Outdoor Tank Experiments Research Articles

Purification of selenium-containing leachate in wastewater tanks at a tunnel construction site

The leachate containing heavy metals which generated from excavated soil and rock in the civil engineering works appropriate measures are required. We conducted indoor and outdoor experiments to purify heavy metal-containing leachate using a water tank, and proposed a method for treating heavy metals using the purification function of plants at civil engineering works. The plant used was Eleocharis acicularis, which belongs to the Cyperaceae family. The results of the indoor tank experiment on selenium indicated a decrease in the selenium concentration in the leachate from 0.093 to 0.008 mg/L in 14 days. The selenium content per kg of Eleocharis acicularis based on dry weight increased from 0.010 to 0.205 mg, indicating that the plant absorbed selenium. The outdoor tank experiment revealed that the selenium concentration in the leachate decreased from 0.090 to 0.007 mg/L in 21 weeks, and the daily absorption of selenium was 0.0005 mg/L. The lead concentration decreased from 0.004 to 0.001 mg/L in one week, and the arsenic concentration decreased from 0.003 to less than 0.001 mg/L in three weeks. Calculation of the leachate purification cost using Eleocharis acicularis under the current outdoor experiment conditions resulted in a 56% treatment cost reduction compared with the regular treatment cost.

Persistence of seaweed forests in the anthropocene will depend on warming and marine heatwave profiles.

Marine heatwaves (MHWs), discrete periods of extreme warm water temperatures superimposed onto persistent ocean warming, have increased in frequency and significantly disrupted marine ecosystems. While field observations on the ecological consequences of MHWs are growing, a mechanistic understanding of their direct effects is rare. We conducted an outdoor tank experiment testing how different thermal stressor profiles impacted the ecophysiological performance of three dominant forest-forming seaweeds. Four thermal scenarios were tested: contemporary summer temperature (22°C), low persistent warming (24°C), a discrete MHW (22-27°C), and temperature variability followed by a MHW (22-24°C, 22-27°C). The physiological performance of seaweeds was strongly related to thermal profile and varied among species, with the highest temperature not always having the strongest effect. MHWs were highly detrimental for the fucoid Phyllospora comosa, whereas the laminarian kelp Ecklonia radiata showed sensitivity to extended thermal stress and demonstrated a cumulative temperature threshold. The fucoid Sargassum linearifolium showed resilience, albeit with signs of decline with bleached and degraded fronds, under all conditions, with stronger decline under stable control and warming conditions. The varying responses of these three co-occurring forest-forming seaweeds under different temperature scenarios suggests that the impact of ocean warming on near shore ecosystems may be complex and will depend on the specific thermal profile of rising water temperatures relative to the vulnerability of different species.

Competitive Consumption of the Lake Kinneret (Israel) Plankton by <i>Hypophthalmichthys molitrix</i> and <i>Sarotherodon galilaeus</i>

An outdoor tank experiment was carried out for the assessing of the impacts of Sarotherodon galilaeus (Galilee Saint Peter’s Fish; Cichlidae) (SG) and Hypophthalmichthys molitriox (Silver Carp; Cyprinidae) (SC) on Lake Kinneret (Israel) plankton. In order to evaluate the interaction effect, the experiments were of replicated 2 × 2 factorial design: TG × SC. A lot of interaction effects were indicated showing that the effects of the two fishes were not independent and potentially competitors. SG suppressed most crustaceans and rotifers while increasing gross and net primary production and chlorophyll concentration. SC had less intense effects on zooplankton than SG. Although SC suppressed most crustaceans and rotifers, it had less interaction effects than SG. SC had no statistically significant effects on phytoplankton production or chlorophyll concentration. It is suggested that these experiments indicate that although the plankton community impacts of SG and SC do differ, both fishes utilize similar food resources in Lake Kinneret. Fingerlings of SG and SC are planted in Lake Kinneret annually aimed at the improvement of fishermen’s income and prevention of water quality deterioration. SC is known as efficient consumer of Microcystis. It is therefore recommended to limit SC introduction to periods when Microcystis is abundant.

The effects of herbivore exclusion and nutrient enrichment on growth and reproduction of Halimeda macroloba

The questions on how Halimeda macroloba allocates resources to growth and sexual reproduction when encountering herbivores and elevated nutrient concentrations were experimentally examined in the natural subtidal zone and in water tanks. The field experimental design comprised 96 plots (50 50 cm 2 ), with and without herbivores, and two nutrient levels. Cages were used to exclude fish herbivores: uncaged plots and fully caged plots; and 2 nutrient levels were manipulated: enriched and ambient levels in order to determine the effect of nutrients. Osmocote slow-release fertilizer was placed in each enriched plot. For the outdoor water tank experiments, mechanical clipping was used to simulate grazing on algae. Nutrient enrichment had a positive effect on the growth and reproduction of H. macroloba both in the field and water tank experiments, and herbivory or simulation of grazing did have a significant effect on the growth of algae in the water tank experiments. H. macroloba produced gametangia within 1-2 weeks after nutrient enrichment, to indicate that enrichment might be the trigger for reproduction of H. macroloba. From the tissue nutrient levels, the C:N, C:P, and N:P (18.9, 639, and 33.7) ratios indicated that the productivity of H. macroloba was phosphorus limited.

Sediment tolerance of Sargassum algae inhabiting sediment-covered rocky reefs

Although sediment deposition has detrimental effects on macroalgal settlement and recruitment, fucoid algae (mainly Sargassum duplicatum) thrive on rocky reefs always overlaid with fine sediments in sheltered sites of Kagoshima, Japan. The aim of the present study was to assess their ability to settle and recruit onto sediment-covered substrata. A transplant experiment using boulders with Sargassum juveniles attached showed that the 30-day survival rate was as high as 50% even for the juvenile stage (<10 mm) on boulders completely buried with sediment. In addition, an outdoor tank experiment testing the effects of different sediment thicknesses (0–4 mm) on already settled 4-day old S. duplicatum germlings indicated significant reductions in growth by the presence of sediment cover even at 0.5 mm but no significant increase in mortality up to 2 mm. Furthermore, an in situ experiment in which sterilized cobbles were placed at a sediment-covered site to allow sediment to settle over them before the embryo release showed a uniformly high recruitment of Sargassum over the cobbles. This suggests the presence of unknown mechanisms to allow the settlement of propagules on substrata thinly but completely covered by fine sediments.

Physiological acclimation of floating Macrocystis pyrifera to temperature and irradiance ensures long-term persistence at the sea surface at mid-latitudes

Large numbers of giant kelp rafts are floating along temperate coasts of the southern hemisphere, carrying a wide diversity of associated organisms with them. During voyages, floating kelps are exposed to strong variations in environmental conditions such as UV-radiation (UVR) and temperature that affect algal physiology, growth, and reproductive output. Consequently, it was predicted that the interactive effects of high temperature and UVR suppress algal persistence and reproductive output at the sea surface. This hypothesis was tested by exposing Macrocystis pyrifera (Linnaeus) C. Agardh sporophytes to two irradiance (PAR, PAR + UV) and three temperature (cool, ambient, warm) conditions. An outdoor-tank experiment with two consecutive runs (1st and 2nd) was conducted in northern-central Chile (30°S) to assess growth and physiological responses (pigment contents and photosynthesis) of floating M. pyrifera. Results showed that after being afloat for 15 days, algae physiologically acclimated efficiently to changing abiotic conditions by a decrease in pigment contents and dynamic photoinhibition. However, in kelps exposed to 20 °C these acclimation processes operated at the expense of growth, resulting in reduced biomass gains, lower blade elongation rates, and diminished reproduction. Overall, floating M. pyrifera responded with high physiological plasticity to the tested UV regimes (UVB 30–100 kJm − 2 ; UVA 300–2000 kJm − 2 ), but under stressful temperature conditions (~ 20 °C) photoacclimation processes are costly and an important fraction of the energy gained via photosynthesis becomes unavailable for algal growth. We suggest that at mid latitudes (25°S–40°S) detached sporophytes of M. pyrifera have the capacity to float for long time periods and over large distances at water temperatures < 20 °C.

Asymmetric impacts of two herbivore ecotypes on similar host plants

1. Ecotypes may arise following allopatric separation from source populations. The simultaneous transfer of an exotic plant to a novel environment, along with its stenophagous herbivore, may complicate more traditional patterns of divergence from the plant and insect source populations.2. The present study evaluated herbivory effects by two Cyrtobagous salviniae ecotypes on two species of Salvinia: the larger S. molesta and the smaller S. minima. Evaluations were based on relative growth rates, biomass production, coverage, and nutrient cycling in a series of complementary and comparative laboratory and outdoor tank experiments.3. In general, the experiment results indicated that the smaller Florida ecotype of C. salviniae impacted both Salvinia species more than the larger Brazil ecotype. Herbivory, especially by the Florida ecotype, also improved water quality and accelerated nutrient cycling by increasing the rates of litterfall from the standing crops of salvinia.4. The smaller size of the Florida ecotype may be adaptive by allowing maximal exploitation of host plants via internal larval feeding, which presumably reduces predation risk while increasing damage to the plant. These findings provide support for relying on the suppressive effects of the Florida ecotype in Florida, rather than introducing the Brazil ecotype to counter new infestations of S. molesta.

Remote-sensing reflectance characteristics of highly turbid estuarine waters – a comparative experiment of the Yangtze River and the Yellow River

An outdoor tank experiment is carried out to analyse the interrelationships between remote-sensing reflectance and sediment characteristics in the highly turbid waters of the Yangtze River and the Yellow River estuaries. The results show that the sensitivity of remote-sensing reflectance to water turbidity is inversely related to suspended sediment concentration (SSC). SSC estimation in the highly turbid waters (SSC > 0.15 g l−1) is best achieved by using ocean colour ratios, especially the ratio at 810 nm: 700 nm. The effect of particle size of suspended sediment matter (SSM) on the observed remote-sensing reflectance is significant and depends on wavelengths and a SSC range. The mineral composition of SSM has a weak effect on observed reflectance in comparison to that of particle size.

Solar UV reduces Cryptosporidium parvum oocyst infectivity in environmental waters

To determine the effect of solar radiation on Cryptosporidium parvum in tap and environmental waters. Outdoor tank experiments and a cell culture infectivity assay were used to measure solar inactivation of C. parvum oocysts in different waters. Experiments conducted on days with different levels of solar insolation identified rapid inactivation of oocysts in tap water (up to 90% inactivation within the first hour). Increased dissolved organic carbon content in environmental waters decreased solar inactivation. The role of solar ultraviolet (UV) in inactivation was confirmed by long-pass filter experiments, where UV-B was identified as the most germicidal wavelength. Reductions in oocyst infectivity following solar radiation were not related to a loss of excystation capacity. Solar UV can rapidly inactivate C. parvum in environmental waters. This is the first study to assess natural sunlight inactivation of C. parvum oocysts in surface waters and drinking water using an infectivity measure and determines the wavelengths of light responsible for the inactivation. The findings presented here provide valuable information for determining the relative risks associated with Cryptosporidium oocysts in aquatic environments and identify solar radiation as a critical process affecting the oocyst survival in the environment.

PLANKTON BIODIVERSITY ALONG A GRADIENT OF PRODUCTIVITY AND ITS MEDIATION BY MACROPHYTES

We studied the effect of aquatic vegetation on the process of species sorting and community assembly of three functional groups of plankton organisms (phytoplankton, seston-feeding zooplankton, and substrate-dwelling zooplankton) along a primary productivity gradient. We performed an outdoor cattle tank experiment (n = 60) making an orthogonal combination of a primary productivity gradient (four nutrient addition levels: 0, 10, 100, and 1000 microg P/L; N/P ratio: 16) with a vegetation gradient (no macrophytes, artificial macrophytes, and real Elodea nuttallii). We used artificial plants to evaluate the mere effects of plant physical structure independently from other plant effects, such as competition for nutrients or allelopathy. The tanks were inoculated with species-rich mixtures of phytoplankton and zooplankton. Both productivity and macrophytes affected community structure and diversity of the three functional groups. Taxon richness declined with increasing plankton productivity in each functional group according to a nested subset pattern. We found no evidence for unimodal diversity-productivity relationships. The proportional abundance of Daphnia and of colonial Scenedesmus increased strongly with productivity. GLM analyses suggest that the decline in richness of seston feeders was due to competitive exclusion by Daphnia at high productivity. The decline in richness of phytoplankton was probably caused by high Daphnia grazing. However, partial analyses indicate that these explanations do not entirely explain the patterns. Possibly, environmental deterioration associated with high productivity (e.g., high pH) was also responsible for the observed richness decline. Macrophytes had positive effects on the taxon richness of all three functional plankton groups and interacted with the initial productivity gradient in determining their communities. Macrophytes affected the composition and diversity of the three functional groups both by their physical structure and through other mechanisms. Part of the macrophyte effect may be indirect via a reduction of phytoplankton production. Our results also indirectly suggest that the often reported unimodal relationship between primary productivity and diversity in nature may be partially mediated by the tendency of submerged macrophytes to be most abundant at intermediate productivity levels.

Capacitance probe measurements of brine volume and bulk salinity in first-year sea ice

Abstract First-year sea ice plays an important role in the global climate system. It changes the physical properties of the surface of the polar oceans, and modifies the energy and mass transfer between the ocean and the atmosphere. An understanding of the way sea ice affects ocean–atmosphere exchange requires detailed knowledge of the evolution of ice physical properties, which are governed by its temperature and bulk salinity. To this effect, we assessed the utility of commercially available capacitance probes in determining the salinity evolution of first-year sea ice. Measurements of the complex dielectric permittivity, e = e ′ − ie ″, at 50 MHz were carried out in land-fast ice in McMurdo Sound, Antarctica, and in the Chukchi Sea near Barrow, Alaska. For comparison, we also deployed the probes in artificial, young sea ice in an outdoor tank experiment in Fairbanks, AK. The dielectric permittivity data compare well with predictions from a dielectric mixture model. We have derived a simple relation that allows for the derivation of brine volume fraction and bulk salinity in columnar first-year sea ice from the real part of the complex dielectric permittivity. For ice at temperatures below the percolation threshold, the error in the derived bulk salinity is less than 15%. The dependence of dielectric permittivity on brine inclusion morphology needs to be taken into consideration, and measurements indicate that changes in pore morphology are recorded in the capacitance measurements. In this paper we use the real part, e ′, of the complex dielectric permittivity to study the bulk salinity of bubble-free columnar ice. Further investigations, using the imaginary part of the complex dielectric permittivity, e ″, will make it possible to use the same probes to measure the bulk salinity and pore morphology of other types of ice, e.g., frazil, platelet, and multi-year ice.

アオサ類の堆積によるアマモ場への影響

The objective of this study is to clarify the effect of ulvoid (Ulva spp.) accumulation on the formation of an eelgrass bed on the coast of Iwakuni, Seto Inland Sea, Japan. We monitored eelgrass shoot density and height and ulvoid volume in the study site, and then conducted experiments on the effects of ulvoid canopy on eelgrass using outdoor tanks. Eelgrass shoot density decreased when ulvoid accumulated, and seedling density decreased as ulvoid volume increased. We found no eelgrass seedlings, when the ulvoid canopy height was more than 20 cm. According to the outdoor tank experiments, the survival rate of eelgrass in the 13 cm ulvoid canopy height tank for more than one month differed little from that of eelgrass in the control tank. However, eelgrass in the 25 cm ulvoid canopy height tank died out in 38 days. Eelgrass leaves elongated 5-7, 3-6 and 2-3 cm per day in the control tank and in the 13 and 25 cm ulvoid canopy tanks, respectively. The difference between the initial and final (after 30 days) carbon contents in eelgrass leaves and rhizomes in the control tank was not significant, but that in the 25 cm ulvoid canopy height tank was significant. The carbon content in eelgrass 25 cm ulvoid canopy height tank was lower than that in the control tank (without ulvoid).

Effects of habitat nutrients and seed sources on growth and expansion of Typha domingensis

Field reciprocal transplanting and outdoor tank experiments were conducted to determine the relative importance of habitat nutrients, particularly phosphorus (P), and seed sources on the growth and expansion of cattail ( Typha domingensis Pers.) in Everglades slough areas. Cattail plants originating from seeds collected at a P enriched site and two unenriched sites were reciprocally transplanted, and also planted in outdoor tanks. Significant site effects were found in the reciprocal transplanting experiment. After 7 months, plants (per genet) transplanted to the enriched site exhibited a greater biomass (dry weight) accumulation (152 versus 13 g), tissue nutrient concentrations, and proportional leaf biomass allocation than plants transplanted to the unenriched sites. Each original plant transplanted to the enriched site produced an average of 6.7 new ramets and covered approximately 1.2 m 2. However, no ramets were produced at unenriched sites. After 2.5 years, the total biomass for plants transplanted at unenriched sites was only about 6% of that of plants at the enriched site measured 2 years prior. While the field transplanting experiment highlighted the significance of site effects, the outdoor tank experiment demonstrated the importance of seed sources. The light saturated photosynthesis rates of plants from enriched and unenriched sites were 45.1, 19.9, and 17.0 μmol CO 2 m −2 s −1, respectively, and the relative growth rates were 26.9, 18.3, and 19.0 mg (dry weight) g −1 per day, respectively. This study provides evidence for the importance of P availability in species expansion in wetland ecosystems. Whether differences among cattail plants originating from different seed sources were phenotypic and/or genotypic needs to be further studied.

The effects of predation on the survival and size-distribution of estuarine fishes: an experimental approach

The effect of southern flounder,Paralichthys lethostigma, predation on the survival and size-distribution of spot,Leiostomus xanthurus, was investigated using feeding experiments in outdoor tanks and estuarine ponds. In the outdoor tank experiments, southern flounder, 143 mm average standard length (SL), fed for 48 h on spot (25–30 mm SL), over a range of densities (4–20 m−2). In these trials, flounder showed a Type II functional response to spot density. In the estuarine pond experiment, flounder density (2 or 4 flounders 70 m−2) contributed significantly to spot mortality relative to predator-free controls. The effect of flounder density on spot mortality was non-linear; in the 4-flounder treatment the daily instantaneous mortality due to flounder (0.0177) was 3.5 times that in the 2-flounder treatment (0.0051). The total spot mortality rate in the 4-flounder treatment (0.028) was similar to that observed from published field observations. Flounder also altered the size distribution of spot relative to predator-free controls. Predation by flounder resulted in fewer intermediate-sized spot at the end of the experiment when compared to predator-free controls. Flounder also significantly reduced survival and mean length of two killifishes,Cyprinodon variegatus andFundulus heteroclitus, that invaded the pond. Flounder predation was a significant size-structuring force on the prey fish assemblage in the pond. Results from both the outdoor tank experiment and the pond experiment indicate that flounder may represent a significant source of mortality for juvenile estuarine fishes.

Outdoor tank experiments on the influence of soaking time on the catch efficiency of gillnets and entangling nets

An outdoor tank experiment was conducted to study the influence of soaking time on the catch efficiency of gillnets and entangling nets (trammel and semi-trammel nets). The catch efficiency of the nets was also compared with detecting the difference between entangling nets and gillnets in relation to soaking time. Nets of the same mesh sizes were set simultaneously in separate outdoor tanks containing 200 rainbow trout ( Oncorhynchus mykiss) whose composition size was known. The experiment was carried out at night using four soaking times; 0.5, 1, 3 and 5 h. The variations of the catch efficiency of all nets had a U-shaped trend, showing that the efficiency increased at the shortest time (0.5 h), decreased at the intermediate time (1 h), and increased again at the longest soaking time. The average catch efficiency of the semi-trammel net appeared to be slightly higher than that of the gillnet.

Amphipods on seaweeds: partners or pests?

Herbivorous marine amphipods have been implicated as important grazers on filamentous and ephemeral algae, and thus as beneficial to macrophytes in reducing overgrowth by epiphytic competitors. In North Carolina, USA, amphipods comprise 97% of all macroscopic animals inhabiting the abundant brown seaweed Sargassum filipendula, and peak in abundance between late winter and early summer. I used outdoor tank experiments to test the species-specific impact of common phytal amphipods on the growth of Sargassum and its epiphytes. The results show that seaweed-associated amphipods are a trophically diverse group that could either increase or decrease host fitness depending on their feeding preferences. The amphipods Ampithoe marcuzii, Caprella penantis, and Jassa falcata each significantly reduced growth of epiphytes on Sargassum plants relative to amphipod-free controls, while Ericthonius brasiliensis had no significant effect on Sargassum or its epiphytes. However, amphipod grazing was not necessarily beneficial to Sargassum. A. marcuzii consumed Sargassum in one outdoor tank experiment, reducing its mass by 11%, while Sargassum plants without amphipods grew by 81%. Epiphytes (mostly diatoms and the filamentous brown alga Ectocarpus siliculosus) and detritus remained abundant on these plants suggesting that A. marcuzii preferred the host to its epiphytes. Similarly, when given simultaneous access to Sargassum and to several common foliose and filamentous epiphytes in the lab, A. marcuzii ate Sargassum almost exclusively. The other three amphipods ate no macroalgae. In contrast to A. marcuzii, C. penantis consistently reduced epiphytes with no negative effect on Sargassum. Thus the species composition of the amphipod fauna can determine whether these animals increase or decrease seaweed fitness.

水槽実験による刺網の漁獲効率と網目選択性

The difference on the fishing performance of a bottom gillnet and semi-trammel net was elucidated by evaluating the catching efficiency and absolute selectivity of the nets. The data were obtained from an outdoor water tank experiment using a group of rainbow trout Oncorhyncus mykiss of known size composition. The influence of light intensity on the catch taking the mesh size and construction of the net into consideration was also evaluated. The results showed that gillnet was more effective than semi-trammel net when the mesh size of the net was appropriate with the size of fish. Likewise, light has greater influence to the catch of semi-trammel net than a gillnet.

Interdependence of phosphorus, fish, and site effects on phytoplankton biomass and zooplankton

We conducted an outdoor tank experiment of factorial design with three levels of phosphorus addition cross‐classified with two levels of mosquitofish (Gambusia affinis) at two lake sites, allowing us to examine both main effects and interaction effects of phosphorus, fish, and site on phytoplankton biomass and zooplankton. Phosphorus addition significantly increased total phosphorus concentration and chlorophyll and decreased Secchi depth. Fish significantly decreased cladoceran densities and Secchi depth and increased chlorophyll and turbidity. Most phosphorus and fish effects were independent of each other except for a significant phosphorus × fish interaction on rotifers. The two sites had significant differences in total phosphorus concentration, turbidity, Secchi depth, chlorophyll, and densities of cladocerans, copepods, and rotifers. The only significant site ×phosphorus interaction was for total phosphorus. Significant site x fish interactions were detected for turbidity, Secchi depth, chlorophyll, and densities of cladocerans and rotifers. Fish effects were independent of phosphorus addition but dependent on site‐specific plankton community composition.

A statistical study on Mazume phenomenon by outdoor tank experiments.

Etude statistique du phenomene de Mazume (les meilleures captures se produisent generalement au crepuscule)

Planktivory and planktivore biomass effects on zooplankton, phytoplankton, and the trophic cascade1

Five outdoor tank experiments were conducted to evaluate how season, fish biomass, and accidental mortality of introduced fish contributed to enhancement of phytoplankton growth by the zooplanktivorous atherinid fish, Menidia beryllina. Menidia enhanced phytoplankton in all seasons. Three experiments examined effects of fish density. Menidia gained weight when stocked in the experimental tanks at low densities (&lt;1.5 g dry wt m‒3), suppressed crustacean zooplankton, and enhanced blue‐green filaments. Water transparency and other phytoplankton were unaffected. Menidia lost weight and occasionally died when stocked at higher densities (&gt; 1.5 g dry wt m‒3). Under these conditions, Menidia suppressed crustacean zooplankton and reduced water transparency, and enhanced rotifers, algal chlorophyll fluorescence, and seston particles. Two additional experiments of factorial design used live Menidia and dead Menidia as separate, cross‐classified treatment factors. Live fish effects were limited to the suppression of crustacean zooplankton and enhancement of blue‐green filaments, while dead fish reduced water transparency or enhanced other phytoplankton. The importance of lost fish biomass (either weight loss or mortality of introduced fish) to the enhancement of phytoplankton by planktivorous fish in these experiments suggests that zooplankton control of phytoplankton by grazing is not as important as implied by the trophic cascade hypothesis.