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Hydrological pathways and episodic stream acidification were investigated by monitoring water quality in the Coalbum catchment during the later stage of canopy closure. Coalburn is a long-running experimental site, almost completely covered by a commercial coniferous plantation (part of the Kielder Forest in northern England). Regular sampling, event sampling and continuous monitoring were used to establish an extensive water quality data-base between 1993 and 1997. Cloud mist and precipitation at Coalburn are slightly acidic and the catchment can receive moderate levels of dry and wet acid deposition when the winds have tracked from an easterly direction. Coalburn streamwater chemistry displays well-buffered base-flows and acid episodes during high flows. Duration-frequency-magnitude analysis of the Coalburn acid episodes reveals they were less frequent than expected but had a longer duration. The acid events exceeded environment quality standards for freshwaters: pH and aluminium concentrations suggest a toxic impact on freshwater biota. However, the elevated calcium concentrations and presence of humic substances reduce the biological impact. The chemical signatures and variations in solutes were identified and used to postulate the causal mechanisms of the hydrochemical response and to produce the conceptual Coalburn runoff model. Mixing modelling was then applied to introduce a robust analysis into the process and produce the simplified Coalburn Model of acidification. Broadly, the Coalburn hydrochemical response can be explained by pre-event water sources and 'normal' catchment processes. However, during extreme events catchment conditioning and event-water can also influence the response. In improving knowledge of the likely water quality effects of coniferous plantation afforestation, the Coalburn study has contributed to calibrating the temporal and spatial variability of headwater acidification (and hence risks). This allows policy makers and environment managers to make informed decisions about land use/management and to apply the precautionary principle; the research findings were used to suggest a basic policy framework and protocols for catchment assessments to manage acidification issues through the cropping cycle within a headwater catchment.

El comportament hidrodinàmic de les aigües subterrànies en conques intramuntanyoses ve condicionat principalment per la geologia, i especialment pel context estructural i els materials sedimentaris que reomplen la conca. L'estudi d'aquestes àrees requereix un enfocament a gran escala per poder determinar les zones de recàrrega i descàrrega dels diferents sistemes de flux que conformen els recursos hídrics de la zona. Aquestes zones solen estar afectades per un fort desenvolupament humà que pot donar lloc a una modificació de la quantitat i la qualitat de l'aigua subterrània de diferents formes. En aquest sentit, en conques intramuntanyoses és un aspecte clau entendre la importància de la geologia i de les pressions humanes en el flux d'aigua subterrània per arribar a assolir una gestió correcta dels recursos hídrics, així com per assegurar llur disponibilitat a llarg termini. En aquesta tesi s'ha estudiat la depressió de la Selva com a un cas paradigmàtic on té lloc una important pressió sobre els recursos hídrics subterranis. Per tal d'estudiar el paper hidrogeològic que juguen les falles regionals en conques intramuntanyoses, en primer lloc, s'ha realitzat un model hidrogeològic conceptual a partir de la modelització del flux subterrani. Per fer&#8208;ho, s'ha dut a terme una simulació d'una zona de falla subjacent a una formació al&#8729;luvial, on la falla pot recarregar o drenar l'aqüífer al&#8729;luvial. S'han considerat diferents valors de permeabilitat per la zona muntanyosa, la zona de falla i els materials sedimentaris, així com diferents gruixos de falla i condicions de contorn. Els resultats mostren que es poden produir fluxos verticals ascendents i descendents a la part superior de la zona de falla degut a l'acció de la formació al&#8729;luvial, i fins i tot a través del sòcol, influenciant per tant la recàrrega dels materials sedimentaris de la depressió. En segon lloc, s'ha caracteritzat el sistema hidrogeològic de la depressió de la Selva mitjançant mesures del nivell piezomètric i dades hidroquímiques e isotòpiques (&#948;18O, &#948;D) al llarg de diverses campanyes de camp amb un doble objectiu: (i) caracteritzar un sistema hidrodinàmic on els elements tectònics juguen un paper important en la hidrodinàmica subterrània, i (ii) descriure la influència de l'explotació d'aigües subterrànies en la hidrodinàmica del sistema. Els resultats piezomètrics han posat de manifest la relació existent entre les formacions situades a les zones de muntanya que envolten la depressió i els materials sedimentaris que rebleixen aquesta. Les zones de falla tenen un efecte directe en la recarrega, permetent l'existència de fluxos verticals ascendents des del sòcol cap a diferents aqüífers sedimentaris. Les dades hidroquímiques i isotòpiques han validat aquestes observacions. En aquest sentit l'ió fluor (< 15 mg/l) i nitrat (< 217 mg/l) han estat usats com a traçadors dels fluxos profunds i superficials respectivament i han permès posar de manifest l'efecte dels bombejos en la distribució de les línies de flux. La composició isotòpica de la molècula de l'aigua (&#61540;18OH2O, &#61540;D) ha evidenciat canvis estacionals en les aigües captades pels pous posant de manifest l'existència de dos sistemes de flux: un sistema de flux regional amb llargs temps de trànsit i originat a les zones circumdants més elevades, i un sistema de flux local recarregat a la zona de la depressió. Els dos sistemes contribueixen de manera diferent als recursos hídrics que s'estan explotant, i la seva aportació específica defineix el potencial de la depressió per una explotació sostenible a llarg termini. S'han caracteritzat les aigües des d'un punt de vista hidroquímic a partir de la composició en elements majoritaris, minoritats i traça (fluor, brom, liti, TOC) i de dades isotòpiques (&#61540;18OH2O, &#61540;D, triti, &#61540;34SSO4, &#61540;18OSO4). Aquesta caracterització ha permès una descripció acurada dels processos geoquímics que defineixen les fàcies hidroquímiques de l'aigua subterrània al llarg de la depressió de la Selva. Així, s'han definit dos sistemes de flux regional i diferents qualitats de l'aigua associada a la recarrega local, i alhora s'ha corroborat el model hidrogeològic conceptual de la depressió de la Selva. Des d'un punt de vista regional, a la depressió de la Selva el control estructural defineix sistemes de flux locals, intermitjos i regionals, els quals son responsables de la hidrodinàmica a gran escala, fins al punt que aquests son responsables de la recuperació dels descensos del nivell piezomètric després del període de màxima extracció (estiu). A la zona d'estudi, l'origen de la recarrega, a escala regional, és atribuïda a la serralada Transversal, a la zona més septentrional de la conca, i a les Guilleries, especialment a la zona oest. Aquests sistemes hidrogeològics impliquen un flux vertical ascendent des del sòcol que recarrega els nivells aqüífers neògens de la depressió. Els sistemes de flux locals i intermitjos s'originen a la pròpia depressió o a les zones circumdants més properes, els quals estan menys afectats per les zones de falla. La pressió antròpica crea una barreja entre els diferents sistemes de flux modificant la qualitat de l'aigua al llarg de l'any. Els resultats d'aquest estudi mostren que en conques intramuntanyoses per obtenir una caracterització integrada del sistema hidrogeològic i el coneixement necessari per formular estratègies específiques cap a una gestió sostenible dels recursos hídrics, i en concret a la depressió de la Selva, és necessari: i) la utilització de diferents metodologies per abordar l'estudi d'aquests tipus de sistemes hidrogeològics. Així, en el present treball primerament s'aborda des de la caracterització de camp fins a la modelització numèrica passant per l'estudi de nivell piezomètrics i dades hidroquímiques e isotòpiques; ii) caracteritzar l'evolució piezomètrica de les diferents formacions geològiques juntament amb les característiques hidroquímiques/isotòpiques i els processos geoquímics relacionats que defineixen les mostres d'aigua, i per tant, cada un dels extrems de barreja de la recarrega (local, intermitja i regional) que participen en el conjunt del sistema de flux; iii) finalment, identificar les pressions humanes, fins i tot en els sistemes a més gran escala, com una verdadera alteració al comportament natural. Aquesta tesi defineix els sistema hidrogeològic de la depressió de la Selva com a exemple de funcionament hidrodinàmic sota pressions antròpiques aplicable a altres conques intramuntanyoses. Aquest coneixement és necessari per formular estratègies de gestió dels recursos hídrics des d'un punt de vista quantitatiu i qualitatiu, com a eina indispensable per satisfer la demanda lligada a una millora socioeconòmica sense produir un empitjorament de la qualitat ambiental a llarg termini. / Groundwater hydrodynamics in range&#8208;and&#8208;basin areas are essentially determined by their geology, including the tectonic structure and the basin sedimentary infilling. Their study requires a large&#8208;scale approach to determining the location of the recharge and discharge areas of each flow system providing the basin with water resources. Furthermore, most of these areas have undergone heavy human development that can modify groundwater quantity and/or quality in different ways. Understanding geological and human influences on groundwater flow in these areas is a key aspect in achieving an adequate water resources management and therefore its future availability. In this dissertation, the Selva Basin has been studied as a paradigmatic case of a range&#8208;and¬basin area with severe human pressure on its groundwater resources.A conceptual hydrogeological model emphasizing the role of the main fault zones has been developed and tested using numerical flow modeling as a first step. Groundwater flow has been simulated in a range&#8208;and&#8208;basin area affected by a significant fault zone, which may drain or recharge an overlying alluvial aquifer. Various hydraulic conductivity values for the range rocks, the fault¬zone, and the sedimentary infilling of the basin are considered, as well as different fault&#8208;zone widths and boundary conditions. The results show that upward and downward fluxes develop in the upper part of the fault zone controlled by the action of the alluvial aquifer, and even through the basement floor, which influence the recharge of the sedimentary infilling of the basin.Second, the Selva range&#8208;and&#8208;basin hydrogeological system is described using potentiometric, hydrochemical, and isotopic data (&#948;18O, &#948;D) taken from different field surveys, in order to achieve a twofold objective: (i) to describe a hydrogeological system in which tectonic elements play a significant role in the flow dynamics, and (ii) to show the influence of groundwater exploitation on the hydrodynamics of the system. Hydraulic head data indicate the relationships between the geological formations in the range areas and the sedimentary infill of the basin. In this context, fault zones and a fracture network have a direct effect on the recharge, and allow an upward vertical flow from the basement to the sedimentary aquifers. Hydrochemical and isotopic data support this observation. The use of fluoride (up to 15 mg/l) and nitrate (up to 217 mg/l) as tracers for the contribution of deep and shallow flow systems respectively provides a detailed portrait of the effects of pumping on the flowpath distribution. Isotopic data depict seasonal trends in groundwater captured by wells. Two distinct flow systems are differentiated: a regional, large&#8208;scale, long residence time system, originating in the surrounding ranges, and a local flow system constituted by infiltration in the lower areas of the basin. The two systems contribute differently to the resources that are withdrawn, and their specific contributions define the potential for sustainable future water exploitation in the basin. The final part of this hydrogeological study is a more specific description of the geochemical processes that determine the hydrochemical characteristics of groundwater across the Selva basin, based on the interpretation of major, minor and trace elements (such as fluoride, bromide, lithium, TOC, and their ratios to some major elements), and isotope data (&#61540;18OH2O, &#61540;D, tritium,&#61472;&#61540;34SSO4,&#61472;&#61540;18OSO4). It defines two different regional flow systems and different water qualities of local recharge anduses this specific data to corroborates the overall hydrogeologic conceptual model for the Selva range&#8208;and&#8208;basin area. From a methodological perspective, this chapter explores the use of minor elements and isotopes in the interpretation of regional scale system hydrodynamics. It also discusses their use as tracers of the distinct ground water flows originating in distinct recharge areas and influenced by an intricate tectonic setting. The results of this dissertation describe the flow system of the Selva basin. In this basin, structural control defines the local, intermediate and regional flow systems responsible for the large&#8208;scale hydrodynamics of the basin and, more importantly, the recovery of drawdown after the main withdrawal period (summer). The origin of the recharge of the large&#8208;scale, regional flow systems is assigned to the Transversal range on the northern side and to the Guilleries range, especially in the western part. These hydrogeological systems include a groundwater flow within the basement and an upward vertical recharge from the basement to the overlying Neogene sedimentary layers. The local and intermediate flow systems originate in the basin itself or in the less&#8208;elevated surrounding ranges, and the fault system has a minor effect on their flowpaths. Human development modifies the flow paths mixing the different flow systems and changing the water quality along the year seasons. From a broader point of view, this highlights the value of using different methodological insights in the study of these hydrogeological systems, as well as addressing the problem of water management in complex geological environments. First, it presents the outcome of various methodologies ranging from field work to numerical modeling, together with the analysis of hydraulic head, hydrochemical and isotopical data. Second, it shows the relevance of potentiometric evolution in different geological settings, and the treatment of the hydrochemical/isotopic features and related geochemical processes that define groundwater samples and therefore each of the recharge end&#8208;members (local, intermediate, and regional) that participate in the overall flow systems. Finally, it identifies the effect of human pressures even on large&#8208;scale flow systems, as true alterations of natural behavior. The recognition of these effects, together with an integrated characterization of the hydrogeological system, provides the necessary knowledge for formulating specific strategies for assessment focusing on sustainability of water resources management in these geological contexts. In specific terms, these strategies must be based on the importance of the groundwater flow terms in the water balance for a given hydrological basin. These terms are usually overlooked, yet they play an important role, especially when groundwater resources from deep confined (or leaky) aquifers are exploited. In the case of the Selva basin, identifying this contribution is fundamental in establishing potential future exploitation rates that further socio&#8208;economic developments may generate. This dissertation shows the scope of several approaches to describing this term in the water budget in range&#8208;and&#8208;basin areas in order to determine the availability of water resources therein, as a first essential step towards sustainability.

ROCHA, Ludmila Prazeres das Flores Oliveira. Hidroquímica do aquífero costeiro do município de Itarema - Ceará. 2015. 311 f. Tese (doutorado em geologia)- Universidade Federal do Ceará, Fortaleza-CE, 2015. / Submitted by Elineudson Ribeiro (elineudsonr@gmail.com) on 2016-04-01T17:59:56Z No. of bitstreams: 1 2016_tese_lpforocha.pdf: 13564785 bytes, checksum: 22302de9b6f887e706d22e73e6de3766 (MD5) / Approved for entry into archive by José Jairo Viana de Sousa (jairo@ufc.br) on 2016-05-19T20:44:47Z (GMT) No. of bitstreams: 1 2016_tese_lpforocha.pdf: 13564785 bytes, checksum: 22302de9b6f887e706d22e73e6de3766 (MD5) / Approved for entry into archive by José Jairo Viana de Sousa (jairo@ufc.br) on 2016-05-19T20:48:30Z (GMT) No. of bitstreams: 1 2016_tese_lpforocha.pdf: 13564785 bytes, checksum: 22302de9b6f887e706d22e73e6de3766 (MD5) / Made available in DSpace on 2016-05-19T20:48:30Z (GMT). No. of bitstreams: 1 2016_tese_lpforocha.pdf: 13564785 bytes, checksum: 22302de9b6f887e706d22e73e6de3766 (MD5) Previous issue date: 2015 / The study area covers the coastal area of the county of Itarema, 230 km from Fortaleza, West coast of the State of Ceará. In this area, rare are the works aimed at the study of both surface water and groundwater. Although the exploitation of groundwater tends to increase in the area, due to the increase in population density, bringing with it potential risks of water contamination. Therefore it is important to assess the quality of the water and recharge mechanisms for the preservation and rational use of these resources. We collected samples of surface water and groundwater and carried out measurements of physical, chemical and bacteriological variables for all nine (9) sampling campaigns, using titrimetry, spectrophotometric, potenciometric and atomic absorption spectrometry methods. Groundwater is predominantly fresh water. And surface waters, according to the IQA-CETESB classification are good for public supply. Nitrate contamination in groundwaters, even at low concentrations, shows anthropic actions, not featuring seasonal effect. The study of trace elements sometimes presented some elements with higher levels than the VMP estipulated expected in the current legislation. However, these are not related to possible contamination by agrochemicals, according to the results of the analyses for quantification and qualification of organophosphates. Such results can be associated with the construction of the wells, their depth, waste deposition of various materials and even rock formations in the area. With respect to the study of isotopes, prevail lighter waters during the rainy periods than those collected during periods of drought, which characterizes the amount effect in rainfall. Through the water balance was estimated that, on average, about 31% of the total annual precipitation recharge the aquifers. Finally, the study of vulnerability to contamination of the aquifer, through the DRASTIC method, showed that in 79% of the area prevail moderate and high vulnerability. This requires great care with the use and occupation of the soil, in order to prevent damage to groundwater resources. / A área do estudo compreende a Zona Costeira do município de Itarema, distante 230 km de Fortaleza, Litoral Oeste do Estado do Ceará. Nesta área são raros os trabalhos que visam o estudo tanto das águas superficiais quanto subterrâneas. A explotação da água subterrânea tende a aumentar na área, devido ao aumento na densidade demográfica, trazendo com isso riscos potenciais de contaminação da água. Nesse sentido torna-se importante avaliar a qualidade da água e os mecanismos de recarga para a preservação e uso racional dessa. Foram coletadas amostras de águas superficiais e subterrâneas e realizadas medidas de variáveis físicas, químicas e bacteriológicas durante nove (9) campanhas de amostragem, empregando métodos titulométricos, espectrofotométricos e potenciométricos. As águas subterrâneas apresentam-se predominantemente como doce. E as águas superficiais, segundo classificação IQA-CETESB, encontram-se boas para abastecimento público. A contaminação por nitrato em águas subterrâneas, mesmo em baixas concentrações, evidencia ações antrópicas pontuais, não caracterizando efeito sazonal. O estudo dos elementos traço ora apresentou teores de alguns elementos mais elevados que os VMP previstos em legislação vigente, ora não. No entanto, estes não estão relacionados à possível contaminação por agrotóxicos, segundo os resultados das análises para quantificação e qualificação de organofosforados. Tais resultados podem estar associados ao tipo de construção dos poços, à profundidade destes, aos descartes de materiais diversos e até mesmo formação rochosa da área. Com relação ao estudo dos isótopos, prevalecem águas leves durante os períodos chuvosos às coletadas nos períodos de estiagem, o que caracteriza efeito quantidade de chuva. A recarga do aquífero (Ie) na área, foi estimada em 368,73 mm, representando 31% da PPT. E por fim, o estudo de vulnerabilidade à contaminação do aquífero através da aplicação do método DRASTIC apresentou que em 79% da área, predomina vulnerabilidade moderada e alta. Isso exige maiores cuidados com o uso e ocupação do solo, de forma a evitar danos aos mananciais subterrâneos.

Peatlands comprise of approximately half of the Athabasca oil sands region, many of which overlay some of the world’s largest bitumen deposits where surface mining for this resource has permanently altered the landscape. By law, companies must reclaim disturbed landscapes into functioning ecosystems including integrated upland-wetland systems with the objective of forming sustainable peat-forming wetlands. This thesis presents six years (2013 – 2018) of water balance and associated salinity data from one of the two existing constructed upland-wetland systems, the Sandhill Fen Watershed (SFW), a 52-ha upland-wetland built on soft tailings to evaluate the hydrological and hydrochemical performance and its potential to be self-sustaining. Following a considerable decrease in hydrological management, the dominant water balance components changed from primarily horizontal (inflow and outflow) to vertical fluxes (precipitation and evapotranspiration) which increased inundation, encouraged salt accumulation and changed plant communities. Results suggest that current conditions are not favourable for fen-peatland development as marsh-like conditions have developed, limiting water conserving functions and the ability to persist long-term in a changing climate. In terms of winter processes, topography currently controls snow accumulation, redistribution and melt at SFW while the role of vegetation in these processes is expected to increase as it continues to develop. Runoff ratios of snowmelt from hillslopes were drastically different than those previously reported for reclaimed peatland watersheds highlighting the influence of different soil materials used during construction. Under various climate change scenarios of a warmer and wetter climate, results from the Cold Regions Hydrological Model indicate that the influence of winter processes will decrease, potentially putting reclaimed systems at greater risk of moisture stress. Substantial hydrochemical changes have occurred as salinity was relatively low at the study onset as high volumes of inflow and outflow prevented ion accumulation. Over time, salinity continued to increase year-over-year throughout SFW from 2013 to 2018 in the wetland and margin areas. This increase in site-wide salinity was attributed to the shift in dominant water balance fluxes, changes in water table position and increased mixing of SFW waters with deeper saline groundwater that underlies the system. Based on its current conditions, it is unlikely that SFW will support peat-forming vegetation. It is recommended that design strategies shift to incorporate characteristics found in undisturbed saline peatlands that are capable of supporting peat-forming vegetation in a saline environment. / Thesis / Doctor of Philosophy (PhD) / A better understanding of the hydrological functioning of reconstructed peatlands in the Athabasca oil sands region is required as it is a novel approach in this region and there is potential for thousands of hectares of land that will require this reclamation in the future. Due to their recent establishment potential trajectories of constructed peatlands have yet to be fully analyzed as only recently has sufficient data been collected to evaluate the hydrological and hydrochemical functioning and provide insight on its overall success. While design strategies may seem sound, these constructed systems are completely human-made and it is unclear how they will develop and function in a highly disturbed landscape. Thesis results suggest that current conditions are not favourable to sustain a peatland as marsh-like conditions have developed which will limit its ability to persist long-term in a dry and changing climate. It is recommended that design strategies shift to incorporate characteristics found in undisturbed saline peatlands that are capable of supporting peat-forming vegetation in a saline environment. Due to the many challenges associated with reclamation in this region, lessons learned from this pilot project will help guide future peatland construction.

The Mt. Tom Price Mine, located in the Pilbara region of Western Australia, has been the site of major iron ore mining since the 1960s by Rio Tinto Iron Ore/Pilbara Iron. The thesis project area covers approximately 121 km², covering the Mt. Tom Price Mining area and the surrounding catchment boundary. The climate in the Pilbara region is arid, with rainfall driven by seasonal cyclonic events, producing 300 mm/year net rainfall on average. The geology of the Mt. Tom Price area consists of a series of banded iron formations (BIF) and shales that are generally low in hydraulic conductivity values. Iron ore in the region is produced through the process of supergene enrichment whereby gangue minerals are dissolved and replaced with haematite and goethite. Mining is focused in a series of open cast pits including, North Deposit, West Pits, Centre Pits, Southern Ridge, South East Prongs, Section Six, Section Seven, and the proposed Marra Mamba Pits. Due to the impermeable nature and complex geology of the BIF sequence, groundwater flow is dominated by bedrock aquifer flow, with compartmentalization occurring in several areas of the mine. Highly faulted and folded units can also have increased hydraulic conductivity values. Pit floor lowering began to encounter the regional water table in early 1994. A series of dewatering bores and depressurization measurements have been utilized to ensure dry mining practice. This data was used to help understand regional groundwater flow and create the Mt. Tom Price Groundwater Model (MTPGM). A 3D geological model of the project area was created to aid visualisation of semi-regional hydrogeology. From this model, accurate template files were created so that geological detail loss is kept to a minimal when entering hydrogeological parameters into the MTPGM. The MTPGM was setup using PMWIN Pro, a graphical user interface for use with MODFLOW. Stresses such as recharge and pumping were entered via software packages within MODFLOW. The model was run to simulate measured 1994-2007 responses to dewatering and high rainfall events. A Parameter Estimation (PEST) software package and trial and error calibration was used to lower stress response variances that were observed in the model output files. This was achieved by the adjustment of hydrogeological parameters such as hydraulic conductivity and specific yield values. A prediction simulation of final pit lake recovery was created Using the calibrated MTPGM. Recovery curves predicted that full recovery of the water table of the pit voids varied from 96 to 120 years, recovering to levels close to the initial heads measured in 1994 before large-scale pumping commenced. The hydrochemistry of the groundwater in the mining area is highly influenced by geological hosts, with clearly defined hydrochemical signatures approximated for each screened geological unit. Due to the sulphur rich, acid- forming Mt. McRae Shale, regular monitoring of pit and groundwater is essential. Final pit lake water quality was estimated using final pit levels and recovery rates approximated from the MTPGM, combined with historical data and previous groundwater quality reports. Pit lake water quality is dominantly driven by evaporation concentration, caused by high evaporation rates and low throughflow. Pit waters are expected to be brine waters (greater than 100,000 mg/L TDS), with high levels of acidity values occurring in the South East Prongs and Section Six pits due to the exposure of the acid forming Mt. McRae Shale above the pit lakes at these localities. Future studies should focus on more detailed modelling of the compartmentalised aquifer systems. This would produce much more accurate final pit lake levels. Further study of the Mt. McRae Shale formation and its implications on acidity should also be undertaken. Seasonal fluctuations in lake levels will affect acidity due to the continual re-exposure and oxidation of the Mt. McRae Shale. This could be studied to help understand short term pit lake quality conditions and help to predict long term acidity conditions in the pit lakes.

Projections of population growth, urban expansion and decreasing water resources in arid and semi-arid regions have increased the importance of urban runoff as a potential renewable water resource that, through enhanced recharge, can augment groundwater supplies. However, it is unclear how urbanization alters hydrologic and hydrochemical responses of small catchments ( < 5 km²) in these regions. This body of work identified controls on the spatial and temporal variability of hydrologic and hydrochemical responses of urbanized catchments in the Tucson Metropolitan area of semi-arid southern Arizona. The temporal distribution and characteristics of rainfall did not control urban catchment hydrology where overall, there was no evidence of significant seasonal catchment wetting. Land use did not control hydrologic responses although runoff was more frequent and of longer duration in urbanized than in non-urban catchments. Runoff depth and runoff ratios were controlled by the combined effect of imperviousness, the characteristics of the stormwater drainage system and rainfall depth. Runoff hydrochemistry did not vary in response to land cover or imperviousness. Rapid increases in solute stores between rainfall-runoff vents resulted in invariant seasonal runoff solute concentrations. Four major factors controlling runoff hydrochemistry were identified: 1) landscape heterogeneity and catchment connectivity, 2) the spatial extent of pervious and biogeochemically active areas, 3) the efficiency of overland flow and runoff routing mobilization and 4) the extent of catchment wetting. The stormwater drainage system, and specifically the characteristics of the stream channel substrate, emerged as significant controls of runoff responses. Conservative transport of biogeochemically active solutes during runoff was observed in piped, concrete and gravel lined waterways, whereas solute sourcing and retention was more dynamic in grass lined reaches. Biogeochemical processing in the stream channel substrate between runoff events indicates that pervious waterways alter soil solute pools available for subsequent solute transport, and that stream channel biogeochemical processes are tightly linked to the characteristics of the channel substrate and cyclical channel wetting and drying. This body of work indicates that successful stormwater management strategies in the semi-arid Southwest should focus on the stormwater drainage network and the presence, density and characteristics of pervious channels.