Changes in the community structure of urban and rural forest patches in Baltimore from 1998 to 2015

Urban forests are often highly fragmented with many exotic species. Altered disturbance regimes and environmental pollutants influence urban forest vegetation. One of the best ways to understand the impacts of land-use on forest composition is through long-term research. In 1998, the Baltimore Ecosystem Study established eight forest plots to investigate the impacts of urbanization on natural ecosystems. Four plots were located in urban forest patches and four were located in rural forests. In 2015, I revisited these plots to measure abundances and quantify change in forest composition, diversity, and structure. Sapling, shrub, and seedling abundance were reduced in the rural plots. Alpha diversity and turnover was lower in the rural plots. Beta diversity was reduced in the rural plots. The structure of the urban plots was mostly unchanged, except for a highly reduced sapling layer. Beta diversity in the urban plots was consistent across surveys due to high species turnover.

DISSOLVED AND GASEOUS FLUXES OF CARBON AND NITROGEN FROM URBAN WATERSHEDS OF THE CHESAPEAKE BAY

Carbon and nitrogen loading to streams and rivers contributes to eutrophication as well as greenhouse gas (GHG) production in streams, rivers and estuaries. My dissertation consists of three research chapters, which examine interactions and potential trade-offs between water quality and greenhouse gas production in urban streams of the Chesapeake Bay watershed. My first research project focused on drivers of carbon export and quality in an urbanized river. I found that watershed carbon sources (soils and leaves) contributed more than in-stream production to overall carbon export, but that periods of high in-stream productivity were important over seasonal and daily timescales. My second research chapter examined the influence of urban storm-water and sanitary infrastructure on dissolved and gaseous carbon and nitrogen concentrations in headwater streams. Gases (CO2, CH4, and N2O) were consistently super-saturated throughout the course of a year. N2O concentrations in streams draining septic systems were within the high range of previously published values. Total dissolved nitrogen concentration was positively correlated with CO2 and N2O and negatively correlated with CH4. My third research chapter examined a long-term (15-year) record of GHG emissions from soils in rural forests, urban forest, and urban lawns in Baltimore, MD. CO2, CH4, and N2O emissions showed positive correlations with temperature at each site. Lawns were a net source of CH4 + N2O, whereas forests were net sinks. Gross CO2 fluxes were also highest in lawns, in part due to elevated growing-season temperatures. While land cover influences GHG emissions from soils, the overall role of land cover on this flux is very small (< 0.5%) compared with gases released from anthropogenic sources, according to a recent GHG budget of the Baltimore metropolitan area, where this study took place.

INTERGENERATIONAL SUPPORT AND WELL-BEING OF OLDER ADULTS IN CHANGING FAMILY CONTEXTS

This dissertation consists of three papers that examine the complexities in upward intergenerational support and adult children’s influence on older adults’ health in changing family contexts of America and China. The prevalence of “gray divorce/repartnering ” in later life after age 55 is on the rise in the United States, yet little is known about its effect on intergenerational support. The first paper uses the life course perspective to examine whether gray divorce and repartnering affect support from biological and stepchildren differently than early divorce and repartnering, and how patterns differ by parents’ gender. Massive internal migration in China has led to increased geographic distance between adult children and aging parents, which may have consequences for old age support received by parents. This topic has yet to be thoroughly explored in China, as most studies of intergenerational support to older parents have focused on the role of coresident children or have not considered the interdependence of multiple parent-child dyads in the family. The second paper adopts the within-family differences approach to assess the influence of non-coresident children’s relative living proximity to parents compared to that of their siblings on their provision of support to parents in rural and urban Chinese families. The study also examines how patterns of the impact are moderated by parents’ living arrangement, non-coresident children’s gender, and parents’ provision of support to children. Taking a multigenerational network perspective, the third paper questions if and how adult children’s socioeconomic status (SES) influences older parents’ health in China. It further examines whether health benefits brought by adult children’s socioeconomic attainment are larger for older adults with lower SES and whether one of the mechanisms through which adult children’s SES affects older parents’ health is by changing their health behaviors. These questions are highly relevant in contemporary China, where adult children have experienced substantial gains in SES and play a central role in old age support for parents. In sum, these three papers take the life course, the within-family differences, and the multigenerational network perspective to address the complexities in intergenerational support and older adults’ health in diverse family contexts.

Comparison of Hydrologic and Hydraulic Characteristics of the Anacostia River to Non-Urban Coastal Streams

Streams in urban areas often utilize channelization and other bank erosion control measures to improve flood conveyance, reduce channel migration, and overbank flooding. This leads to reductions in evapotranspiration and sediment storage on floodplains. The purpose of this study is to quantify the evapotranspiration and sediment transport capacity in the Anacostia Watershed, a large Coastal Plain urban watershed, and to compare these processes to a similar sized non-urban watershed. Times series data of hydrologic and hydraulic changes in the Anacostia, as urbanization progressed between 1939-2014, were also analyzed. The data indicates lower values of warm season runoff in the non-urban stream, suggesting a shift from evapotranspiration to runoff in urban streams. Channelization in the Anacostia also increased flow velocities and decreased high flow width. The high velocities associated with channelization and the removal of floodplain storage sites allows for the continued downstream transport of sediment despite stream bank stabilization.