Biology
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Item NUTRIENT RETENTION BY RIPARIAN FORESTED BUFFERS IN WESTERN MARYLAND: DO THEY WORK AND ARE THEY WORTH IT?(2021) Siemek, Stephanie Melissa; Eshleman, Keith N; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Riparian buffers are a best management practice (BMP) implemented to improve water quality. In 1997, Maryland established the Conservation Reserve Enhancement Program (CREP) to give landowners incentives to install riparian buffers that would help restore the Chesapeake Bay. Although many studies support riparian buffers as a BMP, many have also reported a wide range of nutrient reductions. It is uncertain what factors control buffer function, yet they continue to be installed with high expectations. Water quality predictions become less accurate in hydrogeologically complex systems such as the Ridge and Valley (R&V) physiographic province. The purpose of this research was to assess the riparian buffer’s nutrient removal function of dissolved nitrogen and phosphorus in the R&V to understand the hydrologic controls further. Throughout western Maryland, we conducted two synoptic stream chemistry studies that contained forest buffers planted under CREP and a range of pre-existing natural forested riparian zones. We used a steady-state reach mass balance model to estimate lateral groundwater inputs and tested several nutrient models to describe the nutrients in groundwater discharge. We then aimed to understand if incentives given through CREP to landowners were adequate by performing a benefit-cost analysis (BCA) using three scenarios. We used the BCA results to estimate nutrient reduction costs using results from the Chesapeake Bay Watershed Model (CBWM) and our synoptic studies. Streams along CREP sites did not show strong evidence of nutrient retention. However, those containing a mix of natural forests with planted buffers showed significant nutrient declines in both synoptic studies. Several models tested (i.e., The Nature Conservancy model, Gburek and Folmar (1999), our base model) inadequately described nutrient discharge; however, our actual flow model performed best. Our BCA results found newly planted forest buffers under CREP provide the greatest financial gains to landowners, but grass buffers are the most cost-effective practice based on CBWM’s estimated nutrient reductions. Although our research did not assess grass buffers, our synoptic studies showed little indication that newly planted forest buffers significantly reduce nutrients in the R&V, suggesting stream water quality greatly depends on the watershed’s hydrogeomorphology that controls how major contributing sources filter through the landscape.Item Phenology of cyanobacterial blooms in three catchments of the Laurentian Great Lakes(2020) Wynne, Timothy; Hood, Raleigh R; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation discusses the cyanobacterial bloom phenology in three anthropogenically impacted regions of the Great Lakes: western Lake Erie, Saginaw Bay, and Green Bay. A detection algorithm was applied to ocean color satellite imagery, and a timeseries was constricted from each of the basins using either data from the MODIS sensor (Saginaw Bay), the MERIS sensor (Green Bay), or a combination of the two (western Lake Erie). The sensors have a high temporal resolution, collecting imagery several times a week. The algorithm used, the Cyanobacterial Index (CI), was applied to the imagery. The CI imagery was then sampled into fifteen 10-day composites throughout the bloom season (defined here as June 1 – October 31). Each of the five months will have three composites (each spanning ~10 days). From this point the bloom climatology is shown and the variability of each region is addressed. The interannual variability of the cyanobacterial blooms can be low (factor of ~2 in Saginaw Bay) or high (differing by a factor of ~20 in Green Bay and western Lake Erie). Various ancillary datasets describing the physical environment of each region were assembled including: field data, modeled data, remotely sensed data, or some combination therein. Impacts of associated cyanobacterial biotoxins were addressed and statistical models were formulated to explain any variability. The dissertation will also cross compare the three basins with one another in an effort to determine the similarities as well as differences among the regions. Management recommendations are given at the end of each of the three subsequent chapters to deter potential detrimental impacts of the blooms and their associated toxins.Item EFFECTS OF THE INVASIVE PHRAGMITES AUSTRALIS ON THE PREDATION OF MOSQUITOES THROUGH CHANGES IN HABITAT COMPLEXITY(2019) Weeks, Virginia Lynn; Leisnham, Paul; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Ephemeral stormwater ponds in the eastern United States are often invaded by non-native Phragmites australis which has been associated with numerous negative impacts on resident systems, including changes in hydrology, displacement of native macrophytes, and degradation of wildlife habitat. Few studies have documented the impacts of invasive P.australis on macroinvertebrate communities. Vegetated edges of stormwater retention facilities are often important developmental habitat for medically significant mosquitoes and the invertebrate predators that regulate their abundances. The displacement of resident macrophytes by P.australis could alter the physical structure of pond vegetation and disrupt the interactions between mosquitoes and their visual predators. The overall goal of my thesis was to evaluate differences in habitat complexity between native macrophytes, T.latifolia and J.effuses, and P.australis, and explore how those differences may impact predation of mosquitoes. I addressed this goal by conducting a controlled laboratory predation experiment and field surveys of four stormwater ponds.Item SUGARCANE AGRICULTURE AS AN AGENT OF GEOMORPHIC CHANGE AND STREAM DEGRADATION IN BRAZIL(2017) Ometto Bezerra, Maira; Palmer, Margaret A; Filoso, Solange; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Intensive agriculture profoundly alters the geomorphology, hydrology and nutrient balances of catchments. The result is the degradation of headwater stream ecosystems via inputs of excess sediments, surface runoff, and nutrients. To mitigate the negative effects on streams, watershed managers can implement riparian buffers, which are designed to intercept, process, store, and remove excess material from upslope agricultural source areas. While extensive research on those topics exists for temperate regions of developed countries, little is known in tropical regions of developing countries. To address this knowledge gap, I investigated the effects of sugarcane agriculture on catchment geomorphology and headwater stream ecosystems in Brazil. I studied 11 first and second order catchments spanning a sugarcane-forest gradient near Piracicaba, SP, to answer three main questions. (1) Is sugarcane agriculture an important agent of geomorphological change via gully formation? (2) Does gully formation influence the effectiveness of riparian buffers while increasing the stream response to storm events, and the amount of sediment in high flows? (3) Can land cover history in terms of sugarcane, and forest cover explain the variability in stream nutrient (nitrogen and phosphorus) concentrations? The overall results suggest that sugarcane agriculture is a driver of geomorphic alteration via gully formation in small order catchments in Brazil. Gullies act as effective conduits of surface runoff from upslope source areas to streams, increasing the magnitude of the stream’s response to storms and the amount of sediment transported in high flows. Consequently, gully formation may overwhelm any protective role played by riparian buffers. Sugarcane agriculture also increases stream nutrient concentrations to a point rarely recorded for streams draining intensive cropping in Brazil. However, there is little evidence that forested riparian buffers significantly mitigates the extent to which sugarcane agriculture affects stream nutrient concentrations. Additional policies to the restoration of riparian forests are needed to effectively protect headwater streams in Brazil.Item Using landscape metrics to predict hydrologic connectivity patterns between forested wetlands and streams in a coastal plain watershed(2016) Epting, Steven Michael; Palmer, Margaret A; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Geographically isolated wetlands, those entirely surrounded by uplands, provide numerous ecological functions, some of which are dependent on the degree to which they are hydrologically connected to nearby waters. There is a growing need for field-validated, landscape-scale approaches for classifying wetlands based on their expected degree of connectivity with stream networks. During the 2015 water year, flow duration was recorded in non-perennial streams (n = 23) connecting forested wetlands and nearby perennial streams on the Delmarva Peninsula (Maryland, USA). Field and GIS-derived landscape metrics (indicators of catchment, wetland, non-perennial stream, and soil characteristics) were assessed as predictors of wetland-stream connectivity (duration, seasonal onset and offset dates). Connection duration was most strongly correlated with non-perennial stream geomorphology and wetland characteristics. A final GIS-based stepwise regression model (adj-R2 = 0.74, p < 0.0001) described wetland-stream connection duration as a function of catchment area, wetland area and number, and soil available water storage.Item Developing Numeric Nutrient Criteria for Streams on the Delmarva Peninsula(2016) Tempinson, Lindsay Ayn; Fisher, Thomas R.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)To better address stream impairments due to excess nitrogen and phosphorus and to accomplish the goals of the Clean Water Act, the U.S. Environmental Protection Agency (EPA) is requiring states to develop numeric nutrient criteria. An assessment of nutrient concentrations in streams on the Delmarva Peninsula showed that nutrient levels are mostly higher than numeric criteria derived by EPA for the Eastern Coastal Plain, indicating widespread water quality degradation. Here, various approaches were used to derive numeric nutrient criteria from a set of 52 streams sampled across Delmarva. Results of the percentile and y-intercept methods were similar to those obtained elsewhere. Downstream protection values show that if numeric nutrient criteria were implemented for Delmarva streams they would be protective of the Choptank River Estuary, meeting the goals of the Chesapeake Bay Total Maximum Daily Load (TMDL).Item Spatial and Temporal Dynamics of Larval Atlantic Menhaden on the East Coast of the United States(2016) Simpson, Cara; Wilberg, Michael J; Bi, Hongsheng; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Atlantic Menhaden Brevoortia tyrannus is a commercially and ecologically important forage fish abundant on the Atlantic Coast of the United States. We conducted spatial and temporal analyses of larval Atlantic Menhaden using data collected from two large-scale ichthyoplankton programs during 1977-1987 and 1999-2013 to construct indices of larval abundance and survival over time, evaluate how environmental factors affect early life survival, and examine how larvae are distributed in space to gain knowledge on spawning and larval dispersal. Over time, we found larval abundance to increase, while early life survival declined. Coastal temperature, wind speed, and Atlantic Multidecadal Oscillation were found to potentially explain some of this decline in survival. Over both periods, we found evidence spawning predominantly occurs near shore, from New York to North Carolina, increasing in intensity southwards. While the general spatial patterns were consistent, we observed some localized variation and overall expansion of occupied area by larvae.Item Nitrogen Uptake and Denitrification in Restored and Degraded-Urban Streams: Impacts of Organic Carbon and Integrated Stormwater Management(2015) Newcomer Johnson, Tamara Ann; Kaushal, Sujay S.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Managing the N cycle and restoring urban infrastructure are major challenges especially in urban ecosystems. Organic carbon is important in regulating ecosystem function and its source and abundance may be altered by urbanization. My research focused on urban-degraded, restored, and forested watersheds at the Baltimore LTER in the Chesapeake Bay watershed. In Chapter 2, I investigated shifts in organic carbon quantity and quality associated with urbanization and ecosystem restoration, and its potential effects on denitrification at the riparian-stream interface. Denitrification enzyme assay experiments showed carbon was limiting in hyporheic sediments and variable carbon sources (grass clippings, decomposing leaves, and periphyton) stimulated denitrification differently. Evidence from stable isotopes, molar C:N ratios, and lipid biomarkers suggested that urbanization can influence organic carbon sources and quality in streams, which may have substantial downstream impacts on ecosystem services such as denitrification. In Chapter 3, I investigated whether stormwater best management practices (BMPs) integrated into restored and degraded urban stream networks can influence watershed N loads. I hypothesized that hydrologically connected floodplains and stormwater BMPs are “hot spots” for N retention through denitrification because they have ample organic carbon, low dissolved oxygen levels, and high residence time. I used reach-scale nitrogen mass balances, in-stream tracer injection studies, and 15N in situ denitrification to measure N retention in stormwater BMPs and their larger stream networks. There were high rates of in situ denitrification in both stormwater BMPs and floodplain features. Hydrologically connected floodplains can be important “hot spots” for N retention at a watershed and stream network scale because these areas likely receive perennial flow through the groundwater-surface water interface during both baseflow and storm events, while BMPs only receive intermittent flow associated with storm events. In Chapter 4, I conducted a literature review of N retention within hydrologically reconnected streams and floodplains. I reviewed 79 stream and floodplain restoration empirical studies from North America, Europe, and Asia and found that methods for measuring N retention varied considerably. I found many diverse strategies for promoting the ecosystem function of N retention in urban and agricultural watersheds.Item Monitoring levels of dissolved methane and metals in Maryland streams overlying the Marcellus Shale prior to hydraulic fracturing(2015) Coulter, Caroline; Schijf, Johan; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In western Maryland above the Marcellus Shale, 25 streams were monitored for baseline concentrations of dissolved CH4, Sr2+, and Ba2+, constituents that may be affected by fracking activity. Migrated shale CH4 may intrude streams, and Sr2+ and Ba2+ may be introduced by fracking fluid leakages or spills. Stream constituents were also measured in Maryland’s coastal plain for reference. In western Maryland, CH4 concentrations are significantly variable yet in agreement with concentrations reported for other North American pristine rivers. Measurements of δ13C-CH4 suggest CH4 is primarily biogenic. Dissolved Sr2+ and Ba2+ are spatially and temporally variable, although Sr/Ba ratios are relatively stable at most sites, indicating these may be useful fracking fluid tracers. Major ions Na+, K+, Mg2+, Ca2+, Cl−, SO42-, and HCO3– were measured. These were elevated relative to Sr2+ and Ba2+ and are not suitable fracking fluid tracers. Major ions were highly variable, indicative of variable bedrock geology in western MD.Item INTERACTIONS BETWEEN CHEMICAL, PHYSICAL, AND BIOLOGICAL PROCESSES DURING DESERTIFICATION OF GROUNDWATER-DEPENDENT SEMI-ARID GRASSLANDS(2015) Gardner, Kimberly Vest; Elmore, Andrew J; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Desertification is estimated to cost $26 billion per year through loss of agricultural production, water reserves, and air quality. Semi-arid grasslands are prone to desertification through many factors including groundwater pumping. Groundwater pumping below the root-zone of groundwater-dependent vegetation leads to a decrease in vegetation cover exposing bare soil to wind erosion. Desertification of semi-arid grasslands can lead to a permanent change in vegetation state. Identifying when and where ecological changes are irreversible is problematic, requiring observations of a new ecological state that favors the continued process of wind erosion and depletion of soil resources. To determine biological, physical, and chemical processes affecting desertification in semi-arid groundwater-dependent grasslands, I examined hydrological and ecological factors across groundwater-dependent meadows in Owens Valley, California. I developed and compared empirical, process-based, and mechanistic models that predict mass transport. I found that scaled gap size explains 56% of the variation in total horizontal flux (Q), and the process-based model predicts Q better than the mechanistic model indicating the importance of scaled gap size in wind erosion modeling of heterogeneous vegetation. I explored the role of landscape connectivity of bare soil in enhancing Q and quantifying the magnitude of desertification across the landscape using circuit theory and Qrule. I found that landscapes that were more connected than neutral landscapes with the same bare soil cover were associated with groundwater decline during the drought and greater Q. This is consistent with the idea that the enhanced formation of connected pathways is evident at plots that arrived at a particular bare-soil cover via groundwater decline and wind erosion, rather than another process. I analyzed vegetation structure and monitored Q, air quality data, and PM10 emissions to evaluate the relationship between meadow degradation and air quality. I found that management practices have generated a new mid-valley meadow source of PM10 pollution. These results provide information and tools for resource managers of groundwater-dependent semi-arid grasslands to identify areas degraded by wind erosion, producing Q and PM10, and prone to desertification. Managers can use the information and tools to better gauge a well-field's health and adjust the amount pumped from wells.