Agnieszka Gałuszka, Neil L. Rose, Andy B. Cundy, Michael Wagreich, Yongming Han, Simon Turner, William Shotyk

Changes in the environment affect all living organisms. The reaction of biota to these changes depends on both their character and scale, and on the ability of an organism or a group of organisms to tolerate them.Environmental changes dramatically accelerated after the mid-twentieth century, which is aproposed starting date of the Anthropocene Epoch, compared to theearlier slow-progressing changes caused solely by natural factors. Rapid human population growth limits the availability of areas and resources necessary for the proper functioning of ecosystems, which causes habitat fragmentation, habitat loss, and the overexploitation of populations. Contaminants emitted into the environment from anthropogenic sources are another example of human-induced stress on all living organisms, including humans. The reactions of biota to such environmental changes include shifts in population ranges, biodiversity loss, species extinctions, as well as adaptive evolutionary response. In this essay we present examples of human-induced changes representing major threats to ecosystems during the Anthropocene. We focus on both physical factors (land-use changes) and on different types of contaminants that can have adverse effects on organisms in the critical zone. The critical zone refers to the terrestrial surface and near-surface environment which supports life on Earth.

Land-use changes, such as the conversion of forests to arable lands and urbanization, promote soil erosion and runoff, which often lead to species decline and extinction through habitat fragmentation, degradation, and/or habitat loss. Even if those changes do not cause immediate species extinctions, they may affect reproductive capacity, modify species interactions such as food webs, and change the structure and functioning of ecosystems. Reduced habitat availability and quality increases competition and predation. Modified habitats provide opportunities for colonization and expansion by new species, including invasive ones. It has been shown that invasive species are generally more tolerant to changes in the environment than non-invasive ones. The predominance of invasive species in an ecosystem causes a loss in biodiversity.

Contaminants can be toxic and have an adverse effect on living organisms at environmentally relevant concentrations. Some contaminants may also react with natural substances or with other pollutants and cause more serious deterioration of the environment. For example, when acidifying compounds (precursors of acidity, such as sulfur oxides and nitrogen oxides in the air) are deposited in lakes and rivers and on land, they cause a drop in the pH of surface waters, groundwaters, and soils. Some of the consequences of the acidification of soils and surface waters include the increased mobility and bioavailability of potentially toxic metals such as aluminum.

Acidification in the terrestrial and marine hydrosphere

In many regions in the world, theacidification of poorly buffered lakes and rivers caused by adrop in the pH value of precipitation led toserious environmental problems, especially in the later part of the twentieth century, such asfish kills andforest decline. Sulfuric and nitric acids (H₂SO₄, HNO₃) produced in the process of chemical transformations of sulfur dioxide and nitrogen dioxide in the air were deposited as acid precipitation. These chemical transformations have anthropogenic sources: livestock farming is a major source of ammonia which undergoes nitrification, producing H⁺ ions and thus lowering the pH of rainfall. Acidification caused by NH₃/NH₄⁺ is delayed in time, but it is as effective as that caused by sulfur and nitrogen dioxides. Although S and N emissions to the atmosphere have declined in many regions of the world, climate change acts to confound recovery from acidification. For example, increased storminess draws up additional chloride ions to surface waters, reducing their acid neutralizing capacity (ANC) and pH.

Ocean acidification, caused by an increase in atmospheric CO₂ emissions, changes the carbonate system which creates a risk of marine biodiversity loss, especially for those organisms that build shells, tests, and skeletons of calcium carbonate, which include corals, mollusks, echinoderms, crustose algae, and foraminifers. Ocean acidification events have had a profound impact on organisms during Earth’s history, and the current pH value of surface ocean water (8.1) is probably the lowest it has been for the last two million years.

Reduced pH often leads to elevated metal mobilization from soils and sediments (due to desorption and dissolution), increased solubility in soil solutions and surface waters, and shifts to more toxic chemical species. For example, before theremediation of the abandoned Iron Mountain Mine (California, USA),water concentrations of Zn, Cu, and Cd ions on site were several grams per liter; these concentrations exceed by thousands of times the concentrations considered safe for aquatic organisms. Measured to have a pH value below 3.0, the mine’s wastewater caused several massive fish kills whendischarged into the Sacramento River. Such local extinctions of acid-sensitive species also cause imbalances in the biogeochemical cycles within freshwater systems. An acidic surface water pH decreases the bioavailability of nutrients and other bioessential elements, such as phosphorus, calcium, and magnesium.

Anthropogenic acidification occurs rapidly. Natural acidification, in contrast, is usually a long-term process, caused by carbonic acid in precipitation, surface and groundwaters, and by the accumulation and dissociation of humic acids (both of these are weak acids). These, combined with a gradual decrease in the rate of soil mineral weathering, as well as the oxidation of N and S compounds, slowly lowers the pH of soils over time. Thus, the response of aquatic organisms to rapid acidification is not based on long-term evolutionary adaptations, and rapid acidification often leads to species decline.

Eutrophication and hypoxia in aquatic environments

Increased industrial nitrogen and phosphorus inputs recorded globally since the early 1900s causeeutrophication (an excess accumulation of nutrients) in aquatic environments. Phosphorus and nitrogen are limiting factors for algal growth and their increased availability results in algal blooms. The growth of algae, in turn, produces a large amount of organic matter, which consumes oxygen during decomposition. This often leads to hypoxia (a depletion in oxygen) or even anoxia (a lack of oxygen) in aquatic systems. Estuaries and coastal areas are especially affected by nutrient overload which has resulted in a significant spread of hypoxia globally.

Eutrophication leads to changes in community structure through the loss of intolerant or sensitive species and the increase of opportunistic species. Theloss of up to 60 percent of coral biodiversity by eutrophication has been observed in parts of Indonesia. In Australia and North America, complete communities ofvascular plant species have disappeared due to the competitive effects of eutrophication. Anoxia resulting from eutrophication causes extensive fish kills. Shallow, coastal, and estuarine areas where low oxygen levels have caused the loss of marine life are often referred to as “dead zones.” One of the best-knownexamples of a hypoxic “dead zone” is found west of the Mississippi delta, taking up an area of approximately 20,000 km².

Potentially toxic trace elements

Anthropogenic pollution with metals started in prehistoric times with thedevelopment of metal ore mining and smelting. This long history of metal use has left a clear signal in different environmental archives. However,global-scale metal pollution accelerated in the mid-twentieth century not only from metal ore mining and smelting, but also from fossil-fuel combustion; this is especially true for lead, copper, mercury, and zinc (see table below). Production and consumption trends forCu, Pb, and Zn show that about 90 percent of each of these metals was used during the twentieth century. The most important source of the chromium, manganese, tin, and thallium present in the environment is coal combustion which, along with artisanal gold mining, is also one of the major sources of environmental mercury. Emissions from oil combustion are the predominant industrial sources of nickel and vanadium in the atmosphere. Many metals present in environments, including Cd, Cr, Cu, Ni, Pb, and Zn originate from non-ferrous metal production. Thefluxes of copper, lead and zinc increased dramatically after the Second World War, and thenstarted to decline around the 1980s in industrialized countries.Lead emissions reached a peak between the 1960s to the 1980s and thendecreased due to a variety of measures: theimplementation of air pollution control technologies,reductions in the maximum allowable concentrations of lead in gasoline followed by theintroduction of unleaded gasoline, and, finally,the phase-out and elimination of leaded gasoline altogether.

Metals, except for mercury, occur in the air as constituents of airborne particulates. In the form of sub-micron aerosols with long atmospheric residence times, they can travel thousands of kilometers from their source regions and are transported to the most remote parts of the globe. Atmospheric deposition of metals in the form of aerosols is one of the most important sources of these elements in surface environments, including waters. The history of the changing sources and intensity of atmospheric metal deposition can be reconstructed using environmental archives such as peat bogs, ice cores, and aquatic sediments. Freshwater (especially varved lakes) and anoxic marine sediments can also be used, although in some instances these sites may be disturbed by complex geochemical processes or bioturbation.

Metals occur in the environment as different chemical species, including elemental forms, free ions, complexes, and inorganic compounds. Their behavior in the environment is complex, and changes in chemical forms are common as a result of both natural processes (e.g., microbially-mediated biomethylation), or anthropogenic activity (e.g., dissolution of salts in acidic waters). The mobilization of metals from polluted sites may increase their bioavailability and toxicity.

Some of these metals are bioessential trace elements, such as zinc, manganese, copper, and iron; others, including cadmium, lead, and mercury are potentially toxic to all living organisms. There are several plant species tolerant to high concentrations of metals (metallophytes), but their tolerance is a result of evolutionary adaptation to soils that are naturally enriched in metals. For example, sap of the tree Pycnandra acuminata growing on nickel-rich ultramafic soil in New Caledonia contains a concentration of up to 25 percent nickel. Anthropogenic metal pollution creates relatively novel environments for living organisms with toxic metals as abiotic stressors. However, some organisms can easily adapt to new environmental conditions and even take advantage of the presence of contaminants: testate amoebae, for example, use fly ash particles for shell construction in a heavily polluted ombrotrophic peatland in the Izery Mountains at the border of Poland, the Czech Republic, and Germany.

Organic contaminants

Organic contaminants are compounds that occur in the environment from either natural (e.g., polycyclic aromatic hydrocarbons) or anthropogenic sources (e.g., polybrominated diphenyl ethers).Organic contaminants began to cause a major concern in the 1960s when theadverse effect of organochlorine pesticides became evident. Numerous organic compounds, with a wide range of molecular structures and properties, have been released into the environment from anthropogenic sources. They are usually liquids or solids showing hydrophobic and semi-volatile characteristics. Their tendency to be soluble in lipids gives them their bioaccumulative properties, a tendency for accumulation in sediments and soils, and for biomagnification in the food chain. Many organic contaminants are resistant to microbial and oxidative degradation, and therefore have a long residence time in the environment. In the atmosphere, they are subjected to long-range transport either in the gaseous phase or adsorbed onto solid particulates. Because of these properties, organic contaminants have been recorded in the most remote areas of the world.

Because of their toxicity, bioaccumulative properties, and very long residence time in the environment, the most important group of organic pollutants are persistent organic pollutants (POPs). POPs can be divided into three classes: pesticides, industrial chemicals, and by-products. Pesticides are mostly used in agriculture as insecticides and herbicides. They are also applied to control insect-borne diseases, although their use for this purpose has been restricted to several locations. In the 1970s,many countries banned the use of organochlorine pesticides, the best-known example of which is dichlorodiphenyltrichloroethane (DDT). The other main persistent pollutants of this class are dieldrin, endrin, hexachlorophene, and hexachlorocyclohexane isomers.

The POP class of industrial chemicals includes polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), and per- and polyfluorinated compounds (PFCs). PCBs had a number of industrial applications, mostly as liquids in capacitors and transformers. They were also added to paints, lubricants, solvents, and plasticizers. Theuse and production of PCBs was banned in the US in the late 1970s, andin Europe in the 1980s.PBDEs, produced since the 1970s andbanned in Europe in the 2000s, wereutilized as flame retardants, fumigants, and antifungals. PFCs are mainly used as protective coatings on paper and textiles, as fire-fighting foams, and as leveling agents for paints and lubricants. They are very resistant to degradation because the carbon-fluorine bond present in their molecule is one of the strongest chemical bonds—for this reason they have been labelled “forever chemicals.” Concentration trends of both pesticides and industrial chemicals in environmental archives usually follow their trends in production and use, and show sharp decline after they are banned. However, there can be a lag in reduction in concentrations of these compounds in sediments due to delayed transport within catchments subsequent to deposition.

Dioxins and polycyclic aromatic hydrocarbons (PAHs) are examples of the third class of POPs, the by-products, which are not intentionally produced for specific applications. These compounds may also originate from natural sources under specific conditions, such as volcanic emissions and wildfires. However, most come from anthropogenic sources, such as fossil fuel combustion and the combustion of organic materials in the presence of chlorine releasing dioxins. Various dates for maximum inputs of PAHs have been recorded in sediments worldwide. The peaks of PAH concentrations were found in sediments layers from the 1950s inEurope and the US, the 1960–70s inSouth America, from the 1980s to the present inChina, and in the 1940s inJapan.Dioxins in sediment cores from Europe and the US show increasing trends from the 1940s andpeak concentrations between the 1960s and the 1970s.

POPs are toxic to humans, and chronic exposure to low doses of POPs can be carcinogenic. Some of the POPs, for example PCBs and dioxins, are endocrine disruptors. PCBs cause growth defects, liver damage, and may be carcinogenic to aquatic organisms. Although thelevels of PCBs in the environment decreased after restrictions on their use in many countries, the high persistence of these pollutants often allows their presence to remain at toxic concentrations, and such legacypollutants still appear to adversely affect biota. Because POPs bioaccumulate as they are transferred through the food chain, their toxicity mostly affects top predators, reducing reproduction and causing long-term population decline. For example, after prolonged exposure to POPs, regional extinctions in predatory birds were observed. Insecticides cause regional decline in terrestrial insects, fish, and bird populations. Some POPs impair physiological processes in individuals, including immune suppression. Such effects were found in seals and white-tailed eagles in the Baltic Sea environment. Organometallic compounds, such as organotin compounds (e.g., tributyltin, triphenyltin) used in antifouling paints, cause reproductive failure in marine gastropods.

Pharmaceuticals represent another important group of biologically active chemicals in the aquatic environment. They consist of thousands of individual compounds used for diagnosis, treatment and prevention of diseases in humans and domesticated animals. These include, amongst others, antibiotics, hormonal contraceptives, anti-inflammatory drugs, antihypertensives, and analgesics. Some pharmaceuticals are extremely stable in the environment. For example, gadolinium complexes used as contrast agents in magnetic resonance imaging are not degraded in wastewater treatment plants, and may be transported several kilometers after their release into rivers. Some pharmaceuticals are endocrine disruptors (e.g., 17β-estradiol); others, such as antibiotics and anti-inflammatory drugs, induce oxidative stress in cells, cause changes in enzymatic processes, and are genotoxic and cytotoxic.

Microplastics

Microplastics are polymers with dimensions <5 mm, however some authors define their size as <1 mm or even 0.06-0.5 mm. Microplastic fragments, microbeads, and fibers are ubiquitous in aquatic and surface environments. They have been found on the coastlines of every continent, in deep-sea and remote locations, in lake and river sediments, soils, air, plants, as well as animal and human tissues. Microplastics have also been found in food consumed by humans. Recent studies have documented the ingestion of 39,000-52,000 particles per year per person in North America. Considering other sources of microplastics in humans (inhalation and intake with drinking water) increases these estimates dramatically.

The most important sources of microplastics are residential households (with washing machines producing 100 particles/L), landfills, industrial facilities, ships and marine platforms, agriculture, and tire abrasion. It has been shown that toxic organic compounds in seawater are preferentially adsorbed into plastic particles. Microplastics are able to adsorb, accumulate and transport POPs in the environment; however, the potential health hazards from desorption of POPs from microplastics to biota or humans have not been assessed. The toxicity of microplastic can be caused by additives such as plasticizers, antioxidants, anti-static agents, and flame retardants. Some of these compounds interfere with metabolic processes mediated by hormones (e.g., phthalates). These additives are leached directly into fresh and marine waters, and they can also be absorbed by organisms that consume microplastic particles.

It has been estimated that in marine environments, over 250 species are regularly ingesting plastic. Microplastics disrupt algal feeding, cause a significant decline in freshwater invertebrate and amphibian populations, decrease copepod fertility, impair water filtering in sessile animals, and induce an inflammatory response in a wide range of organisms. Trophic level transfer of microplastics in the marine food web is also a cause for concern. Current environmental concentrations of microplastics include a considerable legacy component due to plastic durability, the recycling of microplastics through food chains, and the transfers between storage and release in dynamic sedimentary systems.11Chiara E. P. Bancone, Simon D. Turner, Juliana A. Ivar do Sul, and Neil L. Rose, “The Paleoecology of Microplastic Contamination.” Frontiers in Environmental Science, vol. 8 (2020): p. 154, https://www.frontiersin.org/articles/10.3389/fenvs.2020.574008/full.

Other human-induced changes

Of the other factors which may have an impact on the proper function of ecosystems, the most important are light pollution and noise. Light pollution in terrestrial environments is primarily caused by building and area lighting, advertising, and streetlights, whereas in marine environments light pollution comes mostly from the artificial light from coastal cities. Noise pollution originates from numerous sources on land, including industry and traffic. Recreational boating, shipping, and industrial activity are examples of noise pollution sources in the aquatic environment. Changes in environmental light levels result in shifts in the timing of living activities, which can lead to reduced foraging success, such as in the case of marine turtles showing impaired seaward orientation. Noise can be considered as a factor disrupting effective communication in animals. After exposure to noise levels of about 40 dBA, different responses were observed on individual, population, and ecosystem levels: The most important effects of noise on animals are altered vocal behavior, avoidance of noisy habitats, and altered vigilance and foraging behavior, all of which can produce changes in ecosystem structure. Acoustic pollution in the marine environment is also believed to adversely affect reproduction of marine mammals.

Documenting anthropogenic changes in environmental archives

Past anthropogenic changes can be reconstructed from analyses of certain indicators such as contaminants in dateable samples. Environmental archives are natural depositories of information, which happen to record the history of anthropogenic impacts on the environment. In order to obtain new knowledge of temporal changes of the compounds of interest that are preserved in environmental archives (e.g., contaminant concentrations during the Anthropocene), a multistep approach is needed. Five major steps in such studies are schematized here:

Both abiotic and biotic environmental archives that register emission trends over time can be used for paleoenvironmental reconstructions (see below). Samples are collected, divided into increments, and then split into subsamples which are subjected to age dating and all of the analyses of interest (e.g., physical, chemical, mineralogical, and isotopic measurements).

Samples corresponding to the Anthropocene should be dated with a high degree of resolution, preferentially using more than one method. Some environmental archives, such as ice cores, tree rings, and laminated lake sediments, show annual or seasonal layers which can be used for high-precision dating.

Natural archive samples typically require dedicated and unique sampling strategies and specific methods of sample treatment. Undisturbed cores of peat and unconsolidated sediments are critical for accurate dating and precise reconstructions. Usually, two parallel cores are sampled with specialized devices in order to minimize errors from sampling. Ice core sampling and analysis requires additional, special precautions: because of the extremely low concentrations of contaminants and other Anthropocene signals in polar regions, the outermost layers must be careful removed in a clean lab environment to allow study of the innermost, uncontaminated samples. In the case of studying microplastics as an Anthropocene signal, density separation in salt solutions varying in concentration is required for isolation of microplastics from the matrix.

The Anthropocene signals can be measured and determined using a variety of optical methods and analytical techniques (summarized above). For the determination of metals, a wide variety of spectroscopic methods can be used. Persistent organic pollutants are determined with applications of chromatographic methods. Stable isotopes and many radioactive isotopes are measured using a range of mass spectrometry techniques.22More details about the methods of the Anthropocene signal determinations in environmental archive samples can be found in Gałuszka et al., 2017.

Anthropogenic changes in the environment, beyond just their character and scale, are remarkable because they affect all living organisms and all environments. Numerous responses of biota to these changes have been observed, from behavioral avoidance to the adaptation to new habitats. Pollution with metals, persistent organic compounds, organometallic compounds and microplastics, and light and noise are new limiting factors to all species, especially to sensitive ones. This leads evolutionary ecologists to claim that humans have become a new evolutionary force. Anthropogenic changes in the environment are rapid in comparison with most natural changes and have created evolutionarily novel conditions for organisms. However, not all parts of the world have been equally affected by anthropogenic activities. Spatial and temporal trends in contamination show different patterns in the Northern and Southern Hemispheres, with greater intensity of contamination in more industrialized regions. However, some of the pollutants, including many pharmaceuticals and persistent organic pollutants, are biologically active even at very low concentrations. Biodiversity loss as a consequence of anthropogenic activity has reached rates unprecedented in the history of human civilization.

Although our knowledge on how multiple stressors might interact to affect living organisms in their habitats is still limited, the interactive effects of surface water acidification with toxic metals have been studied in more detail. What is clear is that changes in ecosystem structure and functioning, often leading to population declines, regional extinctions, and the predominance of opportunistic, invasive species, will leave a signal in future fossil records which, together with historical trends in accumulation of contaminants in the environmental archives, will document the history of the human impact on the environment in the Anthropocene Epoch.

Agnieszka Gałuszka is Full Professor at the Institute of Chemistry, of the Jan Kochanowski University in Kielce. She is an expert in geochemistry and biogeochemistry.

Neil L. Rose is Professor of Environmental Pollution and Palaeolimnology in the Department of Geography, University College London. His research uses natural archives, especially lake sediments, to assess the spatial and temporal distributions of pollutants.

Andy B. Cundy is Professor of Environmental Radioactivity, and Research Director of the University consultancy and research unit GAU-Radioanalytical, in the School of Ocean and Earth Science at the University of Southampton.

Michael Wagreich is Full Professor of Geology at the Department of Geology, Faculty of Earth Sciences, Geography and Astronomy, of the University of Vienna.

Yongming Han is a professor at the Institute of Earth Environment, Chinese Academy of Sciences. His research focuses on the use of biomass burning and fossil fuel markers to study environmental and climate change.

Simon Turner is a Senior Research Fellow in Geography at University College London, United Kingdom (UK). He has recently started as Scientific Coordinator for the Haus der Kulturen der Welt (HKW) and Anthropocene Working Group (AWG) project to define a global boundary stratotype section and point (GSSP) for the start of the Anthropocene.

William Shotyk is Professor and Bocock Chair for Agriculture and the Environment at the University of Alberta, Faculty of Agricultural, Life & Environmental Sciences, in the Department of Renewable Resources.

Cover art by Protey Temen, © all rights reserved Protey Temen

Please cite as: Gałuszka, A, N L Rose, A Cundy, M Wagreich, Y Han, S Turner, W Shotyk (2022) Anthropogenic Threats to Ecosystems in the Anthropocene. In: Rosol C and Rispoli G (eds) Anthropogenic Markers: Stratigraphy and Context, Anthropocene Curriculum. Berlin: Max Planck Institute for the History of Science. DOI: 10.58049/r2r5-9q50