Course:EOSC270/2023/Group4 - The Overlooked Impacts of Sand Mining on Marine Ecosystems
Sand Mining and its Destructive Problems
The basics of sand mining
Sand mining is a common term for the extraction of sand and rock fragments from sediment deposits. Sand is the second most used resource on Earth, second only to water. Sand mining occurs on land and in marine ecosystems, with almost 40% of sand being extracted from marine sources[1]. Due to competition for land for agricultural use and urbanization, marine sources of sand are rapidly gaining popularity[1].
The human actions that cause a need for sand mining
Sand is used in most industrial processes and also used for shoreline and land restructuring[1]. Its main industrial uses are for glass production and as a binder in concrete[2]. With increasing urbanization, the demand for sand is rapidly growing to build city components like skyscrapers, thus sand mining activity has also amplified in recent decades[2]. Roughly 50 billion tonnes of sand are needed to meet global demand as of 2019[2].
Where sand mining occurs
Sand grains found in desert regions like the Sahara are too fine for industrial use, and most of the useful sands are found in river and coastal areas[2]. This includes beaches and wetlands, where mining of sediments contained in the banks is done through surface mining[3]. Another popular area for sand mining is the ocean floor, where dredging is the main extraction method of sand above 200m [4]. The effects of sand dredging on marine ecosystems are illustrated in figure 1. Majority of the ocean’s biodiversity inhabits the epipelagic layer of the ocean, or the top 200m, which makes sand mining a significant factor in ocean biodiversity endangerment. Because of the economic incentives, illegal sand mining operations and sand mafias exist in around 70 countries[2]. These illegal operations rarely follow environmental regulation, which has led to severe ecosystem health declines globally.
The pervasiveness of sand mining repercussions
Shorelines and beaches
Removal of sand from river shores and beaches drastically changes the structural soundness of shorelines and often leads to erosion[2]. This leads to flooding, river re-channeling, and recession of shorelines[3]. An example of this can be seen in the Umngi River in northern Bangladesh: mining from 2010 to 2017 caused the shorelines to become unstable, and erosion resulted in the river quadrupling in size in certain regions[2]. These impacts compound and effect agriculture and coastal infrastructure through flooding of land and shoreline deterioration[3].
Sea beds
Removal of sand from sea beds and reefs results in immediate habitat loss and deterioration of water quality[5], but the long term effects are more severe. Removal of sand causes changes in morpho dynamics; sand carried by the currents is being deposited in different regions than it normally would have without exposure to sand mining[4]. This disrupts the environment and destroys habitats, resulting in dead zones as shown in figure 3[6]. This affects fish populations in areas surrounding sand mining operations, resulting in loss of fisheries and livelihoods for coastal communities[4].
Sand Mining Impacts on Marine Ecosystems
The effects of sand mining on identified ecosystems
Sand mining has many large impacts on marine ecosystems. Everything about sand extraction affects the physical properties of coastal ecosystems. These factors include water turbidity, shoreline erosion, seafloor abrasion, nutrient removal, and many more[6][7].
Water turbidity
Water turbidity is an extremely important characteristic of oceanic ecosystems, especially along coastlines. Sand mining can greatly increase water turbidity. This decreases the photic zone, therefore, reducing primary production, which is the basis for coastal ocean life. Without primary production, life could not sustain itself (Figure 4). Water turbidity also has large effects on the ability of nekton to perform necessary life functions. Murkier waters make it more difficult for these organisms to hunt, reproduce, and even breathe.
Shoreline erosion
The erosion of shorelines poses a massive threat to many organisms. Shorelines are depended on by a large number of marine organisms such as sea turtles[8], marine birds, crabs, and many more. Without well-defined shores, these organisms may see a decrease in abundance. Another problem is the removal of sandbanks, which assist in lessening the amount of damage that storms can cause to shoreline communities[9].
Seafloor abrasion
Destruction of the seafloor has many consequences. Benthic organisms are at a large risk to due their immobility. Changing the ocean floor can also redirect ocean currents, which can have large effects on nutrient dispersal, and movement of plankton, and may also contribute to more sand movement, causing a positive feedback loop.
Nutrient removal
The ocean floor acts as a large sink for many nutrients. While many nutrients are ingested or absorbed by organisms, there is still a large amount that escapes into the ocean floor. Many of these nutrients will be naturally recycled back into the ecosystem via a combination of seafloor spreading, terrestrial rock disintegration, precipitation and many other factors. When sand is removed from the sea floor, nutrients are also removed and therefore, are taken out of that ecosystem, reducing the total amount of nutrients in the environment as a whole[10].
Unique characteristics that make oceans especially vulnerable
Marine ecosystems are especially vulnerable due to their balance of physical, biological and chemical processes (Figure 5). Examples of physical processes include ocean currents, waves, and tides. Biological processes include photosynthesis, predation, and decomposition. Chemical processes include nutrient cycles and ocean acidification. These processes heavily rely on each other and when one of the three is disturbed, the others are affected. Secondly, there are also many positive feedback loops in the ocean, meaning small changes can compound into large problems. An example of a positive feedback loop is algal blooms. Algal blooms are the result of changes in the nutrient composition of seawater that is then accelerated up to the biological level by positive feedback loops. Lastly, many areas of the ocean are nutrient-limited. A few nutrients that are limited in the ocean but are essential for growth are Nitrogen, Phosphorus, Iron, and Silica[11]. By removing nutrients from sand sediments, sand mining is only making it more difficult for marine ecosystems to obtain what they require for life.
Organisms that are impacted by sand mining
Coastal sand mining
The sand beaches are an important environment for a lot of species. It provides homes and purifies the water, thus supporting huge biodiversity of species that live and interact with sand beaches such as crabs[12], and sea turtles[13]. Also, shorebirds do not always live on sand beaches but rely on coastal food resources[14]. As an example of sand mining impact, the distribution of Ghost crabs found in tropical and subtropical sand beaches is determined to be impacted by sand mining[12]. F.E. Jonah et al. (2015) discussed that ghost crabs themselves and the food resources for ghost crabs could be taken through the process of sand mining which heavily impacts the population and size of crabs.
Seafloor sand mining
Sand mining from the seafloor is also found to impact the organisms living on the seafloor. Seafloor sediments contain polymetallic nodules which are important food sources for sessile fauna like corals and sponges, and mobile fauna like octopuses and squids[15]. Seafloor sediments are also used as their home, and it is said to be important for the interaction between species that live and interact with the seafloor sediments. The polymetallic particles in the seafloor sediments are also used by anchored species to catch the jelly falls and enhance the food supply for surrounding environments[15]. Removing these important materials and organisms that can provide resources for so many species is a significant action, which decreases the diversity and richness of the organisms on the seafloor environment, and thus negatively impacts the seafloor ecosystems.
The distribution and density of the coral reefs are also impacted by sand mining. Removing seafloor sediments can remove or bury corals during the process, and decrease the diversity of coral and coral reef fish in the sand mining area[16]. Sand mining could also cause the disturbance of the sediments during the process and could decrease the light transparency[17]. Light is a very important resource for phytoplankton, which are the primary producers of the marine ecosystem, and it supports huge biomass of zooplankton, followed by secondary consumers and so on, thus sand mining negatively impacts the marine food web and affects so many species distribution.
The extent of the impacts of sand mining
Measurable ecosystem changes due to sand mining
Sand mining increases erosion and turbidity, and decreases biodiversity in marine ecosystems. Large sand extractions lead to erosion because sediments cannot be transported fast enough to replenish the extracted sand[18] (Figure 8). Sand mining results in greater turbidity[19][20], meaning that light cannot penetrate as deep as it could with clear water conditions, and mostly supplies organisms near the water surface. Sand extraction disturbs the breeding locations[21] (Figure 8) and the migration of marine organisms[22], leading to reduced biodiversity[21]. Figure 8 shows the trenches on the seafloor that exceed 2.5 m deep, which once supported horse mussel bed habitats in Pakiri, in Auckland, New Zealand[23]. Over the past 80 years, it is estimated that the amount of sand mined in Pakiri has reached up to 10 million cubic metres[24]. Dredging companies insist that extracting Pakiri’s sand is necessary to support the expanding infrastructure in Auckland[24]. The impacts of sand mining extend further, since its effects are seen across the interconnected marine ecosystem, affecting the whole food chain[22].
The present status of sand mining compared to the past
Compared to when sand mining first started in the early 20th century, rates have tripled over the past two decades [25]. There exists limited knowledge of the effects of sand mining in the ocean, as it’s difficult to measure and evaluate. Thus, although the effects of sand mining are known, the specific numbers regarding the extent of damage are mostly not. Some of these unknown measurements include: change of water column depth, sediment composition, and shoreline change.
The effects of sand mining can be seen in locations for more than 35 years after mining has ceased [26] (Figure 9). Many effects on the physical and biological components of mined areas have stayed the same up to now with little to no improvement, including, but not limited to, seafloor morphology and the regeneration of benthic organisms. Due to the removal of sediment, there has been a reduction in seabed topography, and rising sea levels [27]. Sand mining can also have an impact on a community’s flora and fauna [26]. During recovery, areas that are mined recover with different taxonomic compositions which can affect community structure and trophic energy flow [27] (Table 1).
Numerous countries do not have laws on sand mining[20]. Presently, we lack sand mining regulations that are recognized internationally[21]. The need for global regulations arose due to the involvement of international dredging companies in sand mining[21]. In areas with regulations or where sand mining is prohibited, illegal sand mining can take place due to the high demand for sand[28]. Examples of regulations include areas that are off-limits to sand mining and restrictions in the amount and depths that could be mined[24]. Data from satellites have been used to monitor illegal sand mining activity during the night[24]. In some areas, loopholes in current regulations exist that allow dredging companies with expired permits to continue to mine sand while waiting for their permits to be renewed[24]. To developers, purchasing illegally extracted sand is attractive due to its lower cost[28]. To demonstrate the extent of this problem, illegal sand mining in India brings in $23 million (CAD) in revenue per month[28]. While expensive machinery can be used to extract large amounts of sand, sand mining can also be done with low-cost equipment by fisherman or members of the community[28]. The absence of laws and the growing demand for sand is causing unsustainable sand mining practices[20].
With its greater demand and the continued development of urban areas, the present status of sand mining has worsened compared to the past[22]. From 1900 to 2010, the worldwide need for sand grew by over 20 times[29]. Figure 10 illustrates the increase in the use of material stocks, including concrete, in the span of 110 years[29]. Sand is a component of aggregate and is used to make concrete and asphalt[29]. The majority of studies identify construction as the main reason for aggregate extraction[19]. Sand provides beneficial economic gains towards infrastructure and is used heavily in construction, as it makes up three-quarters of concrete[20]. Unrestricted sand mining hinders the work on proposed solutions to lessen the negative effects of sand mining.
The prognosis for the future if we continue on our current trajectory
In 2016, the US' production and use of construction sand and gravel was valued at $8.9 billion [30]. Due to urbanization and infrastructure development, current needs for sand amount to 50 billion tons per year and are expected to rise 5.5% per year to meet future demands [31]. At this rate, the world will deplete its sand by 2050 [32].
Long term effects from sand mining include loss of land to erosion, impact to sand and water quality, physical and biological alterations to coastal ecosystems, change in hydrological behaviour such as waves and currents, damage to urban infrastructure, and lack of protection against natural disasters [27]. If action isn’t taken to switch to a more sustainable replacement, numerous adversities can unfold. As mentioned previously, without beaches and wetlands as protection, communities may experience additional damage from floods and storm surges due to the erosion [32]. For example, because of sand mining, the Eastern Black Sea Regions has undergone coastal erosion and shoreline recession [33]. Sand particles deemed too fine to be used are discarded by dredging boats, developing dust plumes, increasing water turbidity and disturbing marine habitats[31]. As seen in Figure 9, the consequences of dredging operations can result in depressions, furrow, and pits which affects benthic communities and can hurt their chances or regeneration, since these consequences affect sand sediment and community composition [27]. Furthermore, changes in seabed elevation due to the removal of sediment can influence the waves that reach the coast, and the velocity of the current, thus affecting sediment transport, accretion patterns, and erosion.
Changes in regulations are slowly being made across many countries [31]. However, even after sand mining stops at a location, the consequences of it can last many years after [26]. Without action towards recovery for affected communities, it is likely that these conditions will prolong and worsen (Figure 11).
Potential solutions given the impacts of sand mining
International recommendations
As shown above, in recent decades the environmental impacts of sand mining have become increasing prevalent as rates of extraction increase on a global scale - with a disproportionate emphasis in poorer and rapidly industrializing countries. This has thrust sand mining to the forefront of international discussions on conservation and sustainability. With this increased awareness, international organizations such as the United Nations (UN)[34] and the World Wide Fund for Nature (WWF)[35] have released recommendations (such as figure 12) on how to prevent further damages from sand mining, as well as alternatives that may reduce industry reliance on virgin sand (sand that has never been used in the manufacturing process). Although extensive, these recommendations generally fall under four distinct categories:
- Legislation which aims to identify sand as a limited strategic resource, and in turn standardize and regulate it accordingly.
- Research which aims to map, monitor and report on sand resources to help better understand both the implications of sand mining on our ecology and to find novel alternative resources and recycling techniques.
- Sustainability which aims to incentivize the use of recycled resources and push ethical sourcing, as well as founding programs to restore ecosystems and compensate for losses.
- Education which aims to increase public awareness surrounding the harsh reality of sand mining, and aims to further educate engineers and architects on less resource dependent designs and infrastructure.
Canada's priorities
Every country is different, and each has its own priorities and concerns that they must address first. Canada's priority - as a first world country with strongly upheld industrial regulations and restrictions, as well as a GDP that isn’t reliant on sand extraction - is uncovering the ramifications of sand mining[36], and developing environmentally sustainable extraction methods and alternatives to sand as a resource . This includes taking steps to:
- Increase public awareness towards the growing demand, and finite supply of sand
- Conduct research into methods capable of driving a reduction in sand extraction and use
- Further pressing to better understand the ecological ramifications of sand mining.
Global priorities
For countries that lack strong regulations[37], and actively rely on sand extraction for both the rapid growth of their infrastructures, as well as their economies[38], the priorities shift. We focused our research on India and Bangladesh as they are model countries for rapid industrialization and consumption of sand on the global stage. Their priorities align much closer to:
- Increasing, and or establishing strong policies and legal framework around sand mining
- Increasing the enforcement of these policies in order to manage the supply of sand extraction, with the goal of reducing rates of illegal activity, as well as mitigating the damages that they have incurred
- Investments into the strict mapping, monitoring, and reporting of sand resources which would allow for a better understanding of ecological damages, locations of illegal extraction, and reduction in potential harm to those living near the site of extraction
These steps would allow countries to better understand the significance of the effects of sand mining, provide the resources and groundwork to better regulate the industry, limit the illegal exploitation of sand as a resource, and together hopefully reduce the destructive impacts that sand mining has on marine ecosystems.
References
- ↑ 1.0 1.1 1.2 Hobbs, Carl (2021). "Sand Mining". Encyclopedia of Coastal Science: 1460–1466 – via Springer Link.
- ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 Bendixen, Mette; Best, Jim; Hackney, Chris; Iversen, Lars (2019). "Time is Running Out for Sand". Nature. 571: 29–31 – via Springer Nature Limited.CS1 maint: multiple names: authors list (link)
- ↑ 3.0 3.1 3.2 Aliu, Ibrahim; Akoteyon, Isaiah; Soladoye, Olayemi (2022). Introduction to Sand Mining Activity. Cham Springer. ISBN 978-3-031-16521-4.CS1 maint: multiple names: authors list (link)
- ↑ 4.0 4.1 4.2 Miller, Kathryn; Thompson, Kirsten; Johnston, Paul; Santillo, David (2017). "An Overview of Seabed Mining Including the Current State of Development, Environmental Impacts, and Knowledge Gaps". Frontiers. 4: 418 – via Frontiers Media.CS1 maint: multiple names: authors list (link)
- ↑ Saviour, Naveen (2012). "Environmental Impact of Soil and Sand Mining: A Review" (PDF). International Journal of Science, Environment, and Technology. 1: 125–134 – via Academia.edu.
- ↑ 6.0 6.1 Beiser, Vince (February 27 2017). "Sand mining: the global environmental crisis you've probably never heard of". The Guardian. Check date values in:
|date=
(help) - ↑ Sonak, Sangeeta; Pangam, Prajwala; Sonak, Mahesh; Mayekar, Deepak. "Multiple dimensions of global environmental change". Impact of sand mining on local ecology. 5: 102–121.
- ↑ Mortimer, Jeanne A. (sep 1990). "The Influence of Beach Sand Characteristics on the Nesting Behavior and Clutch Survival of Green Turtles (Chelonia mydas)" (PDF). American Society of Ichthyologists and Herpetologists. 1990: 802–817 – via JSTOR. Check date values in:
|date=
(help) - ↑ Montague, Clay L. (July 2008). "Recovering the Sand Deficit from a Century of Dredging and Jetties along Florida's Atlantic Coast: A Reevaluation of Beach Nourishment as an Essential Tool for Ecological Conservation" (PDF). Journal of Coastal Research. 24: 899–916 – via Coastal Education & Research Foundation Inc.
- ↑ "The Sulfur Cycle". Lumenlearning.
- ↑ Bristow, Laura A.; Mohr, Wiebke; Ahmerkamp, Soeren; Kuypers, Marcel M.M. (June 2017). "Nutrients that limit growth in the ocean". Current Biology. 27: R474–R478 – via ScienceDirect.
- ↑ 12.0 12.1 Jonah, F.; Agbo, N.; Agbeti, W.; Adjei-Boateng, D.; Shimba, M. (August 2015). "The ecological effects of beach sand mining in Ghana using ghost crabs (Ocypode species) as biological indicators". Ocean and Coastal Management. 112: 18–24 – via Science Direct.
- ↑ Anthony, E. J.; Brunier, G.; Gardel, A.; Hiwat, M. (2019). Chenier morphodynamics on the Amazon-influenced coast of Suriname, South America: Implications for beach ecosystem services. Frontiers in Earth Science, 7. https://doi.org/10.3389/feart.2019.00035
- ↑ Aarif, K. M.; Nefla, A.; Nasser, M.; Prasadan, P. K.; Athira, T. R.; Muzaffar, S. B. (2021). Multiple environmental factors and prey depletion determine declines in abundance and timing of departure in migratory shorebirds in the west coast of India. Global Ecology and Conservation, 26. https://doi.org/10.1016/
- ↑ 15.0 15.1 Stratmann, T; , Soetaert, K;, Kersken, D; van Oevelen, D (2021). Polymetallic nodules are essential for food-web integrity of a prospective deep-seabed mining area in Pacific Abyssal Plains. Scientific Reports, 11(1). https://doi.org/10.1038/s41598-021-91703-4
- ↑ Brown, B. E., & Dunne, R. P. (1988). The environmental impact of coral mining on coral reefs in the Maldives. Environmental Conservation, 15(2), 159–165. https://doi.org/10.1017/s0376892900028976
- ↑ Supriharyono.(2004). Effects of Sand Mining on Coral Reefs in Riau Islands. Journal of Coastal Development, 7(2), 89-100.
- ↑ Jordan, Christian; Tiede, Jan; Lojek, Oliver; Visscher, Jan; Apel, Heiko; Quan Nguyen, Hong; Nguyen Xuan Quang, Chau; Schlurmann, Torsten (2019). "Sand mining in the Mekong Delta revisited - current scales of local sediment deficits". Scientific Reports. 9: 17823–14 – via UBC Library.
- ↑ 19.0 19.1 Koehnken, Lois; Rintoul, Max; Goichot, Marc; Tickner, David; Loftus, Anne-Claire; Acreman (2020). "Impacts of riverine sand mining on freshwater ecosystems: A review of the scientific evidence and guidance for future research". River Research and Applications. 36: 362–370 – via UBC Library.
|first7=
missing|last7=
(help) - ↑ 20.0 20.1 20.2 20.3 Rentier, Eline; Cammeraat, Erik. "The environmental impacts of river sand mining". The Science of the Total Environment. 838: 155877–155877 – via UBC Library.
- ↑ 21.0 21.1 21.2 21.3 UN Environment Programme (2022, April 26). "Our use of sand brings us "up against the wall", says UNEP report". UN Environment Programme. Retrieved 2023, February 8. Check date values in:
|access-date=, |date=
(help) - ↑ 22.0 22.1 22.2 Torres, Aurora; Brandt, Jodi; Lear, Kristen; Liu, Jianguo (2017). "A looming tragedy of the sand commons". Science (American Association for the Advancement of Science). 357: 970–971 – via UBC Library.
- ↑ Lee, Shaun (2022). "The direct effects of sand mining". Shaun Lee. Retrieved 2023, February 8. Check date values in:
|access-date=
(help) - ↑ 24.0 24.1 24.2 24.3 24.4 Verboeket, Anna (September 2022). "Pakiri sand miner offers a last-minute concession". Newsroom. Retrieved https://www.newsroom.co.nz/pakiri-sand-miner-offers-last-minute-concession. Check date values in:
|access-date=
(help) - ↑ Peduzzi, Pascal (April 26, 2022). "UNEP - Press Conference: Sand and Sustainability 2022 Report".
- ↑ 26.0 26.1 26.2 Mielck, Finn; Rune, Rune; Hass, H. Christian; Hertel, Sarah; Caroline, Ganal; Werner, Armonies (March 2021). "Persistent effects of sand extraction on habitats and associated benthic communities in the German Bight". Biogeosciences. 18: 3565–3577 – via European Geosciences Union.
- ↑ 27.0 27.1 27.2 27.3 Nairn, Rob; Johnson, Jay A.; Hardin, Dane; Michel, Jacqueline (2004). "A Biological and Physical Monitoring Program to Evaluate Long-term Impacts from Sand Dredging Operations in the United States Outer Continental Shelf". Journal of Coastal Research. 20(1): 126–137 – via BioOne Complete.
- ↑ 28.0 28.1 28.2 28.3 Rege, Aunshul (2016). "Not biting the dust: using a tripartite model of organized crime to examine India's Sand Mafia". International Journal of Comparative and Applied Criminal Justice. 40: 101–121.
- ↑ 29.0 29.1 29.2 Krausmann, Fridolin; Wiedenhofer, Dominik; Lauk, Christian; Haas, Willi; Tanikawa, Hiroki; Fishman, Tomer; Miatto, Alessio; Schandl, Heinz; Haberl, Helmut (2017). "Global socioeconomic material stocks rise 23-fold over the 20th century and require half of annual resource use". Proceedings of the National Academy of Sciences - PNAS. 114: 1880–1885 – via UBC Library.
- ↑ Aurora, Torres; Liu, Jianguo; Brandt, Jodi; Lear, Kristen (Sep 2017). "The High Cost Sand Mining Extracts from Coastal Ecosystems". The New Humanitarian. Oceans Deeply.
- ↑ 31.0 31.1 31.2 Dybas, Cheryl Lyn (2020). "Sand: A Resource That's Washing Away". Oceanography. 33: 8–10 – via Oceanography.
- ↑ 32.0 32.1 Rentier, E.S. Rentier; Cammeraat, L.H. (2022). "The environmental impacts of river sand mining". Science of the Total Environment. 838(1): 155877 – via Elsevier.
- ↑ Sonak, Sangeeta; Pangam, Prajwala; Sonak, Mahesh; Mayekar, Deepak (2006). "Impacts of sand mining on local ecology".
- ↑ Velpen, A., Smeets, A., Torres, A., Matheson, A., Friot, D., Franks, D., Cuperus, Geert., Yusuf, H., van der Vegt, H., Selby, I., Lynggaard, J., Dawson, K., Pereira, K., Gallagher, L., Goichot, M., Russell, M., Hemon, N., Chuah, S., Wagenaar, S., Peduzzi, P., Lancker, V., Guigoz, Y. (2022, May). UNEP 2022. Sand and sustainability: 10 strategic recommendations to avert a crisis. GRID-Geneva, United Nations Environment Programme, Geneva, Switzerland https://unepgrid.ch/en/resource/2022SAND
- ↑ Uncovering sand mining’s impacts on the world’s rivers. (2018, August 24). Retrieved from https://wwf.panda.org/wwf_news/?333451/Uncovering-sand-minings-impacts-on-the-worlds-rivers
- ↑ Zaidi, D. (2021, December 21). Our demand for sand is leading to a sustainability crisis: experts. CTV. Retrieverd from https://www.ctvnews.ca/sci-tech/our-demand-for-sand-is-leading-to-a-sustainability-crisis-experts-1.5715512
- ↑ Khan, Mohd Imran (August 25, 2022). "Illegal sand mining is destroying rivers in Bihar". Scroll.in. Retrieved March 1, 2023.
- ↑ Rentier, E.S.; Cammeraat, L.H. (May 13, 2022). "The environmental impacts of river sand mining". Science of The Total Environment. 838 – via Elsevier Science Direct.