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Influence of relief and vegetation on soil properties in a disturbed chernozem soil landscape
(2017)
In central and southeastern Alberta, chernozems dominate the soil landscape and are divided into several groups
that follow the climate gradient from Northwest to Southeast: Dark Grey Chernozems, Black Chernozems, Dark
Brown Chernozems; Brown Chernozems. Principles controlling development and distribution of these chernozem
subtypes along the ecotone transect are quite well known. However, intensive land use over the last century has
affected soils that originally have formed under natural conditions during the Holocene in more than 10,000 years.
There is a lack of knowledge regarding soil development in these landscapes on the decadal to centennial time
scale. Within this time frame the most important factor of soil formation may be relief, although this has not been
properly studied.
This study aims to compare soil properties in a typical chernozem landscape where soils have been highly
disturbed and parent materials have been re-arranged by surface coal mining.We hypothesize that within 50 years,
soils develop with significant differences based on vegetation type and slope aspect. Our study site is the former
Diplomat Mine near Forestburg, Alberta where spoils form a small scale ridge and graben topography. The south
facing slopes of the piles are covered by grassland, whereas on the north exposition has trees and shrubs.
Samples were taken from six sites with differences in topography and vegetation type. Diplomate T1 is at the top
of the ridge with grassland, Diplomate S1 is on the southern slope with grassland, Diplomate N1 is on the northern
slope with trees, and Diplomate N2 is on the northern slope with shrubs. For comparison we took samples from
two sites without slope aspect. One site was an undisturbed grassland (Diplomate Z1) and the other sites were
reclaimed piles (Diplomate R1). At each site, five soil profiles were examined and volumetrically sampled (250
cm3 steel ring) in steps of five centimeters to a depth of 30 centimeters.
We present first results of basic physical and chemical soil parameters (bulk density, water content, pH, Cstock,
N-stock).
At the former Diplomat Mine near Forestburg, Alberta, Canada we find a diverse soil landscape which can help to conceptualize factors and processes controlling initial pedogenesis and soil distribution on very young landforms in prairie environments. Due to differing reclamation practices in the 1950s and landslides occurring after spoil dumping, four areas can be distinguished by GoogleMaps/LiDAR evaluation and onsite field survey: (i) not-mined, (ii) stock piled and unreclaimed, (iii) stock piled and reclaimed and (iv) affected by post-mining geomorphodynamics and quasi-natural redeposition. The parent material for areas (ii) to (iv) was initially dumped by spreaders but only (ii) didn’t undergo further change. Landscape (iii) has seen levelling of the piles by heavy machinery. Features of landscape (iv) are formed by reshaping the originally dumped and levelled structures. This last landscape unit marks the rim of
the former mine adjacent to the river valley. In practice, mining activities formed new valley slopes. In contrast
to the naturally developed slopes the mine slopes were less stable. Vegetation, which could have hindered slope
wash erosion, was missing after dumping the spoil slopes. Slopes were very steep (or practically undercut) and
therefore, substrates were naturally re-located by mass movements such as sliding and slumping. Characteristic
sliding and slumping structures can be identified in the close-ups of the LiDAR images. Both processes, mass movement and slope wash erosion, may have overlapped. Landscape (ii) is the most contrasting one. Dumped stock piles formed elongated, curved and steep ridges. These landforms do not have a natural analogue but clearly show their technological origin. Most interesting are differences in vegetation. South and southwest facing slopes are covered with grassland whereas north and northeast facing slopes are covered with aspen trees. Some of the ditches are filled with water and form small elongated ponds. The characteristic geomorphology of the prairie can be found in landscape (i). Distinct differences are found in properties and types of soils in these four landscapes. Natural soils and pile soils characteristically differ in parent material and soil horizons. No information is gathered yet for the reclaimed soils and the landslides soils due to prohibited access. However, based on what we find at the former Diplomat Mine we can conclude that distribution, development and properties of unreclaimed soils in historical open cast mines in Alberta are primarily controlled by parent material and topography. The geomorphological set-up is dominating the trajectory of vegetation development and post-mining geomorphodynamics. Contrasting slope aspects determine micro climatic conditions and lead to different vegetation types. This has likely had an effect on soil development and soil properties (especially carbon stocks). Further studies will be conducted to quantify these differing soil properties to refine this conceptual model of initial pedogenesis and soil distribution on very young landforms in the prairie landscapes.
On many post mining sites in the Lusatian Mining District (East Germany) soil heterogeneity consists of sandy soil with embedded clay-silt fragments. Those clays silt fragments might act as nutrient hotspots. Arbuscular mycorrhizal fungi in an infertile ecosystem could enhance a plant’s ability to selectively forage for those nutrients and thus to improve plants nutrient supply. In our study we investigated whether silt-clay fragments within a sandy soil matrix induced preferential root growth of Lotus corniculatus and Calamagrostis epigeios, whether arbuscular mycorrhizae influenced root foraging patterns, and to what extent selective rooting in clay silt fragments influenced plant growth were addressed in this research. Soil types were sterile and non-sterile sandy soil and clay-silt fragments. Treatments were with and without arbuscular mycorrhizae, with and without soil solution, and soil solution and mycorrhizal inoculum combined. Root biomass, root density and intraradical fungal alkaline phosphatase activity and frequency were determined in fragments relative to sandy soil. Furthermore, temporal relationship of number of roots in fragments and plant height was assessed. Lotus corniculatus showed strong selective rooting into fragments especially with those plants treated with commercial cultivated arbuscular mycorrhizae; Calamagrostis epigeios did not. Without arbuscular mycorrhizae, L. corniculatus growth was significantly reduced and selective rooting did not occur. Selective rooting induced significant growth spurts of L. corniculatus. Roots in fragments had higher fungal alkaline phosphatase activity suggesting that mycorrhizal efficiency and related plants phosphorus supply is enhanced in roots in fragments. The application of cultivated arbuscular mycorrhizal fungi significantly and quickly influenced root foraging patterns, especially those of L. corniculatus, suggesting mycorrhizae may also enhance the ability of other plants to selectively forage for nutrients and could therefore play an important role in early plant establishment on infertile reclamation sites.
Nutrient-poor, sandy soils form the prevailing substrate at post-mining sites and present a challenge for plants. We studied the organic acid quantity and composition of three commonly occurring pioneer plant species, the legumes Lotus corniculatus L. and Trifolium arvense L. and the grass Calamagrostis epigeios (L.) Roth, to determine if plant growth and exudation differed with (nonsterile soil) and without (sterile soil) an indigenous soil microbial community. We investigated whether organic acids were found in the rhizosphere and surrounding soil and whether this influenced nutrient mobilization. This study consists of linked field investigations and a greenhouse experiment. Plants were grown in the greenhouse in either steriled or non-steriled sandy soil from a reclamation site in the Lusatian mining landscape (Welzow S¨ud, East Germany). After seven months, the plant biomass, root morphology, organic acids, and water-soluble nutrients and root colonization with arbuscular mycorrhizal fungi (AMF) and dark septate endophytes (DSE) were analyzed. Roots of all three plants in the field and greenhouse experiments were highly colonized with AMF. Calamagrostis epigeios and T. arvense had a significantly higher colonization frequency with DSE than L. corniculatus. The quantity and composition of organic acids strongly differed among plant species, with the highest number of organic acids found for L. corniculatus and lowest for C. epigeios. The quantity of organic acids was greatly reduced in all plants under steriled soil conditions. However, the composition of organic acids and plant growth in steriled soil were reduced for both legumes, but not for C. epigeios, which had a higher biomass under steriled conditions. Changes in nutrient concentrations in the field rhizosphere soil relative to those in the control were measurable after seven months. While the spectrum of organic acids and the growth of legumes seemed to be dependent on a highly diverse soil microbial community and a symbiotic partner, the grass C. epigeios appeared capable of mobilizing enough nutrients without an indigenous microbial community, and might be more competitive on sites where soil microbial diversity and activity are low.
ln 2005, a 7-ha artificial watershed (Hühnerwasser) was built an a post mined Iandscape in Lusatia, Germany from sandy Substrates of Pleistocene origin, commonly used in reclamation. The watershed was developed to investigate the initial phase of soil and ecosystem development under natural conditions. At this early stage, nutrients in young sandy soils are limited and pioneer plants become key components of natural succession. Local abundant pioneering legumes Lotus corniculatus and Trifolium arvense and one pioneer grass species Calamagrostis epigeios were investigated 5 years after watershed construction. ln the present study, we investigated the influence of spatial root distribution of these species an soil nitrogen accumulation and on nutrient redistribution. Soil, including roots, was sampled from field monoliths covered with the aforementioned plant species. Root systems of both legumes were mainly restricted to the upper 20 cm of soil, whereas roots of C. epigeios also developed strongly at greater depths. A positive relationship was found, with higher plant densities associated with higher root densities, which were related with higher nodule densities for legumes and which were all associated with significantly higher soil nitrogen concentration relative to non-vegetated areas.
This research provides rare information on the role root systems of pioneer legumes play in soil nitrogen input and development of nutrient patterns in the early stage of soil and ecosystem development during revegetation by natural succession.