Dominant species, functional assemblages and frequency of equilibrium phases in late summer phytoplankton assemblages in Hungarian small shallow lakes

Late summer phytoplankton associations were studied qualitatively and quantitatively in 80 Hungarian lakes altogether (mostly shallow salt lakes, reservoirs, oxbows, gravel pit lakes). Equilibrium phases sensu Sommer et al. (1993) were found only in 17 lakes. Most of them were under some kind (high salt content or very low level of nutrients) of stress factor. It is concluded that environmental stress forces phytoplankton communities towards equilibrium. No relationship between occurrence of equilibria and trophic state was found. Species number of non-equilibrated lakes was almost three times as high as those in equilibrium. Of the 31 recently described (Reynolds et al., 2002) phytoplankton assemblages most of those were recognized that are likely to occur in shallow lakes. Separation of a functional group W _S from W2 for Synura dominated lakes is suggested. It seemed also necessary to raise a group (Y _Ph) for lakes dominated by Phacotus. Sorting of Dinophyta species into different already described functional groups is desirable.     

The impact of free-floating plant cover on phytoplankton assemblages of oxbow lakes (The Bug River Valley, Poland)

In the present study we focused on the impact of macrophyte cover (composed mainly of the Lemna genus) on phytoplankton taxonomic and functional diversity. Some important environmental parameters, mainly light (Kd_PAR), and the chemical conditions (pH, dissolved oxygen, ammonium, soluble and total forms of phosphorus) were closely related to the pleustophyte cover. Among them, the key factor in the phytoplankton ecology of the studied oxbow lakes was the dense macrophyte cover which strongly reduced the illumination of water. Neither differences in the mean nutrient concentrations between the lakes with FFP (Free Floating Plants) absence and those with FFP dominance nor significant relationships between nutrients and the phytoplankton structure were observed. The species composition of phytoplankton and the functional (FG) and morpho-functional (MFG) groups reflected the differences between the habitats connected with hydromacrophytes. The free-floating macrophyte cover favours mixotrophic and heterotrophic species, mainly Euglenophyta (coda W1 and W2) and chrysophytes (codon Ws) as well as shade-adapted cyanobacteria with the high tolerance of the low oxygen content (codon K). In lakes with FFP absence — taxa from Chlorophyta and Bacillariophyceae (associations X1, J, and D), or filamentous cyanobacteria (codon S1) dominated the phytoplankton. MFG were less related to the oxbow type and exhibited greater similarity between lakes independently of the presence or absence of FFP. Only unicellular Cyanoprokaryota which created MFG 4 and colonial chroococcales (MFG 5b and 5c) reached a greater percentage share, especially in oxbow lakes with FFP dominance.     

Functional groups of phytoplankton shaping diversity of shallow lake ecosystems

Phytoplankton of eutrophic shallow lakes are frequently dominated by one species or species of the same functional group, resulting in species-pure algal assemblages. Knowledge of the structure of these assemblages is essential to understand their functioning; therefore, species and functional diversity were investigated in five sub-types of eutrophic shallow lake. Among the sub-types, astatic saline lakes and hypertrophic ponds had type-specific assemblages dominated by S_N and W0, W1 codons. The diversity of the phytoplankton in the sub-types was quite similar, except for the astatic saline lakes, which were characterised by lower values of both functional and species diversity. We found that both functional and species diversity were low when bloom-forming cyanobacteria (H1, S_N functional groups) became dominant. Dominance of other groups (J, Y, L_O and W1) did not coincide with decrease in species diversity. Analysis of the biovolume versus diversity relationships revealed that decrease in diversity might be expected at biovolume >20 mm³ l⁻¹ for shallow lakes.     

Is Hybridization Responsible for Invasive Growth of Non-indigenous Water-milfoils?

Heterosis, or hybrid vigor, has recently been proposed as a factor promoting invasive growth of some non-indigenous aquatic plant species, particularly those capable of spreading rapidly within and among lakes through clonal reproduction. We tested this hypothesis for variable-leaf water milfoil (Myriophyllum heterophyllum), a non-indigenous aquatic plant that has become a major management and conservation concern in New England. Using nuclear ribosomal DNA, we looked for F₁ hybrid populations of invasive M. heterophyllum in 25 New Hampshire (NH) lakes. In contrast to a previous study that found F₁ hybrid lineages of invasive M. heterophyllum in Connecticut, we did not find hybrids in our study lakes. This result has two implications: (1) pure lineages of M. heterophyllum are also capable of invasive growth, and (2) the distribution of invasive M. heterophyllum lineages (hybrid vs. pure) may be spatially structured across New England. We stress the importance of more detailed distributional and ecological studies for understanding the invasive potential of this species.     

Geographic distribution of genetic diversity in populations of Rio Grande Chub <Emphasis Type="Italic">Gila pandora</Emphasis>

In the southwestern United States (US), the Rio Grande chub (Gila pandora) is state-listed as a fish species of greatest conservation need and federally listed as sensitive due to habitat alterations and competition with non-native fishes. Characterizing genetic diversity, genetic population structure, and effective number of breeders will assist with conservation efforts by providing a baseline of genetic metrics. Genetic relatedness within and among G. pandora populations throughout New Mexico was characterized using 11 microsatellite loci among 15 populations in three drainage basins (Rio Grande, Pecos, Canadian). Observed heterozygosity (H_O) ranged from 0.71–0.87 and was similar to expected heterozygosity (0.75–0.87). Rio Ojo Caliente (Rio Grande) had the highest allelic richness (A_R = 15.09), while Upper Rio Bonito (Pecos) had the lowest allelic richness (A_R = 6.75). Genetic differentiation existed among all populations with the lowest genetic variation occurring within the Pecos drainage. STRUCTURE analysis revealed seven genetic clusters. Populations of G. pandora within the upper Rio Grande drainage (Rio Ojo Caliente, Rio Vallecitos, Rio Pueblo de Taos) had high levels of admixture with Q-values ranging from 0.30–0.50. In contrast, populations within the Pecos drainage (Pecos River and Upper Rio Bonito) had low levels of admixture (Q = 0.94 and 0.87, respectively). Estimates of effective number of breeders (N _b ) varied from 6.1 (Pecos: Upper Rio Bonito) to 109.7 (Rio Grande: Rio Peñasco) indicating that populations in the Pecos drainage are at risk of extirpation. In the event that management actions are deemed necessary to preserve or increase genetic diversity of G. pandora, consideration must be given as to which populations are selected for translocation.     

Associations and distribution of benthic nematodes in the Ethiopian Rift Valley lakes

The nematode associations in six Ethiopian rift lakes, one man-made lake, and three crater lakes were studied and related to water conductivity, lake depth and sediment particle size. The lakes investigated lie at moderate altitudes (1200–2000 m), are alkaline and vary in their conductivities. The rift lakes Abijata and Shala and the crater lakes Aranguadi, Kilotes and Chitu are soda lakes (K₂₅ > 6000 μS cm⁻¹), while the remaining five lakes and the man-made Lake Koka are within the freshwater range of conductivity (K₂₅ < 6000 μS cm⁻¹). A total of 16 species were identified including six new species. The nematode associations varied between lakes and were restricted to very few species in each lake. Most nematodes were restricted to non-saline lakes. The most dilute L. Zwai had a higher number of nematode species (12) and abundance than other lakes. The saline lakes Shala and Kilotes had nematode assemblages made up of only a single species (Mesodorylaimus macrospiculum). No nematodes were found in the hypersaline crater L. Chitu. Tobrilus africanus appeared more euryhaline than other nematodes occurring at conductivities as high as 15 000 μ S cm⁻¹ (L. Abijata). Five of the most common species (Dorylaimus sp., Monhystera stagnalis, Aphanolaimus tudoranceai, Tobrilus africanus and Actinolaimus perplexus) were associated with medium grained sand. A monthly variation in density of nematodes in L. Zwai is also shown.     

Ammonia may play an important role in the succession of cyanobacterial blooms and the distribution of common algal species in shallow freshwater lakes

With the human intensification of agricultural and industrial activities, large amount of reduced nitrogen enter into the biosphere, which consequently results in the development of global eutrophication and cyanobacterial blooms. However, no research had reported the effect of ammonia toxicity on the algal succession. In this study, we investigated the ammonia toxicity to 19 algal species or strains to test the hypothesis that ammonia may regulate the succession of cyanobacterial blooms and the distribution of common algal species in freshwater lakes. The bloom‐forming cyanobacterium Microcystis aeruginosa PCC 7806 suffered from ammonia toxicity at high pH value and light intensity conditions. Low NH₄Cl concentration (0.06 mmol L^?1) resulted in the decrease of operational PSII quantum yield by 50% compared with the control exposed to 1000 μmol photons m^?2 s^?1 for 1 h at pH 9.0 ± 0.2, which can be reached in freshwater lakes. Furthermore, the tolerant abilities to NH₃ toxicity of 18 freshwater algal species or strains were as follows: hypertrophication species > eutrophication species > mesotrophication species > oligotrophication species. The different sensitivities of NH₃ toxicity in this study could well explain the distributing rule of common algal species in the freshwater lakes of different trophic states. Meanwhile, the cyanobacterial bloom (e.g. M. aeruginosa) always happened at the low concentration of ammonia in summer, and disappeared with the decrease of ammonia. This may be attributed to the toxic effect of ammonia to M. aeruginosa in spring (the average and maximum ammonia concentration were 0.08 and 0.72 mmol L^?1 in 33 Chinese lakes), and the low level of NH₃‐N in summer and fall in the lakes might be used as preferred nitrogen nutrition by M. aeruginosa, rather than with toxicity. Therefore, ammonia could be a key factor to determine the distribution of common algal species and cyanobacterial bloom in the freshwater systems.     

Elevated CO2 affects plant responses to variation in boron availability

Aim

Effects of elevated CO₂ on N relations are well studied, but effects on other nutrients, especially micronutrients, are not. We investigated effects of elevated CO₂ on response to variation in boron (B) availability in three unrelated species: seed geranium (Pelargonium x hortorum), barley (Hordeum vulgare), and water fern (Azolla caroliniana).

Methods

Plants were grown at two levels of CO₂ (370, 700?ppm) and low, medium, and high B. Treatment effects were measured on biomass, net photosynthesis (P_n) and related variables, tissue nutrient concentrations, and B transporter protein BOR1.

Results

In geranium, there were interactive effects (P?<?0.05) of B and CO₂ on leaf, stem, and total plant mass, root:shoot ratio, leaf [B], B uptake rate, root [Zn], and P_n. Elevated CO₂ stimulated growth at 45?μM B, but decreased it at 450?μM B and did not affect it at 4.5?μM B. P_n was stimulated by elevated CO₂ only at 45?μM B and chlorophyll was enhanced only at 450?μM B. Soluble sugars increased with high CO₂ only at 4.5 and 45?μM B. High CO₂ decreased leaf [B] and B uptake rate, especially at 450?μM B. Though CO₂ and B individually affected the concentration of several other nutrients, B x CO₂ interactions were evident only for Zn in roots, wherein [Zn] decreased under elevated CO₂. Interactive effects of B and CO₂ on growth were confirmed in (1) barley grown at 0, 30, or 1,000?μM B, wherein growth at high CO₂ was stimulated more at 30?μM B, and (2) Azolla grown at 0, 10, and 1,000?μM B, wherein growth at high CO₂ was stimulated at 0 and 10?μM B.

Conclusion

Thus, low and high B both may limit growth stimulation under elevated vs. current [CO₂], and B deficiency and toxicity, already common, may increase in the future.     

A comparison of zooplankton communities in saline lakewater with variable anion composition

Although salinity and aquatic biodiversity are inversely related in lake water, the relationship between types of salts and zooplankton communities is poorly understood. In this study, zooplankton species were related to environmental variables from 12 lakes: three saline lakes with water where the dominant anions were SO₄ and CO₃, four saline lakes with Cl-dominated water, and five dilute, subsaline (0.5–3 gl^?1 total dissolved solids) lakes of variable anion composition. Although this study comprised only 12 lakes, distinct differences in zooplankton communities were observed among the two groups of chemically defined saline lakes. Canonical correspondence analysis identified total alkalinity, sulphate, chloride, calcium, sodium, potassium, and total phosphorus as all contributing to the first two ordination axes (λ₁ = 0.97 and λ₂ = 0.62, P<0.05). The rotifer Brachionus plicatilis and the harpactacoid copepod Cletocamptus sp. prevailed lakes with Cl-dominated water. In contrast, the calanoid copepods Leptodiaptomus sicilis and Diaptomus nevadensis were dominant in the SO₄/CO₃-dominated lake water with elevated potassium (79–128 mg l^?1) and total phosphorus concentrations (1322-2915 μg l^?1). The contrasting zooplankton species distribution among these two saline lake types is likely explained by variable selective pressure on zooplankton and their predators from differing physiological tolerances to salt stress and specific ions. While inland saline lakes with Cl as the dominant anion are relatively rare in Canada and SO₄/CO₃ are the common features, our study provided an opportunity to compare zooplankton communities across the two groups of lakes.     

Alkalinity generation and sediment CO2 uptake influence establishment of Sparganium angustifolium in softwater lakes

1. Softwater lakes are generally dominated by slow growing, small, isoetid plant species that are adapted to the carbon‐ and nutrient‐limited conditions in these lakes. We investigated the strategy of a fast growing species, Sparganium angustifolium, for occupying softwater lakes. A field survey was carried out in Norwegian carbon‐limited Isoëteto‐Lobelietum softwater lakes to compare abiotic conditions at locations with and without S. angustifolium. In addition, long term abiotic changes (1995–2008) related to the sudden establishment of the species on experimentally limed plots were studied. Based on the results, the carbon acquisition mechanism of S. angustifolium was tested in eco‐physiological laboratory experiments. 2. The redox potential was significantly lower at locations with S. angustifolium (220 ± 2.3) compared to locations without S. angustifolium (338.1 ± 13.9). The lower redox potential was accompanied by significantly higher concentrations of HCO₃^?, CO₂ and Fe²⁺ in the sediment pore water, indicating in‐lake alkalinity generation due to higher iron reduction rates in the generally iron‐rich sediments. In addition, the lower redox potential was accompanied by a higher nutrient availability (NH₄⁺ and PO₄^3?) in the sediment pore water. Since there were no differences in water quality between the lakes, the ability of S. angustifolium to grow in softwater lakes very likely depends upon the higher dissolved inorganic carbon (DIC) and nutrient concentrations present in the sediment pore water. 3. Results from the liming experiment revealed that appearance of S. angustifolium on limed plots was related to the dissolution of Ca and Mg carbonates and development of a lower redox potential in the sediment. These processes were accompanied by a sustained increase in the availability of DIC in the sediment pore water. 4. The eco‐physiological experiments indicated that S. angustifolium can increase in biomass and produce floating leaves at a relatively high DIC availability in the root medium. In addition, it appeared that S. angustifolium can take up CO₂ by the roots. As far as we know, the ability to use sediment CO₂ has only been described as an adaptation typical for isoetid plant species. Use of the relatively large sediment CO₂ pools present in these sediment types (>1000 μmol L^?1) to enable development of long floating leaves for additional uptake of atmospheric CO₂ is a very different strategy to colonise softwater lakes as compared to isoetid plant species.     

Effects of competition on induction of crassulacean acid metabolism in a facultative CAM plant

Abiotic drivers of environmental stress have been found to induce CAM expression (nocturnal carboxylation) in facultative CAM species such as Mesembryanthemum crystallinum. The role played by biotic factors such as competition with non-CAM species in affecting CAM expression, however, remains largely understudied. This research investigated the effects of salt and water conditions on the competition between M. crystallinum and the C₃ grass Bromus mollis with which it is found to coexist in California’s coastal grasslands. We also investigated the extent to which CAM expression in M. crystallinum was affected by the intensity of the competition with B. mollis. We found that M. crystallinum had a competitive advantage over B. mollis in drought and saline conditions, while B. mollis exerted strong competitive effects on M. crystallinum in access to light and soil nutrients in high water conditions. This strong competitive effect even outweighed the favorable effects of salt or water additions in increasing the biomass and productivity of M. crystallinum in mixture. Regardless of salt conditions, M. crystallinum did not switch to CAM photosynthesis in response to this strong competitive effect from B. mollis. Disturbance (i.e., grass cutting) reduced the competitive pressure by B. mollis and allowed for CAM expression in M. crystallinum when it was grown mixed with B. mollis. We suggest that moderate competition with other functional groups can enhance CAM expression in M. crystallinum, thereby affecting its plasticity and ability to cope with biological stress.     

Decline of charophytes during eutrophication: comparison with angiosperms

1. Charophytes have disappeared from several enriched lakes in Scania (southern Sweden) since the 1940s. Poor light conditions, rather than a toxic effect of phosphorus or negative impact of fish, are the most probable reason for this decline. 2. Small species of charophytes (shoot diameter 0.5–1.0 mm), which are able to form dense, low mats, still occur in eutrophic lakes with high phosphorus concentrations, but are restricted to areas of shallow water. In contrast, large species (shoot diameter 1–4 mm) have totally disappeared from the most turbid lakes. I suggest that these species are unable to grow in very shallow water because of damage by ice and wave action. 3. Maximum depth distribution (z_e) and Secchi depth (D) were measured in Scanian lakes for both charophytes and angiosperms and combined with data obtained from Chambers & Kalff (1985). According to the combined data, z_c and D are closely correlated with each other for both angiosperms and charophytes. 4. The z_c of charophytes is higher than z_c of angiosperms in clear lakes but lower in turbid lakes. Higher z_c of angiosperms in the most turbid lakes is explained by special adaptations of these species to poor light availability (shoot elongation, canopy formation, rapid growth during spring).     

Chironomid fauna of the lakes from the Pechora river basin (east of European part of Russian Arctic): Ecology and reconstruction of recent ecological changes in the region

We investigated chironomid fauna of surface sediments and a short sediment core (Bol’shoy Kharbey Lake) from Pechora river basin, Northern Russia. Twenty three investigated lakes have thermokarst, glacial or floodplain origin and are characterised by low mineralization, mostly hydrocarbon-calcium type of water and low concentration of nutrients. Most of the lakes have circumneutral pH around ≤7 and only two lakes are slightly more acidic with pH ≤ 6. Ninety six chironomid taxa were identified in the surface sediments. Distribution of chironomids in the studied region is driven by continentality, mean T_July and рН. Chironomid communities from the core of the B. Kharbei Lake demonstrate the highest similarity with the fauna of the deeper lakes of the glacial origin. The glacial lakes have the highest indices of continentality and the lowest winter temperatures within the investigated data set. The chironomid fauna of the glacial lakes is composed of the profundal, oligotrophic and cold-stenotherm taxa. The fauna of the floodplain and thermokarst lakes is more closely related to T_July and is composed of littoral and phytophilic taxa of meso–or eutrophic waters and moderate temperature conditions. The fauna of the acidic thermokarst lakes considerably differs from the other lakes. Chironomid communities here are represented by tolerant to acidification taxa, and by the typically littoral and shallow water acid-tolerant taxa that apparently also can tolerate acidification. Studied sediment record covers ca last 200 years. The reconstructed T_July during the entire period remain slightly below the modern temperatures. From 1970 reconstructed T_July shows steady increase to the modern level. The reconstructed water depths (WDs) of the lake are higher than today till 1980. The highest WDs are reconstructed for ca 1970. After that the WDs gradually decrease to the modern level. Changes of the WDs are most probably related to changes in the precipitation rate.     

Quantitative analysis of freshwater ostracode assemblages in southwestern Yukon Territory,Canada

Relations between modern ostracode assemblages and environmental variables from lakes in the southwest Yukon and northern British Columbia were explored. A total of 29 freshwater species representing 8 genera were identified from the sediments of 36 lakes, with the number of species ranging between 3 and 8 per lake. Species widespread throughout the study area include Cyclocypris ampla, Candona candida, Cypria turneri, Cypria ophtalmica, and Candona protzi. The Mg/Ca ratio is an important factor determining the ostracode species composition of a lake. Species richness is at a maximum when the lake water has intermediate values of conductivity. Lakes in which one species clearly dominates the assemblage (‰>‰70% relative abundance) have water saturated with respect to CaCO₃. Mg/Ca ratio, depth and Sr are the environmental factors that are most highly correlated with species distributions in this region.     

An evaluation of the diet of <Emphasis Type="Italic">Mysis relicta</Emphasis> using gut contents and fatty acid profiles in lakes with and without the invader <Emphasis Type="Italic">Bythotrephes longimanus</Emphasis> (<Emphasis Type="Italic">Onychopoda,Cercopagidae</Emphasis>)

Diets of Mysis relicta from four lakes in central Ontario that had been invaded by Bythotrephes longimanus and three lakes that had not been invaded were investigated using gut content analysis and fatty acid (FA) composition. Gut content analysis of M. relicta revealed a high incidence of cannibalism in all lakes, and consumption of B. longimanus and native zooplanktivorous midges in the genus Chaoborus in lakes where these were present. Cladocera other than B. longimanus were present in the guts of all M. relicta examined except those from Bernard Lake, the lake with the most B. longimanus. In that lake, B. longimanus was the most frequent diet item. Copepod remains were found in 60–100% of M. relicta guts with the lowest frequency occurring in Bernard Lake. Fatty acids (FA) that contributed strongly to the variation in FA composition in M. relicta, as revealed by a principal component analysis, were C16:0 (palmitic acid), C16:1n7 (palmitoleic acid), C18:1n9c (oleic acid), C20:4n6 (arachidonic acid), C20:5n3 (eicosapentaenoic acid), and C22:6n3 (docosahexaenoic acid). Significant differences in FA amount and composition of M. relicta were found between invaded and non-invaded lakes, and among lakes within these groups. Generally, M. relicta in non-invaded lakes had higher concentrations of C16:0, C18:1n9c, C18:2n6c (linoleic acid), C18:3n3 (α-linolenic acid) and C20:4n6, while M. relicta in invaded lakes had higher concentrations of C22:6n3. Two of the non-invaded lakes had lower water transparency, as measured by Secchi depth, which may be the reason why mysids and abundant populations of Chaoborus spp. could be found in the water column during the day. However, differences in FA profiles and gut contents of M. relicta between invaded and non-invaded lakes are consistent with competition for Cladocera in the presence of the invader rather than pre-existing differences among lakes. We conclude that the diet of M. relicta is affected by the invasion of B. longimanus.     

Heptacoordinate dithiophosphate W(II) and Mo(II) complexes of diphosphines and iodide

New complexes [MI(CO)₂(dppe){S₂P(OEt)₂}] (M=W, 1a; M=Mo, 1b), [MI(CO)₂(dppm){S₂P(OEt)₂}] (M=W, 2a; M=Mo, 2b) and [W(CO)(dppe){S₂P(OEt)₂}₂][O₂dppe] (3a), were synthesised from [MI₂(CO)₃(NCMe)₂] (M=Mo, W), after treatment with ammonium diethyldithiophosphate and phosphine under different conditions. The structure of the tungsten complexes was determined by single crystal X-ray diffraction. During the synthesis of 3a, oxidation of the phosphine took place and a molecule of oxidised phosphine occupies channels in the crystal. DFT/B3LYP calculations on models of 1a and 2a showed the capped octahedron structure, observed in most dicarbonyl complexes of this family, to be preferred by 1.4 and 2.6 kcal mol⁻¹ for the dppm and the dppe complexes, respectively. Strong steric repulsions can reverse this trend, as happens with the rigid dppm ligand. Complex 1a adopts a pentagonal bipyramidal geometry, which is often found in related monocarbonyl complexes.     

Effect of Rural Sewage Irrigation Regime on Water-Nitrogen Utilization and Crop Growth of Paddy Rice in Southern China

Reclaimed water irrigation has become an effective mean to alleviate the contradiction between water availability and its consumption worldwide. In this study, three types of irrigation water sources (rural sewage’s primary treated water R1 and secondary treated water R2, and river water R3) meeting the requirements of water quality for farmland irrigation were selected, and three types of irrigation water levels (low water level W1 of 0–80 mm, medium water level W2 of 0–100 mm, and high water level W3 of 0–150 mm) were adopted to carry out research on the influence mechanismS of different irrigation water sources and water levels on water and nitrogen use and crop growth in paddy field. The water quantity indicators (irrigation times and irrigation volume), soil ammonium nitrogen (NH₄⁺-N) and nitrate nitrogen (NO₃⁻-N), rice yield indicators (thousand-grain weight, the number of grains per spike, and the number of effective spikes), and quality indicators (the amount of protein, amylose, vitamin C, nitrate and nitrite content) of rice were measured. The results showed that, the average irrigation volume under W3 was 2.4 and 1.9 times of that under W1 and W2, respectively. Compared with R3, the peak consumption of rice was lagged behind under R1 and R2, and the nitrogen form in 0–40 cm soil layers under rural sewage irrigation was mainly NH₄⁺-N. The changes of NO₃⁻-N and NH₄⁺-N in the 0–40 cm soil layer showed the trend of declining and then increasing. The water level control only had a significant effect on the change of NO₃⁻-N in the 60–80 cm soil layer. Both irrigation water use efficiency and crop water use efficiency were gradually reduced with the increase of field water level control. The nitrogen utilization efficiency under rural sewage irrigation was significantly higher than that under R3. Compared with the R3, rural sewage irrigation could significantly increase the yield of rice, and as the field water level rose, the effect of yield promotion was more obvious. It was noteworthy that the grain of rice under R1 monitored the low nitrate and nitrite content, but no nitrate and nitrite was discovered under R2 and R3. Therefore, reasonable rural sewage irrigation (R2) and medium water level (W2) were beneficial to improve nitrogen utilization efficiency, crop yield and crop quality promotion.

     

Computational studies of metal carbonyl complexes of 3[4-ethyl(phenly)imino][indoline-2-one] and 3[4-butyl(phenly)imino][indoline-2-one]

Use and application of Schiff bases are extended to many different fields of technology. (ISE)M(CO)₅ complex [M?=?Cr (1), Mo (2), W (3), and where ISE is 3[4-ethyl(phenly)imino][indoline-2-one]; and (ISB)M(CO)₅ [M?=?Cr (4), Mo (5), W (6)], where ISB is 3[4-butly(phenly)imino][indoline-2-one] were investigated by computational methods. Computations were carried out using density functional theory (DFT) with B3LYP and CAM-B3LYP functionals, in conjunction with LanL2DZ basis set for metals and cc-PVTZ basis set for other atoms. Time-dependent density functional theory (TDDFT) was used at the same level to obtain the electronic transitions. Molecular orbital energies, UV-Vis spectra, and total electron densities of investigated molecules were shown in the gas phase and in THF. Metal complexes showed higher absorption coefficients compared to ISE and ISB in the visible region. Additionally, they displayed absorption peaks at longer wavelengths and full MLCT character in solution, and W complexes required less energy compared to the complexes of other investigated metal ions. Among the investigated systems, (ISE)W(CO)₅ and (ISB)W(CO)₅ complexes with lowest HOMO-LUMO gaps are found to be the best candidates for photosensitive material production.

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Graphical Abstract UV-Vis absorption spectra of ISE and (ISE)W(CO)₅

     

A mosaic community of macrophytes for the ecological remediation of eutrophic shallow lakes

The restoration of macrophytes in eutrophic shallow lakes has been the focus of active research in the past decade. The approach of building up a mosaic community of macrophytes (MCMs) to improve water quality and remediate the ecosystems of lakes is proposed in this paper. Several species of floating, floating-leaved, and submerged macrophytes were introduced in experimental enclosures in eutrophic shallow lakes. These macrophytes were intercropped in small patches and formed mosaic communities of spatial and temporal combinations (spatial and seasonal mosaic patterns) in the lakes. Macrophytes can improve water transparency quickly and the MCM system can stabilize this clear water state over a long time in turbid eutrophic shallow lakes. The constructed MCM created heterogeneous habitats that are favourable for different macrophytes and for the growth and succession of other organisms, as well as for removing water pollutants. When the eutrophic water flowed through the MCM system at a retention time of 7 days, the removal efficiency rates of the MCM system for algae biomass, NH₄⁺–N, TN, TP and PO₄^3?–P were 58%, 66%, 60%, 72% and 80%, respectively.