Mesocosm Scale Research Articles

Previous exposure advances the degradation of an anthropogenic s-triazine regardless of soil origin

Previous investigations—field samplings and laboratory experiments—support the hypothesis that the degradation of s-triazines is enhanced in previously exposed as compared to pristine soils in terrestrial environments. Despite this, bottlenecks of soil sampling and various soil modification practices in microcosm studies have made it difficult to guarantee that previous contamination history enhances contaminant degradation regardless of soil origin in terrestrial ecosystems. We test the hypothesis that the degradation of simazine (2-chloro-4,6-bis(ethylamino)-s-triazine) is enhanced in previously exposed soils as compared to pristine soils in 10 l buckets at the mesocosm scale. We collected soil at three separate sites consisting of a previously exposed and a pristine field. At every field, soil was collected at three separate plots and simazine degradation (days 0 and 65) and the response to atzB degrader gene primers (days 0 and 110) were followed. We analyzed the results using analysis of covariance (ANCOVA). Previous exposure and field site were assessed as fixed factors and initial simazine concentration and abiotic soil conditions as covariates. After the 65-day exposure, remaining simazine concentrations depended on previous exposure but not on collection site. The response to atzB gene primers was positive in all mesocosms where simazine degradation had been rapid. Soil moisture, pH, and organic matter content were insignificant. If soil moisture was not included in the ANCOVA model, previous exposure did not appear as a significant factor. The results support the hypothesis that simazine is degraded more rapidly in previously exposed soils as compared to pristine environments, provided that degradation genes are available. Previously exposed soil might be used to enhance the degradation of simazine in recently contaminated terrestrial soils, supposing that the central requirements for microbial growth are adequate.

Removal rates of dissolved munitions compounds in seawater

The historical exposure of coastal marine systems to munitions compounds is of significant concern due to the global distribution of impacted sites and known toxicological effects of nitroaromatics. In order to identify specific coastal regions where persistence of these chemicals should be of concern, it is necessary to experimentally observe their behavior under a variety of realistic oceanographic conditions. Here, we conduct a mesocosm scale pulse addition experiment to document the behavior of two commonly used explosives, 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in simulated marine systems containing water and sediments collected from Long Island Sound, CT. The addition of sediments and sediment grain-size had a major influence on the loss rates of all compounds detected. RDX and reduced TNT products were removed from seawater only in the presence of sediment, and TNT degraded significantly faster in the presence of sediment. Both compounds were removed from the system faster with decreasing grain-size. Based on these findings and a thorough review of the literature, we hypothesize that in addition to bacterial abundance and nutrient availability, TNT removal rates in coastal marine waters may be controlled by sorption and rapid surface-mediated bacterial transformation, while RDX removal rates are controlled by diffusion into sedimentary anoxic regions and subsequent anaerobic bacterial breakdown. A comparison of published removal rates of RDX and TNT highlights the extreme variability in measured degradation rates and identifies physicochemical variables that covary with the breakdown of these munitions compounds.

Impacts of dust deposition on dissolved trace metal concentrations (Mn, Al and Fe) during a mesocosm experiment

Abstract. The deposition of atmospheric dust is the primary process supplying trace elements abundant in crustal rocks (e.g. Al, Mn and Fe) to the surface ocean. Upon deposition, the residence time in surface waters for each of these elements differs according to their chemical speciation and biological utilization. Presently, however, the chemical and physical processes occurring after atmospheric deposition are poorly constrained, principally because of the difficulty in following natural dust events in situ. In the present work we examined the temporal changes in the biogeochemistry of crustal metals (in particular Al, Mn and Fe) after an artificial dust deposition event. The experiment was contained inside trace metal clean mesocosms (0–12.5 m depths) deployed in the surface waters of the northwestern Mediterranean, close to the coast of Corsica within the frame of the DUNE project (a DUst experiment in a low Nutrient, low chlorophyll Ecosystem). Two consecutive artificial dust deposition events, each mimicking a wet deposition of 10 g m−2 of dust, were performed during the course of this DUNE-2 experiment. The changes in dissolved manganese (Mn), iron (Fe) and aluminum (Al) concentrations were followed immediately after the seeding with dust and over the following week. The Mn, Fe and Al inventories and loss or dissolution rates were determined. The evolution of the inventories after the two consecutive additions of dust showed distinct behaviors for dissolved Mn, Al and Fe. Even though the mixing conditions differed from one seeding to the other, Mn and Al showed clear increases directly after both seedings due to dissolution processes. Three days after the dust additions, Al concentrations decreased as a consequence of scavenging on sinking particles. Al appeared to be highly affected by the concentrations of biogenic particles, with an order of magnitude difference in its loss rates related to the increase of biomass after the addition of dust. In the case of dissolved Fe, it appears that the first dust addition resulted in a decrease as it was scavenged by sinking dust particles, whereas the second seeding induced dissolution of Fe from the dust particles due to the excess Fe binding ligand concentrations present at that time. This difference, which might be related to a change in Fe binding ligand concentration in the mesocosms, highlights the complex processes that control the solubility of Fe. Based on the inventories at the mesocosm scale, the estimations of the fractional solubility of metals from dust particles in seawater were 1.44 ± 0.19% and 0.91 ± 0.83% for Al and 41 ± 9% and 27 ± 19% for Mn for the first and the second dust addition. These values are in good agreement with laboratory-based estimates. For Fe no fractional solubility was obtained after the first seeding, but 0.12 ± 0.03% was estimated after the second seeding. Overall, the trace metal dataset presented here makes a significant contribution to enhancing our knowledge on the processes influencing trace metal release from Saharan dust and the subsequent processes of bio-uptake and scavenging in a low nutrient, low chlorophyll area.

Impact of plant assemblages on nutrient removal in constructed wetlands

Four different mesocosm scale constructed wetlands – monoculture (Carexstipata), self-designed (passive) community, mixed planted monoculturepassive community and a non-vegetated control were compared to assess the effects of plant community composition on the removal of inorganic nutrients from agricultural runoff (synthetic tile water). The mixed and self-designed systems consistently produced effl uent NO3–N concentrations signifi cantly below 10 mg/L, and had higher rates of evapotranspiration. Results indicate the type and composition of the plant community can impact the performance of constructed wetlands. Therefore, self-design of the plant community through the existing seed bank may increase the effectiveness of wetlands in treating agricultural runoff.

Design configurations affecting flow pattern and solids accumulation in horizontal free water and subsurface flow constructed wetlands

The aim of this study was to evaluate the effect of different horizontal constructed wetland (CW) design parameters on solids distribution, loss of hydraulic conductivity over time and hydraulic behaviour, in order to assess clogging processes in wetlands. For this purpose, an experimental plant with eight CWs was built at mesocosm scale. Each CW presented a different design characteristic, and the most common CW configurations were all represented: free water surface flow (FWS) with different effluent pipe locations, FWS with floating macrophytes and subsurface flow (SSF), and the presence of plants and specific species (Typha angustifolia and Phragmites australis) was also considered. The loss of the hydraulic conductivity of gravel was greatly influenced by the presence of plants and organic load (representing a loss of 20% and c.a. 10% in planted wetlands and an overloaded system, respectively). Cattail seems to have a greater effect on the development of clogging since its below-ground biomass weighed twice as much as that of common reed. Hydraulic behaviour was greatly influenced by the presence of a gravel matrix and the outlet pipe position. In strict SSF CW, the water was forced to cross the gravel and tended to flow diagonally from the top inlet to the bottom outlet (where the inlet and outlet pipes were located). However, when FWS was considered, water preferentially flowed above the gravel, thus losing half the effective volume of the system. Only the presence of plants seemed to help the water flow partially within the gravel matrix.

Natural attenuation is enhanced in previously contaminated and coniferous forest soils

Prevalence of organic pollutants or their natural analogs in soil is often assumed to lead to adaptation in the bacterial community, which results in enhanced bioremediation if the soil is later contaminated. In this study, the effects of soil type and contamination history on diesel oil degradation and bacterial adaptation were studied. Mesocosms of mineral and organic forest soil (humus) were artificially treated with diesel oil, and oil hydrocarbon concentrations (GC-FID), bacterial community composition (denaturing gradient gel electrophoresis, DGGE), and oil hydrocarbon degraders (DGGE + sequencing of 16S rRNA genes) were monitored for 20 weeks at 16°C. Degradation was advanced in previously contaminated soils as compared with pristine soils and in coniferous organic forest soil as compared with mineral soil. Contamination affected bacterial community composition especially in the pristine mineral soil, where diesel addition increased the number of strong bands in the DGGE gel. Sequencing of cloned 16S rRNA gene fragments and DGGE bands showed that potential oil-degrading bacteria were found in mineral and organic soils and in both pristine and previously contaminated mesocosms. Fast oil degradation was not associated with the presence of any particular bacterial strain in soil. We demonstrate at the mesocosm scale that previously contaminated and coniferous organic soils are superior environments for fast oil degradation as compared with pristine and mineral soil environments. These results may be utilized in preventing soil pollution and planning soil remediation.

Plant and mycorrhizal driven silicate weathering: Quantifying carbon flux and mineral weathering processes at the laboratory mesocosm scale

Abstract The rise of vascular land plants in the Paleozoic is hypothesized to have driven lower atmospheric CO 2 levels through enhanced weathering of Ca and Mg bearing silicate minerals and rocks. However, this view overlooks the co-evolution of roots and mycorrhizal fungi, with many of the weathering processes ascribed to plants potentially being driven by the combined activities of roots and fungi. Here mesocosm scale controlled laboratory experiments quantifying the effects of plant and fungal evolution on silicate rock weathering under ambient and elevated CO 2 concentrations are described. A snapshot is presented of C allocation through roots and mycorrhizal fungi and biological activity associated with geochemical changes in weathered mineral substrates via transfer of elements from solid phases into solution.

Recolonisation of mine tailing by meiofauna in mesocosm and microcosm experiments

The Batu Hijau copper/gold mine in Sumbawa, Indonesia processes ore at approximately 130,000tpd and discharges tailing via a submarine pipeline to depths below 3000m at the base of a submarine canyon. The study investigated recolonisation of tailing by meiofauna and its dependence on subsequent accumulation of natural sediment. Microcosm and mesocosm scale experiments were carried out using two tailing and two control samples, the latter comprising defaunated and unaffected natural sediment. All test materials were similar in physical and chemical respects, except for the higher copper concentration in the tailing. The abundances of meiofauna colonising defaunated controls and both tailing samples increased from zero to levels statistically indistinguishable from natural unaffected controls after 97 and 203days. Colonisation was well established in tailing from freshly mined ore after 40days, and in oxidized tailing from stockpiled ore after 65days, and was not dependent on settled natural material.

A Small-Scale Sulfate-Reducing Bioreactor for Manganese Removal from a Synthetic Mine Drainage

This research evaluated the efficiency of a mesocosm scale bioreactor to remove Mn from a synthetic mine drainage in the presence of selected organic and inorganic substrate combinations that could enhance sulfate reduction and induce Mn sulfide precipitation. The mine drainage tested was slightly acidic (pH 6.2) and had average Mn and SO4 concentrations of 90 and 1,500 mg/L, respectively. The substrates used were creek sediment amended with either wood mulch or a wood mulch and biosolid mixture. Greater than 90% of Mn and 70% of sulfate was removed over a 65-day test period. The results suggested multiple Mn removal mechanisms including sorption, complexation, and Mn sulfide, Mn oxide, and/or Mn carbonate precipitation.

A comparative study of the fatty acid profile of Artemia franciscana and A. persimilis cultured at mesocosm scale

The goal of this study was to examine the fatty acid (FA) profile of two Artemia species, A. persimilis (Argentina) and A. franciscana (Great Salt Lake,Utah; USA) in coexistence at mesocosm scale. The experiment was carried out to 1) evaluate putative differences in the fatty acid composition of both species while they share resources and 2) to investigate the causes of such differences. Although the coexistence of these species in nature has not yet been observed, it remains possible that this situation may arise in the future mainly due to the invasive ability of A. franciscana. FA analyses were performed on individuals as well as on pooled biomasses of each species, and integrated in multivariate principal components analysis (PCA). Comparison of the relative abundance of FA between the two species revealed that interspecific differences in FA composition are greater than intraspecific variability. Higher percentages of unsaturation were found in the fatty acids of A. persimilis compared to A. franciscana, demonstrating that aside from a high phenotypic effect of diet on the FA composition of the animals, a species-specific genotypic effect should not be discarded.

Molecular characterization of uranium(VI) sorption complexes on iron(III)-rich acid mine water colloids

A mixing of metal-loaded acid mine drainage with shallow groundwater or surface waters usually initiates oxidation and/or hydrolysis of dissolved metals such as iron (Fe) and aluminum (Al). Colloidal particles may appear and agglomerate with increasing pH. Likewise chemical conditions may occur while flooding abandoned uranium mines. Here, the risk assessment of hazards requires reliable knowledge on the mobility of uranium (U). A flooding process was simulated at mesocosm scale by mixing U-contaminated acid mine water with near-neutral groundwater under oxic conditions. The mechanism of U-uptake by fresh precipitates and the molecular structure of U bonding were determined to estimate the mobility of U(VI). Analytical and spectroscopic methods such as Extended X-ray Absorption Fine-Structure (EXAFS) spectroscopy at the Fe K-edge and the U L III-edge, and Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy were employed. The freshly formed precipitate was identified as colloidal two-line ferrihydrite. It removed U(VI) from solution by sorption processes, while surface precipitation or structural incorporation of U was not observed. EXAFS data suggest a mononuclear inner-sphere, edge-sharing complex of U(VI) with ferrihydrite in the absence of dissolved carbonate. By employing a novel EXAFS analysis method, Monte Carlo Target Transformation Factor Analysis, we could for the first time ascertain a 3-D configuration of this sorption complex without the necessity to invoke formation of a ternary complex. The configuration suggests a slightly tilted position of the adsorbed UO 2 2 + unit relative to the edge-sharing Fe(O, OH) 6 octahedra. In the presence of dissolved carbonate and at pH ∼8.0, a distal carbonate O-atom at ∼4.3 Å supports formation of ternary U(VI)-carbonato surface complexes. The occurrence of these complexes was also confirmed by ATR-FTIR. However, in slightly acidic conditions (pH 5–6) in equilibrium with atmospheric CO 2, the U(VI) sorption on ferrihydrite was dominated by the binary complex species Fe(O) 2 UO 2, whereas ternary U(VI)-carbonato surface complexes were of minor relevance. While sulfate and silicate were also present in the mine water, they had no detectable influence on U(VI) surface complexation. Our experiments demonstrate that U(VI) forms stable inner-sphere sorption complexes even in the presence of carbonate and at slightly alkaline pH, conditions which previously have been assumed to greatly accelerate the mobility of U(VI) in aqueous environments. Depending on the concentrations of U(VI) and carbonate, the type of surface complexes may change from binary uranyl-ferrihydrite to ternary carbonato-uranyl-ferrihydrite complexes. These different binding mechanisms are likely to influence the binding stability and retention of U(VI) at the macroscopic level.

Microbial Indicators of Nutrient Enrichment

Microbial communities are in close contact with the wetland soil microenvironment and can therefore function effectively as monitors of soil pollution. The objective of this study was to determine changes in the functional responses of microbial communities as a result of an external input of nutrients, while controlling for vegetation. A controlled experiment was performed at the mesocosm scale, consisting of two 1 m by 13 m raceways containing an organic peat soil, each planted with Cladium sp. and Typha sp. communities. One of the mesocosms was loaded with N (2 g N m−2 yr−1) and P (1 g P m−2 yr−1) for 18 mo. Nutrient loading resulted in increases in the soil and detritus labile nutrient pools, however, insufficient N and P where added to significantly alter their total levels. Over the experimental period, the extracellular enzyme acid phosphatase showed a significant decrease in activity across both plant communities (P < 0.01) in contrast to β‐glucosidase activity, which varied primarily by plant community. Other microbial response variables such as the microbial activities (CO2 and CH4 production, P = 0.0016 and 0.0213, respectively), microbial biomass (P = 0.0018) also varied primarily by vegetation type, with Typha sp. dominated areas exhibiting the highest level of activities. The nutrient dosing experiment indicated that the most immediate microbial response measures to nutrient enrichment are those directly associated to specific nutrients, such as P or N, while other measures showed a more complex response involving C source (e.g., vegetation type).

Phosphorus removal from Everglades agricultural area runoff by submerged aquatic vegetation/limerock treatment technology: an overview of research

The 1994 Everglades Forever Act mandates the South Florida Water Management District and the Florida Department of Environmental Protection to evaluate a series of advanced treatment technologies to reduce total phosphorus (TP) in Everglades Agricultural Area runoff to a threshold target level. A submerged aquatic vegetation/limerock (SAV/LR) treatment system is one of the technologies selected for evaluation. The research program consists of two phases. Phase I examined the efficiency of SAV/LR treatment system for TP removal at the mesocosm scale. Preliminary results demonstrate that this technology is capable of reducing effluent TP to as low as 10 microg/L under constant flows. The SAV component removes the majority of the influent soluble reactive P, while the limerock component removes a portion of the particulate P. Phase II is a multi-scale project (i.e., microcosms, mesocosms, test cells and full-size wetlands). Experiments and field investigations using various environmental scenarios are designed to (1) identify key P removal processes; (2) provide management and operational criteria for basin-scale implementation; and (3) provide scientific data for a standardized comparison of performance among advanced treatment technologies.

The use of passive integrated transponder systems (PIT) triggered by infrared‐gates for behavioural studies in nocturnal, bottom‐dwelling fish species

The movements of juvenile burbot Lota lota were monitored continuously with an overall efficiency of 92·5%. The results show that passive integrated transponder (PIT) systems (or variations of them) are highly valuable for behavioural studies of small nocturnal fish species at the laboratory or mesocosm scale.

Evaluation of the Galega–Rhizobiumgalegae system for the bioremediation of oil-contaminated soil

The bioremediation potential of a nitrogen-fixing leguminous plant, Galega orientalis, and its microsymbiont Rhizobium galegae was evaluated in BTX (benzene, toluene, xylene)-contaminated soils in microcosm and mesocosm scale. To measure the intrinsic tolerance of the organisms to m-toluate, a model compound representing BTX, G. orientalis and R. galegae were cultivated under increasing concentrations of m-toluate alone and in association with Pseudomonas putida pWWO, a bacterial strain able to degrade toluene-derived compounds. The test plants and rhizobia remained viable in m-toluate concentrations as high as 3000 ppm. Plant growth was inhibited in concentrations higher than 500 ppm, but restituted when plants were transferred into m-toluate-free medium. Nodulation was blocked under the influence of m-toluate, but was restored after the plants were transferred into the non-contaminated media. In the mesocosm assay the Galega plants showed good growth, nodulation and nitrogen fixation, and developed a strong rhizosphere in soils contaminated with oil or spiked with 2000 ppm m-toluate. Thus, this legume system has good potential for use on oil-contaminated sites

Carbon budgeting in plant–soil mesocosms under elevated CO2: locally missing carbon?

SummaryStudies have suggested that more carbon is fixed due to a large increase in photosynthesis in plant–soil systems exposed to elevated CO2 than could subsequently be found in plant biomass and soils –‐ the locally missing carbon phenomenon. To further understand this phenomenon, an experiment was carried out using EcoCELLs which are open‐flow, mass‐balance systems at the mesocosm scale. Naturally occurring 13C tracers were also used to separately measure plant‐derived carbon and soil‐derived carbon. The experiment included two EcoCELLs, one under ambient atmospheric CO2 and the other under elevated CO2 (ambient plus 350 μL L− 1). By matching carbon fluxes with carbon pools, the issue of locally missing carbon was investigated. Flux‐based net primary production (NPPf) was similar to pool‐based primary production (NPPp) under ambient CO2, and the discrepancy between the two carbon budgets (12 g C m− 2, or 4% of NPPf) was less than measurement errors. Therefore, virtually all carbon entering the system under ambient CO2 was accounted for at the end of the experiment. Under elevated CO2, however, the amount of NPPf was much higher than NPPp, resulting in missing carbon of approximately 80 g C m− 2 or 19% of NPPf which was much higher than measurement errors. This was additional to the 96% increase in rhizosphere respiration and the 50% increase in root growth, two important components of locally missing carbon. The mystery of locally missing carbon under elevated CO2 remains to be further investigated. Volatile organic carbon, carbon loss due to root washing, and measurement errors are discussed as some of the potential contributing factors.

EcoCELLs: tools for mesocosm scale measurements of gas exchange.

We describe the use of a unique plant growth facility, which has as its centerpiece four 'EcoCELLs', or 5x7 m mesocosms designed as open-flow, mass-balance systems for the measurement of carbon, water and trace gas fluxes. This system is unique in that it was conceived specifically to bridge the gap between measurement scales during long-term experiments examining the function and development of model ecosystems. There are several advantages to using EcoCELLs, including (i) the same theory of operation as leaf level gas exchange systems, but with continuous operation at a much larger scale; (ii) the ability to independently evaluate canopy-level and ecosystem models; (iii) simultaneous manipulation of environmental factors and measurement of system-level responses, and (iv) maximum access to, and manipulation of, a large rooting volume. In addition to discussing the theory, construction and relative merits of EcoCELLs, we describe the calibration and use of the EcoCELLs during a 'proof of concept' experiment. This experiment involved growing soybeans under two ambient CO2 concentrations (approximately 360 and 710 micromoles mol-1). During this experiment, we asked 'How accurate is the simplest model that can be used to scale from leaf-level to canopy-level responses?' in order to illustrate the utility of the EcoCELLs in validating canopy-scale models.