Salt marsh ecosystem restructuring enhances elevation resilience and carbon storage during accelerating relative sea-level rise

Salt marshes respond to sea-level rise through a series of complex and dynamic bio-physical feedbacks. In this study, we found that sea-level rise triggered salt marsh habitat restructuring, with the associated vegetation changes enhancing salt marsh elevation resilience. A continuous record of marsh elevation relative to sea level that includes reconstruction of high-resolution, sub-decadal, marsh elevation over the past century, coupled with a lower-resolution 1500-year record, revealed that relative sea-level rose 1.5 ± 0.4 m, following local glacial isostatic adjustment (1.2 mm/yr). As sea-level rise has rapidly accelerated, the high marsh zone dropped 11 cm within the tidal frame since 1932, leading to greater inundation and a shift to flood- and salt-tolerant low marsh species. Once the marsh platform fell to the elevation favored by low-marsh Spartina alterniflora, the elevation stabilized relative to sea level. Currently low marsh accretion keeps pace with sea-level rise, while present day high marsh zones that have not transitioned to low marsh have a vertical accretion deficit. Greater biomass productivity, and an expanding subsurface accommodation space favorable for salt marsh organic matter preservation, provide a positive feed-back between sea-level rise and marsh platform elevation. Carbon storage was 46 ± 28 g C/m2/yr from 550 to 1800 CE, increasing to 129 ± 50 g C/m2/yr in the last decade. Enhanced carbon storage is controlled by vertical accretion rates, rather than soil carbon density, and is a direct response to anthropogenic eustatic sea-level rise, ultimately providing a negative feedback on climate warming

Geographies of urban crime: An intraurban study of crime in Nashville, Tennessee; Portland, Oregon; and Tucson, Arizona

Understanding the context of crime is key to developing informed policy that will reduce crime in communities. In exploring criminal contexts, this dissertation tests criminal opportunity theory, which integrates social disorganization and routine activity theories. Methodologically, the dissertation presents unique ways of modeling space in crime studies. Analyses are undertaken in three cities, Nashville, TN; Portland, OR; and Tucson, AZ, chosen for their similar crime rates and varied demographic and social characteristics. This dissertation includes three papers submitted for publication. Crime data were collected for nine crimes over the period 1998-2002. Census data, used to create an array of socioeconomic measures, and land use data were also used in the analyses, presented at the census block group level. The first paper attempts to determine whether certain structural associations with violence are generalizable across urban areas. The idea is tested by first developing an Ordinary Least Squares model of crime for all three cities, then replicating the results for each city individually. The models provide support for a general relationship between violence and several structural measures, but suggest that the exploration into geographic variation of crime and its covariates both within urban areas and across urban areas should be undertaken. The second paper explores an alternative to crime rates: location quotients of crime. A comparison of location quotients and rates is provided. The location quotients are then used in a regression modeling framework to determine what influences the crime profile of a place. The results demonstrate the efficacy of simple techniques and how location quotients can be incorporated into statistical models of crime. The models provide modest support for the opportunity framework. The final paper explores possible spatial variation in crime and its covariates through a local analysis of crime using Geographically Weighted Regression (GWR). Those results are compared to the results of a 'base' global OLS model. Parameter estimate reaps confirm the results of the OLS model for the most part and also allow visual inspection of areas where specific measures have a strong influence in the model. This research highlights the importance of considering local context when modeling urban violence

Changes in Personal Social Networks across Individuals Leaving Their Street Gang: Just What Are Youth Leaving Behind?

Despite a small but growing literature on gang disengagement and desistance, little is known about how social networks and changes in networks correspond to self-reported changes in street gang membership over time. The current study describes the personal or “ego” network composition of 228 street gang members in two east coast cities in the United States. The study highlights changes in personal network composition associated with changes in gang membership over two waves of survey data, describing notable differences between those who reported leaving their gang and fully disengaging from their gang associates, and those who reported leaving but still participate and hang out with their gang friends. Results show some positive changes (i.e., reductions) in criminal behavior and many changes toward an increase in prosocial relationships for those who fully disengaged from their street gang, versus limited changes in both criminal behavior and network composition over time for those who reported leaving but remained engaged with their gang. The findings suggest that gang intervention programs that increase access to or support building prosocial relationships may assist the gang disengagement process and ultimately buoy desistance from crime. The study also has implications for theorizing about gang and crime desistance, in that the role of social ties should take a more central role

Comparing Firearm Proxies to Legal Firearm Prevalence in Massachusetts

This project introduces legal firearm prevalence, a measure based on the population of firearm licenses in Massachusetts, in order to evaluate candidate proxies for firearm prevalence in a variety of research designs

Determinants of How Firearms Are Stored in Households with Children: Implications for Interventions to Reduce Firearm Mortality

Using data from our 2019 National Firearm Survey we will examine the role of CAP laws in motivating safe storage of household firearms (Aim 1), the role of clinical counseling in affecting safe storage in homes with children (Aim 2), and because our survey includes not only 4,000 US adults who live in households with firearms (two-thirds of whom personally own firearms) but also a sub-sample of 400 adolescents 13-17 years of age who live with one of the adult survey respondents, we will be able to assess (Aim 3) the extent to which parental beliefs about their own adolescents’ knowledge and behavior around guns is contradicted by their child’s report (e.g., how often do adolescents report having easy access to household firearms when their parents think otherwise), how such discordance varies by adolescent and parental characteristics, and whether discordant beliefs are related to parental firearm storage practices. Our 400 dyads will also allow us to assess to what extent storage practices commonly described as “safe” (e.g., locking and unloading all household guns) are readily overcome, per the child’s report, and what characteristics of adolescents and parents predict easy access despite what is generally considered to be safe storage

The association between substance use disorders and suicide in North Carolina claims data

This project aims to estimate the association of substance use disorders and other mental health disorders with firearm suicide. We will do this by linking North Carolina Medicaid claims (2013-2017) to the North Carolina Violent Death Reporting System, which contains detailed information on all suicides in the state