• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 49
  • 23
  • 4
  • 2
  • 2
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 90
  • 19
  • 18
  • 16
  • 15
  • 13
  • 11
  • 11
  • 10
  • 10
  • 9
  • 9
  • 9
  • 8
  • 8
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Effects of grazing and nitrogen enrichment on the taxonomic structure of periphyton assemblages in lotic ecosystems

Lundberg, Chris H. 10 December 1996 (has links)
Graduation date: 1997
2

Spatial and temporal variation in greenhouse gas emissions from two open water prairie wetlands

Phipps, Kimberly Jennette 19 October 2006
Prairie wetlands provide valuable habitat for waterfowl and wildlife and buffer the impacts of upland land uses. Their contribution to Canadas greenhouse gas inventory is poorly understood. The purpose of this study was to compare the spatial and temporal variation in nitrous oxide (N2O), carbon dioxide (CO2), and methane (CH4) emissions from Pond 1 at the St. Denis Wildlife Management Area, Saskatchewan and the Deep Crop Wetland (DCW) at the Manitoba Zero Tillage Research Association farm, Manitoba. Nitrous oxide flux was low on all measurements days: at Pond 1 flux ranged from -1.47 to 6.01 ng N2O-N m-2 s-1 in 2004 and -6.98 to 5.74 ng N2O-N m-2 s-1 in 2005 and flux from the DCW never exceeded 2.50 ng N2O-N m-2 s-1 in 2005. Methane flux from Pond 1 was substantially higher in 2005 (-469.10 to 3776.08 µmol CH4 m-2 d-1) than in 2004 (-251.55 to 191.55 µmol CH4 m-2 d-1). This increase in methane from Pond 1 followed a major increase in water volume in 2005 after snowmelt. Methane flux in 2005 from the open water and riparian sampling points at the DCW ranged from -13.64 to 110.47 µmol CH4 m-2 d-1 and -4.51 to 40.23 µmol CH4 m-2 d-1, respectively. Carbon dioxide flux from Pond 1 and the DCW in 2005 were very similar: open water flux ranged from -96.42 to 95.42 mmol CO2 m-2 d-1 at Pond 1 and 3.21 to 38.94 mmol CO2 m-2 d-1 at the DCW. Despite the similarity in CO2 flux, the DCW had 10- to 15-fold higher levels of macrophytes, phytoplankton and metaphyton biomass and similar levels of periphyton to Pond 1 in 2005. These biomass differences were not, however, reflected in the CO2 or CH4 flux. Pond 1 and the DCW were net sources for greenhouse gases but contributed less greenhouse gas than reports from other aquatic systems.
3

Effects of substrate relief, light intensity and herbivory on the distribution and abundance of periphyton in laboratory streams

DeNicola, Dean M. 26 April 1990 (has links)
Graduation date: 1991
4

Spatial and temporal variation in greenhouse gas emissions from two open water prairie wetlands

Phipps, Kimberly Jennette 19 October 2006 (has links)
Prairie wetlands provide valuable habitat for waterfowl and wildlife and buffer the impacts of upland land uses. Their contribution to Canadas greenhouse gas inventory is poorly understood. The purpose of this study was to compare the spatial and temporal variation in nitrous oxide (N2O), carbon dioxide (CO2), and methane (CH4) emissions from Pond 1 at the St. Denis Wildlife Management Area, Saskatchewan and the Deep Crop Wetland (DCW) at the Manitoba Zero Tillage Research Association farm, Manitoba. Nitrous oxide flux was low on all measurements days: at Pond 1 flux ranged from -1.47 to 6.01 ng N2O-N m-2 s-1 in 2004 and -6.98 to 5.74 ng N2O-N m-2 s-1 in 2005 and flux from the DCW never exceeded 2.50 ng N2O-N m-2 s-1 in 2005. Methane flux from Pond 1 was substantially higher in 2005 (-469.10 to 3776.08 µmol CH4 m-2 d-1) than in 2004 (-251.55 to 191.55 µmol CH4 m-2 d-1). This increase in methane from Pond 1 followed a major increase in water volume in 2005 after snowmelt. Methane flux in 2005 from the open water and riparian sampling points at the DCW ranged from -13.64 to 110.47 µmol CH4 m-2 d-1 and -4.51 to 40.23 µmol CH4 m-2 d-1, respectively. Carbon dioxide flux from Pond 1 and the DCW in 2005 were very similar: open water flux ranged from -96.42 to 95.42 mmol CO2 m-2 d-1 at Pond 1 and 3.21 to 38.94 mmol CO2 m-2 d-1 at the DCW. Despite the similarity in CO2 flux, the DCW had 10- to 15-fold higher levels of macrophytes, phytoplankton and metaphyton biomass and similar levels of periphyton to Pond 1 in 2005. These biomass differences were not, however, reflected in the CO2 or CH4 flux. Pond 1 and the DCW were net sources for greenhouse gases but contributed less greenhouse gas than reports from other aquatic systems.
5

Natural stream flow fields measurements and implications for periphyton /

Stone, Mark Charles, January 2005 (has links) (PDF)
Thesis (Ph.D. in civil engineering)--Washington State University. / Includes bibliographical references.
6

Diversity and community organization in the periphyton of recirculating stream channels are fined by current velocity and nutrient supply

Larson, Chad A. January 2009 (has links)
Thesis (Ph.D.)--University of Texas at Arlington, 2009.
7

Toxicant-releasing substrates : a new method for delivering copper to microbial communities in SITU /

Arnegard, Matthew E., January 1993 (has links)
Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 125-126). Also available via the Internet.
8

The ecology of the nuisance macroalga, Cladophora glomerata, and its resurgence in Lake Ontario

Malkin, Sairah January 2007 (has links)
Cladophora glomerata is the dominant spring and summer epilithic macroalga in the lower Laurentian Great Lakes, and was a notorious nuisance prior to nutrient management of the early 1970s. It is an indicator of excessive nutrient supply and appears to be experiencing a resurgence in the nearshore of the lower Great Lakes. This thesis examines the ecology of C. glomerata in an urbanized location of Lake Ontario and addresses decadal scale environmental changes to the lake and their impact on this macroalga. A Cladophora growth model (CGM) was calibrated and validated to simulate attached and sloughed Cladophora biomass using two years of collected input data and independent measurements of Cladophora biomass. The CGM was used to hindcast Cladophora growth using multiplicative factors of seasonal minimal tissue phosphorus concentrations (QP) and seasonal mean nearshore light attenuation (KdPAR) of the early 1970s and 1980s relative to contemporary data. Cladophora QP in Lake Ontario is currently lower than in the early 1980s, resulting in reduced Cladophora biomass at all depths in the euphotic zone. KdPAR has also declined, most strongly since the mid-1990s, following Dreissena mussel invasion, driving an increase in macroalgal biomass between 3.5 and 10 m depth. Combining these effects, the CGM predicted that biomass is currently lower in Lake Ontario than in the early 1980s. However, increases in QP in this post-dreissenid mussel period are predicted to result in greater Cladophora proliferation than in previous decades due to increased nearshore water clarity. The in situ rates of primary production on Cladophora-dominated rocky substrata at 1m depth were measured through the spring and summer. Net primary production (NPP) was measured as change in dissolved inorganic carbon (using IRGA) in benthic incubation chambers flushed continuously with water. Incubations were of 15- 20 minutes duration, permitting measurements of productivity rates over diurnal and seasonal scales. Maximum biomass-specific net photosynthetic rates (PBmax) were highest in the spring and late-summer/fall (2.39, 1.98 mgC gDM-1 hr-1, respectively) and decreased to negative rates by early summer (−0.76 mgC gDM-1 hr-1). Directly measured rates of net primary production were simulated with the CGM. Simulated depth-integrated rates of Cladophora primary production were compared with published depth-integrated measurements of planktonic primary production from Lake Ontario. From the shoreline to the 12 m depth contour, the benthos was estimated to contribute 70% of the areal primary production. On a seasonal basis, attached macroalgae are an important component of the energy flux in the Lake Ontario nearshore. This phenology of Cladophora glomerata growing in the western end of Lake Ontario is also described. Based on internal stoichiometric ratios (C:P and N:P), and a positive correlation between the decrease in the biomass-specific maximum photosynthetic rate (PBm) and phosphorus quota (QP), Cladophora productivity at shallow depths was shown to be P limited. In addition, light attenuation through the Cladophora canopy was estimated to be 24.1 ± 3.3 (standard deviation) m-1 using paired light loggers deployed in situ. Acclimation to lower light levels through the Cladophora stand was demonstrated by significantly higher Cladophora chlorophyll concentrations at the base of the canopy. Decreases in Cladophora canopy cover in the summer resulted in increased PBm, even when QP remained near the minimal cell quota, indicating potential co-limitation of Cladophora productivity by light during peak standing crop. Cladophora growing at 1m depth was also shown here to be tolerant of high irradiance, with an average decline of less than 10% in Fv/Fm at during peak midday insolation, regardless of nutrient status or ambient water temperature. In conjunction with its role as a seasonally important nearshore primary producer, Cladophora appears to play a role as a seasonal nutrient regulator in the nearshore of Lake Ontario. The nutrient chemistry of nearshore lake water, Cladophora tissue, and a dominant tributary to western Lake Ontario were examined over the growing season of 2 years. As Cladophora grew and assimilated nutrients in the spring, total phosphorus (TP) and soluble reactive P (SRP) concentrations declined in the nearshore. Detachment and sloughing of Cladophora in the late summer was associated with increasing TP in the water column. These changes in nearshore nutrient concentrations were correlated with Cladophora phenology and not catchment loading. Nutrient loading from Oakville Creek was compared with the nutrient uptake of an adjacent Cladophora stand. The TP supply directly from the creek during the growing season was insufficient to meet the concentration of stored P in Cladophora tissue. It appears Cladophora is growing on P regulated by recycling within the lake, supporting the hypothesis that dreissenid mussels are sustaining Cladophora growth through recycling of TP in the lake. Cladophora remains P limited, however, such that increases in catchment loading would further augment its resurgence.
9

The ecology of the nuisance macroalga, Cladophora glomerata, and its resurgence in Lake Ontario

Malkin, Sairah January 2007 (has links)
Cladophora glomerata is the dominant spring and summer epilithic macroalga in the lower Laurentian Great Lakes, and was a notorious nuisance prior to nutrient management of the early 1970s. It is an indicator of excessive nutrient supply and appears to be experiencing a resurgence in the nearshore of the lower Great Lakes. This thesis examines the ecology of C. glomerata in an urbanized location of Lake Ontario and addresses decadal scale environmental changes to the lake and their impact on this macroalga. A Cladophora growth model (CGM) was calibrated and validated to simulate attached and sloughed Cladophora biomass using two years of collected input data and independent measurements of Cladophora biomass. The CGM was used to hindcast Cladophora growth using multiplicative factors of seasonal minimal tissue phosphorus concentrations (QP) and seasonal mean nearshore light attenuation (KdPAR) of the early 1970s and 1980s relative to contemporary data. Cladophora QP in Lake Ontario is currently lower than in the early 1980s, resulting in reduced Cladophora biomass at all depths in the euphotic zone. KdPAR has also declined, most strongly since the mid-1990s, following Dreissena mussel invasion, driving an increase in macroalgal biomass between 3.5 and 10 m depth. Combining these effects, the CGM predicted that biomass is currently lower in Lake Ontario than in the early 1980s. However, increases in QP in this post-dreissenid mussel period are predicted to result in greater Cladophora proliferation than in previous decades due to increased nearshore water clarity. The in situ rates of primary production on Cladophora-dominated rocky substrata at 1m depth were measured through the spring and summer. Net primary production (NPP) was measured as change in dissolved inorganic carbon (using IRGA) in benthic incubation chambers flushed continuously with water. Incubations were of 15- 20 minutes duration, permitting measurements of productivity rates over diurnal and seasonal scales. Maximum biomass-specific net photosynthetic rates (PBmax) were highest in the spring and late-summer/fall (2.39, 1.98 mgC gDM-1 hr-1, respectively) and decreased to negative rates by early summer (−0.76 mgC gDM-1 hr-1). Directly measured rates of net primary production were simulated with the CGM. Simulated depth-integrated rates of Cladophora primary production were compared with published depth-integrated measurements of planktonic primary production from Lake Ontario. From the shoreline to the 12 m depth contour, the benthos was estimated to contribute 70% of the areal primary production. On a seasonal basis, attached macroalgae are an important component of the energy flux in the Lake Ontario nearshore. This phenology of Cladophora glomerata growing in the western end of Lake Ontario is also described. Based on internal stoichiometric ratios (C:P and N:P), and a positive correlation between the decrease in the biomass-specific maximum photosynthetic rate (PBm) and phosphorus quota (QP), Cladophora productivity at shallow depths was shown to be P limited. In addition, light attenuation through the Cladophora canopy was estimated to be 24.1 ± 3.3 (standard deviation) m-1 using paired light loggers deployed in situ. Acclimation to lower light levels through the Cladophora stand was demonstrated by significantly higher Cladophora chlorophyll concentrations at the base of the canopy. Decreases in Cladophora canopy cover in the summer resulted in increased PBm, even when QP remained near the minimal cell quota, indicating potential co-limitation of Cladophora productivity by light during peak standing crop. Cladophora growing at 1m depth was also shown here to be tolerant of high irradiance, with an average decline of less than 10% in Fv/Fm at during peak midday insolation, regardless of nutrient status or ambient water temperature. In conjunction with its role as a seasonally important nearshore primary producer, Cladophora appears to play a role as a seasonal nutrient regulator in the nearshore of Lake Ontario. The nutrient chemistry of nearshore lake water, Cladophora tissue, and a dominant tributary to western Lake Ontario were examined over the growing season of 2 years. As Cladophora grew and assimilated nutrients in the spring, total phosphorus (TP) and soluble reactive P (SRP) concentrations declined in the nearshore. Detachment and sloughing of Cladophora in the late summer was associated with increasing TP in the water column. These changes in nearshore nutrient concentrations were correlated with Cladophora phenology and not catchment loading. Nutrient loading from Oakville Creek was compared with the nutrient uptake of an adjacent Cladophora stand. The TP supply directly from the creek during the growing season was insufficient to meet the concentration of stored P in Cladophora tissue. It appears Cladophora is growing on P regulated by recycling within the lake, supporting the hypothesis that dreissenid mussels are sustaining Cladophora growth through recycling of TP in the lake. Cladophora remains P limited, however, such that increases in catchment loading would further augment its resurgence.
10

Periphyton growth in the Waipara River, North Canterbury

Hayward, Shirley January 2003 (has links)
Periphyton was monitored monthly at four sites on the Waipara River from July 1999 to January 2002. Interactions with river flows, nutrients and invertebrates were examined to determine how these factors controlled periphyton development. Comparison of the Waipara River to other New Zealand streams indicated that periphyton biomass at the uppermost site (Site 1) was generally low to moderate. Further downstream, moderate to high biomass occurred at sites 2 and 4. Biomass at Site 3 was generally low, although some very high values occurred on occasions. Periphyton biomass at sites 2 and 4 exceeded periphyton guidelines for the protection of aesthetic/recreational values at least once during each full year monitored. In contrast, the guidelines were rarely exceeded at Site 1. Dissolved inorganic nutrients were generally poor indicators of the nutrient status of the river because of plant uptake. Cellular N and P values indicated nutrient enrichment at sites 2 and 4, which correspondingly had the highest biomass values. Conductivity tended to positively correlate with temporal and spatial patterns in periphyton biomass and was useful as a surrogate indicator of nutrient supply regimes. It correlated negatively with river flows, indicating higher nutrient concentrations may occur during reduced flows. Notable differences occurred in biomass development between periods of contrasting flow regimes. In particular, annual mean and maximum biomass at the three downstream sites was considerably higher during a period of low stable flows compared to a period of higher base flows. However, at the uppermost site, differences in biomass between these periods were much less pronounced. Invertebrate densities increased significantly with increasing periphyton biomass at the three downstream sites. There was little indication that invertebrates had any major control on periphyton biomass at these sites. However, at the uppermost site, although the invertebrate densities were generally much lower than at the other sites, they are more likely to have a controlling influence on periphyton biomass. Overall, the nutrient supply regime of the Waipara River is the primary controller on biomass development. Flow regimes (both frequency of disturbance and extent of low flows) operate as secondary controls of biomass.

Page generated in 0.1405 seconds