Biology

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    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.
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    TWO MARINE SPONGES, LENDENFELDIA CHONDRODES AND HYMENIACIDON HELIOPHILA, AND THEIR MICROBIAL SYMBIONTS: ROLES IN MARINE PHOSPHORUS CYCLING.
    (2021) Jonas, Lauren; Hill, Russell; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Marine sponges have emerged as major players within coral reef biogeochemical cycles, facilitating intake and release of carbon, nitrogen, and phosphorus. The majority of studies have investigated the role of sponges in transforming dissolved carbon and nitrogen; however, the same breadth of insights has not been extended to phosphorus. This study uses 32P-labeled orthophosphate and ATP to determine that two marine sponges, Lendenfeldia chondrodes and Hymeniacidon heliophila, both rapidly take up ambient dissolved inorganic phosphate and dissolved organic phosphorus. Subsequent genetic analysis and chemical extraction showed that sponge symbionts store phosphorus in the form of energy-rich polyphosphate (poly-P). L. chondrodes, a sponge from oligotrophic habitats and with a microbiome dominated by cyanobacterial symbionts, stores more phosphorus as poly-P (6–8%) than H. heliophila (0.55%), a eutrophic sponge with low cyanobacterial abundance. This work adds new insights to the roles of the sponge holobiont in cycling the crucial element, phosphorus.
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    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.
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    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.
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    Sediment Biogeochemistry Across the Patuxent River Estuarine Gradient: Geochronology and Fe-S-P Interactions
    (2007-12-21) OKeefe, Jennifer; Cornwell, Jeffrey C; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Although salinity and redox gradients are defining features of estuarine biogeochemistry, compositional changes in sediment characteristics associated with these factors are poorly described in U.S. coastal plain estuaries. Understanding the basics of nutrient sources and sinks, in the context of these defining characteristics, is required to make efficient and effective management decisions regarding estuarine eutrophication. In this study, detailed analysis of long-term nutrient burial has been used as a tool to understand the trajectory of nutrient cycling at 7 stations along an oligohaline to mesohaline transect in the Patuxent River estuary. Sediment mass accumulation rates were determined for 3 of the 7 sites. Cores analyzed for total P, total N, organic C, biogenic silica, δ13C, and δ15N did not provide evidence of historical nutrient reduction actions taken in this watershed. Burial rates of Fe-S mineral phases and inorganic P (IP) indicated pyrite formation limited the availability of Fe-oxides for adsorption and retention of IP.
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    Nutrient Removal by Tidal Fresh and Oligohaline Marshes in a Chesapeake Bay Tributary
    (2005-11-22) Greene, Sarah E; Boynton, Walter R; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Located at the interface between estuaries and surrounding uplands, tidal marshes are in position to receive and transform material from both adjacent systems. Of particular importance in eutrophic estuarine systems, tidal marshes permanently remove nutrients via two mechanisms - denitrification and long-term burial. Denitrification was measured (monthly) in two marshes in a Chesapeake Bay tributary for 7 months, using the MIMS technique. Burial of nitrogen (N) and phosphorus (P) was measured using 210Pb techniques. Strong spatial and temporal patterns emerged, and there was a Michaelis-Menten type response in denitrification rates to experimentally elevated nitrate levels. Denitrification rates measured may account for removal of 22% of N inputs to the upper estuary on an annual basis. Burial rates could account for 30% of N inputs and 60% of P inputs. Based on the cost of nutrient control technologies, Patuxent marsh nutrient removal may be valued at $10 to 30 million yr-1.
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    Vegetation and Nutrient Dynamics of Forested Riparian Wetlands in Agricultural Settings
    (2005-05-03) Herbert, Rachel; Baldwin, Andrew H; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Exported agricultural nutrients have been a major supply of excess nutrients into the environment. Riparian wetlands may play an important part in mitigating these nutrients and thus preventing them from migrating downstream in high concentrations. Two riparian wetland systems, one was influenced by agriculture (agricultural site) and one was not (reference site), were studied in Maryland. Both the plant community structure and abiotic factors were studied. The agricultural site had lower overall species richness and tree diversity than the reference site. Also the tree leaf litter and herbaceous leaves at the agricultural site had higher nitrogen and phosphorus concentrations and higher productivity based on fixed carbon than the reference site. Two nutrient enrichment experiments were conducted at the reference site to determine the nature of nutrient limitation. The results from these studies indicate that both plant communities are nitrogen limited. Furthermore, individual species showed a response to increased nutrients.