College of Agriculture & Natural Resources
Permanent URI for this communityhttp://hdl.handle.net/1903/1598
The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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Item Urbanization Altered Bacterial and Archaeal Composition in Tidal Freshwater Wetlands Near Washington DC, USA, and Buenos Aires, Argentina(MDPI, 2019-03-06) Gonzalez Mateu, Martina; Park, Cedric Evan; McAskill, Cullen Patrick; Baldwin, Andrew H.; Yarwood, Stephanie A.Urban expansion causes coastal wetland loss, and environmental stressors associated with development can lead to wetland degradation and loss of ecosystem services. This study investigated the effect of urbanization on prokaryotic community composition in tidal freshwater wetlands. Sites in an urban, suburban, and rural setting were located near Buenos Aires, Argentina, and Washington D.C., USA. We sampled soil associated with two pairs of functionally similar plant species, and used Illumina sequencing of the 16S rRNA gene to examine changes in prokaryotic communities. Urban stressors included raw sewage inputs, nutrient pollution, and polycyclic aromatic hydrocarbons. Prokaryotic communities changed along the gradient (nested PerMANOVA, Buenos Aires: p = 0.005; Washington D.C.: p = 0.001), but did not differ between plant species within sites. Indicator taxa included Methanobacteria in rural sites, and nitrifying bacteria in urban sites, and we observed a decrease in methanogens and an increase in ammonia-oxidizers from rural to urban sites. Functional profiles in the Buenos Aires communities showed higher abundance of pathways related to nitrification and xenobiotic degradation in the urban site. These results suggest that changes in prokaryotic taxa across the gradient were due to surrounding stressors, and communities in urban and rural wetlands are likely carrying out different functions.Item Urbanization Altered Bacterial and Archaeal Composition in Tidal Freshwater Wetlands Near Washington DC, USA, and Buenos Aires, Argentina(MDPI, 2019-03-06) Gonzalez Mateu, Martina; Park, Cedric Evan; McAskill, Cullen Patrick; Baldwin, Andrew H.; Yarwood, Stephanie A.Urban expansion causes coastal wetland loss, and environmental stressors associated with development can lead to wetland degradation and loss of ecosystem services. This study investigated the effect of urbanization on prokaryotic community composition in tidal freshwater wetlands. Sites in an urban, suburban, and rural setting were located near Buenos Aires, Argentina, and Washington D.C., USA.We sampled soil associated with two pairs of functionally similar plant species, and used Illumina sequencing of the 16S rRNA gene to examine changes in prokaryotic communities. Urban stressors included raw sewage inputs, nutrient pollution, and polycyclic aromatic hydrocarbons. Prokaryotic communities changed along the gradient (nested PerMANOVA, Buenos Aires: p = 0.005; Washington D.C.: p = 0.001), but did not differ between plant species within sites. Indicator taxa included Methanobacteria in rural sites, and nitrifying bacteria in urban sites, and we observed a decrease in methanogens and an increase in ammonia-oxidizers from rural to urban sites. Functional profiles in the Buenos Aires communities showed higher abundance of pathways related to nitrification and xenobiotic degradation in the urban site. These results suggest that changes in prokaryotic taxa across the gradient were due to surrounding stressors, and communities in urban and rural wetlands are likely carrying out different functions.Item Cumulative impacts of stream burial on network structure and functional connectivity in headwater stream systems(2015) Weitzell, Jr, Roy Everett; Elmore, Andrew J; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Stream burial is common during urbanization, and disproportionately affects headwater streams. Burial undermines the physical, chemical, and spatial processes governing aquatic life, with consequences for water quality and biodiversity, both within headwaters and in downstream waters. Network changes associated with headwater burial have not been explored, limiting our understanding of changes in biotic composition with urbanization of these critical ecosystems. To address this need, I predicted stream burial across the Potomac River Basin (PRB) from impervious cover data and training observations from high-resolution aerial photography. Results across the PRB urban gradient reveal consistent burial patterns related to catchment area and topographic slope. I discuss these results in the context of physiographic constraints on stream location and urban development, including implications for management of aquatic resources. Second, I examined burial-related changes to headwater network structure and habitat connectivity, using a series of topological and distance measures, and a novel application of circuit-theoretical modeling to stream networks. Results show stream burial significantly affects both the number and size of remnant stream segments and their spatial orientation. Significant decreases in landscape connectivity were observed with burial, around ecologically important features such as confluences, and for urbanized headwater systems as a whole. Third, I used biological data to compare environmental and spatial controls on species turnover in fish and insect communities across headwater systems. Turnover was analyzed using generalized dissimilarity modeling, which accommodates variation in rates of species turnover along and between gradients, and two novel measures of resistance distance, which combine aspects of space and environment, specifically the spatial extent, orientation, and relative favorability of habitat across the landscape. Results show headwater species are more sensitive to environmental parameters, with less mobile species more sensitive to habitat fragmentation and required dispersal distances. Rapid compositional turnover occurred within short distances from the sampled reaches, suggesting headwater taxa disperse only short distances, with even small obstructions or habitat loss having potential to impact diversity within headwater systems. Knowledge gained from this research is critical for understanding the cumulative impact to stream networks, and for future decision-making allowing for urban development while protecting stream ecosystem function.Item THE EFFECTS OF FUTURE GLOBAL CHANGE ON ARBUSCULAR MYCORRHIZAL FUNGI AND SOIL CARBON: USING URBANIZATION AS A SURROGATE FOR FUTURE CONDITIONS IN FIELD STUDIES(2012) Wolf, Julie; Needelman, Brian; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Carbon, fixed photosynthetically by plants, cycles through plant, microbial biomass, soil, and atmospheric carbon pools. The effects of global change on this cycling will impact future levels of atmospheric carbon dioxide, but are poorly understood. In urban areas, temperature and carbon dioxide concentrations are often elevated to levels that simulate near-future climate changes. These elevations are not sudden, uniform step increases but are gradual and variable; as such urbanization may provide a means to simulate the effects of near-future climate changes. The dissertation research encompasses two studies utilizing urban macroclimate to study the effects of future climate change. In the first study, plots containing a common imported soil and seed bank were established at three locations along a 50 km urban-to-rural transect. In these plots, plant community development, temperature, carbon dioxide concentrations, and other factors had been monitored for five years. Subsequently, arbuscular mycorrhizal fungal structures in bulk soil were quantified. These fungi receive carbon directly from plant roots, grow into bulk soil, and can transfer immobile soil minerals to their plant hosts. In contrast to expectations, fewer fungal structures were found closer to the urban side of the transect. The second study was an observational study of soil carbon in minimally managed, long-undisturbed soils located at varying distances from urban areas. In sampling sites at 62 golf courses, similar communities of cool-season grasses had been undisturbed for at least 25 years. At each site, total and active soil carbon and many potential explanatory factors were measured and examined with multiple regression analysis. Contrary to expectations, soil carbon was positively correlated with warmer February-only mean daily minimum soil temperatures, suggesting that winter temperatures are more important than mean annual temperature for soil C storage in temperate grassland. Other correlations, including positive correlations with soil cation exchange capacity, soil lead levels, and tropospheric ozone exposure during the peak ozone season, were also detected. Potential mechanisms for the detected relationships are explored. The results of both experiments demonstrate that commonly-held expectations based on single-factor global change experiments or models are not always borne out in complex natural systems.