Mark Johnson
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Biography
Our work in ecohydrology and watershed biogeochemistry includes field-based research involving real-time measurements of water quantity and quality which we complement through GIS-based modeling, laboratory analysis and stakeholder input. The overarching goal is to leverage this research towards the development of more sustainable land-use practices and urban systems.
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Dissertations completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest dissertations.
The full abstract for this thesis is available in the body of the thesis, and will be available when the embargo expires.
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Terrestrial evaporation (also referred to as evapotranspiration) is a central variable controlling water, energy, and carbon cycles. However, our ability to estimate evapotranspiration is hampered by the uncertainties in parameterizations of land surface conditions in currently available models. Although the near-surface atmosphere both drives evapotranspiration and is also changed by evapotranspiration (i.e., land-atmosphere feedback), some evapotranspiration models cannot properly address this feedback process. This thesis addresses this critical knowledge gap by introducing a series of alternative theories that consider land-atmosphere interactions, predict potential evaporation, and estimate actual evapotranspiration. Overall, the goal of this thesis is to provide improved tools for use in hydrology and water resources management along with a detailed analysis derived from the application of these tools over multiple spatial and temporal scales.Chapter 1 provides a general background to the research topic. Chapter 2 introduces a novel physical expression of evapotranspiration that shows how land-atmosphere interactions control evapotranspiration. The proposed physical expression is evaluated using field observations and a global-scale evapotranspiration product. Chapter 3 focuses on climatic controls on evapotranspiration, which is also known as potential evaporation. In this chapter, a scientific debate regarding the trend of the potential evaporation is addressed by extending the land-atmosphere coupling theory introduced in Chapter 2. To this end, field-scale observations, watershed-scale observations, and climate simulations are used to assess model performance and to evaluate trends of potential evaporation. Chapter 4 derives a physically-based evapotranspiration model that requires only readily obtainable meteorological information. This new approach is evaluated using field-scale observations around the globe. Finally, Chapter 5 provides the overall conclusions from the research detailed in the preceding chapters.Overall, this thesis improves the estimation of evapotranspiration by minimizing empirical parameters required for modeling purposes, and by advancing our understanding of how land-atmosphere interactions control terrestrial evapotranspiration. In particular, the results suggest that the near-surface atmosphere should be understood as a reflection of the land surface dryness instead of as an atmospheric demand for soil moisture that is independent of surface conditions. This perspective underlies the models presented in this thesis, and by extension will facilitate more accurate predictions of evapotranspiration.
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Tropical ecosystems are key in regulating global carbon (C), water and energy budgets, and are thus central to the global climate system. However, deforestation and land-use and land-cover change (LULCC) continue to rapidly expand in these areas, negatively affecting the ecosystem services they provide. Understanding how C and water fluxes and their main drivers and controlling mechanisms vary depending on biome and land-use change is crucial to predict the effect that further changes in land use and climatic conditions could have on these ecosystems (and by extension, the global climate system). Moreover, this information can be used to develop policies for climate change mitigation and land management. However, our understanding of tropical ecosystems is still limited, mainly because fluxes and their controls can vary greatly due to multiple, interacting factors, and the lack of ground observations. This thesis investigates the effects of LULCC on C and water fluxes using a network of eddy covariance towers located across the state of Mato Grosso, Brazil, including flux towers in natural and managed sites within Amazon forest, Cerrado savanna and Pantanal wetland biomes. Data from the tower network showed that water limitations caused a reduction in carbon and water fluxes during the dry season, particularly in managed sites. Fluxes at natural sites had a strong correlation to a mix of biotic (leaf area index) and environmental drivers (radiation, temperature, soil water content), whereas fluxes were tightly correlated to crop cycles at managed sites. LULCC changed the seasonality of both carbon and water fluxes, which could eventually increase precipitation variability in the region. Increasing the intensity of management (i.e., using irrigation and incorporating cover crops into crop rotations) increased carbon uptake and evapotranspiration, but climate conditions, the choice of cover crop and the time of planting all affected the magnitude of C and water fluxes. The information in this thesis can be used to parameterize and validate climatic models and remote sensing products to improve current and future predictions of carbon and water fluxes, and also to inform management policies in the region.
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With a changing climate and a growing population, droughts are becoming more frequent in many watersheds across the world, necessitating new approaches to improve water security in communities. Drought is typically caused by a combination of hydrological and social drivers. In this thesis, I apply the emerging framework of socio-hydrology (coupled human-water systems). Specifically, the objective of this thesis is to assess current and future socio- and hydrological dynamics and impacts on surface water and groundwater supplies with the goal of informing drought adaptation and improving water security. I focused hereby on two drought-prone rural watersheds in the seasonally-dry tropics of Costa Rica. Using a community-based approach, I implemented a hydrological monitoring network of streams and groundwater with open-source data loggers, and worked with local communities to assemble societal water use data. I then synthesized the watersheds in a hydrological model and assessed current social (water use) and hydrological vulnerabilities to drought. Results showed that communities dominantly relied on groundwater supplies, and that a temporal mismatch between water availability and needs, high domestic water use, and increasing extraction rates are increasing pressure on groundwater. Results also indicated high streamflows during the wet season, and thus a potential to increase surface water use while streamflows are high. Next, I explored the impacts of the El Niño Southern Oscillation (ENSO), future climate change and water use change on water resources in the study watersheds. During an extreme El Niño, groundwater recharge and streamflow decreased by 60% relative to ENSO Neutral. I also found that future climate change may lead to groundwater storage decline, especially if combined with high population growth. In the seasonally-dry tropics, wet season rainfall is essential for recharging groundwater that serves as primary water supply during long dry seasons. Therefore, I developed a novel ‘groundwater recharge indicator’ as a tool to support water managers to respond adaptively to reduced wet season rainfall and increase socio-hydrological resilience to seasonal drought. Overall, this thesis contributes to the field of socio-hydrology and provides novel approaches to improve water security under drought in the seasonally-dry tropics.
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Since its inception in 2002, the water footprint (WF) has brought new insight into the direct and indirect (or supply chain) uses of water in the production and consumption of goods and services. Today, this emerging field is mainly represented by two distinct communities following distinct WF approaches: the water resources management community which follows guidelines from the WF Network, and the life cycle assessment (LCA) community which focuses on assessing impacts from water use. This thesis seeks to harmonize WF assessments by combining and contrasting methods and objectives from both communities with the overarching goal of informing water decision-making by (1) considering limits to water resources within a river basin (the “Nature” domain), and (2) considering water use in production systems (the “Production” domain). Following this proposed framework to combine WF assessments (Chapter 2), I assess how each approach may address water management for agricultural production in Southern Amazonia (Mato Grosso, Brazil), a region that has dramatically increased its soybean and cattle production through deforestation. In Chapters 3 and 4, I respectively measure and model the WF of cropland and cattle to highlight on-farm water use strategies for agricultural production (the volumetric WF assessment phase). Chapter 5 focuses on the Xingu Basin of Mato Grosso for which I assess water scarcity of current and future agricultural production (the volumetric WF sustainability assessment phase). Finally, in Chapter 6, I integrate existing water use in LCA methods to highlight water use efficiencies through impact assessment (the WF impact assessment phase). Results show different land and water management options for crops and cattle in Southern Amazonia, but also demonstrate that water use for future production could reach sustainable limits, should cropland irrigation and cattle confinement become more widespread. Moreover, the role of water vapour supply to the atmosphere through evapotranspiration is stressed as an important process that could affect future water availability due to the importance of moisture recycling on regional precipitation. This research provides context on the role of land management on water resources, while combining water decisions affecting both production systems and resource limits imposed by the water cycle.
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Arenosols (sandy soils) in the Cerrado region of Mato Grosso, Brazil are increasingly used for maize production. These soils are typically nutrient poor with low soil water retention. Since biochar has been shown to improve both nutrient and water retention, this thesis aimed to evaluate biochar effect on physical and chemical properties of a Cerrado Arenosol using four biomass wastes (cotton husks, swine manure, eucalyptus sawmill residue, and sugarcane filtercake) pyrolyzed at three temperatures (400°, 500°, 600°C). These biomass wastes were chosen based on their prevalence in the state of Mato Grosso and their environmental impact. Three greenhouse experiments were carried out with the following objectives: 1) to assess the effects of biochar feedstock type and temperature of pyrolysis on soil water retention; 2) to examine the effect of different biochars on soil nutrients and maize growth applied to soil at different rates, and 3) to observe how different biochar feedstocks and temperatures of pyrolysis affect DOC and NO₃- leaching from a Cerrado Arenosol. All the biochars showed potential to reduce water drainage in the soil compared to the control (no biochar). At application rates 1-4% w/w, filtercake biochar led to the highest mean biomass compared to the other biochars. Eucalyptus biochar did not contribute much to soil fertility, but filtercake biochar led to high soil nutrient concentrations, e.g. Ca, Fe, Mn. Although swine manure biochar was rich in nutrients, low plant biomass in the cotton and swine manure biochar treatments was likely due to higher pH, salinity, and/or excessive water retention. Lastly, DOC and NO₃- concentrations were low in leachate from soils with filtercake and eucalyptus biochars, and high in leachate from soils with cotton and swine manure biochars. This thesis provides an outlook of the agronomic potential of these biochars. Further analyses, such as their effect on soil biological properties, are required to develop well-rounded biochar-soil management practices for Cerrado Arenosols.
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Water management approaches that are scientifically sound and societally relevant are critical, given the myriad demands and threats posed to this resource and its necessity for environmental and human life. This thesis reflects the inherently complex and multifaceted nature of water management by investigating issues of water quality, as well as societal participation within science outlining the health of water resources, and policy that determines admissible human impacts.First, the technical details of deploying in situ water quality monitoring networks are examined, given challenges of installing sensitive and costly sensors within remote and physically dynamic stream environments. A year of high frequency measurements explicates the necessity of measuring concentrations at adequate time intervals to accurately calculate fluxes of dissolved organic carbon (DOC).Secondly, these spectrophotometric approaches were used to investigate how forest harvest affects in-stream DOC biogeochemistry within a small headwater stream on Vancouver Island, British Columbia. Forest harvest has a large impact on catchment biogeochemistry and hydrology. Harvest increases DOC concentration and flux within the stream. It also alters the chemical composition of DOC, signifying impacts on the catchment scale mechanisms by which DOC is created and transported.Thirdly, the impacts of citizen participation on scientific data outcomes within the burgeoning field of citizen science are detailed. Six critical lessons learned were distilled from a citizen science water quality monitoring program (concerning DOC concentration and characteristics). Scientific data was used alongside qualitative vignettes to explicate the importance of citizen perspectives, contextual knowledge, and motivations for involvement on critical data outcomes.Lastly, the process and outcomes of public participation through consultation in the creation of provincial-level water policy are discussed. The extensive public consultation process undertaken during the modernization of BC’s Water Sustainability Act was used to examine what was expressed during consultation, and how this compared to the contents of the Act. Differences between consultation outcomes and Act contents (especially related to water allocation) bring to bear questions regarding the function of consultation within participatory policy processes, including how consultation was (and should be) used, and the possible influence of elite groups.
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Forest management for carbon sequestration is a valuable tool to combat rising greenhouse gas (GHG) concentrations in the Earth’s atmosphere. This thesis examined the use of biochar, a product of the thermal decomposition of waste organic matter in a reduced oxygen environment (i.e. pyrolysis) that is applied to soil, as an option for increasing carbon sequestration in a Coastal Douglas-fir forest soil in British Columbia when applied with and without urea fertilizer at 200 kg N ha-¹. Biochar produced from Douglas-fir forestry slash materials was used in this study to address this from a systems-based perspective. A soil incubation study showed that biochar application at high rates (10% oven dry soil basis) significantly increased CO₂ and N₂O emissions when applied without fertilizer and at both low (1%) and high rates (10%) decreased CH₄ consumption without fertilization. In terms of carbon dioxide equivalent emissions (CO₂e), it was shown that CO₂ accounted for >98% from all treatments. In a field study, GHG fluxes were measured after application of 5 t ha-¹ of biochar to a Douglas-fir forest soil in the first year followed by urea-N fertilization in the second year. The results showed that 5 t ha-¹ of biochar had little effect on GHG fluxes and their total CO₂e fluxes. Applying biochar prior to fertilizer application following industry-standard practices did not significantly change treatment CO₂e fluxes. It was concluded that low rates of biochar application to this forest soil would improve soil C sequestration with or without fertilization. In the field and laboratory experiments, soil pore water was extracted and analyzed for C and N concentrations and dissolved organic carbon using spectral indices. The results showed that low biochar application rates could be beneficial for both increasing C-sequestration and N-retention. Changes in spectral indices measured in the laboratory suggested that alterations in the dissolved organic matter pool could lead to changes in GHG emissions due to changing substrate supply for microbes as application rates increased. There is a recognized need for further studies prior to large-scale industrial applications; however, as result of this work it is possible to provide recommendations for large-scale pilot studies.
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Commodity prices and rural development in Brazil are driving the rapid conversion of the Cerrado biome, a highly diverse ecosystem with nutrient-poor soils. The expanding agricultural footprint includes sugarcane for bioethanol production, which boasts one of the highest net energy yields of commercial biofuels. However, energetic assessments fail to consider ecosystem costs, including soil degradation and impacts on water quality through the release of organic effluents. This thesis examined the use of charcoal or biochar made of ‘waste’ biomass (filtercake) as a soil amendment to reduce soil carbon (C) loss and water quality impairment. The effect of biochar on the leaching of a liquid waste with high eutrophication potential, vinasse, was also examined. Soil amendment with filtercake biochar improved soil pH, cation exchange capacity (CEC), nutrient availability (P, K, Mg, Ca, Mg, Fe, Mn, and Zn), and water retention. Amendment with filtercake biochar rather than raw filtercake also greatly decreased CO₂ loss to rapid mineralization. Furthermore, biochar amendment decreased the loss of dissolved organic carbon (DOC) from a cultivated Ferralsol, with or without co-application of vinasse, through preferential retention of larger and more complex, humified DOC species. In contrast, biochar did not attenuate nitrate (NO₃-) leaching. Finally, δ¹³C isotope analyses were used to examine the effect of raw vs. pyrolyzed residues on C turnover in an uncultivated soil, which suggested that whereas raw filtercake appeared to be mineralized preferentially over native soil organic carbon (SOC), biochar application appeared to provoke mineralization of native SOC. Overall, this project suggest that filtercake biochar may represent a valuable opportunity to better manage solid and liquid organic agricultural wastes in bioethanol production, with the potential to close nutrient loops and improve soil quality. However, further work is required to better understand the effect of filtercake biochar on soil C turnover and its long-term stability.
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Master's Student Supervision
Theses completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest theses.
As the majority of Canada obtains its drinking water from forested watersheds, forest management to better address the effects of land use changes related to industries such as logging and urban development are of high public interest. To understand impacts on aquatic ecosystems from land use change it is essential to understand how carbon is cycled, transported, and stored throughout the ecosystem. Aquatic ecosystem metabolism (AEM), a key component of carbon cycling, can be evaluated by determining gross primary productivity (GPP) and ecosystem respiration (ER) within the water column of streams, rivers, lakes, and wetlands. AEM controls energy and material flow through aquatic ecosystems therefore linking environmental change and food webs to provide a useful framework for examining ecosystem function and productivity. The objective of this research was to investigate the role of AEM as a control on carbon transport, turnover, and fate in forested ecosystems under varying land use and streamflow conditions. The study was conducted in the University of British Columbia (UBC) Malcolm Knapp Research Forest (MKRF) located approximately 50 km east of Vancouver, BC containing forested and harvested blocks along a single 3.4 km stream reach containing four monitoring stations during late summer to winter 2022. This study examined the seasonal and spatial differences of AEM inputs and found that temporal and spatial disparities can have a significant effect on AEM and gas exchange rates at finer spatial scales. Overall, the stream reach demonstrated R exceeding GPP therefore indicating a negative net ecosystem production (NEP) and a heterotrophic stream reach. This study provides an exploratory investigation into AEM in a headwater stream of the Pacific Northwest.
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The latest global estimates of CO₂ emissions from inland waters are equivalent to half of the annual anthropogenic emissions. However, this estimate categorized large emitting headwater streams in the same classification as lower turbulent rivers. To better understand the role of headwater stream, I monitored the same stream spaced 3.3 km apart (drainage areas of 7.8 and 9.0 km² respectively) in the UBC Malcolm Knapp Research Forest near Maple Ridge, British Columbia. The integrated an upstream-downstream perspective in the dataset can characterize the evolution of dissolved carbon as it moves through the landscape. Through PCA analysis and visualizing data in hydrographs, I identified differing water quality characteristics associated with a range of discharge conditions. Through timeseries analysis, this study identified seasonal trends, with DOC being highest in winter and correlated strongly with storm events. Dissolved CO₂ was highest in early spring to late summer and lowest in the winter. Additionally, I found distinct seasonal patterns of DOC export and pCO₂ evasion and changes in transport patterns that were associated with the transition from dry to wet conditions. During storm events, the CO₂ evasion became larger and DOC concentrations for the sites became more similar with each other. This study showed the complex coupling of DOC and pCO₂ with the surrounding landscape. In particular, periods of high turbulence might not coincide with periods of high pCO₂ supply, meaning that CO₂ evasion can be seen as supply and transport limited at different points in the hydrologic year. This field-centric study provided an annual dataset to a data scarce region and provided an evasion estimate of a turbulent headwater stream draining a carbon rich landscape. Overall, this study helps to quantify dissolved carbon processes from mountainous streams draining high carbon supply landscapes, contributing to future regional estimates.
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Conventional agricultural practices contribute to soil degradation and soil organic carbon (SOC) losses. To address the climate crisis and improve soil quality, increasing the soil carbon pool through alternative agricultural practices is of global interest. Biochar shows promise in positively influencing SOC and soil quality. However, the strength of these benefits varies, especially on dissolved organic carbon (DOC), a labile form of carbon. Additionally, studies examining DOC concentrations past the growing season are limited. The chemical characteristics of the DOC quality are important indicators impacts on soil microbes, soil carbon stabilization and aquatic systems. Understanding biochar’s impact on DOC concentrations, flux and chemical characteristics is crucial for comprehending its role in SOC and carbon sequestration. This thesis examines the effects of biochar and manure-activated biochar amendments applied to experimental plots at Totem Field Plant Science Station on DOC concentrations, characteristics, and flux from August 2022 to March 2023. Results indicate that seasonal DOC concentrations are correlated with soil temperature. The activated biochar increased the average DOC concentrations and flux in the topsoil, while the pristine biochar decreased DOC concentrations in the fall and decreased the flux from the topsoil. Spectral analysis of the soil solution suggested that the biochar likely decreased the DOC concentrations and flux due to its capacity to retain the high-weight humic-like components in the DOM. Notably, treatment effects were predominantly limited to the topsoil, suggesting that the DOC became stabilized in the subsoil, whereas the pristine biochar stabilized DOC levels in the topsoil. This research highlights that biochar effects on DOC are affected by biochar properties as well as soil and climate characteristics. Understanding the effects of these amendments on carbon losses and storage at depth is crucial for decisions on biochar’s role in sustainable soil management practices.
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Dissolved organic matter (DOM) is a key aspect of source water quality in forested headwaters and a subject of concern in drinking water treatment due to its potential for adverse chemical reactions. Forest soils contribute a substantial fraction of DOM entering freshwater systems and can be altered by land use practices such as forest harvest, with implications for water quality downstream. This study investigated the relationship between forest clear-cutting and the biodegradability of soil-derived DOM. The potential for water-extractable soil DOM to be metabolized was measured via in-laboratory incubation and quantified via two methods: loss of dissolved organic carbon (DOC) and changes in fluorescence and absorbance properties. Through comparison of clear-cut stands of differing histories with nearby forested hillslopes, a chronology of the extent of DOM alteration with time elapsed since harvest was established. Biodegradable DOC did not differ significantly between forested and clear-cut sites of any age, though the variability was greater for clear-cuts (forested: 9 ± 1% mean ± standard error; clear-cut: 8 ± 2%). DOM character was different in the most recent clear-cut (harvested in 2017), with a greater fraction of high molecular weight, plant-derived compounds resistant to biodegradation. Incubation did not affect forest and clear-cut DOM differently except for the 2017 sites, where the clear-cut sample showed reduced microbial metabolism and a greater degree of humification. These results may be attributable to the prevalence of woody debris at the more recent clear-cuts, a remnant of the logging process. Overall, DOM character pre- and post-incubation were similar, suggesting soil DOM is relatively refractory and may persist in aquatic systems. The higher fraction of terrestrial, refractory DOM, if sustained downstream, would increase coagulant demand during drinking water treatment, but observable differences in water quality are not projected to last beyond 10 years after harvest in regions similar to the study site.
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Most drinking water in Canada originates in forested headwaters, therefore drinking water security is tied to forest management for many communities. Monitoring source water quality is crucial to a multi-barrier approach to clean drinking water. This research established a stream water sampling program across a second-growth forested drinking water supply area (Greater Victoria, British Columbia, Canada) to evaluate spatiotemporal patterns and variance in natural organic matter (NOM). Over sixteen months (October 2018 to February 2020), 426 stream water samples were collected from twelve sites (ranging from 9.6 to 37 km², elevation 215 to 870 m a.s.l) and analyzed for NOM quality (via UV-Vis absorbance) and quantity (as dissolved organic carbon, DOC). Mean sub-basin DOC concentrations ranged from 4.2 ± 1.8 mg/L⁻¹ to 9.9 ± 3.4 mg/L⁻¹ (DOC range 1.64 - 19.1 mg/L⁻¹). Six of the twelve sites in Leech River watershed (~96 km²) were equipped with vertical passive sampling racks to evaluate rising hydrograph limb NOM dynamics. Hydrologic connectivity to terrestrial source pools increased throughout wet seasons and antecedent wetness was important for stream NOM molecular quality, which shifted from predominantly aliphatic in the dry-season to predominantly aromatic in the wet-season. Sample sub-sets were evaluated for drinking water treatability parameters (n = 8) and total metals contents (n = 42). DOC was correlated with several metals (R² values for Hg: 0.99; Al: 0.81; Fe: 0.72; Cu: 0.47; Ba: 0.25; Mn: 0.21), evidence that aqueous NOM is indeed a master variable important for contaminant transport. More than specific UV absorbance (SUVA₂₅₄) or DOC concentration, the spectral absorbance coefficient at 254 nm (SAC254) was well correlated to disinfection byproduct formation-potential (total trihalomethanes, r = 0.9882; and total haloacetic acids, r = 0.9927). Approximately 80% of the time, DOC concentration peaked with stream stage. Random Forest variable importance measure (RF VIM) identified warm and wet conditions as key drivers for NOM dynamics. RF VIM showed that forest age and harvest history were important predictor variables for NOM aromaticity and molecular size, but that subsurface parent material was a more important driver for NOM quantity and quality.
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Dissolved organic carbon (DOC) is important to ecosystem functioning and of interest to drinking water treatment as it is costly to remove from source water. The effects of land use change (e.g. forest harvest) on DOC are not fully understood. Past studies of the effects of forestry on DOC have found mixed results, and covariate effects complicate mechanistic understanding and may underlie regional differences. DOC is typically highest during storm events, and detailed time-resolved measurements of DOC over longer periods are just becoming feasible with advances in in situ sensors. In this thesis, I investigated DOC concentration and character for headwater streams of contrasting forest harvest history in the UBC Malcolm Knapp Research Forest near Maple Ridge, British Columbia, and discussed implications for water treatment through expert interviews with water treatment engineers at Metro Vancouver. I took a two-pronged approach to the field study by measuring not only temporally detailed DOC concentration at two contrasting sites, but also spatially broad DOC concentration and character at 24 sites for six time points during the same study period. From the temporal analysis, I found base flow DOC concentration to be lower in the clear-cut stream (Clear cut: 2.26 ± 0.43 mg/L; Forested: 4.30 ± 0.83 mg/L), but storm response to be stronger (mean increase DOC: Clear cut: 2.42 mg/L, Forested: 1.99 mg/L). Lower DOC concentration after cutting may be due to reductions in carbon inputs like leaf litter, though differences in drainage area and the presence of a bog lake may also account for some of the observed difference. Elevated storm responses may be due to changes in flow paths related to forest harvesting. From the broad sampling analysis, I found differences in DOC character between the two land use types: DOC in clear-cut sites was more protein-like whereas DOC in forested sites it was more humic-like, although once random factors were taken into account in generalized linear mixed models, the relationship was no longer significant. Using categorization and regression tree modeling, I found drainage area to be the most important covariate related to DOC followed by time of year (i.e. seasonality).
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Dam removal has been occurring across the United States as old infrastructure deteriorates andas people recognize the environmental disruptions dams create. Although dam removal projectsare becoming more common, studies on their impacts, particularly on groundwater, are limited.A planned dam removal project on Van Norden Meadow, in the California Sierra Nevada Rangeat Donner Pass, provides an excellent case study to consider dam removal impacts on shallowgroundwater in the associated meadow system. Mountain meadows are a valuable resource inCalifornia’s Sierra Nevada range, providing an important source of water, supporting naturalcommunities, and serving as a climate change refugia. Using MODFLOW, an open-sourcefinite-difference groundwater modeling program, I established a baseline groundwater model forVan Norden Meadow and assessed potential dam removal impacts on plant vegetationcommunities and subsurface water balance. Model layers were derived from surface topography,interpolated depth-to-bedrock, and literature values. Hydraulic parameters were calibrated andvalidated using summer groundwater levels from 28 monitoring wells in 2016 and 2017. Aftercalibration, the lower meadow (below a recessional moraine) showed both the thickest sediments(up to 36 m) and the highest calibrated hydraulic conductivity (70 m/d). Dam removal wassimulated using data from summer 2016 with altered reservoir boundary conditions. The modelpredicted a slight decrease in the water table of the lower meadow and no impact to the watertable in the upper meadow (above the moraine)—influenced by modeled transmissivity. Theareas most at risk of losing wet meadow vegetation are those adjacent to the dam along thereservoir footprint. The model also suggested that in the absence of other measures, dam removalwill lead to increased mobilization of stored groundwater to baseflow drainage below themeadow (on average 3% from May to October). This increase is partially offset by decreased evapotranspiration from the model area (on average 8% from May to October). While no actionsmay be needed in the upper meadow, restoration activities, such as channel filling, pond-and-plug,or beaver dam analogs, may offset both the decrease in the water table and promote wetmeadow habitats in the lower meadow.
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Evasion of carbon dioxide (CO₂) from headwater streams is a dominant process controlling the fate of terrestrially-derived carbon (C) in inland waters. However, methodological limitations associated with determining the gas transfer velocity of carbon dioxide (kCO₂) in headwater streams inhibit efforts to accurately quantify CO₂ emissions. In this thesis, I present a proof of concept for a tracer gas method that mitigates common issues associated with conventional methods for determining kCO₂. In this method, a datalogger controls in situ stream sensors that measure the partial pressure of CO₂ (pCO₂) and other stream parameters as well as a solenoid valve connected to a compressed CO₂ cylinder. Automated injections of CO₂ were made via an aquatic diffuser located on the stream bed. Infrared gas-analyzing (IRGA) CO₂-type sensors enclosed in waterproof, gas-permeable membranes located downstream from the diffuser continuously measured aqueous pCO₂ and equilibrate to elevated values during CO₂ injections. The difference between upstream and downstream pCO₂ values during CO₂ injection relative to pre-injection concentrations permitted calculation of both the CO₂ flux from the reach and kCO₂. This method improves upon conventional methods due to its automation, in situ measurement, and use of CO₂ as a tracer rather than another gas, thereby reducing analytical error and increasing the frequency and timing with which measurements can be made relative to conventional methods. I tested this method in a headwater stream in southwestern British Columbia. I calculated kCO₂ and continuous CO₂ emissions from the reach and compared both datasets to hydrogeomorphic parameters as well as values in the literature. Values of kCO₂ were generally above the average values reported in the literature, but they corresponded well to values reported for steep, turbulent headwater streams. Values of kCO₂ varied in relation to discharge, flow velocity, and stream temperature. CO₂ emissions from the stream were highest during high flow events. Headwater streams, which have been shown to be "hotspots" for CO₂ emissions, can also be considered as exhibiting "hot moments" of CO₂ evasion.
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Peatlands are wetlands where gross primary production exceeds organic matter decomposition causing an accumulation of partially decomposed matter, also called peat. Peat ecosystems can accumulate more carbon (C) than tropical rainforests. However, dissolved fluxes of C (as dissolved organic carbon (DOC), carbon dioxide (CO₂) and methane (CH₄)) must also be considered to determine if these ecosystems are net sinks or sources of greenhouse gases (GHGs) to the atmosphere. This research was conducted in Burns Bog, Delta, BC, Canada, one of the largest bogs on the west coast of the Americas, but which has been heavily impacted by a range of human activities. Currently, ecological restoration efforts are underway by a large-scale ditch blocking program, with the aim of re-establishing water table conditions that promote peat accumulation. Here I present data on ecosystem-scale fluxes of CO₂ and CH4 determined by eddy covariance (EC), together with data on (i) evasion fluxes of CO₂ and CH₄ from the water surface, and (ii) the flux and characteristics of DOC in water draining Burns Bog. The net ecosystem carbon balance (NECB) was determined as the sum of EC fluxes and DOC export. Concentrations of dissolved CO₂ and CH₄ were determined by headspace equilibration, and evasion rates from the water surface were quantified and used to estimate the role of the hydrosphere in the ecosystem-scale measurements. Water samples collected from five saturated areas in the flux tower footprint were analyzed for DOC concentrations and characteristics. Satellite imaging showed that during the dry season 10% of the area was covered by water, while on the wet season, it was 60%. The hydrosphere was found to be a continual C source, emitting 271 g C m-² yr-¹. NECB was found to be -98 g C m-² yr-¹. DOC export was found to offset about 60% of the apparent net C emissions determined by EC during the wet season and 3% of the net C uptake during the dry season, indicating that the EC measurements by themselves underestimate C emissions during the wet season and overestimate C accumulation in the dry season by not accounting for DOC drainage.
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Incineration of municipal solid waste practiced in Europe has been noted as a best practice, and if not for NIMBYism, it is one that the US could adopt more broadly. At present waste-to-energy technologies, such as incineration, are used to manage 24% of municipal solid waste generated per year in the EU, while the US incineration is used to manage slightly under 12% of municipal solid waste per year. Additionally, incineration in the EU has increased over the past 20 years whereas incineration in the US has been on a lingering decline over this same time period. However, the use of incineration was once greater in the US than it is today in the EU. This study analyzed the reasons for this divergence in incineration use through investigation of historical events beginning in the early 1800s in both regions. Identification and analysis of key drivers and critical junctures in the US and Europe are compared. Over time, these events created path dependencies which explain the evolution of municipal solid waste management in the US and Europe. Particularly important path dependent drivers of this evolution include local control, availability of funds, and availability of resources. The historical analysis indicates that European municipalities having a long history of local control, the financial capacity to fund infrastructure and service projects, and an awareness of benefits gained from waste-to-energy technology have resulted in the increased adoption of municipal solid waste incineration. Conversely, US municipalities had local authority eroded and constrained over time, had a lack of financial capacity and assistance to fund municipal projects, and also had access to relatively abundant land and fossil fuel resources. The result was the decline of reliance on incineration in the US since 1960. An understanding of the importance of path dependencies in shaping current renewable technology adoption, such as waste-to-energy, can better inform other policy discussions including climate change.
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Soils contain the largest terrestrial organic carbon (C) stock, representing two-thirds or more of terrestrial C. Soils can act as a source or sink for carbon dioxide (CO₂) and methane (CH₄). One common technique for studying soil surface effluxes of CO₂ (FCO₂) and of CH₄ (FCH₄) is the soil chamber. This involves placing an enclosure over the soil surface and measuring the change in headspace concentration of the gas of interest over time. Due to the air-filled pore spaces within the near-surface soil, and adsorption of gases of interest onto chamber walls, the effective volume (Veff) of the chamber which contributes to FCO₂ and FCH₄ measurements is generally higher than the geometric volume (Vg) of the chamber. It is necessary that Veff be known in order to estimate fluxes accurately. This study coupled a flow-through non-steady-state automated chamber system to a laser-based cavity ring-down spectrometer (CRDS) to estimate Veff of the chamber system using separate standard additions of CO₂ and CH₄ calibration gases. The system was then mounted onto soil cylinders which had been filled with a forest soil from Vancouver Island, British Columbia, Canada. There has been recent interest in the ability of biochar to provide multiple environmental benefits upon application to soil, including the long-term sequestration of C. There are conflicting studies as to the effect of biochar on FCO₂ and FCH₄ and overall greenhouse gas (GHG) emissions.After making background measurements of FCO₂ and FCH₄ in soil columns, biochar was applied to one of the columns and the resulting FCO₂ and FCH₄ were measured. The results from this study showed that the coupling of the CRDS to the automated chamber system proved to be successful. The estimated Veff during CO₂ and CH₄ calibration gas injections agreed with past studies as the Veff was 5 to 10% larger than the geometric volume of the chamber. Following biochar application, the amended soil produced 36.9% more CO₂ and consumed 20.4% less CH₄ than the control over the four month experiment. The results showed that soil water content was an important factor in controlling FCO₂ and FCH₄ following biochar amendment.
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The blue water - green water paradigm has been increasingly used to describe water resources. Blue water represents liquid flows in rivers or aquifers, while green water (GW) represents vapour exchanges with the atmosphere either as evaporation from soil or as transpiration from plants. This study assesses the impacts of land use change on GW fluxes in the Brazilian state of Mato Grosso, an ideal candidate for the study of GW in light of recent deforestation for pasture and soybean expansion, and the near complete reliance of its agricultural land base on precipitation as the GW source. Fluxes were estimated for 2000-2009 by combining the MODerate Resolution Imaging Spectroradiometer (MODIS) evapotranspiration product with forest cover change from Brazil’s National Institute of Space Research (INPE), as well as guidelines from the Food and Agriculture Organization (FAO) to model soybean, maize, sugar cane, cotton and pasture GW. In 2000, forest cover represented one third of the state’s land base and returned half of the state’s water vapour to the atmosphere. Annual total GW volumes decreased by 10 % between 2000 and 2009 at a rate of 16.2 km³y⁻¹ per year. Deforestation explained up to 27 % of variance in annual total volumes while agricultural expansion, as cropland and pasture, explained up to 20 %. Cropland GW doubled within the study time period, 75 % to 83 % of which constituted soybean GW. Pasture GW was 5 times larger than soybean GW and offset the increase in cropland GW. The greatest uncertainty lies in the role played by residual land use GW fluxes which were attributed to Brazilian savanna (cerrado), the Pantanal wetland, as well as unaccounted agricultural land left as fallow.
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Surface water is critical for meeting water needs in British Columbia’s Okanagan Basin, but the timing and magnitude of its availability is being altered through climate and land use changes and growing water demand. WEAP, an integrated water management model, was used to consider future scenarios for water supply and demand in an unregulated and a reservoir-supported stream that supply the District of Peachland. Potential changes to the magnitude and timing of streamflow were evaluated in response to the following scenarios: (i) climate change (derived from the HadCM3 and CGCM2 GCMs for the 2020s and 2050s), (ii) a simulated prolonged drought, (iii) land cover change resulting from a Mountain Pine Beetle (MPB) outbreak, and (iv) combinations of these conditions. These changes, in combination with likely demand increases and reservoir operating rules were evaluated in terms of stress on water availability for human use and aquatic life. Results demonstrate that anticipated future climate conditions will critically reduce streamflow relative to demand (societal and ecological) in at least a few months of “normal” and “dry” years. On the unregulated creek, an earlier recession of peak spring snowmelt, accompanied by higher demands at the beginning of the summer outdoor watering season as early as the 2020s, reduced the ability to meet downstream needs. On the regulated stream, two “very dry” years under a climate change scenario resulted in deficits for municipal water users under a higher reservoir release scenario. In all scenarios, even with the higher flows expected under the MPB scenario, some combinations of demand, reservoir operations and climate variability resulted in less than optimal conditions for instream ecological flow needs. Beyond the implications for the District of Peachland, this work demonstrates a method of using an accessible modeling tool for integrating knowledge from the fields of climate science, forest hydrology, water systems management and stream ecology to aid in water and land management decision-making.
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Publications
- Carbon exchange in rainfed and irrigated cropland in the Brazilian Cerrado (2022)
Agricultural and Forest Meteorology, - Eddy covariance data reveal that a small freshwater reservoir emits a substantial amount of carbon dioxide and methane (2022)
- On the Potential of Biochar Soil Amendments as a Sustainable Water Management Strategy (2022)
Sustainability, - Changing Water Resources Under El Niño, Climate Change, and Growing Water Demands in Seasonally Dry Tropical Watersheds (2021)
Water Resources Research, - Drone-Based Hyperspectral and Thermal Imagery for Quantifying Upland Rice Productivity and Water Use Efficiency after Biochar Application (2021)
Remote Sensing, - Relative humidity gradients as a key constraint on terrestrial water and energy fluxes (2021)
Hydrology and Earth System Sciences, - Gap‐filling approaches for eddy covariance methane fluxes: A comparison of three machine learning algorithms and a traditional method with principal component analysis (2020)
Global Change Biology, 26 (3), 1499--1518 - Greenhouse gas exchange over a conventionally managed highbush blueberry field in the Lower Fraser Valley in British Columbia, Canada (2020)
Agricultural and Forest Meteorology, 295, 108152 - Hyperspectral and Thermal Sensing of Stomatal Conductance, Transpiration, and Photosynthesis for Soybean and Maize under Drought (2020)
Remote Sensing, 12 (19), 3182 - Supplementary material to "Relative humidity gradients as a key constraint on terrestrial water and energy fluxes" (2020)
- Net Ecosystem Carbon Balance of a Peat Bog Undergoing Restoration: Integrating CO 2 and CH 4 Fluxes From Eddy Covariance and Aquatic Evasion With DOC Drainage Fluxes (2019)
Journal of Geophysical Research: Biogeosciences, 124 (4), 884--901 - Radiative forcing of methane fluxes offsets net carbon dioxide uptake for a tropical flooded forest (2019)
Global Change Biology, 25 (6), 1967--1981 - Streams with Riparian Forest Buffers versus Impoundments Differ in Discharge and DOM Characteristics for Pasture Catchments in Southern Amazonia (2019)
Water, - Water quality and greenhouse gas fluxes for stormwater detained in a constructed wetland (2019)
Journal of Environmental Management, 231, 1232--1240 - Water Use Dynamics in Double Cropping of Rainfed Upland Rice and Irrigated Melons Produced Under Drought‐Prone Tropical Conditions (2019)
Water Resources Research, - A contribution to harmonize water footprint assessments (2018)
Global Environmental Change, 53, 252--264 - Biochar feedstock and pyrolysis temperature effects on leachate: DOC characteristics and nitrate losses from a Brazilian Cerrado Arenosol mixed with agricultural waste biochars (2018)
Journal of Environmental Management, 211, 256--268 - Determining the Stability of Sugarcane Filtercake Biochar in Soils with Contrasting Levels of Organic Matter (2018)
Agriculture, - Ecohydrological responses to rewetting of a highly impacted raised bog ecosystem (2018)
Ecohydrology, , e1922 - Evaluating Water Use for Agricultural Intensification in Southern Amazonia Using the Water Footprint Sustainability Assessment (2018)
Water, - Gas Transfer Velocities Evaluated Using Carbon Dioxide as a Tracer Show High Streamflow to Be a Major Driver of Total CO 2 Evasion Flux for a Headwater Stream (2018)
Journal of Geophysical Research: Biogeosciences, 123 (7), 2183--2197 - Spectral entropy as a mean to quantify water stress history for natural vegetation and irrigated agriculture in a water-stressed tropical environment (2018)
- Annual greenhouse gas budget for a bog ecosystem undergoing restoration by rewetting (2017)
Biogeosciences, 14 (11), 2799--2814 - Application of biochar and nitrogen influences fluxes of CO2, CH4 and N2O in a forest soil (2017)
Journal of Environmental Management, 192, 203--214 - Biochar influences on soil CO2 and CH4 fluxes in response to wetting and drying cycles for a forest soil (2017)
Scientific Reports, 7 (1) - Citizen science for water quality monitoring: Data implications of citizen perspectives (2017)
Journal of Environmental Management, 200, 456--467 - Impact of Different Agricultural Waste Biochars on Maize Biomass and Soil Water Content in a Brazilian Cerrado Arenosol (2017)
Agronomy, - Soil CO2 concentrations and efflux dynamics of a tree island in the Pantanal wetland (2017)
Journal of Geophysical Research: Biogeosciences, - Spatial patterns of DOC concentration and DOM optical properties in a Brazilian tropical river-wetland system (2017)
Journal of Geophysical Research: Biogeosciences, - A review of green- and blue-water resources and their trade-offs for future agricultural production in the Amazon Basin: what could irrigated agriculture mean for Amazonia? (2016)
Hydrology and Earth System Sciences, 20 (6), 2179-2194 - Land Use in LCA: Including Regionally Altered Precipitation to Quantify Ecosystem Damage (2016)
Environmental Science & Technology, 50 (21), 11769-11778 - Physiological responses to extreme hydrological events in the Pantanal wetland: heterogeneity of a plant community containing super-dominant species (2016)
Journal of Vegetation Science, 27 (3), 568-577 - Summertime greenhouse gas fluxes from an urban bog undergoing restoration through rewetting (2016)
Mires and Peat, 17 - Supplementary material to "Annual greenhouse gas budget for a bog ecosystem undergoing restoration by rewetting" (2016)
- Supplementary material to "What could irrigated agriculture mean for Amazonia? A review of green and blue water resources and their trade-offs for future agricultural production in the Amazon Basin" (2016)
- What could irrigated agriculture mean for Amazonia? A review of green and blue water resources and their trade-offs for future agricultural production in the Amazon Basin (2016)
- Attenuation of urban agricultural production potential and crop water footprint due to shading from buildings and trees (2015)
Environmental Research Letters, 10 (6) - Biochar decreases dissolved organic carbon but not nitrate leaching in relation to vinasse application in a Brazilian sugarcane soil (2015)
Journal of environmental management, 149, 9-16 - DYNAMICS OF CHEMICAL AND PHYSICAL ATTRIBUTES AND SEASONAL VARIATION OF SOIL CARBON STOCKS IN DIFFERENT VEGETATION TYPES OF NORTH PANTANAL OF MATO GROSSO (2015)
Revista Arvore, 39 (2), 325-336 - Nitrogen enrichment potential of biochar in relation to pyrolysis temperature and feedstock quality (2015)
Journal of Environmental Management, 152, 140-144 - Biochar from Sugarcane Filtercake Reduces Soil CO2 Emissions Relative to Raw Residue and Improves Water Retention and Nutrient Availability in a Highly-Weathered Tropical Soil (2014)
Plos One, 9 (6) - Environmental footprints show China and Europe's evolving resource appropriation for soybean production in Mato Grosso, Brazil (2014)
Environmental Research Letters, 9 (7) - Estimation des composantes du bilan hydrique en saison seche des lacs des zones humides tropicales du Pantanal (Bresil) (2014)
Hydrological Sciences Journal-Journal Des Sciences Hydrologiques, 59 (12), 2158-2172 - Inundation and groundwater dynamics for quantification of evaporative water loss in tropical wetlands (2014)
Hydrology and Earth System Sciences Discussions, 11 (4), 4017--4062 - Contrasting CO2 concentration discharge dynamics in headwater streams: A multi-catchment comparison (2013)
Journal of Geophysical Research-Biogeosciences, 118 (2), 445-461 - MONITORING THE SOIL REDOX POTENTIAL AND ITS INTERACTIONS WITH ASSOCIATED VARIABLES IN THE NORTHERN PANTANAL (2013)
Revista Brasileira De Ciencia Do Solo, 37 (3), 632-639 - Soil CO2 Dynamics in a Tree Island Soil of the Pantanal: The Role of Soil Water Potential (2013)
Plos One, 8 (6) - Stream water nutrient and organic carbon exports from tropical headwater catchments at a soil degradation gradient (2013)
Nutrient Cycling in Agroecosystems, 95 (2), 145-158 - Future Water Supply and Demand in the Okanagan Basin, British Columbia: A Scenario-Based Analysis of Multiple, Interacting Stressors (2012)
Water Resources Management, 26 (3), 667-689 - LITHOLOGICAL DISCONTINUITY OF GRANITE REGOLITH IN A SMALL WATERSHED IN THE AMAZON FOREST, IN JURUENA, MATO GROSSO (2012)
Revista Brasileira De Ciencia Do Solo, 36 (2), 317-324 - Stream Discharge in Tropical Headwater Catchments as a Result of Forest Clearing and Soil Degradation (2012)
Earth Interactions, 16 - Submersible UV-Vis Spectroscopy for Quantifying Streamwater Organic Carbon Dynamics: Implementation and Challenges before and after Forest Harvest in a Headwater Stream (2012)
Sensors, 12 (4), 3798-3813 - Temporal Variability of Nitrous Oxide from Fertilized Croplands: Hot Moment Analysis (2012)
Soil Science Society of America Journal, 76 (5), 1728-1740 - Water use by terrestrial ecosystems: temporal variability in rainforest and agricultural contributions to evapotranspiration in Mato Grosso, Brazil (2012)
Environmental Research Letters, 7 (2) - Discharge-calcium concentration relationships in streams of the Amazon and Cerrado of Brazil: soil or land use controlled (2011)
Biogeochemistry, 105 (1-3), 19-35 - Ecohydrology and Biogeochemistry of the Rhizosphere in Forested Ecosystems (2011)
Forest Hydrology and Biogeochemistry: Synthesis of Past Research and Future Directions, 216, 483-498 - Fluorescence index as an indicator of dissolved organic carbon quality in hydrologic flowpaths of forested tropical watersheds (2011)
Biogeochemistry, 105 (1-3), 149-157 - Land-Water interactions in the amazon (2011)
Biogeochemistry, 105 (1-3), 1-5 - Modeling to discern nitrogen fertilization impacts on carbon sequestration in a Pacific Northwest Douglas-fir forest in the first-postfertilization year (2011)
Global Change Biology, 17 (3), 1442-1460 - Runoff sources and land cover change in the Amazon: an end-member mixing analysis from small watersheds (2011)
Biogeochemistry, 105 (1-3), 7-18 - Direct and continuous measurement of dissolved carbon dioxide in freshwater aquatic systems-method and applications (2010)
Ecohydrology, 3 (1), 68-78 - Nitrogen aboveground turnover and soil stocks to 8 m depth in primary and selectively logged forest in southern Amazonia (2010)
Global Change Biology, 16 (6), 1793-1805 - Public Participation and Perceptions of Watershed Modeling (2009)
Society & Natural Resources, 22 (1), 79-87 - The Role of Rivers in the Regional Carbon Balance (2009)
Amazonia and Global Change, 186, 489-504 - Training Tomorrow's Environmental Problem Solvers: An Integrative Approach to Graduate Education (2009)
Bioscience, 59 (6), 514-521 - A simple, direct method to measure dissolved CO2 using soda lime (2008)
Oecologia Brasiliensis, 12 (1), 85-91 - Carbon trading should not reduce social equity (2008)
FRONTIERS IN ECOLOGY AND THE ENVIRONMENT, 6 (1), 10 - CO2 efflux from Amazonian headwater streams represents a significant fate for deep soil respiration (2008)
GEOPHYSICAL RESEARCH LETTERS, 35 (17) - Fallow management practices in Guatemala's Western Highlands: Social drivers and biophysical impacts (2008)
LAND DEGRADATION & DEVELOPMENT, 19 (2), 178-189 - Spatial distribution of soil texture, color and soil organic carbon across a headwater transect in the southern Amazon (2008)
Acta Amazonica, 38 (4), 715-722 - Distribuicao espacial de carbono em solo sob floresta primaria na Amazonia Meridional (Spatial distribution of soil carbon under primary forest cover in southern Amazonia) (2007)
Revista Arvore (Tree Journal, Brazil), 31, 83-92 - Land-use change and stream water fluxes: Decadal dynamics in watershed nitrate exports (2007)
ECOSYSTEMS, 10 (7), 1182-1196 - Litterfall production and fluvial export in headwater catchments of the southern Amazon (2007)
JOURNAL OF TROPICAL ECOLOGY, 23, 329-335 - Relationships between soil hydrology and forest structure and composition in the southern Brazilian Amazon (2007)
JOURNAL OF VEGETATION SCIENCE, 18 (2), 183-194 - Spatial variability of soil physical attributes used for soil mapping in small headwater catchments of the southern Amazon (2007)
REVISTA BRASILEIRA DE CIENCIA DO SOLO, 31 (1), 91-100 - Storm pulses of dissolved CO2 in a forested headwater Amazonian stream explored using hydrograph separation (2007)
WATER RESOURCES RESEARCH, 43 (11) - DOC and DIC in flowpaths of Amazonian headwater catchments with hydrologically contrasting soils (2006)
BIOGEOCHEMISTRY, 81 (1), 45-57 - Double-funneling of trees: Stemflow and root-induced preferential flow (2006)
ECOSCIENCE, 13 (3), 324-333 - Organic carbon fluxes within and streamwater exports from headwater catchments in the southern Amazon (2006)
HYDROLOGICAL PROCESSES, 20 (12), 2599-2614 - Spatial and temporal variability of soil water repellency of Amazonian pastures (2005)
AUSTRALIAN JOURNAL OF SOIL RESEARCH, 43 (3), 319-326 - Application of SMR to modeling watersheds in the Catskill Mountains (2004)
Environmental Modeling & Assessment, 9 (2), 77-89 - Application of two hydrologic models with different runoff mechanisms to a hillslope dominated watershed in the northeastern US: a comparison of HSPF and SMR (2003)
JOURNAL OF HYDROLOGY, 284 (1-4), 57-76
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