Mesocosm System Research Articles

Microbial food web changes induced by terrestrial organic matter and elevated temperature in the coastal northern Baltic Sea

Climate change has been projected to cause increased temperature and amplified inflows of terrestrial organic matter to coastal areas in northern Europe. Consequently, changes at the base of the food web favoring heterotrophic bacteria over phytoplankton are expected, affecting the food web structure. We tested this hypothesis using an outdoor shallow mesocosm system in the northern Baltic Sea in early summer, where the effects of increased temperature (+ 3°C) and terrestrial matter inputs were studied following the system dynamics and conducting grazing experiments. Juvenile perch constituted the highest trophic level in the system, which exerted strong predation on the zooplankton community. Perch subsequently released the microbial food web from heavy grazing by mesozooplankton. Addition of terrestrial matter had a stronger effect on the microbial food web than the temperature increase, because terrestrial organic matter and accompanying nutrients promoted both heterotrophic bacterial production and phytoplankton primary production. Moreover, due to the shallow water column in the experiment, terrestrial matter addition did not reduce the light below the photosynthesis saturation level, and in these conditions, the net-autotrophy was strengthened by terrestrial matter enrichment. In combination with elevated temperature, the terrestrial matter addition effects were intensified, further shifting the size distribution of the microbial food web base from picoplankton to microphytoplankton. These changes up the food web led to increase in the biomass and proportion of large-sized ciliates (>60 µm) and rotifers. Despite the shifts in the microbial food web size structure, grazing experiments suggested that the pathway from picoplankton to nano- and microzooplankton constituted the major energy flow in all treatments. The study implies that the microbial food web compartments in shallow coastal waters will adjust to climate induced increased inputs of terrestrial matter and elevated temperature, and that the major energy path will flow from picoplankton to large-sized ciliates during the summer period.

Mitigation of soil nitrous oxide emissions during maize production with basalt amendments

Nitrous oxide (N2O) is a potent and long-lived greenhouse gas that accounts for roughly 6% of global anthropogenic greenhouse gas emissions, and it has risen from its preindustrial concentration of 270 ppb N2O to 332 ppb N2O as a result of human activities. The majority of anthropogenic N2O emissions (52–80%) come from agricultural settings due to high rates of reactive nitrogen fertilizer application. Amending soils with fine-grained basalt is gaining traction as a carbon dioxide removal (CDR) pathway, and model simulations suggest that this process may also significantly decrease soil N2O emissions. Here, we continuously measure N2O fluxes from large-scale maize mesocosms in a greenhouse setting and use a machine learning framework to assess the relative importance of the levers on N2O fluxes. We observe significant decreases in cumulative N2O emissions (between 29–32%) from mesocosm systems with basalt addition. We find that basalt application rate, soil pH, and surface soil moisture are the strongest levers on N2O emissions depending on the system settings. These results provide empirical support for a potentially significant co-benefit of deploying enhanced rock weathering of silicates (ERW) on managed lands, particularly those subject to elevated rates of reactive nitrogen input.

Investigating the behavior of ultratrace levels of nanoparticulate and ionic silver in a seawater mesocosm using single particle inductively coupled plasma – mass spectrometry

Silver nanoparticles (AgNPs) nowadays appear in close to 24% of consumer products that contain engineered nanomaterials. Thus, they are expected to be released into the environment, where their fate and effect are still undetermined. Considering the evidenced efficacy of the single particle Inductively Coupled Plasma – Mass Spectrometry (sp ICP-MS) technique in the study of nanomaterials, this work reports on the use of sp ICP-MS along with an online dilution sample introduction system for the direct analysis of untreated and spiked seawater samples, as part of a larger scale experiment studying the fate of Ag (ionic and nanoparticles) in seawater mesocosm systems. Silver nanoparticles coated with branched polyethyleneimine (BPEI@AgNPs) or ionic silver (Ag+) were introduced gradually into the seawater mesocosm tanks at very low, environmentally relevant concentrations (50 ng Ag L−1 per day, for 10 consecutive days, up to a total of 500 ng Ag L−1), and samples were collected and analyzed daily, within a consistent time window. Using very low detector dwell time (75 μs) and specialized data treatment, information was obtained on the nanoparticles’ size distribution and particle number concentration, as well as the ionic silver content, of both the AgNPs and the Ag+ treated seawater mesocosm tanks. The results for the AgNP treated samples indicated the rapid degradation of the added silver particles, and the subsequent increase of ionic silver, with recoveries close to 100% for the first days of the experiment. On the other hand, particle formation was observed in the Ag+ treated seawater tanks, and even though the number concentration of silver-containing nanoparticles increased throughout the experiment, the amount of silver per particle remained relatively constant from the early days of the experiment. In addition, the online dilution sample introduction system for the ICP-MS proved capable of handling the untreated seawater matrix without significant contamination issues and downtime, while the low dwell time and data treatment procedure developed were shown to be suitable for the analysis of nanomaterials at the low nm-scale, despite the complex and heavy matrix introduced into the ICP-MS.

Sequential application of activated sludge and phytoremediation with aquatic macrophytes on tannery effluents: in search of a complete treatment.

Tannery effluents with a high organic matter load (indicated by their COD level) have to be treated before they are discharged, so as to minimize their negative impact on the environment. Using field mesocosm systems, this study evaluated the feasibility of treating such effluents through bioaugmentation with activated sludge, followed by phytoremediation with aquatic macrophytes (Lemnoideae subfamily). Regardless of its quality, the activated sludge was able to remove approximately 77% of the COD from effluents with a low initial organic load (up to 1500 mg/L). The macrophytes then enhanced removal (up to 86%), so the final COD values were permissible under the current legislation for effluent discharge. When the initial organic load in the undiluted effluents was higher (around 3000 mg/L), the COD values obtained after consecutive bioaugmentation and phytoremediation were close to the legally allowed limits (583 mg/L), which highlights the potential of phytoremediation as a tertiary treatment. This treatment also brought total coliform counts down to legally acceptable values, without plant biomass decreasing over time. Moreover, the plant biomass remained viable and capable of high COD removal efficiency (around 75%) throughout two additional reuse cycles. These findings indicate that the efficiency of the biological treatments assayed here depends largely on the initial organic load in the tannery effluents. In any case, the sequential application of activated sludge and aquatic macrophytes proved to be a successful alternative for remediation.

Dolomite and organic compost application for preventing acid mine drainage formation in a mesocosm system

Acid mine drainage (AMD) is one of most serious environmental problems facing mining industries. It results from oxidation of sulfide minerals contained in mining wastes, such as rock disposals in mine sites. This study was to investigate AMD formation from waste rocks containing potentially-acid forming (PAF) materials treated with dolomite and compost in a mesocosm system. The system comprised a plastic drum of 150-cm height and 50-cm diameter filled with 15-cm sand at the botom layer, over-laid by 50-cm mixture of PAF+10% of either dolomite or compost, and 35-cm top-soil layer on the top. The drum surface of the sand layer was equipped with a valve to drain leached water into a collecting container. The control was a similar constructed mesocosm without addition of either ameliorant. The drums were installed into the ground of the mined land so that their surfaces were as high as the surrounding soil surface and left under field condition. The leachate samples were taken two-weekly in the early two months and monthly until the day 487. The system demonstrated that both dolomite and compost significantly increased pH from around 3 to pH>6 and reduced dissolved Al and Fe concentrations. However, the dissolved Mn concentration was still high (>20 mg L−1) in all treatments even at the pH reached >6. .

How climate warming and plant diversity affect carbon greenhouse gas emissions from boreal peatlands: Evidence from a mesocosm study

Understanding synchronous vegetation changes are crucial to assess the impact of carbon cycle on climate warming in peatlands. We established a mesocosm system to monitor ecosystem respiration (Re) and methane (CH4) fluxes in the growing season from 2020 to 2021 under different scenarios, including warming and manipulations of species diversity. Overall, the mean Re and CH4 fluxes varied in the ranges of 1.38 ± 0.18 to 46.25 ± 6.62 mg CO2–C m−2 h−1 and 2.72 ± 2.36 to 319.55 ± 96.22 μg CH4–C m−2 h−1, respectively, with the highest values appearing in the middle of growing season. The Re and CH4 fluxes in L-III and L-IV mesocosms showed significant increases of 38.86% and 54.28%, and 56.38% and 107.54%, respectively, compared to the monoculture treatment. The primary controls for this phenomenon were the plant biomass and the concentrations of dissolved organic carbon and phenolics. Warming significantly increased the emissions of CO2 by ∼40% during the study period, but it reduced the fluxes of CH4 in 2021. Sustained warming and soil water loss may destroy the original anaerobic environment, which plays a role in inhibiting the generation and emission of CH4 in the long term. Interestingly, although warming has reduced CH4 emissions, a mixture of three and four species seems to buffer more than 50% of this impact, further demonstrating the positive contribution of species diversity. Our results indicate that an increase in species diversity, specifically manifested in the expansion of vascular plants as a community process adapting to warming, can strongly affect carbon fluxes in peatlands and create potential feedback on future climate environments.

Temporal disturbance of a model stream ecosystem by high microbial diversity from treated wastewater.

Microbial communities in freshwater streams play an essential role in ecosystem functioning via biogeochemical cycling. Yet, the impacts of treated wastewater influx into stream ecosystems on microbial strain diversity remain mostly unexplored. Here, we coupled full-length 16S ribosomal RNAgene Nanopore sequencing and strain-resolved metagenomics to investigate the impact of treated wastewater on a mesocosm system (AquaFlow) run with restored river water. Over 10 days, community Bray-Curtis dissimilarities between treated and control mesocosm decreased (0.57 ± 0.058 to 0.26 ± 0.046) based on ribosomal protein S3 gene clustering, finally converging to nearly identical communities. Similarly, strain-resolved metagenomics revealed a high diversity of bacteria and viruses after the introduction of treated wastewater; these microbes also decreased over time resulting in the same strain clusters in control and treatment at the end of the experiment. Specifically, 39.2% of viral strains detected in all samples were present after the introduction of treated wastewater only. Although bacteria present at low abundance in the treated wastewater introduced additional antibiotic resistance genes, signals of naturally occurring ARG-encoding organisms resembled the resistome at the endpoint. Our results suggest that the previously stressed freshwater stream and its microbial community are resilient to a substantial introduction of treated wastewater.

Disposable surgical masks affect the decomposition of Zostera muelleri

The coronavirus pandemic has caused a surge in the use of both disposable and re-usable mask pollution globally. It is important to understand the potential impact this influx of novel pollution has on key ecological processes, such as detrital dynamics. We aimed to understand the impact mask pollution has on the decomposition of a common coastal seagrass, Zostera muelleri. Using an outdoor mesocosm system with heater chiller units and a gas mixer, we were able to test the impact of both re-usable single-ply homemade cotton masks and disposable surgical masks on samples of Z. muelleri detritus under different environmental conditions. We found that disposable masks, but not re-usable masks, significantly increased decomposition of Z. muelleri detritus. This may be due to the increased surface area available for detritivorous microorganism colonisation, driving further decomposition. This could have negative ramifications for seagrass communities and adjacent ecosystems.

Fragmentation and depolymerization of microplastics in the earthworm gut: A potential for microplastic bioremediation?

The accumulation of microplastics poses potential risks to soil health. Here, we did a preliminary exploration on the potential of Lumbricus terrestris (Oligochaeta) to reduce low-density polyethylene (LDPE), polylactic acid (PLA), and polybutylene adipate terephthalate (PBAT) microplastic (20–648 µm) contamination in soils. The ingestion of microplastics-contaminated soil (1% of microplastics, dw/dw) in a mesocosm system and the ingestion of pure microplastics in the Petri Dish by earthworms were studied. Results show that earthworms survived in the microplastics-contaminated soil (0% mortality in 35 days) but barely when exposed solely to microplastics (30–80% mortality in 4 days). Size-dependent ingestion of microplastics was not observed. The fragmentation of LDPE microplastics in the gizzard facilitated by soil was confirmed by the significantly increased ratio of small-sized (20–113 µm) microplastics from the bulk soil to the gut (from 8.4% to 18.8%). PLA and PBAT microplastics were fragmented by gizzard without the facilitation of soil, the ratios of small-sized (20–113 µm) PLA and PBAT microplastics in the gut were 55.5% and 108.2% higher than in respective pristine distributions. Substantial depolymerization of PLA (weight-average molar mass reduced by 17.7% with shift in molecular weight distribution) and suspected depolymerization of PBAT were observed in the worm gut, while no change in the molar mass was observed for PLA and PBAT microplastics buried in the soil for 49 days. Our results suggest that ingested microplastics could undergo fragmentation and depolymerization (for certain polymers) in the earthworm gut. Further research is needed to reveal the mechanisms of polymer depolymerization in the earthworm gut and to evaluate the feasibility of microplastic bioremediation with earthworms.

Responses of rubber tree seedlings (Hevea brasiliensis) to phosphorus deficient soils

ABSTRACT While the adaptation and responses of model plants to phosphorus (P) deficiency are well documented, those of the rubber tree remain unclear. Here, we investigated above‐ and below‐ground responses of rubber tree seedlings over the development of the first to third extension unit in a mesocosm system. Rubber tree seedlings were grown in high and low phosphorus soil for 7 months. Tissue nutrient contents, morphological, and physiological traits were quantified. We found that low P significantly reduced leaf P content, photosynthetic capabilities, and induced the accumulation of phenolic and flavonoid compounds, particularly in old leaves. Root traits were significantly affected by P stress early in their development. Root surface area and volume were increased through reduced lateral root branching and increased lateral root length. The alteration of root architectural traits took place prior to the reduction of P content in roots and leaves. Our findings provide new insights into rubber tree physiology and the effective fertilization management of rubber plantation in low P soils.

Evaluating the survival and growth rate of Acropora digitifera in wild and mesocosm systems

The growing interest in coral culture for restoration and biotechnological applications has prompted researchers to improve their understanding of coral culture, with a focus on ex-situ production. This study aimed to understand the performance of common hard coral, Acropora digitifera by examining their survival and growth at Pulau Bidong (in-situ) and in a mesocosm system (ex-situ). First, three branches were tagged from each of eight A. digitifera colonies (n = 24). Mortality and linear extension rate were recorded monthly, from July - November 2018. Meanwhile, five branches from each tagged colony were brought back to a mesocosm set up at the hatchery in the Institute of Tropical Aquaculture (AKUATROP), Universiti Malaysia Terengganu (UMT) for the ex-situ experiment. All coral nubbins (n=40) were then divided into two coral size groups: small (<5cm) and large (>5cm). After four months, small nubbins showed 100% survivorship, while large nubbins survived for only two months. In contrast, 67% of wild colonies remained alive. However, nubbins in mesocosm extent with almost 2-folds slower (0.091 + 0.027 mm day-1) than those in the wild (0.166 + 0.033 mm day-1). Coral nubbins in mesocosm form a basal self-attachment “disc” at the bottom. This suggests that fragmented corals invest more energy in self-stabilization, especially in the early stage of transplantation, which affects their linear growth. This study demonstrates the different demographic traits for corals in both the environments.

Benthic macroinvertebrate community shifts based on Bti-induced chironomid reduction also decrease Odonata emergence

Chironomid larvae (Diptera: Chironomidae) often dominate aquatic macroinvertebrate communities and are a key food source for many aquatic predators, such as dragonfly and damselfly larvae (Odonata). Changes in aquatic macroinvertebrate communities may propagate through terrestrial food webs via altered insect emergence. Bacillus thuringiensis israelensis (Bti)-based larvicides are widely used in mosquito control but can also reduce the abundance of non-biting chironomid larvae. We applied the maximum field rate of Bti used in mosquito control three times to six mesocosms in a replicated floodplain pond mesocosm (FPM) system in spring for two consecutive years, while the remaining six FPMs were untreated. Three weeks after the third Bti application in the first year, we recorded on average a 41% reduction of chironomid larvae in Bti-treated FPMs compared to untreated FPMs and a shift in benthic macroinvertebrate community composition driven by the reduced number of chironomid, Libellulidae and Coenagrionidae larvae (Odonata). Additionally, the number of emerging Libellulidae (estimated by sampling of exuviae in the second year) was reduced by 54% in Bti-treated FPMs. Since Odonata larvae are not directly susceptible to Bti, our results suggest indirect effects due to reduced prey availability (i.e., chironomid larvae) or increased intraguild predation. As Libellulidae include species of conservation concern, the necessity of Bti applications to their habitats, e.g. floodplains, should be carefully evaluated.

Antifouling coatings can reduce algal growth while preserving coral settlement

In the early stages after larval settlement, coral spat can be rapidly overgrown and outcompeted by algae, reducing overall survival for coral reef replenishment and supply for restoration programs. Here we investigated three antifouling (AF) coatings for their ability to inhibit algal fouling on coral settlement plugs, a commonly-used restoration substrate. Plugs were either fully or partially coated with the AF coatings and incubated in mesocosm systems with partial recirculation for 37 days to track fouling succession. In addition, settlement of Acropora tenuis larvae was measured to determine whether AF coatings were a settlement deterrent. Uncoated control plugs became heavily fouled, yielding only 4–8% bare substrate on upper surfaces after 37 days. During this period, an encapsulated dichlorooctylisothiazolinone (DCOIT)-coating was most effective in reducing fouling, yielding 61–63% bare substrate. Antiadhesive and cerium dioxide (CeO2−x) nanoparticle (NP) coatings were less effective, yielding 11–17% and 2% bare substrate, respectively. Average settlement of A. tenuis larvae on the three types of AF-coated plugs did not statistically differ from settlement on uncoated controls. However, settlement on the NP-coating was generally the highest and was significantly higher than settlement found on the antiadhesive- and DCOIT-coating. Furthermore, on plugs only partially-covered with AF coatings, larval settlement on coated NP- areas was significantly higher than settlement on coated antiadhesive- and DCOIT-areas. These results demonstrate that AF coatings can reduce fouling intensity on biologically-relevant timescales while preserving robust levels of coral settlement. This represents an important step towards reducing fine-scale competition with benthic fouling organisms in coral breeding and propagation.

Brownification of freshwater promotes nitrogen-cycling microorganism growth following terrestrial material increase and ultraviolet radiation reduction

Brownification is an increasingly concerning phenomenon faced by aquatic ecosystems in the changing environments, and the microbiome plays an irreplaceable role in material circulation and food web construction. Insight into the influence of brownification on microbial communities is crucial from an ecological standpoint. In this study, we simulated brownification using a the mesocosm system and explored the relationship between the characteristics of microbial communities and brownification using excitation-emission matrix (EEM) fluorescence spectroscopy and ultraviolet (UV) spectroscopy combined with high-throughput amplicon sequencing techniques. The results showed that brownification reduced the richness of the microbial community and selectively promoted the growth of nitrogen-cycling microorganisms, including hgcI_clade, Microbacteriaceae, and Limnohabitans. Brownification affected microbial communities by altering the carbon source composition and underwater spectrum intensity; UV, blue, violet, and cyan light were significantly (p < 0.05) correlated with microbial community richness, and random forest analysis revealed that UV, C1 (microbial humic-like), and C3 (terrestrial humic-like) were the major factors significantly influencing microbiome variation. We found that brownification affected microorganisms in shallow lakes, especially nitrogen cycling microorganisms, and propose that controlling terrestrial material export is an effective strategy for managing freshwater brownification.

In-situ manipulations of aquatic optical depth and its effect on small unoccupied aerial systems–derived spectral reflectance

The collection of spectral data with sensors fixed to various platforms (e.g., satellites, occupied aerial vehicles, and small unoccupied aerial systems (sUAS)) has allowed for the estimation of optically active constituents (OACs) common in surface waters. However, in small, complex, and optically shallow waters where multiple OACs (e.g., chlorophyll-a and total suspended solids) impact the spectral signature, these technologies have experienced significant limitations. Altering the scale at which these examinations are performed on surface waters (e.g., ponds and lakes) to mesocosm systems (37 cm in height and 30 cm in diameter) provides information on the interactions between multiple OACs and insight on the impact aquatic optical depth has on remotely sensed spectra. This field study examines optically shallow and optically deep mesocosm systems simulated in five-gallon buckets to determine the role aquatic optical depth has on developing accurate surface-water quality models. Results demonstrated an accurate representation of OACs in optically deep mesocosms compared with optically shallow mesocosms when assessed with sUAS (i.e., relative percent differences in predicted iron concentrations of −86 and 16 for optically shallow and deep waters, respectively). The interferences observed under these conditions were comparable to literature values when studying optically complex water bodies with hyperspectral data. This study provides a basis for understanding the benefits and limitations of monitoring in-situ water quality via sUAS.

The effects of ecological selection on species diversity and trait distribution: predictions and an empirical test.

Ecological selection is a major driver of community assembly. Selection is classified as stabilizing when species with intermediate trait values gain the highest reproductive success, whereas selection is considered directional when fitness is highest for species with extreme trait values. Previous studies have investigated the effects of different selection types on trait distribution, but the effects of selection on species diversity have remained unclear. Here, we propose a framework for inferring the type and strength of selection by studying species diversity and trait distribution together against null expectations. We use a simulation model to confirm our prediction that directional selection should lead to lower species diversity than stabilizing selection despite a similar effect on trait community-weighted variance. We apply the framework to a mesocosm system of annual plants to test whether differences in species diversity between two habitats that vary in productivity are related to differences in selection on seed mass. We show that, in both habitats, species diversity was lower than the null expectation, but that species diversity was lower in the more productive habitat. We attribute this difference to strong directional selection for large-seeded species in the productive habitat as indicated by trait community-weighted mean being higher and community-weighted variance being lower than the null expectations. In the less productive habitat, we found that community-weighted variance was higher than expected by chance, suggesting that seed mass could be a driver of niche partitioning under such conditions. Altogether, our results suggest that viewing species diversity and trait distribution as interrelated patterns driven by the same process, ecological selection, is helpful in understanding community assembly.

Morphological, physiological and behavioral responses of an intertidal snail, Acanthina monodon (Pallas), to projected ocean acidification and cooling water conditions in upwelling ecosystems

Ocean acidification (OA) is expected to rise towards the end of the 21st century altering the life history traits in marine organisms. Upwelling systems will not escape OA, but unlike other areas of the ocean, cooling effects are expected to intensify in these systems. Regardless, studies evaluating the combined effects of OA and cooling remain scarce. We addressed this gap using a mesocosm system, where we exposed juveniles of the intertidal muricid snail Acanthina monodon to current and projected pCO2 (500 vs. 1500 ppm) and temperature (15 vs. 10 °C) from the southeast Pacific upwelling system. After 9 weeks of experimental exposure to those conditions, we conducted three estimations of growth (wet weight, shell length and shell peristomal length), in addition to measuring calcification, metabolic and feeding rates and the ability of these organisms to return to the normal upright position after being overturned (self-righting). Growth, feeding and calcification rates increased in projected cooling conditions (10 °C) but were unaffected by pCO2 or the interaction between pCO2 and temperature. Instead, metabolic rates were driven by pCO2, but a significant interaction with temperature suggests that in cooler conditions, metabolic rates will increase when associated with high pCO2 levels. Snail self-righting times were not affected across treatments. These results suggest that colder temperatures projected for this area would drive this species growth, feeding and calcification, and consequently, some of its population biology and productivity. However, the snails may need to compensate for the increase in metabolic rates under the effects of ocean acidification. Although A. monodon ability to adjust to individual or combined stressors will likely account for some of the changes described here, our results point to a complex dynamic to take place in intertidal habitats associated with upwelling systems.

Solar Radiation as an Isolated Environmental Factor in an Experimental Mesocosm Approach for Studying Photosynthetic Acclimation of Macrocystis pyrifera (Ochrophyta).

Solar radiation effects on the ecophysiology and biochemical responses of the brown macroalga Macrocystis pyrifera (L.) C. Agardh were evaluated using a mesocosm approach in Southern Chile. Treatments with different radiation attenuations were simulated with three vertical attenuation coefficients: (1) total (Kd = 0.8 m−1), (2) attenuated (Kd = 1.2 m−1), and (3) low (Kd = 1.6 m−1) radiation levels. Nutrient concentration and temperature did not show differences under the three light conditions. Photosynthetic activity was estimated by in vivo chlorophyll a (Chla) fluorescence under the three light treatments as an isolated physical factor in both in situ solar radiation in the field. This was achieved using a pulse amplitude-modulated (PAM) fluorometera—Diving PAM (in situ). Photosynthetic activity and biochemical composition were measured in winter during two daily cycles (1DC and 2DC) in different parts of the thalli of the plant: (1) canopy zone, (2) middle zone, and (3) down zone, associated with different depths in the mesocosm system. Nevertheless, the in situ electron transport rate (ETRin situ) was higher in the exposed thalli of the canopy zone, independent of the light treatment conditions. The concentration of phenolic compounds (PC) increases in the down zone in the first daily cycle, and it was higher in the middle zone in the second daily cycle. The Chla increased in the morning time under total and attenuated radiation in the first daily cycle. Solar radiation increasing at midday prompted the photoinhibition of photosynthesis in the canopy zone but also an increase in productivity and phenol content. Therefore, light attenuation in the water column drove key differences in the photo-physiological responses of M. pyrifera, with the highest productivity occurring in thalli positioned in the canopy zone when exposed to solar irradiance.

Exposure to elevated nutrient load results in structural and functional changes to microbial communities associated with riparian wetland plants Phalaris arundinaceae and Veronica anagallis-aquatica

The goal of this study was to better understand the resilience of rhizosphere microbial communities located in riparian wetlands subjected to high nutrient loads following effluent or runoff exposure. Specifically, this research monitored functional profiles of mesocosm communities during an artificial high nitrogen load exposure following adaptation to high or low water quality conditions. Based on prior research, two species of wetland plants were chosen, Phalaris arundinaceae and Veronica anagallis-aquatica, both located in local riparian zones, and planted in wetland mesocosms. Rhizosphere bacterial community response was monitored for approximately three weeks after exposure to elevated nutrient loads, following prior adaptation for several months to either high or low (poor) water quality conditions. The impact of prior acclimation conditions was then assessed. Changes to rhizosphere bacterial community structure and function were monitored using PCR-denaturing gel gradient electrophoresis (DGGE) and Biolog™ Ecoplates, respectively. Plants were also sampled to assess any impact on mycorrhizal associations over the exposure period. As an additional indicator of functionality and nitrogen utilization within the mesocosm system, inorganic intermediate N species were monitored at the outflow. Significant differences were observed over time following elevated nutrient exposure in bacterial structural diversity and richness, as well as functional diversity and richness (p < 0.001). The effects of interactions between time, plant species and water quality exposure were also significant for both structural (p = 0.002) and functional (p = 0.05) community diversity. Elevated nutrient exposure resulted in changes to microbial carbon source utilization profiles, specifically, bacterial usage of amino acids (p = 0.032), polymers (p = 0.029) and carboxylic and ketonic acids (p = 0.042). Carboxylic and ketonic acid utilization by bacterial communities was positively correlated with the removal of nitrate and nitrite from experimental mesocosms. Mycorrhizal associations as measured by percent colonization also decreased significantly in P. arundinaceae following elevated nutrient exposure (p < 0.001). Furthermore, abundance of nitrogenous compounds in outflow water differed between plant species treatments, with V. anagallis-aquatica removing more nitrate from the outflow (p = 0.005) while P. arundinaceae removed higher levels of ammonia (p = 0.03). This study provides insight into how microbial communities respond to transient nutrient loads such as that experienced by overland runoff following a high rain event and will assist in the design and rehabilitation of wetlands or riparian buffer strips to manage higher nutrient loads resulting from increasing human activity impacting our freshwater systems.

Making realistic wave climates in low‐cost wave mesocosms: A new tool for experimental ecology and biogeomorphology

AbstractWave flume facilities that are primarily designed for engineering studies are often complex and expensive to operate, and hence not ideal for long‐term replicated experiments as commonly used in biology. This study describes a low‐cost small wave flume that can be used for biological purposes using fresh‐ or seawater with or without sediment. The wave flume can be used as a mesocosm to study interactions between wave hydrodynamics and benthic organisms in aquatic ecosystems. The low‐costs wave maker (&lt; 2000 USD) allows for experimental setups which can be easily replicated and used for longer term studies; hence the term wave mesocosm. Waves were generated with a pneumatic piston and wave heights ranged between 3 and 6 cm. Maximum orbital flow velocities ranged between 10 and 50 cm s−1 representing shallow coastal areas with a short fetch. The system can generate both regular waves (i.e., the wave period and orbital velocity remains constant), using a wave absorber, and irregular waves (i.e., varying wave period and orbital velocity) using a fast push and slow pull motion of the wave paddle. This wave mesocosm system is particularly useful in biogeomorphology to quantify interactions between organisms, sediment, and hydrodynamics and for aquatic ecologist aiming to simulate realistic bed shear stress where short‐ and long‐term experiments (weeks–months) can be replicated.