No description available.

No description available.

Intensely managed and modified catchments in the Great Lakes are linked to eutrophication and hypoxia of receiving water bodies downstream, resulting in water quality impairment, and adverse impacts on aquatic ecology. While much focus has been on the role of phosphorous and nitrogen, dissolved organic carbon (DOC) plays a complex and critical role in lake biogeochemical cycles, as it influences the interations between nutrients and contaminants in water and soil through processes of mobilization, transport, biological uptake, and deposition. Human-dominated landscapes have a range of consequences on DOC dynamics as catchment hydrology, plant cover, and nutrient inputs are altered in these environments. As such, the objectives of this study were to identify the controls and drivers of DOC quantity and DOM quality in the Spencer Creek watershed, which is the largest contributor of water to Cootes Paradise that ultimately drains into Lake Ontario. The 159 km2 study area of the catchment is complex, as the present landscape is composed of a mosaic of various land uses including agriculture, forest, wetland, urban, and industrial regions. Flow alterations contribute to the complexity of the watershed as there are managed reservoirs and alterations in water courses. From 2016- 2018, hydrometric data was collected across 9 monitoring sites, along with surface water samples that were analyzed for DOC concentration and optical properties. Results indicate differences in flow magnitudes and stream DOC between dry and wet conditions, where concentrations during wet conditions were significantly higher compared to dry. Additionally, there was substantial variation in DOC concentration and quality across the Spencer Creek watershed. DOC concentrations were found to be the lowest at groundwater influenced sites in the headwaters of the watershed, and the highest in the mid-catchment region where DOC quality was strongly influenced by wetland sources. The reservoir-influenced sites showed relatively intermediate concentrations of DOC, with quality that exhibited strong microbial signatures. At the outlet, DOC concentrations were attenuated and DOC quality was intermediate between allochthonous and autochthonous end members, reflecting upstream mixing processes. These processes were presented as a conceptual model of water and DOC movement through the Spencer Creek watershed. The implications of this research suggest that with anticipated wetter and warmer conditions DOC concentrations would increase in the watershed. The repercussions of increased DOC concentrations overall imply a decrease of terrestrial carbon storage, and greater input into more reactive and susceptible pools, which may result in further water quality degradation. Overall, the findings from this research provide insight into the fate and transport of water and DOC in a complex, managed catchment in the Great Lakes region, with the aims of providing key information for local stakeholders. / Thesis / Master of Science (MSc)

Conversion of native forests to turfgrass-dominated residential landscapes under a wide range of management practices results in dramatic changes to vegetation and soils, which may affect soil carbon storage. To better understand the effects of landscape conversion and management on soil carbon, we conducted a study on residential properties in the Valley and Ridge physiographic province of southwest Virginia to compare soil carbon storage and dynamics between turfgrass landscapes and the surrounding mixed oak forests from which they were developed. Sixty-four residential properties ranging from 5 to 52 years since site development were investigated. Soil samples were collected from lawns and adjacent forest stands to a depth of 30 cm and analyzed for carbon and nitrogen content. Additional measurements taken were soil bulk density, temperature, moisture, and total soil CO₂ efflux rate. Homeowners participating in the study completed a survey on their lawn management practices so that the effects of specific practices (e.g. fertilization) and intensity levels on carbon dynamics could be analyzed. Also included in the survey were 11 questions regarding the homeowners' commitment to the environment. Homeowners were assigned an environmental commitment score based on their responses which was compared with lawn management practices in order to identify any connection between environmental attitude and lawn management practices. Total soil carbon content to 30 cm depth of lawn (6.5 kg C/m²) and forest (7.1 kg C/m²) marginally differed (P=0.08); however, lawn soil contained significantly greater C than forest soil at the 20-30 cm depth (0.010 vs. 0.007 g C/cm³, P=.0137). There was a weak negative relationship between carbon in the lawn and time since development at the 20-30 cm depth (P=0.08), but no significant relationship between time and C content at shallower depths. We found a positive relationship between time since development and percent C of lawn at the 0-5 cm depth (P=0.04), whereas there was a negative relationship with percent C and time at the 20-30 cm depth (P=0.03). Based on the homeowner survey, we found a positive correlation between lawn fertilization frequency and both lawn nitrogen content (P=.07) and lawn carbon content (P=.0005) in the top 0-5 cm of soil. Nitrogen content was greater in lawn than forest soil at the 0-5 cm depth (0.0025 vs. 0.0018 g/cm³³, P<.0001) and the 5-10 cm depth (0.0013 vs. 0.0009 g/cm³, P <.0001). There was a positive relationship (P=0.059) between overall environmental commitment score and level of management intensity. Higher environmental commitment (EC) score corresponded with a higher level of management intensity (fertilizer and pesticide use). Our results indicate that converting unmanaged Appalachian hardwood forest into managed, turf-grass dominated residential homesites results in similar soil organic concentration and depth distribution as the previous forest within a short period of time following development. Although total soil carbon does not differ between lawn and forest, lawn may develop greater density at 20-30cm depth over time. Fertilization enhances carbon and nitrogen content in the upper 0-5cm in lawns. Homeowners who feel that they are more strongly committed to the environment are more likely to apply higher levels of fertilizer to their lawn. / Master of Science

Arctic soils store half of the global soil organic carbon (OC) pool and twice as much C as is currently present in the atmosphere. A considerable part of these carbon pools are stored in permafrost. Amplified climate warming in the Arctic will thaw permafrost and remobilize some of these substantial carbon stocks into the active carbon cycle, potentially causing positive feedback to global warming. Despite the global importance of this mechanism, our understanding of the fate of these thawing organic carbon (OC) pools is still poor, particularly regarding its degradation potential. This makes good estimates on greenhouse gas emissions versus coastal reburial impossible. This doctoral thesis aims to improve our understanding on the fate of high-latitude terrestrial OC during fluvial and coastal transport. In two study regions, the Bothnian Bay and the East Siberian Sea, we apply a wide range of bulk, molecular and isotopic geochemical analyses to reveal information on sources, age, degradation and transport routes. Our results show that both study regions receive and store large amounts of terrestrial OC, largely derived from peatlands (paper I, II and IV). This terrestrial matter undergoes extensive degradation in both the water column and surface sediments (paper I, III and IV). Surface sediments in the East Siberian Sea show a offshore-decreasing input of riverine OC and a considerable and constant input of OC from coastal erosion. The strong imprint of rapidly settling coastal OC far out on the shelf may be explained by a strong benthic boundary layer transport in combination with offshore ice-transport and selective preservation of erosion OC compared to riverine OC (paper IV). Molecular radiocarbon data allowed us to distinguish between two (sub-)Arctic soil OC pools that show a remarkably different susceptibility to degradation upon arrival in the coastal system; a young and easily degradable pool originating in surface peatlands, and an old and recalcitrant pool originating in deep mineral soils and coastal mineral Pleistocene deposits (paper III and IV). Our first estimates suggest that, in the Bothnian Bay coastal system, mineral soil OC is at least 20 times less susceptible to degradation than peatland OC (paper III). Hence, a considerable part of the thaw-released mineral OC pool may simply be relocated to coastal sediments instead of being emitted to the atmosphere. / At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 3: Accepted. Paper 4: Manuscript.

High Arctic permafrosted soils represent a massive sink in the global carbon cycle, accounting for twice as much carbon as what is currently stored as carbon dioxide in the atmosphere. However, with current warming trends this sink is in danger of thawing and potentially releasing large amounts of carbon as both carbon dioxide and methane into the atmosphere. It is difficult to make predictions about the future of this sink without knowing how it has reacted to past temperature and climate changes. This dissertation summarizes the results of the first study to look at long term, fine scale organic carbon delivery by the high-Arctic Colville River into Simpson’s Lagoon in the near-shore Beaufort Sea. Modern delivery of organic carbon to the Lagoon was determined to come from a variety of sources through the use of a three end-member mixing model and sediment biomarker concentrations. These sources include the Colville River in the western area of the Lagoon near the river mouth, marine sources in areas of the Lagoon without protective barrier islands, and coastal erosional sources and the Mackenzie River in the eastern area of the Lagoon. Downcore organic carbon delivery was measured on two cores in the Lagoon, one taken near the mouth of the Colville River (spans about 1800 years of history) and one taken on the eastern end of the Lagoon (spans about 600 years of history). Bulk organic parameters and biomarkers were measured in both cores and analyzed with Principle Component Analysis to determine long-term trends in organic carbon delivery. It was shown that at various times in the past, highly degraded organic carbon inputs of what is likely soil and peat carbon were delivered to the Lagoon. At other times, inputs of fresher, non-degraded, terrestrially-derived organic carbon inputs of what are likely higher amounts of plant and vegetative material was delivered to the Lagoon. Inputs of degraded soil carbon were also shown to correspond to higher temperatures on the North Slope of Alaska, likely indicating that warmer temperatures lead to a thawing of permafrost and in turn organic carbon mobilization to the coastal Beaufort Sea.

Existing terrestrial carbon accounting models have mainly investigated atmosphere-vegetationsoil stocks and fluxes but have largely ignored the hydrological flux of organic carbon. It is generally assumed that biomass and soil carbon are the only relevant pools in a landscape ecosystem. However, recent findings have suggested that significant amounts of organic carbon can dissolve (dissolved organic carbon or DOC) or particulate (particulate organic carbon or POC) in water and enter the hydrological flux at the catchment scale. A significant quantity of total organic carbon (TOC) sequestered through photosynthesis may be exported from the landscape through the hydrological flux and stored in downstream stocks.¶ This thesis presents a catchment-scale case study investigation into the export of organic carbon through a river system in comparison with carbon that is produced by vegetation through photosynthesis. The Cotter River Catchment was selected as the case study. It is a forested catchment that experienced a major wildfire event in January 2003. The approach is based on an integration of a number of models. The main input data were time series of in-stream carbon measurements and remotely sensed vegetation greenness. The application of models to investigate diffuse chemical substances has dramatically increased in the past few years because of the significant role of hydrology in controlling ecosystem exchange. The research firstly discusses the use of a hydrological simulation model (IHACRES) to analyse organic carbon samples from stream and tributaries in the Cotter River Catchment case study. The IHACRES rainfall-runoff model and a regionalization method are used to estimate stream-flow for the 75 sub-catchments. The simulated streamflow data were used to calculate organic carbon loads from concentrations sampled at five locations in the catchment.¶ The gross primary productivity (GPP) of the vegetation cover in the catchment was estimated using a radiation use efficiency (RUE) model driven by MODIS TERRA data on vegetation greenness and modeled surface irradiance (RS). The relationship between total organic carbon discharged in-stream and total carbon uptake by plants was assessed using a cross-correlation analysis.¶ The IHACRES rainfall-runoff model was successfully calibrated at three gauged sites and performed well. The results of the calibration procedure were used in the regionalization method that enabled streamflow to be estimated at ungauged locations including the seven sampling sites and the 75 sub-catchment areas. The IHACRES modelling approach was found appropriate for investigating a wide range of issues related to the hydrological export of organic carbon at the catchment scale. A weekly sampling program was implemented to provide estimates of TOC, DOC and POC concentrations in the Cotter River Catchment between July 2003 and June 2004. The organic carbon load was estimated using an averaging method.¶ The rate of photosynthesis by vegetation (GPP) was successfully estimated using the radiation use efficiency model to discern general patterns of vegetation productivity at sub-catchment scales. This analysis required detailed spatial resolution of the GPP across the entire catchment area (comprising 75 sub-catchment areas) in addition to the sampling locations. Important factors that varied at the catchment scale during the sampling period July 2003 – June 2004, particularly the wildfire impacts, were also considered in this assessment. ¶ The results of the hydrologic modelling approach and terrestrial GPP outcome were compared using cross correlation and regression analysis. This comparison revealed the likely proportion of catchment GPP that contributes to in-stream hydrological flux of organic carbon. TOC Load was 0.45% of GPP and 22.5 - 25% of litter layer. As a result of this investigation and giving due consideration to the uncertainties in the approach, it can be concluded that the hydrological flux of organic carbon in a forested catchment is a function of gross primary productivity.

The main aim of this thesis was to assess the status of soil organic carbon in newly shaped soils called Velká podkrušnohorská dump in the Sokolov district and evaluate the information in relation to the physic-chemical properties of soils. Another objective was to determine the relationship between the stable and labile fractions of soil organic carbon. The amount of soil carbon (stable fraction) was measured in the solid soil samples and there was the analysis of basic physic-chemical parameters of the soil performed. The highest concentration of soil carbon was measured in the stand alders and larch. The amount of soil carbon (labile fraction) was measured in the water extract. The highest values were measured in the stand silver birch and alders. Based on this data the quotient of the labile fraction from the stable fraction was determined and the correlation of the labile and stable fractions was made. It was found out that the higher quality soils are located at the leafy trees, but it leads to leaching of organic carbon. The bulk density and coarse-grained soil fraction was determined from the physical properties and these data were used to calculate the stock of soil organic carbon. The highest value was measured in deciduous forests with small-leaved linden, in coniferous forests with larch. The stocks of soil organic carbon were converted into codes by land cover categories and the thematic map was created. It was found out that the leafy trees are much more appropriate for forest restoration, because they are characterized by the rapid initial growth, easily degradable plant litter and stable form humus. Deciduous forests are also characterized by more developed soil substrate, which is however unstable.

The interest in using sugarcane straw as a feedstock for bioenergy production has been increased considerably. However, indiscriminate straw removal may negatively affect soil functioning. Therefore, this work aimed to quantify and characterize soil solution translocating along the profile, under straw removal rates from the soil surface. Lysimeter systems were built with 1, 20, 50, and 100 cm soil columns, with a sandy clay loam texture, from a commercial sugarcane field in Piracicaba-SP, southeastern Brazil. The experiment was conducted in open area, where the lysimeters were subjected to rainfall and sun radiation. After the soil stabilization within the lysimeters, the treatments were added, consisting of four straw amounts (0, 3, 6, and 12 Mg ha-1), representing straw removal rates of 100 (bare soil), 75, 50, and 0%, respectively. After one year of the first straw addition, the same straw amounts were added again simulating the second harvest. Drained solution was collected and quantified by 17 months and soil moisture was determined over a period of two months using sensors. Dissolved organic carbon (DOC) concentration was measured in automatic analyzer. The soil solution and straw solution, made in water infusion, were characterized in High performance liquid chromatography (HPLC) to verify the presence of toxic compounds. After that, straw and soil solution were used in tests with soybean seed to evaluate the effects in plant germination and initial growth. At the end of the experiment, soil bulk density and soil organic carbon (SOC) analyses were performed. Remaining straw was weight before the new addition, and weight again at the end to determine the decomposition rates. The accumulated volume of solution drained was 30, 11 and 4% lower under 100, 75 and 50% removal rates compared to no removal. Bare soil stored less water, indicating susceptibility to lose water by evaporation. Simulation showed that 100% and 75% removal can induce longer periods of water restriction, which impair sugarcane growth. The DOC production on topsoil was higher in no straw removal; the retention was higher in 1 to 20 cm in no removal and higher in 20 to 50 cm in 50 and 75% removal rates. Bare soil released more DOC below 01 cm indicating a possible C loss. Below 100 cm DOC leachate was quite similar in all treatments, what shows a higher C retention and small C loss even in higher DOC production. Even with differences in DOC retention, increases in C stock below 5 cm were not noticed. We found many phenolic compounds in the straw solution, not found in the soil solution, indicating that in natural conditions straw does not release toxic compounds into soil solution. Plant growth was negatively affected by straw solution, but not by soil solution. Our findings suggest that the medium straw maintenance prevents variations and loss on soil water content. Higher straw amount increases DOC production, which likely alters its composition and subsequent retention in soil. Carbon stock did not increase in the soil subsurface, but probably will in the long-term. The higher straw removal, proportionally, the higher the C losses in the form of CO2 and DOC, consequently the lower soil C retention. More straw on soil surface release more C amounts to the soil, retained or translocated with soil water, may be stored in deeper soil layers. Higher water percolation in the soil profile does not mean higher C losses by leaching in deeper soil. This study has the practical objective of finding an amount of straw to be maintained in the field that ensures the C storage and the better soil functioning, and also supply feedstock for bioenergy production. / O interesse no uso da palha de cana-de-açúcar como matéria-prima para a produção de bioenergia vem crescendo consideravelmente. No entanto, a remoção excessiva da palha pode afetar negativamente o funcionamento do solo. Portanto, o objetivo deste trabalho foi quantificar e caracterizar a solução ao longo do perfil sob níveis de remoção de palha da superfície do solo. Para isso, foi construído um sistema de lisímetros com colunas de 1, 20, 50 e 100 cm de solo, de textura franco argilo arenosa, proveniente de área comercial de cana-de-açúcar em Piracicaba-SP, Brasil. O experimento foi conduzido em área aberta, sujeito a precipitação e luz natural. Depois da estabilização do solo dentro dos tubos, foram adicionados os seguintes tratamentos: 0, 3, 6 e 12 Mg ha-1 de massa seca, representando 100 (solo nu), 75, 50 e 0% de intensidade de remoção de palha, respectivamente, sendo adicionados novamente após um ano. A solução percolada foi coletada e quantificada por 17 meses, a umidade do solo foi determinada por dois meses usando sensores. A concentração de carbono orgânico dissolvido (COD) foi mensurada com analisador automático. A solução do solo e solução da palha, feita por infusão em água, foram caracterizadas em HPLC para verificar a presença de compostos tóxicos. Posteriormente, as soluções da palha e solo foram usadas em testes de sementes de soja para avaliar os efeitos na germinação e crescimento inicial. Ao final do experimento, foram realizadas análises de densidade do solo e carbono orgânica do solo (COS). A palha remanescente foi pesada após um ano, anterior a nova adição, e pesada novamente ao final do experimento, para determinar a taxa de decomposição. O volume de solução percolado foi 30, 11 e 4% menor em 100, 75 e 50% do que em 0% de remoção, respectivamente. O solo descoberto armazenou menos água, indicando susceptibilidade à perda de água por evaporação. A simulação mostrou que 100 e 75% de remoção induzem longos períodos de restrição hídrica, que pode prejudicar o crescimento da planta. A produção de COD na camada superficial foi maior no solo sem remoção; a retenção foi maior de 1 a 20 cm em solo sem remoção, e maior em 20 a 50 cm em 50 e 75% de remoção. O solo descoberto liberou mais COD em de 20 cm do que em superfície, indicando perda de C. Abaixo de 100 cm, o COD lixiviado foi similar nos tratamentos, indicando grande retenção de C e pequenas perdas por lixiviação, mesmo em alta produção de COD. Mesmo com diferenças na retenção de COD, não foi identificado aumento no estoque de C abaixo de 5 cm. Foram encontrados compostos fenólicos na solução da palha, não encontrados na solução do solo, indicando que em condições naturais a palha não libera quantidades significativas de compostos tóxicos na solução do solo. O crescimento de plantas foi negativamente afetado pela solução da palha, mas não pela solução do solo. Nossos resultados sugerem que a manutenção de quantidade média de palha previne perdas e variação no conteúdo de água do solo. Maior quantidade de palha aumenta a produção de COD, que provavelmente altera sua composição, alterando a retenção no solo. O estoque de C não aumentou consideravelmente em subsuperfície, mas muito provavelmente aumentará em escala de tempo maior. Quanto maior a remoção de palha, proporcionalmente maior as taxas de C liberadas na forma de CO2 e COD em subsuperfície, consequentemente, menor a retenção de C no solo. Maiores quantidades de palha na superfície liberam mais C para o solo, retido ou translocado com a água, podendo ser estocado em maiores profundidades do solo. Maior percolação de água no solo não significa maiores perdas de C por lixiviação em profundidade.

The interest in using sugarcane straw as a feedstock for bioenergy production has been increased considerably. However, indiscriminate straw removal may negatively affect soil functioning. Therefore, this work aimed to quantify and characterize soil solution translocating along the profile, under straw removal rates from the soil surface. Lysimeter systems were built with 1, 20, 50, and 100 cm soil columns, with a sandy clay loam texture, from a commercial sugarcane field in Piracicaba-SP, southeastern Brazil. The experiment was conducted in open area, where the lysimeters were subjected to rainfall and sun radiation. After the soil stabilization within the lysimeters, the treatments were added, consisting of four straw amounts (0, 3, 6, and 12 Mg ha-1), representing straw removal rates of 100 (bare soil), 75, 50, and 0%, respectively. After one year of the first straw addition, the same straw amounts were added again simulating the second harvest. Drained solution was collected and quantified by 17 months and soil moisture was determined over a period of two months using sensors. Dissolved organic carbon (DOC) concentration was measured in automatic analyzer. The soil solution and straw solution, made in water infusion, were characterized in High performance liquid chromatography (HPLC) to verify the presence of toxic compounds. After that, straw and soil solution were used in tests with soybean seed to evaluate the effects in plant germination and initial growth. At the end of the experiment, soil bulk density and soil organic carbon (SOC) analyses were performed. Remaining straw was weight before the new addition, and weight again at the end to determine the decomposition rates. The accumulated volume of solution drained was 30, 11 and 4% lower under 100, 75 and 50% removal rates compared to no removal. Bare soil stored less water, indicating susceptibility to lose water by evaporation. Simulation showed that 100% and 75% removal can induce longer periods of water restriction, which impair sugarcane growth. The DOC production on topsoil was higher in no straw removal; the retention was higher in 1 to 20 cm in no removal and higher in 20 to 50 cm in 50 and 75% removal rates. Bare soil released more DOC below 01 cm indicating a possible C loss. Below 100 cm DOC leachate was quite similar in all treatments, what shows a higher C retention and small C loss even in higher DOC production. Even with differences in DOC retention, increases in C stock below 5 cm were not noticed. We found many phenolic compounds in the straw solution, not found in the soil solution, indicating that in natural conditions straw does not release toxic compounds into soil solution. Plant growth was negatively affected by straw solution, but not by soil solution. Our findings suggest that the medium straw maintenance prevents variations and loss on soil water content. Higher straw amount increases DOC production, which likely alters its composition and subsequent retention in soil. Carbon stock did not increase in the soil subsurface, but probably will in the long-term. The higher straw removal, proportionally, the higher the C losses in the form of CO2 and DOC, consequently the lower soil C retention. More straw on soil surface release more C amounts to the soil, retained or translocated with soil water, may be stored in deeper soil layers. Higher water percolation in the soil profile does not mean higher C losses by leaching in deeper soil. This study has the practical objective of finding an amount of straw to be maintained in the field that ensures the C storage and the better soil functioning, and also supply feedstock for bioenergy production. / O interesse no uso da palha de cana-de-açúcar como matéria-prima para a produção de bioenergia vem crescendo consideravelmente. No entanto, a remoção excessiva da palha pode afetar negativamente o funcionamento do solo. Portanto, o objetivo deste trabalho foi quantificar e caracterizar a solução ao longo do perfil sob níveis de remoção de palha da superfície do solo. Para isso, foi construído um sistema de lisímetros com colunas de 1, 20, 50 e 100 cm de solo, de textura franco argilo arenosa, proveniente de área comercial de cana-de-açúcar em Piracicaba-SP, Brasil. O experimento foi conduzido em área aberta, sujeito a precipitação e luz natural. Depois da estabilização do solo dentro dos tubos, foram adicionados os seguintes tratamentos: 0, 3, 6 e 12 Mg ha-1 de massa seca, representando 100 (solo nu), 75, 50 e 0% de intensidade de remoção de palha, respectivamente, sendo adicionados novamente após um ano. A solução percolada foi coletada e quantificada por 17 meses, a umidade do solo foi determinada por dois meses usando sensores. A concentração de carbono orgânico dissolvido (COD) foi mensurada com analisador automático. A solução do solo e solução da palha, feita por infusão em água, foram caracterizadas em HPLC para verificar a presença de compostos tóxicos. Posteriormente, as soluções da palha e solo foram usadas em testes de sementes de soja para avaliar os efeitos na germinação e crescimento inicial. Ao final do experimento, foram realizadas análises de densidade do solo e carbono orgânica do solo (COS). A palha remanescente foi pesada após um ano, anterior a nova adição, e pesada novamente ao final do experimento, para determinar a taxa de decomposição. O volume de solução percolado foi 30, 11 e 4% menor em 100, 75 e 50% do que em 0% de remoção, respectivamente. O solo descoberto armazenou menos água, indicando susceptibilidade à perda de água por evaporação. A simulação mostrou que 100 e 75% de remoção induzem longos períodos de restrição hídrica, que pode prejudicar o crescimento da planta. A produção de COD na camada superficial foi maior no solo sem remoção; a retenção foi maior de 1 a 20 cm em solo sem remoção, e maior em 20 a 50 cm em 50 e 75% de remoção. O solo descoberto liberou mais COD em de 20 cm do que em superfície, indicando perda de C. Abaixo de 100 cm, o COD lixiviado foi similar nos tratamentos, indicando grande retenção de C e pequenas perdas por lixiviação, mesmo em alta produção de COD. Mesmo com diferenças na retenção de COD, não foi identificado aumento no estoque de C abaixo de 5 cm. Foram encontrados compostos fenólicos na solução da palha, não encontrados na solução do solo, indicando que em condições naturais a palha não libera quantidades significativas de compostos tóxicos na solução do solo. O crescimento de plantas foi negativamente afetado pela solução da palha, mas não pela solução do solo. Nossos resultados sugerem que a manutenção de quantidade média de palha previne perdas e variação no conteúdo de água do solo. Maior quantidade de palha aumenta a produção de COD, que provavelmente altera sua composição, alterando a retenção no solo. O estoque de C não aumentou consideravelmente em subsuperfície, mas muito provavelmente aumentará em escala de tempo maior. Quanto maior a remoção de palha, proporcionalmente maior as taxas de C liberadas na forma de CO2 e COD em subsuperfície, consequentemente, menor a retenção de C no solo. Maiores quantidades de palha na superfície liberam mais C para o solo, retido ou translocado com a água, podendo ser estocado em maiores profundidades do solo. Maior percolação de água no solo não significa maiores perdas de C por lixiviação em profundidade.