Rapid Transit Research Articles

Dissecting household carbon and energy inequality: A decade's insight into regional disparities and urban-rural dynamics in China

Substantial inequalities exist in carbon and energy footprints across households in China, due to variations in income and consumption patterns. Examining these inequalities and their driving factors amid the rapid economic and energy transition is crucial for making informed climate policies. Here, we investigate the variations and driving factors of household carbon and energy inequality across urban and rural areas and ten income groups in China during 2007–2017 by employing the environmentally extended multiregional input–output approach and national household consumption survey data. The results reveal that urban regions tend to exhibit higher carbon and energy footprints, coupled with greater inequality, compared to rural regions. The carbon and energy inequalities in the less developed provinces are mainly attributed to urban-rural differences, whereas in the more developed provinces, intra-urban differences play a dominant role. The carbon and energy inequality declined in China during 2007–2017. We argue that the reduction in carbon and energy inequality in China can be attributed to footprints increases in rural regions, a trend that should be carefully considered in future low carbon development policy formulation.

Challenges and facilitating factors in interorganizational knowledge acquisition: evidence from the Orange Line Metro Train System and Sustainable Bus Rapid Transit Corridor

PurposeThis paper aims to identify challenges and facilitating factors in interorganizational knowledge acquisition. For this purpose, the interorganizational settings of the Orange Line Metro Train System and Sustainable bus rapid transit (BRT) Corridor in Pakistan are examined.Design/methodology/approachThis study uses an exploratory multiple case study approach. The empirical data encompasses semi-structured interviews and archival documents. Within and cross-case analyses are used for analyzing the data.FindingsThe findings identify challenges such as time pressure, knowledge hiding, finding credible information sources, organizational red tape and facilitating factors such as clear objectives, individual interest and personal commitment, and revisiting the organizational culture and environment in which interorganizational knowledge acquisition takes place.Originality/valueBy examining knowledge acquisition in interorganizational projects, this study contributes to the literature on knowledge-based theory.

Multi-criteria decision-making for the selection of best airport ground access mode with a new fuzzy rough-entropy based method

In order to cope with the inherent complexities and uncertainties of settings such as transportation problems, the adoption of proper decision procedures becomes a pivotal issue. Particularly, multi-criteria group decision-making (MCGDM) uses multiple evaluations of the options based on several criteria to select the optimal choice and/or rank the alternatives. In this paper we are interested in the Entropy-REGIME method for MCGDM and its ability to handle uncertainty in the presence of fuzzy rough numbers (that allow the practitioner to represent and process imprecise data). To this end we propose a hybrid framework of the fuzzy rough-entropy based REGIME method that involves two main components: fuzzy rough-entropy for the evaluation of the objective weights of the decision criteria, and fuzzy rough-REGIME to rank the alternatives based on the weighted criteria. Its motivation is a case study that concerns the selection of the best transport mode to access Istanbul newly constructed airport. We consider four alternatives for ground access options, namely, underground metro, bus rapid transit, light rail transit, and premium bus services. Our findings show that an underground metro system is the optimal mode, followed by light rail transit, bus rapid transit, and premium bus services. Additionally, to demonstrate the superiority and effectiveness of the proposed technique, comparisons are made with existing methods.

Public transit and the needs of people experiencing homelessness: a directed content analysis guided by Maslow’s hierarchy of needs

ABSTRACT Transportation has rarely been a variable of interest in studying homelessness, yet its role in the lives of people experiencing homelessness (PEH), especially those in U.S. urban areas, is critical. The National Academies of Sciences, Engineering, and Medicine found transit agencies often frame riders experiencing homelessness as a problem to solve. Examining the experiences of PEH riders and appreciating the centrality of transit vehicles, properties, and personnel in the lives of PEH are critical to craft ethical solutions. Research question: How does the Dallas Area Rapid Transit system meet the daily needs of individuals experiencing homelessness? We utilized a descriptive phenomenological research design to frame the interview questions and then used Maslow’s hierarchy of needs in service of directed content analysis. We interviewed 42 PEH in Dallas, Texas, who also used the local transit system. Themes included “Transit Meets Basic Needs of Rest and Homeostasis,” “Ambivalent Safety on Transit,” “Transit and Recognition Needs,” and “Transit as a Metaphor for Being Needs.” Findings are discussed in light of previous literature and the potential for critical intervention.

The wildfire impacts of the 2017-2018 precipitation whiplash event across the Southern Great Plains

The Southern Great Plains of the United States is a region with a sharp zonal precipitation gradient that is prone to rapid transitions in precipitation extremes. Transitions from pluvial to drought conditions can lead to the green-up of vegetation during extreme rainfall, posing a considerable fire risk as the region rapidly transitions into drought. Such transitions have been studied in depth across regions such as California; however, limited studies have examined their impacts across the Southern Great Plains. The aim of this study was to examine the role of preceding precipitation whiplash events in providing fuel for wildfires, with 2017–2018 investigated as a case study. This study specifically demonstrates the relationship between precipitation, vegetation, and wildfires for the first time across the Southern Great Plains. Lag correlation analysis of historical data at our study site showed anomalously high precipitation 8 months prior to Spring wildfires, resulting in a significantly higher number of wildfires and acres burned. In particular, this study examined a highly impactful precipitation whiplash event that occurred during the Fall of 2017 across the Oklahoma and Texas panhandles, which preceded a mega-fire event in the Spring of 2018. Precipitation anomalies that were 137% of normal during the 2017 growing season rapidly cascaded into drought conditions with precipitation anomalies 21% of normal throughout the cool winter season. Excessive precipitation supported vigorous vegetation recovery and growth, with vegetation indices peaking at approximately 1 standard deviation above average during August 2017. However, the subsequent drought period rapidly desiccated the terrestrial surface. As a result, dozens of wildfires burned a total of 556 347 acres during March and April 2018, resulting in at least two fatalities, dozens of homes destroyed, and over 500 personnel dispatched to fight and mitigate the fires. Overall, this study highlights the significant role of preceding Fall precipitation whiplash events in fueling Spring wildfires across the Southern Great Plains, particularly exemplified by the impactful 2017–2018 case, highlighting the complex dynamics between extreme precipitation, vegetation growth, and subsequent fire risks in the region.

Socio-political dynamics in clean energy transition

A rapid and effective transition to low-carbon energy production is essential to limit climate change impacts. While the scientific community has mostly focused on research and development and techno-economic aspects, quantifying the role of public acceptability and policy in shaping emission trajectories has been much more elusive. This study investigates the coupled dynamics of nonlinear socio-political acceptance and anthropogenic CO2 emissions, with implications for climate policies and clean energy investments. Our findings show that a top-down policy approach alone may not be sufficient for effective emission cuts, highlighting the need for a multi-level strategy that combines top-down and bottom-up approaches. Additionally, opinion polarization can trigger detrimental CO2 emission oscillations when governments decide to take heavy-handed policy interventions in highly polarized socio-political systems. Delayed perception of climate change damage or abrupt reactions to extreme weather events may also significantly affect emission reduction efforts, although in the opposite direction. Integrating these socio-political dynamics into climate models can enhance our understanding of the complex interplay between human and natural systems, enabling the development of more effective and resilient mitigation strategies.

Relevance of the legal regulation of military infrastructure capital construction objects during of the initial period of the Great Patriotic war

The article attempts to summarize some aspects of the experience of legal regulation of capital construction of military infrastructure facilities, which was accumulated during the Great Patriotic War, especially during its most difficult, first period, when the initiative was in the hands of the aggressor, and the Soviet state faced the vital issue of rapid economic transition, including military-the construction complex — on the rails of functioning in conditions of a real military threat. The idea of the continuing relevance of this experience in the current situation of a real threat to the sovereignty of Russia is consistently carried out, proposals are formulated on the need, taking into account the specifics of the construction of the above-mentioned facilities, to codify the norms governing the capital construction of military defense infrastructure facilities in the Military Construction Code of the Russian Federation with the unity of command of the federal body in the field of defense — the Ministry of Defense of the Russian Federation at all stages capital construction of these facilities.

An Effective Model for Capturing the Role of Excitonic Interactions in the Wave-Packet Dynamics of DNA Nucleobases

Investigating exciton dynamics within DNA nucleobases is essential for comprehensively understanding how inherent photostability mechanisms function at the molecular level, particularly in the context of life’s resilience to solar radiation. In this paper, we introduce a mathematical model that effectively simulates the photoexcitation and deactivation dynamics of nucleobases within an ultrafast timeframe, particularly focusing on wave-packet dynamics under conditions of strong nonadiabatic coupling. Employing the hierarchy equation of motion, we simulate two-dimensional electronic spectra (2DES) and calibrate our model by comparing it with experimentally obtained spectra. This study also explores the effects of base stacking on the photo-deactivation dynamics in DNA. Our results demonstrate that, while strong excitonic interactions between nucleobases are present, they have a minimal impact on the deactivation dynamics of the wave packet in the electronic excited states. We further observe that the longevity of electronic excited states increases with additional base stacking and pairing, a phenomenon accurately depicted by our excitonic model. This model enables a detailed examination of the wave packet’s motion on electronic excited states and its rapid transition to the ground state. Additionally, using this model, we studied base stacks in DNA hairpins to effectively capture the primary exciton dynamics at a reasonable computational scale. Overall, this work provides a valuable framework for studying exciton dynamics from single nucleobases to complex structures such as DNA hairpins.

Refining the scale of the rural-urban landscape: A policy-relevant application to Chile

The rural-urban divide has traditionally been used to characterize key features of regions, including features of economic geography like density and connectivity that determine the prospects for economic growth and other dimensions of territorial development. In this paper, we develop a methodology that identifies areas along the urban-rural continuum according to their key features of population density and distance to large urban settlements at a more-detailed scale than the smallest administrative areas, taking Chile as a case study, a country that has experienced a rapid socio-economic transition over the last three decades. Information derived from the application of this methodology allows the identification of geographic categories according to observable density and distance. We also present geographic definitions of urban, rural, and mixed areas, which allow a practical, policy-relevant taxonomy of the rural-urban landscape, consistent with the 3-tier approach taken in most OECD countries. We demonstrate the relevance and practical importance of this smaller-scale approach by showing that, in the case of Chile, there is a significant mismatch between the official, cruder definitions, based on political subdivisions and currently in use by the government, and the realities of the country's present rural-urban landscape. Our results demonstrate that a focus on the scale at which information can be interpreted and summarized is not merely an academic exercise, but a way of correctly identifying, within the policymaking framework, communities according to the realities of their needs and capabilities.

Epidemiological analysis of hospitalization of the elderly in Brazil between 2019 and 2023

Brazil has seen an increase in the elderly population as a result of falling mortality rates. Associated with the ageing process, there is an increased risk of developing comorbidities, which is why the health system has found it difficult to keep up with the rapid demographic transition and support this more fragile section of the population. The aim of this study was to describe the epidemiological aspects of hospitalization of the elderly in Brazil. This is a retrospective epidemiological study, with a quantitative approach, which used data from the Hospital Information System and the Unified Health System, made available by the Department of Informatics of the Unified Health System, for the period 2019 to 2023. The variables analyzed were: type of care, gender, race, reason for hospitalization, cause of death and region with the highest incidence. 16,779,162 elderly people were admitted to hospital units: 78% (n= 16,069,729) were admitted as emergencies. Of these individuals, 51% (n= 8,595,199) were male and 41% (n= 6,892,500) were white. Initially, 21% (n= 3,485,803) were hospitalized for diseases related to the circulatory system, but the main cause of death was pneumonia, which accounted for 7% (n= 1,195,048) of these patients, and was most prevalent in the southeast region with 508,696 deaths. Hospitalizations of the elderly in Brazil are on the rise, and epidemiological characteristics, a reduction in the number of public investments and social factors are determining factors in this variation. The main related diseases are those affecting the cardiovascular and respiratory systems, accounting for almost half of the deaths in this age group. The increase in the number of hospitalizations demonstrates the need to formulate public policies to improve the quality of life of the elderly population.

Single-Cell RNA Sequencing of Mutant Whole Mouse Embryos: From the Epiblast to the End of Gastrulation.

Over the last decade, single-cell approaches have become the gold standard for studying gene expression dynamics, cell heterogeneity, and cell states within samples. Before single-cell advances, the feasibility of capturing the dynamic cellular landscape and rapid cell transitions during early development was limited. In this paper, a robust pipeline was designed to perform single-cell and nuclei analysis on mouse embryos from embryonic day E6.5 to E8, corresponding to the onset and completion of gastrulation. Gastrulation is a fundamental process during development that establishes the three germinal layers: mesoderm, ectoderm, and endoderm, which are essential for organogenesis. Extensive literature is available on single-cell omics applied to wild-type perigastrulating embryos. However, single-cell analysis of mutant embryos is still scarce and often limited to FACS-sorted populations. This is partially due to the technical constraints associated with the need for genotyping, timed pregnancies, the count of embryos with desired genotypes per pregnancy, and the number of cells per embryo at these stages. Here, a methodology is presented designed to overcome these limitations. This method establishes breeding and timed pregnancy guidelines to achieve a higher chance of synchronized pregnancies with desired genotypes. Optimization steps in the embryo isolation process coupled with a same-day genotyping protocol (3 h) allow for microdroplet-based single-cell to be performed on the same day, ensuring the high viability of cells and robust results. This method further includes guidelines for optimal nuclei isolations from embryos. Thus, these approaches increase the feasibility of single-cell approaches of mutant embryos at the gastrulation stage. We anticipate that this method will facilitate the analysis of how mutations shape the cellular landscape of the gastrula.

Smart Mobility and Sensor Based-BRT Crusade, the Challenge for Auto Mechanics and Technicians in Africa

African countries with no globally recognized auto manufacturing factories are flooded with the most modern automobiles as soon as they are commercialized in the absence of commensurate skilled local auto mechanics across the continent. In the wake of the Bus Rapid Transit (BRT) scheme in Abuja Nigeria, the first set of luxurious buses purchased ended up as junks within a short period of operation largely due to lack of technician competency. The continuous patronage of a few multinational workshop garages like Toyota, Honda, Kia Motors, etc is hindering the transport agencies from breaking even. This paper is therefore aimed at evaluating the state of bus auto-mechanics and technicians in Nigeria for sustainable hybrid buses for effective BRT in the country. Google search engine was used to source secondary data from dedicated transport and energy-related sites like National Research Council (NRC) Agora Verkehrswende and GIZ, Smart city study, USDoT, and Africa Transport Solution, for the current paradigm shift in automobile energy management. Participatory surveys were carried out in two major motor mechanic villages that house over two hundred (200) workshops. The study reveals that there is a yawning gap between the societal ideal auto-mechanic expectations and the operational woe realities. This work becomes very relevant in view of global urbanization and the crusade for Hybrid Bus Rapid Transit (HBRT) in urban mobility as a panacea to COP28 carbon emission reduction. It is recommended that policymakers in urban transportation at all levels should ensure the certification and re-training of the motor mechanics to be able to maintain those imported modern buses while investing in ITS-based road infrastructure for sustainable BRT in their country

The Influence of the Auxiliary Ligand in Monofunctional Pt(II) Anticancer Complexes on the DNA Backbone.

Monofunctional platinum complexes offer a promising alternative to cisplatin in cancer chemotherapy, showing a unique mechanism of action. Their ability to induce minor helix distortions effectively inhibits DNA transcription. In our study, we synthesized and characterized three monofunctional Pt(II) complexes with the general formula [Pt(en)(L)Cl]NO3, where en = ethylenediamine, and L = pyridine (py), 2-methylpyridine (2-mepy), and 2-phenylpyridine (2-phpy). The hydrolysis rates of [Pt(en)(py)Cl]NO3 (1) and [Pt(en)(2-mepy)Cl]NO3 (2) decrease with the bulkiness of the auxiliary ligand with k(1) = 2.28 ± 0.15 × 10-4 s-1 and k(2) = 8.69 ± 0.98 × 10-5 s-1 at 298 K. The complex [Pt(en)(2-phpy)Cl]Cl (3) demonstrated distinct behavior. Upon hydrolysis, an equilibrium (Keq = 0.385 mM) between the complexes [Pt(en)(2-phpy)Cl]+ and [Pt(en)(2-phpy-H+)]+ was observed with no evidence (NMR or HR-ESI-MS) for the presence of the aquated complex [Pt(en)(2-phpy)(H2O)]2+. Despite the kinetic similarities between phenanthriplatin and (2), complexes (1) and (2) exhibit minimal activity against A549 lung cancer cell line (IC50 > 100 μΜ), whereas complex (3) exhibits notable cytotoxicity (IC50 = 41.11 ± 2.1 μΜ). In examining the DNA binding of (1) and (2) to the DNA model guanosine (guo), we validated their binding through guoN7, which led to an increased population of the C3'-endo sugar conformation, as expected. However, we observed that the rapid transition 2E (C2'-endo) ↔ 3E (C3'-endo), in the case of [Pt(en)(py)(guo)](NO3)2 ([1-guo]), slows down in the case of [Pt(en)(2-mepy)(guo)](NO3)2 ([2-guo]), resulting in separate signals for the two conformers in the 1H NMR spectra. This phenomenon arises from the steric hindrance between the methyl group of pyridine and the sugar moiety of guanosine. Notably, this hindrance is absent in [2-(9-MeG)] (9-MeG = 9-methylguanine), probably due to the absence of a bulky sugar unit in 9-MeG. In the case of (3), where the bulkiness of the substitution on the pyridine is further increased by a phenyl group, we observed a notable proximity between 9-MeGH8 and the phenyl ring of 2-phpy. Considering that only (3) exhibited good cytotoxicity against the A549 cancer cell line, it is suggested that auxiliary ligands, L, with an extended aromatic system and proper orientation in complexes of the type cis-[Pt(en)(L)Cl]NO3, may enhance the cytotoxic activity of such complexes.

Cognitive abilities are associated with rapid dynamics of electrophysiological connectome states

Abstract Time-varying changes in whole-brain connectivity patterns, or connectome state dynamics, hold significant implications for cognition. However, connectome dynamics at fast (> 1Hz) timescales highly relevant to cognition are poorly understood due to the dominance of inherently slow fMRI in connectome studies. Here, we investigated the behavioral significance of rapid electrophysiological connectome dynamics using source-localized EEG connectomes during resting-state (N=926, 473 females). We focused on dynamic connectome features pertinent to individual differences, specifically those with established heritability: Fractional Occupancy (i.e., the overall duration spent in each recurrent connectome state) in beta and gamma bands, and Transition Probability (i.e., the frequency of state switches) in theta, alpha, beta, and gamma bands. Canonical correlation analysis found a significant relationship between the heritable phenotypes of sub-second connectome dynamics and cognition. Specifically, principal components of Transition Probabilities in alpha (followed by theta and gamma bands) and a cognitive factor representing visuospatial processing (followed by verbal and auditory working memory) most notably contributed to the relationship. We conclude that rapid connectome state transitions shape individuals' cognitive abilities and traits. Such sub-second connectome dynamics may inform about behavioral function and dysfunction and serve as endophenotypes for cognitive abilities.

Double malnutrition and associated factors in a middle-aged and older, rural South African population

IntroductionDouble malnutrition (co-existing overnutrition and undernutrition) is increasingly prevalent in sub-Saharan Africa due to rapid epidemiological and nutritional transitions. In this region, studies of double malnutrition have largely been conducted at country and household level, with individual-level studies primarily limited to children and women of reproductive age. We investigated the prevalence and determinants of individual-level double malnutrition in middle-aged and older adults who constitute an increasing proportion of the sub-Saharan African population.Methods250 individuals aged 40–70 years (50% women) and resident in the Agincourt Health and socio-Demographic Surveillance System in rural Mpumalanga province, South Africa, were randomly selected. Double malnutrition was defined as overweight/obesity and anaemia only, overweight/obesity and iodine insufficiency, or overweight/obesity and any micronutrient deficiency (anaemia and/or iodine insufficiency). The Chi-squared goodness of fit test was used to compare the expected and observed numbers of individuals with the type of double malnutrition. Logistic regression was used to investigate determinants of each type of double malnutrition.ResultsDouble malnutrition was present in 22–36% of participants, depending on the definition used. All types of double malnutrition were more common in women than in men (overweight/obesity and anaemia: 34% vs. 10.2%, p < 0.01; overweight/obesity and iodine insufficiency: 32% vs. 12.2%, p < 0.01 and overweight/obesity and any micronutrient deficiency: 50.5% vs. 20.4%, p < 0.01). There were no differences between the overall expected and observed numbers of individuals with combinations of overweight and micronutrient deficiencies [overweight/obesity and anaemia (p = 0.28), overweight/obesity and iodine insufficiency (p = 0.27) or overweight/obesity and any micronutrient deficiency (p = 0.99)]. In models adjusted for socio-demographic factors, HIV and antiretroviral drug status, and food security or dietary diversity, men were 84–85% less likely than women to have overweight/obesity and anaemia, 65% less likely to have overweight/obesity and iodine insufficiency and 74% less likely to have overweight/obesity and any micronutrient deficiency.ConclusionsIndividual-level double malnutrition is prevalent in middle-aged and older adults in a rural sub-Saharan African community. Interventions to improve nutrition in similar settings should target individuals throughout the life course and a focus on women may be warranted.

Advancing sustainable development through circular economy and skill development in EV lithium-ion battery recycling: a comprehensive review

The rapid worldwide transition to electric vehicles (EVs), propelled by progress in lithium-ion battery (LIB) technology, brings opportunities and problems in sustainable development and resource management. This study examines how incorporating circular economy ideas and enhancing skills in EV LIB recycling can be a strategic approach to meeting the 2030 Agenda for Sustainable Development. The article explores the relationship between environmental sustainability, economic growth, and social fairness by studying EV battery recycling, the workforce skills gap, and the economic ramifications of a circular approach. Based on the existing literature, the study highlights the importance of circular economy practices in improving resource efficiency, decreasing environmental pollution, and supporting various Sustainable Development Goals (SDGs), especially those concerning responsible consumption and production (SDG 12), climate action (SDG 13), and industry, innovation, and infrastructure (SDG 9). The study highlights the significance of Education for Sustainable Development (ESD) in preparing the workforce with the essential skills to adapt to a more sustainable and circular economy. It also highlights significant obstacles in present recycling methods, such as technological limitations, legislative discrepancies, and the necessity for worldwide collaboration and standardization. The paper suggests practical policy suggestions and future research paths to improve the sustainability of EV battery recycling. The initiatives involve establishing global recycling standards, promoting circular economy models through incentives, boosting technological innovation, and facilitating international collaboration and knowledge exchange.

Successful Rapid Transition from Methadone to Buprenorphine without Bridging Methods: A Case Report

Background: Patients with opioid use disorders often require methadone or buprenorphine during their treatment. For safety and convenience, buprenorphine is preferred over methadone during the treatment course, but transitioning a patient from methadone to buprenorphine can be challenging.

Governing offshore wind: is an ‘Asia-Pacific Model’ emerging?

ABSTRACT The Asia-Pacific region is emerging as central to the deployment of offshore wind power. Large scale offshore wind involves complex governance challenges, and governments can choose to centralize and streamline processes enabling the construction of offshore wind farms. We develop a framework for comparing site selection and consenting processes for offshore wind farms, and examine whether a more streamlined and centralized model of offshore wind governance is emerging in the major Asia-Pacific markets of Japan, the People’s Republic of China, South Korea, Taiwan, and Vietnam. We also examine whether policy targets and framework legislation are used in these markets, and whether renumeration schemes are being applied. We find limited evidence of convergence in some aspects of offshore wind governance, but that governance models in the region remain diverse. We suggest there remains scope for facilitating learning across different Asia-Pacific markets as governments work to ensure the governance of siting and consenting meets the needs of stakeholders, while enabling offshore wind supports rapid low carbon energy transition goals.

Fast reversion of hydrophility-superhydrophobicity on textured metal surface by electron beam irradiation

Reversible hydrophilic-hydrophobic transitions on metal surfaces are challenging in surface-wetting treatment. Existing preparation methods have the disadvantages of requiring a long time, producing a metal oxide layer, and being difficult to implement. In this paper, a rapid reversible transitions between hydrophilicity and superhydrophobicity was achieved on the surface of 316L stainless steel using laser etching combined with electron beam irradiation. The contents of C–C/C–H hydrophobic functional groups was found to be notably increased by low electron dose in the experiments. The contents of C-O-C, O-C = O and –OH hydrophilic functional groups decreased. The interaction of excited secondary electrons with precursor molecules generated free radical fragments that adsorbed onto surfaces and formed new chemical bonds, changing the content of the functional groups. Reversible hydrophilic and superhydrophobic transitions could be achieved by adjusting the electron dose. The contact angle continually changed from 91° to 160° with a beam current of 100 μA, to 17° with 300 μA, and back to 90° with cleaning. The entire procedure required only four minutes. Meanwhile, the superhydrophobic state with contact angle of 160° has a sliding angle of 6°, presenting excellent resistance to bacterial adhesion, UV irradiation, and delayed icing.

Complex hydrology and variability of nitrogen sources in a karst watershed.

Streams draining karst areas with rapid groundwater transit times may respond relatively quickly to nitrogen reduction strategies, but the complex hydrologic network of interconnected sinkholes and springs is challenging for determining the placement and effectiveness of management practices. This study aims to inform nitrogen reduction strategies in a representative agricultural karst setting of the Chesapeake Bay watershed (Fishing Creek watershed, Pennsylvania) with known elevated nitrate contamination and a previous documented groundwater residence time of less than a decade. During baseflow conditions, streamflow did not increase with drainage area. Headwaters and the main stem lost substantial flow to sinkholes until eventually discharging along large springs downstream. Seasonal hydrologic conditions shift the flow and nitrogen load spatially among losing and gaining stream sections. A compilation of nitrogen source inputs with the geochemistry and the pattern of enrichment of δ15N and δ18O suggest that the nitrogen in streams and springs during baseflow represents a mixture of manure, fertilizer, and wastewater sources with low potential for denitrification. The pH and calcite saturation index increased along generalized flow paths from headwaters to springs and indicate shorter groundwater residence times in baseflow during the spring versus summer. Given the substantial investment in management practices, fixed monitoring sites could incorporate synoptic water sampling to properly monitor long-term progress and help inform management actions in karst watersheds. Although karst watersheds have the potential to respond to nitrogen reduction strategies due to shorter groundwater residence times, high nitrogen inputs, effectiveness of conservation practices, and release of legacy nutrients within the karst cavities could confound progress of water quality goals.