Biological Water Quality Monitoring Research Articles

Survey on machine vision-based intelligent water quality monitoring techniques in water treatment plant: Fish activity behavior recognition-based schemes and applications

Abstract Water is a vital resource essential to the survival and development of all creatures. With the rapid growth of industry and agriculture, people face a severe threat of ecological destruction and environmental pollution while living earthly lives. Water pollution, in particular, harms people’s health the most. As a result, water supply security has become a top priority. As a critical point in water supply safety, monitoring water quality effectively and forecasting sudden water contamination on time has become a research hotspot worldwide. With the rapid development and wide applications of artificial intelligence and computer vision technologies, biological activity identification-based intelligent water quality monitoring methods have drawn widespread attention. They were taking fish activities as the water-quality indicator has gained extensive attention by introducing advanced computer vision and artificial intelligence technologies with low cost and ease of carrying. This article comprehensively reviews recent progress in the research and applications of machine vision-based intelligent water quality monitoring and early warning techniques based on fish activity behavior recognition. In detail, it addresses water quality-oriented fish detection and tracking, activity recognition, and abnormal behavior recognition-based intelligent water quality monitoring. It analyzes and compares the performance and their favorite application conditions. Finally, it summarizes and discusses the difficulties and hotspots of water quality monitoring based on the fish’s abnormal behavior recognition and their future development trends.

Biological-based techniques for real-time water-quality studies: Assessment of non-invasive (swimming consistency and respiration) and toxicity (antioxidants) biomarkers of zebrafish

Swimming consistency and respiration of fish are recognized as the non-invasive stress biomarkers. Their alterations could directly indicate the presence of pollutants in the water ecosystem. Since these biomarkers are a routine process for fish, it is difficult to monitor their activity manually. For this reason, experts employ engineering technologies to create sensors that can monitor the regular activities of fish. Knowing the importance of these non-invasive stress biomarkers, we developed online biological behavior monitoring system-OBBMS and online biological respiratory response monitoring system-OBRRMS to monitor real-time swimming consistency and respiratory response of fish, respectively. We continuously monitored the swimming consistency and respiration (OCR, CER and RQ) of zebrafish (control and atrazine-treatments) for 7 days using our homemade real-time biological response monitoring systems. Furthermore, we analyzed oxidative stress indicators (SOD, CAT and POD) within the vital tissues (gills, brain and muscle) of zebrafish during stipulated sampling periods. The differences in the swimming consistency and respiratory rate of zebrafish between the control and atrazine treatments could be precisely differentiated on the real-time datasets of OBBMS and OBRRMS. The zebrafish exposed to atrazine toxin showed a concentration-dependent effect (hypoactivity). The OCR and CER were increased in the atrazine treated zebrafish. Both Treatment I and II received a negative response for RQ. Atrazine toxicity let to a rise in the levels of SOD, CAT and POD in the vital tissues of zebrafish. The continuous acquisition of fish signals is achieved which is one of the main merits of our OBBMS and OBRRMS. Additionally, no special data processing was done, the real-time data sets were directly used on statistical tools and the differences between the factors (groups, photoperiods, exposure periods and their interactions) were identified precisely. Hence, our OBBMS and OBRRMS could be a promising tool for biological response-based real-time water quality monitoring studies.

Ecotoxicology of Trace Elements in European Oyster (Ostrea edulis), Seawater, and Sedimentsacross Boston Harbor, Massachusetts,USA.

European oyster (Ostrea edulis) can be used for biological monitoring of water and sediment quality and serve as a conduit of trace elements to humans via consumption. Trace element concentrations in seawater, sediment, O. edulis edible tissues and shells from Boston Harbor were studied and found to be elevated relative to comparative studies in native ecosystems in the Adriatic Sea and Bay of Biscay. Average edible oyster tissues concentrations (mg/kg) were: arsenic 6, cadmium 1.7, cobalt 3.1, chromium 1.9, copper 153, mercury 0.265, nickel 1.8, lead 3.3, and zinc 2390. Arsenic was elevated in seawater and oyster shells. Mercury was elevated in sediments and oyster tissues. Lead was elevated in suspended sediments. Total Hazard Quotient (THQ) was < 1 but when summed across trace elements, THQ was nominally > 1 for all sites. Further study is warranted to determine mechanisms and spatial extent of bioaccumulation.

Differences in planktonic and benthic diatoms reflect water quality during a rainstorm event in the Songhua River Basin of northeast China

Diatoms are useful indicators of lotic ecosystem environmental conditions, but little is known of differences between benthic and planktonic diatom assemblages as it relates to water quality changes in large lotic systems. Heavy rainfall event in Songhua River Basin is infrequent. The water quality of Songhua River Basin is closely implication for regional ecological health and food safety. The aim of this study was to compare the effectiveness of benthic and planktonic diatom assemblages for indicating water quality during a rainstorm event, which has been little studied. Spatial variation of benthic and planktonic diatom assemblages were investigated in Songhua River Basin during a rainstorm event. Firstly, we found that richness and abundances of benthic and planktonic diatom communities were low. Secondly, results of two-way cluster analysis (TWCA) and principal component analysis (PCA) revealed that diatom assemblage still had the potential to indicate water quality despite the strong flow caused by rainstorm event. Thirdly, alpha diversity indices (Shannon-weaver, Margalef, and Pielou indices) had a weak ability in indicating water quality during rainstorm event. Conversely, trophic diatom index (TDI) was observed closely associate with water quality change. Fourthly, Redundancy analysis (RDA) indicating that planktonic diatoms assemblages were more sensitive to changes in turbidity. RDA also revealed that benthic diatom assemblages was closely related to chemical oxygen demand (CODcr), total phosphorus (TP), and dissolved oxygen (DO) concentrations. These results demonstrate the effectiveness of water quality assessment between planktonic and benthic diatoms had a significant different. The results of the study provide a key information about diatom-based biomonitoring in the extreme condition at lotic ecosystem. Our study highlights that rational choices of appropriate diatom metrics for biological monitoring of water quality in large lotic ecosystems are critical for assessments during a rainstorm event. More studies during rainstorm period at different precipitation are required to fully understand how natural disturbance shape diatom assemblage in lotic ecosystem with aims to improve biomonitoring efforts.

Rapid transcriptomic and physiological changes in the freshwater pennate diatom Mayamaea pseudoterrestris in response to copper exposure.

Diatoms function as major primary producers, accumulating large amounts of biomass in most aquatic environments. Given their rapid responses to changes in environmental conditions, diatoms are used for the biological monitoring of water quality and for performing ecotoxicological tests in aquatic ecosystems. However, the molecular basis for their toxicity to chemical compounds remains largely unknown. Here, we sequenced the genome of a freshwater diatom, Mayamaea pseudoterrestris NIES-4280, which has been proposed as an alternative strain of Navicula pelliculosa UTEX 664 for performing the Organisation for Economic Co-operation and Development ecotoxicological test. This study shows that M. pseudoterrestris has a small genome and carries the lowest number of genes among freshwater diatoms. The gene content of M. pseudoterrestris is similar to that of the model marine diatom, Phaeodactylum tricornutum. Genes related to cell motility, polysaccharide metabolism, oxidative stress alleviation, intracellular calcium signalling, and reactive compound detoxification showed rapid changes in their expression patterns in response to copper exposure. Active gliding motility was observed in response to copper addition, and copper exposure decreased intracellular calcium concentration. These findings enhance our understanding of the environmental adaptation of diatoms, and elucidate the molecular basis of toxicity of chemical compounds in algae.

Community Structure, Function, and Influencing Factors of Planktonic Fungi in the Danjiangkou Reservoir

Planktonic fungi are important components of aquatic ecosystems, and analyses of their community composition and function have far-reaching significance for the ecological management and maintenance of the Danjiangkou reservoir. The composition and function of the planktonic fungal community in the surface water layer of the Danjiangkou Reservoir in October 2019 was investigated using Illumina MiSeq sequencing combined with FUNGuild analyses. According to the results, the reservoir community is primarily composed of 6 phyla 213 genera, with Ascomycota and Basidiomycota being the dominant phyla. The water quality monitoring results for the Danjiangkou Reservoir met the Grade Ⅰ or Ⅱ water quality standards for the Environmental Quality Standards for Surface Water (GB 38382-2002). A redundancy analysis (RDA) of the planktonic fungal community and environmental factors showed that TN, TP, T, ORP, and TLI are important factors influencing the distribution of planktonic fungi. The Spearman correlation analysis showed that Alternaria, Cladosporium, Penicillium, Lodderomyces, and Acremonium were significantly correlated with physical and chemical water quality parameters. FUNGuild was used to predict the nutritional and functional groups of planktonic fungi, and the results showed that pathotrophs, saprotrophs, and pathotroph-saprotrophs were the major components. The pathotroph composition analysis showed that the proportions of plant pathogens and animal pathogens in the Heijizui samples were significantly higher than those observed in the other monitoring sites. The community composition, function, and influencing factors of the planktonic fungi community in the Danjiangkou Reservoir were investigated and indicated that it is potentially at ecological risk and more attention needs to be paid to planktonic fungi in the biological monitoring of water quality.

Chemical and biological monitoring of water quality on a hydrographic basin in the State of Santa Catarina

The inappropriate destination of urban effluents, deforestation along the banks of watercourses, expanding agricultural activities, as well as the lack of public management plans for the prevention and adequacy of the use of urban rivers, compromise the efficiency of basic sanitation services and consequently the health of the population. The objective of this research is to monitor the water quality of the Itajaí-Açu river, the largest watercourse in the Itajaí hydrographic basin, located in the State of Santa Catarina, based on the seasonal chemical and biological indicators, in addition to verifying the statistically significant difference between the sample points. For this purpose, five collection points were allocated along the river, for the aforementioned indicators, in the seasons, spring and summer (2019); autumn and winter (2020), totaling 80 samples. To verify the statistically significant difference between the sample points, the Statistical Software R, version 3.6.3 was used. The results pointed to the chemical and biological contamination along the entire length of the Itajaí-Açu river, regardless of the seasonal aspect. There is an urgent need to implement Municipal Basic Sanitation Plans in all the municipalities that are part of the Itajaí watershed. The absence or precariousness of a planning instrument for the provision of public sanitation services in the municipalities, in addition to violating the legal principle of human dignity of access to clean water and adequate sanitation, contributes to the increase of the environmental degradation of the territory as well as the health of its population.

Spatial and temporal variations of the diatom communities in megacity streams and its implications for biological monitoring.

Diatoms have been proven to be good indicators of natural stream conditions, but little is known about the seasonal variability of diatom communities in megacity streams. We investigated the spatial and temporal variation of diatom communities along an urban-to-rural gradient in megacity streams, Beijing, China. We found that the composition and diversity of diatom community was significantly different along the urban-to-rural gradient in streams of Beijing city. The diatom community was subtle temporal variation in the reference stream and urban upstream, but the temporal variation of diatoms was relatively greater in the urban downstream. Overall, the composition of the diatom community was relatively stable in the streams among different seasons, and the dominant species did not change much over seasons. For example, during the sampling periods, the species Achnanthidium minutissimum in reference streams had the average relative abundance of 20.3 ± 3.5%; the species Pseudostaurosira brevistriata and Staurosira construens var. venter in urban upstream had average relative abundances of 17.0% ± 0.9% and 17.3% ± 1.2%, respectively; and the species Nitzschia palea in urban downstream had average relative abundances of 18.8 ± 4.7%. There were significant correlations between the relative abundances of the dominant species and environmental variables, suggesting that the environmental variables had significant effects on the diatom distribution. Our results demonstrate that the diatom communities are relatively stable among seasons in different sampling areas, suggesting that diatoms can be used as reliable indicators for the biological monitoring of water quality in megacity streams across seasons.

Abnormal Water Quality Monitoring Based on Visual Sensing of Three-Dimensional Motion Behavior of Fish

In the context of the problem of water pollution, the movement characteristics and patterns of fish under normal water quality and abnormal water quality are clearly different. This paper proposes a biological water quality monitoring method combining three-dimensional motion trajectory synthesis and integrated learning. The videos of the fish movement are captured by two cameras, and the Kuhn-Munkres (KM) algorithm is used to match the target points of the fish body. The Kalman filter is used to update the current state and find the optimal tracking position as the tracking result. The Kernelized Correlation Filters (KCF) algorithm compensates the targets that are lost in the tracking process and collision or occlusion in the movement process, reducing the errors caused by illumination, occlusion and water surface fluctuation effectively. This algorithm can directly obtain the target motion trajectory, avoiding the re-extraction from the centroid point in the image sequence, which greatly improves the efficiency. In order to avoid the one-sidedness of the two-dimensional trajectory, the experiment combines the pixel coordinates of different perspectives into three-dimensional trajectory pixel coordinates, so as to provide a more authentic fish swimming trajectory. We then select a representative positive and negative sample data set; the number of data sets should have symmetry. The base classifier capable of identifying different water quality is obtained by training. Finally, support vector machine(SVM), eXtreme Gradient Boosting (XGBoost) and pointnet based classifiers are combined into strong classifiers through integrated learning. The experimental results show that the integrated learning model can reflect the water quality effectively and accurately under the three-dimensional trajectory pixel coordinates of fish, and the recognition rate of water quality is above 95%.

Using native and invasive livebearing fishes (Poeciliidae, Teleostei) for the integrated biological assessment of pollution in urban streams

Invasive species are increasingly replacing native species, especially in anthropogenically transformed or polluted habitats. This opens the possibility to use invasive species as indicator taxa for the biological assessment of pollution. Integrated biological assessment, however, additionally relies on the application of multiple approaches to quantify physiological or cytogenetic responses to pollution within the same focal species. This is challenging when species are restricted to either polluted or unpolluted sites. Here, we make use of a small group of neotropical livebearing fishes (family Poeciliidae) for the integrated biological assessment of water quality. Comparing urban and suburban stream sections that receive varying degrees of pollution from industrial and domestic waste waters in and around the Brazilian city of Uberlândia, we demonstrate that two members of this family may indeed serve as indicators of water pollution levels. The native species Phalloceros caudimaculatus appears to be replaced by invasive guppies (Poecilia reticulata) at heavily polluted sites. Nevertheless, we demonstrate that both species could be used for the assessment of bioaccumulation of heavy metals (Pb, Cu, and Cr). Ambient (sediment) concentrations predicted concentrations in somatic tissue across species (R2-values between 0.74 and 0.96). Moreover, we used cytogenetic methods to provide an estimate of genotoxic effects of water pollution and found pollution levels (multiple variables, condensed into principal components) to predict the occurrence of nuclear abnormalities (e.g., frequencies of micro-nucleated cells) across species (R2 between 0.69 and 0.83). The occurrence of poeciliid fishes in urban and polluted environments renders this family a prime group of focal organisms for biological water quality monitoring and assessment. Both species could be used interchangeably to assess genotoxic effects of water pollution, which may facilitate future comparative analyses over extensive geographic scales, as members of the family Poeciliidae have become invasive in tropical and subtropical regions worldwide.

Diversity and Ecosystem Services of Trichoptera.

The holometabolous insect order Trichoptera (caddisflies) includes more known species than all of the other primarily aquatic orders of insects combined. They are distributed unevenly; with the greatest number and density occurring in the Oriental Biogeographic Region and the smallest in the East Palearctic. Ecosystem services provided by Trichoptera are also very diverse and include their essential roles in food webs, in biological monitoring of water quality, as food for fish and other predators (many of which are of human concern), and as engineers that stabilize gravel bed sediment. They are especially important in capturing and using a wide variety of nutrients in many forms, transforming them for use by other organisms in freshwaters and surrounding riparian areas. The general pattern of evolution for trichopteran families is becoming clearer as more genes from more taxa are sequenced and as morphological characters are becoming understood in greater detail. This increasingly credible phylogeny provides a foundation for interpreting and hypothesizing the functional traits of this diverse order of freshwater organisms and for understanding the richness of the ecological services corresponding with those traits. Our research also is gaining insight into the timing of evolutionary diversification in the order. Correlations for the use of angiosperm plant material as food and case construction material by the earliest ancestors of infraorder Plenitentoria—by at least 175 Ma—may provide insight into the timing of the origin of angiosperms.

Water quality monitoring method based on feedback self correcting dense connected convolution network

This paper presents a method of water quality monitoring using a Feedback self correcting system combined with a Densely Connected Convolution Network. We find an effective method to correct the model output and innovate the method of biological water quality monitoring. Fish movement trajectory is a comprehensive expression of various water quality classification characteristics used in all the literature, and it is an important basis for classification of biological water quality. In this paper, we use the image segmentation method of Mask-RCNN to obtain the centroid coordinates of the fish and draw the trajectory image of the fish in a certain period of time. The trajectory image data sets are divided into normal and abnormal water quality. Densely connected convolution network(DenseNet) is used to classify the quality of water. The experiment is based on normal and abnormal water quality image data, and the model correction system with deviation feedback can be designed by the output of softmax. The learning ability of the classification model in practical application is greatly improved and enhance the stability of the detection system. The experimental results show that the water quality identification rate of the model reaches 99.38%, which is far higher than that of all previous water quality classification models.

Using benthic macroinvertebrates as indicators for assessment the water quality in River Nile, Egypt

ABSTRACTMacrobenthic invertebrate’s species are differently sensitive to a biotic and biotic parameters in their environment. So they are used as bioindicators of stat and water quality of aquatic environment. The main objective of this research is using benthic invertebrates for biological assessment of water quality. Twenty-three stations along River Nile from Aswan to Cairo were selected for sampling of benthic macroinvertebrates. Benthic fauna were collected seasonally by a Naturalist Rectangle Dredge with a net 500 µm mesh size. During the monitoring period (four seasons), forty taxa were identified. They belong to benthos sensitive individuals (25%) and medium tolerant benthos (10%) and tolerant benthos individuals (65%). Relations between macrobenthic communities and circumstances of aquatic ecosystem have been lately used to perform the Biological Monitoring Water Quality (BMWQ) score to evaluate quality level in River Nile water. The total BMWQ (T-BMWQ) score and the average BMWQ (A-BMWQ) score are calculated, and their relations with MacArther, Margalef, Menhinick diversity indices and family richness are also examined. BMWQ scores are more subtle measures to assess the response of macroinvertebrates to organic pollution than diversity indices and total population density. However, the A-BMWQ score is more sensitive to changes in family composition than the T-BMWQ score, whereas T-BMWQ score is more subtle to family richness and size of sample. A-BMWQ score is suggested for the biological evaluation of freshwater quality. Also Trent Biotic Index (TBI) was calculated in each station. All these biological indices examined in this study using benthic macroinvertebrates proved that some stations in Nile River were classified as good water quality, most of studied stations were moderate water quality and very few stations were classified as poor water quality.

An Algorithm for Tracking Multiple Fish Based on Biological Water Quality Monitoring

Abnormal water quality will increase the occlusion rate among fish schools, which causes difficulties in fish detection and tracking. In order to solve this problem, a multiple fish tracking algorithm for red snapper is proposed in this paper. In the detection stage, we use the Otsu adaptive segmentation algorithm to extract fish targets based on the background subtraction method, following which the fish tracking feature parameters can be obtained based on the fish geometric features. In the tracking stage, the Kalman filter is employed to first estimate the motion state, and then the cost function is constructed from the position of the fish body, target area, and the direction information. Finally, fish school tracking is realized by the interframe relationship matrix. We applied several tracking methods with various schemes to experimental videos of swimming fish schools in different environments. The experimental results show that the proposed tracking algorithm exhibits improved performance and robustness.

Positive responses of benthic macroinvertebrates to spatial and temporal reductions in water pollution downstream from a trout farm outlet

Inland trout farms can cause important adverse effects on freshwater communities due to the discharge of wastewater effluents into recipient rivers. In this research, responses of benthic macroinvertebrates to diminished water pollution downstream from a trout farm outlet were examined at spatial and temporal scales. Field studies were carried out in the Upper Tajuña River (Central Spain) during the springs of 2007 and 2015. Water pollution decreased, with increasing the downstream distance from the trout farm effluent, and also from 2007 to 2015 as a likely consequence of the lowered annual production of farmed rainbow trout following the 2008 economic recession. Reductions in water pollution resulted in increased concentrations of dissolved oxygen and decreased levels of turbidity and inorganic nutrients (ammonia and phosphate). Benthic macroinvertebrates responded positively to diminished water pollution by decreasing the relative abundance of collector-gatherers (oligochaetes and chironomids) and increasing the relative abundance of shredders and scrapers (ephemeropterans, plecopterans and trichopterans). In addition, values of taxonomic diversity and Biological Monitoring Water Quality biotic indices tended to increase. It is concluded that the wastewater treatment system of the trout farm should be improved to minimize the environmental impact on the recipient river.

An assessment of pollution in aquatic environment using bioindicators: a review

This review highlights the importance of biological indicators in monitoring presence of pollution in aquatic environment. This assessment involves the use of living organisms (macro or microorganisms and plants or animals) as bioindicators of pollution in water bodies. These organisms are believed to show higher sensitivity to pollution than the best chemical indicators. Bioindicators or test of relevance to water study includes: test based on Chlorella vulgaris , Daphnia magna straus, test Spirotox , Microtox , using macroinvertebrates, algae and vertebrates (such as fishes). Variety of biotic indices based on macroinvertebrates community as indicators have been highlighted which includes: Microinvertebrate Biotic Index (MBI), Extended Trend Biotic index (ETBi), Belgian Biotic index (BBi), Rapid Bioassessment Protocols (RBPs), Biological Monitoring Water Quality (BMWQ) and Family level Biotic Index (FBI). Based on Microinvertebrate Biotic Index (MBI), grading of water quality alone with the taxonomic group of macroinvertebrate was divided into grade I, II, III, IV and V representing clean water, mildly, moderately, highly and severely polluted water with the tolerance rating of 2, 4, 6, 8 and 10 respectively. The review emphasized the need for the use of bioindicators in detecting water pollution, because bioindicators are much more sensitive than the best chemical indicators. Keywords: aquatic environment, bioassessment, bioindicators, pollutant, tolerance rating

Water Quality Monitoring Method Based on TLD 3D Fish Tracking and XGBoost

Aiming at the problem of water quality monitoring, this paper presents a method of biological water quality monitoring based on TLD (Tracking-Learning-Detection) framework and XGBoost (eXtreme Gradient Boosting). Firstly, under the framework of TLD, an independent tracking system is designed; TLD captures 3D coordinate information of fish based on video and calculates the behavior of fish movement parameters which can reflect the change of water quality via processing the coordinate information of the fish body. The data of coordinate information will be more prominent via the data processing. The integration of all built XGBoost water quality monitoring model which is based on characteristic parameters; the model was used to analyze and evaluate fish behavior parameters under unknown water quality to achieve the purpose of water quality monitoring.

Diatom-based water quality monitoring in southern Africa: challenges and future prospects

Diatoms are of significant ecological importance in aquatic ecosystems, which stems from their dynamic position at the base of the trophic web as primary producers. Because diatom communities have specific environmental requirements and respond rapidly to changes in environmental conditions they are often employed as a cost-effective method to assess anthropogenic impacts and health statuses of aquatic ecosystems, particularly in Europe and North America. The purpose of this review is to summarise the challenges and future prospects associated with biological water quality monitoring using diatoms with special focus on southern Africa. Much work still needs to be carried out on diatom tolerances, ecological preferences and ecophysiology. It is recommended that past research pertaining to African diatom taxonomy should be made readily accessible to all through electronic media for use as a reference point. Moreover, following the same approach as for macroinvertebrate biomonitoring, African and other developing countries can resort to intermediate diatom taxonomy (i.e. genus), which is easier, less time-consuming and requires less-skilled personnel. While the lack of capacity and baseline information on diatom community composition and ecological requirements represent significant hurdles, diatom biomonitoring potentially holds much promise for understanding the ecological functioning and management of aquatic ecosystems in southern Africa. The application of diatom-based water quality assessment protocols has direct and immediate value for use as an ‘added-value’ assessment tool in addition to the use of macroinvertebrates and fish indices as these can indicate anthropogenically impacted and pristine sites. Keywords: application, biomonitoring, ecology, taxonomy, rivers, water quality

“The pump don’t work, ‘Cause the vandals took the handles”; why invasive amphipods threaten accurate freshwater biological water quality monitoring

The 2010 invasion of Great Britain by the eastern European ‘killer shrimp’ Dikerogammarus villosus (Crustacea: Amphipoda) was just the latest of several amphipod invasions of British freshwaters and just one of many amphipod invasions occurring on a global scale. Using examples of previous invasions of other amphipods, Gammarus pulex and Crangonyx pseudogracilis in The Isle of Man and Northern Ireland, I show that these invaders have the potential to undermine the accuracy of ecological assessment programmes of freshwater, such as those employed in the Water Framework directive (WFD) in Europe and similar schemes used by environmental protection agencies all over the world. Such assessment programmes invariably rely on biological water quality monitoring using biotic indices derived from resident macroinvertebrate assemblages. All three amphipod invaders can greatly undermine accurate water quality biomonitoring in river systems. This can be by invasive amphipods predating upon and/or outcompeting resident macroinvertebrates and thus radically altering resident biodiversity and assemblage structure. This can also occur because these invaders tend to be more physico-chemically tolerant than the resident taxa they are replacing and this greater tolerance of poor organic chemical water quality is not acknowledged in biotic scoring indices. A way forward would be to measure the biological pressure invaders may exert in a biocontamination index or similar, while simultaneously carrying out routine water quality monitoring using biotic indices.

Chironomid distribution along a pollution gradient in Ethiopian rivers, and their potential for biological water quality monitoring

Water pollution resulting from the rapidly intensifying use of freshwater resources in Ethiopia is increasing the need for continuous follow-up and monitoring of the country's aquatic ecosystems, in order to maintain their biological diversity and water quality. Chironomids (non-biting dipteran midges) are often used for biological water quality assessment because their larvae tend to respond rapidly and sensitively to changes in the aquatic environment. Larval chironomid assemblages from 37 sites in 20 Ethiopian rivers were analysed in 2010 to assess the relationship between species composition and water quality. Cluster analysis of local physical and chemical variables was used to classify sites into three different water quality classes: 15 sites were classified as not or slightly polluted, 16 as moderately polluted and six as heavily polluted. We recovered 21 chironomid taxa, representing three subfamilies, with Chironominae (13 taxa) making the largest contribution, followed by Tanypodinae and Orthocladinae (four taxa each). Polypedilum nubifer, P. wittei, Polypedilum type Wabe, Cryptochironomus sp. and Conchapelopia sp. were the dominant species in unpolluted or slightly polluted sites. Chironomus alluaudi and C. imicola were indicators of heavily polluted sites, typified by low (<2 mg l−1) concentrations of dissolved oxygen. Heavily polluted sites, such as the Modjo and Sebata rivers, also held a lower number of species and genera than less-impacted sites. Larval chironomid assemblages proved useful as indicators of river water quality in Ethiopia when taxa are identified at the species and/or genus level.