Embora o nitrogênio seja um nutriente limitado, em excesso, ele pode causar a degradação de sistemas aquáticos. Apesar de, no âmbito nacional, o Brasil não apresentar problemas de escassez hídrica, regiões altamente populosas já tem enfrentado problemas de déficit hídrico, inclusive em função da poluição difusa de nitrogênio. Zonas ripárias têm sido apontadas como um dos atributos da bacia hidrográfica que pode ajudar na melhoria e manutenção da qualidade hídrica devido a sua capacidade de retirar nitrogênio do sistema terrestre oriundo de fontes difusas. Essa característica lhe é conferida por serem ambientes favoráveis ao processo de desnitrificação. A desnitrificação é um dos processos, se não o primeiro, responsável por converter o nitrato para formas gasosas N2O e N2. Considerando que os estudos sobre a função desempenhada por vegetações ripárias como sumidouro de nitrogênio se concentraram em países de clima temperado e que paisagens alteradas são o uso da terra majoritário no Estado de São Paulo, onde o problema de déficit hídrico já é uma realidade. Entender o papel que zonas ripárias desempenham sobre a dinâmica do nitrogênio torna-se fundamental para o desenvolvimento de estratégias de manejo do uso da terra voltadas para a manutenção da qualidade de sistemas aquáticos em regiões tropicais. O objetivo do trabalho é investigar se existe mudança dos processos que regulam a dinâmica do nitrogênio no solo em paisagens alteradas, enfatizando o papel desempenhado por vegetações ripárias como sumidouros de nitrogênio. A bacia hidrográfica do ribeirão Caxambu, com elevada influência antrópica, foi selecionada. Dentro dela dois rios foram escolhidos: (i) ribeirão Cachoeira drenando uma vertente com uso pastoril, na qual o pasto se estende até a zona ripária e (ii) ribeirão Caxambu drenando uma vertente agrícola com presença de floresta ripária. Extratores de solução do solo foram instalados ao longo de ambas vertentes para a quantificação do nitrogênio inorgânico dissolvido (NID) transportado ao longo de um ano. Amostras de solo foram coletadas nas porções: ripária e encosta de ambas vertentes para a quantificação das taxas líquidas de mineralização e nitrificação e também da desnitrificação potencial em cinco meses ao longo de um ano. Variáveis físico-químicas, incluindo NID, foram monitoradas em ambos os ribeirões. Os resultados indicam que as florestas ripárias estão processando o nitrogênio mais ativamente do que pastos ripários. As taxas líquidas de mineralização e nitrificação foram significativamente superiores no solo de florestas ripárias em relação ao solo de pasto ripário. No entanto, não houve diferença estatística significativa entre solo de floresta ripária e pasto ripário com relação à desnitrificação potencial. Não houve mudança das concentrações de NID na solução do solo ao longo da vertente pastoril, sendo estas relativamente baixas. Contrariamente, na vertente agrícola, submetida à fertilização, houve redução da concentração de NID na solução do solo quando se passou da encosta agrícola para a floresta ripária. Essa redução pode ser atribuída também ao processo de desnitrificação. Porém, outros processos além da desnitrificação devem estar atuando como moduladores da dinâmica do nitrogênio no solo de florestas ripárias. Tendo em vista que houve redução da ciclagem de nitrogênio na pastagem em relação à floresta, a inferência sobre o papel que o pasto ripário poderia desempenhar caso haja um elevado aporte de nitrogênio para essa zona ripária foi limitada. Concluí-se que as florestas ripárias podem atuar como sumidouro de nitrogênio em ambientes tropicais alterados. Portanto, podem ser uma ferramenta para o manejo sustentável de recursos hídricos na propriedade rural / Although nitrogen is a limiting nutrient, in excess, it can lead to the degradation of aquatic systems. Despite the fact that at national level Brazil does not have problems of water scarcity; regions highly populated are already facing deficit of water, caused among other things by nitrogen diffuse pollution. Riparian zones have been indicated as an attribute of the watershed that can maintain quality of water because their capacity in preventing diffuse pollution. Denitrification is one, if not the primary process responsible for this function, converting nitrate to gaseous N2O or N2. Considering that studies about the role of riparian vegetations in removing nitrogen loads are concentrated in temperate countries, and that altered landscapes is the main land cover of the State of Sao Paulo, where water scarcity is already a problem; understanding about the role of riparian zones on nitrogen dynamics is fundamental to orient land management practices aiming at preservation of aquatic systems in tropical regions. The objective of this study is to investigate whether processes that regulate the nitrogen dynamic in the soil change among altered landscapes, emphasizing the role of riparian vegetations as nitrogen sinks. The study area is the Caxambu watershed which is under intense anthropogenic influence. Two streams were selected: (i) Cachoeira stream draining a pasture slope with a riparian zone under pasture use and (ii) Caxambu stream draining an agricultural slope with riparian forests. Soil solution extractors were installed in each slope to quantify the concentration of dissolved inorganic nitrogen (DIN) at 50 cm deep during one year. Soil samples were collected at four sites: riparian zone with pasture, upland with pasture, riparian zone with forest, and upland with agriculture in order to quantify net mineralization, net nitrification, and denitrification potential during five months, in a period of one year. Physical-chemical variables, including DIN, in each stream were monitored during one year. The results show that nitrogen cycling in riparian forests soils is more intense than riparian pastures. Net mineralization and net nitrification are higher at riparian forests in relation to riparian pastures and other sampled sites. However there is no significant difference between riparian forests and riparian pastures in relation to denitrification potential. There is no significant difference between DIN concentration in the soil solution at pasture slope, and these concentrations are relatively low. On the contrary, at the agricultural slope under fertilization DIN concentrations are reduced significantly as soil solution moves through the riparian forests. This reduction could be the result of higher denitrification that occurs at riparian forest soils. However, besides denitrification other processes may be playing important role as modulators of nitrogen dynamic in the soils of riparian forests. Because the results show that nitrogen cycling is lower in the pasture compared to forest, inferring about the role that riparian pastures could play as nitrogen sinks was limited. In conclusion there is an indication that riparian forests can play an important role as nitrogen sink at altered landscapes in tropical region. Therefore restoring riparian zones could be an interesting tool to further deterioration of aquatic systems

Estuarine ecosystems are under enormous stress due to rapid coastal developments and climate change. Proper management of these important ecosystems requires a good understanding of their key processes. In this thesis, riparian groundwater-surface water interaction is explored for an aquifer-estuary system primarily by a series of numerical experiments. The work focuses on riparian-scale groundwater flow and salinization. The overall aim of the study was to extend our understanding of aquifer-estuary exchange, which is currently centered on the lower marine estuarine reach, to middle estuaries (i.e., the estuary reach that has variable salinity). The numerical experiments were guided by previous studies and observations made from an exploratory field investigation conducted in and next to Sandy Creek, a macro-tidal estuary incised in the alluvial aquifer of the Pioneer Valley, North-eastern Australia (Longitude 49.11°, Latitude -21.27°). The following observations were made from the field investigation: Sandy Creek estuary experiences a variable salinity regime in its mid reaches that consists of periods of 1) freshwater flushing due to up catchment-derived flooding, 2) persistent freshwater conditions for at least 2 months following the flooding, 3) tidal salinity fluctuations and 4) constant near-seawater salinity; laterally extensive and disconnected aquitards were found to occur at the field site; Sandy Creek had an essentially ‘vertical’ bank slope. Numerical simulations were conducted using the finite element modeling code FEFLOW for saturated unsaturated, variable-density groundwater flow and solute transport, to examine the influence of the following factors on aquifer-estuary exchange: a tidally varying estuarine salinity and hydraulic head, a seasonal freshwater flush (i.e., estuary with freshwater and an elevated stage due to an up catchment sourced flood), near estuary aquitard layers, lateral asymmetry (about the estuary centerline) in hydraulic conductivity and regional hydraulic gradients. The simulations neglected seepage face development after numerical experiments showed that for a vertical bank estuary interacting with a sandy loam aquifer, seepage face effects on groundwater flow and associated salinity distribution were minimal. The following observations were drawn from the range of numerical experiments considered. Tidal salinity fluctuations in the estuary (varying between 0 and 1 - i.e., using a relative salinity scale where a salinity of 1 is seawater) produced flow paths and residence times that were distinctly different to the constant seawater salinity case. While the constant average 0.5 salinity case and the corresponding tidally-varying salinity case (i.e., salinity varying between 0 and 1) produced somewhat comparable results in terms of RUC and RLC (RUC represents groundwater discharge to the estuary that originated from recharge to the estuary bank and RLC groundwater discharge to the estuary that originated from recharge through the estuary bed), whereas flow paths and the total salt mass in the aquifer differed. Freshwater flushing simulations indicated that the near-estuary aquifer responds rapidly to a 2-day ‘wet season’ flushing event with a short-lived freshwater lens created through freshening of the hyporheic zone. Annual cycling of the seasonal flushing led to significant disruption of the estuary water circulation in the aquifer thereby impacting on residence times, transport pathways, and RUC and RLC, and acting to potentially remobilize groundwater and contaminants previously trapped in continuous and semi-continuous re-circulation cells. Although groundwater flow paths determined using tide-averaged velocity vectors were representative of flow paths from transient tidally driven flow vector field, residence times calculated from the two flow fields were markedly different. The influence of riparian scale aquitards and lateral asymmetry (about the estuary centreline) in hydraulic gradients and hydraulic conductivity on groundwater flow and associated salinity distribution was also found to be sensitive to estuarine salinity conditions. The results indicate that observations made about aquifer-estuary interaction in the lower estuary may not be directly applicable to the middle estuary. According to the simulations, tidal salinity variations in the estuary are important factors that affect hyporheic-riparian salt transport processes and that the use of a time averaged estuarine salinity as an approximation to variable salinity conditions is unsuitable for the accurate prediction of the near-estuary dynamics in middle estuaries. This study was based on a two dimensional representation of the riparian scale interaction and it is clear that future research needs to focus on the three-dimensionality of the aquifer-estuary system, incorporating spatially and temporally varying flow and transport characteristics. That is, many estuaries are tortuous and the aquifer geology spatially complex such that assumptions required for the two-dimensional section will most likely restrict application to the field. The tidal dynamics in the middle estuary is also expected to generate three dimensional aspects to the aquifer-estuary interaction. Thus further investigation that explicitly models the hydrodynamics and salt transport in the estuary and estuarine morphology is required to refine the insight provided by the simple conceptual model adopted in this study.

Estuarine ecosystems are under enormous stress due to rapid coastal developments and climate change. Proper management of these important ecosystems requires a good understanding of their key processes. In this thesis, riparian groundwater-surface water interaction is explored for an aquifer-estuary system primarily by a series of numerical experiments. The work focuses on riparian-scale groundwater flow and salinization. The overall aim of the study was to extend our understanding of aquifer-estuary exchange, which is currently centered on the lower marine estuarine reach, to middle estuaries (i.e., the estuary reach that has variable salinity). The numerical experiments were guided by previous studies and observations made from an exploratory field investigation conducted in and next to Sandy Creek, a macro-tidal estuary incised in the alluvial aquifer of the Pioneer Valley, North-eastern Australia (Longitude 49.11°, Latitude -21.27°). The following observations were made from the field investigation: Sandy Creek estuary experiences a variable salinity regime in its mid reaches that consists of periods of 1) freshwater flushing due to up catchment-derived flooding, 2) persistent freshwater conditions for at least 2 months following the flooding, 3) tidal salinity fluctuations and 4) constant near-seawater salinity; laterally extensive and disconnected aquitards were found to occur at the field site; Sandy Creek had an essentially ‘vertical’ bank slope. Numerical simulations were conducted using the finite element modeling code FEFLOW for saturated unsaturated, variable-density groundwater flow and solute transport, to examine the influence of the following factors on aquifer-estuary exchange: a tidally varying estuarine salinity and hydraulic head, a seasonal freshwater flush (i.e., estuary with freshwater and an elevated stage due to an up catchment sourced flood), near estuary aquitard layers, lateral asymmetry (about the estuary centerline) in hydraulic conductivity and regional hydraulic gradients. The simulations neglected seepage face development after numerical experiments showed that for a vertical bank estuary interacting with a sandy loam aquifer, seepage face effects on groundwater flow and associated salinity distribution were minimal. The following observations were drawn from the range of numerical experiments considered. Tidal salinity fluctuations in the estuary (varying between 0 and 1 - i.e., using a relative salinity scale where a salinity of 1 is seawater) produced flow paths and residence times that were distinctly different to the constant seawater salinity case. While the constant average 0.5 salinity case and the corresponding tidally-varying salinity case (i.e., salinity varying between 0 and 1) produced somewhat comparable results in terms of RUC and RLC (RUC represents groundwater discharge to the estuary that originated from recharge to the estuary bank and RLC groundwater discharge to the estuary that originated from recharge through the estuary bed), whereas flow paths and the total salt mass in the aquifer differed. Freshwater flushing simulations indicated that the near-estuary aquifer responds rapidly to a 2-day ‘wet season’ flushing event with a short-lived freshwater lens created through freshening of the hyporheic zone. Annual cycling of the seasonal flushing led to significant disruption of the estuary water circulation in the aquifer thereby impacting on residence times, transport pathways, and RUC and RLC, and acting to potentially remobilize groundwater and contaminants previously trapped in continuous and semi-continuous re-circulation cells. Although groundwater flow paths determined using tide-averaged velocity vectors were representative of flow paths from transient tidally driven flow vector field, residence times calculated from the two flow fields were markedly different. The influence of riparian scale aquitards and lateral asymmetry (about the estuary centreline) in hydraulic gradients and hydraulic conductivity on groundwater flow and associated salinity distribution was also found to be sensitive to estuarine salinity conditions. The results indicate that observations made about aquifer-estuary interaction in the lower estuary may not be directly applicable to the middle estuary. According to the simulations, tidal salinity variations in the estuary are important factors that affect hyporheic-riparian salt transport processes and that the use of a time averaged estuarine salinity as an approximation to variable salinity conditions is unsuitable for the accurate prediction of the near-estuary dynamics in middle estuaries. This study was based on a two dimensional representation of the riparian scale interaction and it is clear that future research needs to focus on the three-dimensionality of the aquifer-estuary system, incorporating spatially and temporally varying flow and transport characteristics. That is, many estuaries are tortuous and the aquifer geology spatially complex such that assumptions required for the two-dimensional section will most likely restrict application to the field. The tidal dynamics in the middle estuary is also expected to generate three dimensional aspects to the aquifer-estuary interaction. Thus further investigation that explicitly models the hydrodynamics and salt transport in the estuary and estuarine morphology is required to refine the insight provided by the simple conceptual model adopted in this study.

Estuarine ecosystems are under enormous stress due to rapid coastal developments and climate change. Proper management of these important ecosystems requires a good understanding of their key processes. In this thesis, riparian groundwater-surface water interaction is explored for an aquifer-estuary system primarily by a series of numerical experiments. The work focuses on riparian-scale groundwater flow and salinization. The overall aim of the study was to extend our understanding of aquifer-estuary exchange, which is currently centered on the lower marine estuarine reach, to middle estuaries (i.e., the estuary reach that has variable salinity). The numerical experiments were guided by previous studies and observations made from an exploratory field investigation conducted in and next to Sandy Creek, a macro-tidal estuary incised in the alluvial aquifer of the Pioneer Valley, North-eastern Australia (Longitude 49.11°, Latitude -21.27°). The following observations were made from the field investigation: Sandy Creek estuary experiences a variable salinity regime in its mid reaches that consists of periods of 1) freshwater flushing due to up catchment-derived flooding, 2) persistent freshwater conditions for at least 2 months following the flooding, 3) tidal salinity fluctuations and 4) constant near-seawater salinity; laterally extensive and disconnected aquitards were found to occur at the field site; Sandy Creek had an essentially ‘vertical’ bank slope. Numerical simulations were conducted using the finite element modeling code FEFLOW for saturated unsaturated, variable-density groundwater flow and solute transport, to examine the influence of the following factors on aquifer-estuary exchange: a tidally varying estuarine salinity and hydraulic head, a seasonal freshwater flush (i.e., estuary with freshwater and an elevated stage due to an up catchment sourced flood), near estuary aquitard layers, lateral asymmetry (about the estuary centerline) in hydraulic conductivity and regional hydraulic gradients. The simulations neglected seepage face development after numerical experiments showed that for a vertical bank estuary interacting with a sandy loam aquifer, seepage face effects on groundwater flow and associated salinity distribution were minimal. The following observations were drawn from the range of numerical experiments considered. Tidal salinity fluctuations in the estuary (varying between 0 and 1 - i.e., using a relative salinity scale where a salinity of 1 is seawater) produced flow paths and residence times that were distinctly different to the constant seawater salinity case. While the constant average 0.5 salinity case and the corresponding tidally-varying salinity case (i.e., salinity varying between 0 and 1) produced somewhat comparable results in terms of RUC and RLC (RUC represents groundwater discharge to the estuary that originated from recharge to the estuary bank and RLC groundwater discharge to the estuary that originated from recharge through the estuary bed), whereas flow paths and the total salt mass in the aquifer differed. Freshwater flushing simulations indicated that the near-estuary aquifer responds rapidly to a 2-day ‘wet season’ flushing event with a short-lived freshwater lens created through freshening of the hyporheic zone. Annual cycling of the seasonal flushing led to significant disruption of the estuary water circulation in the aquifer thereby impacting on residence times, transport pathways, and RUC and RLC, and acting to potentially remobilize groundwater and contaminants previously trapped in continuous and semi-continuous re-circulation cells. Although groundwater flow paths determined using tide-averaged velocity vectors were representative of flow paths from transient tidally driven flow vector field, residence times calculated from the two flow fields were markedly different. The influence of riparian scale aquitards and lateral asymmetry (about the estuary centreline) in hydraulic gradients and hydraulic conductivity on groundwater flow and associated salinity distribution was also found to be sensitive to estuarine salinity conditions. The results indicate that observations made about aquifer-estuary interaction in the lower estuary may not be directly applicable to the middle estuary. According to the simulations, tidal salinity variations in the estuary are important factors that affect hyporheic-riparian salt transport processes and that the use of a time averaged estuarine salinity as an approximation to variable salinity conditions is unsuitable for the accurate prediction of the near-estuary dynamics in middle estuaries. This study was based on a two dimensional representation of the riparian scale interaction and it is clear that future research needs to focus on the three-dimensionality of the aquifer-estuary system, incorporating spatially and temporally varying flow and transport characteristics. That is, many estuaries are tortuous and the aquifer geology spatially complex such that assumptions required for the two-dimensional section will most likely restrict application to the field. The tidal dynamics in the middle estuary is also expected to generate three dimensional aspects to the aquifer-estuary interaction. Thus further investigation that explicitly models the hydrodynamics and salt transport in the estuary and estuarine morphology is required to refine the insight provided by the simple conceptual model adopted in this study.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv., 2008. / Härtill 6 uppsatser.

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Ferreira.pdf: 696113 bytes, checksum: ee5dd4958bf29e5a41d8a7568cc07d33 (MD5) Previous issue date: 2015-04-06 / FAPEAM - Fundação de Amparo à Pesquisa do Estado do Amazonas / Description of distribution patterns of species and the mechanisms that generate them are essential to understanding the relationships between organisms and environmental gradients. Riparian zones are distinguished form non-riparian zones by topography, hydrological regimes, soil types and plant and animal communities. In central Amazônia, distinctive bird assemblages have been described in riparian an non-riparian zones. Negative effects as those produced by human disturbance interfere directly on the richness and abundance of birds in forests, mainly through changes in some components of vegetation, affecting the availability of food resources and microclimate conditions. A pattern often observed in areas with urban influence is the homogenization of communities resulting in communities of mostly generalist species after the extinction of specialist species. Thus, it is important to know if in a forest with a strong influence of urbanization, bird assemblages respond to environmental variation generated by the proximity to water courses, as observed in undisturbed forests. It is also important to know if edge effects generated by the urbanization process negatively affect the distribution of these bird communities locally. This study was conducted in an urban forest of about 600 hectares in the city of Manaus (AM) in which the campus of the Federal University of Amazonas - UFAM is found. The forest includes the university campus and is surrounded by residential neighborhoods, streets and urban areas with different uses. To characterize the avifauna of the understory in riparian and non- riparian zones we used the capture-recapture technique and mist-nets. We selected 20 sampling sites, with 10 riparian sites and 10 non- riparian sites. At each site we used a mist-net line (120m) activated for two consecutive days from 06:30h to 11:30h from July to November 2013. Birds were identified, measured, weighed and banded, except humming birds. We, captured 27 species of 12 families with a total of 118 individuals of which 9.3% were recaptures. We found a similar total abundance (T = -0.17 , df = 9 , p = 0.86 ) and species richness (T = -0.2641 , df = 9 , p = 0.79) in riparian and non-riparian sites. We also found that quantitative composition of bird assemblages was not different between riparian and non- riparian sites. However, when the effect of distance to the edge was included into the models we found a different pattern. The best model to explain the variation of biomass of birds, was the one with an interaction between the effect of the distance to the edge and the effect of environment (riparian and non-riparian) (AICweight = 0.716). Thus, according to this model there was a positive relationship between the bird biomass and the distance to the edge in riparian zones while the opposite pattern was observed in non-riparian zones. Regarding similarity between riparian and non-riparian zones, we observed a pattern of increasing similarity between pairs of riparian sites and non-riparian sites with decreasing distance to the forest edge, that is, pairs of riparian / non-riparian sites that are closer to the forest edge are more similar to each other than sites that are in the interior of the forest. We conclude that the edge effect generated by the negative influence of the urban matrix into the forest is the determining factor in increasing the similarity between riparian and non- riparian zones, thus leading to a community homogenization process. / A descrição de padrões de distribuição de espécies e os mecanismos que os geram são essenciais para entender as relações entre os organismos e os gradientes ambientais. Zonas ripárias se distinguem de zonas-não ripárias pela topografia, regimes hidrológicos, tipos de solo e comunidades de plantas e animais. Em florestas primárias na Amazônia central existem assembleias de aves diferenciadas entre as zonas riparias e não ripárias. No entanto, efeitos negativos como os produzidos por perturbações antrópicas interferem diretamente sobre a riqueza e abundância de aves em florestas, principalmente através de mudanças em alguns componentes da vegetação, afetando a disponibilidade de recursos alimentares e as condições microclimáticas. Um padrão frequentemente observado em zonas com influência urbana é a homogenização das comunidades resultando em uma comunidade composta por espécies principalmente generalistas após a extinção das espécies especialistas. Assim, é importante conhecer se em uma floresta com forte influência da urbanização as assembleias de espécies de aves respondem à variação ambiental gerada pela proximidade de igarapés como observado em florestas não-perturbadas e se o efeito de borda gerado pelo processo de urbanização afeta negativamente a distribuição dessas aves localmente. Este estudo foi realizado em uma floresta urbana de aproximadamente 600 hectares na cidade de Manaus (AM) na qual se encontra o campus da Universidade Federal do Amazonas - UFAM. A floresta que compreende o campus universitário é circundada por bairros residenciais, avenidas e áreas urbanas de diferentes usos. Para caracterizar a avifauna de sub-bosque nas zonas ripárias e não-ripárias utilizamos a técnica de captura-recaptura com o uso de redes de neblina. Selecionamos 20 sítios de amostragem, sendo 10 sítios ripários e 10 sítios não ripários. Em cada sítio utilizamos uma linha de rede (120m) ativadas durante dois dias consecutivos das 06:30h às 11:30h no período de julho a novembro de 2013. Identificamos, medimos, pesamos e anilhamos todas as aves capturadas, exceto beija-flores. No total, capturamos 27 espécies de 12 famílias com um total de 118 indivíduos dos quais 9,3% foram recapturas. A abundância foi similar nos sítios ripários e não ripários (T = -0.17, df = 9, p = 0,86) assim como riqueza também não variou entre sítios ripários e não ripários (T = -0.2641, df = 9, p = 0,79). Também verificamos que a composição quantitativa da assembleia de aves não se diferenciou nas zonas ripárias e não ripárias. Contudo, quando incluímos o efeito da distância à borda nos modelos os resultados mostrarem um padrão diferente. O melhor modelo para explicar a variação da biomassa de aves, foi aquele que considerou uma interação entre o efeito da distância à borda como o efeito do ambiente (ripário ou não ripário) (AICw = 0,716). Assim, de acordo com este modelo observamos uma relação positiva entre a biomassa de aves e a distância à borda nas áreas ripárias sendo que o padrão inverso foi observado para as áreas não riparias. Com relação a similaridade entre as áreas ripárias e não ripárias, observamos um padrão de aumento da similaridade entre pares de sítios ripários e não ripários com a diminuição da distância a borda, ou seja, aqueles pares de sítios que estão mais próximos a borda são mais similares entre si do que os sítios que estão no interior da floresta. Concluímos que o efeito de borda gerado pela influencia negativa da matriz urbana para o interior da floresta é o fator determinante no aumento da similaridade entre as zonas ripárias e não ripárias, acarretando assim ao processo de homogenização de comunidades.

Progressive scholars have found in community-engaged research and participatory methodologies a synergistic approach for pursuing transformative co-production of knowledge to understand the complexity of critical social and environmental issues. According to Jasanooff (2004), the co-production of knowledge is "the simultaneous process through which modern societies form their epistemic and normative understandings of the world." This dissertation project has sought the co-production of geographic knowledge in socio-environmental research on stream restoration, co-produced between academics and community activists in Medellin, Colombia. Specifically, the intent of the research has been to examine the latent power of affect and feeling to promote the ecological care of streams and their surrounding basins, and to understand the possibilities of mapping the desires that local ecological actors have for stream restoration. Papers one and two also made key contributions to understanding how environmental and social actors surrounding La Honda stream are or could contribute to a scenario of the stream basin’s ecological care. In paper three I detailed my work on the ElAtlas initiative. There I documented the rich historical process we went through to build ElAtlas. I described how the initiative involved the convergence of different participatory approaches in GIS, such as Public Participatory GIS (PPGIS), and Volunteered Geographic Information (VGI), and richly detailed the three different stages of the initiative. / Geography

Methane (CH4) tree stem-atmosphere flux is viewed as a new frontier in the global carbon cycle and may be of great importance. The effect on flux from different tree species, forest ecosystems and seasons is still uncertain. This study aims to investigate how CH4 flux from stems of spruces and birches in a boreal riparian zone in northern Sweden was affected during the spring flood. Spatial and temporal patterns were examined in combination with tree species differences. A closed stem chamber system was applied to estimate CH4 flux from 28 trees during pre-snowmelt and snowmelt conditions. A three-way ANOVA analysis and Tukey´s HSD test was applied to test for main effects and interaction effects from “Field day”, “Distance to the stream” and “Species”. The study revealed that i) there was a significant increase in stem flux over the course of the spring flood while not unequivocal, ii) spruces and birches displayed no significant difference in flux, iii) the distance to the stream had no undisputable significant effect on stem flux. However, a trend in flux variation was observed with distance to the stream. No significant interaction effects were detected. Cumulative seasonal environmental changes or natural variability might explain temporal patterns. Spatial patterns may be connected to hot spots close to the stream. Results for species and interaction effects might facilitate estimations of fluxes in forested ecosystems. Methane flux rates are affected over the course of the spring flood, but further studies are needed to determine the cause for it.

Streams and rivers are a vital part of our ecosystem. They are imperiled by human ecological activities such as urbanization, industrialization, and agriculture which discharge excess nitrate and other pollutants into our waterways. Here, this dissertation seeks to understand the physical and biogeochemical processes which attenuate pollutants in stream corridors. The focus is hyporheic zones which form the interface between surface water and groundwater below and adjacent to stream channels, and riparian zones which form the interface between channels and adjacent uplands, both of which can attenuate pollutants. In this context, soil-pipes can dominate subsurface hydraulics. This research first employed MODFLOW and MT3D-USGS to model transient hyporheic hydraulics and nitrate transport in a length of riparian/riverbank soil to probe the effects of soil pipes on hydraulics and denitrification due to peak flow events in the channel. Findings showed that inserting just one soil pipe 1.5 m in length caused a ~75% increase in both hyporheic exchange and denitrification. A rough upscaling showed soil pipes could remove up to ~3% of nitrate along a 1-km reach. Next, the ability of soil pipes to bypass the often championed ability of riparian buffers to remove nitrate migrating from uplands to the channel was evaluated. This effort also employed MODFLOW and MT3D-USGS to simulated hydraulics and nitrate removal along a length of riparian soil. Findings showed that soil pipes increased flow of nitrate to the banks by five orders of magnitude in some cases. We posited a non-dimension parameter which governs when nitrate bypass is significant. In addition to soil pipes, dune bedforms can also enhance hyporheic exchange, primarily in the stream/riverbed. Again employing MODFLOW but now pairing with the transport code SEAM3D to simulate microbially-mediated aerobic metabolism of dissolved organic carbon and dissolved oxygen, the combined effects of dune translation and microbial growth and death were explored. Major findings include that neglecting microbial growth can lead to inaccurate modeling of biogeochemistry, and that aerobic metabolism increased with celerity. The results herein bolster knowledge of natural pollutant attenuation in stream and river corridors, and have implications for pollutant mitigation strategy and stream credit allocation. / Doctor of Philosophy / Streams are a vital part of our ecosystem. They are imperiled by human ecological activities such as urbanization, industrialization, and agriculture which discharge nitrate and other pollutants into our waterways. Here, this dissertation seeks to understand the physical and biological processes which attenuate pollutants. The hyporheic zone is the interface between surface water and groundwater below the bed and adjacent to stream banks, and can attenuate pollutants. Transient peak flow events such as a storm or snow melt raise the stream water levels, causing the water pressure in the stream channel to temporarily outweigh the water pressure in the soil pore spaces adjacent to the stream channel. This drives water into the banks subjecting it to pollutant attenuation processes. Soil pipes (long cylindrical void spaces created by decayed plant roots) are prevalent along stream banks, and they dominate subsurface hydraulics. This dissertation implemented a numerical study on a chunk of riparian soil to probe the effects of soil pipes on hydraulics and denitrification. Findings showed that inserting just one – 1.5 m soil pipe caused a ~75% increase in both water flow volume into the bank and nitrate removal. Riparian buffers are the vegetated strips adjacent to stream channels and have long been championed as stalwarts of pollutant removal. Soil pipes undermine this by acting as a bypass mechanism. A numerical study was again performed on a chunk of riparian soil to quantify the effects soil pipes on riparian bypass of nitrate. Findings showed that soil pipes increased flow of nitrate to the banks by five orders of magnitude in some cases. This means that a buffer enhancement strip with fine roots that prevent the formation of soil pipes should be installed along riparian buffers. In addition to soil pipes, dune bedforms can increase flowrate of water into the hyporheic zone. This dissertation modeled the combined effects of dune translation and microbial growth and death. Major findings include that neglecting microbial growth can lead to inaccurate modeling of biogeochemistry, and that biodegradation increases with increased dune velocity. The results herein bolster knowledge on natural pollutant attenuation in streams, and have implications in terms of pollutant mitigation strategy and stream credit allocation.

Riparian zones are increasingly being adopted as best management practices (BMPs) to control nonpoint source pollution. The effectiveness of these zones in mitigating pollution is a function of the distribution, nature, and rate of water and sediment movement through these zones. The intent of this research was to investigate the influence of site conditions on the hydrologic and sediment transport response of riparian zones/hillslopes. Research investigations were focused in two major areas: field investigations of riparian hillslopes and development of a riparian hillslope model. The objective of the field investigations was to characterize and quantify geomorphic features of riparian slopes that can be used to quantify flow concentration on hillslopes. The riparian hillslope model was used to investigate the dynamics of hydrologic and sediment transport processes. Field investigations revealed that riparian hillslopes were dissected into distinct convergent, divergent, or straight slope segments. In profile, these segments were either concave, straight, or convex. It was hypothesized that the size of such segments reflects the "representative hillslope scale". Probability distributions of catchment area showed that catchment area decreases with slope gradient. Distributions of catchment shape revealed that catchment shape elongates with increasing gradient. Distributions of drainage channel cross-sectional shape data showed a decreasing trend in width to depth ratio with increasing slope gradient. These results indicate that geomorphic features characterizing flow concentration vary with slope gradient and should not be neglected when simulating riparian hillslopes. Model simulations revealed that site conditions such as slope gradient, slope shape, flow concentration, and soil horizon thickness and characteristics play a significant role in shaping the hydrologic and sediment phenomena on these hillslopes. These results underscore the need for evaluation of riparian zones considering specific site conditions. Interflow was the dominant hillslope runoff mechanism. A large fraction of the interflow occurred via macropores. Macropore flow was orders of magnitude quicker than soil matrix flow. Overland flow was found to occur primarily due to saturation excess or return flow. Simulations showed that thinning of soil layers and/or concave-convergent slope shapes provide favorable conditions for generation of saturation excess or return flow. Sediment delivery down the slope increased with increasing flow concentration. / Ph. D.