Few field studies have assessed the temporal and spatial dynamics of wood in small streams (bankfull widths < 5 m) flowing through forest ecosystems dominated by stand replacing wildfires. Comparisons of instream wood loads associated with clearcut harvesting, wildfire, and undisturbed, old forests are also scarce. The two main objectives of this research were: (1) to document the temporal and spatial variability of wood and its geomorphic role in relation to stand development stage; and (2) to compare wood loads and its geomorphic role in relation to streamside clearcut harvesting, wildfires and older, undisturbed forest stands. This research focused on 38 small streams with gradients less than 14% situated in the plateau regions of south-central British Columbia, Canada. A distinct temporal trend in wood loading was observed, with elevated volumes present 30-50 years subsequent to the wildfire disturbances following a “reverse J-shaped” trend in relation to time since the last major wildfire disturbance. The number of wood pieces was highly variable and few of the wood characteristics exhibited a significant trend in relation to time since the last major wildfire disturbance. Except at the smallest spatial scale (<3 m segments longitudinally along the stream) the spatial distribution of wood followed a random pattern with no trend, indicating that wood loads are related to local wood recruitment processes associated with episodic or chronic tree mortality and low wood transport. Instream wood volumes were three times higher in streams recently (30 – 50 years ago) disturbed by wildfire as compared to the older riparian forest stands, confirming that wildfire disturbance is an important mechanism to recruit wood into streams. No significant differences in wood loads were identified between the streamside clearcut streams and the wildfire-disturbed or older, undisturbed streams. The lack of reductions in wood loads are likely related to the low transport capacity of our study streams, retention of non-merchantable trees and recruitment of slash from harvesting. A lack of morphologic variability was observed in relation to the disturbances indicating that the streams included in this study are relatively robust and unresponsive to wildfire or streamside clearcut harvesting disturbances.

In the southern Great Plains, the encroachment of grassland ecosystems by mesquite (Prosopis glandulosa), is widespread, and prescribed fire is commonly used in its control. Despite this, substantial quantitative information concerning their influences on the community composition, functional dynamics, and soil organic carbon (SOC) storage potential of grassland ecosystems is lacking. The objectives of this study were to: a) quantify the effects of seasonal prescribed fire treatments and mesquite encroachment on aboveground net primary productivity (ANPP) and herbaceous community composition; b) characterize SOC pool sizes, turnover, and storage potential relative to vegetation type and fire treatment; c) evaluate the structure and diversity of soil microbial communities relative to vegetation type; and d) characterize the functional diversity of these same microbes using the GeoChip functional gene microarray. Repeated winter and summer fires led to increased ANPP rates (average, 434 and 313 g m-2 y-1, respectively), relative to unburned controls (average, 238 g m-2 y-1), altered herbaceous community composition, and increased the storage of resistant forms of SOC, but did not affect overall SOC storage. Herbaceous ANPP rates did not differ significantly as a result of mesquite encroachment, but herbaceous community composition and SOC storage did. Mesquite soils contained significantly more total, slow-turnover, and resistant forms of SOC than those that occurred beneath C3 or C4 grasses. Similarity among the soil bacterial and fungal communities associated with the major vegetation types in this system was low to moderate. Significant differences were detected among soil fungi, with the mesquite-associated fungi harboring significant differences in community structure relative to the fungal communities associated with each of the other vegetation types examined. Despite this result, few significant differences were detected with respect to the functional diversity of these communities, suggesting either a high degree of functional redundancy, or that the functional differences harbored by these communities are beyond the scope of the GeoChip. The results of this study demonstrate that both fire and mesquite encroachment have the potential to alter ecosystem components and processes significantly, providing new insight regarding the effects of these widespread land use and land cover changes on ecosystem structure and function.

Spiranthes parksii Correll is an endemic terrestrial orchid to the Post Oak Savannah of East Texas and is currently listed as federally endangered. The construction of Twin Oaks landfill, approximately 20 km east of College Station, TX, will destroy an estimated 379 S. parksii individuals and 44.7 ha of its habitat. Research has been funded to mitigate for this loss and includes documenting demographics, life cycle, local and landscape habitat, and on-site transplantation of S. parksii. Results found that S. parksii was highly variable between years at Twin Oaks and might be due to seasonal rainfall in rosette and early flowering growth. It was also found variable in its production of a rosette and influorescence from year to year. Individual plants were found to occur farther from drainages in higher count years, probably due to soil moisture, although further research should be conducted to confirm this hypothesis. A significant difference (p = 0.026) was found for percent canopy cover > 2 m above 1 m x 1 m quadrats with and without S. parksii, with a mean of 55 percent with S. parksii and 97 percent without S. parksii. A Non-Metric Multidimensional Scaling ordination revealed three different combinations of herbaceous species that occur with S. parksii, which were driven by the presence of three dominant bunch grasses of the Post Oak Savannah: Schizachyrium scoparium, Chasmanthium laxum var. sessiliflorum, and Andropogon ternarius. A close to significant difference (p = 0.07) was found for the leaf litter depth between quadrats with and without S. parksii, with a fewer number of stacked leaves with S. parksii. Analysis of aerial images indicated woody encroachment on Twin Oaks from 1958 to 2004 in areas that have not been mechanically cleared. Additionally, S. parksii was found to persist in an open savannah landscape and likely occurred in the same locations and more widespread in 1958 than are currently found. Transplantation of S. parksii was documented to be successful by a soil-intact method. While a bare-root method showed success with S. cernua, no conclusions can be made of its success for S. parksii due to a low sample size (n = 10).

Anthropogenic activities are responsible for increases in atmospheric CO₂ and climate change. These increases are partly counterbalanced by natural processes, such as carbon uptake in land surfaces. These processes are themselves subject to climate change, creating a coupled carbon-climate system. I investigated the carbon sink that woody encroachment represents, using a Central Texas savanna as study site, and studied how climatic factors influence this carbon sink. Woody plant encroachment, a worldwide structural change in grassland and savanna ecosystems, alters many ecosystem properties, but the net effect on the carbon balance is uncertain. Woody encroachment represents one of the key uncertainties in the US carbon balance, and demands a more detailed understanding. To come to a process-based understanding of the encroachment effect on carbon dynamics, I analyzed patterns of carbon exchange using eddy-covariance technology. I expected the imbalance between carbon uptake and release processes associated with the encroaching trees specifically, to be responsible for the carbon sink. I also expected that the sink would vary in time, due to strong links between carbon fluxes and soil water in this semi-arid ecosystem. I further studied the ecophysiology of the dominant species, as well as soil respiration processes under different vegetation types, and scaled these findings in space and time. I found that the ecosystem was a significant carbon sink of 405 g C m⁻² yr⁻¹. The encroaching trees increased photosynthesis by 180% and decreased soil respiration by 14%, compared to the grassland, resulting in a strong carbon sink due to the encroachment process. The encroaching process also altered carbon dynamics in relation to climatic drivers. The evergreen species Ashe juniper effectively lengthened the growing season and widened the temperature range over which the ecosystem acts as a carbon sink. The drought resistance of the encroaching trees reduced the sensitivity of this savanna to drought. I conclude that encroachment in Central Texas savannas increased the carbon sink strength by increasing the carbon inputs into the ecosystem. Woody encroachment also reduced the sensitivity to climatic drivers. These two effects constitute a direct effect, as well as a negative feedback to the coupled carbon-climate system. / text

River-groundwater exchange (hyporheic exchange) influences temperature, water chemistry, and ecology within rivers and alluvial aquifers. Rates and patterns of hyporheic exchange depend on riverbed permeability, pressure gradients created by current-obstacle interactions, and river stage fluctuations. I demonstrate the response of hyporheic exchange to three examples of these driving forces: fine-scale permeability structure in cross-bedded sediment, current interactions with large woody debris (LWD), and anthropogenic river stage fluctuations downstream of dams. Using numerical simulations, I show that cross-bedded permeability structure increases hyporheic path lengths and modifies solute residence times in bedforms. The tails of residence time distributions conform to a power law in both cross-bedded and internally homogeneous riverbed sediment. Current-bedform interactions are responsible for the decade-scale tails, rather than permeability heterogeneity. Like bedforms, wood debris interacts with currents and drives hyporheic exchange. Laboratory flume experiments and numerical simulations demonstrate that the amplitude of the pressure wave (and thus hyporheic exchange) due to a channel-spanning log increases with channel Froude number and blockage ratio (log diameter : flow depth). Upstream from LWD, downwelling water transports the river’s diel thermal signal deep into the sediment. Downstream, upwelling water forms a wedge of buffered temperatures. Hyporheic exchange associated with LWD does not significantly impact diel surface water temperatures. I tested these fluid and heat flow relationships in a second-order stream in Valles Caldera National Preserve (NM). Log additions created alternating zones of upwelling and downwelling in a reach that was previously losing throughout. By clearing LWD from channels, humans have reduced hydrologic connectivity at the meter-scale and contributed to degradation of benthic and hyporheic habitats. Dams also significantly alter hydrologic connectivity in modern rivers. Continuous water table measurements show that 15 km downstream of the Longhorn dam (Austin, Texas), river stage fluctuations of almost 1 m induce a large, unsteady hyporheic exchange zone within the bank. Dam-induced hyporheic exchange may impact thermal and geochemical budgets for regulated rivers. Together, these three case studies broaden our understanding of complex drivers of hyporheic exchange in small, natural streams as well as large, regulated rivers. / text

Forest managers concerned with maintaining soil productivity must consider the impacts of forestry practices upon the features of a site. One critical feature is the amount and type of organic matter on a site, which may affect soil development. This study addresses the question of whether CWD accumulations increase the intensity of podzolization, thus reducing the long-term productivity of a site.

Few field studies have assessed the temporal and spatial dynamics of wood in small streams (bankfull widths < 5 m) flowing through forest ecosystems dominated by stand replacing wildfires. Comparisons of instream wood loads associated with clearcut harvesting, wildfire, and undisturbed, old forests are also scarce. The two main objectives of this research were: (1) to document the temporal and spatial variability of wood and its geomorphic role in relation to stand development stage; and (2) to compare wood loads and its geomorphic role in relation to streamside clearcut harvesting, wildfires and older, undisturbed forest stands. This research focused on 38 small streams with gradients less than 14% situated in the plateau regions of south-central British Columbia, Canada. A distinct temporal trend in wood loading was observed, with elevated volumes present 30-50 years subsequent to the wildfire disturbances following a “reverse J-shaped” trend in relation to time since the last major wildfire disturbance. The number of wood pieces was highly variable and few of the wood characteristics exhibited a significant trend in relation to time since the last major wildfire disturbance. Except at the smallest spatial scale (<3 m segments longitudinally along the stream) the spatial distribution of wood followed a random pattern with no trend, indicating that wood loads are related to local wood recruitment processes associated with episodic or chronic tree mortality and low wood transport. Instream wood volumes were three times higher in streams recently (30 – 50 years ago) disturbed by wildfire as compared to the older riparian forest stands, confirming that wildfire disturbance is an important mechanism to recruit wood into streams. No significant differences in wood loads were identified between the streamside clearcut streams and the wildfire-disturbed or older, undisturbed streams. The lack of reductions in wood loads are likely related to the low transport capacity of our study streams, retention of non-merchantable trees and recruitment of slash from harvesting. A lack of morphologic variability was observed in relation to the disturbances indicating that the streams included in this study are relatively robust and unresponsive to wildfire or streamside clearcut harvesting disturbances.

Issues of regulated streams naturalization were analyzed in the dissertation. Subject of the research was the streams regulated for drainage purposes in a hilly relief region of the Southeast Lithuania. Self-naturalization was researched only in plain relief. Since naturalization processes are running differently, it was decided to evaluate them in a hilly relief in the region of the Southern Lithuania. Researches of regulated streams are important due to the fact, that naturalization of regulated streams with growing woody vegetation on the slopes of a stream bed almost does not decrease its hydraulic conductivity but helps to restore regime of natural flows and restore damaged aqueous ecosystems at the same times. The main target of the research is to determine regularities of self-overgrowth of regulated streams with woody vegetation and assess influence of its distribution on bed’s hydraulic conductivity and flood dynamics. Following tasks are solved in the work: regularities of woody vegetation specie composition, frequency, density distribution, influence of woody and grass vegetation on regulated stream’s hydraulic conductivity. The dissertation is composed of introduction, five chapters, general conclusions, recommendations. Introduction describes relevance of the problem, aim of the work, tasks are introduced, scientific novelty of the work is described, presentations on scientific conferences and publications are introduced. Chapter one is dedicated for analysis of... [to full text] / Disertacijoje nagrinėjami reguliuotų upelių natūralizacijos klausimai. Tyrimo objektas yra Pietryčių Lietuvos sausinimo reikmėms reguliuoti upeliai, esantys kalvoto reljefo regione. Savaiminė natūralizacija tirta tik lyguminiame reljefe. Kadangi natūralizacijos procesai vyksta skirtingai, nuspręsta įvertinti juos kalvotame Pietryčių Lietuvos regione. Reguliuotų upelių tyrimai svarbūs tuo, kad reguliuotų upelių natūralizacija, sumedėjusiai augalijai augant ant upelio vagos šlaitų, beveik nemažina jų hidraulinio laidumo, tačiau padeda atkurti natūralių tėkmių režimą ir tuo pačiu atstatyti pažeistas vandens ekosistemas. Pagrindinis tyrimų tikslas – nustatyti reguliuotų upelių savaiminio apaugimo sumedėjusia augalija dėsningumus ir įvertinti jos pasiskirstymo įtaką vagos hidrauliniam laidumui bei potvynių dinamikai. Darbe sprendžiami šie uždaviniai: sumedėjusios augalijos rūšinės sudėties, dažnio, tankio pasiskirstymo dėsningumai, sumedėjusios ir žolinės augalijos poveikis reguliuotų upelių hidrauliniam laidumui. Disertaciją sudaro įvadas, penki skyriai, bendrosios išvados, rekomendacijos. Įvadiniame skyriuje nagrinėjamas problemos aktualumas, pateiktas darbo tikslas, uždaviniai, aprašomas mokslinis darbo naujumas, pristatomi mokslinių konferencijų pranešimai ir publikacijos. Pirmasis skyrius skirtas natūralių upelių reguliavimo tendencijoms analizuoti. Apibūdintas augalijos plitimas reguliuotuose upeliuose, jų įtaka hidrauliniam vagos laidumui. Antrajame skyriuje pateikta... [toliau žr. visą tekstą]

Disertacijoje nagrinėjami reguliuotų upelių natūralizacijos klausimai. Tyrimo objektas yra Pietryčių Lietuvos sausinimo reikmėms reguliuoti upeliai, esantys kalvoto reljefo regione. Savaiminė natūralizacija tirta tik lyguminiame reljefe. Kadangi natūralizacijos procesai vyksta skirtingai, nuspręsta įvertinti juos kalvotame Pietryčių Lietuvos regione. Reguliuotų upelių tyrimai svarbūs tuo, kad reguliuotų upelių natūralizacija, sumedėjusiai augalijai augant ant upelio vagos šlaitų, beveik nemažina jų hidraulinio laidumo, tačiau padeda atkurti natūralių tėkmių režimą ir tuo pačiu atstatyti pažeistas vandens ekosistemas. Pagrindinis tyrimų tikslas – nustatyti reguliuotų upelių savaiminio apaugimo sumedėjusia augalija dėsningumus ir įvertinti jos pasiskirstymo įtaką vagos hidrauliniam laidumui bei potvynių dinamikai. Darbe sprendžiami šie uždaviniai: sumedėjusios augalijos rūšinės sudėties, dažnio, tankio pasiskirstymo dėsningumai, sumedėjusios ir žolinės augalijos poveikis reguliuotų upelių hidrauliniam laidumui. Disertaciją sudaro įvadas, penki skyriai, bendrosios išvados, rekomendacijos. Įvadiniame skyriuje nagrinėjamas problemos aktualumas, pateiktas darbo tikslas, uždaviniai, aprašomas mokslinis darbo naujumas, pristatomi mokslinių konferencijų pranešimai ir publikacijos. Pirmasis skyrius skirtas natūralių upelių reguliavimo tendencijoms analizuoti. Apibūdintas augalijos plitimas reguliuotuose upeliuose, jų įtaka hidrauliniam vagos laidumui. Antrajame skyriuje pateikta... [toliau žr. visą tekstą] / Issues of regulated streams naturalization were analyzed in the dissertation. Subject of the research was the streams regulated for drainage purposes in a hilly relief region of the Southeast Lithuania. Self-naturalization was researched only in plain relief. Since naturalization processes are running differently, it was decided to evaluate them in a hilly relief in the region of the Southern Lithuania. Researches of regulated streams are important due to the fact, that naturalization of regulated streams with growing woody vegetation on the slopes of a stream bed almost does not decrease its hydraulic conductivity but helps to restore regime of natural flows and restore damaged aqueous ecosystems at the same times. The main target of the research is to determine regularities of self-overgrowth of regulated streams with woody vegetation and assess influence of its distribution on bed’s hydraulic conductivity and flood dynamics. Following tasks are solved in the work: regularities of woody vegetation specie composition, frequency, density distribution, influence of woody and grass vegetation on regulated stream’s hydraulic conductivity. The dissertation is composed of introduction, five chapters, general conclusions, recommendations. Introduction describes relevance of the problem, aim of the work, tasks are introduced, scientific novelty of the work is described, presentations on scientific conferences and publications are introduced. Chapter one is dedicated for analysis of... [to full text]

Ozonation has been utilized for water treatment for over 100 years. During that time, the range of applications has grown considerably, and includes the remediation of nursery and greenhouse irrigation water. Ozone is dissolved into irrigation water to kill pathogens and degrade chemical contaminants. By convention, growers remove ozone from solutions, prior to distribution to the crop, to avoid phytotoxic effects. The available literature regarding aqueous ozone (O3(aq)) phytotoxicity is limited, making this a sagacious practice, although the removal does preclude any ancillary benefits beyond the point of treatment. The effects of applying O3(aq) under two irrigation systems are examined. Initial studies suggested O3(aq) concentrations as high as 20 mg⋅L-1 could be applied directly to mineral wool substrate in a limited (one time) fashion without a negative response. To be effective as a remediation tool, however, ozone would need to be applied more frequently (e.g. daily). The effects of daily O3(aq) application, via drip irrigation in mineral wool hydroponic tomato culture, was examined. In the first of two studies, daily applications of 3.0 mg⋅L-1 O3(aq) elicited an overall positive growth response. In a follow-up study, 6.0 mg L-1 elicited a negative response. Nursery operators often utilize overhead irrigation. A study was conducted to determine if overhead irrigation utilizing O3(aq) was compatible with select woody perennial nursery species. The amount of ozone lost from solution during application was examined, as well as crop response to the ozone environment generated. It was shown that 60 to 70% of the ozone was unaccounted for at canopy level, while phytotoxic effects were elicited at emitter concentrations above 1.5 mg L-1. Marchantia polymorpha is a significant weed species in greenhouse and nursery production; a species with few control options. Anatomical features of M. polymorpha suggested sensitivity to O3(aq). Studies were performed to examine contact time (CT) and exposure frequencies required for M. polymorpha suppression. A CT of 0.84 mg⋅L-1⋅min at an application frequency of 3-times/week achieved measurable suppression. / Natural Science and Engineering Research Council (NSEARC); Ontario Ministry of Agriculture Food and Rural Affairs (OMAFRA); Ontario Centres of Excellence (OCE); Purification Research Technologies INC (PRTI); Flowers Canada (Ontario).