Ecological responses of periphyton dry mass and epilithic diatom community structure for different atrazine and temperature scenarios

Climate change–induced temperature increase may influence the ecotoxicity of agricultural herbicides such as atrazine and consequently negatively impact aquatic biota. The objective of this study was to assess the effects of increased temperature on the ecotoxicity of atrazine to diatom community structure and stream periphyton load using laboratory microcosm experiments. A natural periphyton community from the Mukwadzi River, Zimbabwe, was inoculated into nine experimental systems containing clean glass substrates for periphyton colonisation. Communities were exposed to 0 µg∙L-1 (control), 15 µg∙L-1 and 200 µg∙L-1 atrazine concentrations at 3 temperature levels of 26°C, 28°C and 30°C. Periphyton dry weight and community taxonomic composition were analysed on samples collected after 1, 2 and 3 weeks of colonisation. A linear mixedeffects model was used to analyse the main and interactive effects of atrazine and temperature on dry mass, species diversity, evenness and richness. Temperature and atrazine had significant additive effects on species diversity, richness and dry mass. As temperature increased, diatom species composition shifted from heat-sensitive species such as Achnanthidium affine to heat-tolerant species such as Achnanthidium exiguum and Epithemia adnata. Increasing temperature in aquatic environments contaminated with atrazine results in sensitive and temperature-intolerant diatoms being eliminated from periphyton communities. Climate change will exacerbate effects of atrazine on periphyton dry mass and diatom community structure.Keywords: ecotoxicology, microcosm, biomonitoring, climate chang

Assessment of water quality based on diatom indices in a small temperate river system, Kowie River, South Africa

This study aimed to assess the impact of land use patterns on water quality and benthic diatom community structure and to test the applicability of diatom indices developed in other regions of the world to a small temperate southern African river system. Sampling was conducted at eight study sites along the length of the river on four separate occasions. Multivariate data analyses were performed on the diatom community dataset to specify the main gradients of floristic variation and to detect and visualize similarities in diatom samples in relation to land-use patterns within the catchment. One hundred and twelve (112) diatom species belonging to 36 genera were recorded during the study. Canonical correspondence analysis (CCA) demonstrated that variations in the benthic diatom community structure were best explained by ammonium, nitrate, conductivity, pH, temperature, resistivity and water flow. OMNIDIA was used for calculation of selected diatom water quality indices. A number of the indices, e.g., the trophic diatom index (TDI), eutrophication/pollution index and biological index of water quality (BIWQ), either under- or over-estimated the water quality of the system. With few exceptions, there were no significant correlations (p> 0.05) between the diatom indices’ values and the nutrient variables. The absence of any significant correlations between the diatom indices’ values and selected physico-chemical variables suggests that indices developed in other regions of the world may not be suitable for temperate southern African rivers

A spatial assessment of stream-flow characteristics and hydrologic alterations, post dam construction in the Manyame catchment, Zimbabwe

The global hydrologic regime has been intensively altered through activities such as dam construction, water abstraction, and inter-basin transfers. This paper uses the Range of Variability Approach (RVA)  and daily stream flow records from nine gauging stations to characterize stream-flow post dam construction in the Manyame catchment, Zimbabwe. We identify which variables continue to be altered, upstream and at different distances downstream, to distinguish sections with the highest  potential for ecological disruption and to understand how hydrological alterations dissipate downstream of dams. Our results indicate that different sections of the same river have different stream-flow  characteristics post dam construction. The most adverse effects of dams were on downstream stretches of the river which were characterized by low flows, extreme low flows and an increased number of zero-flow days. These differences reflect the  operation rules of the Manyame catchment dams. While the change in stream-flow characteristics is  apparent in the 0–10 km range, it is slightly felt in the 11–20 km range and totally disappears at distances >20 km downstream of dams. These changes in stream characteristics, and that damming is only restricted to the upper third of the catchment, make the hydrologic fragmentations in the catchment minor. However, the continued hydrologic alterations post dam construction raise important concerns about the interactions of hydrology with other factors like sediment deposition upstream of dams and climate change. We  recommend that catchment managers target enhancing the natural flow variability of the river instead of meeting target flows.Keywords: damming, range of variability approach, stream-flow characteristic

Challenges of diatom-based biological monitoring and assessment of streams in developing countries

Stream biomonitoring tools are largely lacking for many developing countries, resulting in adoption of tools developed from other countries/regions. In many instances, however, the applicability of adopted tools to the new system has not been explicitly evaluated. The objective of this study was to test the applicability of foreign diatom-based water quality assessment indices to streams in Zimbabwe, with the view to highlight challenges being faced in diatom-based biological monitoring in this developing country. The study evaluated the relationship between measured water quality variables and diatom index scores and observed some degree of concordance between water quality variables and diatom index scores emphasising the importance of diatom indices in characterization and monitoring of stream ecological conditions in developing countries. However, ecological requirements of some diatom species need to be clarified and incorporated in a diatom-based water quality assessment protocol unique to these regions. Resources should be channelled towards tackling challenges associated with diatom-based biological monitoring, principally taxonomic studies, training of skilled labour and acquiring and maintaining the necessary infrastructure. Meanwhile, simpler coarse taxonomy-based rapid bioassessment protocol, which are is less time and resource consuming and require less specialised manpower can be developed for the country

The Impact of Sewage Effluent and Natural Self-purification in the Upper Chinyika River Below Hatcliffe Sewage Works, Harare.

The impact of sewage effluent and natural self-purification in the upper Chinyika River was investigated during the period October 2004 to February 2005. The physico-chemical and river flow variables, and water samples, were colleted on monthly basis. The samples were analysed for total nitrogen, total phosphorus, chemical oxygen demand and total dissolved solids using the appropriate methods. Sediment samples were also collected once during the dry months and also once during the wet months and were analysed for total nitrogen, total phosphorus and heavy metals. The nutrient concentrations in the water column and loading levels in the sediments were high just below sewage outflow in to the river, generally decreasing with increasing distance from the point of sewage outflow because of self-purification. The nutrient concentration was high during the dry months with the highest mean values (N = 6.35; P = 4.01 mg l-1) being recorded in November and was low during the wet months with the lowest values (N = 1.33; P = 0.57 mg l-1) being recorded in January and December respectively, suggesting dilution effect. The nutrient load, on the other hand, was high during the wet months with the highest mean values (N = 8704.80 ; P = 2434.00 kg month-1) being recoded in January suggesting that organic matter was washed away from the catchment (diffuse inputs) in to the river channel resulting in high nutrient loading levels. The nutrient level in the sediments was high during the dry months (mean N = 1.01; mean P = 0.39 mg g-1 dry sediment) and low during the wet months (mean N = 0.37; mean P = 0.06 mg g-1 dry sediment) probably due to sediment re-suspension and the subsequent transportation because of storm action. There were no detectable temporal and spatial trends observed in heavy metal levels in the sediments. The other physico-chemical variables showed a general tendency of deteriorating just below sewage outflow and then improving with increasing distance downstream because of self-purification, except conductivity. High self-purification capacity was observed in the upper Chinyika River during the dry and wet months though it was generally lower in the latter coinciding with the observed riparian vegetation senescence, thus, emphasizing the importance of riparian vegetation in water quality monitoring in river channels. Conservation of riparian wetlands is, thus, central to sound watershed management. The capacity of rivers to purify themselves should be managed so that they can absorb pollution before discharging into lakes and reservoirs

Assembléias de diatomáceas como indicadores de condições de campo e de laboratório em sistemas lóticos: conservação e gestão da qualidade da água na captação de São Carlos-SP, Brasil

Comunidades perifíticas (especialmente diatomáceas) constituem um sistema rico em informações para o monitoramento ambiental, colocando-as entre os indicadores mais importantes das condições ecológicas em sistemas lóticos. Nesta tese, os estudos de campo e experimentos de laboratório foram realizados para esclarecer os confusos efeitos da seleção do substrato, eutrofização, poluição orgânica, força iônica, padrões de uso do solo e poluição por metais pesados nas comunidades bentônicas de diatomáceas. Características das comunidades bentônicas de diatomáceas em relação ao nível e tipo de poluição foram analisadas através de critérios gerais (clorofila a, peso seco, peso seco de cinza e densidade celular no caso dos experimentos de laboratório) e critérios específicos (método de valor de indicador, técnicas de análise multivariada e índices baseados nas diatomáceas). Para estudos de campo, as comunidades de diatomáceas epilíticas, epífitas, epipsâmicas e epipelicas, além das que crescem em tijolos e vidros, foram avaliadas, assim como a qualidade da água. Um gradiente decrescente da qualidade da água foi observado a partir da área agrícola/florestal até a área urbana. A estrutura da comunidade de diatomáceas refletiu este gradiente. Pontos em áreas de nascentes, com boa qualidade da água, foram caracterizados por espécies como Eunotia bilunaris, E. intermedia, Aulacoseira alpigena, Cymbopleura naviculiformis e Stauroneis phoenicenteron. Pontos em áreas urbanas, com média à baixa qualidade da água foram caracterizados por espécies como Frustulia rhomboids, Nitzschia linearis, Cyclotella pseudostelligera, Pinnularia gibba e Achnanthidium minutissimum e os pontos em áreas urbanas próximo à jusante, com baixa qualidade da água, por espécies como Luticola geoppertiana, Nitzschia palea, Sellaphora pupula, Planotidium lanceolatum e Fallacia monoculata. Espécies comuns de diatomáceas não foram restritas em um único substrato, embora a preferência fosse geralmente alta para natural (especialmente macrófitas) em comparação com substratos artificiais. Os resultados da análise multivariada da qualidade da água baseados em diatomáceas amostradas em diferentes substratos demonstraram ser intercambiáveis. Variância nos dados das diatomáceas foi dividida entre dois conjuntos de variáveis exploratórias, ou seja, força iônica (26,9%), outras variáveis como, eutrofização e poluição orgânica (23,0%), variância compartilhada (11,3%) e variação não explicada (38,8%). Finalmente, 17 índices desenvolvidos em outras regiões provaram ser úteis para fornecer uma indicação da qualidade das águas estudadas. 4 Para os experimentos de laboratório, os efeitos do cádmio, cromo III e chumbo sobre as comunidades perifíticas naturais amostradas no rio Monjolinho, foram estudados. Hormese foi demonstrado com um EC50 de 0,077 mgL-1 Cd registrado. Boa capacidade de acumulação de metal (total e intracelular) pelo perifíton foi demonstrada, dependendo da concentração do metal e duração da exposição. Pb e Cr III diminuíram os efeitos da toxicidade de Cd em comunidades perifíticas sugerindo antagonismo. Finalmente, os efeitos combinados de freqüência, duração, período de recuperação, tipo de produto químico e tempo de pulsos com elevadas concentrações de Cd, Cr III e Pb em comunidades perifíticas foram avaliados. Quanto mais a freqüência e a duração do pulso se aproximam de uma exposição contínua, maiores serão os efeitos dos contaminantes sobre a vida aquática. Quanto maior a freqüência de pulsos de curta duração, mais provável é a produção de efeitos semelhantes aos das exposições de longa duração. A luminosidade mostrou ter um papel importante na modulação dos efeitos de toxicidade de metais sobre a vida aquática. Mudanças na composição de espécies (desenvolvimento de espécies mais resistentes como A. minutissimum e redução das espécies mais sensíveis, como Navicula viridula, Navicula cryptocephala e E. bilunaris), diminuição da riqueza e diversidade, alterações morfológicas (deformidade) das células de diatomáceas, aumento da concentração de metais, duração de exposição e diferentes cenários de exposição foram observados.Universidade Federal de Sao CarlosPeriphyton communities (especially diatoms) constitute a system rich in information for environmental monitoring, placing them among important indicators of ecological conditions in lotic systems. In this thesis, field studies and laboratory experiments were conducted to elucidate the confounding effects of substrate selection, eutrophication, organic pollution, ionic strength, land-use patterns, and heavy metal pollution on benthic diatom communities. Characteristics of benthic diatom communities in relation to pollution level and type were analysed through general criteria (chlorophyll a, dry weight, ash-free dry weight, and cell densities in the case of laboratory experiments) and specific criteria (indicator value method, multivariate techniques and diatom-base indices). For field studies, epilithic, epiphytic, epipsammic and epipelic diatom communities and those growing on bricks and glasses and water quality were assessed. A gradient of decreasing water quality was observed from the agricultural/forested area to the urban area. Diatom community structure closely reflected this gradient. Upstream sites with good water quality were characterized by such species as Aulacoseira alpigena, Cymbopleura naviculiformis, Eunotia bilunaris, E. intermedia and Stauroneis phoenicenteron. Urban sites with medium to bad water quality were characterised by such species as Frustulia rhomboids, Nitzschia linearis, Cyclotella pseudostelligera, Pinnularia gibba and Achnanthidium minutissimum. Downstream urban sites with very bad water quality were characterised by such species as Luticola geoppertiana, Nitzschia palea, Sellaphora pupula, Planotidium lanceolatum and Fallacia monoculata. Common diatom species were not restricted to a single substrate, though preference was generally high for natural (especially macrophytes) compared to artificial substrates. The results of diatom-based multivariate water quality assessment based on different substrates were shown to be interchangeable. Variance in diatom data was partitioned between two sets of exploratory variables, i.e. ionic strength (26.9%), other variables, particularly eutrophication and organic pollution (23.0%), shared variance (11.3%) and unexplained variance (38.8%). Finally, 17 indices developed in other regions proved useful in providing an indication of the quality of the investigated waters. For laboratory experiments, effects of cadmium, chromium III and lead on natural periphyton community sampled from the Monjolinho River were studied. Hormesis was demonstrated with a Cd EC50 of 0.077 mg.L-1 being recorded. High metal accumulation 2 capacity (total and intracellular) by periphyton was demonstrated depending on metal concentration and exposure duration. Pb and Cr III were shown to decrease the toxicity effects of Cd on periphyton communities suggesting antagonism. Finally, combined effects of frequency, duration, recovery period, chemical type and timing of pulses with elevated Cd, Cr III and Pb concentrations on periphyton communities were assessed. The closer the frequency and duration of the pulse is to a continuous exposure, the greater the effects of the contaminant on aquatic life. The higher the frequency of short duration pulses the more likely they are to produce effects similar to that of long duration exposures. Light was shown to have a potential role in modulating the effects of metal toxicants on aquatic life. Shifts in species composition (development of more resistant species like A. minutissimum and reduction of sensitive ones like Navicula viridula, Navicula cryptocephala, and Eunotia bilunaris), decreases in species richness and diversity and morphological alterations (deformities) of diatom cells with increasing metal concentration and exposure duration and different exposure scenarios were observed

Cadmium and lead toxicity on tropical freshwater periphyton communities under laboratory-based mesocosm experiments

Periphyton constitutes an important community that is useful for assessment of ecological conditions in lotic systems. The objective of this study was to assess the effects of different mixtures of Cd and Pb on periphyton growth as well as Cd and Pb mixtures toxicity to diatom assemblages in laboratory mesocosm experiments. A natural periphyton community sampled from the Monjolinho River (South of Brazil) was inoculated into five experimental systems containing clean glass substrates for periphyton colonization. The communities were exposed to mixtures of dissolved Cd and Pb concentrations of 0.01 and 0.1 mg l-1 Cd and 0.033 and 0.1 mg l-1 Pb. Periphyton ash-free dry weight, growth rate, diatom cell density and diatom community composition were analyzed on samples collected after 1, 2 and 3 weeks of colonization. High Cd concentration (0.1 mg l-1) has negative effects on periphyton growth while high concentration of Pb (0.1 mg l-1) decreased the toxic effects of Cd on periphyton growth. Shifts in species composition (development of more resistant species like Achnanthidium minutissimum and reduction of sensitive ones like Cymbopleura naviculiformis, Fragilaria capucina, Navicula cryptocephala, Encyonema silesiacum, Eunotia bilunaris, and Gomphonema parvulum), decreases in species diversity of diatom communities with increasing Cd and Pb concentrations and exposure duration have been demonstrated in this study making diatom communities appropriate monitors of metal mixtures in aquatic systems

Diatom-based water quality assessment in streams influence by urban pollution: effects of natural and two selected artificial substrates, São Carlos-SP, Brazil

Diatoms are good indicators of water quality in lotic systems. The purpose of this study was to provide information about the effects of natural and artificial substrates on diatom-based water quality assessment. Two artificial substrates (bricks and glass) were placed at 6 sampling sites and left for a month during summer base-flow period (2008). Water quality variables were measured at the beginning and end of the experiment. The IndVal method was used to find indicator species and species assemblages characterizing the three substrates. Species richness, diversity and equitability differed among sampling sites, tending to be higher in relatively unpolluted compared to polluted sites. The relatively less polluted upstream sites were characterized by such species as Aulacoseira ambigua, Aulacoseira granulata, Cymbopleura naviculiformis, Eunotia bilunaris, Fragilaria capucina and Gomphonema angustatum. On the other hand, the highly polluted downstream sites were characterized by Gomphonema parvulum, Nitzschia palea, Pinnularia amazonica and Synedra ulna. Species diversity and richness differed between the substrates, tending to be high on natural compared artificial substrate. Indicator species analysis showed that common diatom species were not restricted to single substrate. However, some species tended to prefer certain substrates as suggested by their highest indicator values in these preferred substrates. Specificity was generally high for natural compared to artificial substrates. Among the artificial substrates, more species tended to prefer glasses compared to bricks. Pollution tolerant species, N. palea, G. parvulum and Achnanthidium minutissimum, were highly associated with artificial substrates. Substrate differences may affect the interpretation of water quality results because the absence of a particular species on a given site is can be mistaken for the effects of the perturbations under study. The use of natural substrate is recommended compared to artificial substrate given the advantages of the former compared to the latter

Use of biological monitoring tools beyond their country of origin: a case study of the South African Scoring System Version 5 (SASS5)

Biological monitoring tools are largely lacking for many countries, resulting in adoption of tools developed from other countries/regions, but in many instances, their applicability to the new system has not been explicitly evaluated. The objective of the study was to test the applicability of the South African Scoring Systems Version 5 (SASS5) to urban streams in Zimbabwe. The study evaluated the relationship between water quality variables and SASS5 indices/metrics [(SASS and average score per taxon (ASPT)] and found high degree of concordance between water chemistry parameters and SASS5 metrics, indicating that both SASS and ASPT scores are sensitive to detect environmental changes. This result can be attributed to occurrence of ubiquitous macroinvertebrate taxa sharing similar environmental tolerances with those recorded for South African systems. The applicability of SASS5 metrics need to be tested across different geographical and climatic regions in the country (taking into consideration seasonal variations that are important drivers of benthic faunal assemblages in lotic systems) and disparities among the regions compared for the adoption of the index in the entire country. The SASS5 metrics can also be further strengthened by (a) taking into account the relative abundance of taxa and (b) also improving on its ability to reflect other forms of perturbations besides eutrophication and organic pollution such heavy metal pollution

Applicability of the Pampean Diatom Index (PDI) to streams around São Carlos-SP, Brazil

The objective of the current study was to assess the applicability of the Pampean Diatom Index (the PDI) to natural communities other than epipelic diatom communities as well as those growing on artificial substrates in Monjolinho River and its tributaries, São Carlos-SP, Brazil. Benthic diatoms and water quality sampling was done at 10 sites during summer base flow period (2008 and 2009). The PDI scores were calculated based on epilithic, epiphytic, epipsammic and epipelic diatom communities as well as those growing on bricks and glass substrates. Pearson correlation was used to determine the relationship between the PDI scores from different substrates sampled and measured physical and chemical water quality data. Two-way ANOVA was used to compare these correlation values among substrates. The PDI scores based on all the substrates showed significant correlations with physical and chemical variables. Insignificant differences in the PDI scores based on different natural substrates were recorded, with all substrates classifying the sites into to roughly the same categories. In the light of these results, the PDI can be applied to communities other than epipelic, and is applicable to the study area. The choice of substrate sampled may not affect accuracy of the PDI-based water quality assessment