BIOTIC AND ABIOTIC FACTORS INFLUENCING THE LONG-TERM STABILITY OF COVERS ON WASTE ROCK PILES IN THE MINING DISTRICT OF SAXONY AND ()

by

1 3 Martin Heinze , Mirko Kohler2 and Hartmut Siinger

Abstract: This report presents the results of basic investigations of root penetration on various partially covered excavation discard material mounds of the Saxonian-Thuringian region (Germany) in comparison to root penetration in autochthonous (native) soils. Bioturbation is an essential, unavoidable impact to consider in addition to root penetration. With increasing age, the functionality of each layer of a cover system becomes diminished through the workings of the local flora and fauna. Pedological cover layers can only temporarily maintain their initial positions and technical functionality. Considering actual prevail- ing biotic and abiotic influences (e. g. site-specific transpiration rates), the planning and installation of cover systems should take into account (within acceptable balances) factors which are able to at least partially compensate for eventual diminishing of technical functionality.

Additional Key Words: uranium mining, cover systems, root penetration, bioturbation

1 Prof. Dr. rer. silv. habil. Martin Heinze, Fachhochschule fiir Forstwirtschaft, D-07427 Schwarzburg 2 Dipl.-Agr.-Ing. Mirko Kohler, WISMUT GmbH, Jagdsch!inkenstra8e 29, D-09117 3 Dr.-Ing. Hartmut S!inger (Dipl.-Biol.), Bergasse 6, D-08451 Crimmitschau

Introduction Therefore a good knowledge with re- spect to root penetration and bioturba- The WISMUT Limited Liability tion has a great importance for the Corporation as a successor to the for- evaluation of long-term stability of co- mer Soviet-German WISMUT Corpo- ver systems. ration was charged by the Federal Go- vernment of Germany to rehabilitate Cover Systems of the WISMUT the abandonments of uranium mining Limited Liability Corporation in Saxony and Thuringia. These consist of mainly excavation discard rock Rehabilitation of excavation dumps, tailings, and operation areas. discard material mounds, whether in The cover systems are an essential re- place or by replacement, requires a habilitation technology for these ob- closure cover system. The design and jects. To realize the rehabilitation tasks, installation of cover systems must take both chemical and radiological investi- into account site specific conditions gations for excavation discard material which determine how the qualitative mound characterization and compre- and quantitative parameters of the hensive soil physical, pedological, and individual cover layers and the plant physiological investigations are complete layering system are to be necessary. optimized (Table 1).

435 Table 1: Presentation of a Maximum-Conception for Excavation Discard Material Mound Cover Systems

Laver Function Thickness (annrox.)

Soil use orientated, with soil improving <0.5m additives if necessarv

Storage vegetation orientated usable field 0.6 - 1.0 m capacity, promotion of evapotranspiration, desiccation protection, drainal(e retardation, frost nrotection

Suffosion protection protection of the drainage layer 0.2m al(ainst fine orain intrusion

Drainage Allowance of hvnodermic drainage 0.2m

Insulation Prevention of water infiltration and 0.3 - 0.5 m radon exahaltion

Fill variable Dump contour smoothing and correction

With regard to the qualitative concep- Cover system for tailings tion of individual layers within cover (Seelingstadt site: i.e. systems of mining excavation discard Triinzig/Culmitzsch tailings) material mounds, the dimensioning and construction must be carried out ac- Soil cording to the existing conditions of the Storage Layer individual rehabilitation project areas. Drainage Layer The following are examples of prefer- Insulation Layer (kf-value between 10·9 10 red cover systems: and 10· ) Fill Layer Cover system for excavation discard Geotextile and Excavation Rock material mounds rehabilitated in place (Ronneburg site: i.e. Cover systems for excavation discard Beerwalde mound) material mounds ( site)

Soil Soil Storage Layer (till) Storage Layer (till) Insulation Layer (loess loam)

436 Cover Systems under the Influence The functionality of the cover system of the Bioturbation layers decreases with increasing age and is limited by the pedological Bioturbation is generally defined development potential of the used as the mixing of soil by animals. Even substrata. All cover layers have a so, included in this term are arboturba- limited functional lifetime. Therefore tion (tree heave) and the so called acceptable balances with regard to "stomping" caused by the wind moving biotic and abiotic factors of influence trees. All of these kinds of bioturbation should be aimed at compensation for are regionally different and influenced losses in technical functionality of the by ecosystem conditions. Therefore it is layers (increasing field capacity by necessary for the WISMUT GmbH bioturbation, root penetration of drain cover system designers to consider layers connected with loss of technical qualitative and quantitative factors of functionality). It is especially important bioturbation in the rehabilitation con- to evaluate the influence of the ceptions of the abondonments of the bioturbation on succession and open uranium mmmg in Saxony and land areas, since the lack of ur- Thuringia. An extensive literature study banization aids in the resettlement of and field investigations were carried relevant animal species (Table 3). out in consideration of this problem. In all planning of cover systems up to the In any case, at least some measures in present, bioturbation is viewed as es- consideration of the bioturbation rate sential, non-avoidable parameter of are always feasible and necessary. An influence, as is root penetration. initial evaluation of the faunistic in- fluence potential on earthen cover syst But in opposition to root penetration, ems shows the necessity to take bioturbation has the tendency to ho- preventative steps for the maintainance mogenize individual technically de- of the systems. signed cover layers.

Table 3: Depth influence by relevant animals (WEIHRAUCH und SCHEIBERT, 1998)

Species maximum depth of influence (m) soil eater (earthworms) 2.0 shovel diirn:er (mole) 2.0 scrape digger (ants) 0.7 rooter - rabbits 2.7 - mice, pigs 0.5

441 To maintain qualitative and quantitative Additional methods of regulation are parameters of the cover systems, one possible through selection of suitable possibility is to establish soil barrier plant species and depend on the water layers that are unattractive to intrusive content (infiltration water) given by fauna. These layers are for the most root penetration intensity and depth part characterized by infiltration pro- (stability) associated with the particular moting properties that work in combi- species and their distribution density. nation with drainage layers. A further possibility for influencing the rate of In the first years, substantial differences bioturbation is the intensity of later use. exist between the root penetration After installation of the cover and first behavior of covers and comparable cultivation, at least 3 to 5 years should autochthonous soils. A explanation for be set aside for a homeostasis to be this is the deviated soil physical reached (through cultivation of forests parameters of the constructed cover and green cuts of open areas) to attain systems in comparison to the better conditions for the predators of autochthonous soils. The initial the species which contribute to biotur- condition of synthetic cover systems is bation. Stone debris (rip rap) placed on characterized by a disturbed soil of the top of the cover can provide texture. And so begins pedogenesis small habitat spaces, serving both through its associated processes of root nature protecting and bioturbation penetration (root growth, symbioses), preventing ends. bioturbation, and soil texture formation (suffusion, clay deposition). Long Term Stability of Excavation Discard Material Mound Covers The most essential and deciding optimization factors, in terms of long- Root penetration and bioturbation term stability and promotion of are essential influence factors on rehabilitation progress, are founded in pedogenesis. After installation, the the assessment of the potential of the covers are exposed to the soil building existing horizontal formation of the processes. But decreases in the embedded substrata and its actual technical functionality of the covers is technical parameters (kf-value, dry bulk not inevitable. It is necessary to design density) as well as the induction of this and install the cover layers development through the design and corresponding to the future use of the installation of a cover configuration. area. The effective field capacity is a decisive factor that determines the effective root space, which in turn restricts root penetration and protects the insulation layer. This is of key important in realization of the technical parameters of the cover.

442 Literature Cited

Heinze, M. und H. Sanger, 1996. Un- tersuchungen zur Langzeitwir- kung von Abdeckschichten unter dem EinfluB einer miiglichen Durchwurzelung. Consulting und Engineering GmbH Che- mnitz & Fachhochschule flir Forstwirtschaft Schwarzburg.

Weihrauch, F. und C. Scheibert, 1998. Untersuchungen zur qualitativen und quantitativen Beeinflussung von Abdecksystemen

Pittelkow, U. et.al. 1997. Substrat- und bewuchsspezifische Untersu- chungen in der Bodenmodellan- lage. Verband flir Agrarfor- schung und -bildung Thiiringen e.V. Jena.

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