Physical and chemical properties determine zebra mussel invasion success in lakes

To address the question whether the abundance of an invasive species can be explained by physical and chemical properties of the invaded ecosystems, we gathered density data of invasive zebra mussels and the physical and chemical data of ecosystems they invaded. We assembled published data from 55 European and 13 North American lakes and developed a model for zebra mussel density using a generalized additive model (GAM) approach. Our model revealed that the joint effect of surface area, total phosphorus and calcium concentrations explained 62% of the variation in Dreissena density. Our study indicates that large and less productive North American lakes can support larger local populations of zebra mussels. Our results suggest that the proliferation of an exotic species in an area can partially be explained by physical and chemical properties of the recipient environment.     

Biodegradation of Petroleum Hydrocarbons in a Soil Polluted Sample by Oil-Based Drilling Cuttings

Microbial degradation of hydrocarbons in soils polluted by oil-based drilling mud and cuttings has been investigated by static methods such as composting or biopiling. Bioremediation of polluted soils by oil-based drilling cuttings through a slurry bioreactor has not previously been reported. The main aim of this work is to monitor hydrocarbon biodegradation in slurry of drilling cuttings and unpolluted soils and the effects of nutrients on it. Indigenous, bacterial-mixed culture isolated from a polluted soil by drilling cuttings adapted to drilling mud concentrations up to 15% (v/v) was done during a 15-month program. The total petroleum hydrocarbons’ (TPHs) removal efficiency in C/N/P 100/5/1 ratio was 90.5 and 79.85% under experimental and control conditions, respectively. The microbial count on the first day, 15 × 10⁷ CFUg^?1, reached 20 × 10⁹ CFUg^?1on the twenty-first day at experimental conditions. The TPH removal efficiency in C/N/P 100/10/2 was 92.5 and 82.25% at experiment and control, respectively. Increasing nitrogen and phosphorous amount couldn't increase microbial count in comparison with C/N/P ratio 100/5/1. The measured biomass contents and microbial counts in experiments were significantly higher than the control and confirmed hydrocarbons’ biodegradation during the time. Results showed that slurry bioreactors could accelerate the biodegradation of TPHs and reduce remediation time in soil polluted by oil-based drilling cuttings.     

Study of PM10, PM2.5, and PM1 levels in during dust storms and local air pollution events in urban and rural sites in Tehran

The aim of this study is to survey the PM₁₀, PM_2.5, and PM₁ concentrations in rural and urban areas in Tehran province during cold, warm and dust storm days from December 22, 2016 to June 5, 2017 using Grimm Model aerosol spectrometer. During the study period, daily PM₁₀, PM_2.5, and PM₁ concentrations ranged from 27.2 to 244.96, 8.4 to 77.9, and 6.5 to 56.8 μg/m³ in urban sites, and 22.8 to 286.4, 6 to 41.1, and 2.1 to 20.2 μg/m³ in rural parts, respectively. Particularly, both daily WHO limits for outdoor PM₁₀ (50.0 μg/m³) and PM_2.5 (25.0 μg/m³) exceeded in 95% and 83% of the outdoor measurements in winter and 82% and 58% in total sampled days in urban site, respectively. The 24-h average PM₁₀ and PM_2.5 concentrations also exceeded by 59% and 18% in winter and by 36% and 14% of all sampling days in rural site, respectively. During the dust storm, the 24-h average PM₁₀, PM_2.5, and PM₁ concentrations were, respectively 4.7, 2, and 1.96 times higher than those in urban site and 2, 1.7, and 1.3 times more than those in rural site in all sampled days.     

Determination of culturable indoor airborne fungi during normal and dust event days in Ahvaz, Iran

The first purpose of our study was to determine culturable indoor airborne fungi in different places in Ahvaz during normal and dust event days. Ahvaz is the biggest city in southwest of Iran which has suffered from dust storms in recent decade. To minimize personal exposure to polluted air, governmental and private sectors excluding critical places such as hospitals, fire department and security organization are closed during dust event days. Therefore, the second objective of this survey was to see whether this plan (forced shutdown) is in place. Samples were collected from July 2010 to March 2011 by using quick take 30 equipped with a single-stage sampler. Fungal population was measured in school, university and hospital during normal and dust event days. Five dominant fungi genera in three sampling stations were Cladosporium, Alternaria, Aspergillus, Penicillium and Rhizopus the concentrations (CFU/m³) of which were higher during dust events than normal days. Airborne fungi such as Aspergillus, Mucor and Rhizopus are opportunistic fungi which can cause aspergillusis and mucormycosis infections in immunodeficiency individuals, vulnerable groups as well as healthy people. The results of this study confirmed the measure of forced shutdown in Ahvaz city due to increased concentration of fungi during dust event days.     

Age, growth and reproduction of the Caspian roach (Rutilus rutilus caspicus) in the Anzali and Gomishan wetlands, North Iran

The hypothesis of environmentally related life history variations between two Rutilus rutilus caspicus populations was investigated by comparing Gomishan and Anzali populations along the southern shores of the Caspian Sea. The roach growth rate in the Anzali wetland was higher than in the Gomishan wetland. There were significant differences in growth patterns between males and females from both wetlands, however the sex ratios were not significantly different. Fecundity or reproductive investment (Gonadosomatic index – GSI) of the Gomishan roach was significantly more than the Anzali roach. In both areas the absolute fecundity was significantly positive correlated to age and total length.     

Concentration and distribution characteristics of airborne fungi in indoor and outdoor air of Tehran subway stations

The concentration and distribution characteristics of airborne fungi were investigated in indoor and outdoor air of two metro stations (Imam Khomeini and Sadeghiyeh stations) in Tehran subway. Samples were taken from indoor air at each station from platform and ticket office area also from adjacent outdoor air of each station. Indoor sampling was conducted for two types of trains, old and new. The concentration of airborne fungi ranged from 21 CFU/m³ at the outdoor air of Imam Khomeini station to 1,402 CFU/m³ in the air samples collected from the platform of this station. Results showed that airborne fungi concentrations at indoor air were higher than the outdoor air (p < 0.05), and fungal levels significantly correlated with the number of passengers (p < 0.05; r = 0.68) and RH % (p < 0.05; r = 0.43). Sixteen genera of fungi were isolated in all sampled environments. The predominant genera identified in indoor and outdoor air were Penicillium spp. (34.88 % of total airborne fungi) and Alternaria spp. (29.33 % of total airborne fungi), respectively. The results of this study showed that the indoor air quality in subway is worse than the outdoor air.     

Predator‐induced morphological defences in two invasive dreissenid mussels: implications for species replacement

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Non-lethal predator effects on the feeding rate and prey selection of the exotic zebra mussel Dreissena polymorpha

Predators may induce changes in prey feeding that indirectly influence both the impact of prey on resource abundances and their interactions with other species in their community. We evaluated whether clearance and excretion (faeces plus pseudofaeces) of phytoplankton by zebra mussels were affected by the presence of predatory cues from roach, Rutilus rutilus, and signal crayfish, Pasifastacus leniusculus . We found that non-lethal effects of predators can alter zebra mussel clearance rate and thus the impact of zebra mussels on phytoplankton. Risk cues released by both predators had similar negative effects on clearance rate of zebra mussels and cascading positive indirect effects on phytoplankton resources. Predation risk had a stronger effect on zebra mussels' clearance rate of cyanobacteria and diatoms than cryptophytes and chrysophytes. The presence of predators did not significantly affect the rate at which zebra mussels expelled and excreted phytoplankton, although there was a tendency for more chlorophyll to be expelled and excreted in the presence of predators. Our results contribute to the growing evidence that predators indirectly affect resource dynamics and food web structure through their non-lethal effects on consumers. Our results suggest that exotic species such as zebra mussels can show behavioural responses to both native (e.g. roach) and exotic (e.g. crayfish) predators.     

Retention of N and P by zebra mussels (<Emphasis Type="Italic">Dreissena polymorpha</Emphasis> Pallas) and its quantitative role in the nutrient budget of eutrophic Lake Ekoln,Sweden

We quantified cover, population densities, size distribution and biomass of zebra mussels along 7 transects in eutrophic Lake Ekoln (Sweden). We also analyzed the elemental (C, N, P) composition of zebra mussel soft tissue and computed their retention rates of N and P their quantitative role in the lake’s nutrient budget. We hypothesized that zebra mussels play an important role in the nutrient budget of the lake and speculate that the successive harvesting of cultured mussels could contribute to the lake’s rate of recovery from cultural eutrophication. At depths exceeding 5 m, mussels covered consistently less than 5% or were absent. Similarly, mean densities were 3,158 ± 2,143 ind m⁻² between 2 and 4 m, but rapidly declined at larger depths. Calculated clearance rates averaged 19.4 ± 2.3 km³ y⁻¹, implying the entire lake is filtered every 8–10 days. Concentrations of N and P in mussel soft tissue averaged 100.9 ± 1.5 mg N g⁻¹ DW and 9.3 ± 0.2 mg P g⁻¹ DW. The lake population was estimated to 22.2 ± 2.6 × 10¹⁰ mussels, corresponding to a standing stock biomass of 362 ± 42 ton DW, or conservative estimates of 36.6 ± 4.3 ton N and 3.4 ± 0.4 ton P. Assuming a life span of 2–3 years gives a retention estimate of 1.2–1.8 ton P y⁻¹ by mussels, corresponding to 50–77% of the annual P influx from Uppsala sewage treatment plant to the lake. Similarly, annual N-retention by zebra mussels makes up 13–20 ton N y⁻¹, largely equaling the annual N-deposition from atmospheric sources on the lake’s surface. These retention rates correspond to only a few percent of the annual P-load from agricultural sources, but we argue that the quantitative role of zebra mussels in nutrient budgets is much larger if these budgets are adjusted for the bias introduced by coarse estimates of N and P pools that include a large share of refractory P.