Theses and Dissertations from UMD

Permanent URI for this communityhttp://hdl.handle.net/1903/2

New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM

More information is available at Theses and Dissertations at University of Maryland Libraries.

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    LEAF-ASSOCIATED PERIPHYTON IN HETEROTROPHIC STREAMS: EFFECT ON MACROINVERTEBRATE ASSEMBLAGES AND GROWTH
    (2020) Eckert, Rebecca A; Lamp, William O; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Temperate headwater streams are often shaded, limiting autochthonous production, and therefore energetically supported by allochthonous material, e.g., leaves, via fungal and bacterial decomposition. Macroinvertebrate shredders feed on this leaf matrix, providing food for other organisms. Recent work indicates that periphyton (e.g., diatoms, green algae, cyanobacteria; hereafter, algae) interacts with microbial decomposers and provides higher quality food. Little work has, however, examined these interactions in natural settings. I investigated leaf-associated algae’s impact on macroinvertebrate leaf colonization in the field, followed by measuring growth and food preferences in the lab based on field results. First, I manipulated leaf light availability in high- and low-nutrient streams in winter and spring. Leaf-associated algal and fungal biomass were positively correlated in winter. Leaf C:N negatively correlated to algae in winter and fungi in spring, while N:P and C:P negatively correlated to fungi in winter and algae in spring. These factors predicted functional feeding guild biomass and abundance, e.g., predator biomass by algal and fungal biomass and spring shredder biomass by leaf stoichiometry. Algal biomass elicited differential taxon responses; e.g., Ephemerella (Ephemeroptera:Ephemerellidae) and Stenonema (Ephemeroptera:Heptageniidae) responded positively while Tipula (Diptera:Tipulidae) responded negatively. Second, I fed light- and dark-conditioned leaves to Ephemerella invaria and Caecidotea communis (Isopoda:Asellidae), which both consumed leaves and algae. C. communis experienced greater growth on light-conditioned leaves, indicating a high-quality resource, while E. invaria had no growth differences between treatments. Third, light- and dark-conditioned leaves were offered to five taxa, Amphinemura (Plecoptera:Nemouridae), Tipula, Stenonema, Lepidostoma (Trichoptera:Lepidostomatidae), and Caecidotea communis. Tipula alone demonstrated a preference which was for dark-conditioned leaves. These results indicate that leaf-associated algae are a food resource and attractant for some macroinvertebrates and a deterrent to others. Natural headwater streams are heterogeneous with leaves exposed to varying light levels, altering leaf-associated algae and providing differential food resources. Anthropogenic impacts often homogenize these streams. Although restoration seeks to restore heterogeneity, headwater stream algae are largely ignored. This work demonstrates the important role algae play in macroinvertebrate interactions with senescent leaves, highlighting the need to incorporate allochthonous and autochthonous resources into stream restoration and management efforts to support biodiversity.
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    Denitrification, N2O emissions, and nutrient export in Maryland coastal plain streams
    (2014) Gardner, John Robert; Fisher, Thomas R; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Small streams are hotspots for denitrification, emissions of a potent greenhouse gas nitrous oxide (N2O), and are also highly connected to their watersheds via groundwater flowpaths. In-stream, reach scale denitrification and N2O production as well as biogenic nitrogen gases delivered by groundwater were investigated in one small agriculturally impacted watershed. Groundwater was an important source of biogenic N2, but most N2O was produced in-stream and emissions were relatively high. In addition, agricultural streams significantly contribute to nutrient loading and degradation of downstream aquatic ecosystems. Export and transport mechanisms of nitrogen and phosphorus were investigated during base and stormflow in three watersheds with varying amounts of agricultural and forested land use. Quickflow, which is associated with storms, transported most of the phosphorus and ammonium in the agricultural watersheds, but quickflow had little impact on nutrient concentrations and export in the forested watershed.