitrate, most of the nitrate being denitrified in the columns after biofilm development. Heavy metal ions are precipitated mainly as sulfides in the first 25 cm (which provide anaerobic conditions) after the sewage left the sewers. If oxygen would be available, re-oxidation and solubilization of metal sulfides would be possible. In a sandy/silty soil the grains themselves would adsorb most of the metal ions presumably by ion exchange reactions.

A biofilm is formed with time on the sand particles of the soil, which influences the trickling rates to some extend and which stabilizes the purification effect of the soil. More than 99 % of the microbial flora of the sewage are filtered off or attached to the biolfilm during trickling of sewage. Never-the-less, more micororganisms leave the sandy soil after 125 cm trickling stretch than allowed e.g. by the European Bath Water Directive. Most of the bacteria have an increased multiple antibiotic resistance spectrum against therapeutically applied antibiotics and antibiotics produced from the indigeneous soil flora, such as pseudomonads or Streptomycetes sp..

The residual organic compounds in the effluent of the soil columns resemble humic compounds (humification), have a higher proportion of non readily degradable organic matter such as aromatic compounds, in comparison to the non-aromatic residues and are distributed with the groundwater.

The above mentioned investigations were part of a multi-discipline research project on “Risk assessment of sewage from leaky sewers for soil and groundwater” at the University of Karlsruhe, funded by Deutsche Forschungsgemeinschaft and coordinated by J. Winter.

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