Mesocosm-scale Experiment Research Articles

Slurry acidification is as effective as slurry injection at reducing ammonia emissions without increasing N2O emissions: A short-term mesocosm study

Agriculture currently accounts for 90% of UK ammonia (NH3) emissions, however, national legally-binding targets are seeking to reduce this by 16% by 2030, relative to 2005 levels. One area which has been targeted to help achieve this target is the lowering of NH3 emissions during livestock manure handling and storage. Slurry acidification represents one potential strategy to abate NH3 throughout the slurry management chain, however, is not currently used in the UK. To address this knowledge gap, two mesocosm-scale experiments were set up to assess the potential for slurry acidification to reduce NH3 emissions at application and to measure impacts on NH3 emissions and short-term changes to soil mineral dynamics and N2O emissions. Experiment 1 determined the impacts of acidified cattle slurry (pH 6.5, 5.5, and 4.8) to conventional (non-acidified) slurry when simulating surface broadcasting. Experiment 2 assessed the impact of conventional and acidified slurry (pH 5.5) using simulated surface broadcasting and shallow injection of cattle slurry. Our results showed that acidification significantly abated NH3 (% of NH4-N applied) from 61.6% for conventional slurry to 26.6% at pH 5.5, and 2.5% at pH 4.8. Acidified surface broadcast was as effective at abating NH3 emissions to injected conventional slurry, and also delayed nitrification, while not significantly altering N2O emissions from conventional slurry. Our results strongly suggest that slurry acidification could be a viable strategy to help the UK reach its NH3 reduction target and exceed the current abatement potential through combining low emissions spreading techniques with acidification.

Soil amendments reduce CH4 and CO2 but increase N2O and NH3 emissions in saline-alkali paddy fields

Limited research has been conducted on ammonia (NH3) volatilization and greenhouse gases (GHGs) emissions in saline-alkali paddy fields, along with complex interaction involving various genes (16sRNA, amoA, narG, nirK, nosZ, and nifH). This study employed mesocosm-scale experiment to investigate NH3 volatilization and GHGs emissions, focusing on bacterial communities and genic abundance, in saline-alkali paddy fields with desulfurized gypsum (DG) and organic fertilizer (OF) amendments. Compared to the control (CK) treatment, DG and OF treatments reduced methane (CH4) and carbon dioxide (CO2) emissions by 78.05 % and 26.18 %, and 65.84 % and 11.62 %, respectively. However, these treatments increased NH3 volatilization by 26.26 % and 45.23 %, and nitrous oxide (N2O) emission by 41.00 % and 12.31 %. Notably, NH3 volatilization primarily stemmed from ammonia nitrogen (NH4+-N), rather than total nitrogen (TN) in soil and water. N2O was mainly produced from nitrate nitrogen (NO3−-N) in soil and water, as well as NH4+-N in water. The increase in NH3 volatilization and N2O emission in DG and OF treatments, was attributed to the reduced competition among bacterial communities, rather than the increased bacterial activity and genic copies. These findings offer valuable insights for managing nutrient loss and gaseous emissions in saline-alkali paddy fields.

Assessing the efficacy and mechanisms of glycol-contaminated water treatment through floating treatment wetlands

Abstract The growing concerns surrounding water pollution and the degradation of ecosystems worldwide have led to an increased use of nature-based solutions (NbSs). This study assessed the feasibility of using floating treatment wetlands (FTWs) as an NbS to treat propylene glycol-contaminated water and quantitatively investigated different removal pathways. With an environmentally relevant concentration of propylene glycol (1,250 mg/L), FTWs containing Acorus calamus and mixed species demonstrated the highest average glycol mass removal efficacy (99%), followed by Carex acutiformis (98%), Juncus effusus (93%), and the control group without plants (10%) after 1 week. Additional mesocosm-scale experiments with varying FTW configurations, including surface coverage to reduce evaporation and photodegradation processes, and the addition of antibiotics to inhibit microbial activity, were conducted to quantify glycol removal pathways. Mass balance analysis results revealed that microbial biodegradation (33.3–39.7%) and plant uptake (37.9–45.2%) were the primary pathways for glycol removal. Only 15.5–19.5% of the glycol removal via evaporation and photodegradation was accounted in this study, which may be attributed to the mesocosm experimental setup (static water and no wind). Aligned with the broader discussion regarding biodiversity improvements and carbon storage capacity, this study demonstrated that FTWs are an environmentally friendly and effective NbS for addressing glycol-contaminated water.

Contrasting effects of biochar application rate in an alkaline desert cropland soil

Improving water and nutrient retention in desert croplands using soil organic amendments can be a major challenge because organic matter decomposes quickly under irrigated conditions in a hot climate. Biochar—a long-lasting carbon-rich soil organic amendment—has been proposed to improve soil water and nutrient retention, but only by carefully selecting an appropriate application rate. To better understand effects of biochar application rate on soil water and nutrient retention in desert croplands, we set up a mesocosm-scale experiment with biochar added at rates of 0, 19.8, 39.7, 79.4, 119.0, and 158.7 t ha−1 to an alkaline, sandy loam soil. After initial water retention measurements, we added fertilizer and then measured gaseous nitrogen losses as well as soil nitrate (NO3−) and phosphate (PO₄³⁻) leaching. Then, we measured biochar's effect on the soil's capacity to hold plant-available water (i.e., available water capacity, or AWC) using Tempe cells and a dewpoint potentiometer. We found contrasting effects of low and high biochar application rates. First, we found that applying a minimum of 79.4 t ha−1 biochar was necessary to improve soil water and PO₄³⁻ retention; application rates below 79.4 t ha−1 exacerbated PO₄³⁻ leaching whereas treatments above 79.4 t ha−1 improved AWC by up to 34% compared to the control treatment. While biochar application rate did not affect soil nitric oxide or ammonia emissions, we did find that low biochar application rates increased soil nitrous oxide emission while higher application rates reduced emission compared to soil with no biochar. Overall, we found that lower and higher rates of biochar application can have contrasting effects on soil water and nutrient retention in an alkaline, desert cropland soil. Therefore, farmers and other land managers must consider potential drawbacks of lower application rates and threshold responses of higher application rates prior to large-scale biochar use in arid agroecosystems.

Ammonia volatilization, greenhouse gas emissions and microbiological mechanisms following the application of nitrogen fertilizers in a saline-alkali paddy ecosystem

The application of nitrogen (N) fertilizer can promote rice yield, but is accompanied by considerable quantities of ammonia (NH3) volatilization and greenhouse gas (GHG) emissions. The effect of N-fertilization to these gas emissions in saline-alkali paddy ecosystems is unclear. A 137-day mesocosm-scale experiment was carried out to clarify the effect of different N-fertilizer application strategies on NH3 volatilization and GHG emissions in saline-alkali paddy ecosystems and to determine the microbiological mechanisms. Five N-fertilizer treatments consisting of control without N-fertilizer (CK), urea (U), urea with urease-nitrification inhibitors (UI), organic–inorganic compound fertilizer (OCF) and carbon-based slow-release fertilizer (CSF) were established. During the entire rice-growing season, the cumulative NH3 emissions of UI, OCF and CSF treatments were 22.60–25.55 % significantly (p < 0.05) higher than U, respectively. The cumulative methane emissions in all N-fertilizer treatments were decreased by 9.23–28.24 % compared with CK. The cumulative carbon dioxide emissions were U > CSF > OCF > CK > UI, and the cumulative nitrous oxide (N2O) emissions were U > CSF > UI > CK > OCF. The global warming potential of UI was 5.39–32.35 % lower than all the other treatments. Compared with the other N-fertilizer treatments, the relative abundance of N-related functional bacteria (e.g., Sphingomonas and Alphaproteobacteria) in OCF treatment was increased, and the (nirS + nirK)/nosZ ratio was reduced, thereby decreasing the N2O emission. Overall, U is a better choice for controlling NH3 volatilization in saline-alkali paddy ecosystems, whereas UI and OCF are more beneficial for reducing GHG emissions.

Application of floating wetlands for the improvement of degraded urban waters: Findings from three multi-year pilot-scale installations

Floating Treatment Wetlands (FTWs) are an emerging ecological engineering technology being applied the restoration of eutrophic urban water bodies. Documented water-quality benefits of FTW include nutrient removal, transformation of pollutants, and reduction in bacterial contamination. However, translating findings from short-duration lab and mesocosm scale experiments, into sizing criteria that might be applied to field installations is not straightforward. This study presents the results of three well established (>3 years) pilot-scale (40–280 m2) FTW installations in Baltimore, Boston, and Chicago. We quantify annual phosphorus removal through harvesting of above-ground vegetation and find an average removal rate of 2 g-P m−2. In our own study and in a review of literature, we find limited evidence of enhanced sedimentation as a pathway for phosphorus removal. In addition to water-quality benefits, FTW planted with native species, provide valuable wetland habitat; and theoretically improve ecological function. We document efforts to quantify the local effect of FTW installations on benthic and sessile macroinvertebrates, zooplankton, bloom-forming cyanobacteria, and fish. Data from these three projects suggest that, even on a small scale, FTW produce localized changes in biotic structure that reflect improving environmental quality. This study provides a simple and defensible method for sizing FTW for nutrient removal in eutrophic waterbodies. We propose several key research pathways which would advance our understanding of the effects FTW have on the ecosystem they are deployed in.

A Preliminary Study on Lupinus albus and Raphanus sativusGrown in Soil Affected by Oil Spillage.

Oil spills from pipelines are a hazardous contamination source for agricultural soils. We investigated the effects of petroleum hydrocarbon (PHC) soil contamination, resulting from a real diesel oil pipeline spill, on the growth of Lupinus albus and Raphanus sativus plants. These species are widely cultivated for food purposes and have not been previously tested in soils affected by oil spills. Mesocosm-scale experiments were conducted in a greenhouse, and the potential transfer of hydrocarbons from soil to plant was evaluated.The results indicated that hydrocarbons in soil altered the soil nutrient balance and adversely affected plant growth. The C > 12 content in the aerial part was lower in plants grown in the contaminated soil than in plants grown in the control soil. The reduction in plant growth was not related to the accumulation of hydrocarbons in plant tissue, but rather to the deterioration in soil quality due to the oil spill.

Co-incorporating leguminous green manure and rice straw drives the synergistic release of carbon and nitrogen, increases hydrolase activities, and changes the composition of main microbial groups

Rice straw (RS) was incorporated into paddy soil together with leguminous green manure (e.g., Chinese milk vetch, Astragalus sinicus L., MV) in a mesocosm-scale experiment and the enzyme activity and composition of main microbial groups were measured. Mixing MV and RS caused a synergistic release of residual C and N, leading to a low C/N ratio at the middle and late decomposition stages of the mixture and shortening the time to complete decomposition. Furthermore, the highest abundances of Gram-negative (G−) bacteria and fungi and the highest activities of α- and β-glucosidase, β-cellobiosidase, β-xylosidase, N-acetyl-glucosaminidase, and acid phosphomonoesterase were observed in the residue mixture, especially at the middle and late stages of the experiment. The residue decomposition rate was positively correlated with residual N and mineral N concentrations. Most hydrolases and both oxidase (phenol oxidase and peroxidase) activities, and G− bacterial (especially 18:1 ω5c, Photobacterium) abundance explained the decomposition of mixing residues. In conclusion, co-incorporation of MV and RS could stimulate their decomposition by retaining a relatively low C/N ratio, enhancing G− bacterial abundance and hydrolase activities. Introducing leguminous green manures in paddy fields may be an effective way to accelerate the decomposition of rice straw.

Effects of a native New Zealand freshwater mussel on zooplankton assemblages, including non-native Daphnia: a mesocosm experiment

Few studies have examined the effects of freshwater mussels on zooplankton in their native regions. We undertook an outdoor mesocosm-scale experiment to examine the effects of Echyridella menziesii, an endemic New Zealand mussel, on zooplankton composition. Experiments were undertaken in 125-L cylindrical drums that were randomly separated into the following three groups: seven control tanks with no mussels, seven treatment tanks with five mussels, and seven treatment tanks with 10 mussels each. Tanks were seeded with algae and zooplankton from a variety of small local water bodies, and monitored on Days 0, 5, 14 and 42. ANOSIM indicated that zooplankton composition among control and treatment tanks differed from Day 5 onward. Small, planktonic rotifers were commonly found to be most greatly affected by the presence of freshwater mussels. Benthic rotifers and larger crustacean zooplankton were typically unaffected or favoured when mussels were present. Overall, our results are consistent with removal of zooplankton by filtration, rather than competition for resources, being the primary driver of mussel influence on zooplankton community composition.

A mesocosm study of electrokinetic-assisted phytoremediation of atrazine-polluted soils

Phytoremediation, an ecological remediation technology based on the use of plants, can be combined with electrokinetic treatment for the removal of both inorganic and organic pollutants from soils. Electrokinetic-assisted phytoremediation (EKPR) of atrazine was tested in a mesocosm scale experiment using ryegrass (Lolium perenne L.). Two mock-ups with dimensions of 2.25 (L) × 0.49 (W) × 0.50 (H) m were initially filled with an unpolluted low plasticity clay soil and used to carry out an EKPR test and another electrokinetic remediation (EKR) one after spiking the soil with atrazine at a dose of 2 mg kg−1. Experiments were conducted for 19 days using a DC electrical field of 0.6 V cm−1 applied continuously without changing polarity. Samples of soil, plants and soil pore water corresponding to ten different soil sections of each mock-up were taken and analysed throughout the experiment. Soil pH followed an increasing profile from the anode to the cathode, although it kept moderate values in the range of 7.53–9.62. Electro-osmosis, gravity and plant roots (in the EKPR series) influenced the final distribution of water and atrazine in the soil. Additionally, the electromigration flux had a relevant role in the atrazine residues transport during the EKPR process. Concentration values of atrazine residues remaining in the different soil sections were in good agreement with those of the soil pore water, with most of the atrazine being accumulated in the cathode section. Atrazine was mainly removed from soils by biochemical degradation, which was greatly improved by ryegrass plants; the overall atrazine removal yield was increased from 40.20% (unplanted mock-up) to 61.01% (planted mock-up).

Combining electrokinetic transport and bioremediation for enhanced removal of crude oil from contaminated marine sediments: Results of a long-term, mesocosm-scale experiment

Marine sediments represent an important sink of harmful petroleum hydrocarbons after an accidental oil spill. Electrobioremediation techniques, which combine electrokinetic transport and biodegradation processes, represent an emerging technological platform for a sustainable remediation of contaminated sediments. Here, we describe the results of a long-term mesocosm-scale electrobioremediation experiment for the treatment of marine sediments contaminated by crude oil. A dimensionally stable anode and a stainless-steel mesh cathode were employed to drive seawater electrolysis at a fixed current density of 11 A/m2. This approach allowed establishing conditions conducive to contaminants biodegradation, as confirmed by the enrichment of Alcanivorax borkumensis cells harboring the alkB-gene and other aerobic hydrocarbonoclastic bacteria. Oil chemistry analyses indicated that aromatic hydrocarbons were primarily removed from the sediment via electroosmosis and low molecular weight alkanes (nC6 to nC10) via biodegradation.

Nutrient dynamics in core sediments of an artificial basal medium prepared with steelmaking slag and dredged materials

The availability of steelmaking slag, an industrial by-product, was examined as a component of a basal medium for the creation and regeneration of shallow habitats in coastal ecosystems. We investigated nutrient dynamics in sediments prepared with slag and dredged materials by conducting a core incubation experiment for 379 days. Silica sand was used as the reference material. Although slag caused alkalization of pore water, the pH in the surface layer recovered within a few days. The use of slag had limited influence on the dissolved inorganic nitrogen content, but pore water phosphate concentrations were considerably suppressed in slag-based media, especially when the pH was high. Nutrient diffusion fluxes from slag- and sand-based sediment cores were comparable to those in natural coastal environments. After 379 days, more than 90 % of the nutrients remained in the top 5 cm of the cores. Moreover, the sustained release of nutrients from basal media prepared with slag may play an important role in sustaining the productivity of macrophytobenthic ecosystems, including seagrass meadows. The mesocosm-scale experiment we proposed could evaluate long-term variations of nutrient dynamics in the artificial basal media. Because of wide variations in chemical properties among the different types of slag and dredged materials, approaches similar to this study may be essential before any large-scale application to marine environments.

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.

Ecotoxicity of contaminated sediments, a matter of bioavailability

Marine and freshwater mesocosm-scale experiments with contaminated sediments have shown that there is a direct relationship between the accumulated contaminant levels and the feeding habits of the organisms used. The highest levels of PAHs and PCBs were found in the sediment feeding lugworm Arenicola marina and in Tubifex worms. The levels of contaminants in the suspension feeding mussels Mytilus edulis and the zebra mussels, Dreissena polymorpha, were not influenced by the contaminant content of the sediments, but were related instead to the level of contaminants in the sea water above. Intermediate levels were found in the baltic tellin, Macoma balthica, which is a filter feeder as well as a deposit feeder, depending on the availability of food. These results show that there is no simple relationship between contaminant concentration in the sediments and bioavailability. Higher levels of contaminants do not necessarily lead to higher levels of these contaminants in Arenicola, due to differences in the sediment structure and the ageing of the contamination. On the other hand, toxic effects are related to the internal concentrations of certain chemicals. The internal concentrations observed in Arenicola may provide a good estimation of the true bioavailability of sedimentary contaminants and can also be used as an indicator for potential environmental effects.

Ecotoxicity of contaminated sediments, a matter of bioavailability

Marine and freshwater mesocosm-scale experiments with contaminated sediments have shown that there is a direct relationship between the accumulated contaminant levels and the feeding habits of the organisms used. The highest levels of PAHs and PCBs were found in the sediment feeding lugworm Arenicola marina and in Tubifex worms. The levels of contaminants in the suspension feeding mussels Mytilus edulis and the zebra mussels, Dreissena polymorpha, were not influenced by the contaminant content of the sediments, but were related instead to the level of contaminants in the sea water above. Intermediate levels were found in the baltic tellin, Macoma balthica, which is a filter feeder as well as a deposit feeder, depending on the availability of food.These results show that there is no simple relationship between contaminant concentration in the sediments and bioavailability. Higher levels of contaminants do not necessarily lead to higher levels of these contaminants in Arenicola, due to differences in the sediment structure and the ageing of the contamination. On the other hand, toxic effects are related to the internal concentrations of certain chemicals. The internal concentrations observed in Arenicola may provide a good estimation of the true bioavailability of sedimentary contaminants and can also be used as an indicator for potential environmental effects.

BIOAUGMENTATION AND BIOSTIMULATION: A PARADOX BETWEEN LABORATORY AND FIELD RESULTS

ABSTRACT In both shaker-flask and mesocosm-scale experiments, a commercial oleophilic bioremediation agent containing biostimulation (nutrients) and bioaugmentation (bacterial inocula) properties was more effective in enhancing oil biodegradation rates than that of no treatment and/or periodic inorganic nutrient addition. However, similar results were not obtained from a subsequent 129-day field trial conducted in a sand beach environment. In this case, periodic additions of inorganic nutrients, with and without the commercial bioremediation agent, enhanced the number of heterotrophic bacteria and microbial respiration rates within the oiled sediments. The commercial product appeared to elevate the number of oil-degrading bacteria within the oiled sediment between days 17 and 89. However, the addition of inorganic nutrients alone, on a periodic basis, was the most effective means of enhancing the extent of oil biodegradation within the residual oil and of reducing sediment toxicity. By retaining residual oil and altering the physical and chemical characteristics of the treated sediment, the oleophilic product suppressed both the rate and extent of oil loss by tidal activity and biodegradation. This is not to say that the use of the product was ineffective in protecting the environment or was detrimental to it; the product does enhance natural biodegradation rates, and it limits the transport of beached oil to more sensitive areas. This study clearly illustrates the complexity associated with the selection of bioremediation agents, the need for improved experimental protocols for evaluating the performance and toxicity of bioremediation agents, and the potential of nutrient enrichment as a bioremediation strategy.

Kinetic Models for Describing Degradation of AOX in the Waste Water of a Mill Producing Bleached Sulphate Pulp

In the study, submodels for describing degradation of organic chlorine (measured as AOX) coming from a mill producing bleached sulphate pulp were developed. The submodels coupled to a hydrodynamic model can then be used in assessing the behaviour of AOX in receiving waters. The data used in developing the models was based on mesocosm-scale experiments carried out in two lakes. Waste waters of two mills were used at two dilutions (2% and 10%). Part of the mesocosms were darkened in order to study the effect of light on degradation. In the first phase of the modelling first-order kinetics with a constant coefficient were used. The next steps were to include the effect of temperature and light in the model. Including temperature and light did not much contribute to the modelling results. It was found that more than half of the degradation was caused by the light-dependent component of the degradation reaction. The reaction obeys first order kinetics satisfactorily. However, the reaction coefficient is greater in the beginning of the experiment than later. A correction function describing the decrease of the reaction coefficient was included in the model. The correction function is based on the idea that the most readily decaying components of AOX disappear from the solution in the beginning and therefore the apparent reaction coefficient decreases. Only data on AOX was available in this study but the approach can be applied for different chloro- organic compounds and also for other organic substances.