Assessing risks of algal blooms in water transfer based on algal growth potential.

Water transfer is an effective way to solve the unequal distribution of water resources to meet the needs of urban residents and industry. Annual wet weight data indicated that there may be algal blooms during water transfer. We explored the ecological risk of water transfer from Xiashan to the Jihongtan reservoir through algae growth potential (AGP) tests. The results showed that the Jihongtan reservoir had certain self-regulation abilities. When the total dissolved phosphorus (TDP) concentration was not more than 0.04 mg/L, the risk of algal bloom was low. When the N/P ratio (by mass) was less than 40, the ecological imbalance of algal growth may be caused. When the N/P ratio was 20, it was the best environment for algal growth. Under the current nutrient condition of the Jihongtan reservoir, the volume of ecological safety threshold in water transfer was 60% of the Jihongtan reservoir's capacity. If the nutrient level was further increased, the water transfer threshold would rise to 75%. In addition, water transfer may cause the homogenization of water quality and accelerate the eutrophication process of reservoirs. Regarding risk assessment, we believe that controlling nitrogen and phosphorus are more consistent with the natural evolution of reservoirs than controlling phosphorus alone for solving the problem of eutrophication.

The integrative effect of periphyton biofilm and tape grass (Vallisneria natans) on internal loading of shallow eutrophic lakes.

The response of periphyton biofilm and the submerged macrophyte tape grass (Vallisneria natans) to internal loading from eutrophic lake sediments were evaluated in microcosms. The sediments from the littoral zone and center of a lake were selected to carry out the microcosm experiment. To determine how the differences in the periphyton biofilm and V. natans growth alone or in combination, we measured changes in water quality, growth, and TP in the periphyton biofilm and V. natans in microcosms containing these sediments. The results showed that the average daily TN and TP removal rates were 32.6 and 35.4%, respectively, in the microcosms containing the lake center sediments by V. natans and the periphyton biofilm. The presence of the periphyton biofilm and V. natans increased the pH, dissolved oxygen, and redox potential and decreased the conductivity in the overlying water in all treatments. Compared to the state before the treatments, V. natans grew well, with a significant increase in biomass (3.1- to 5.5-fold growth) and TP amount (5.1- to 8.8-fold) in all treatments after 48 days. However, the growth of V. natans that combined with the periphyton biofilm was better than that of V. natans alone, as reflected by the dry weight, chlorophyll a content, malondialdehyde content, and TP amount. In conclusion, the periphyton biofilm was beneficial for the growth of V. natans, and the appropriate combination of V. natans and periphyton biofilm would be a potential method for the ecological restoration of eutrophic lakes.

Using benthic diatom assemblages to assess human impacts on streams across a rural to urban gradient.

Benthic diatom assemblages on the natural substrata were investigated at 21 sites of the Ganhe River watershed (China) once per season and in addition, early spring in 2013. A total of 487 diatom taxa from 36 genera were identified during five investigations. The assemblages were dominated by Achnanthidium minutissimum (Kützing) Czarnecki and Cocconeis placentula in the rural reach, whereas Navicula, Nitzschia, and Gomphonema species were characteristic of urbanized sites. Our results suggest that biodiversity was positively related to high nutrient levels and strongly negatively related to diatom-based indices. The periphyton biomass (expressed as chlorophyll a and ash-free dry mass) was not related to water quality. Canonical correspondence analysis (CCA) showed that the nutrient concentration gradient was the most important factor that affected the diatom assemblage composition and species distribution. The diatom-based indices (specific pollution sensitivity index (IPS), biological diatom index (IBD), and trophic diatom index (TDI)) were significantly positively correlated with water quality and are adequate for use in China. Slight changes in the biodiversity and diatom-based indices followed a temporal pattern. The species composition was less related to the season or hydrological characteristics of the river but more strongly related to differences in the trophic status. In this region, urbanization masked the impact of rural land use on benthic diatoms. The research will expand the understanding of using benthic diatom assemblages for water quality monitoring in urban streams and improve watershed-scale management and conservation efforts in the Ganhe River, China.

Removal and retention of phosphorus by periphyton from wastewater with high organic load.

The total phosphorus (TP) removal efficiency from organic wastewater (pig farm and distillery wastewater) were estimated by using filamentous green algae (FGA) and benthic algal mats (BAM) treatment systems under laboratory conditions, and the contents of periphyton phosphorus fractions were determined by using a sequential extraction. The removal rates of TP reached 59-78% within the first 8 days of all treatment systems and could achieve average 80% during 30 day period, and the phosphorus removal rates by using BAM was higher than that of FGA. The ability of retention TP of periphyton enhanced gradually, the BAM TP contents were higher than that of FGA, the highest TP concentrations of BAM and FGA were 26.24 and 10.52 mg P g(-1)·dry weight. Inorganic phosphorus (IP) always exceeded 67.5% of TP, but the organic phosphorus fraction only made up less than 20% of TP. The calcium-binding phosphorus (Ca-P) was the dominant fraction and its relative contribution to TP was more than 40%. The TP was also strongly and positively correlated with the IP and Ca-P (p < 0.01) in periphyton. It showed that the periphyton had a potential ability of rapid phosphorus removing and remarkable retention from wastewater with high load phosphorus.

Inheritance and mechanism of resistance to Bacillus sphaericus in Culex quinquefasciatus (Diptera: Culicidae) from China and Brazil.

Investigations on the inheritance and mechanism of resistance to Bacillus sphaericus Neide in Culex quinquefasciatus Say colonies, selected with strains C3-41 (RLCq1/C3-41) and 2362 (CqRL1/2362), were performed in China and Brazil, respectively. The progeny of reciprocal F1 crosses (susceptible female x resistant male and vice versa) from both resistant colonies responded alike in bioassays, indicating recessive inheritance. Data on larvae susceptibility from the backcross offspring between F1 and their respective susceptible and resistant parental colonies are consistent with a monofactorial and autosomal mode of inheritance. In vitro binding assays between 125I binary (Bin2) toxin and the brush border membrane fractions (BBMF) from CqRL1/2362 and RLCq1/C3-41 larvae showed that resistance, in both colonies, is caused by a failure in the binding step of the B. sphaericus Bin2 toxin to its specific midgut receptor. The specific and saturable binding of Bin2 toxin to BBMF from F1 larvae (CqRL1/2362 X susceptible counterpart) confirms the recessive inheritance of the resistance gene. Further studies are needed to advance understanding of B. sphaericus resistance.

A strain of Bacillus sphaericus causes slower development of resistance in Culex quinquefasciatus.

Two field-collected Culex quinquefasciatus colonies were subjected to selection pressure by three strains of Bacillus sphaericus, C3-41, 2362, and IAB59, under laboratory conditions. After 13 and 18 generations of exposure to high concentrations of C3-41 and IAB59, a field-collected low-level-resistant colony developed >144,000- and 46.3-fold resistance to strains C3-41 and IAB59, respectively. A field-collected susceptible colony was selected with 2362 and IAB59 for 46 and 12 generations and attained >162,000- and 5.7-fold resistance to the two agents, respectively. The pattern of resistance evolution in mosquitoes depended on continuous selection pressure, and the stronger the selection pressure, the more quickly resistance developed. The resistant colonies obtained after selection with B. sphaericus C3-41 and 2362 showed very high levels of cross-resistance to B. sphaericus 2362 and C3-41, respectively, but they displayed only low-level cross-resistance to IAB59. On the other hand, the IAB59-selected colonies had high cross-resistance to both strains C3-41 and 2362. Additionally, the slower evolution of resistance against strain IAB59 may be explained by the presence of another larvicidal factor. This is in agreement with the nontoxicity of the cloned and purified binary toxin (Bin1) of IAB59 for 2362-resistant larvae. We also verified that all the B. sphaericus-selected colonies showed no cross-resistance to Bacillus thuringiensis subsp. israelensis, suggesting that it would be a promising alternative in managing resistance to B. sphaericus in C. quinquefasciatus larvae.