O Brasil se destaca na produção agrícola intensiva omitindo em diversas situações práticas conservacionistas acarretando a má estrutura do solo, que por sua vez, propicia a dispersão da argila quando submetida em meio líquido. A argila prontamente dispersa em água (APDA) é a que sofre pequena agitação e pode ser quantificada pelo método do turbidímetro por definir desde os mais elevados graus de turvação até os menores (10000:1) em solução. O uso da espectroscopia tem sido crescente como uma ferramenta eficaz na quantificação das propriedades do solo. Diante disso, objetivou-se comparar métodos de determinação da APDA pelo turbidímetro e pela espectroscopia nas regiões espectrais VisNIR-SWIR-MidIR (400-25000 nm). 68 amostras foram adquiridas do horizonte B de Latossolos e subsuperficial de Neossolos Quartzarênicos e apresentam ampla variabilidade textural, química e mineralógica pertencentes aos estados de Goiás, Mato Grosso do Sul e São Paulo, estas foram avaliadas química e fisicamente. A determinação da APDA ocorreu por turbidimetria e esta foi relacionada com a argila total (AT) quantificada nos comprimentos de onda VisNIR-SWIR (350-2500 nm) e MidIR (4000-400 cm-1) via espectroscopia. Através da determinação da APDA, modelos foram criados por análise de regressão múltipla e estes foram ajustados conforme o resultado da análise de variância enquanto que a AT foi quantificada através da regressão por mínimos quadrados parciais (PLSR) por meio da validação cruzada, a ACP e o PLSR foram pressupostos e os modelos foram escolhidos levando em consideração o coeficiente de determinação, erro quadrado médio e a previsão para intervalo interquartil. Ocorreu uma relação negativa entre as variáveis AT, Ca, K, Mg, C e Al com a APDA e uma relação positiva da CTC, P e m com a APDA. Ao serem transformadas para logaritmo as variáveis estiveram mais próximas da normalidade. Das 9 variáveis independentes testadas 5 foram significativamente correlacionadas com a APDA em até 95% (log(AT), log(Ca), log(CTC), log(Al) e log(P)), o modelo foi adquirido por exclusão das variáveis não significativas equivalente ao modelo gerado pelo stepwise. Houve correlação negativa entre a APDA e AT (R2=0,27). A curva espectral evidenciou elevadas discrepâncias na amplitude de reflectância e nas feições das curvas, em razão das diferenças físicas, químicas e mineralógicas dos diferentes solos estudados. Para a AT o desempenho do modelo mensurado na faixa espectral MidIR foi superior (R2 ≥ 0,6; RMSE ≥ 103; RPIQ ≥ 249). Para a APDA os modelos validados sofreram pequena variação (R2 ≥ 0,5; RMSE ≥ 3,5; RPIQ ≥ 10,2) sendo a região MidIR a melhor desempenhada. O turbidímetro mostrou-se ser um método eficaz sendo portanto recomendado para futuros trabalhos. O conteúdo de argila total dos solos estudados foi a variável mais explicativa da APDA. A espectroscopia de reflectância foi eficiente em estimar a APDA tanto quanto o turbidímetro. / Brazil stands out in the intensive agricultural production omitting in several situations conservationist practices causing poor soil structure, which in turn, propitiates the dispersion of the clay when submitted in a liquid environment. The readily-dispersible clay in water (APDA) is the one that undergoes slight agitation and can be quantified by the turbidimeter method to be defined from the highest turbidity to the lowest turbidity (10000: 1) in solution. The use of spectroscopy has been increasing as an effective tool in the quantification of soil properties. The aim of this study was to compare APDA methods by the turbidimeter and by spectroscopy in the VisNIR-SWIR-MidIR (400-25000 nm) spectral regions. 68 samples were obtained from the B horizon of Latosols and subsurface of Quartzarenic Neosols and present wide textural, chemical and mineralogical variability belonging to the states of Goiás, Mato Grosso do Sul and São Paulo, which were evaluated chemically and physically. The determination of APDA occurred by turbidimetry and this was related to the total clay (AT) quantified at the wavelengths VisNIR-SWIR (350-2500 nm) and MidIR (4000-400 cm-1) via spectroscopy. Through the determination of the APDA, models were created by multiple regression analysis and these were adjusted according to the result of the analysis of variance while the AT was quantified through the partial least squares regression (PLSR) through the cross validation, the ACP and The PLSR were assumptions and the models were chosen taking into account the coefficient of determination, mean square error and the forecast for interquartile range. There was a negative relationship between the variables AT, Ca, K, Mg, C and Al with APDA and a positive relation of CTC, P and m with APDA. When they were transformed to logarithm the variables were closer to normal. Of the 9 independent variables tested 5 were significantly correlated with APDA in up to 95% (log (AT), log (Ca), log (CTC), log (Al) and log (P)), the model was acquired by excluding the Non-significant variables equivalent to the model generated by stepwise. There was a negative correlation between APDA and AT (R2 = 0.27). The spectral curve showed high discrepancies in reflectance amplitude and curves, due to the physical, chemical and mineralogical differences of the studied soils. For AT, the performance of the model measured in the MidIR spectral range was higher (R2> 0.6, RMSE> 103, RPIQ> 249). For the APDA, the validated models suffered a small variation (R2> 0.5, RMSE> 3.5, RPIQ> 10.2), with the MidIR region being the best performed. The turbidimeter proved to be an effective method and is therefore recommended for future work. The total clay content of the studied soils was the most explanatory variable of APDA. Reflectance spectroscopy was efficient in estimating APDA as much as the turbidimeter.

A demanda para tratamento de efluentes industriais tem sido maior a cada dia e a indústria tem buscado melhoria constante nos processos para tratamento. Nesse contexto, a eletrofloculação surge como uma técnica promissora, devido à sua eficiência, econômica e ambiental, com possibilidade de reuso da água. O presente trabalho tem como objetivo estudar o tratamento de água de produção de plataforma de petróleo, pelo processo de eletrofloculação, em reator batelada, com eletrodo de alumínio. Foi avaliada a influência de parâmetros como: condutividade, pH, intensidade de corrente aplicada e tempo de operação. O estudo teve foco na remoção de poluentes como óleos e graxas, cor, turbidez e boro. Os resultados alcançados indicam que o processo de eletrofloculação, nas condições operacionais estudadas, é uma alternativa tecnicamente viável para a remoção de óleos e graxas, cor e turbidez, obtendo remoção média de 84%, 83% e 83%, respectivamente. Entretanto, não foi observada eficiência na remoção de boro / Treatment of industrial wastewaters has grown in the last years and the industry searches continuous improvements in treatment processes. In this context, the electrofloculation comes such as a promising alternative, due to its economic and environmental efficiencies, with possibility to reuse water. This dissertation aims to study the treatment of oil production water, by electrofloculation process, with aluminum electrode, in a batch reactor. The influence of parameters such as conductivity, pH, current density and operation time was evaluated. The study focused on removal oils and greases, color, turbidity and boron. The results indicate that the process of electrofloculation is a technically viable alternative for removal of oils and greases, color and turbidity, obtaining removal average of 84%, 83% and 83%, respectively. However, it wasnt efficient to remove boron

Advanced monitoring of water quality in order to perform a real-time hazard analysis prior to Water Treatment Works (WTW) is more of a necessity nowadays, both to give warning of any contamination and also to avoid downtime of the WTW. Downtimes could be a major contributor to risk. Any serious accident will cause a significant loss in customer and investor confidence. This has challenged the industry to become more efficient, integrated and attractive, with benefits for its workforce and society as a whole. The reality is that water companies are not yet prepared to invest heavily in trials, before another company announces its success in implementing a new monitoring strategy. This has slowed down the development of the water industry. This research has taken the theoretical idea that the use of advanced online monitoring technique in the water industry would be beneficial and a step further; demonstrating by means of a state-of-the-art assessment, usability trials, case studies and demonstration that the barriers to mainstream adoption can be overcome. The findings of this work have been presented in four peer-reviewed papers. The research undertaken has shown that Turbidity levels in rivers can be measured from the rivers' mean flow rate, using either Doppler Ultrasound device for real-time readings or based on past performance history. In both cases, the Turbidity level can also help estimate both the Colour and Conductivity levels of the subject river. Recalibration of the equations used is a prerequisite as each individual river has its own unique "finger print".

A falta de água potável é um agravo que atinge populações em nível mundial e nacional e as pequenas comunidades isoladas são as que estão mais suscetíveis à essa vulnerabilidade. Essas localidades demandam soluções descentralizadas, como o filtro lento domiciliar (FLD). Nesse contexto, nesta tese propõe-se a construção de FLD com materiais de PVC, de fácil aquisição e montagem simples. Na Fase 1 do trabalho, compararam-se FLDs com regime de fluxo intermitente, com (FI) e sem (FIS) controle do nível da água por boia; e contínuo, com (FC) e sem (FCS) boia, tratando mistura de água subterrânea com caulinita. Analisaram-se turbidez remanescente, redução de Escherichia coli, tempo de amadurecimento e duração das carreiras de filtração para investigar o efeito da boia nos dois regimes. Na Fase 2, estudou-se a aceleração do amadurecimento nos dois regimes, usando como acelerador o pó de cacto Opuntia cochenillifera, tratando água natural. Compararam-se unidades intermitentes com (FIA) e sem (FI) acelerador, e unidades contínuas com (FCA) e sem (FC) acelerador. Nessa fase consideraram-se também a redução de coliformes totais, consumo de oxigênio dissolvido e remoção de cistos de Giardia e oocistos de Cryptosporidium além das variáveis consideradas na Fase 1. Nas duas fases estudaram-se as correlações de variáveis operacionais (taxa de filtração, perda de carga dividida por espessura de meio filtrante, tempo de operação, tempo após a manutenção) com eficiências para redução de bactérias e turbidez remanescente. O custo dos FLDs em PVC foi estimado em cerca de R$ 420,00. Os resultados indicaram que na Fase 1, FI demonstrou maiores carreiras de filtração que FIS, sem diferenças para as outras variáveis. FC apresentou turbidez remanescente média menor que FCS (1,24 ± 0,91 versus 1,90 ± 1,36 NTU). Na Fase 2, FIA apresentou melhor eficiência para redução de E. coli (2,32 ± 0,79 versus 1,936 ± 0,61 log) e menor turbidez remanescente média que FI, entre os contínuos, não houve diferença de eficiências (p.e. 2,51 ± 0,60 e 2,60 ± 0,56 log de E. coli), no entanto, FCA apresentou carreiras de filtração mais curtas que FC (33 ± 13 versus 60 ± 14 dias). A variável perda de carga nos primeiros 2 cm foi a com maior correlação com a redução de bactérias na Fase 1, enquanto que na Fase 2, a redução de bactérias se correlacionou melhor com turbidez remanescente. No estudo sobre de remoção de (oo)cistos de protozoários, 92% de 30 amostras não apresentaram os parasitos, no entanto, em duas amostras detectaram-se a presença de um oocisto de Cryptosporidium. Apesar de elevadas reduções de bactérias por FLDs, não houve amostras filtradas com ausência de coliformes, para tanto, fizeram-se testes com hipoclorito de sódio, que resultaram ausência de bactérias na água tratada. O controle por boia prolongou a carreira de filtração no regime intermitente e melhorou a turbidez filtrada no fluxo contínuo. O uso do acelerador de amadurecimento foi efetivo para eficiências dos FLDs apenas no fluxo intermitente. Dentre os modelos estudados, o FC apresentou melhores resultados em termos de eficiência e duração das carreiras de filtração. / The lack of drinking water is an aggravation affecting populations at the global and national levels and the small and isolated communities are the most susceptible to this vulnerability. These locations require decentralized solutions, such as the household slow sand filter (HSSF). In this context, in the present thesis is proposed the construction of a HSSF with PVC materials, of easy acquisition and simple assemble. In Phase 1 of the study, it was compared HSSFs with intermittent flow regime, with (FI) and without (FIS) water level control by float; and continuous, with (FC) and without (FCS) float, treating groundwater with kaolinite. Remaining turbidity, Escherichia coli reduction, ripening time and filtration run times were investigated to explore the effect of the float in the two regimes. In Phase 2 the acceleration of ripening was studied in both regimes, using as accelerator Opuntia cochenillifera cactus powder, treating natural water. Intermittent units were compared with (FIA) and without (FI) accelerator, and continuous units with (FCA) and without (FC) accelerator. In this phase, the reduction of total coliforms, dissolved oxygen consumption and removal of Giardia cysts and Cryptosporidium oocysts in addition to the variables considered in Phase 1 were also studied. In the two phases it was studied the correlation of operational variables (filtration rate, head loss divided by filter media thickness, time of operation, time after maintenance) with efficiencies for bacterial reduction and remaining turbidity. The cost of FLDs in PVC was estimated at around R$ 420.00. The results indicated that in Phase 1, FI had larger filtration runs than FIS, with no differences for the other variables. FC had turbidity remaining mean lower than FCS (1.24 ± 0.91 versus 1.90 ± 1.36 NTU). In Phase 2, FIA had a better efficiency to reduce E. coli (2.32 ± 0.79 versus 1.936 ± 0.61 log) and lower average remaining turbidity than FI, there were no differences in efficiencies (e.g. 2, 51 ± 0.60 and 2.60 ± 0.56 log of E. coli), however, FCA had shorter filtration runs than FC (33 ± 13 versus 60 ± 14 days). The variable head loss in the first 2 cm was the one with the highest correlation with E. coli reductions in Phase 1, while in Phase 2, the bacterial reduction correlated better with remaining turbidity. In the study on the removal of protozoa (oo)cysts, 92% of 30 samples did not present the parasites, however, in two samples the presence of a Cryptosporidium oocyst was detected. Despite high bacterial reductions by HSSFs, there were no filtered samples with absence of coliforms; therefore, sodium hypochlorite tests were performed, which resulted in no bacteria in the treated water. The float control extended the filtration run in the intermittent regime and improved the turbidity filtered in the continuous stream. The use of the ripening accelerator was effective for FLD efficiencies only in the intermittent flow. Between the studied models of filters, FC was the one with the better results of efficiencies and duration of filters run.

O presente trabalho teve como objetivo avaliar a potencialidade de aplicação da Flotação por Ar Dissolvido (FAD) na redução da turbidez da água do Rio Gualaxo do Norte, o qual foi poluído por, pelo menos, 40 bilhões de litros de rejeito do processamento de minério de ferro após a ruptura da barragem de rejeitos da Samarco, em novembro de 2015. Com isto, o estudo visa determinar as condições ótimas de coagulação (dosagem e pH), floculação (gradiente médio de velocidade e tempo de floculação) e taxa de reciclo (percentual de mistura água-ar dissolvido), visando obter parâmetros satisfatórios de qualidade em termos de turbidez residual e eficiência de remoção turbidez para amostras compostas por variados valores de turbidez (419 NTU, 785 NTU 1412 NTU e 3517 NTU), a fim de se simular a resposta da FAD frente a eventuais variações na concentração de sólidos na água de estudo. Dentro do universo deste estudo, foi possível demonstrar que a elevada turbidez, a baixa hidrofobicidade e a elevada densidade das partículas minerais suspensas levou à redução da capacidade de flotação das microbolhas, resultando em uma fração de material sedimentado (em média 25%). Todavia, foi constatado que, em geral, o coagulante cloreto férrico foi eficiente na remoção de sólidos via FAD, promovendo, com 18% de taxa de reciclo, turbidez residual de 49 NTU para a amostra mais turva (de turbidez inicial 3517 NTU). O coagulante natural Tanfloc SL apresentou desempenho promissor, pois foi possível a clarificação das amostras altamente turvas (com até 1412 NTU) com a aplicação de uma diminuta dosagem (2,0 mg/L) e baixa taxa de reciclo (6%), resultando em turbidez residual próxima a 59 NTU. Além disto, o coagulante Tanfloc SL permitiu maior flotabilidade dos flocos, enquanto o coagulante cloreto férrico levou a maiores percentuais de sedimentação destes. Após o tratamento com o coagulante cloreto férrico, a concentração de ferro dissolvido na água foi elevada, inclusive a valores superiores ao limite estabelecido pela legislação. Em contrapartida, o coagulante Tanfloc SL manteve baixa concentração de metais dissolvidos na água, o que reforça a vantajosa aplicação de um coagulante natural e biodegradável. / This research project aimed to evaluate the viability of the application of the Dissolved Air Flotation (FAD) technique in the reduction of the River Gualaxo do Norte water turbidity, polluted by at least 40 billion liters of iron ore tailings after the rupture of the Samarco tailings dam, in November of 2015. Therefore, this study\'s purpose is to determine the optimum coagulation conditions (dose and pH), flocculation (mean velocity gradient and flocculation time) and recycle rate (water-dissolved air mixture percentage) in order to obtain satisfactory quality parameters in terms of residual turbidity and removal efficiency for samples presenting varying turbidity values (1412 NTU 419 NTU 785 NTU and 3517 NTU) aiming to simulate the DAF reponse to any variations in solids concentration. Within the universe of this study, it was possible to demonstrate that the high turbidity, and especially the high density of the suspended mineral particles, led to the reduction of the flotation capacity of the microbubbles, resulting in a sediment fraction (25% - mean value). However, it was found that, in general, the coagulant ferric chloride was effective in removal of solids via FAD, promoting with 18% recycle rate, residual turbidity of 49 NTU for the most turbid water sample (initial turbidity 3517 NTU). The natural coagulant Tanfloc SL presented a favorable performance, as it was possible to clarify highly turbid samples (up to 1412 NTU) using a low dosage (2.0 mg / L) and low recycle rate (6%), resulting in in residual turbidity close to 59 NTU. In addition, the coagulant Tanfloc SL allowed greater flotation of the flocs, while the coagulant ferric chloride led to higher sedimentation percentages. With the use of ferric chloride as coagulant the iron concentration dissolved in the water was elevated, even to values higher than the limit established by the legislation. In contrast, the coagulant Tanfloc SL maintained a low concentration of dissolved metals in the water, which reinforces the advantageous application of a natural and biodegradable organic coagulant.

The runoff of suspended solids and nutrients from land into the nation's lakes and rivers can have severe impacts on the health of these systems and their uses. High-frequency environmental data from sensors can provide insight into fundamental biogeochemical processes that dictate water quality and provide regulators with valuable knowledge on how to manage critical resources. The goal of this research was to utilize sensor technology, telemetry hardware, cyberinfrastructure, and water quality models to create a sensing system that will allow the investigation of the fate and transport of dissolved oxygen, suspended solids, nutrients, and other water quality parameters throughout a watershed dominated by agricultural activity. Deploying these sensors at multiple locations along the stream enabled the investigation of these processes from the fine scale to the larger watershed scale. Results from this research addressed both fundamental science and resource management issues regarding water quality. Using high-frequency data, a dramatic diel cycle in dissolved oxygen was observed with nonlinear dynamics which was successfully modeled mathematically, and excursions in water quality criteria were observed. In addition, a diel pattern in turbidity was discovered with higher levels at night likely caused by bioturbation (i.e. nocturnal activity of bottom feeding fishes) which resulted in higher suspended solids loadings during nighttime. Furthermore, the QUAL2K model was successfully calibrated for water quality using sensor measurements and grab samples from volunteer, IOWATER data. Nutrient loading rates (nitrate-N, orthophosphate, and total dissolved solids) were estimated along the entire creek and were similar to other Iowa streams. Volunteer environmental data were found to be helpful in model calibration for some parameters (e.g. TSS and nitrate). The construction and operation of a sensing system in Clear Creek contributed to water quality science and engineering. Findings from the configuration and field testing of sensing station components such as water quality sensors, power systems and communication hardware will aid the design of future sensing systems and environmental observatories. Integrating the methodology of this research with future observing systems will further our understanding of water quality processes and help maintain the health and value of our nation's water environment.

Due to increasingly stringent regulations, concerns about disinfection byproduct formation, and the need for improved control of distribution system water quality, there has been a shift towards the use of alternative disinfectants and oxidants in the production of drinking water. Technologies that modify water chemistry, such as hydrogen peroxide, UV irradiation, chlorine and/or chloramines may result in the generation of mineral and organic precipitates. Turbidity provides an indirect measure of the presence of particles by evaluating the light scattering properties of water. Turbidity levels are currently not monitored or regulated in treated groundwater. An important water quality parameter that influences groundwater quality is hydrogen sulfide. The control of sulfides in groundwater is of importance because its presence can cause odor and taste complaints, corrosion of pipes and other plumbing fixtures, and black-water problems in distribution systems (Levine et. al, 2004). In addition, sulfides can impose a significant oxidant demand and possibly interfere with disinfection treatments. Characteristics of particles from untreated and treated groundwater were tested as part of a field study to evaluate alternative wellhead treatment approaches for controlling hydrogen sulfide. A 1 gallon per minute (gpm) pilot-plant was used to test several groundwater treatment scenarios. The chemicals tested included chlorine, monochloramine, and hydrogen peroxide either alone or in tandem. Photochemical oxidation was evaluated using UV and advanced oxidation was evaluated using hydrogen peroxide coupled with UV. Testing was conducted either on water pumped directly from the well at ambient (7.0-7.5), or pretreated with caustic soda to evaluate the impact of elevated pH (8.2) conditions. The formation of particles was quantified using turbidity, solids (total, dissolved and suspended), and particle counts before and after oxidation. The particulate matter was characterized using a particle size analyzer in conjunction with scanning electron microscopy coupled with energy dispersive spectroscopy (SEM/EDS). Treatment systems that rely on in-line treatment lack mechanisms for particle removal, therefore particles generated through treatment are introduced into the distribution system. It is evident from this project that treatment systems should be optimized to prevent particle formation.

<p>Eutrophication is an increasing problem in the Baltic Sea and is caused by an excess of nutrients in the water which are primarily transported with the runoff from cultivated land. The peninsula Vikbolandet in Östergötland is dominated by arable land and has stream outflows to the bays of Bråviken and Slätbaken. In this study five streams of Vikbolandet have been sampled during the spring flood period with the aim of connecting concentrations of nutrients in the streams with turbidity and runoff in the catchment. This analysis has then been related to the land use in the small catchment of Vadsbäcken in order to investigate the impact of land uses with areal losses of phosphorus. The results indicate that there are increasing concentrations of phosphorus downstream in the sites of Vadsbäcken and that the transported amounts of phosphorus increases with the spring flood and at a rainstorm event. It is shown that the distribution of agricultural blocks in the catchment of Vadsbäcken has a major impact on the nutrient leakage. There is a co-variation between turbidity and runoff during a rainstorm event and between particulate-bound phosphorus and runoff over time. A further aim has been to investigate possibilities for use of an easily managed, cost-effective environmental monitoring method for nutrient measurements in watercourses. Within four out of five streams at Vikbolandet there is a significant co-variation between turbidity and total phosphorus. Using field measurements of turbidity for environmental monitoring could provide a viable alternative for environmental monitoring of watercourses but will need further investigations of co-variation before being brought into use. Further, this study shows that the transport of phosphorus is underestimated in environmental monitoring</p>

The number of species extinctions is increasing at an alarming rate. Long-lived freshwater mussels of the order Unionoida, which include a parasitic stage on a host fish, are highly threatened. Habitat degradation by turbidity and sedimentation is thought to be one major reason for their decline. The objective of this thesis was to examine recruitment patterns and identify the causes of the lack of recruitment in the threatened unionoid freshwater pearl mussel (Margaritifera margaritifera). In addition, I investigated the effects of turbidity on non-endangered dreissenid mussels, where turbidity was manipulated through use of bioturbating mayflies. In a survey of 107 Swedish streams, mussel population size and trout density were both positively correlated to recruitment probability of M. margaritifera. A more in-depth study of the age-structure of nine populations revealed that four of these populations showed no signs of recruitment over the last ten years. Within-stream variation in recruitment was high as both mussels and trout had patchy distribution, and may be important for population regulation. Moreover, examination of different life stages revealed no differences in the gravid mussel stage or the stage when mussels infect salmonid fish. Instead, differences were observed for the juvenile, benthic stage, presumably related to differences in turbidity and sedimentation. High turbidity may affect filter-feeding efficiency of mussels and high sedimentation may reduce survival by clogging sediments, thereby altering, for example, oxygen and food conditions. In the study of the effects of turbidity, bioturbating mayflies increased turbidity and filter-feeding dreissenid mussels reduced turbidity. Mussel growth both decreased and increased with increasing turbidity, depending on sediment type. Turbidity and sedimentation often impact entire stream systems, and a holistic, catchment-based management strategy may be needed to reduce the effects of sedimentation on freshwater pearl mussels. The effects of restoration take a long time and must start soon if recruitment of mussels is to be re-established. Restoration may also be more urgent in some streams than in others, as the maximum age of M. margaritifera populations in my study differed by as much as 60 years. As mussel and trout densities seem to be important for recruitment success, one conservation method may be to concentrate mussels into sites where trout density is high.

Animals experience variation in their environment because of natural changes. However, due to anthropogenic disturbance, the speed and severity of these changes have recently increased. This thesis investigates how reproductive behaviours may be affected by human induced environmental change. In specific, I investigate how visual and chemical changes in the aquatic environment, caused by eutrophication, affect mating systems and sexual selection in fish. Broad-nosed- and straight-nosed pipefish, which both have been studied in detail for a long period, were used as model organisms. These two species are particularly suitable model organisms since they perform complex courtship behaviours, including the advertisement of ornaments and a nuptial dance. Further, two distinct populations were studied, one on the Swedish west coast and one in the Baltic Sea, as these two locations vary in the degree and extent of environmental disturbance, in particular turbidity. I found that changes in the visual environment had no impact on the development of female sexual ornaments in these sex-role reversed pipefishes, but it hampered adaptive mate choice. Turbidity also had a negative effect on reproductive success in the Baltic Sea population. Changes in the chemical environment in the form of increased pH reduced the probability to mate, while hypoxia did not alter mating propensity. However, hypoxic water delayed the onset of both courting and mating. Hence, human induced change in aquatic environments may alter the processes of sexual selection and population dynamics.