Publications by Year
Spatiotemporal Dynamics of Riparian Land-Cover Change and Impervious-Cover Expansion in a Rapidly Urbanising Himalayan Capital City Land
Urbanisation and impervious-cover expansion are reshaping riparian landscapes, particularly in mountain cities where steep terrain concentrates development along valley floors. This study examined spatiotemporal land-cover change within the regulated riparian corridors of…
Urbanisation and impervious-cover expansion are reshaping riparian landscapes, particularly in mountain cities where steep terrain concentrates development along valley floors. This study examined spatiotemporal land-cover change within the regulated riparian corridors of Thimphu City, Bhutan, over a 25-year period from 1997 to 2022 using Landsat imagery, Random Forest classification and Google Earth Engine. Results show substantial transformation of riparian land cover, with impervious cover increasing from 26.14% to 32.63%, equivalent to an overall increase of 24.83%, while agriculture/barren/low-vegetation declined from 30.59% to 26.01%, equivalent to an overall decrease of 14.98%. A modest increase in detectable vegetation cover was also observed, although this should be interpreted cautiously because the study measured land-cover extent rather than vegetation condition, floristic composition or ecological quality. Classification performance was robust, with overall accuracies ranging from 89.9% to 94.5%, exceeding the commonly accepted 85% benchmark, although uncertainty remains in narrow riparian corridors due to Landsat’s 30 m spatial resolution. Mann–Kendall analysis provided supplementary evidence of monotonic land-cover trends, but the limited number of temporal observations means these results should be interpreted as indicative, rather than definitive. Spatial analysis revealed uneven transformation, with the southern valley recording the greatest increase in impervious cover. These findings demonstrate sustained development pressure within legally regulated riparian buffers and highlight the need for routine spatial monitoring, place-specific buffer management and stronger integration of riparian protection into urban planning. The study provides a quantitative baseline for assessing future riparian land-cover change and supporting more resilient land governance in rapidly urbanising Himalayan mountain cities.
Does poor regulation lead to pollution? Key takeaways from a systematic review.
Formal recycling of used lead acid batteries (ULAB) is a multibillion-dollar industry, valued at US$12.12 billion in 2024, and expected to grow to more than $26 billion within eight years. Demand for…
Formal recycling of used lead acid batteries (ULAB) is a multibillion-dollar industry, valued at US$12.12 billion in 2024, and expected to grow to more than $26 billion within eight years. Demand for recycled lead (Pb) for new batteries grows in developing countries where costs limit the uptake of lithium-ion batteries. ULAB recycling in these regions poses significant danger to human health and the environment. Stringent regulatory approaches for ULAB recycling in developing countries, intended to reduce pollution, have thus far been ineffective as they typically do not adequately cover small-scale informal recycling in rural and remote communities. We examine what characterises effective environmental regulation for ULAB recycling in developing countries through the use of a systematic review of 85 papers covering three decades of literature from 1977 to 2023, and applied constructivist grounded theory-informed thematic analysis using NVivo 14 to code and analyse data. We generated three key frameworks that characterise regulatory conditions associated with effectiveness in developing countries: well-crafted policies, adequate governance mechanisms, and mitigation measures to avoid pollution. The results indicate that effective regulation emerges from complex interactions that are simultaneously flexible and structured, inclusive yet focused, and locally relevant while also considering global efforts to address pollution-related Sustainable Development Goals.
Contrasting effects of impervious cover on riparian plant and soil bacterial communities in a rapidly urbanising Himalayan city.
Rapid urbanisation—particularly the expansion of impervious surfaces—is reshaping riparian landscapes worldwide. These areas are frequently targeted for development due to their favourable topography, abundant water resources, and aesthetic appeal. However, the impact…
Rapid urbanisation—particularly the expansion of impervious surfaces—is reshaping riparian landscapes worldwide. These areas are frequently targeted for development due to their favourable topography, abundant water resources, and aesthetic appeal. However, the impact of increasing impervious cover on soil bacterial communities in biodiverse urban riparian zones remains poorly understood, especially in developing countries, raising concerns about potential declines in essential ecosystem functions. In this study, we investigated the effects of impervious cover, quantified as the Percentage of Total Impervious Area (PTIA), on the taxonomic and functional diversity of riparian soil bacteria in Thimphu City, Bhutan. Using plot-based taxonomic profiling and metagenomic analysis across a PTIA gradient, we tested the hypothesis that bacterial diversity and functional pathways would decline beyond 40 % PTIA, mirroring patterns observed in riparian plant communities. Contrary to our hypothesis, plots with PTIA exceeding 40 % exhibited greater bacterial richness and functional diversity. These findings suggest opposing responses to impervious cover, with belowground microbial communities increasing in diversity while aboveground plant diversity declines. A significantly lower carbon-to‑nitrogen ratio in urban plots—likely driven by nutrient enrichment—emerged as the primary factor promoting bacterial diversity in high PTIA areas. This enrichment appeared to favour copiotrophic bacteria, enhancing both diversity and functional capacity. Our results suggest that bacterial communities may be effective bioindicators of riparian ecosystem health than plant communities. Incorporating microbial metrics into urban riparian management and monitoring could therefore provide valuable insights for sustaining ecosystem functions in rapidly urbanising regions
Urbanisation and specifically impervious cover alter riparian plant communities in a rapidly urbanising landscape in the Himalayas.
Impervious covers, such as roads, pavements, buildings, and parking lots, prevent water infiltration, thereby increasing surface runoff. The expansion of impervious cover along riverbanks in urban areas poses a significant threat to…
Impervious covers, such as roads, pavements, buildings, and parking lots, prevent water infiltration, thereby increasing surface runoff. The expansion of impervious cover along riverbanks in urban areas poses a significant threat to riparian ecosystems by altering species diversity and composition through hydrological changes. As dynamic ecosystems at the interface between aquatic and terrestrial environments, riparian areas play a crucial role in aquatic ecology, particularly in terms of biodiversity, bank stability, nutrient dynamics, and hydrological processes. Employing plot-based floristic sampling, this study investigated the effects of urbanisation, particularly impervious cover (quantified as PTIA, Percentage of Total Impervious Area), on riparian plant communities in the rapidly urbanising landscapes of Thimphu City, Bhutan. Additionally, other environmental variables and soil chemical properties were examined to determine whether they confounded the impacts of PTIA. The results showed that PTIA had a significant impact on the diversity and composition of riparian plant communities. Overall, higher levels of PTIA supported a greater number of plant species, including exotic species, but exhibited the lowest α-diversity and reduced tree abundance compared to reference sites (p < 0.001). These areas favoured Rumex nepalensis–Equisetum spp. community, while low PTIA supported the Calamagrostis scabrescens–Elaeagnus umbellata community. Significant changes in species diversity and community structure were observed at a PTIA threshold of approximately 60% (p < 0.05), indicating substantial ecological alterations beyond this point. Except for soil pH, which influenced plant communities independently rather than confounding PTIA’s effects, other environmental variables and soil chemical properties did not have any significant effects on riparian plant communities. Our study revealed that PTIA was the primary predictor for changes in plant communities in rapidly developing urban riparian landscapes. The relationship between PTIA and plant communities highlights the importance of considering PTIA in urban biodiversity management, as it can predict the extent of vegetated land required to sustain healthy riparian ecosystems. These findings suggest that rapidly urbanising cities can realign their urban development and riparian biodiversity management strategies by assessing existing impervious cover and establishing appropriate PTIA thresholds to balance urban growth with the conservation of riparian environments.
Microplastic Pollution in Riparian Soils of the Rapidly Growing City of Thimphu, Bhutan
Plastic has become a vitally important material for humans; however, the large amount of plastic waste generated annually pollutes the environment. Plastic decomposition generates microplastics (MPs), which have emerged as a concerning…
Plastic has become a vitally important material for humans; however, the large amount of plastic waste generated annually pollutes the environment. Plastic decomposition generates microplastics (MPs), which have emerged as a concerning global environmental pollutant because of their potential to be more harmful to the environment than their larger counterparts. This study examined the occurrence and abundance of MPs in riparian soils (RS) of a rapidly growing city in Thimphu, Bhutan. Additionally, the study investigated the relationships between the abundance of MP and several variables, such as the physicochemical properties of the soil, land use, the distance to impervious cover (IC), the plot IC%, surface plastic, textile waste, and the distance to upstream drainage outlets within the riparian zone (RZ). A density separation technique was used to extract MPs. The results showed that RS in urban sites had higher concentrations of MPs (93.3%) than in other land use (7.7%, p = 0.04). Blue MPs (46.2%) were the most common plastic colour. In urban RS, MPs ranged from 0 to 500 particles/kg. MP concentration showed a positive correlation with available phosphorus (p = 0.01) and the distance to the upstream drainage outlets (p = 0.01). Our findings highlight the nature and pathways of MP pollution in rapidly growing cities, where economic growth often overshadows environmental management. We also identify opportunities for these cities to mitigate MP pollution by reclaiming surface plastic and textile waste, stepping up recycling initiatives, and disposing of plastic-ridden waste in low-impact landfills.
Closing pit lakes as aquatic ecosystems: Risk, reality, and future uses.
Mine pit lakes are formed when open-cut pits flood with water, and these lakes occur by the thousands on every inhabited continent. The remediation and closure of pit lakes is a pressing…
Mine pit lakes are formed when open-cut pits flood with water, and these lakes occur by the thousands on every inhabited continent. The remediation and closure of pit lakes is a pressing issue for sustainable development and provision of freshwater ecosystem services. While pit lakes can be spectacular examples of recreation and renewal, pit lakes may be better known for their poor water qualities and risks to communities and the environment. Often the public wants to simply “fill the pits in” to restore a terrestrial landscape, but this is not always possible. Therefore, planning for remediation and future uses is likely to provide the best outcome. Poor water quality is not necessarily a barrier to future use, although it may limit the number of uses. Short-term future uses tend to require commercial viability, active infrastructure investment, and maintenance, and should transition to complementary long-term uses that promote biodiversity. Long-term future uses require relatively less ongoing maintenance beyond the initial investment and adhere to the principles that pit lakes should be safe, sustainable, and non-polluting in perpetuity. Pit lakes will eventually develop “ecosystem values,” and the time to do so depends on the nature of the intervention and the values ascribed by the community. Where possible, closing pit lakes as sustainable ecosystems is the most realistic goal that permits a variety of future uses that is likely to see pit lakes valued by future generations.