Taxonomic composition and spatio-temporal variability of macroinvertebrates inhabiting snags were examined from an 8-km segment of the Elm Fork of the Trinity River. Seventy-seven macroinvertebrate taxa were collected from submerged wood during the study. Assemblages were highly variable spatially and temporally, especially among seasons. An ordination of species and environment did not find snag taxa to have striking correlations with many of the selected environmental variables, although there were some trends in flow-mediated species distributions. There were significant seasonal differences in the abundances of some taxa, particularly among the Chironomidae (Diptera). The Tribe Orthocladiini was numerically abundant during the winter, while the Tribes Chironomini and Tanytarsini dominated the summer and autumn. Additionally, this study included a secondary production and microdistribution analysis of a population of the caddisfly Cyrnellus fraternus. Distributions of C. fraternus were restricted to snags, the most stable substratum for retreat building and for resisting periodic high waters. Larvae were not found in the soft sand and mud benthic habitats near submerged wood. The insects were multivoltine with a minimum of three generations per year. Pupae were collected July through September and adults emerged from May through October. The population overwintered as larvae. Estimated annual production was 1,015.4 mg/m2/yr. Mean standing stock biomass was 61.24 mg/m2, the cohort production/biomass ratio was 4.59, and the annual production/biomass rate was 16.58/yr for this population. Standing stock biomass ranged from 1.6 to 349.1 mg/m2 during the year and was significantly higher in autumn and summer than winter. Larvae were more abundant in the lower portions of the study area where flow was reduced for much of the year, than in the upper reaches, characterized by higher current velocities. C. fraternus larvae were found in their highest numbers on snags with dense deposits of silt and sand.

<p>The work in this thesis deals with effects of changed species richness on process rates among stream-living macroinvertebrates. Global biodiversity is decreasing rapidly and it is poorly known what the consequences of this loss may be for ecosystems and the services they provide. Hence, it is important to investigate the potential effects of losing species. In streams, deforestation, introduction of non-native species, pollution and channelization are examples of events that may affect species richness negatively. In this thesis emphasis is on changes in species richness within functional feeding groups (FFGs) of stream-living macroinvertebrates. The FFGs used were shredding detritivores, grazers, filter feeders and predators - all of which uphold important ecological processes in streams. Along with an observational field study, species richness was manipulated in laboratory and field experiments to investigate the effects of changed species richness on process rates and thus ecosystem functioning.</p><p>The results show that effects of changed species richness on process rates may be dramatic. Among the shredding detritivores there were negative effects on leaf mass loss, regardless whether fixed, random or predicted sequences of species loss was investigated. These effects could be attributed to either species richness per se or species composition. However, among the other FFGs the relationship between species richness and process rates was less consistent. In filter feeders, there was no or a negative effect of decreasing species richness while both grazers and predators showed positive effects of species loss.</p><p>The results also show that the most important interactions between species in an experiment, thus potentially in a natural community, are likely to determine what the effect of species loss on process rates will be. Facilitation and niche differentiation lead to reduced process rates if species are lost, while mechanisms, such as interspecific resource or interference competition, produce the opposite effect. Furthermore, in systems with a diminishing resource, the first two mechanisms may become more important over time enhancing the effect of species loss in the long term.</p><p>In conclusion, effects of species loss may be dramatically negative or positive even if lost species are classified as redundant. The effect in the short term most likely depends on which species are lost, on the original species composition and on the underlying mechanisms. Questions remaining to be answered are how important the observed effects are in more complex systems and if they are persistent over time? Future studies will tell. </p>

Résumé Ce travail est un premier pas dans l’étude de la qualité des eaux du fleuve Niger à Niamey. Il est basé sur la physico-chimie et les macroinvertébrés de cet écosystème aquatique. L’approche physico-chimique met en évidence les changements de la qualité des eaux, le long des rives, en relation avec les rejets de la ville et en fonction du régime du fleuve. L’impact de ces rejets est très négligeable à l’échelle de l’écosystème à cause de la forte dilution. La demande chimique en oxygène, l’oxygène dissous, l’ammonium, les orthophosphates et le phosphore total sont les principaux facteurs environnementaux qui déterminent la pollution des eaux liée aux matières organiques et oxydables, aux matières azotées et phosphorées dans ce fleuve. L’étude des macroinvertébrés fait ressortir 83 taxons répartis le long du fleuve Niger à Niamey. La description des peuplements de macroinvertébrés montre une variation de structure des communautés, en passant de l’amont à l’aval des points de rejets, caractérisée par une baisse de la richesse et de la diversité taxonomique en aval immédiat des rejets. La présence, dans certaines stations en aval immédiat des rejets, des taxons tels que Chironomus gr. plumosus, Melania sp., les familles des Syrphidae et des Culicidae, est une indication de la dégradation de la qualité des eaux liée à la matière organique. Par contre, les taxons comme Thraulus sp., Elassoneuria sp., Afronurus sp., Centroptiloides sp., Adenophlebia sp., Dipseudopsis sp. et Neoperla sp., appartenant aux Ephéméroptères, Trichoptères et Plécoptères, reflètent une meilleure qualité de l’eau dans les stations de référence situées en amont de tous les points de rejets. L’importante diversité de la famille des Chironomidae (20 taxons) dans ce cours d’eau offre de bonnes perspectives pour son utilisation dans l’étude de la qualité des eaux du fleuve Niger à Niamey. Les descripteurs qui expliquent significativement la distribution des communautés de macroinvertébrés le long du fleuve Niger à Niamey sont la matière organique (demande chimique en oxygène) et les nutriments (ammonium, orthophosphates et phosphore total). La technique d’échantillonnage au filet troubleau explique beaucoup plus d’inertie que les substrats artificiels. Quant à la jacinthe d’eau, elle présente peu d’intérêt dans l’étude de la qualité des eaux du fleuve Niger à Niamey à cause de sa présence uniquement en période de crue. Summary This survey is a first step in the study of water quality of the River Niger in Niamey. It is based on physicochemical factors and the macroinvertebrates inhabiting this aquatic ecosystem. The physicochemical approach underlines the changes in water quality, along the banks, in relation with wastewater from the city of Niamey, and as a response to seasonal variations of water level. The impact of wastewater on the scale of the entire ecosystem appears very limited, because of the strong dilution. Chemical oxygen demand, dissolved oxygen, ammonium, phosphates and total phosphorus levels are the main environmental factors that determine both the pollution due to organic (and oxidizable) matter, and the pollution resulting from nitrogen and phosphorus-based chemicals in this river. In this survey 83 taxa of macroinvertebrates were found along the River Niger in Niamey. The description of macroinvertebrates shows a variation of community structure, from upstream to downstream, that is characterized by a decrease of taxonomic richness and diversity downstream wastewater discharges. The presence of Chironomus gr. plumosus, Melania sp., families of Syrphidae and Culicidae indicates a deterioration of water quality due to organic matter in some stations near wastewater discharges. However, taxa like Thraulus sp., Elassoneuria sp., Afronurus sp., Centroptiloides sp., Adenophlebia sp., Dipseudopsis sp. and Neoperla sp. reflect a better quality of water in the reference stations located upstream of all wastewater discharges. The high diversity of Chironomidae (20 taxa) in this river makes them a good candidate taxonomic group to be used for the assessment of water quality in the River Niger near Niamey. The factors which significantly explain the distribution of macroinvertebrates communities along the River Niger in Niamey are organic matter (chemical oxygen demand) and nutrients (ammonium, phosphates, total phosphorus). Results from net hand samples explain a higher fraction of total inertia than the ones obtained using artificial substrata. Water hyacinths play a limited role in the survey of water quality in the Niger near Niamey, because they are only present during floodperiods.

The work in this thesis deals with effects of changed species richness on process rates among stream-living macroinvertebrates. Global biodiversity is decreasing rapidly and it is poorly known what the consequences of this loss may be for ecosystems and the services they provide. Hence, it is important to investigate the potential effects of losing species. In streams, deforestation, introduction of non-native species, pollution and channelization are examples of events that may affect species richness negatively. In this thesis emphasis is on changes in species richness within functional feeding groups (FFGs) of stream-living macroinvertebrates. The FFGs used were shredding detritivores, grazers, filter feeders and predators - all of which uphold important ecological processes in streams. Along with an observational field study, species richness was manipulated in laboratory and field experiments to investigate the effects of changed species richness on process rates and thus ecosystem functioning. The results show that effects of changed species richness on process rates may be dramatic. Among the shredding detritivores there were negative effects on leaf mass loss, regardless whether fixed, random or predicted sequences of species loss was investigated. These effects could be attributed to either species richness per se or species composition. However, among the other FFGs the relationship between species richness and process rates was less consistent. In filter feeders, there was no or a negative effect of decreasing species richness while both grazers and predators showed positive effects of species loss. The results also show that the most important interactions between species in an experiment, thus potentially in a natural community, are likely to determine what the effect of species loss on process rates will be. Facilitation and niche differentiation lead to reduced process rates if species are lost, while mechanisms, such as interspecific resource or interference competition, produce the opposite effect. Furthermore, in systems with a diminishing resource, the first two mechanisms may become more important over time enhancing the effect of species loss in the long term. In conclusion, effects of species loss may be dramatically negative or positive even if lost species are classified as redundant. The effect in the short term most likely depends on which species are lost, on the original species composition and on the underlying mechanisms. Questions remaining to be answered are how important the observed effects are in more complex systems and if they are persistent over time? Future studies will tell.

As land use transformations are the main driver of biological diversity loss at the global scale, it is essential to provide predictions and understanding of their impacts in order to improve the mitigation of ecosystem perturbations. The first objective of this project was to describe the response of biological assemblages along a gradient of urbanization and to compare metrics of watershed imperviousness in order to determine, as has been suggested in the literature, whether effective imperviousness, which represents the proportion of impervious area directly connected to the stream by storm sewers, is a better predictor of stream impairement than total imperviousness in the watershed. Decline in sensitive taxa abundance is initiated at 14% total imperviousness and 3% effective imperviousness in the Ottawa-Carleton region and, total and effective imperviousness have equivalent predictive power. The second objective of this project was to describe how the structure of metazoan assemblages in urban streams, as described by size spectra attributes (i.e. slopes, intercepts, number of logarithmic size classes occupied, and residual variance), varies with watershed size, land use and water quality. Streams size spectra of the Ottawa-Gatineau region have relatively shallow slopes, reflecting relatively higher densities of organisms in the larger size classes compared to other ecosystem types (e.g. lakes, oceans, soils, coastal waters). Size spectra slopes, density corrected for size, number of size classes, and residual variance vary predictably along gradients of watershed size, watershed proportion of natural land use and periphyton chlorophyll a. A systematic trend of declining spectra slopes with increasing periphyton biomass suggests that ecological efficiency declines in urban eutrophic streams.

Στην Ελλάδα γενικά, αλλά και στο Νομό Αχαΐας ειδικότερα, υπάρχουν αρκετές μονάδες παραγωγής χάρτου. Αρκετές από αυτές δεν βρίσκονται εντός των ορίων Βιομηχανικών Περιοχών (ΒΙ.ΠΕ.), με συνέπεια τα ακατέργαστα απόβλητά τους να συμβάλλουν σημαντικά στη ρύπανση του περιβάλλοντος. Το μεγαλύτερο περιβαλλοντικό πρόβλημα που προκαλείται από τις συγκεκριμένες μονάδες είναι η εναπόθεση μεγάλων ποσοτήτων υγρών ακατέργαστων αποβλήτων κυρίως στα υδάτινα οικοσυστήματα. Τα απόβλητα αυτά περιέχουν μεγάλο οργανικό φορτίο, οργανοαλογονωμένες ενώσεις, υψηλά επίπεδα αιωρούμενων στερεών , φαινολών και λιγνινών, με αποτέλεσμα να προκαλούν δυσμενείς επιπτώσεις στους υδάτινους αποδέκτες, όπως τοξικότητα στους υδρόβιους οργανισμούς, ευτροφισμό και άνοδο της θερμοκρασίας. Η παρούσα μελέτη έχει ως βασικό σκοπό την εκτίμηση της τοξικότητας των αποβλήτων δυο μονάδων παραγωγής χάρτου, εγκατεστημένων στην ΒΙ.ΠΕ. Πατρών, με τη χρήση βιοδεικτών. Ως βιοδείκτες χρησιμοποιήθηκαν τόσο ψάρια του γλυκού νερού (πέστροφες του είδους Oncorhynchus mykiss), όσο και μακροασπόνδυλα (των ειδών Daphnia pulex και Thamnocephalus platyurus) με τη μορφή των μικροβιοτέστ Thamnotoxkit F και Daphtoxkit FTM pulex. Συνολικά ελήφθησαν 16 δείγματα (τέσσερα διπλά δείγματα από την κάθε μονάδα). Στα τεστ τοξικότητας που εφαρμόστηκαν (Thamnotoxkit F, Daphtoxkit FTM pulex και πέστροφες), υπολογίσθηκαν τα L(Ε)C50 24h, 48h και 96h αντίστοιχα σύμφωνα με τα πρωτόκολλα εργασίας. Για το μικροβιοτέστ Thamnotoxkit F, τα απόβλητα και από τις δυο μονάδες δεν ήταν τοξικά. Μετά από την μετατροπή των τιμών αυτών σε τοξικές μονάδες, ευρέθη ότι στο Daphtoxkit FTM pulex κυμαίνονταν από 0,79 εώς 1,12 για την ΜΠΧ1 και 1,21 έως 1,38 για την ΜΠΧ2, ενώ στις πέστροφες μεταξύ 2,92 και 4,85 για την ΜΠΧ2. Τα απόβλητα της ΜΠΧ1 δεν ήταν τοξικά για την πέστροφα. Οι τιμές αυτές και για τους τρεις ελέγχους κατατάσσουν τα απόβλητα ως «τοξικά», εκτός από το δείγμα Β της ΜΠΧ1 που ταξινομείται ως «ελαφρά τοξικό». Τα προαναφερθέντα αποδεικνύουν ότι η μονάδα παραγωγής χάρτου με πρώτη ύλη ανακυκλωμένο χαρτί (ΜΠΧ2) είναι σε κάθε περίπτωση πιο τοξική από εκείνη που παράγει χαρτί από καθαρό χαρτοπολτό (ΜΠΧ1). Τέλος, θα πρέπει να σημειωθεί ότι η παρούσα μελέτη είναι η πρώτη μελέτη εκτίμησης της τοξικότητας με βιοδείκτες των αποβλήτων μονάδων παραγωγής χάρτου που γίνεται στη χώρα μας, παρ’ ότι αυτά συμμετέχουν στην επιβάρυνση του περιβάλλοντος. Εκτιμάται ότι τα στοιχεία τοξικότητας που παρατίθενται στη παρούσα εργασία θα είναι χρήσιμα τόσο για την εκπόνηση διαχειριστικών μοντέλων, όσο και μοντέλων εκτίμησης της επικινδυνότητάς τους (risk assessment). / In Greece in general and subsequently in the Achaias Prefecture, several units of paper production exist. Many of them are not located in Industrial Areas and so they contribute significantly to the environmental pollution. The most adverse environmental problem caused by these manufacturing units, is considered to be the release of large quantities of raw liquid effluents, mainly into the aquatic ecosystems. These wastes contain a high organic load, chlorinated compounds (AOCl), high levels of suspended solids, as well as phenols and lignins resulting in hazardous effects on aquatic receivers, like toxicity and eutrophication. In this study, the toxicity of the wastewaters from two paper mills (PM1 and PM2) located in Achaias prefecture is estimated, firstly by using macroinvertebrates (Daphnia pulex και Thamnocephalus platyurus) in the form of microbiotests Thamnotoxkit F and Daphtoxkit FTM pulex, and secondly by using the trout (Onchorynchus mykiss) as a test organism. Sixteen samples were collected from both units overall (four duplicated samples from each mill). In the toxicity tests Thamnotoxkit F, Daphtoxkit FTM pulex and trout, the L(E)C50 in 24, 48 and 96 hours respectively were calculated according to the protocols. Thamnotoxkit F showed no sensitivity for the wastewaters from both mills. After the transformation of these values in toxic units, for Daphtoxkit FTM pulex ranged from 0,79 - 1,12 for PM1 and 1,21 - 1,38 for PM2. In the trout bioassay they varied from 2,92 - 4,85 for PM2, while the values for PM1 were zero. These values classify the tested paper mill effluents as “toxic”, except sample B from PM1 which was classified as “slightly toxic”. Therefore, it is shown that the paper mill which uses recycled paper as primary raw material (PM2) has more toxic waste for the environment than the paper mill which uses pre-treated paper pulp (PM1). Finally, it must be noted that the present study is the first toxicity evaluation study with bioindicators for paper mill wastewaters in our country, even though they contribute significantly to the environmental pollution. It is estimated that the measured toxicity parameters in the present study will be very useful for the designing of management plans, as well as for risk assessment models.

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal

Cattle are responsible for the deterioration of aquatic and riparian ecosystems throughout the North American prairies. Marked preference for riparian areas has resulted in vegetation loss, stream bank destabilization, changes in sediment particle size, and increased nutrient loads in the streams. A grazing experiment in Grasslands National Park of Canada manipulated the density of cattle to represent a range of grazing intensities (from no grazing to very heavy grazing, 70% forage utilization). This experiment provided the opportunity to study how streams in the semi-arid mixed-grass prairie environment respond to a range of grazing pressure. Nine experimental pastures located on previously ungrazed land within the park boundary and four located within the adjacent community pastures were created, each subjected to a specified grazing treatment. Sampling occurred in the autumn from 2007 to 2009 and included the measurement of 33 physical, chemical, and biological habitat metrics and the characterization of the aquatic invertebrate community. Linear regressions were performed to determine if the habitat variables had a significant relationship to grazing intensity (P < 0.05). Of the habitat variables, two sediment particle size categories were significantly related to grazing intensity: per cent of fine gravel (4-8 mm diameter) (P =0.003) and per cent of medium gravel (8-16 mm diameter) (P = 0.007). The only other habitat variable with a significant linear relationship to grazing intensity was the concentration of suspended carbon in the stream water (P = 0.050). Three invertebrate community metrics were focused on for their expected response to changes associated with cattle impacts: iii per cent Chironomidae (%Chiron), per cent Ephemeroptera, Odonata, and Trichoptera (%EOT), and taxa richness. There was a significant non-linear relationship between %Chiron (P = 0.005) and grazing intensity, no linear or non-linear relationship between %EOT and grazing intensity, and a non-linear trend between richness and grazing intensity (P = 0.083). A Reference Condition Approach was used to test for the effects of grazing on the invertebrate community. Multiple regression was used to create a model predicting the invertebrate community from habitat metrics. Of the three community metrics, only richness resulted in a model with acceptable predictive ability. The predicted richness values for each test site were calculated and their residuals were determined and compared to the distribution of residuals observed in the reference sites. Using this technique, I determined that 73.3% of the sites subjected to grazing deviated significantly for the reference condition and were therefore deemed to be impacted. There was no significant relationship between the test site residuals and grazing intensity. The macroinvertebrate community in this semi-arid environment is already under a lot of stress, the addition of cattle to the environment, even at low intensities, pushed the community beyond the reference condition.

Made available in DSpace on 2016-06-02T19:32:08Z (GMT). No. of bitstreams: 1 5535.pdf: 7207431 bytes, checksum: 523a8fec3f0f24a0756174126c56beba (MD5) Previous issue date: 2013-08-29 / Universidade Federal de Sao Carlos / Lotic systems are highly influenced by the landscape through which they flow, and changes in the landscape are the main threat to their ecological integrity. Evaluating the ecological "health" of lotic systems is essential and of great importance to the management of water resources worldwide. In this study, we evaluated the integrity of streams in southeastern Brazil using the protocol WHEBIP (Watershed Habitat Evaluation and Biotic Integrity Protocol), which combines information about the coverage of riparian vegetation, geomorphology, land cover and human activities to assess the physical characteristics of the sub-basin and to evaluate the integrity of streams. We compared this protocol with the protocol RCE (Riparian, Channel and Environmental), already widely used in tropical regions, to directly assess stream physical condition. As a measure of the functional integrity of streams, we estimated leaf breakdown rates, an important process in lotic systems. Furthermore, we sorted and identified the macroinvertebrates that colonized leaves in the 2nd and 28th days of the decomposition experiment and calculated environmental quality metrics related to these communities to test their relationship with WHEBIP. The protocols WHEBIP and RCE were significantly correlated to each other, with greater differentiation among streams especially when RCE was high. Possibly, the WHEBIP, by incorporating spatial variables on a large scale in the landscape, best differentiates these streams. None of the protocols tested were correlated with leaf breakdown rates. However, when calculating variation of decay rates (standard error), we observed a positive relationship with the protocol WHEBIP. Thus, we grouped the metrics of the protocol WHEBIP in a Principal Component Analysis (PCA), noting the trend to a significant correlation between changes in leaf breakdown rates and the first axis of the PCA, which indicates that the increase of forest cover in the microbasin could reduce variation in leaf breakdown rates in streams. The WHEBIP and RCE showed no correlation with the environmental quality metrics related to macroinvertebrate communities. But we tested the hypothesis that higher values of WHEBIP decreases the variation in leaf breakdown rates due to higher stability of macoinvertebrate communities, we found a significant correlation to withdraw one of the streams of the analysis. This stream differed greatly from the rest, because even getting down in value in WHEBIP, showed a differentiation between communities, due to the dominance of certain taxa in the days analyzed. This is the first study in the tropics that relates the variation in leaf breakdown rates in streams and forest cover of the microbasin within they are inserted. Our results suggest that WHEBIP protocol can be used to assess the integrity of streams in tropical regions. This protocol showed significant relationships with the variation in leaf breakdown rates, which may prove to be an interesting metric for use in monitoring, and the stability of the macroinvertebrate community, which is greater in less impacted streams, as suggested by other studies. / Os sistemas lóticos são extremamente influenciados pela paisagem através da qual fluem, e as transformações na paisagem são a principal ameaça à sua integridade ecológica. Avaliar a saúde ecológica dos sistemas lóticos é fundamental e de grande importância para o manejo dos recursos hídricos em todo o mundo. Neste estudo, avaliamos a integridade de córregos no sudeste brasileiro utilizando o protocolo WHEBIP (Watershed Habitat Evaluation and Biotic Integrity Protocol), que combina informações sobre a cobertura de vegetação ripária, geomorfologia, cobertura da terra e atividades humanas para avaliar as características físicas da sub-bacia e estimar a integridade de córregos. Comparamos esse protocolo com o protocolo RCE (Riparian, Channel and Environmental), já bastante utilizado em regiões tropicais, para avaliação física direta dos córregos. Como medida da integridade funcional dos córregos, estimamos a taxa de decomposição foliar, importante processo nos sistemas lóticos. Além disso, triamos e identificamos os macroinvertebrados que colonizaram as folhas referentes ao 2º e ao 28º dias do experimento de decomposição e calculamos métricas de qualidade ambiental relacionadas às comunidades desses organismos, para testar sua relação com o WHEBIP. Os protocolos WHEBIP e RCE foram significativamente correlacionados entre si, havendo maior diferenciação entre os córregos principalmente quando o RCE foi alto. Possivelmente o WHEBIP, por incorporar variáveis espaciais em uma escala maior na paisagem, diferencia melhor esses córregos. Nenhum dos protocolos testados apresentou correlação com as taxas de decomposição. No entanto, ao calcularmos a variação das taxas de decomposição (erro padrão), observamos uma relação positiva com o protocolo WHEBIP. Assim, agrupamos as métricas do protocolo WHEBIP em uma Análise de Componentes Principais (PCA), observando tendência a uma correlação significativa entre a variação das taxas de decomposição e o primeiro Eixo da PCA, o que indica que o aumento da cobertura florestal na microbacia poderia reduzir a variação nas taxas de decomposição foliar nos córregos. O WHEBIP e o RCE não apresentaram correlações com as métricas de qualidade ambiental relacionadas às comunidades de macroinvertebrados. Mas ao testarmos a hipótese de que os maiores valores do WHEBIP diminuiriam a variação das taxas de decomposição devido a maior estabilidade das comunidades de macroinvertebrados, encontramos uma correlação significativa ao retirarmos um dos córregos das análises. Esse córrego diferenciava-se bastante do restante, pois mesmo obtendo baixo valor no protocolo WHEBIP, apresentou uma baixa diferenciação entre as comunidades, devido à dominância de alguns táxons nos dias analisados. Este é o primeiro trabalho para os trópicos que relaciona a variação nas taxas de decomposição foliar nos córregos e a cobertura florestal das microbacias em que estão inseridos. Nossos resultados sugerem que o protocolo WHEBIP pode ser utilizado para avaliar a integridade de córregos em regiões tropicais. Esse protocolo apresentou relações significativas com a variação nas taxas de decomposição, que pode vir a ser uma métrica interessante para o uso em monitoramento, e com a estabilidade da comunidade de macroinvertebrados, que é maior em córregos menos impactados, conforme sugerido por outros estudos.

The River Medlock is a small (22km) urbanised river, and is one of the five main tributaries which forms part of the River Irwell Catchment in Greater Manchester, UK. The river has a legacy of pollution from the 18th century and continues to be affected by anthropogenic factors including point source pollution from waste water treatment works (WwTWs) and combined sewer overflows (CSOs). In order to investigate the impact of CSOs and the WwTWs on the river hydrology, water quality and ecology of the lower largely urbanised reach, data sets were obtained from the Environment Agency and from direct sampling of the river. Load estimations from continuous discharge records from the river's gauging station plus estimates of sub-catchment area indicate the lower sites, classified as a "highly modified water body" and downstream of treatment works had had a higher load of discharge and phosphate-P linked to point sources and episodic discharges. Short term, continuous monitoring revealed that CSOs were active during high velocity, but increased concentrations of nutrients post high velocity indicate WwTW effects and possibly diffuse sources. This project reveals that the WwTW are a major source of phosphate-P and that the impact of CSOs on the river quality is short-lived and depends on the degree of precipitation. Other parameters indicate good water quality although the benthic macroinvertebrate community is degraded as a result of episodic increases in the quantity of water destabilising the river bed. Therefore, pollution from the CSOs, the WwTW and rapid changes in discharge are the reasons for the river's failure to conform to EU's requirements of the Water Framework Directive.