Stream denitrification across biomes and its response to anthropogenic nitrate loading.

Anthropogenic addition of bioavailable nitrogen to the biosphere is increasing and terrestrial ecosystems are becoming increasingly nitrogen-saturated, causing more bioavailable nitrogen to enter groundwater and surface waters. Large-scale nitrogen budgets show that an average of about 20-25 per cent of the nitrogen added to the biosphere is exported from rivers to the ocean or inland basins, indicating that substantial sinks for nitrogen must exist in the landscape. Streams and rivers may themselves be important sinks for bioavailable nitrogen owing to their hydrological connections with terrestrial systems, high rates of biological activity, and streambed sediment environments that favour microbial denitrification. Here we present data from nitrogen stable isotope tracer experiments across 72 streams and 8 regions representing several biomes. We show that total biotic uptake and denitrification of nitrate increase with stream nitrate concentration, but that the efficiency of biotic uptake and denitrification declines as concentration increases, reducing the proportion of in-stream nitrate that is removed from transport. Our data suggest that the total uptake of nitrate is related to ecosystem photosynthesis and that denitrification is related to ecosystem respiration. In addition, we use a stream network model to demonstrate that excess nitrate in streams elicits a disproportionate increase in the fraction of nitrate that is exported to receiving waters and reduces the relative role of small versus large streams as nitrate sinks.

Nitrous oxide emission from denitrification in stream and river networks.

Nitrous oxide (N(2)O) is a potent greenhouse gas that contributes to climate change and stratospheric ozone destruction. Anthropogenic nitrogen (N) loading to river networks is a potentially important source of N(2)O via microbial denitrification that converts N to N(2)O and dinitrogen (N(2)). The fraction of denitrified N that escapes as N(2)O rather than N(2) (i.e., the N(2)O yield) is an important determinant of how much N(2)O is produced by river networks, but little is known about the N(2)O yield in flowing waters. Here, we present the results of whole-stream (15)N-tracer additions conducted in 72 headwater streams draining multiple land-use types across the United States. We found that stream denitrification produces N(2)O at rates that increase with stream water nitrate (NO(3)(-)) concentrations, but that <1% of denitrified N is converted to N(2)O. Unlike some previous studies, we found no relationship between the N(2)O yield and stream water NO(3)(-). We suggest that increased stream NO(3)(-) loading stimulates denitrification and concomitant N(2)O production, but does not increase the N(2)O yield. In our study, most streams were sources of N(2)O to the atmosphere and the highest emission rates were observed in streams draining urban basins. Using a global river network model, we estimate that microbial N transformations (e.g., denitrification and nitrification) convert at least 0.68 Tg·y(-1) of anthropogenic N inputs to N(2)O in river networks, equivalent to 10% of the global anthropogenic N(2)O emission rate. This estimate of stream and river N(2)O emissions is three times greater than estimated by the Intergovernmental Panel on Climate Change.

Women Veterans' perspectives, experiences, and preferences for firearm lethal means counseling discussions.

AIMS: Firearms have become an increasingly common method of suicide among women Veterans, yet this population has rarely been a focus in firearm suicide prevention research. Limited knowledge is available regarding the preferences, experiences, or needs of women Veterans with respect to firearm lethal means counseling (LMC), an evidence-based suicide prevention strategy. Understanding is necessary to optimize delivery for this population. METHOD: Our sample included forty women Veterans with lifetime suicidal ideation or suicide attempt(s) and firearm access following military separation, all enrolled in the Veterans Health Administration. Participants were interviewed regarding their perspectives, experiences, and preferences for firearm LMC. Data were analyzed using a mixed inductive-deductive thematic analysis. RESULTS: Women Veterans' firearm and firearm LMC perspectives were shaped by their military service histories and identity, military sexual trauma, spouses/partners, children, rurality, and experiences with suicidal ideation and attempts. Half reported they had not engaged in firearm LMC previously. For those who had, positive aspects included a trusting, caring relationship, direct communication of rationale for questions, and discussion of exceptions to confidentiality. Negative aspects included conversations that felt impersonal, not sufficiently comprehensive, and Veterans' fears regarding implications of disclosure, which impeded conversations. Women Veterans' preferences for future firearm LMC encompassed providers communicating why such conversations are important, how they should be framed (e.g., around safety and genuine concern), what they should entail (e.g., discussing concerns regarding disclosure), whom should initiate (e.g., trusted caring provider) and where they should occur (e.g., safe spaces, women-specific groups comprised of peers). DISCUSSION: This study is the first to examine women Veterans' experiences with, and preferences for, firearm LMC. Detailed inquiry of the nuances of how, where, why, and by whom firearms are stored and used may help to facilitate firearm LMC with women Veterans.

Women Veterans' experiences discussing household firearms with their intimate partners: collaborative, devalued, and deferential relational types.

BACKGROUND: Rates of firearm suicide have increased among women Veterans. Discussing firearm access and reducing access to lethal means of suicide when suicide risk is heightened are central tenets of suicide prevention, as is tailoring suicide prevention strategies to specific populations. While research has begun to explore how to optimize firearm lethal means safety counseling with women Veterans, there is limited knowledge of women Veterans' perspectives on including their intimate partners in such efforts. This gap is notable since many women Veterans have access to firearms owned by other household members. Understanding women Veterans' experiences and perspectives regarding including their partners in firearm lethal means safety conversations can provide important information for tailoring firearm lethal means safety counseling for women Veterans. METHODS: Qualitative interviews were conducted with 40 women Veterans with current or prior household firearm access. Interview questions focused on the roles of women Veterans' partners in household firearm access and storage, as well as women Veterans' perspectives regarding including intimate partners in firearm lethal means safety counseling. Inductive thematic analysis was performed. RESULTS: Three relational types characterized how household firearms were discussed between women Veterans and their partners: collaborative, devalued, and deferential. These types were distinguished via women Veterans' agency in decision-making related to household firearms, partners' receptivity to women Veterans' mental health or trauma histories, and willingness (or lack thereof) of partners to change household firearm access and storage considering such histories. Intimate partner violence was common in the devalued relational subtype. CONCLUSIONS: Findings extend knowledge regarding the context of women Veterans' household firearm access, including relational dynamics between women Veterans and their partners. The acceptability, feasibility, challenges, and facilitators of including women Veterans' partners in firearm lethal means safety efforts likely vary for each relational type. For example, in dyads with a collaborative dynamic, incorporating partners may create opportunities for increased firearm safety, whereas including partners in devalued dynamics may present unique challenges. Research is warranted to determine optimal methods of navigating firearm lethal means safety counseling in the presence of each relational dynamic.