The increasing commercial production of engineered nanoparticles (ENPs) has led to concerns over the potential adverse impacts of these ENPs on biota in natural environments. Silver nanoparticles (AgNPs) are one of the most widely used ENPs and are expected to enter natural ecosystems. Here we examined the effects of AgNPs on germination and growth of eleven species of common wetland plants. We examined plant responses to AgNP exposure in simple pure culture experiments (direct exposure) and for seeds planted in homogenized field soils in a greenhouse experiment (soil exposure). We compared the effects of two AgNPs–20-nm polyvinylpyrrolidine-coated silver nanoparticles (PVP-AgNPs) and 6-nm gum arabic coated silver nanoparticles (GA-AgNPs)–to the effects of AgNO₃ exposure added at equivalent Ag concentrations (1, 10 or 40 mg Ag L⁻¹). In the direct exposure experiments, PVP-AgNP had no effect on germination while 40 mg Ag L⁻¹ GA-AgNP exposure significantly reduced the germination rate of three species and enhanced the germination rate of one species. In contrast, 40 mg Ag L⁻¹ AgNO₃ enhanced the germination rate of five species. In general root growth was much more affected by Ag exposure than was leaf growth. The magnitude of inhibition was always greater for GA-AgNPs than for AgNO₃ and PVP-AgNPs. In the soil exposure experiment, germination effects were less pronounced. The plant growth response differed by taxa with Lolium multiflorum growing more rapidly under both AgNO₃ and GA-AgNP exposures and all other taxa having significantly reduced growth under GA-AgNP exposure. AgNO₃ did not reduce the growth of any species while PVP-AgNPs significantly inhibited the growth of only one species. Our findings suggest important new avenues of research for understanding the fate and transport of NPs in natural media, the interactions between NPs and plants, and indirect and direct effects of NPs in mixed plant communities.

A large fraction of engineered nanomaterials in consumer and commercial products will reach natural ecosystems. To date, research on the biological impacts of environmental nanomaterial exposures has largely focused on high-concentration exposures in mechanistic lab studies with single strains of model organisms. These results are difficult to extrapolate to ecosystems, where exposures will likely be at low-concentrations and which are inhabited by a diversity of organisms. Here we show adverse responses of plants and microorganisms in a replicated long-term terrestrial mesocosm field experiment following a single low dose of silver nanoparticles (0.14 mg Ag kg⁻¹ soil) applied via a likely route of exposure, sewage biosolid application. While total aboveground plant biomass did not differ between treatments receiving biosolids, one plant species, Microstegium vimeneum, had 32 % less biomass in the Slurry+AgNP treatment relative to the Slurry only treatment. Microorganisms were also affected by AgNP treatment, which gave a significantly different community composition of bacteria in the Slurry+AgNPs as opposed to the Slurry treatment one day after addition as analyzed by T-RFLP analysis of 16S-rRNA genes. After eight days, N₂O flux was 4.5 fold higher in the Slurry+AgNPs treatment than the Slurry treatment. After fifty days, community composition and N₂O flux of the Slurry+AgNPs treatment converged with the Slurry. However, the soil microbial extracellular enzymes leucine amino peptidase and phosphatase had 52 and 27% lower activities, respectively, while microbial biomass was 35% lower than the Slurry. We also show that the magnitude of these responses was in all cases as large as or larger than the positive control, AgNO₃, added at 4-fold the Ag concentration of the silver nanoparticles.

Groundwater irrigation of cropland is expanding worldwide with poorly known implications for climate change. This study compares experimental measurements of the net global warming impact of a rainfed versus a groundwater‐irrigated corn (maize)–soybean–wheat, no‐till cropping system in the Midwest US, the region that produces the majority of U.S. corn and soybean. Irrigation significantly increased soil organic carbon (C) storage in the upper 25 cm, but not by enough to make up for the CO₂‐equivalent (CO₂e) costs of fossil fuel power, soil emissions of nitrous oxide (N₂O), and degassing of supersaturated CO₂ and N₂O from the groundwater. A rainfed reference system had a net mitigating effect of −13.9 (±31) g CO₂e m⁻² year⁻¹, but with irrigation at an average rate for the region, the irrigated system contributed to global warming with net greenhouse gas (GHG) emissions of 27.1 (±32) g CO₂e m⁻² year⁻¹. Compared to the rainfed system, the irrigated system had 45% more GHG emissions and 7% more C sequestration. The irrigation‐associated increase in soil N₂O and fossil fuel emissions contributed 18% and 9%, respectively, to the system's total emissions in an average irrigation year. Groundwater degassing of CO₂ and N₂O are missing components of previous assessments of the GHG cost of groundwater irrigation; together they were 4% of the irrigated system's total emissions. The irrigated system's net impact normalized by crop yield (GHG intensity) was +0.04 (±0.006) kg CO₂e kg⁻¹ yield, close to that of the rainfed system, which was −0.03 (±0.002) kg CO₂e kg⁻¹ yield. Thus, the increased crop yield resulting from irrigation can ameliorate overall GHG emissions if intensification by irrigation prevents land conversion emissions elsewhere, although the expansion of irrigation risks depletion of local water resources.

As we build a more diverse, equitable, and inclusive culture in the ecological research community, we must work to support new ecologists by empowering them with the knowledge, tools, validation, and sense of belonging in ecology to succeed. Undergraduate research experiences (UREs) are critical for a student's professional and interpersonal skill development and key for recruiting and retaining students from diverse groups to ecology. However, few resources exist that speak directly to an undergraduate researcher on the diversity, equity, and inclusion (DEI) dimensions of embarking on a first research experience. Here, we write primarily for undergraduate readers, though a broader audience of readers, especially URE mentors, will also find this useful. We explain many of the ways a URE benefits undergraduate researchers and describe how URE students from different positionalities can contribute to an inclusive research culture. We address three common sources of anxiety for URE students through a DEI lens: imposter syndrome, communicating with mentors, and safety in fieldwork. We discuss the benefits as well as the unique vulnerabilities and risks associated with fieldwork, including the potential for harassment and assault. Imposter syndrome and toxic field experiences are known to drive students, including students from underrepresented minority groups, out of STEM. Our goal is to encourage all students, including those from underrepresented groups, to apply for UREs, build awareness of their contributions to inclusion in ecology research, and provide strategies for overcoming known barriers.

Groundwater quantity and quality may be affected by climate change through intricate direct and indirect mechanisms. At the same time, population growth and rapid urbanization have made groundwater an increasingly important source of water for multiple uses around the world, including southern Africa. The present study investigates the coupled human and natural system (CHANS) linking climate, sanitation, and groundwater quality in Ramotswa, a rapidly growing peri-urban area in the semi-arid southeastern Botswana, which relies on the transboundary Ramotswa aquifer for water supply. Analysis of long-term rainfall records indicated that droughts like the one in 2013–2016 are increasing in likelihood in the area due to climate change. Key informant interviews showed that due to the drought, people increasingly used pit latrines rather than flush toilets. Nitrate, fecal coliforms, and caffeine analyses of Ramotswa groundwater revealed that human waste leaching from pit latrines is the likely source of nitrate pollution. The results in conjunction indicate critical indirect linkages between climate change, sanitation, groundwater quality, and water security in the area. Improved sanitation, groundwater protection and remediation, and local water treatment would enhance reliable access to water, de-couple the community from reliance on surface water and associated water shortage risks, and help prevent transboundary tension over the shared aquifer. La qualité et la quantité des eaux souterraines peuvent être impactées par le changement climatique par le biais de mécanismes directs et indirects complexes. Dans le même temps, la croissance démographique et l’urbanisation rapide ont fait des eaux souterraines une ressource de plus en plus importante pour de multiples usages à travers le monde, y compris en Afrique australe. La présente étude examine le système couplé homme-environnement (Coupled Human and Natural System ou CHANS) qui lie le climat, l’assainissement et la qualité des eaux souterraines de Ramotswa, une zone périurbaine à croissance rapide dans la région semi-aride du sud-est du Botswana dont l'approvisonnement en eau dépend de l'aquifère transfrontalier de Ramotswa. L'analyse des données pluviométriques à long terme a montré que le risque de sècheresse comme celle de 2013–2016 a tendance à augmenter dans cette région du fait du changement climatique. Des entretiens avec des acteurs clés montrent qu’en raison de la sécheresse, les gens utilisent de plus en plus les latrines à fosse plutôt que les toilettes à chasse d’eau. Les analyses des eaux souterraines de Ramotswa en nitrates, coliformes fécaux et caféine révélent que les rejets anthropiques depuis les latrines sont la principale source de pollution par les nitrates. L’ensemble des résultats indique le lien indirect crucial entre climat, assainissement, qualité des eaux souterraines et sécurité en eau dans cette région. L’amélioration de l’assainissement, la protection et la restauration des eaux souterraines, et le traitement local de l’eau devraient permettre d’assurer un accès sûr à l’eau, de diminuer la dépendance de la communauté à l’eau de surface avec ses risques de coupured'eau, et d’aider à prévenir les tensions transfrontalières liés à cet aquifère partagé. La cantidad y la calidad del agua subterránea pueden verse afectadas por el cambio climático a través de intrincados mecanismos directos e indirectos. Al mismo tiempo, el crecimiento de la población y la rápida urbanización han convertido al agua subterránea en una fuente de agua cada vez más importante para usos múltiples en todo el mundo, incluso en el sur de África. El presente estudio investiga el sistema humano y natural acoplado (CHANS) que vincula el clima, el saneamiento y la calidad del agua subterránea en Ramotswa, un área periurbana de rápido crecimiento en la parte semiárida del sudeste de Botswana, que depende del acuífero transfronterizo de Ramotswa para el suministro de agua. El análisis de los registros de precipitaciones a largo plazo indicó que las sequías como la ocurrida en 2013–2016 están aumentando con probabilidad en la zona debido al cambio climático. Las entrevistas con informantes clave mostraron que, debido a la sequía, las personas usaban cada vez más letrinas de pozo en lugar de inodoros. Los análisis de nitratos, coliformes fecales y cafeína del agua subterránea de Ramotswa revelaron que la lixiviación de desechos humanos de las letrinas de pozo es la fuente probable de contaminación por nitratos. Los resultados en conjunto indican vínculos indirectos críticos entre el cambio climático, el saneamiento, la calidad del agua subterránea y la seguridad del agua en el área. Mejoras en el saneamiento, protección y remediación del agua subterránea y el tratamiento local de agua mejorarían el acceso confiable al agua, desvincularían a la comunidad de la dependencia de las aguas superficiales y los riesgos asociados de escasez de agua, y ayudarían a prevenir la tensión transfronteriza sobre el acuífero compartido....

Denitrification is an important ecosystem service that removes nitrogen (N) from N-polluted watersheds, buffering soil, stream, and river water quality from excess N by returning N to the atmosphere before it reaches lakes or oceans and leads to eutrophication. The denitrification enzyme activity (DEA) assay is widely used for measuring denitrification potential. Because DEA is a function of enzyme levels in soils, most ecologists studying denitrification have assumed that DEA is less sensitive to ambient levels of nitrate (NO₃⁻) and soil carbon and thus, less variable over time than field measurements. In addition, plant diversity has been shown to have strong effects on microbial communities and belowground processes and could potentially alter the functional capacity of denitrifiers. Here, we examined three questions: (1) Does DEA vary through the growing season? (2) If so, can we predict DEA variability with environmental variables? (3) Does plant functional diversity affect DEA variability? The study site is a restored wetland in North Carolina, US with native wetland herbs planted in monocultures or mixes of four or eight species. We found that denitrification potentials for soils collected in July 2006 were significantly greater than for soils collected in May and late August 2006 (p<0.0001). Similarly, microbial biomass standardized DEA rates were significantly greater in July than May and August (p<0.0001). Of the soil variables measured—soil moisture, organic matter, total inorganic nitrogen, and microbial biomass—none consistently explained the pattern observed in DEA through time. There was no significant relationship between DEA and plant species richness or functional diversity. However, the seasonal variance in microbial biomass standardized DEA rates was significantly inversely related to plant species functional diversity (p<0.01). These findings suggest that higher plant functional diversity may support a more constant level of DEA through time, buffering the ecosystem from changes in season and soil conditions.