As the world's population shifts toward living in cities, urbanization and its deleterious effects on the environment are a cause of increasing concern. The hyporheic zone is an important part of stream ecosystems, and here we focus on the effect of urbanization on the hyporheic zone from ten first-to-second-order streams within the Virginia Piedmont. We use sediment hydraulic conductivity and stream geomorphic complexity (vertical undulation of thalweg, channel sinuosity) as metrics of the potential for hyporheic exchange (hyporheic potential). Our results include bivariate plots that relate urbanization (e.g., total percent impervious) with hyporheic potential at several spatial scales. For example, at the watershed level, we observed a decrease in horizontal hydraulic conductivity with urbanization and an increase in vertical hydraulic conductivity, which ultimately results in a negligible trend from conflicting processes. Vertical geomorphic complexity increased with total percent impervious cover. This trend was somewhat unexpected and may be due to erosion of legacy sediment in stream banks. At the reach level, hydraulic conductivity increased and sinuosity decreased as the riparian buffer width increased; these trends are weak and are essentially negligible. The hydraulic conductivity results conform to expected trends and are a product of aforementioned concomitant processes. Our results emphasize the complexity of hydrologic and geomorphic processes occurring in urban stream systems at multiple scales. Overall, the watershed level effects enhancing hyporheic exchange, which is contrary to expectations. Given the importance of hyporheic exchange to stream function, further study is warranted to better understand the effects of urbanization. / Master of Science

Detailed information about negative effects of fine sediments on early life stages of brook trout (Salvelinus fontinalis) in southern Appalachian streams is lacking. Information on survival to different stages of egg and alevin development could indicate critical timing of sediment impacts. This study was designed to determine the effects of fine sediments (0.43-0.85 rom in diameter) on survival of brook trout eggs through early development stages under controlled laboratory and field conditions. Recently fertilized eggs were loaded into Whitlock-Vibert (W-V) boxes lined with 0.4 rom Nitex netting that contained mixtures of gravel and fine sediments. Survival to eyed, hatched, and emerged stages of development was determined for six amounts of fine sediment (0-25% by weight) in the laboratory study and for three amounts of fine sediment (0-20% by weight) in the field study. Survival in laboratory systems to each stage of development was inversely related to the percentage of fine sediment; even at low levels of fine sediment survival was reduced. In the field study, fine sediment may have played a role in the survival success of developing embryos, but determining a definitive relationship was confounded by effects of scouring flows and fungal infestations. The fungus Saprolegnia spp., may have increased the mortality rate of viable eggs and facilitated the disintegration of nonviable embryos, especially in the field study. Brook trout are sensitive to increasing levels of fine sediment through early development. However under field conditions such an effect may be difficult detect. / Master of Science

This study compared physical characteristics used when selecting comparison (healthy) watersheds for the All-Forested Load Multiplier (AllForX) Approach, and examined a quantitative watershed characteristic as a selection criterion. The AllForX Approach uses a regression relationship between Virginia Stream Condition Index (VSCI) scores and AllForX values (a unit-less multiplier that is the ratio of a modeled existing sediment load divided by a modeled all-forested load condition) for an impaired watershed and several comparison watersheds to develop sediment TMDL target loads. The Generalized Watershed Loading Function (GWLF) model was used to simulate sediment loads for 20 watersheds (four impaired and 16 comparison) in the Upper James and New River basins in Virginia's Ridge and Valley physiographic region. Results suggest that within Virginia's Ridge and Valley physiographic region it may be possible to select comparison watersheds that are of a different stream order (watershed size) and lie in different river basins from the impaired watershed. Results further indicated that the topographic index (TI) distributions were not different across the modeled watersheds, indicating the watersheds are hydrologically similar. These results support selecting comparison watersheds regardless of river basin or stream order within Virginia's Ridge and Valley physiographic region. Finally, there was no statistical difference between the AllForX regressions when using the entire period of record or the two most recent VSCI data points. Therefore, for the watersheds modeled for this study, either all of the VSCI samples or the two most recent may be used in the AllForX Approach. / Master of Science

In 2016 the Panama Canal expansion is set to open, allowing a new class of ships to call on east coast ports. The dredging involved in deepening navigation channels to ensure safe passage of these vessels will place an increased amount of pressure on containment facilities up and down the coast. With limited disposal space, and increasing volumes, many ports have begun to rethink the treatment of this excess material. This thesis explores the prospect of dredge material being more than engineered fill. It suggests that dredge processing can become the basis for a new form of productive recreational landscape, one that can engage the public in a conversation of the spatial and material operations that sustain our lives. It works blur and dissolve the boundaries that have been erected between working landscapes and the public realm, and seeks to create a landscape that establishes a new sense of place prepared to mark the future of the new working urban waterfront; one where industrial operations generate new ecological substrates, and where productive frameworks become recreation networks. / Master of Landscape Architecture

The accuracy of sediment transport models depends on identifying an appropriate sediment settling velocity. Determining this value for mud suspensions can be difficult because cohesive mud particles can aggregate, forming flocs whose sizes are a function of hydrodynamic and physiochemical conditions of the suspension. Here we present a new model refining the predicted floc size based on hydrodynamic conditions and inherited floc sizes, as well as on the salinity of the fluid environment. The improvements come from modifications made to the Winterwerp (1998) (W98) model. These improvements include: limiting floc size to the Kolmogorov microscale and including an initial salinity dependence. Limiting floc size in this way brings the model predictions more in line with flocculation theory and experimental observations. The salinity dependence was introduced based on a preliminary set of experiments that were conducted to examine floc growth rate and equilibrium size under different salinity conditions. In these experiments, increasing salinity from 2.5 to 10 PSU did not affect equilibrium floc size. However, the increases in salinity did result in longer times to equilibrium and an apparent increase in floc density or fractal dimension. The modified W98 model allows calibrated aggregation and breakup coefficients obtained under one set of concentration values (for both sediment and salinity) to be used to predict floc size under other concentration conditions. Comparing the modified W98 model with laboratory data shows more accurate predictive values, indicating that the modified W98 equation is a promising tool for incorporation into larger sediment transport models. / Master of Science

Black Creek is a small watershed located in Wise County, Virginia, west of the town of Norton. At the time of this survey, the watershed encompassed approximately 929 hectares of mine and forest lands with a small recreational area. Black Creek proper is a third-order stream approximately 6.7 km in length from its headwaters to its confluence with the Powell River in Kent Junction. Black Creek and several of the tributaries within the watershed were previously identified as areas impacted by acid mine drainage. The watershed was used in a study to identify sources of acid mine drainage and the best methods for its evaluation. The acid mine drainage sources were first identified using visual inspection and field chemistry. Additional stream segments were then included in the assessment process using metal (aluminum, copper, iron, magnesium, manganese, and zinc) analyses of both overlying water column and sediments. Using an upstream reach of Black Creek as a reference, short-term toxicity testing was employed, as well as a long-term purge study. The pH at sampling locations ranged from 2.75 to 7.87 SU, and conductivity ranged from 196 μmhos/cm to 2040 μmhos/cm. All metals were elevated when compared to the reference. Water column samples collected from locations with low pH were acutely toxic to Daphnia magna and Pimephales promelas. Mortality was high in the elutriant test at locations where pH was low, conductivity was elevated, metals were high, or a combination of these. In the initial sediment tests, all sampling locations were significantly different than the reference for survival of Chironomus tentans and reproduction of D. magna. One location was significantly different than the reference for survival of D. magna. In the sediment tests completed after two months, survival of C. tentans was only different from the control in three locations but was significantly different for growth at all locations. Reproduction by D. magna was again significantly less than the reference at all locations. At eight months, only two locations were significant for survival of C. tentans and after 15 months, no significant differences occurred between any stations. The study indicates that stream segments that are severely impaired by acid mine drainage are easy to identify using visual inspection and field water chemistry. Those that are moderately impaired require more investigation and may not be responsive to short-term toxicity tests. Benthic macroinvertebrates, leaf packs, and periphyton were evaluated in the field. Benthic macroinvertebrate communities and leaf-pack breakdown were evaluated at nine locations, while periphyton was evaluated at the mouth of Black Creek, as well as five sites in the Powell River receiving system. While leaf-pack information and benthic macroinvertebrate samples yielded similar information, benthic sampling was much simpler and less time consuming. Additionally, benthic macroinvertebrate sampling, particularly over several sampling events, was more sensitive at the most severely impacted AMD stations. The stations were broken down into five different categories in order to better determine which evaluation techniques were most sensitive and cost-effective. The five categories were Non-Impaired, Slightly Impaired, Moderately Impaired, Severely Impaired, and Severely pH impaired. Once the locations were categorized, each method used to evaluate toxicity was examined to determine which methods best identified acid mine drainage impairment in the Black Creek watershed. The methods utilized include the following: basic water chemistry; metals analysis of sediments and water column; acute toxicity testing using both D. magna and P. promelas; short-term elutriant and sediment tests; chronic sediment test using C. tentans and D. magna; a purge study; benthic macroinvertebrate sampling; leaf-pack and algal-tile studies. After evaluating these methods, it was determined that using basic water chemistry and benthic macroinvertebrate sampling were the best methods for evaluating acid mine drainage impairment in this watershed. The reference station was identified as Non-Impaired. Two stations located in the lower portions of Black Creek (L11 and L1) were also Non-Impaired or only Slightly Impaired with the benthic macroinvertebrate results indicating little impairment. Stations U2, U6, U7, and BBM were also found to be Slightly Impaired. The station on the margin of the wetland, U5, was Moderately Impaired. Two previously identified areas of impairment, U9 and U10, (Cherry et al. 1995) were identified as Severely pH Impaired and Severely Impaired, respectively. / Master of Science

Agriculture, urbanization, and human activities, if not managed carefully, can expose a water body to environmental degradation, decreased water quality, and ultimately impaired benthic macroinvertebrate assemblage conditions. In streams where the benthic macroinvertebrates are impaired, the stream itself will not be meeting the water quality standards set forth in the Clean Water Act. As a result, the goal of this study was to establish relationships between benthic macroinvertebrates and their stressors so that stressor levels that would not adversely impact the benthic macroinvertebrates could be determined. Stressors such as sediment, habitat, water quality, landuse, watershed characteristics, and livestock numbers impact the benthic macroinvertebrate assemblage conditions. Since sediment is recognized as the Nation's leading pollutant and since the benthic macroinvertebrates live in the sediment on a stream bottom, this study placed emphasis upon the investigation of sediment as a primary stressor to the benthic macroinvertebrates. The specific objectives of this study were to develop relationships between the benthic macroinvertebrates and sediment and other stressors for Virginia streams, to evaluate the accuracy of the stressor/benthos relationships, and to discuss the implications of the study results for development of benthic TMDLs. A procedure to determine the relationships between stressors and benthic macroinvertebrate assemblage conditions was developed. Existing data on sediment, habitat, water quality, landuse, watershed characteristics, livestock numbers, and benthic macroinvertebrate assemblage conditions were compiled for 34 stations with 105 samples collected from the fall of 1996 to the fall of 1998. The 34 stations were located within 13 counties in Virginia (Rockbridge, Rockingham, Augusta, Frederick, Shenandoah, Page, Loudoun, Fairfax, Prince William, Fauquier, Culpeper, Rappahannock, and Madison) and in watersheds dominated by agricultural, urban, and forested landuses. Virginia currently uses the Rapid Bioassessment Protocol (RBP) method in its Biological Assessment Program. The RBP compares habitat and biological measures of the benthic macroinvertebrates to reference conditions using individual metrics. VADEQ's Biomonitoring Database, together with Ambient Water Quality Monitoring reports, GIS data layers, and VADCR's Hydrologic Unit Animal Census Database provided all of the necessary information for the stressor variables and benthic macroinvertebrate conditions. Accordingly, the stressor/benthos relationships were evaluated using statistical analyses procedures such as forward, backward, and stepwise multiple regression techniques; correlation analysis; principal component analysis; and r-square analysis. The statistical results indicated that sediment alone cannot be used to assess the benthic macroinvertebrate assemblage conditions. Other stressors such as dissolved oxygen, flow, % urban land, total suspended solids, temperature, stream velocity, substrate, hardness and alkalinity greatly impact the benthic macroinvertebrate assemblage conditions. The study results also indicate that the individual metrics within the RBP procedure are just as critical as the final RBP values in describing the benthic macroinvertebrate assemblage conditions. Upon completing the steps needed to develop stressor/benthos relationships, the validity of the relationships were verified for their application to other streams in Virginia. Validation was completed using 10 stations with 29 samples from the fall of 1996 to the fall of 1998. The 10 stations were located within 8 counties in Virginia (Bedford, Montgomery, Pulaski, Giles, Botetourt, Albemarle, Orange, and Culpeper) and in watersheds dominated by agricultural, urban, and forested landuses to correspond with the stations used to develop the stressor/benthos relationships. The implications of the relationships with regard to TMDLs were also studied using total suspended solids (TSS) loadings, turbidity levels, and embeddedness levels as the stressors of concern. The results for all benthic stations within Virginia showed that moderately impaired streams generally need to reduce the amount of embeddedness by 11, reduce turbidity levels by 5 FTU (57%), and reduce TSS values by 7 mg/L (68%) to meet a threshold value that would no longer adversely impact the benthic macroinvertebrates. Similarly, for the severely impaired stations throughout Virginia to meet threshold values, embeddedness amounts need to be reduced by 22, turbidity reduced by 57 FTU (93%), and TSS reduced by 74 mg/L (96%). This study was important since the proposed stressor/benthos relationships can provide policymakers with a useful tool to determine stressor thresholds that will not adversely impact the benthic macroinvertebrate assemblage conditions for use in developing benthic TMDLs in Virginia. The stressor/benthos relationships could also be used to determine the impact of certain activities or stressors on the benthic macroinvertebrates assemblage conditions in a given stream. / Master of Science

The study of lake sediments can provide valuable insights into lake history and climate variation throughout time. In-depth studies have been carried out at Lake Miragoane, Haiti and in high- and mid-elevation sites in the Dominican Republic, and a few other inland and coastal locations throughout the Caribbean; however, to date little has been published on prehistoric conditions in other coastal areas of Hispaniola. Laguna Alejandro (informally named by researchers) (~18.31°N, 71.03°W), on the southwest coast of the Dominican Republic, was examined to expand our knowledge of long-term environmental history in this region. This ~25 hectare lake is separated from the Caribbean Sea by a 100 m wide limestone ridge about 3–5 m tall. We recovered two consecutive cores (0–100 cm, 100–185.5 cm) close to the limestone barrier to investigate the potential for paleotempestology and other paleoenvironmental reconstructions. Three AMS 14C dates indicate that the lake is ~1100 years in age. Sediment analyses revealed three major events that correlate with bands of uncharacteristic sediment composition and particle size at 74–77.5 cm, 150.5–153 cm, and 183.5–185.5 cm. Four distinct strata containing serpulids and several pockets of Ammonia beccarii provided insights on changes in salinity and the connections between the lagoon and the ocean. The upper deposit (74–77.5 cm, 620 ±60 YBP) contains gypsum and represents a period of increased salinity within the lake brought on by drought. The two lower bands are composed of sand consistent with nearby beach sands. The 150.5–153 cm band provides evidence of a hurricane landfall at 1022 ± 60 YBP. The combination of biological data from 165–183.5 cm and sediments within the 183.5–185.5 cm band provide evidence for salinity fluctuations that indicate the closure of the lake. Sediments contained a variety of invertebrates that helped to document changes in lake chemistry through time. This study of Laguna Alejandro sediments documented lake history and provided information on recent climatic shifts in the region. / Master of Science

Tropical regions have extensive networks of unpaved roads which can be the largest contributor of sediment loading within a watershed in terms of both sediment generation and delivery. A number of erosion and sediment prediction models have been developed for unpaved roads and applied across a wide range of locations. However, little work has been devoted to the comparison of these models or to their application in tropical environments. A 13 square kilometer mixed land use watershed in Eastern Brazil was used as a case study area for model application and comparison. Models chosen for evaluation were WEPP: Road, SEDMODL, and STJ-EROS. To determine the applicability of these models to the case study watershed, a classification system was developed to score road segments according to sediment production and delivery potential. Field observations provided data for the input parameters of the models as well as to identify which road segments appear to be high contributors of sediment within the watershed. These road segments were compared with the segments estimated by the models to have high sediment yields. The models identified less than 50% of those roads categorized by field observation as having high erosion potential. WEPP: Road matched more closely to the field observations than SEDMODL and STJ-EROS. To be useful tools for watershed management in the tropics, a unified method for calculating sediment delivery is needed as well as an adjustment to model input parameters so that they better reflect conditions in tropical watersheds. / Master of Science

Many methods and equations have been developed to predict bed load transport rates, most of which use some comparison between shear stress and critical shear stress. The critical shear stress is determined by the point of incipient motion. Researchers have attempted to predict bed load transport both deterministically with mean parameters and stochastically attempting to take into account the fluctuations of velocity at points near threshold. This work attempts to show that more than simple force balances are needed to determine the point at which a particle will move. Turbulent fluctuations in velocity seem to have an effect of particle entrainment. The fluctuations in velocity can be several times greater than their time averaged counterparts. These short durations of high velocity often result in particle movement even though the mean flow may be less than or very near critical conditions. Through experiments of a single spherical particle on a simple bed geometry in air without the effects of water, it is shown that time duration of force has an effect on entrainment. This shows that there may be a constant force-time combination, or impulse, required to entrain sediment. / Master of Science