FundaÃÃo de Amparo à Pesquisa do Estado do Cearà / O estudo foi desenvolvido em um trecho de 50 km do Rio Salgado, objetivando propor uma metodologia capaz de determinar o padrÃo de emissÃo de poluentes adequado à capacidade de autodepuraÃÃo de um rio em regiÃo semi-Ãrida. Foram realizadas as etapas: (i) reconhecimento da Ãrea a partir do mapeamento do rio Salgado e seus afluentes; (ii) diagnÃstico da qualidade de Ãgua (Fase I, 1300 anÃlises): entre marÃo e setembro de 2005, tendo-se selecionado oito seÃÃes do rio para a coleta e anÃlise de amostras, observando-se 27 parÃmetros em seis campanhas de monitoramento; (iii) diagnÃstico da qualidade de Ãgua (Fase II, 1500 anÃlises): entre fevereiro de 2006 e janeiro de 2007, feito atravÃs de doze campanhas de monitoramento em 14 seÃÃes com os parÃmetros OD, DBO, Coliformes termotolerantes, coliformes totais, pH, turbidez, condutividade elÃtrica, temperatura da Ãgua e do ar; (iv) experimento social, processo participativo envolvendo CSBH-Salgado e demais atores sociais da bacia de estudo, fomentando-se a discussÃo sobre o enquadramento das Ãguas; (v) modelagem da qualidade da Ãgua usando QUAL2E, calibrando-se dois de seus parÃmetros: coeficiente de decaimento de DBO e coeficiente de decaimento de coliformes. A validaÃÃo do modelo QUAL2E foi feita utilizando doze campanhas entre fevereiro de 2006 e janeiro de 2007, distinguindo os perÃodos Ãmido e seco. A simulaÃÃo de cenÃrios foi feita para o padrÃo de emissÃo de DBO com concentraÃÃes de 5 a 100 mg/L, e para o padrÃo de coliformes com as concentraÃÃes de 103 a 107 NMP/100mL. Este trabalho de tese conclui que o Rio Salgado, no trecho em estudo, encontra-se poluÃdo. Foi comprovado que pelo menos cinco parÃmetros se encontram em desacordo com os padrÃes de qualidade, inclusive da classe IV: oxigÃnio dissolvido (OD), demanda bioquÃmica de oxigÃnio (DBO), coliformes termotolerantes (CTT), nitrogÃnio amoniacal e fÃsforo total. O modelo provou ser vÃlido para simulaÃÃo de OD, DBO e CTT para o perÃodo Ãmido com coeficientes de Nash e Sutcliffe (NSE) entre 0,61 e 0,96. Para o perÃodo seco, o modelo mostrou-se aceitÃvel para OD e DBO (NSE entre 0,33 e 0,49) e vÃlido para CTT (NSE 0,83). Os atores sociais identificaram os âpadrÃes de emissÃo â como instrumento essencial para a sustentabilidade ambiental da bacia. A proposta desta pesquisa de se admitir uma âtolerÃnciaâ aos parÃmetros de qualidade de Ãgua foi aceita pelos membros do comità como ferramenta vÃlida. Os membros do comità indicaram, para o trecho em estudo, Classe II com tolerÃncia de aproximadamente 10%. A simulaÃÃo de cenÃrios usando o modelo QUAL-2E mostrou valores do padrÃo de emissÃo de DBO, para a Classe II nos perÃodos Ãmido e seco, de 6 mg/L. Caso o rio seja enquadrado na Classe III, os valores seriam de 20 e 17 mg/L para os perÃodos Ãmido e seco, respectivamente. Apesar de a Classe II ser a desejada para o enquadramento do rio pelo comitÃ, verificou-se que os valores dos padrÃes de emissÃes seriam muito baixos para DBO, tornando inviÃvel a sua adoÃÃo, pois as atividades poluidoras sÃo incapazes de alcanÃar tal eficiÃncia no estado atual. Jà para o padrÃo de emissÃo de coliformes termotolerantes, o padrÃo de emissÃo seria de 103 NMP/100mL (perÃodo seco) e 104 NMP/100mL (perÃodo Ãmido) para que o rio seja de Classe II, enquanto que, para a Classe III, o padrÃo de emissÃo seria da ordem de 105 NMP/100mL, tanto para o perÃodo Ãmido quanto para o perÃodo seco. De acordo com a anÃlise feita nesta tese, o enquadramento mais adequado para o trecho do rio Salgado entre a Fonte da Batateira e a Cachoeira de MissÃo Velha, nas condiÃÃes atuais à a Classe III com tolerÃncia de 10% / This study was carried out on a 50 km length of the Salgado River, aiming to propose a methodology to determine an adequate pattern of pollutants emission, compatible with the natural recovery capacity of a river in a semi-arid region. The following steps were taken: (i) characterization of the study area based on the map of Salgado river and its tributaries; (ii) water quality diagnostic (Phase I, 1300 analysis): from March to September, 2005, in which eight river sections were selected for sampling, and 27 parameters were analysed in six monitoring campaigns; (iii) water quality diagnostic (Phase II, 1500 analysis): from February 2006 to January 2007, composed of twelve monitoring campaigns in 14 river sections with the parameters DO, BOD, faecal coliforms, total coliforms, pH, turbidity, electric conductivity, water and air temperature; (iv) social experiment, a participatory process involving CSBH-Salgado (Salgado Watershed Committee) and other social actors of the study watershed, promoting the discussion on water quality classification; (v) water quality modelling with the QUAL-2E model, calibrating two parameters: BOD and coliforms decay coefficients. Model validation was carried out using twelve campaigns from February 2006 to January 2007, distinguishing wet and dry periods. Scenarios simulation was performed for the BOD emission pattern with concentrations varying from 5 to 100 mg/L, and for the coliforms pattern with concentrations from 103 to 107 PN/100mL. This thesis concludes that the Salgado River, on the study reach, is polluted. It was identified that at least five parameters are in disagreement with the quality standards, inclusive for the Class IV: dissolved oxygen (DO), biochemical oxygen demand (BOD), faecal coliforms (FC), ammonia nitrogen and total phosphorus. The model was valid for the DO, BOD and FC simulations for the wet period, with Nash and Sutcliffe coefficient (NSE) from 0.61 to 0.96. For the dry period, the model was acceptable for DO and BOD (NSE) from 0.33 to 0.49) and valid for FC (NSE 0.83). The social actors identified the âemission patternsâ as an essential instrument for the watershed environmental sustainability. The proposal of this research in admitting a âtoleranceâ to the water quality parameters was accepted by the committee members as a valid tool. The committee members indicated, for the study reach, Class II with tolerance of approximately 10%. The scenarios simulation using the QUAL-2E model indicated values of emission pattern for BOD, for the Class II in the wet and dry periods, of 6 mg/L. In the case the river is classified in the Class III, the values would be 20 and 17 mg/L for the wet and dry period, respectively. Although Class II is desired for the river classification by the committee, it was observed that the emission patterns would be too low for BOD, making its adoption impracticable, since the polluting activities are not capable of reaching such efficiency on their current stage. For the faecal coliforms, the emission pattern would be 103 MPN/100mL (dry period) and 104 MPN/100mL (wet period) in the case the river is classified in the Class II, whereas for the Class III, the emission pattern would be of the order of 105 MPN/100mL, for both wet and dry periods. According to the analysis performed in this thesis, the most adequate water quality classification for the Salgado River on the reach between the Batateira Fountain and the MissÃo Velha Waterfall, on the current conditions, is the Class III with tolerance of 10%

Abstract Community assembly results from a combination of deterministic and stochastic mechanisms, whose relative effects can vary in response to environmental heterogeneity, connectivity, disturbance regimes and anthropogenic stressors. Understanding how community assembly mechanisms vary in response to environmental changes and connectivity is crucial for the management and conservation of river ecosystems. In this thesis, I tested the effects of connectivity and natural flow disturbances on riverine invertebrate communities by assessing assembly mechanism changes in response to (I) habitat connectivity, (II) seasonal flow intermittency and (III) inter–annual hydrological variability. I also conducted a field experiment to test for (IV) the effects of human–induced nutrient enrichment on community assembly of microorganisms (diatoms and aquatic fungi) and stream ecosystem functioning under different environmental settings. Invertebrate community assembly changed gradually with habitat connectivity. While limited dispersal resulted in higher community variability in the most isolated streams, mass effects caused community homogenization in the most connected ones. Natural and human induced disturbances lead to changes in the relative importance of deterministic and stochastic factors but often through different, or even opposite, mechanisms depending on the natural background of the ecosystem and organism type considered. For instance, seasonal drying and high–flow periods in intermittent Mediterranean rivers promoted deterministic and stochastic assembly processes respectively, whereas environmental sorting and stochastic processes respectively dominated during high and low flow years in boreal streams. Diatom and fungal communities responded differently to nutrient enrichment, with detrital processes and fungal communities responding more in naturally acidic than in circumneutral streams. The results of this thesis highlight the complexity of community assembly mechanisms: they tend to be highly context dependent and temporally variable. Therefore, stream bioassessment and conservation will benefit from explicitly incorporating connectivity and natural disturbance regimes. Assessing the interactive effects of connectivity and disturbances at the river network scale would provide a greater understanding of community assembly mechanisms and river ecosystem functioning. / Tiivistelmä Eliöyhteisöjen koostumus heijastelee determinististen ja stokastisten mekanismien vuorovaikutusta. Niiden suhteellinen merkitys vaihtelee suhteessa yhteisöjen kytkeytyneisyyteen sekä luontaisiin ja ihmisen aiheuttamiin häiriöihin. Yhteisöjen säätelymekanismit vaihtelevat jokiverkoston eri osissa ja tietoa tästä vaihtelusta tarvitaan jokiekosysteemien hoidon kehittämiseksi. Tässä tutkielmassa testasin elinympäristöjen kytkeytyneisyyden ja luontaisten häiriöiden (virtaamavaihtelut) vaikutuksia jokien selkärangatonyhteisöihin. Suoritin myös kenttäkokeen, jossa testattiin ihmisen aiheuttaman rehevöitymisen vaikutuksia mikro–organismeihin (piilevät, mikrobit) ja ekosysteemitoimintoihin erilaisissa ympäristöoloissa (luontaisesti happamat vs. neutraalit purot). Selkärangattomien yhteisökoostumus muuttui asteittain jokiverkostossa. Yhteisökoostumuksen vaihtelu oli suurinta eristäytyneimmissä latvapuroissa, kun taas isommissa, uomaston keskivaiheilla sijaitsevissa koskissa voimakas levittäytyminen eri suunnista (ns. massatekijät) aiheutti yhteisöjen rakenteen homogenisoitumista. Kuivuusjaksot ja niitä seuraavat korkean virtaaman jaksot edistivät determinististen prosessien merkitystä Välimeren alueen joissa, kun taas boreaalisissa puroissa Pohjois–Suomessa äärevät virtaamaolot, erityisesti poikkeuksellisen kuivat kesät, edistivät satunnaismekanismien vaikutusta. Perustuottajat (piilevät) ja hajottajat (akvaattiset sienet) vastasivat eri tavoin ravinnelisäykseen. Sienten hajotustoiminta nopeutui ravinnelisäyksen myötä, mutta vain luontaisesti happamissa puroissa. Tämän opinnäytetyön tulokset korostavat yhteisön kokoonpanomekanismien monimutkaisuutta: ne ovat usein erittäin tilanneriippuvaisia ja ajallisesti vaihtelevia. Siksi jokien ekologisen tilan arvioinnissa tulisi huomioida tutkimuspaikkojen kytkeytyneisyys jokimaisemassa.