Looking beyond leaves: variation in nutrient leaching potential of seasonal litterfall among different species within an urban forest.

Urban litterfall that is deposited on impervious surface leaches nutrients into stormwater, contributing to downstream eutrophication. Previous studies have focused on the leaching potential of deciduous leaf litter, while other smaller-volume litterfall types-such as blossoms and fruit-may leach significant amounts of nitrogen, phosphorus, and carbon. These additional litterfall types represent an unaccounted-for source of nutrients to urban stormwater. We explored variation in leaching potential of dissolved nutrients and organic carbon across litter types and species by collecting litterfall (blossoms, fruit, leaves) from ten common urban tree species. After 24 h of leaching, we measured total phosphorus (TP), total dissolved nitrogen (TDN), and dissolved organic carbon (DOC) contributions and compared differences across litter types and species. Litter basket estimates then allowed us to quantify annual litterfall inputs. We found that blossoms leached 3-20 times more TDN and 1.5-7 times more TP than leaves of the same species. Furthermore, considering litterfall mass, several species had greater springtime nutrient-leaching potential compared to fall due to high leaching potential in blossoms and lower potential in leaves. We found mixed effects of leaf crushing and leachate solution (stormwater, salinity) on leaching rates. This study highlights the need to consider all litterfall types as well as variation in urban forest communities and conditions when seeking to budget, control, and maintain for potential nutrient sources from the urban forest. Supplementary information: The online version contains supplementary material available at 10.1007/s11252-022-01217-8.

COVID-19 Reveals Vulnerabilities of the Food-Energy-Water Nexus to Viral Pandemics.

Food, energy, and water (FEW) sectors are inextricably linked, making one sector vulnerable to disruptions in another. Interactions between FEW systems, viral pandemics, and human health have not been widely studied. We mined scientific and news/media articles for causal relations among FEW and COVID-19 variables and qualitatively characterized system dynamics. Food systems promoted the emergence and spread of COVID-19, leading to illness and death. Major supply-side breakdowns were avoided (likely due to low morbidity/mortality among working-age people). However, COVID-19 and physical distancing disrupted labor and capital inputs and stressed supply chains, while creating economic insecurity among the already vulnerable poor. This led to demand-side FEW insecurities, in turn increasing susceptibility to COVID-19 among people with many comorbidities. COVID-19 revealed trade-offs such as allocation of water to hygiene versus to food production and disease burden avoided by physical distancing versus disease burden from increased FEW insecurities. News/media articles suggest great public interest in FEW insecurities triggered by COVID-19 interventions among individuals with low COVID-19 case-fatality rates. There is virtually no quantitative analysis of any of these trade-offs or feedbacks. Enhanced quantitative FEW and health models are urgently needed as future pandemics are likely and may have greater morbidity and mortality than COVID-19.

Dry Wetlands: Nutrient Dynamics in Ephemeral Constructed Stormwater Wetlands.

Constructed stormwater wetlands (CSWs) are used to address contaminants in urban stormwater such as nitrogen (N) and phosphorus (P), but their performance is variable. Ephemeral CSWs tend to be less effective than perennial CSWs at removing N and P. We asked: How does wetland vegetation and sediment affect nutrient cycling/release from sediment and vegetation in ephemeral CSWs? We focused on two ephemeral urban CSWs in Pocatello, ID, USA, one densely vegetated and the other nearly bare. We rewetted intact cores of dry wetland sediments and, separately, senesced vegetation for 1 week at the end of the summer dry period to assess whether wetland sediments and vegetation acted as sources or sinks of N and P. For both CSWs, there was a pulse of nutrients immediately following rewetting, but the magnitude of that pulse and subsequent changes in nutrient concentrations suggest different processes dominate at each wetland, driven by differences in wetland vegetation and associated sediment characteristics. There was evidence of denitrification between and during events at the vegetated wetland, but larger fluxes of P at this site suggests a tradeoff between denitrification and P release. While the experimental results suggested specific biogeochemical controls, CSW nutrient concentrations during three events were more dynamic and suggested more biogeochemical complexity than that represented in our experiment, both within events and seasonally. Ephemeral CSWs may create unique biogeochemical conditions and require careful design to ensure N and P retention. Managers will also need to consider whether perennial water sources would improve CSW function.

Distributing regionally, distinguishing locally: examining the underlying effects of local land use on airborne bacterial biodiversity.

Airborne bacteria are abundant and can vary with land use. Urban expansion is increasing rapidly at a global scale, altering natural sources of airborne bacterial biodiversity, as soils and native plants are replaced by pavement and managed yards. Urbanization homogenizes the biodiversity of larger organisms, but its effects are understudied with respect to microbes. This study uses categorical and gradient approaches to examine airborne bacterial communities in southwest Michigan (USA). Airborne communities carried a gut-microbial signature and were equally homogenous above urban and rural sites, despite greater homogeneity of soil communities at urban sites. Ruminococcaceae were abundant, the source of which is likely wildlife. Beyond the gut-microbial signature, there were underlying effects of land use, which were evident in the shared airborne taxa across urban and rural sites. Bacillales, Burkholderiales, Alteromonadales and Pseudomonadales were shared more across urban sites, while Xanthomonadales, which contains crop-plant pathogens, were shared across rural agricultural sites. These results suggest that taxa which may distribute globally, coupled with localized sources, contribute to urban communities, while regional rural activities drive rural composition. We determined that soils were unlikely to contribute to broad distribution of some plant-associated taxa, but may be a source for distribution of others.

Socio-environmental consideration of phosphorus flows in the urban sanitation chain of contrasting cities.

Understanding how cities can transform organic waste into a valuable resource is critical to urban sustainability. The capture and recycling of phosphorus (P), and other essential nutrients, from human excreta is particularly important as an alternative organic fertilizer source for agriculture. However, the complex set of socio-environmental factors influencing urban human excreta management is not yet sufficiently integrated into sustainable P research. Here, we synthesize information about the pathways P can take through urban sanitation systems along with barriers and facilitators to P recycling across cities. We examine five case study cities by using a sanitation chains approach: Accra, Ghana; Buenos Aires, Argentina; Beijing, China; Baltimore, USA; and London, England. Our cross-city comparison shows that London and Baltimore recycle a larger percentage of P from human excreta back to agricultural lands than other cities, and that there is a large diversity in socio-environmental factors that affect the patterns of recycling observed across cities. Our research highlights conditions that may be "necessary but not sufficient" for P recycling, including access to capital resources. Path dependencies of large sanitation infrastructure investments in the Global North contrast with rapidly urbanizing cities in the Global South, which present opportunities for alternative sanitation development pathways. Understanding such city-specific social and environmental barriers to P recycling options could help address multiple interacting societal objectives related to sanitation and provide options for satisfying global agricultural nutrient demand.

Sources and transport of nitrogen in arid urban watersheds.

Urban watersheds are often sources of nitrogen (N) to downstream systems, contributing to poor water quality. However, it is unknown which components (e.g., land cover and stormwater infrastructure type) of urban watersheds contribute to N export and which may be sites of retention. In this study we investigated which watershed characteristics control N sourcing, biogeochemical processing of nitrate (NO3-) during storms, and the amount of rainfall N that is retained within urban watersheds. We used triple isotopes of NO3- (δ15N, δ18O, and Δ17O) to identify sources and transformations of NO3- during storms from 10 nested arid urban watersheds that varied in stormwater infrastructure type and drainage area. Stormwater infrastructure and land cover--retention basins, pipes, and grass cover--dictated the sourcing of NO3- in runoff. Urban watersheds were strong sinks or sources of N to stormwater depending on runoff, which in turn was inversely related to retention basin density and positively related to imperviousness and precipitation. Our results suggest that watershed characteristics control the sources and transport of inorganic N in urban stormwater but that retention of inorganic N at the time scale of individual runoff events is controlled by hydrologic, rather than biogeochemical, mechanisms.

The contribution of prescription chart design and familiarity to prescribing error: a prospective, randomised, cross-over study.

PURPOSE OF STUDY: Initiatives to standardise hospital paper-based prescription charts are underway in various countries in an effort to reduce prescribing errors. The aim of this study was to investigate the extent to which prescribing error rates are influenced by prescription chart design and familiarity. STUDY DESIGN: In this prospective, randomised, cross-over study, Foundation Year 1 doctors working in five Scottish National Health Service (NHS) Boards participated in study sessions during which they were asked to prescribe lists of medications for five fictional patients using a different design of paper prescription chart for each patient. Each doctor was timed completing each set of prescriptions, and each chart was subsequently assessed against a predefined list of possible errors. A mixed modelling approach using three levels of variables (design of and familiarity with a chart, prescribing speed and individual prescriber) was employed. RESULTS: A total of 72 Foundation Year 1 doctors participated in 10 data-collection sessions. Differences in prescription chart design were associated with significant variations in the rates of prescribing error. The charts from NHS Highland and NHS Grampian produced significantly higher error rates than the other three charts. Participants who took longer to complete their prescriptions made significantly fewer errors, but familiarity with a chart did not predict error rate. CONCLUSIONS: This study has important implications for prescription chart design and prescribing education. The inverse relationship between the time taken to complete a prescribing task and the rate of error emphasises the importance of attention to detail and workload as factors in error causation. Further work is required to identify the characteristics of prescription charts that are protective against errors.

Phosphorus in Phoenix: a budget and spatial representation of phosphorus in an urban ecosystem.

As urban environments dominate the landscape, we need to examine how limiting nutrients such as phosphorus (P) cycle in these novel ecosystems. Sustainable management of P resources is necessary to ensure global food security and to minimize freshwater pollution. We used a spatially explicit budget to quantify the pools and fluxes of P in the Greater Phoenix Area in Arizona, USA, using the boundaries of the Central Arizona-Phoenix Long-Term Ecological Research site. Inputs were dominated by direct imports of food and fertilizer for local agriculture, while most outputs were small, including water, crops, and material destined for recycling. Internally, fluxes were dominated by transfers of food and feed from local agriculture and the recycling of human and animal excretion. Spatial correction of P dynamics across the city showed that human density and associated infrastructure, especially asphalt, dominated the distribution of P pools across the landscape. Phosphorus fluxes were dominated by agricultural production, with agricultural soils accumulating P. Human features (infrastructure, technology, and waste management decisions) and biophysical characteristics (soil properties, water fluxes, and storage) mediated P dynamics in Phoenix. P cycling was most notably affected by water management practices that conserve and recycle water, preventing the loss of waterborne P from the ecosystem. P is not intentionally managed, and as a result, changes in land use and demographics, particularly increased urbanization and declining agriculture, may lead to increased losses of P from this system. We suggest that city managers should minimize cross-boundary fluxes of P to the city. Reduced P fluxes may be accomplished through more efficient recycling of waste, therefore decreasing dependence on external nonrenewable P resources and minimizing aquatic pollution. Our spatial approach and consideration of both pools and fluxes across a heterogeneous urban ecosystem increases the utility of nutrient budgets for city managers. Our budget explicitly links processes that affect P cycling across space with the management of other resources (e.g., water). A holistic management strategy that deliberately couples the management of P and other resources should be a priority for cities in achieving urban sustainability.

Chloride effects on nitrogen dynamics in forested and suburban stream debris dams.

Organic debris dams (accumulations of organic material) can function as "hotspots" of nitrogen (N) processing in streams. Suburban streams are often characterized by high flows that prevent the accumulation of organic debris and by elevated concentrations of solutes, especially nitrate (NO(3)(-)) and chloride (Cl(-)). In this study we (1) studied the effects of urbanization on the extent and characteristics of debris dams in large and small streams and (2) evaluated the effects of NO(3)(-) and Cl(-) on rates of N cycle processes in these debris dams. In some suburban streams debris dams were small and rare, but in others factors that reduce the effects of high stream flows fostered the maintenance of debris dams. Ambient denitrification enzyme activity (DEA) in these suburban and forested streams was positively correlated with stream NO(3)(-) concentrations. In laboratory microcosms, DEA in debris dam material from a forested reference stream was increased by NO(3)(-) additions. Chloride additions constrained the response of DEA to NO(3)(-) additions in material from the forested stream, but had no effect on DEA in material from streams with a history of high Cl(-) levels. Chloride additions changed the sign of net N mineralization from negative (consumption of inorganic N) to positive in debris dam material from the forested reference stream, but had no effect on net mineralization in material from streams with a history of exposure to Cl(-). Understanding the factors regulating the maintenance and N cycling activity of organic debris, and incorporating them into urban stream management plans could have important effects on N dynamics in suburban watersheds.