Biology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2749
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Item Characterizing nutrient budgets on and beyond farms for sustainable nutrient management(2023) Zou, Tan; Zhang, Xin; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The production and security of food are heavily reliant on adequate nitrogen (N) and phosphorus (P) inputs in agriculture. However, ineffective management of N and P from the farm to the table can result in nutrient pollution, triggering both environmental and social issues. Moreover, another important challenge for P management is limited and unevenly distributed P resources, leading to P scarcity in many parts of the world. Inefficient use of nutrients in agriculture-food systems is the root cause of both nutrient pollution and scarcity. To improve nutrient use efficiency and reduce nutrient loss, it is crucial to address key knowledge gaps in nutrient management research, which include inadequate quantification of nutrient budgets, as well as identifying and addressing nutrient management challenges across various systems and spatial scales. This dissertation tackles the knowledge gaps in two studies, including a global-scale study and a case study of the Chesapeake Bay watershed. In the global-scale study, I establish and utilize a unique P budget database to assess historical P budget and usage patterns at the national and crop type level from 1961 to 2019. This analysis reveals the impacts of various agricultural and socioeconomic drivers on cropland P use efficiency (PUE), including N use efficiency (NUE), fertilizer-to-crop-price ratio, farm size, crop mix, and agricultural machinery. The findings indicate that P management challenges vary by country and spatial scale, necessitating tailored country-level strategies. The regional-scale study applies a framework adapted from N studies to the Chesapeake Bay watershed, analyzing nutrient (N and P) management across systems and spatial scales. This approach uncovers that nutrient loss potential beyond crop farms is larger than that at crop farms. This highlights the need to enhance nutrient management and curb nutrient loss in animal production, food processing and retail, and human consumption. This study also identifies a large potential for meeting cropland nutrient demand by increasing the recycling of nutrients in manure, food waste, and human waste. To tackle the challenges surrounding nutrient management in the watershed, it is imperative to target factors significantly related to nutrient management, such as agricultural practices, soil properties, climate change, and socioeconomic conditions. This dissertation contributes to a deeper understanding of N and P management challenges, gaps, priorities, hidden drivers, and potential solutions at various scales, from regional to national and global levels. The analytical procedures and statistical tools developed in this dissertation are generalizable, allowing for their adaptation to similar nutrient management studies in different regions and for diverse research purposes.Item PHYTOPLANKTON AND NUTRIENT DYNAMICS WITH A FOCUS ON NITROGEN FORM IN THE ANACOSTIA RIVER, IN WASHINGTON, D.C. AND WEST LAKE, IN HANGZHOU, CHINA(2016) Jackson, Melanie Leigh; Glibert, Patricia M.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Nutrient loading has been linked with severe water quality impairment, ranging from hypoxia to increased frequency of harmful algal blooms (HABs), loss of fisheries, and changes in biodiversity. Waters around the globe are experiencing deleterious effects of eutrophication; however, the relative amount of nitrogen (N) and phosphorus (P) reaching these waters is not changing proportionately, with high N loads increasingly enriched in chemically-reduced N forms. Research involving two urban freshwater and nutrient enriched systems, the Anacostia River, USA, a tributary of the Potomac River feeding into the Chesapeake Bay, and West Lake, Hangzhou, Zhejiang Province, China, was conducted to assess the response of phytoplankton communities to changing N-form and N/P-ratios. Field observations involving the characterization of ambient phytoplankton communities and N-forms, as well as experimental (nutrient enrichment) manipulations were used to understand shifts in phytoplankton community composition with increasing NH4+ loads. In both locations, a >2-fold increase in ambient NH4+:NO3- ratios was followed by a shift in the phytoplankton community, with diatoms giving way to chlorophytes and cyanobacteria. Enrichment experiments mirrored this, in that samples enriched with NH4+ lead to increased abundance of chlorophytes and cyanobacteria. This work shows that in both of these systems experiencing nutrient enrichment that NH4+ supports communities dominated by more chlorophytes and cyanobacteria than other phytoplankton groups.Item Ecosystem dynamics in tidal marshes constructed with fine grained, nutrient rich dredged material(2015) Staver, Lorie Winchell; Stevenson, J. Court; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)An ecological study was undertaken of the tidal marshes at Poplar Island, a restoration project utilizing fine grained dredged material from the shipping channels in upper Chesapeake Bay. The goals of the study were to examine the effect of a nutrient rich substrate on vegetation development, elevation change, and nutrient cycling in the constructed tidal marshes. Specifically, I examined macrophyte production, nitrogen (N), carbon (C) and silicon (Si) budgets, as well as the success of a silica amendment in enriching plant tissue concentrations. Establishment of Spartina alterniflora and S. patens on fine grained dredged material was rapid, and growth peaked in the second year. Thereafter S. alterniflora dieback occurred sporadically during the growing season, but the causes remain unclear. Elevation change averaged 7.9 ±0.8 mm y-1 in the dredged material marshes (low marsh only), compared to 7.4 ±1.4 mm y-1 in a low nutrient onsite reference marsh. Elevation change was significantly correlated with biomass production suggesting that inputs of organic matter from high rates of aboveground biomass production on nutrient rich dredged material offset the reduced contribution of belowground biomass to vertical accretion. However, dieback may have a detrimental effect on vertical accretion, which is essential for keeping up with apparent sea level rise (13.6 and 11.0 mm y-1 at Baltimore and Solomon’s tide gauges, respectively) since elevation monitoring began at Poplar Island. The tidal flux study revealed that the marsh exports ~665 kg of N y-1, including 100 kg NH4+-N y-1, and 67,874 kg y-1 TSS, and imports 35 kg NO3-N y-1. Silicon is also exported on both a seasonal and annual basis, including 4,337 kg dissolved Si y-1 and 3,924 kg biogenic Si y-1, with highest exports in July, an overlooked benefit of dredged material restoration projects. Soil Si amendments increased plant tissue concentrations significantly, but this study did not show increased resistance to N related stress effects on the vegetation. Overall, this study suggests that when considering trajectories of vegetation development, nutrient exchanges and elevation change in constructed marshes, it is essential to consider the initial nitrogen content of the substrate.Item Physiological responses of Acartia and Eurytemora spp. to changes in the nitrogen:phosphorus quality of their food(2014) Bentley, Katherine Marie; Glibert, Patricia; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This study addressed how copepods respond to varying nutrient content in their prey. Copepod physiological responses were measured along a gradient of prey nitrogen:phosphorus (N:P) ratios created by altering the P content in diatom prey grown at a constant rate. Acartia tonsa, a broadcast spawner, and Eurytemora carolleeae, a brood spawner, increased excretion of P as prey N:P declined (i.e. P increased). E. carolleeae had higher somatic tissue nutrient content, while A. tonsa had higher egg nutrient content overall and higher P in eggs as N:P decreased. E. carolleeae egg production was greatest when eating high N:P prey while A. tonsa showed the opposite. Egg viability declined at high N:P for both copepods, yet A. tonsa viability was always greater than E. carolleeae viability. Both copepods responded physiologically to food of varying quality, yet regulated their homeostasis differently. Prey nutrient content may be significant in the environmental selection of different copepods.Item 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.Item EVALUATION OF THE INFLUENCE OF NITROGEN ON PRIMARY PRODUCTION USING RETROSPECTIVE DATA, REGRESSION ANALYSIS, AND MODELING(2012) Ziombra, Katherine Elizabeth Davis; Harris, Lora A; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Anthropogenic activities have negatively affected water quality in the Chesapeake Bay and its tributaries. The Potomac River (PR), the largest tributary, is a primary study site for water quality research and new management strategies. The Blue Plains Wastewater Treatment Plant (BP), located in the tidal fresh portion of the PR, is the largest total nitrogen (TN) point source. Retrospective examination of water quality data for the PR revealed relationships among discharge, N loading and concentration, light and primary production. Regression analysis revealed BP (TN) load was an important variable influencing production, coupled with local dissolved inorganic nitrogen concentrations and photic depth prior to installation of biological nutrient removal (BNR) at BP. After 100% BNR implementation, BP TN did not influence production. Four existing primary production models were evaluated for applicability to tidal fresh systems. Regression analysis demonstrated all models were significant but the BZpI0t model provided the most robust results.Item Importance of channel networks on nitrate retention in freshwater tidal wetlands, Patuxent River, Maryland(2009) Seldomridge, Emily Dawn; Prestegaard, Karen; Cornwell, Jeffrey C; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Freshwater tidal marshes border stream channels near the upstream end of the tidal limit, and are likely to undergo significant changes in salinity, tidal inundation, and biogeochemical processes due to sea-level rise. Tidal channel networks enhance nutrient processing by delivering nitrate-rich water far into the marsh. The purpose of this study is to examine the geomorphological, hydrological, and biogeochemical processes that influence the delivery and processing of nutrient-rich waters into tidal marshes. In this study, field measurements were made to calculate water and nitrate flux for stream channels of varying order. These mass balance calculations indicate there is an exponential increase in net nitrate retention with channel order. This calculation could be compared with calculations of denitrification at different sites within the system to evaluate the role of these processes in total nitrate loss.Item Hydrologic and Biogeochemical Storm Response in Choptank Basin Headwaters(2008) Koskelo, Antti; Fisher, Thomas R; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This study quantified the effect of hydric soils on the hydrology and biogeochemistry of sub-watersheds across the Delmarva Peninsula. For hydrology, long-term data were compiled for 13 United States Geological Survey sites and evaluated for hydric soil effects. Results show that hydric soils reduce baseflow by increasing ponding and subsurface water storage, resulting in greater evapotranspiration. In contrast, hydric soils were unrelated to stormflow, which was instead driven by topography. During hourly sampling of 18 storms in the Choptank Basin, most forms of nitrogen and phosphorus increased in concentration due to erosion and re-suspension of sediments. Nitrate, however, decreased during storms due to dilution of nitrate-rich groundwater by runoff. Baseflow nitrate concentrations decreased with forested hydric soils, likely due to greater denitrification in forested hydric areas. Annually, much of the total nitrogen and phosphorus export occurred during storms, emphasizing the need to sample a wide range of flows to improve estimates of nutrient losses.Item Comparative Ecological Modeling for Long-term Solution of Excess Nitrogen Loading to Surface Waters and Related Chronic and Systemic Human-Environment Problems(2007-04-25) Fiscus, Daniel Avery; Ulanowicz, Robert E; Gates, J Edward; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Concurrent environmental problems including 1) excess CO2 emissions and climate change, 2) excess nitrogen export and eutrophication of surface waters, and 3) dependence on non-renewable fossil fuel energy supplies can be considered interdependent symptoms of a single systemic "humans in the environment disorder". This dissertation presents results from three integrated research projects to frame and solve this general human-environmental problem. As an interdisciplinary whole, the projects help define and characterize organizing principles for future human-environment systems without major carbon (C), nitrogen (N), energy and related problems. Forests and other non-human ecosystems provide model systems, as these communities self-sustain for 10,000 years and longer. Comparative studies of soils, C and N emissions, and food web networks provide transferable principles to guide local action for sustainability. Soils in long-term forest land-use stored more C and organic matter than soils in long-term agricultural use. These results recommend permaculture, agroforestry and perennial agriculture to provide food and other human needs while building soil and enhancing soil fertility. Audits of the Appalachian Laboratory in Frostburg, MD, showed this environmental science facility causes emissions of 70 times more C and 60 times more N than local forests can absorb. The Lab also is 99% dependent on non-renewable energy sources. This study provides data necessary to alter operations toward environmental sustainability. Comparisons of the U.S. beef supply network showed unusually high network ascendency (a whole-system efficiency measure), higher dependency on a few compartments and lower network connectance than four non-human food webs. Results support efforts to increase U.S. food supply reliability via local agriculture and diversified food network pathways. Overall, the research identifies a systemic cultural cause of the human-environment crisis in subordination of environmental value, quality and capacity to values in economic, social, scientific and other arenas. Elevation of environmental value to equal standing with other human values thus promises a solution to the global ecological crisis. Realization of such a cultural paradigm shift likely requires revisions to fundamental scientific definitions, theories and understanding of life, evolution and ecology, all of which now operate with a predominantly organismal model of life that likewise de-emphasizes the environment.Item Eutrophication and coastal wetlands: Linking nutrient enrichment to tidal freshwater marsh ecosystem structure and function(2006-07-27) Egnotovich, Michael Steven; Ulanowicz, Robert E.; Baldwin, Andrew H.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The Chesapeake Bay watershed has been affected by human activities for over 300 years, causing an increase in nutrients entering its coastal aquatic ecosystems. Yet most of the efforts identifying the consequences of coastal eutrophication have not observed its effects on the marginal tidal wetlands of the Bay. The tidal freshwater marshes of Broad Creek and Marshyhope Creek, two tidal tributaries of the Nanticoke River (Delmarva Peninsula, USA), have been exposed to different levels of nutrient input, that appear to be adversely affecting Broad Creek. The Broad Creek watershed has had historically higher fertilizer application rates and more animal production facilities than Marshyhope Creek, both of which have been linked to increased availability of nutrients in coastal ecosystems. This study collected emergent macrophytes and aquatic macrofauna of tidal freshwater marshes in these two creeks from 2000 through 2002. Analysis of plant community composition indicated that Broad Creek had fewer plant species than Marshyhope Creek, yet greater overall plant biomass. Comparisons of nekton in the two creeks determined that there were more fish and macroinvertebrate species, individuals and biomass in Marshyhope Creek. Multivariate analysis identified strong seasonal patterns that extended across both creeks in floral and faunal distributions, but also suggested that animal abundance patterns were related to the creeks. Ecological network analysis suggested both creeks appear to be resistant to environmental stressors, but probably lack resilience. Broad Creek, however, had higher levels of total ecosystem activity than Marshyhope Creek, although ecosystem organization and development was similar between both creeks, suggesting nutrient enrichment in Broad Creek but not necessarily eutrophication. Stable isotope analysis indicated that the nitrogen circulating through Broad Creek is more enriched in 15N than Marshyhope Creek, although both creeks have enriched nitrogen signatures. Nevertheless, the high d15N in Broad Creek is indicative of larger nitrogen inputs to the system originating from animal waste. These results, however, must be tempered by an acknowledgement of the effects of a severe drought that caused an increase in salinity from October 2001 through August 2002, affecting animal and plant abundance throughout 2002.