Holocene biomass burning and global dynamics of the carbon cycle

Fire regimes have changed during the Holocene due to changes in climate, vegetation, and in human practices. Here, we hypothesise that changes in fire regime may have affected the global CO2 concentration in the atmosphere through the Holocene. Our data are based on quantitative reconstructions of biomass burning deduced from stratified charcoal records from Europe, and South-, Central- and North America, and Oceania to test the fire-carbon release hypothesis. In Europe the significant increase of fire activity is dated approximately 6000 cal. yr ago. In north-eastern North America burning activity was greatest before 7500 years ago, very low between 7500-3000 years, and has been increasing since 3000 years ago. In tropical America, the pattern is more complex and apparently latitudinally zonal. Maximum burning occurred in the southern Amazon basin and in Central America during the middle Holocene, and during the last 2000 years in the northern Amazon basin. In Oceania, biomass burning has decreased since a maximum 5000 years ago. Biomass burning has broadly increased in the Northern and Southern hemispheres throughout the second half of the Holocene associated with changes in climate and human practices. Global fire indices parallel the increase of atmospheric CO2 concentration recorded in Antarctic ice cores. Future issues on carbon dynamics relatively to biomass burning are discussed to improve the quantitative reconstructions.     

The chemical and biogenotoxic characterization of organic xenobiotics in aquatic sediment materials 1. The application and comparison of chemically non-specific and biogenotoxic methods

The aim of this work was to evaluate the Ames assay and mixed function oxidase (MFO)-Induct Test used in parallel with chemical group tests (ECD fingerprint and PAH estimation) for the characterization of the organic pollution of water sediment materials. Sediment materials were collected from “clean” and relatively heavily polluted locations in the Middle Adriatic Sea, and from some locations in continental Croatia polluted with wastewaters from different enterprises. Characterization of the organic extracts of the sediment materials investigated was performed chemically using UV spectrofluorometry for the determination polyaromatic hydrocarbons (PAH) and gas chromatography for the determination of volatile EC detector sensitive materials. Genotoxic analysis of the extracts was performed using the MFO-Induct Test and mutagenicity testing using the Standard Plate Incorporation Test as described by Maron and Ames with Salmonella typhimurium TA 98. Measurement of the BaPMO enzyme activity in the livers of carp treated i.p. with total extracts of the sediment investigated confirmed that the methanol extracts generally contained more inducing matter than the petroleum ether extracts. Ames assay showed that for all the samples following the elimination of the sulfur, there was an increase in the number of revertants in comparison to the control number, which indicates that the samples contained mutagenic substances. The larger doses of extracts generally demonstrated cytotoxicity, as evidenced by a reduced number of spontaneous revertants in the Salmonella/Microsome Test. Investigation of the correlation of the chemical parameters with the biological parameter showed that the induction of BaPMO exhibited a statistically significant correlation with the level of the ECD fingerprint of the petroleum ether sediment extract.     

Reductive dechlorination of chlorinated methanes and ethanes by reduced iron (II) porphyrins

The reaction of a reduced iron (II) porphyrin with a series of chlorinated methanes and ethanes was examined under neutral conditions in buffered aqueous solutions containing an excess of the reducing agent. Carbon tetrachloride, chloroform and 1,1,1-trichloroethane were reduced to lower chlorinated homologs, while methylene chloride, 1,1,2-trichloroethane and 1,1-dichloroethane did not appear to be degraded in this system.     

Long term investigation of 137Cs in chicken meat and eggs from northwest Croatia

Abstract

This paper presents the results of long-term investigations of ¹³⁷Cs activity concentrations in chicken meat and eggs from northwest Croatia for the period 1987–2018. The research has been done as a part of monitoring program of radioactive contamination in Croatia. The highest activity concentrations in both of these foodstuffs were measured in 1987 and have been decreasing exponentially ever since. The Fukushima-Daiichi accident in 2011 did not cause any increase of ¹³⁷Cs activity concentrations. The ecological half-life for ¹³⁷Cs was estimated to be 8.0 and 8.4?years for chicken meat and eggs respectively. The correlation between ¹³⁷Cs in fallout and chicken meat as well as between ¹³⁷Cs in fallout and eggs is very good, the respective correlation coefficients being 0.79 and 0.72, indicating that fallout was the main source of ¹³⁷Cs contamination in both foodstuffs. The estimated effective doses received by adult members of the Croatian population due to the intake of radiocaesium by chicken meat and egg consumption for the overall observed period are very small, 2.0 and 0.6 µSv respectively. Therefore, chicken meat and chicken egg consumption was not a critical pathway for the transfer of radiocaesium to humans.     

Study of MCPA and MCPP herbicides mobility in soils from North-West Croatia as affected by presence of fertilizers

The mobility of acid herbicide (4-chloro-2-methylphenoxy)acetic acid [MCPA] and 2-(4-chloro-2-methylphenoxy)propionic acid [MCPA] in soils of North-West Croatia has been studied by soil thin-layer chromatography (STLC). Mobility of MPCA and MCPP was influenced by the change in concentration of soluble salts and the effect of mineral composition of the system studied, i.e. content of kaolin and sand in soil thin layer. The objective of this work was also to investigate how the mobility of phenoxy herbicides MCPA and MCPP is altered by the presence of fertilizers when both coexist in soil as a result of human activity. It has been found that mobility of acidic herbicides increases with application of fertilizers especially on soil with low clay and low organic matter content.     

Post-war levels of persistent organic pollutants (POPs) in air from Serbia determined by active and passive sampling methods

For the duration of the war accident in former Yugoslavia, several industrial and military targets were burnt and damaged, resulting in a significant release of persistent organic pollutants. Locations heavily targeted in the attacks were later defined by UNEP as four “hot spots”: Kragujevac, Novi Sad, Pancevo and Bor. We analyzed concentration levels of pollutants collected in 2004 and 2005 in air samples from the city of Kragujevac, Serbia, following the war accident of 1999. Pollutants included polycyclic aromatic hydrocarbons (PAHs), hexachlorocyclohexane (HCH), dichloro-diphenyl-trichloroethane (DDT), dichloro-diphenyl-dichloroethylene (DDE), dichloro-diphenyl-dichloroethane (DDD) and polychlorinated biphenyls (PCBs). We present results obtained during air sampling campaign conducted in July 2004 by the active sampling method; and during September 2004–June 2005 by the passive sampling method. Our findings show the occurrence of residual quantities of DDT, HCH, PCBs and PAHs in air samples. High levels of PCBs are probably due to the destruction of transformers during the war accident.     

Automatic construction of concept hierarchies: The case of foliage-dwelling spiders

In this paper, we present the hierarchical variable dependencies that were obtained from raw data with the use of two machine learning techniques on an ecological data set. The data set contains features of field margins and the corresponding number of spider species inhabiting them. This data set was used before by domain experts to construct a fuzzy qualitative model with hierarchical variable dependencies, which we use for comparison with our results. One of the machine learning methods constructs a hierarchical structure similar to the one in the experts’ model, while revealing some additional interesting relations of environmental features with respect to the number of spider species. The other method constructs a different hierarchy from the one proposed by the experts, which, according to our classification performance experiments, might be even more appropriate.     

Application of machine learning methods to palaeoecological data

A palaeoecological study was conducted to investigate past environmental conditions and vegetation dynamics around the southwestern Ljubljana Moor. In order to find potential regularities and/or dependencies among co-existent plant species through time, different machine learning methods were applied to pollen records from the cores taken at Bistra and Ho?evarica. The data comprised relative pollen frequencies of the most common plant genera/families at particular core depths that correspond to particular ages in the Early and Mid Holocene periods. The applied methods include equation discovery and hierarchical clustering. Both methods have found plausible and explainable relationships among identified plant genera/families.