Oili Kiikkilä

Organic material as a copper immobilising agent: a microcosm study on remediation

Remediation of heavy metal polluted forest soil was studied using nine different organic immobilising agents in a laboratory microcosm study. Composted sewage sludge, compost of organic household waste, a mixture of compost and woodchips, a mixture of compost and barkchips, garden soil, birch leaves, barkchips, humus or peat was applied on the surface of a polluted soil. Changes in the exchangeable Cu concentration, microbial respiration activity, microbial biomass and structure of the microbial community were assessed at four points during a 16-month period. Cu fractions, Cu 2+ and complexed Cu, and toxicity of the soil solution to bacteria, bacterial growth rate, number of bacterial cells, and bacterial copper tolerance were determined on samples taken after 16 months. Sewage sludge, compost, the compost mixtures, and garden soil decreased the exchangeable Cu concentration in the polluted soil, but had no effect on microbial activities, bacterial tolerance to copper or on the structure of the microbial community directly attributable to remediation. Zur Remediation von Schwermetall belasteten Waldboden wurden in einem Mikrokosmosversuch neun verschiedene Schwermetall immobilisierende organische Substanzen getestet. Klarschlamm, Haushaltskompost, eine Mixtur von Haushaltskompost und Holzspanen, eine Mixtur von Haushaltskompost und Rindenspanen, Gartenerde, Birkenblatter, Rindenspane, Humus oder Torf wurde einem belasteten Waldboden als neue organische Schicht aufgetragen. Uber den 16 Monate lang andauernden Laborversuch haben vier Beprobungen stattgefunden und die Konzentration von austauschbaren Cu, die Mikrobielle Respiration, die Mikrobielle Biomasse, und die Zusammensetzung der Bodenmikroflora wurden jeweils bestimmt. Zusatzlich wurden bei der letzten Beprobung (16 Monate) auch zwei verschiedene Cu Fraktionen, Cu ++ und komplekziertes Cu, die Toksizitat des Bodenwassers gegenuber Bakterien, die Bakterielle Wachstumsrate, die Bakterienanzahl und die Tolreranz der Bakterien gegen Cu bestimmt. Die Auftragung von Klarschlamm, Kompost, der beiden Kompostmixturen oder Gartenerde auf die Bodenoberflache erniedrigte die Konzentration von austauschbaren Cu des Bodens aber hatte keine lang anhaltenden Remedierungsefekte auf die Bodenbiologie des Schwermetal belasteten Waldbodens.

Microbial ecology in a future climate: effects of temperature and moisture on microbial communities of two boreal fens

Impacts of warming with open-top chambers on microbial communities in wet conditions and in conditions resulting from moderate water-level drawdown (WLD) were studied across 0-50 cm depth in northern and southern boreal sedge fens. Warming alone decreased microbial biomass especially in the northern fen. Impact of warming on microbial PLFA and fungal ITS composition was more obvious in the northern fen and linked to moisture regime and sample depth. Fungal-specific PLFA increased in the surface peat in the drier regime and decreased in layers below 10 cm in the wet regime after warming. OTUs representing Tomentella and Lactarius were observed in drier regime and Mortierella in wet regime after warming in the northern fen. The ectomycorrhizal fungi responded only to WLD. Interestingly, warming together with WLD decreased archaeal 16S rRNA copy numbers in general, and fungal ITS copy numbers in the northern fen. Expectedly, many results indicated that microbial response on warming may be linked to the moisture regime. Results indicated that microbial community in the northern fen representing Arctic soils would be more sensitive to environmental changes. The response to future climate change clearly may vary even within a habitat type, exemplified here by boreal sedge fen.

Copper mobility and toxicity of soil percolation water to bacteria in a metal polluted forest soil

In order to assess the success of in situ remediation of coniferous forest soil polluted by a Cu–Ni smelter, the total Cu concentration in soil percolation water, the fluxes of Cu down through the soil profile, and the toxicity of soil percolation water to soil bacteria were studied. Total Cu in percolation water was also fractionated into free ionic and complexed forms. The toxicity of the percolation water was measured by the [3H]-thymidine incorporation method, which measures bacterial growth rates. Soil percolation water was collected during one growing season by zero tension lysimeters inserted at depths of 0.2 and 0.4 m in the soil. The treatments consisted of a control, mulch application to the forest floor (M) and mulch application after removing the polluted organic soil layer (MR). The mulch consisted of a mixture of compost and woodchips (1/1; vol/vol). Analysis of Cu species and dissolved organic carbon (DOC) indicated that DOC leached from the mulch and complexed Cu into forms that were less toxic to soil bacteria. At 0.2 m depth percolation water toxicity was 19% lower in the M and 42% lower in the MR treatment than in the control. Toxicity correlated with the Cu2+ concentration, which was 61 and 84% lower in the M and MR treatments, respectively, compared to the control. However, there were signs that total Cu had leached down through the soil profile, the leaching being more pronounced in the MR treatment.

Soil microbial activity in relation to dissolved organic matter properties under different tree species

Background and aimsThe total concentration of dissolved organic carbon (DOC) has often been observed to correlate positively with soil microbial respiration. The aim was to explain the correlation with the properties of dissolved organic matter (DOM).MethodsA dataset from previously published papers was gathered together and subjected to multivariate analyses. Samples were collected from five tree species experiments in Finland. The degradability of DOM was assessed by measuring bacterial and fungal growth in DOM. The chemical properties of DOM were assessed by XAD resin fractionation and molecular weight. Soil microbial activity was assessed as C and N mineralization and microbial biomass.ResultsBoth low and high molecular weight compounds, as well as hydrophilic neutral compounds, seemed to be relatively easily degradable. In contrast to our presupposition, easily degradable DOM seemed to be less abundant in soil where variables describing microbial activity were higher. Birch soil with higher microbial biomass N seemed to contain less easily degradable DOM than spruce soil.ConclusionWe suggest that DOM collected and characterized at a certain point reflects more the accumulation of refractory compounds following high microbial activity than the easily degradable compounds that microbes would be using when measured.

Leaching of Dissolved Organic Carbon and Trace Elements After Stem-Only and Whole-Tree Clear-cut on Boreal Peatland

The aim of this work was to study the short-term effect of clear-cut harvest on concentrations of dissolved organic carbon (DOC), B, Al, Zn, Cu, Ni, Cr, Cd and Pb in drainage water from northern peatland catchments in Finland underlain by granitic or black shale bedrock, the latter having higher concentrations of several trace elements, such as Ni and Zn. Stem-only harvest (SOH) or whole-tree harvest (WTH) with stump removal were carried out at coniferous sites. Controls were left unharvested. DOC and trace element concentrations were monitored during one pre-treatment and two post-treatment years. There was no constant increase in the element concentrations. However, there were signs that both SOH and WTH clear-cut harvest on northern peatland catchments increases the concentrations of DOC, B, Al, Zn and Ni in ditchwater in some sites irrespective of the bedrock type. The greatest increases were observed in WTH sites but the study does not allow us to assess the statistical significance of the magnitude of the difference between SOH and WTH. We conclude that the element concentrations in ditchwater depend largely on site characteristics masking the possible effect of harvest.

Some observations on the copper tolerance of bacterial communities determined by the (3H)-thymidine incorporation method in heavy metal polluted humus

Abstract Changes in pH after filtration of bacterial suspensions are important when applying the radioactive thymidine incorporation method to heavy-metal polluted soils with low microbial activity. In the original method (Baath 1992; Soil Biology and Biochemistry 24, 1157–1165) the blended and centrifuged suspension was filtered through glass wool to remove humus particles from the suspension. When we filtered the bacterial suspension through glass wool the pH increased by 2 units and the thymidine incorporation rate decreased. This made the community copper tolerance measurement ambiguous. When using soil samples with very low activity, we recommend the use of acid-washed glass wool or polyester net filtration which eliminates changes in pH.

Diversity of leaf litter leachates from temperate forest trees and its consequences for soil microbial activity

Leaching of water-soluble compounds is a dominant process during the first stages of litter decomposition, providing the microorganisms in the underlying soil with an important source of labile carbon and nutrients. Leachate composition (quantity and quality) can vary considerably among different plant species, but its consequences for soil microbially-driven processes remains largely unexplored. Here, we evaluated the differences in leachate quantity and quality from freshly fallen leaf litter of widely distributed coniferous and deciduous broadleaf tree species of European temperate forests, and their effects on soil microbial responses in a microcosm experiment under controlled conditions. Leachates of broadleaf litter contained higher amounts of carbon and nitrogen available for microbes, but with substantially higher aromaticity than leachates from coniferous litter. A one-time leachate addition to soils immediately increased soil microbial respiration with longer lasting effects of deciduous broadleaf compared to coniferous litter leachates leading to a microbial community with an apparently more efficient use of carbon. When leachates of different species were mixed, the observed microbial responses differed in some cases from that expected based on soils to which leachates from single species were added. These non-additive effects were partly explained by the functional dissimilarity of leachate traits, suggesting complementary resources for microorganisms when leachates of different species are available. Our data show that species-specific litter-derived leachates of varying quantity and quality and their mixtures distinctly affect soil microorganisms. In forest ecosystems with recurrent leaf litter inputs from the same species, such leachate effects may determine soil processes also in the longer term, controlling biogeochemical cycling to an important degree.

Impact of Re-wetting of Forestry-Drained Peatlands on Water Quality—a Laboratory Approach Assessing the Release of P, N, Fe, and Dissolved Organic Carbon

A laboratory column study with peats from four sites from south-central Finland and two sites from blanket peats in the west of Ireland was established to assess the factors contributing to P, N, Fe, and dissolved organic carbon (DOC) transfer to receiving water courses from restored forestry-drained peatlands. The study indicated that the DOC and Fe release from re-wetted peats are likely governed by the amount of Fe in peat and the degree of Fe reduction upon re-wetting. In contrast to our other hypothesis concerning DOC, high degradability of organic matter was not related to high DOC release. Nitrate release was found to largely cease along with oxygen depletion, but ammonium release was considerable from a site with high nitrification potential before wetting. The release of P from anoxic peat was complicated in the sense that it appeared to be controlled by many factors simultaneously. In the nutrient-poor sites, the P release increased following re-wetting, probably because of their high easily soluble peat P content and low Al and Fe content, resulting in high anoxic P mobilization, but limited re-sorption of the mobilized P. Among the three nutrient-rich sites, there was either no P release upon re-wetting or higher P release than from the nutrient-poor sites. Low risk for P release following re-wetting in nutrient-rich sites was associated with low content in peat of easily soluble P and a high molar Fe/P ratio.

Effects of Acidic Deposition on Forest Soil Microbiology

The organic material deposited on or in the soil is decomposed and mineralised primarily through the activity of fungi, bacteria and soil animals. They convert the carbon in organic matter into CO2, thus completing the biological carbon cycle initiated in photosynthesis. Mineralisation releases nutrients into the soil where they are available for uptake by plants. The biological activity of the soil is therefore of prime importance in maintaining the fertility of terrestrial habitats.