LS Bodenschutz und Rekultivierung
Phytoremediation of sites contaminated with iron cyanides can be performed using poplar and willow trees. Poplar and willow trees were grown in potting substrate spiked with ferrocyanide concentrations of up to 2,000 mg kg-1 for 4 and 8 weeks respectively. Soil solution and leaf tissue of different age were sampled for total cyanide analysis every week. Chlorophyll content in the leaves was determined to quantify cyanide toxicity. Results showed that cyanide in the soil solution of spiked soils differed between treatments and on weekly basis and ranged from 0.5 to 1,200 mg l-1. The maximum cyanide content in willow and poplar leaves was 518 mg kg-1 fresh weight (FW) and 148 mg kg-1 FW respectively. Cyanide accumulated in the leaves increased linearly with increasing cyanide concentration in the soil solution. On the long term, significantly more cyanide was accumulated in old leaf tissue than in young tissue. Chlorophyll content in poplar decreased linearly with increasing cyanide in the soil solution and in leaf tissue, and over time. The inhibitory concentration (IC50) value for poplars after 4 weeks of exposure was 173 mg l-1 and for willow after 8 weeks of exposure—768 mg l-1. Results show that willows tolerate much more cyanide and over a longer period than poplars, making them very appropriate for remediating sites highly contaminated with iron cyanides.
Stimulated by the rising demand for bioenergy, forestry practices for energy production are of increasing importance worldwide. Black locust (Robinia
pseudoacacia L.) is a suitable tree species for biomass production in shortrotation plantations in East Germany, especially on marginal land where insufficient water and nutrients are a limiting factor for tree growth. Our study aims to clarify the spatial and temporal variability of the black locust growth through the analysis of the plant water status, and to evaluate the effect of adverse edaphic conditions on growth performances, amplified by periods of summer drought. The study was carried out at two sites presenting comparable climatic but different edaphic conditions: (i) fertile agricultural soil; and (ii) heterogeneous unstructured soil from a reclaimed post-mining area. During the vegetation period, the growth rate decreased in both sites following the plant water status in terms of pre-dawn leaf water potential. Particularly in the post-mining area, due to the adverse edaphic conditions, below the critical pre-dawn water potential value of -0.5 MPa, the stem growth was drastically reduced during a period of summer drought. However, the trees could cope with the extreme soil and weather conditions in the post-mining site without perishing.
Understanding of soil carbon dynamics after establishment of alley-cropping systems is crucial for mitigation of greenhouse CO2 gas. This study investigates soil CO2 fluxes in an alley-cropping system composed of tree strips of black locust (Robinia pseudoacacia L.) and poplar (Populus nigra 9 P. maximowiczii, Max 1) trees and adjacent to them crop strips (Lupinus/Solarigol). Soil CO2 flux was measured monthly over a period from March to November 2012, using a LI-COR LI-8100A automated device. Concurrently with CO2 flux measurements, soil and air temperature, soil moisture, microbial C and hot water-extractable C were determined for the soils nearby soil collars. Root biomass was determined to a depth of 15 cm. In all sampling areas, soil CO2 flux increased from May to July, showing a significant positive correlation with air and soil temperature, which can be a reflection of increase in photosynthesis, and therefore supply of carbohydrates from leaves to rhizosphere, over the warm summer months. A positive correlation between CO2 flux and soil moisture over the warm period indicates an enhancing role of soil moisture on microbial mineralization and root respiration. Average CO2 flux values observed over March–November period did not differ significantly between sampling areas, showing 2.5, 3.2, and 2.9 lmol m-2 s-1 values for black locust, poplar and crops, respectively. Significantly higher CO2 flux values over the summer period in trees could be attributed to the higher photosynthetic activity and higher root density compared to crops.
Short-term effects of plant litter addition on mineral surface characteristics of young sandy soils
(2015)
Initial stages of soil development are characterized by structural changes of mineral surfaces over time. The specific surface area (SSA) is closely related to pedogenic properties and soil organic matter (SOM). Interactions between SOM and mineral surfaces induce quantitative and qualitative changes in SSA and corresponding soil properties. However, the knowledge about ranges, effects and mechanisms of organic coverage in the very initial phase of pedogenesis is very limited. Therefore, our objective was to study these processes in young sandy soils and the effects of plant litter addition. Soil samples taken from the constructed catchment “Chicken Creek” were used in a microcosm experiment over 80 weeks. The silt and clay fractions of samples (b63 μm) were analyzed before the experiment and after 40 and 80 weeks. The effects of litter addition and weathering on SSA were assessed using the BET-N2 sorption approach. We found increases of SSA between 16.4% and 41.6% within the 80 week experimental period, but a relative reduction in S. A due to organic coverage of these new surfaces after plant litter addition. The removal of the soil organic matter (SOM) by muffling increased SSA (6.8–12.9%). The results for SSA corresponded to changes in surface specific parameters like cation exchange capacity (CEC), surface enthalpy and the fractional coverage of mineral surfaces by SOM. In conclusion, the results showed that the soilswere clearly in a very initial state of soil development. However, the potential of these young sandy soils to adsorb nutrients and soil organic matter as one of the main important soil functions clearly increased within the relatively short experimental period and changes in SSA indicate relatively large increases in mineral surfaces within short time periods during the initial phase of soil development compared to long-term pedogenesis.
The soil in the vicinities of former Manufactured Gas Plant (MGP) sites is commonly contaminated with iron-cyanide complexes (ferric ferrocyanide). The phenomenon of cyanide mobility in soil, according to the literature, is mainly governed by the dissolution and precipitation of ferric ferrocyanide, which is only slightly soluble (<1 mg L¡1) under acidic conditions. In this paper, retention properties of the sandy loam soil and the potential vertical movement of the solid iron-cyanide complexes, co-existing with the dissolution, sorption and precipitation reactions were investigated. Preliminary research conducted on a former MGP site implied colloidal transport of ferric ferricyanide from the initial deposition in the wastes layer towards the sandy loam material (secondary accumulation), which possibly retarded the mobility of cyanide (CN). A series of batch and column experiments were applied in order to investigate the retardation of iron-cyanide complexes by the sandy loam soil. Batch experiments revealed that in circumneutral pH conditions sandy loam material decreases the potassium ferro- and ferricyanide concentration. In column experiments a minor reduction in CN concentration was observed prior to addition of iron sulfide (FeS) layer, which induced the formation of the Prussian blue colloids in circumneutral pH conditions. Precipitated solid iron-cyanide complexes were mechanically filtered by the coherent structure of the investigated soil. Additionally, the reduction of the CN concentration of the percolation solutions by the sandy loam soil was presumably induced due to the formation of potassium manganese iron-cyanide (K2Mn[Fe(CN)6]).