Weathering releases lithogenic elements to soil and stream waters that support life in catchment ecosystems. Seasonal and inter-annual variations in hydrologic conditions change subsurface flowpaths, modifying the influence of weathering on stream waters. This study, over two climatically variable years, determined seasonal and inter-annual changes in solute sources to streams using a multi-tracer approach including major cations, strontium isotopes, germanium (Ge)/silica ratios, carbon species, and trace metals. Stream water cations display constant concentrations although discharge response was highly variable, suggesting that there is a consistent subsurface water supply. However, Sr isotope ratios, and concentrations of Ge, Fe, Al, and dissolved organic carbon, which originate from shallow soil waters, increase with the hydrograph during a wet winter snowmelt. This indicates that during a year with a thick snowpack, stream waters contain components of both shallow soilwater and groundwater during snowmelt, whereas during all other times groundwater contributes predominantly to the stream.

Pothole wetlands are ubiquitous throughout the Prairie Pothole Region and since 1900, 40-70% of potholes in the region have been drained to increase agricultural production. This thesis describes factors influencing spatial and temporal variations in wetland water quality and characteristics of drainage water. Research was conducted at Smith Creek watershed, southeastern Saskatchewan, where there has been controversy over recent renewed efforts to drain wetlands. Following snowmelt in 2009, 67 wetlands were sampled to determine whether spatial variations in wetland water quality were attributable to land cover, permanence classes, and surface drainage characteristics. Wetlands with cropped uplands had greater TP and K than wetlands with wooded and grassed uplands; TP, TDN, and DOC were higher in seasonally than permanently ponded wetlands; and salts were lower in wetlands with wooded uplands compared to wetlands with cropped and grassed uplands. Measurements of water quality of one permanently ponded wetland over a 20 week period in 2008 showed that the wetland acted as a solute trap. Variations in salts and DOC were influenced by hydrological processes such as runoff, evaporation, and shallow groundwater seepage, whereas variations in nitrogen, phosphorus, and bacteria were influenced by biotic, sorption, and hydrological processes. The experimental drainage of this wetland in November 2009 demonstrated that its water quality was an important control of drainage water quality. Further, the wetland ditch acted as a simple conduit, i.e., little solutes loss or gain occurred along it. In spring 2009, water quality along seven ditches and five natural connections that form between wetlands (termed spills) was compared. Concentrations of most solutes were similar, except TDN, DOC, HCO₃^-, K⁺, and Ca²⁺ that were higher in ditches than spills. Minimal changes in water quality along ditches and spills occurred, likely due to the low temperatures occurring in spring that restrict biotic processing and sorption. Notably, because ditches connect wetlands to streams, as opposed to spills that connect adjacent wetlands, ditches have a greater potential to contribute to downstream solute loading. Wetland drainage efficiency and wetland water quality were deemed the factors critical to determining solute exports via ditches. Results of wetland water quality and drainage characteristics can be useful to future modeling exercises and could be used to inform wetland drainage practices and policies.

Pothole wetlands are ubiquitous throughout the Prairie Pothole Region and since 1900, 40-70% of potholes in the region have been drained to increase agricultural production. This thesis describes factors influencing spatial and temporal variations in wetland water quality and characteristics of drainage water. Research was conducted at Smith Creek watershed, southeastern Saskatchewan, where there has been controversy over recent renewed efforts to drain wetlands. Following snowmelt in 2009, 67 wetlands were sampled to determine whether spatial variations in wetland water quality were attributable to land cover, permanence classes, and surface drainage characteristics. Wetlands with cropped uplands had greater TP and K than wetlands with wooded and grassed uplands; TP, TDN, and DOC were higher in seasonally than permanently ponded wetlands; and salts were lower in wetlands with wooded uplands compared to wetlands with cropped and grassed uplands. Measurements of water quality of one permanently ponded wetland over a 20 week period in 2008 showed that the wetland acted as a solute trap. Variations in salts and DOC were influenced by hydrological processes such as runoff, evaporation, and shallow groundwater seepage, whereas variations in nitrogen, phosphorus, and bacteria were influenced by biotic, sorption, and hydrological processes. The experimental drainage of this wetland in November 2009 demonstrated that its water quality was an important control of drainage water quality. Further, the wetland ditch acted as a simple conduit, i.e., little solutes loss or gain occurred along it. In spring 2009, water quality along seven ditches and five natural connections that form between wetlands (termed spills) was compared. Concentrations of most solutes were similar, except TDN, DOC, HCO₃^-, K⁺, and Ca²⁺ that were higher in ditches than spills. Minimal changes in water quality along ditches and spills occurred, likely due to the low temperatures occurring in spring that restrict biotic processing and sorption. Notably, because ditches connect wetlands to streams, as opposed to spills that connect adjacent wetlands, ditches have a greater potential to contribute to downstream solute loading. Wetland drainage efficiency and wetland water quality were deemed the factors critical to determining solute exports via ditches. Results of wetland water quality and drainage characteristics can be useful to future modeling exercises and could be used to inform wetland drainage practices and policies.

Isotopes and hydrochemistry were used to define groundwater flow systems and better understand the hydrogeological setting of the Karijini National Park within the Central Pilbara region, this study was initiated because of the near proximity of the Marandoo iron ore mine to the National Park. Based on the stable isotope composition of the water samples, two main groups of water can be identified. Groundwater is characterised by depleted δD and δ¹⁸O, suggesting no significant evaporation effect. Surface water on the other hand is more enriched in δD and δ¹⁸O due to evaporation. The relatively high concentration of Cl- compared to rainfall and depleted δD and δ¹⁸O values of groundwater indicate that recharge of the aquifers is occurring during intense rainfall events when rapid infiltration occurs. Evapotranspiration then acts to concentrate ionic species prior to recharge. The presence of CFCs in the groundwater indicates the presence of modern recharge water. Relationships between various ionic species has shown that infiltration through the Tertiary sequence and subsquent dissolution of carbonate minerals is main influence on increasing concentrations of Ca²⁺ , Mg²⁺ , HCO₃⁻ . The TDS concentration of the groundwater in the Marra-Mamba Iron Formation that hosts the Marandoo ore body is higher than most of the water bodies surrounding the mining area. This suggests that either significant chemical modification is occuring or it is recharged by different mechanisms to that of the Karijini groundwater. Relationships between the major ion concentration and catchment area, surficial Tertiary cover and distance between recharge and discharge were identified. The results show that the hydrochemistry of the water discharging at each location within the National Park can be justified by groundwater evolution within it’s own catchment.

Isotopes and hydrochemistry were used to define groundwater flow systems and better understand the hydrogeological setting of the Karijini National Park within the Central Pilbara region, this study was initiated because of the near proximity of the Marandoo iron ore mine to the National Park. Based on the stable isotope composition of the water samples, two main groups of water can be identified. Groundwater is characterised by depleted δD and δ¹⁸O, suggesting no significant evaporation effect. Surface water on the other hand is more enriched in δD and δ¹⁸O due to evaporation. The relatively high concentration of Cl- compared to rainfall and depleted δD and δ¹⁸O values of groundwater indicate that recharge of the aquifers is occurring during intense rainfall events when rapid infiltration occurs. Evapotranspiration then acts to concentrate ionic species prior to recharge. The presence of CFCs in the groundwater indicates the presence of modern recharge water. Relationships between various ionic species has shown that infiltration through the Tertiary sequence and subsquent dissolution of carbonate minerals is main influence on increasing concentrations of Ca²⁺ , Mg²⁺ , HCO₃⁻ . The TDS concentration of the groundwater in the Marra-Mamba Iron Formation that hosts the Marandoo ore body is higher than most of the water bodies surrounding the mining area. This suggests that either significant chemical modification is occuring or it is recharged by different mechanisms to that of the Karijini groundwater. Relationships between the major ion concentration and catchment area, surficial Tertiary cover and distance between recharge and discharge were identified. The results show that the hydrochemistry of the water discharging at each location within the National Park can be justified by groundwater evolution within it’s own catchment.

Salinization of freshwaters by human activities is of growing concern globally. Salt pollution can cause adverse effects to aquatic biodiversity, ecosystem function, ecosystem services, and human health. In many regions of the world, and in coal-mining-influenced streams of the temperate forests of Appalachia USA, specific conductance (SC), a surrogate measure for the dissolved major ions composing salinity, has been linked to decreased diversity of benthic macroinvertebrates. However, assessments used to reach this conclusion have generally not accounted for temporal variability of salinity, as most studies use "snapshot" SC data collected concurrently with biological data at a single point in time. Effective management of salinization requires tools to accurately monitor and predict salinity while accounting for temporal variability. To improve those tools, I conducted analyses of 4.5 years of salinity and benthic macroinvertebrate data from 25 forested headwater streams spanning a gradient of salinity where non-salinity stressors were minimized. My objectives were to: 1) model the annual pattern of salinity, 2) determine if salinity measures derived from continuous data are more precise than snapshot SC as predictors of aquatic biology, and 3) quantify response to salinity of the benthic macroinvertebrate community. A sinusoidal model of the annual cycle of SC using daily measurements for 4.5 years revealed that salinity naturally deviated ± 20% from annual mean levels, with minimum SC occurring in late winter and maximum SC occurring in late summer. The pattern was responsive to seasonal dilution as driven by catchment evapotranspiration dynamics. Alternative discrete sampling intervals can approximate the pattern revealed by continuous SC data if sampling intervals are ≤ 30 days. Continuous SC variables did not significantly improve precision for prediction of benthic macroinvertebrate metrics (p > 0.1) as compared to snapshot SC using generalized additive mixed models. Results suggest that snapshot SC is a capable predictor of benthic macroinvertebrate community structure if sampling is carefully timed. However, continuous SC data can quantify chronic salt exposure, which supports a hypothesis to explain how temporal variability of field-based observations of salt sensitivity of benthic macroinvertebrate taxa may be influenced by life stage. Benthic macroinvertebrate community structure diverged from reference condition as salinity increased, with stronger relationships in Spring than in Fall. Intra-seasonal variation in community structure was also revealed across sampling dates. Non-Baetidae Ephemeroptera were most sensitive to salinity, with richness and abundance lower than reference at SC > 200 =µS/cm in Spring based on snapshot SC. Equivalent effects were predicted by mean monthly SC of 250-300 µS/cm from the prior Fall. Continuous conductivity monitoring may improve assessment of salinity effects because they can describe life-cycle exposure, which may aid investigations of mechanisms driving field-based observations of benthic-macroinvertebrate community alteration. / Ph. D. / Freshwater ecosystems around the world are at risk of contamination from salt pollution resulting from a variety of human activities. All natural freshwaters contain low levels of dissolved minerals, or salts, the combined concentration of which is referred to as salinity. Activities such as crop irrigation, road de-icing, and mining can cause salt pollution in streams and rivers, and excessive salinity can be toxic to many aquatic organisms. In many regions of the world, including in coal-mining-influenced streams of Appalachia USA, elevated salinity has been linked to decreased diversity of benthic macroinvertebrates, which are primarily aquatic insects, a group critical to healthy stream ecosystems. However, assessments used to reach this conclusion have generally not accounted for annual variability of salinity, as most studies use “snapshot” salinity data collected concurrently with biological data at a single point in time. Effective management of salinity impacts requires tools to accurately monitor and predict salinity while accounting for annual variability. Toward improving those tools, I conducted analyses of 4.5 years of salinity and aquatic insect data from 25 small central Appalachian mountain streams spanning a gradient of salinity. My objectives were to: 1) characterize the annual pattern of salinity using high-frequency salinity data, 2) determine if high-frequency salinity data is better than snapshot data for predicting aquatic insect diversity, and 3) measure the response to salinity of the aquatic insect community and identify salinity levels associated with insect biodiversity loss. High-frequency (daily) data revealed that salinity exhibited a predictable cyclic annual pattern with seasonal deviations of ± 20% from annual average salinity levels. Minimum salinity occurred during late winter and maximum salinity occurred in late summer. Lower-frequency salinity data can approximate the annual pattern if sampling interval is ≤ 30 days. Snapshot salinity was equally capable as high-frequency data of predicting aquatic insect diversity provided that snapshot salinity sampling is carefully timed. Diversity of many aquatic insects, especially mayflies, declined with increasing salinity, with stronger relationships in Spring than in Fall. Variation in diversity measures was also somewhat related to sample timing within seasons. Alteration of aquatic insect communities was evident at total salt concentrations levels of approximately 130 – 200 parts per million, depending on time of year. Efforts to manage salinity impacts to aquatic life may be improved by integrating knowledge of annual salinity patterns with how aquatic insects respond to salt pollution.

O material particulado (MP) presente na atmosfera tem papel importante na reflexão da luz solar, na visibilidade, no regime de chuvas e na saúde da população. As coletas de MP foram realizadas entre 2015 e 2016 na cidade de Ribeirão Preto (campus da USP), utilizando amostrador sequencial. Os íons majoritários solúveis para o material grosso e fino foram analisados por cromatografia de íons. As espécies predominantes na composição química do material particulado fino em ng m-3 (n=50) foram: SO42- (502 ± 306), K+ (149 ± 129) e NH4+ (135 ± 82), sendo estas principalmente derivadas da queima de biomassa. Na fração grossa, as espécies predominantes foram NO3- (216 ± 118), SO42- (146 ± 107), Ca2+ (123 ± 71), que estão correlacionadas à ressuspensão do solo, emissão veicular e absorção de ácido nítrico. Maiores massas de MP foram encontradas no período de safra da cana de açúcar, quando há maior queima de biomassa, maior ressuspensão do solo (devido ao intenso uso de maquinário), e menor quantidade de chuva. Houve um aumento significativo na concentração da maioria das espécies no período de safra da cana (período seco). No caso do material fino, as maiores concentrações de SO42- e NO3- foram observadas no período seco, durante o dia, demonstrando a importância da formação dessas espécies por reações fotoquímicas. Na fração grossa, a maior evidência de sazonalidade foi observada para os íons Ca2+, Mg2+ e K+ relacionados com uma maior ressuspensão do solo. O cálculo do balanço iônico mostrou que há um déficit de ânions, que pode estar relacionado ao fato dos íons HCO3-, CO32- e espécies aniônicas orgânicas, não terem sido quantificadas. A razão entre formiato e acetato (F/A) na fração fina foi de 1,7 ± 1,1 (n=40), demonstrando que a formação secundária de ácido fórmico é predominante em relação a emissão direta dos ácidos. A análise exploratória estatística mostrou que no caso da fração fina, a fonte de emissão de maior relevância é a queima de biomassa no período seco/safra. A ressuspensão do solo foi a principal fonte de emissão da fração grossa principalmente no período seco. Este trabalho demonstrou que as concentrações de todas as espécies analisadas no MP, com exceção do íon amônio na fração grossa, tiveram uma diminuição significativa com relação àquelas obtidas para amostras de MP coletadas em Araraquara, há cerca de 15 anos. Em comparação com trabalhos mais recentes em Araraquara, também foi observada uma diminuição na concentração de cálcio e magnésio na fração grossa, e de todas as espécies na fração fina. / Atmospheric particulate matter (PM) has an important role in the reflection of solar radiation, visibility, rainfall pattern and in the human health. PM samples were collected between 2015 and 2016 at the University of São Paulo campus in the city of Ribeirão Preto, using a sequential sampler. Soluble major ions from coarse and fine fractions were determined by ion chromatography. Predominant species in the chemical composition of fine MP in ng m-3 were (n= 50): SO42- (502 ± 306), K+ (149 ± 129) and NH4+ (135 ± 82), being mainly derived from biomass burning. Predominant species in the course fraction were: NO3- (216 ± 118), SO43- (146 ± 107) and Ca2+ (123 ± 71), being correlated with soil dust resuspension, vehicular emission and nitric acid adsorption. Higher mass of PM was found in the harvest period of sugar cane, when there is still partial burning of the leaves, high soil dust resuspension (due to intense use of agricultural machinery), and less amount of rain. There was a significant increase in the concentration of most species in the sugarcane harvest period. In the case of fine PM, the highest SO42- and NO3- concentrations were observed during the day and in the harvest period, demonstrating the importance of the formation of these species by photochemical reactions. In the case of coarse fraction, the greatest evidence of seasonality was observed for Ca2+, Mg2+ and K+ ions, related to higher soil dust resuspension. The calculation of ionic balance showed that there is a deficit of anions, which may be related to the fact of HCO3-, CO32- ions and organic anionic species have not been quantified. The ratio of formate and acetate (F/A) on the fine fraction was 1.7 ± 1.1 (n=40), demonstrating that the secondary formation of formic acid is predominant over the direct emission of the acids. The statistical exploratory analysis showed that in the case of fine fraction, the emission source of greater relevance in the harvest is the biomass burning, while the photochemical reactions are the major source in the non-harvest period. Soil dust resuspension was the primary source of emission of coarse fraction during the whole year. This study showed that the concentrations of all species analyzed in the PM (except for ammonium ions in the coarse fraction), had a significant decrease compared with those obtained for PM samples collected in Araraquara city, about 15 years ago. In comparison to more recent work in Araraquara it was also observed a decrease in the concentration of calcium and magnesium in the coarse fraction, and all species in the fine fraction.

Amostras de água de chuva foram coletadas no campus da USP Ribeirão Preto (RP) de agosto de 2002 a dezembro de 2005. Cerca de 84% (n=127) das amostras apresentaram excesso de acidez, com pH médio de 5,12. Não se observou sazonalidade no pH de acordo com o período de safra da cana. As concentrações médias ponderadas pelo volume (MPV, em mol L-1): K+ 3,9 (n=175), Na+ 2,1 (n=172), Ca2+ 5,0 (n=175) e Mg2+ 1,8 (n=168), observadas em RP, bem como seus fluxos de deposição por via úmida, foram ligeiramente mais elevadas que aquelas encontradas em chuvas de regiões com características semelhantes. As concentrações destes cátions foram sazonais, com um aumento no período de safra, sendo que a maior diferença foi observada para o íon K+, indicando a sua importante fonte na queima de biomassa. A sazonalidade do íon Ca2+ aponta para a importância das atividades agrícolas, intensificadas no período de safra, na emissão deste cátion para a atmosfera. Observaram-se boas correlações lineares entre as concentrações de Na+ e K+ (0,67626) e de Na+ e Ca2+ (0,77822), indicando a possibilidade de emissões pirogênicas e a ressuspensão do solo serem fontes de emissão de Na+. A MPV de carbono orgânico dissolvido (COD) encontrada em RP foi mais elevada que na Amazônia, onde também há intensa queima de biomassa, porém seus fluxos por via úmida em ambas as regiões foram similares (0,42 molCm-2ano-1). As concentrações de COD em RP apresentaram correlações lineares significativas com K+ (0,70341) e com Ca2+ (0,61638), apontando para a queima de biomassa e ressuspensão do solo como fontes importantes de emissão de carbono orgânico para a atmosfera. As concentrações de COD nas chuvas de Araraquara foram ainda maiores que em RP, indicando pronunciadas fontes locais naquela cidade. As MPV (nmol L-1) de Cd 0,54 (n=56), Pb 3,02 (n=94) e Cu, 19,9 (n=98), encontradas nas chuvas de RP foram semelhantes a regiões urbanas e industriais do hemisfério norte, enquanto a concentração de Al (448 nmol L-1, n=126) foi menor, e a de Zn (405 nmol L-1, n=120) apresentou-se dentro das faixas de concentrações relatadas nestes locais. Com exceção de Cd, os demais metais analisados (Pb, Cu, Zn e Al) também apresentaram concentrações significativamente maiores (P=0,05) nas chuvas durante o período de safra, indicando que a queima de biomassa e as atividades agrícolas podem aumentar a emissão destes metais para a atmosfera de RP. A correlação linear significativa entre Pb e Ca2+ (0,53845), indica a participação da ressuspensão do solo no aporte atmosférico de Pb em RP, enquanto a ausência de correlação linear entre Zn e K+ (0,20182) parece indicar a presença de outras fontes significativas de Zn para a atmosfera de RP, além da queima de biomassa. O cálculo do fator de enriquecimento demonstra que Cd, Zn, Pb e Cu estão enriquecidos com relação ao solo na chuva de RP, sugerindo que estes podem ter fontes antrópicas locais e / ou distantes. A análise preliminar de componentes principais não esclareceu o peso das diferentes fontes de emissão atribuídas neste trabalho. / Rain water samples were collected based on events at the University of São Paulo - campus Ribeirão Preto - from August 2002 to December 2005. About 84% (n=127) of the samples had excess of acidity, with an average pH of 5.12. There was no correlation between the pH values and the sugar cane harvest period. The Volume Weighed Means (VWM, in mol L-1) for K+ 3.9 (n=175), Na+ 2.1 (n=172), Ca2+ 5.0 (n=175) and Mg2+ 1.8 (n=168), and their wet fluxes in RP were slightly higher than those reported to regions with similar characteristics. The concentrations for these cations were seasonal, with higher values during the harvest period. The largest difference was observed for K+, indicating its important source in the biomass burning activity. The seasonality showed for Ca2+ is probably related to the higher soil resuspension during the more intense agricultural activities. A good linear correlation observed between Na+ and K+ (0.67626) and between Na+ and Ca2+ (0.77822), suggest that Na+ may have important pirogenic as well as soil dust sources. The VWM for Dissolved Organic Carbon (DOC) in RP was higher than that reported for rainwater in the Amazon region (where the biomass burning is also intense); however, the wet fluxes from both sites were very similar (0.42 mol C m-2 ano-1). DOC concentrations were well correlated with K+ (0.70341) and Ca2+ (0.61638), suggesting that the biomass burning as well as soil dust can be important sources of organic carbon to the atmosphere. DOC concentrations in rainwater from Araraquara were even higher than those for RP, showing a high local source of organic carbon. The VWM (nmol L-1) for Cd 0.54 (n=56), Pb 3.02 (n=94) and Cu 19.9 (n=98) found in the rainwater from RP were similar to urban and industrialized regions of the Northern Hemisphere, while for Al (448 nmol L-1, n=126) it was lower, and for Zn (405 nmol L-1, n=120) the VWM was within the range reported for such areas. Except for Cd, all the other metals measured (Pb, Cu, Zn and Al) also showed higher concentrations (P=0.05) in rainwater samples during the harvest period, suggesting that biomass burning and intensive agricultural activities can increase these species concentrations in the atmosphere. The significant linear correlation between Pb and Ca2+ (0.53845) indicates that soil inputs can be of relevance for Pb atmospheric inputs in RP. On the other hand, the absence of linear correlation between Zn and K+ (0.20182) seems to indicate the presence of other important sources for Zn to the atmosphere besides biomass burning. The calculated Enrichment Factor showed that Cd, Zn, Pb and Cu are anomalously enriched in RP rainwater in relation to soil, suggesting these metals may have antroprogenic local sources as well as distant ones. The preliminary statistical analysis of principal components did not clarify the weight of the different sources of emission attributed in this work.

Um maior conhecimento sobre a composição química da água de chuva pode auxiliar no entendimento de como as atividades agrícolas da região de Ribeirão Preto podem afetar a composição da atmosfera local e regional. A proposta do presente estudo é determinar a concentração de íons majoritários e etanol na água de chuva de Ribeirão Preto, investigar suas fontes, e avaliar a possível sazonalidade dessas espécies químicas. As amostras de água de chuva foram coletadas no campus da Universidade de São Paulo (USP), no ano de 2007, e de agosto de 2011 a junho de 2012. No período de safra da cana-de-açúcar as concentrações médias ponderadas pelo volume (MPV) dos íons nas amostras de chuva foram mais elevadas (teste-t; P=0,05) do que no período de entressafra, com exceção do íon H+. As maiores razões entre as médias do período de safra e entressafra foram observadas para o K+ (6,7) e NH4+ (4,2), possivelmente porque os respectivos elementos estão presentes em elevadas concentrações na folha da cana, que é queimada antes da colheita manual da planta. O balanço da eletroneutralidade (considerando os íons: H+, K+, Na+, NH4+, Ca2+, Mg2+ Cl-, NO3-, SO42, F-, H3CCOO-, HCOO- e HCO3-) apresentou um déficit de ânions de 13% que foi atribuído às espécies aniônicas orgânicas presentes na água de chuva que não foram quantificadas. O valor médio ponderado pelo volume de pH nas amostras de chuva deste trabalho foi de 5,4, sendo que grande parte dos eventos de chuva (68%) de Ribeirão Preto apresentou excesso de acidez. O método desenvolvido nesse trabalho para a determinação de etanol em água de chuva não necessitou de etapa de pré-concentração, apresentou boa precisão, exatidão, com baixos limites de detecção (0,46 mol L-1) e quantificação (1,54 mol L-1). A concentração de etanol nas amostras de água de chuva (n= 45) variou de 2,5 a 7,4 mol L-1 (MPV = 5,30 1,17), não sendo observada sazonalidade dentro dos períodos estudados. Possivelmente a principal fonte de emissão de etanol é proveniente de combustíveis automotivos, que por sua vez, tem baixa modulação durante o decorrer do ano. As espécies orgânicas dissolvidas totais (voláteis e não purgáveis) na água de chuva são principalmente moduladas pela queima de biomassa, no período de safra. A concentração média ponderada pelo volume de COD na chuva de Ribeirão Preto durante o período deste estudo foi de 311 ± 59 mol L-1. A fração volátil dissolvida na água de chuva (COV) foi em média (MPV) 16,1 ± 4,0 mol L-1, sendo que a concentração média de etanol representa 33% desse valor. Apesar da concentração relativamente baixa de COV com relação ao carbono total dissolvido, esses compostos na fase gasosa podem desempenhar importante papel em reações fotoquímicas que levam a formação de espécies oxidantes de elevada toxicidade. / The improvement of our knowledge about the chemical composition of rainwater can improve our understanding on how the agricultural activities in Ribeirão Preto can affect the composition of the local and the regional atmosphere. The aim of the present study is to determine the concentration of major anions and ethanol in rainwater from Ribeirão Preto to investigate their sources, and to examine the possible seasonal variability of these species. The rainwater samples were collected at the University of São Paulo - campus of Ribeirão Preto during the year 2007, and from August 2011 to June 2012. During the sugar cane harvest period, the volume weighted means (VWM) concentrations for the major ions in the rainwater samples were significantly higher than those obtained during the non-harvest period (t-test, P=0.05), except for H+ ions. The largest ratios between the ions averages obtained for the harvest and for the non-harvest periods were observed for K+ (6.7) and NH4+ (4.2), possibly because these elements are present at elevated concentration in the sugar cane leave (that is burnt before the manual harvest). The electroneutrality balance (considering the ions: H+, K+, Na+, NH4+, Ca2+, Mg2+ Cl-, NO3-, SO42, F-, H3CCOO-, HCOO- e HCO3-) showed an anion deficit of 13%, and it was attributed to the anionic organic species that were present in the samples but were not identified in this work. The pH VWM was 5.4, and 68% of the rainwater samples from Ribeirão Preto analyzed in the work presented an excess of acid. The method developed in this work for the determination of ethanol in rainwater did not need a pre concentration step, and showed a good precision, accuracy, with low detection and quantification limits (0,46 and 1,54 mol L-1 respectively). The ethanol concentrations in the rainwater ranged from 2.8 to 7.4 mol L-1 (VWM = 5.30 1.17, n= 45), and there was not a clear seasonality within the two studied periods. Possibly the main emission source of ethanol was vehicular fuels that have low variability in the inputs during the year. The variability of total organic compounds (volatile and non-purgeable) in the rainwater samples are mainly due to the biomass burning during the sugar cane harvest period. The VWM of dissolved organic carbon (DOC) in the rainwater collected during this study in Ribeirão Preto was 311 ± 59 mol L-1. The volatile fraction VWM was 16.1 ± 4.0 mol L-1, and on average, 33% of these compounds were ethanol. Although this concentration of volatile organic carbon is relatively low compared to the total dissolved carbon concentration, these compounds in the gaseous phase can have an important role in the photochemical reactions that take place in the atmosphere with consequent formation of highly toxic oxidant species.

The Hillsborough River flows southwesterly through Pasco and Hillsborough counties in west central Florida. From its source at the Green Swamp to its mouth in Hillsborough Bay, the river is joined by many tributaries and man-made inputs. Spatial and temporal variations in the river's major ion and CO2 system chemistry were examined in a two-year study between 1999 and 2001. At thirteen sampling stations along approximately 54 miles of the river, water samples were collected in surroundings that ranged from pristine to urban. Samples were collected monthly for the first year and periodically thereafter. Concentrations of major ions were lowest in the river's headwaters, showed only minor spatial variations in mid-river, and sharply increased in tidally influenced waters below a dam on the lower river. A major tributary, Blackwater Creek, exerts a strong influence on the river's phosphate concentrations, and Crystal Springs, upstream of Blackwater Creek, exerts a strong influence on nitrate concentrations in the river. Downstream of Crystal springs, NO3- concentrations decreased steadily to levels that are more than an order of magnitude lower than levels in the upper river. Temporal ion concentration variations can be quite large. Low major ion concentrations were observed in the rainy season (June-September), while phosphate concentrations increased dramatically during extremely wet conditions. Seasonal variations were also observed in the river's CO2 system. Riverwater pH decreased during periods of high precipitation along with CaCO3 saturation state. CaCO3 supersaturation was observed during the exceptionally dry periods of the study, and undersaturation was observed during periods of high rainfall.Overall, the chemistry of the Hillsborough River is greatly influenced by temporal and spatial variations in the river's tributaries, groundwater sources, and anthropogenic inputs.