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.
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.
Incorporating Microbes into Environmental Monitoring and Mine Closure Programs: River Diversions as Test Beds
Sedimentation Rates In Two Pit Lakes: Implications For Riverine Flow-Through As A Closure Strategy
Seasonal River Flow-through As A Pit Lake Closure Strategy: Is It A Sustainable Option In A Drying Climate?
Trophic roles of tadpoles in tropical Australian streams.
Biophysical Closure Criteria Without Reference Sites: Evaluating River Diversions Around Mines.
A global analysis of terrestrial plant litter dynamics in non-perennial waterways.
Bio-physical closure criteria without reference sites: realistic targets in modified rivers.
Impacts of Artisanal Small-Scale Gold Mining on Water Quality of a Tropical River (Surow River, Ghana).
Regulation of artisanal small-scale gold mining (ASGM) in Ghana and Indonesia as currently implemented fails to adequately protect aquatic ecosystems.
Omnivory and opportunism characterize food webs in a large dry-tropics river system.
Dynamics of habitats and macroinvertebrate assemblages in rivers of the Australian dry tropics.
Breach and decant of an acid mine lake by a eutrophic river: river water quality and limitations of use .
Macroinvertebrate assemblages in rivers of the Australian dry tropics are highly variable.
Gut content and stable isotope analyses provide complementary understanding of ontogenetic dietary shifts and trophic relationships among fishes in a tropical river.
Invertebrate assemblages in dry tropical rivers challenges current monitoring programs.
Ecological dynamics of rivers in the dry tropics.
An ecological risk assessment of irrigation in the Ord River catchment, a highly disturbed and poorly understood area in the wet-dry tropics of Australia.
An ecological risk assessment of the impact of irrigation on the ecological values of the Ord River was undertaken. The Ord River is located in the wet-dry tropics of Western Australia and…
An ecological risk assessment of the impact of irrigation on the ecological values of the Ord River was undertaken. The Ord River is located in the wet-dry tropics of Western Australia and has been highly disturbed by grazing and irrigation developments. The construction of two dams has changed the river from being seasonally dry to now having permanent flows downstream of the dams. The Ord River Irrigation Area (15,000 Ha) is fed by waters from the Kununurra Diversion Dam. Approximately 50% of the water is returned to the river downstream mixed with drainage from the farms. Comparatively little is known of the ecology of the Ord River, although recent research efforts are starting to address this. The risk assessment focused on the area between the Ord River Dam and upper boundary of the estuary. A mass balance of nutrients, sediments and water for the Lower Ord River clearly demonstrated that irrigation drainage was the principal source of nutrients. The low knowledge base for the system resulted in a qualitative risk assessment largely guided by expert opinion. Priority ecological consequences were identified as loss of biodiversity and biota kills (primarily through biocides), weeds and lastly algal blooms and channel infilling. The priorities were used to guide further research. Low stakeholder involvement in the assessment was believed to undermine the sense of ownership of the process. A low knowledge base limited the assessment to being purely qualitative and dominated by expert opinion. Further research should allow a second iteration of the process to produce more useful outcomes and some quantitative risk assessments.
Sustainable Futures for Australia’s Tropical Rivers: A strategy for developing research directions for Australia’s tropical river systems
A framework for assessing & managing ecological risks associated with irrigation enterprises.
Preliminary materials budget (nutrients and sediments) in the Ord River: Implications for current and proposed irrigation areas.
An ecological risk assessment (ERA) was undertaken of the impacts of irrigation return on the Lower Ord River catchment. A materials budget (mass balance) for nutrients and sediment was prepared for the…
An ecological risk assessment (ERA) was undertaken of the impacts of irrigation return on the Lower Ord River catchment. A materials budget (mass balance) for nutrients and sediment was prepared for the ERA process to establish the relative contribution of irrigation return to the catchment. The Ord River Dam (forming Lake Argyle) effectively splits the River catchment into two sections. The lower section ranges from downstream of the Ord River Dam to near Carlton Crossing (the upper extent of the salt wedge). This section receives irrigation return from the Ivanhoe Plains and Packsaddle Plains areas and will be the focus of this study. In addition, runoff from rangelands enters through several creeks and the Dunham River. All relevant water quality and flow data from the irrigation area or River were used to prepare the budgets. A high degree of interpolation and assumption was necessary due to the limited data availability, which limits the accuracy of the final budgets. Despite this, it appears that irrigation return water is a substantial contributor of Phosphorus (P) and nitrate/nitrite to the Lower Ord River. In comparison with rangelands, the irrigation area produced significantly higher loads of P, nitrate/nitrite and suspended sediment per unit area and in total. The return water produced a detectable increase in river P and nitrate/nitrite concentrations. This paper will discuss the impact of these results on current planning for the development of Ord Stage II and in moves towards best management practices within the current irrigation area.
Using an environmental risk assessment approach in determining priorities related to the impact of irrigation return on river environments. A case study fo the Ord River Irrigation Area.
The National Program for Irrigation Research and Development has established a research project to develop and test a generic framework for assessing the ecological risks associated with irrigation return. Three irrigation areas…
The National Program for Irrigation Research and Development has established a research project to develop and test a generic framework for assessing the ecological risks associated with irrigation return. Three irrigation areas are involved in the study, Goulburn-Broken, Fitzroy (Qld) and the Ord River. This paper reports on the Ord River project. The aim of the study was to identify likely ecological risks associated with irrigation systems within the Lower Ord River catchment and rank the risks based on the use of conceptual models. The Ord River catchment under consideration was bounded by the Ord River Dam (Lake Argyle) and the upper extent of the salt wedge at Carlton Crossing. Despite limited availability of flow and water quality data for the irrigation area or the Ord River, a mass balance model was produced and general trends observed. A key finding was that irrigation return water was a substantial contributor of Phosphorus (P) and nitrate/nitrite to the Lower Ord River. Initial stakeholder meetings held in Perth and Kununurra identified weeds, channel infilling, biota kills, algal blooms and loss of biodiversity as key ecological consequences of irrigation. Two simple conceptual models were then produced. One shows the role water quantity plays in the risk of ecological consequences occurring. The other model takes a different approach and identifies what factors biota require for their continued health and looks at the risks irrigation poses to those factors. Risks were assigned and then averaged to produce a risk assessment matrix. Subsequent stakeholder meetings ranked the consequences in terms of priority, with biota kills and loss of biodiversity first, followed by weeds. Algal blooms and channel infilling were seen as being of least importance or not substantially impacted by irrigation. Plans for ongoing project work and how results from this study contribute to other community and research activities in the Ord will be discussed.