Monitoring riverine traffic from space: The untapped potential of remote sensing for measuring human footprint on inland waterways

A global systematic map of knowledge of inland commercial navigation effects on freshwater ecosystems

Inland navigation is one of the most sustainable transport alternatives to help decarbonise the world economy. However, the likely impacts of intensifying inland navigation on freshwater ecosystems are difficult to predict. A global map of knowledge that considers both abiotic and biotic responses to increasing shipping traffic and developing infrastructures is lacking. Deriving general evidence-based assessments is challenging, because most studies on inland navigation impacts are merely descriptive and either consist of local case studies, or address single navigation stressors or specific taxa only. We conducted a systematic mapping of the published literature (1908-2021) to provide a global synthesis of the effects of inland navigation on the biotic and abiotic components of freshwater ecosystems. We show that only half of the reported navigation-related impacts were statistically tested. Navigation itself (vessel operation) had mainly negative effects on native taxa (57%), followed by waterway management (40%), and navigation infrastructures (35%). Navigation has direct negative impacts caused by physical disturbances such as vessel-induced waves, and indirect impacts that facilitate the spread of aquatic invasive species, and altering the abiotic habitat conditions. Thirty percent of the tested relationships showed non-significant impacts on the biotic environment, while in 10% of cases impacts were context-dependent. We identified the main gaps of knowledge, namely (i) impacts of waterway management on communities, (ii) underlying processes of navigation impacts on river ecosystems; and (iii) interactions between multiple navigation factors and cascading effects on multi-taxa responses. These future research directions should improve the diagnosis, mitigate the negative impacts of navigation on rivers and provide guidelines for improving navigated river management.

Sand mining in the Mekong Delta: Extent and compounded impacts

Sand mining has accelerated in recent years primarily due to population increase and rapid urbanization. To meet demand, the rate of sand extraction often exceeds the rate of natural replenishment with serious environmental consequences. In this review paper, the Vietnamese Mekong Delta (VMD), a global hotspot for sand mining with a prolonged history of intensive riverbed extraction, is used as a representative case study to highlight the extent and compounded impacts of this activity. The sand mining budget of the VMD ranged from 8.5 to 45.7 Mm3/yr. The large difference is due to the use of different methods to determine the sand mining budget as well as the difficulties associated with measuring the volume of sand extracted from the riverbed. Widespread illegal mining in the region further exacerbates the mismatch. The environmental consequences of riverbed sand mining include deeply incised riverbeds that result in riverbank and coastal erosion. Massive sediment removal has also led to river water level reductions, disrupted hydrological connectivity, and diminished floodplain inundation. In addition, the augmented backwater effect that results from riverbed lowering, amplifies the extent of saltwater intrusion in the dry season. While the physical and hydrological impacts of sand mining is well studied, studies on the ecological and socio-economic ramifications remain sparse. In addition, the ways in which upstream dams, irrigation infrastructure, excessive groundwater extraction, and sea-level rise (SLR) have amplified the effects of sand mining was also considered in this review. This paper concludes by advocating for the adoption of remote sensing-based approaches for effective mapping of sand mining activities and the need to mine sustainably to balance developmental needs with environmental conservation.

A global rise in alluvial mining increases sediment load in tropical rivers

Increasing gold and mineral mining activity in rivers across the global tropics has degraded ecosystems and threatened human health1,2. Such river mineral mining involves intensive excavation and sediment processing in river corridors, altering river form and releasing excess sediment downstream2. Increased suspended sediment loads can reduce water clarity and cause siltation to levels that may result in disease and mortality in fish3,4, poor water quality5 and damage to human infrastructure6. Although river mining has been investigated at local scales, no global synthesis of its physical footprint and impacts on hydrologic systems exists, leaving its full environmental consequences unknown. We assemble and analyse a 37-year satellite database showing pervasive, increasing river mineral mining worldwide. We identify 396 mining districts in 49 countries, concentrated in tropical waterways that are almost universally altered by mining-derived sediment. Of 173 mining-affected rivers, 80% have suspended sediment concentrations (SSCs) more than double pre-mining levels. In 30 countries in which mining affects large (>50 m wide) rivers, 23 ± 19% of large river length is altered by mining-derived sediment, a globe-spanning effect representing 35,000 river kilometres, 6% (±1% s.e.) of all large tropical river reaches. Our findings highlight the ubiquity and intensity of mining-associated degradation in tropical river systems.

Life Cycle Assessment of River Sand and Aggregates Alternatives in Concrete

Urbanization processes in Asia are still ongoing; thus, aggregate demand is expected to increase in following years. Even though construction and demolition waste is a source for secondary building materials in industrialized countries, it is not yet an alternative construction material source in Vietnam as the urbanization process is still ongoing. Thus, there is a need for river sand and aggregates alternatives in concrete, namely manufactured sand (m-sand) from primary solid rock materials and secondary waste materials. The focus in the present study for Vietnam was on m-sand sand as alternative for river sand, and different ashes as alternatives for cement in concrete. The investigations comprised concrete lab tests according to the formulations of concrete strength class C 25/30 in accordance with DIN EN 206, followed by a lifecycle assessment study in order to identify the environmental impact of the alternatives. In total 84 samples were investigated, consisting of 3 reference samples, 18 samples with primary substitutes, 18 samples with secondary substitutes, and 45 samples with cement substitutes. This kind of holistic investigation approach comprising material alternatives and accompanying LCA was the first study for Vietnam, and even for Asia, and represents a substantial added value for future policy development in order to cope with resource scarcity. The results show that with the exception of metamorphic rocks, all m-sands meet the requirements for quality concrete. In terms of cement replacement, the mixes showed that a higher percentage of ash reduces the compressive strength. The compressive strength values of the mixes with up to 10% coal filter ash or rice husk ash were equivalent to the C25/30 standard concrete formulation. Higher ash contents up to 30% lead to the reduction of the concrete quality. The LCA study's results highlighted the better environmental footprints across environmental impact categories in the 10% substitution material in comparison to the use of primary materials. The LCA analysis results showed that cement as a component in concrete holds the highest footprint. The use of secondary waste as alternative for cement provides significant environmental advantage.