Metal accumulation in sediments and benthic invertebrates in lakes of Latvia

The concentrations of cadmium, lead, nickel and copper in waters, sediments (total metal concentrations and their speciation forms) and benthic macroinvertebrates in 11 lakes of Latvia were determined using atomic absorption spectroscopy. Metal concentrations in lake waters, sediments and biota were compared with water chemistry. Compared to total concentrations, metal speciation forms in sediments were better correlated with respective metal concentrations in invertebrates. Therefore, the evaluation of potential metal bioaccumulation should consider metal speciation. The mean concentrations of trace metals in benthic invertebrates in Latvia were much lower than in other countries, which can be explained by comparatively lower anthropogenic loads. However, local areas of anthropogenic impacts were evident.     

Sedimentary humic substances from lakes in Latvia

Humic and fulvic acids, isolated from sediments of lakes in different trophic states (Latvia) were studied. The humic substances (HS) were characterized by their elemental and functional composition, their spectral properties, and molecular mass. The humus properties strongly depend on the origin of the sedimentary HS. Substantial similarity between sedimentary HS from oligotrophic and dystrophic water bodies was found, unless the biology of these lakes greatly differs. Humic molecules from sediments of oligotrophic and dystrophic lakes are smaller, more uniform, and contain lower amounts of carboxyl- and hydroxyl-groups than HS from meso- and eutrophic water bodies. On the other hand, sedimentary HS from meso- and eutrophic lakes are dominated by aliphatic structures, and, possibly chromophore groups are present, and they are rich in polar groups. The macromolecules of HS from meso- and eutrophic lakes show the highest polydispersity.     

The dissipation of three fungicides in a biobed organic substrate and their impact on the structure and activity of the microbial community

Biopurification systems (BPS) have been introduced to minimise the risk for point source contamination of natural water resources by pesticides. Their depuration efficiency relies mostly on the high biodegradation of their packing substrate (biomixture). Despite that, little is known regarding the interactions between biomixture microflora and pesticides, especially fungicides which are expected to have a higher impact on the microbial community. This study reports the dissipation of the fungicides azoxystrobin (AZX), fludioxonil (FL) and penconazole (PC), commonly used in vineyards, in a biomixture composed of pruning residues and straw used in vineyard BPS. The impact of fungicides on the microbial community was also studied via microbial biomass carbon, basal respiration and phospholipid fatty acid analysis. AZX dissipated faster (t _1/2?=?30.1 days) than PC (t _1/2?=?99.0 days) and FL (t _1/2?=?115.5 days). Fungicides differently affected the microbial community. PC showed the highest adverse effect on both the size and the activity of the biomixture microflora. A significant change in the structure of the microbial community was noted for PC and FL, and it was attributed to a rapid inhibition of the fungal fraction while bacteria showed a delayed response which was attributed to indirect effects by the late proliferation of fungi. All effects observed were transitory and a full recovery of microbial indices was observed 60 days post-application. Overall, no clear link between pesticide persistence and microbial responses was observed stressing the complex nature of interactions between pesticides in microflora in BPS.     

The effect of initial concentration, co-application and repeated applications on pesticide degradation in a biobed mixture

A 180 d laboratory experiment was conducted to investigate the degradation rates of chlorpyrifos (10 and 50 mg kg(-1)) and metalaxyl (100 mg kg(-1)) separately and co-applied in a biomix constituted by topsoil, vine-branches and urban-waste-garden compost. The effect of repeated application of metalaxyl was also investigated. Microbial biomass-C (MBC) content and metabolic quotient (qCO(2)) were measured to evaluate changes in microbial biomass size and activity induced by the presence of the two pesticides. Degradation rate decreased with increasing concentration of chlorpyrifos in all treatments. Metalaxyl half-life was significantly reduced in co-application with chlorpyrifos indicating a synergic interaction between the two pesticides in favour of enhanced degradation rate for metalaxyl but not for chlorpyrifos. Furthermore, repeated application resulted in a sharp reduction of metalaxyl half-life from 37 d after first application to 4 d after third application. MBC content was negatively influenced by the addition of pesticides but it started to recover immediately, in both separate and co-applied treatments, reaching the control value when pesticide residues were about 50% of the initial concentration. The qCO(2) reached a steady-state after about 20 d in separately applied and 40 d in co-applied treatments, indicating a tendency to arrive at a new metabolic equilibrium. In conclusion, the biomix tested has been shown to degrade pesticides relatively fast and to have a microbial community that is varied enough to allow selection of those microorganisms able to degrade metalaxyl and chlorpyrifos.     

Retention capacity of an organic bio-mixture against different mixtures of fungicides used in vineyards

A laboratory experiment was carried out to test the efficiency of a bio-mixture made up of pruning residues at two (PR2) and five (PR5) years of composting and wheat straw (STW) in the biological cleaning of water contaminated by different mixtures of fungicides usually employed in vineyards. The experiment was conducted and reproduced at a scale of 1:100 of operating field conditions. Commercial formulates of penconazole (PC), (RS)-1-[2-(2,4-dichlorophenyl)pentyl]-1H-1,2,4-triazole), dimetomorph (DM), (EZ)-4-[3-(4-chlorophenyl)-3-(3,4-dimethoxyphenyl)acryloyl]morpholine), azoxystrobin (AZ), (methyl (E)-2-{2-[6-(2-cyanophenoxy)pyrimidin-4-yloxy]phenyl}-3-methoxyacrylate), iprovalicarb (IP), (isopropyl 2-methyl-1-[(RS)-1-p-tolylethyl]carbamoyl-(S)-propylcarbamate), metalaxyl (MX), (methyl N-(methoxyacetyl)-N-(2,6-xylyl)-DL-alaninate), fludioxonil (FL), (4-(2,2-difluoro-1,3-benzodioxol-4-yl)-1H-pyrrole-3-carbonitrile) and cyprodinil (CY), (4-cyclopropyl-6-methyl-N-phenylpyrimidin-2-amine) were mixed in water and discharged into the bio-mixture following the time schedule of the treatments carried out in the grapevine in real field conditions. At each treatment, contaminated water with fungicides was circulated repeatedly through the bio-mixture to enhance the sorption of fungicides. In fact, it retained them between 98–100% with the exception of MX of which it was able to retain only 90.5%. The adsorption/desorption experiment showed that repeated circulation of water, instead of enhancing MX retention, can easily remove about 30% of MX already adsorbed by the bio-mixture. This finding suggests that water contaminated by very mobile pesticides should be discharged at the end of field treatments without re-circulating the water in order to avoid the release of pesticides weakly adsorbed on the bio-mixture.     

Losses and dissipation of penconazole in vineyard soil as affected by mid-row management system

A field experiment was performed with the aim to assess the amount of penconazole losses during field application and the spatial variability of penconazole concentration in a vineyard soil, under two different management techniques (tilled and grass covered). The field dissipation of penconazole under the two techniques was also followed for 114 days, highlighting the effects of spatial variability of the initial concentration and of the grass covering in terms of the different soil metabolic activity. Data found show that a high percentage of penconazole, from 42.5 % to 67.43 %, can reach the soil during the treatments, despite the fact that penconazole is applied to the foliage. The high values of the coefficient of variation for data within rows show considerable variability in all applications, ranging from 30 to 65 in the first application, from 35 to 79 in the second and from 36 to 75 in the third. Since the applications of penconazole occurred under almost same climatic conditions in terms of wind speed and direction, the high variability of concentration of penconazole found within mid-rows was attributed to the uneven slope of the vineyard causing an irregular speed of the sprayer equipment. However, least significant differences of the mean values did not end in a significant difference of penconazole concentration among mid-rows for all applications, indicating that the variability between rows does not contribute to the overall variability. The calculated half-life values for penconazole in tilled soil were 62.4 days for tilled and 33.0 for grassed soil, highlighting the tendency of penconazole to faster dissipate in grassed than in tilled soil. Grassed soil was characterised by a higher metabolic activity in terms of microbial biomass carbon content, basal respiration and total hydrolytic activity, than tilled soil. A significant correlation between penconazole dissipation and total hydrolytic activity, was found. The faster dissipation of penconazole in grassed soil was attributed to the higher amount of the total hydrolytic activity which, in grassed soil, was 1.5 fold-higher than in tilled soil.     

Moist olive husks addition to a silty clay soil: influence on microbial and biochemical parameters

To investigate the effects of moist olive husks (MOH-residues) on soil respiration, microbial biomass, and enzymatic (o-diphenoloxidase, beta-glucosidase, dehydrogenase and alkaline phosphatase) activities, a silty clay soil was incubated with 0 (control), 8 x 10(3) (D), 16 x 10(3) (2D) and 80 x 10(3) (10D) kg ha-1 of MOH-residues on a dry weight basis. Soil respiration and microbial biomass data indicated that the addition of MOH-residues strongly increased microbial activity proportionally to the amounts added. Data of qCO2 suggested that the respiration to biomass ratio of the microbial population was strongly modified by MOH-residues additions during the first 90 days of incubation. The qCO2 data suggested a low efficiency in energy yields from C oxidation during the first 2 months of soil incubation. qFDA seemed to be relatively unaffected for treatments D and 2D as compared to the control, but was significantly lowered by the application of 10D, showing the lowest hydrolytic activity of microbial biomass in this treatment up to 360 days of incubation. o-Diphenoloxidase activity was delayed, and this delay was extended with the addition of larger quantities of MOH-residues. Alkaline phosphatase, beta-glucosidase and dehydrogenase activities were in line with the findings on microbial biomass changes and activities. The biological and biochemical data suggest that the addition of a large quantity of MOH-residues (80 x 10(3) kg ha-1) strongly modifies the soil characteristics affecting the r- and K-strategist populations, and that these changes last for at least the 360 days of incubation. The data also suggest that application rates exceeding 16 x 10(3) kg ha-1 are not recommended until the agro-chemical and -physical functions of the soil are further studied.     

Long-Term and Seasonal Changes in Chemical Composition of Surface Waters in Latvia

The changes of the chemical composition in Latvianinland waters over the last twenty years weredetermined, based on data of the National MonitoringProgramme. Relationships between the water compositionwere studied. The chemical composition and seasonalchange pattern depend a lot on hydrological factorswhich differed between eastern and western Latvia.Different pattern of long-term changes is found forsubstances which have different sources andsinks, at first for nutrients (decrease only in the lastfew years) and inorganic ingredients (commonlyincreasing trend). An attempt was made to identify themain sources of the major water ingredients and linkchanges of their concentrations with changes inloading to waters.