Development and application of a method for quantifying factors affecting chloramine decay in service reservoirs

Service reservoirs play an important role in maintaining water quality in distribution systems. Several factors affect the reservoir water quality, including bulk water reactions, stratification, sediment accumulation and wall reactions. It is generally thought that biofilm and sediments can harbour microorganisms, especially in chloraminated reservoirs, but their impact on disinfectant loss on disinfectant loss has not been quantified. Hence, debate exists as to the extent of the problem. To quantify the impact, the reservoir acceleration factor (F_Ra) is defined. This factor represents the acceleration of chloramine decay arising from all causes, including changes in retention time, assuming that the reservoir is completely mixed. Such an approach quantifies the impact of factors, other than chemical reactions, in the bulk water. Data from three full-scale chloraminated service reservoirs in distribution systems of Sydney, Australia, were analysed to demonstrate the generality of the method. Results showed that in two large service reservoirs (404 × 10³ m³ and 82 × 10³ m³) there was minimal impact from biofilm/sediment. However, in a small reservoir (3 × 10³ m³), the biofilm/sediment had significant impact. In both small and large reservoirs, the effect of stratification was significant.     

Shotgun metagenomics of dust microbiome from flight deck and cabin in civil aviation aircraft

Microbial exposure is related to the health of passengers on commercial aircraft, but no studies characterized the microbial composition at the species level and identified their ecological determinants. We collected vacuum dust from floor and seat surfaces in flight decks and cabins of 18 aircraft, and amplification-free shotgun metagenomics was conducted to characterize the microbial composition. In total, 7437 microbial taxa were identified. The relative abundance for bacteria, eukaryote, viruses, and archaea was 96.9%, 1.8%, 0.3%, and 0.03%, respectively. The top bacterial species mainly derived from outdoor air and human skin included Sphingomonas, Corynebacterium, Micrococcus luteus, Variovorax paradoxus, Paracoccus dentrificans, and Propionibacterium acnes. The abundance of NIAID-defined pathogens was low, accounted for only 0.23% of total microbes. The microbial species and functional composition were structured by the indoor surface type (R² = 0.38, Adonis), followed by the manufacturer of the aircraft (R² = 0.12) and flight duration (R² = 0.07). Indoor surfaces affected species derived from different habitats; the abundance of dry skin and desiccated species was higher on textile surfaces, whereas the abundance of moist and oily skin species was higher on leather surfaces. The growth rates for most microbes were stopped and almost stopped.     

Combining culturing and 16S rDNA sequencing to reveal seasonal and room variations of household airborne bacteria and correlative environmental factors in nanjing,southeast china

Exposure to bioaerosols poses important health effects on occupants. To elucidate seasonal and room variations of household airborne bacteria, this study investigated 30 residential homes during summer and winter throughout Nanjing, Southeast China, with a humid subtropical climate. Culturing and 16S rDNA sequencing methods were combined in this study. Results showed that the community structure and composition in the same season but different homes show similarity, however, they in the same home but in different seasons show a huge difference, with Sphingomonas (25.3%), Clostridium (14.8%), and Pseudomonas (7.6%) being the dominant bacteria in summer, and Pseudomonas (57.1%) was dominant bacteria in winter. Culturable concentrations of bacteria were also significantly higher in summer (854 ± 425 CFU/m³) than in winter (231 ± 175 CFU/m³), but difference by home or room was relatively minor. More than 80% of culturable bacteria (<4.7 μm) could penetrate into lower respiratory tract. The seasonal variations of bacterial community and concentrations were closely associated with seasonal variations of temperature, humidity, and PM_2.5. Higher concentrations and larger sizes were observed in the bathroom and kitchen, typically with higher humidity than other rooms.     

The effect of anoxia and anaerobia on ciliate community in biological nutrient removal systems using laboratory-scale sequencing batch reactors (SBRs)

Little is known about the effect of anaerobic and anoxic stages on the protozoan community in the activated sludge process and how this subsequently affects performance. Using a laboratory-scale BNR system the effect of different periods of anoxia on both the protozoan community and performance efficiency have been examined. Four SBRs were operated at two cycles per day using a range of combined anoxic/anaerobic periods (0, 60, 120 and 200 min). Effluent quality (TOC, BOD, TP, TN, NH₄-N, NO₃-N and NO₂-N), sludge settleability and ciliate community (species diversity and abundance) were analysed over a periods of up to 24 days of operation. The species richness and total abundance of ciliates were found to decrease with longer anoxic/anaerobic periods. Both, positive and negative significant correlations between the abundance of certain species and the period of anoxia was observed (e.g. Opercularia microdiscum, Epicarchesium granulatum), although other species (i.e. Acineria uncinata, Epistylis sp.) were unaffected by exposure to anoxia. In the laboratory-scale units, the 60 min anoxic/anaerobic period resulted in good process performance (TOC and BOD removal of 97-98% respectively), nitrification (80-90%), denitrification (52%) but poor levels of biological P-removal (12%); with the protozoan community moderately affected but still diverse with high abundances. Increasing the length of anoxia to up to 200 min did not enhance denitrification although P-removal rates increased to between 22 and 33%; however, ciliate species richness and total abundance both decreased and sludge settleability became poorer. The study shows that activated sludge ciliate protozoa display a range of tolerances to anoxia that result in altered ciliate communities depending on the length of combined anoxic/anaerobic periods within the treatment process. It is recommended that anoxic/anaerobic periods should be optimised to sustain the protozoan community while achieving maximum performance and nutrient removal.     

Seasonal periodicity of plankton and benthic fauna community structure and diversity in a small North African reservoir

Aquatic biota in terms of phytoplankton, zooplankton and benthic fauna were qualitatively and quantitatively followed seasonally during 2007 in a North African small reservoir, Aswan Reservoir. Simultaneously, seasonal variations in water quality were investigated in order to determine how far the aquatic biota could be altered by physicochemical and biotic factors. In phytoplankton of the investigated reservoir, 75 species belonging to four systematic groups were recorded, comprising 11 Cyanoprokaryota, 24 Bacillariophyceae, 2 Dinophyceae and 38 Chlorophyceae. Most numerous zooplankton were Rotifera (23 species). Cladocera and Copepoda were less numerous, with only seven and three species, respectively. Early development stages of copepods, nauplii and copepodites were sometimes recorded in considerable numbers. Twenty‐two invertebrate species related to five animal groups were exclusively benthic fauna: three Oligochaeta, nine Mollusca, seven larvae of Chironomidae, one Platyhelminthes, one Hirudinea and one Decapoda. Generally, the estimated values of phytoplankton species richness were relatively higher than those of zooplankton or benthic fauna. In particular, phytoplankton was influenced by physicochemical factors – water transparency, salinity and soluble reactive silica contents – as well as biotic factors – zooplankton and benthic fauna. Levels of pH value, Mg⁺², NO₃‐N and chlorophyll‐a contents appeared to be the most influential parameters dictating the pattern of seasonal periodicity of benthic fauna. Numerically, the phytoplankton was somewhat more abundant in winter and autumn than in spring or summer. The peak of zooplankton population densities was observed in spring season. Benthic fauna tended to be abundant in summer and autumn seasons, showing a reverse seasonal trend from that of zooplankton. Cyanoprokaryota and Bacillariophyceae were the most important groups that determined the seasonal fluctuation pattern of phytoplankton. Rotifera and Copepoda were the most predominant groups influencing the seasonal periodicity of zooplankton. Oligochaeta and Mollusca alternated the dominancy of benthic fauna community in Aswan Reservoir.     

Quantifying quagga mussel veliger abundance and distribution in Copper Basin Reservoir (California) using acoustic backscatter

Quagga mussels (Dreissena bugensis) have been linked to oligotrophication of lakes, alteration of aquatic food webs, and fouling of infrastructure associated with water supply and power generation, causing potentially billions of dollars in direct and indirect damages. Understanding their abundance and distribution is key in slowing their advance, assessing their potential impacts, and evaluating effectiveness of control strategies. Volume backscatter strength (Sv) measurements at 201- and 430-kHz were compared with quagga mussel veliger and zooplankton abundances determined from samples collected using a Wisconsin closing net from the Copper Basin Reservoir on the Colorado River Aqueduct. The plankton within the lower portion of the water column (>18 m depth) was strongly dominated by d-shaped quagga mussel veligers, comprising up to 95-99% of the community, and allowed direct empirical measurement of their mean backscattering cross-section. The upper 0-18 m of the water column contained a smaller relative proportion of veligers based upon net sampling. The difference in mean volume backscatter strength at these two frequencies was found to decrease with decreasing zooplankton abundance (r² = 0.94), allowing for correction of Sv due to the contribution of zooplankton and the determination of veliger abundance in the reservoir. Hydroacoustic measurements revealed veligers were often present at high abundances (up to 100-200 ind L⁻¹) in a thin 1-2 m layer at the thermocline, with considerable patchiness in their distribution observed along a 700 m transect on the reservoir. Under suitable conditions, hydroacoustic measurements can rapidly provide detailed information on the abundance and distribution of quagga mussel veligers over large areas with high horizontal and vertical resolution.     

Influence of housing characteristics on bacterial and fungal communities in homes of asthmatic children

Variations in home characteristics, such as moisture and occupancy, affect indoor microbial ecology as well as human exposure to microorganisms. Our objective was to determine how indoor bacterial and fungal community structure and diversity are associated with the broader home environment and its occupants. Next‐generation DNA sequencing was used to describe fungal and bacterial communities in house dust sampled from 198 homes of asthmatic children in southern New England. Housing characteristics included number of people/children, level of urbanization, single/multifamily home, reported mold, reported water leaks, air conditioning (AC) use, and presence of pets. Both fungal and bacterial community structures were non‐random and demonstrated species segregation (C‐score, P < 0.00001). Increased microbial richness was associated with the presence of pets, water leaks, longer AC use, suburban (vs. urban) homes, and dust composition measures (P < 0.05). The most significant differences in community composition were observed for AC use and occupancy (people, children, and pets) characteristics. Occupant density measures were associated with beneficial bacterial taxa, including Lactobacillus johnsonii as measured by qPCR. A more complete knowledge of indoor microbial communities is useful for linking housing characteristics to human health outcomes. Microbial assemblies in house dust result, in part, from the building's physical and occupant characteristics.     

Investigation of inflammatory and allergic responses to common mold species: Results from in vitro experiments,from a mouse model of asthma,and from a group of asthmatic patients

Most studies on molds focus on Alternaria alternata and Aspergillus fumigatus. Here, we report on inflammatory and allergenic properties of more typical indoor species Aspergillus versicolor, P. chrysogenum, C. cladosporioïdes, and C. sphaerospermum that were compared to A. alternata and A. fumigatus. In a mouse model, after intranasal instillation, A. alternaria, A. versicolor, and C. sphaerospermum induced the early recruitment of neutrophils and the strong expression of inflammatory markers in the bronchoalveolar lavages fluids. A. fumigatus also induced the early accumulation of neutrophils but with lower levels of inflammatory markers. Chronic treatment induced variable response according to species: P. chrysogenum and A. fumigatus appeared strong pro‐allergenic inducers compared to A. alternata and C. sphaerospermum while A. versicolor and C. cladosporioides induced a mixed pro‐allergenic/pro‐inflammatory response. In mold‐sensitized asthmatics, mold‐specific Immunoglobulin E (IgE) were detected with an in‐house dot‐blot assay. A. fumigatus and A. alternata were the most frequent sensitizers. Altogether, P. chrysogenum, P. brevicompactum, C. sphaerospermum, and C. cladosporïoides were the “major sensitizer” (defined as the strongest response against a single mold species) for almost 30% of the asthmatics. These results show that, not only A. alternata and A. fumigatus, but also indoor species have strong inflammatory and allergic properties and a harmful potency.     

The variations of mercury in sediment profiles from a historically mercury-contaminated reservoir, Guizhou province, China

Baihua Reservoir in Guizhou Province, China, experienced serious Hg contamination from Guizhou Organic Chemical Plant (GOCP) between 1971 and 1997. However, the biogeochemical cycling of Hg in this reservoir is not well studied. Sediment cores were collected in fall 2002, spring 2003 and in spring and fall 2004. THg and MeHg concentrations in all sediment profiles ranged from 0.26 to 38.9 mg/kg and from 0.5 to 27.5 μg/kg (d.w.), respectively. The distribution of THg in sediment cores was characterized by a few peaks, which may correspond to the Hg-containing wastewater discharge history of the GOCP. The average THg concentrations in sediments cores decreased from upstream to downstream due to the deposition of particulate Hg, which is the major form of Hg in water. THg and MeHg concentrations in pore water varied from 6.1 to 5860 ng/L and from 0.3 to 15.4 ng/L, respectively, which were significantly higher than levels in the overlying water column. Average diffusive flux from sediment to water is 1642 and 36 ng/m²/day for THg and MeHg. The spatial distribution of THg in pore water from upstream to downstream showed the same trend as the sediment, but MeHg in pore water did not show a declining pattern with distance from the GOCP. These results suggested that sediments experienced serious contamination of Hg, and the contaminated sediment is an important Hg contamination source to the overlying water.     

Responses of aquatic organisms to metal pollution in a lowland river in Flanders: a comparison of diatoms and macroinvertebrates

The role of macroinvertebrates and diatoms as indicator for metal pollution was investigated by assessing both biota along a metal gradient in the Belgian river the Dommel. Macroinvertebrates and diatoms were sampled in summer and winter and physical-chemical characteristics of the water were measured at four different sample periods and related to sediment characteristics. Although metal concentrations, except cadmium, in the water nowhere exceeded water quality standards, high metal concentrations were measured in the sediment, indicating historical contamination of the Dommel. At the sites that were situated downstream of the pollution source, high levels of conductivity and chloride were measured in the water. Redundancy Analysis (RDA) indicated pH, phosphate and zinc as the significant environmental variables explaining each respectively 7.7%, 11.6% and 22.6% of the macroinvertebrate community composition. Two clusters could be separated, with Gammarus pulex, Leptocerus interruptus, Baetis rhodani and Cloeon dipterum associated with low zinc concentrations and Tubificidae, Asellus aquaticus, Erpobdella sp. and Chironomus thummi-plumosus associated with higher zinc concentrations. Ammonium (10.6%), conductivity (16.5%), chloride (11.4%) and zinc (5.9%) turned out to be significant variables explaining the diatom community structure. Based on physical-chemical differences and species composition, three different groups could be separated. With this Tabellaria flocculosa and Fragilaria capucina var. rumpens were associated with low metal concentrations, Gomphonema parvulum and Nitzschia palea with elevated concentrations and Eolimna minima and Sellaphora seminulum with high zinc concentrations. In conclusion, the diatom community best reflected the metal gradient. With regard to water quality indices, those based on macroinvertebrates best followed the metal pollution gradient and were most strongly correlated with physical-chemical variables of water and sediment. This study indicated that to assess the effect of metal pollution in lowland rivers, the combined use of macroinvertebrates and diatoms is more appropriate than the use of both biota separately.     

Fungal compositions and diversities on indoor surfaces with visible mold growths in residential buildings in the Seoul Capital Area of South Korea

Indoor visible mold growths are known to be associated with allergies and respiratory illnesses. However, a question remains of their compositions and diversities. Using swab sampling and high‐throughput DNA sequencing, this study analyzed taxonomic compositions and diversities of fungi on indoor surfaces laden with visible mold growths in residential apartments in South Korea. The sequencing results showed low species diversities with Shannon indices ranging from 0.14 to 2.29 (mean = 1.11). Several allergy‐related genera were detected on the same surface, where the most abundant Cladosporium with a mean relative abundance of 41% co‐occurred with less abundant Aspergillus (0.094%), Rhodotorula (6.3%), Cryptococcus (3.7%), Alternaria (4.1%), and Crivellia (17%). β diversity analyses showed significant differences in the fungal communities between enclosed balconies and other indoor areas (P < 0.05, ANOSIM), emphasizing a need to sample at multiple indoor locations when assessments are made for indoor visible mold growths. High‐throughput sequencing is powerful in characterizing compositions and diversities of fungal communities. Future studies should examine the relationships between taxonomic compositions and diversities of indoor visible molds and health outcomes of allergies and respiratory illnesses in residential buildings.     

Characterization and pro‐inflammatory responses of spore and hyphae samples from various mold species

Mold particles from Aspergillus fumigatus, Penicillium chrysogenum, Aspergillus versicolor, and Stachybotrys chartarum have been linked to respiratory‐related diseases. We characterized X‐ray‐inactivated spores and hyphae fragments from these species by number of particles, morphology, and mycotoxin, β‐glucan and protease content/activity. The pro‐inflammatory properties of mold particles were examined in human bronchial epithelial cells (BEAS‐2B) and THP‐1 monocytes and phorbol 12‐myristate 13‐acetate (PMA)‐differentiated THP‐1. Spores from P. chrysogenum and S. chartarum contained some hyphae fragments, whereas the other preparations contained either spores or hyphae. Each mold species produced mainly one gelatin‐degrading protease that was either of the metallo‐ or serine type, while one remains unclassified. Mycotoxin levels were generally low. Detectable levels of β‐glucans were found mainly in hyphae particle preparations. PMA‐differentiated THP‐1 macrophages were by far the most sensitive model with effects in the order of 10 ng/cm². Hyphae preparations of A. fumigatus and P. chrysogenum were more potent than respective spore preparations, whereas the opposite seems to be true for A. versicolor and S. chartarum. Hyphae fragments of A. fumigatus, P. chrysogenum, and A. versicolor enhanced the release of metalloprotease (proMMP‐9) most markedly. In conclusion, species, growth stage, and characteristics are all important factors for pro‐inflammatory potential.     

Modeling microbial growth in carpet dust exposed to diurnal variations in relative humidity using the “Time-of-Wetness” framework

Resuspension of microbes in floor dust and subsequent inhalation by human occupants is an important source of human microbial exposure. Microbes in carpet dust grow at elevated levels of relative humidity, but rates of this growth are not well established, especially under changing conditions. The goal of this study was to model fungal growth in carpet dust based on indoor diurnal variations in relative humidity utilizing the time-of-wetness framework. A chamber study was conducted on carpet and dust collected from 19 homes in Ohio, USA and exposed to varying moisture conditions of 50%, 85%, and 100% relative humidity. Fungal growth followed the two activation regime model, while bacterial growth could not be evaluated using the framework. Collection site was a stronger driver of species composition (P = 0.001, R² = 0.461) than moisture conditions (P = 0.001, R² = 0.021). Maximum moisture condition was associated with species composition within some individual sites (P = 0.001-0.02, R² = 0.1-0.33). Aspergillus, Penicillium, and Wallemia were common fungal genera found among samples at elevated moisture conditions. These findings can inform future studies of associations between dampness/mold in homes and health outcomes and allow for prediction of microbial growth in the indoor environment.     

Transport of C-labelled PCB compounds from sediment to water and from water to air in laboratory model systems

Tetra-, hexa- and octachlorobiphenyls were added to aquatic model systems composed of undisturbed sediment cores with an overlying water phase. Using impactor plates transport of the compounds from sediment to air was observed. About one per cent of the sediment-bound PCBs recovered in the systems left the water by jet drops from bursting bubbles. The transport of PCBs from the sediment to the air was nearly constant over time, with a transport rate of 0.62 μg · dm⁻² week⁻¹ for tetrachlorobiphenyl. Tetrachlorobiphenyl was mobile in systems with and without macroinvertebrates and in those fixed with HgCl₂. Hexa- and octachlorobiphenyls were transported from sediment to water mainly by bioturbation processes. The two latter substances had a higher adsorption to particles than tetrachlorobiphenyl. Compared to tetrachlorobiphenyl, more hexa- and octachlorobiphenyls accumulated in chironomids and tubificids.     

Changes in polycyclic aromatic hydrocarbon availability in River Tyne sediment following bioremediation treatments or activated carbon amendment

Bioremediation and activated carbon (AC) amendment were compared as remediation strategies for sediment from the River Tyne containing 16.4 ± 7.3 μg/g polycyclic aromatic hydrocarbons (PAHs) and approximately 5% coal particles by total dry sediment weight. Unamended, nutrient amended (biostimulated) and nutrient and Pseudomonas putida amended (bioaugmented) sediment microcosms failed to show a significant decrease in total sediment PAH concentrations over a one month period. Polyethylene passive (PE) samplers were embedded for 21 days in these sediment microcosms in order to measure the available portion of PAHs and accumulated 4.70 ± 0.25, 12.43 ± 1.78, and 23.49 ± 2.73 μg PAHs/g PE from the unamended, biostimulated, and bioaugmented microcosms, respectively. Higher PAH uptake by PE samplers in biostimulated and bioaugmented microcosms coincided with slower degradation of spiked phenanthrene in sediment-free filtrate from these microcosms compared to filtrate from the unamended microcosms. Microbial community analysis revealed changes in the bacterial community directly following the addition of nutrients, but the added P. putida community failed to establish itself. Addition of 2% by dry sediment weight activated carbon reduced PAH uptake by PE samplers to 0.28 ± 0.01 μg PAHs/g PE, a greater than 90% reduction compared to the unamended microcosms.     

Secondary production of a zoobenthic community under metal stress

Little is known about the influence of toxicants on the function of freshwater sediments. To better understand these effects, a long-term microcosm experiment was carried out with cadmium (Cd) as the model pollutant (50 and 400 mg Cd  kg⁻¹  dw). In a seven-month study the effect of Cd was examined on secondary production of the zoobenthos (higher taxonomic level) and specifically of the nematode community (species level). Production of almost all taxa decreased under low Cd stress, with rotifers as the only taxon that was able to thrive under this condition. High Cd stress resulted in a decrease in secondary production of all groups with strong differences between taxa. Nematode production likewise decreased, with strongest effects in the higher Cd concentration. Interestingly, at the end of the study, several bacteria-feeding species had benefited from the low Cd stress, probably due to their rapid development in relation to other species and/or the high bacterial density under this condition. Taken together, the results of this study provide insight into secondary production of sediment communities and the important effects of a toxicant thereon.     

Mercury speciation in the Valdeazogues River-La Serena Reservoir system: Influence of Almadén (Spain) historic mining activities

Mercury (Hg) speciation and partitioning have been investigated in a river-reservoir system impacted by the Almadén mining activities, the world's largest Hg district. This study is the first to simultaneously investigate Hg dynamics from above the mining district and into the La Serena Reservoir (3219 Hm³), being the third largest reservoir in Europe and the largest in Spain.Water, sediment and biota were sampled at different seasons during a 2-year study from the Valdeazogues River, which flows east-west from the mining District, to La Serena Reservoir. Simultaneously, a comprehensive study was undertaken to determine the influence of some major physico-chemical parameters that potentially influence the fate of Hg within the watershed.Concentrations of dissolved Hg in water were below 0.14 µg/L, whereas particulate Hg ranged from 0.1 to 87 µg/g, with significant seasonal variation. Total Hg concentrations varied from 7 to 74 µg/g in sediment from the Valdeazogues River, while in sediments from La Serena Reservoir were below 2 µg/g. On the other hand, methyl-Hg reached concentrations up to 0.3 ng/L in water and 6 ng/g in sediment from La Serena Reservoir, whereas maximum concentrations in Valdeazogues River were 5 ng/L and 880 ng/g in water and sediment, respectively. The distribution of Hg species in the Valdeazogues River-La Serena Reservoir system indicated a source of Hg from the mine waste distributed along the river. Total Hg in water was strongly correlated with total dissolved solids and chlorophyll a concentrations, whereas organic carbon and Fe concentrations seem to play a role in methylation of inorganic Hg in sediment. Total Hg concentrations were low in fish from Valdeazogues River (0.8-8.6 ng/g, wet weight) and bivalves from La Serena Reservoir (10-110 ng/g, wet weight), but most was present as methyl-Hg.     

Dog introduction alters the home dust microbiota

Research has largely reported that dog exposure is associated with reduced allergic disease risk. Responsible mechanism(s) are not understood. The goal was to investigate whether introducing a dog into the home changes the home dust microbiota. Families without dogs or cats planning to adopt a dog and those who were not were recruited. Dust samples were collected from the homes at recruitment and 12 months later. Microbiota composition and taxa (V4 region of the 16S rRNA gene) were compared between homes that did and did not adopt a dog. A total of 91 dust samples from 54 families (27 each, dog and no dog; 17 dog and 20 no dog homes with paired samples) were analyzed. A significant dog effect was seen across time in both unweighted UniFrac and Canberra metrics (both P = .008), indicating dog introduction may result in rapid establishment of rarer and phylogenetically related taxa. A significant dog‐time interaction was seen in both weighted UniFrac (P < .001) and Bray‐Curtis (P = .002) metrics, suggesting that while there may not initially be large relative abundance shifts following dog introduction, differences can be seen within a year. Therefore, dog introduction into the home has both immediate effects and effects that emerge over time.     

The macrobenthic community along a mercury contamination in a temperate estuarine system (Ria de Aveiro, Portugal)

Mercury is a widely distributed environmental pollutant and a toxic element to all living organisms. This study represents an attempt to evaluate its correlation with the macrobenthic community structure in a temperate estuarine system, the Ria de Aveiro (Portugal). The macrobenthic community structure showed significant differences along the mercury gradient. Overall, the increase of mercury contamination was associated with reduced total abundance, lower species richness, and dominance of tolerant taxa. The polychaetes Hediste diversicolor and Alkmaria romijni, and the isopod Cyathura carinata were associated with high levels of mercury in sediment, while the bivalves Scrobicularia plana, Cerastoderma edule and Abra alba showed higher density in lesser contaminated sites. Furthermore, highly contaminated sites showed substantially lower abundances of surface-deposit feeders and herbivores, and higher abundances of subsurface-deposit feeders and omnivores. Salinity was also a significant factor affecting the community, being responsible for seasonal variations in the macrobenthic assemblages.     

Dynamics of benthic macroinvertebrates in created wetlands receiving wastewater

This paper presents results of a study on the status and dynamics of benthic macroinvertebrates in a wetland constructed for wastewater treatment in Nairobi (Kenya), conducted for 16 weeks during the period between December 1995 and March 1996. Seventeen species of macroinvertebrates were recorded in the wetland. Species richness in the wetland was 9.6 ± 1.3 while species diversity index was 0.466. Mean pH and dissolved oxygen increased gradually from the intake point to the outlet while the BOD₅, suspended solids and free and saline ammonia decreased as the wastewater flowed throughout the wetland. The benthic macroinvertebrate community was poorly developed while microbial community appeared to be well developed. It was evident that the community structure improved with the purification of wastewater along the wetland. As discussed in the paper, aquatic benthos are crucial to wetlands ecosystems function and they are potential indicators of health of these ecosystems.