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Anthroturbation and the
Anthropocene: areview of
human influence on the
Earth’s geomorphology
Texas State University
Department of Geography
Biogeomorphology
Spring 2015
Christina Lopez
April 28, 2015
1 Anthroturbation and the Anthropocene: a review of human influence on the Earth’s geomorphology
Anthroturbation and the Anthropocene: a review of human
influence on the Earth’s geomorphology
Abstract
As the field of biogeomorphology develops, the acknowledgement of the human influence on the
planet emerges as a realization of utmost importance. Human population and evolution on the
Earth are making a visible impact on the landscape nearly inescapable. This has led academics and
researchers to debate the creation of a new geologic epoch “the Anthropocene” or the “Age of the
Humans.” Taking this recognition further, some scientists are now refuting a founding principle
of Earth science because of this human influence. The history of human impact as a geomorphic
agent will be reviewed through the expression of the fruition of human development. Defining the
“Anthropocene epoch” within the differing scales of anthroturbation, and the systems of fluvial
geomorphology modifications, generates an overview of the inevitable conclusion that humans are
now the largest geomorphic agent on the planet and have been the dominate force for some time.
Keywords: Anthropocene, Legacy sediment, Human impacts, Fluvial geomorphology
Introduction
Humans have modified their physical environment to improve the quality of life. An indirect effect
of this is the change of land use, which rids the environment of its native species, as well as alters
the geomorphic processes based on the destruction or construction of various structures. The
impacts of wildlife have been well noted throughout the literature. The cultural view of most
humans is to clear their territory of predators. Therefore it is easily recognized that strong
associations between the decline of carnivore populations and high human population density
2 Anthroturbation and the Anthropocene: a review of human influence on the Earth’s geomorphology
exists (Woodroffe 1999). As predators decrease, more people settle into the “safe territory” and
make further modifications to create an urban environment. Consequently, urbanization is the
leading cause of species extinction (McKinney 2005). Urbanization has offered an interesting
outcome to the few species that remain. A phenomenon termed “urban-adaptable” has created a
biological homogenization in major cities worldwide. This has allowed the same few species to
thrive in these urban environments while approximately 785 species have become extinct, with an
additional 16,300 becoming endangered around the globe. (IUCN 2015). A shift to the majority of
humans residing in urban areas has also caused biogeomorphic instabilities with the grouping of
domesticated animals in a managed environment. Impacting most of the world’s wildlife, severe
environmental issues have arisen: soil erosion, overgrazing, soil compaction (resulting in increased
runoff), and surface water quality contamination (Butler 2013). With a global population of 7.2
billion, human dominance over the landscape has imposed multiple challenges to the Earth’s
ecosystem, atmosphere, and geomorphic equilibrium. This paper’s focus is to expose evidence in
support of the proposition that human beings are the greatest geomorphic agents this planet has
yet to support. Through the history of human existence, the consequences of biogeomorphological
progress of humans is evident. There has been an alteration to one of the largest geomorphic forces
of sediment transportation, and stratigraphic disturbances, as well as geological formations, with
human mishaps embedded which form our recent anthroturbated history.
History
Through population increase and the establishment of civilization, the Earth’s surface and
subterranean landscape, have become a resource for a society with never-ending needs. All through
the planet’s history, plants and animals have bioturbated the Earth but not to the extent of humans.
Geologists used the presence of animal burrows in the fossil record to define the Cambrian epoch
3 Anthroturbation and the Anthropocene: a review of human influence on the Earth’s geomorphology
(Zalasiewicz et al. 2014) and may now be adding another epoch based on human bioturbation also
referred to as anthroturbation.
Human progression as geomorphic agents
Paleolithic
There has been little evidence of dinosaur burrowing or primate burrowing (Hooke 2000). The
assumed beginning of landscape modification in various forms through the Homo erectus species
may have begun in the early to middle Paleolithic. The Paleolithic was characterized by the
Pleistocene epoch of geologic time (~2.6 Mya -12,000 years ago). It has also been denoted as the
Stone Age, as well as the time modern humans began moving out of Africa, according to the Out
of Africa Hypothesis. It has been discovered that this now-extinct species of hominid had been
creating sizeable dwellings with the movement of small boulders for walls and stone rubble serving
as foundations. As the name Stone Age implies, during the later period of the Paleolithic, humans
found stones to be useful as simple tools. More specifically, rocks such as flint were mined on the
shallow surface through digging with bones. By the end of the Paleolithic, mining activity had
produced depressions over 10 meters in depth and 10 meters in length (Bromehead 1954)
Mesolithic through the Bronze Age
With the settlement of the hunter gathers in the middle Mesolithic, humans began farming. This
circumstance may have changed due to the increase in population. Alternatively, population
increase may have been the result of farming because of warmer climatic conditions. The
Pleistocene glaciers began to retreat, sea level rose, and an extinction of many large-bodied animals
could have promoted this change in cultural structure and expansion of civilizations. Notable
anthroturbation occurred with the excavating of mud for bricks, tilling the soil for croplands, and
4 Anthroturbation and the Anthropocene: a review of human influence on the Earth’s geomorphology
displacement of soils on a larger scale with small canal construction for water consumption. The
practice of melting copper in the late Mesolithic eventually led to the addition of tin to copper,
thus composing a stronger alloy in the Neolithic about 7,000 years ago. Just as in the early days of
mining flint, history repeated itself as humans used these metallic resources as weaponry and then
advanced to quarrying large amounts for stone structures. Lastly, the most vital concept in human
history transpired during this period (about 5,000 years ago). The development of the wheel led to
increased ability to transport geologic materials as well as human mobility. As people rapidly
learned, a wheel revolves with more ease and speed on paved terrain. Thus more modification and
anthroturbation followed as infrastructure emerged.
Iron Age through the Industrial Revolution
Throughout the dramatic improvements of human progress as geomorphic agents, this age has
altered the surface of the Earth more than the past ages of humanity combined. Nearly 2500 years
ago, the use of iron as a tool increased human’s ability to move Earth with the incorporation of
hammers, chisels, and picks. Iron was readily accessible, making a less expensive resource
available to the common people. An example of the improved technology was the construction of
the first large-scale canal ~2,600 years ago in 600 B.C. The canal diverted water from the
Mediterranean to the Red Sea, and was approximately 160 km (almost 100 miles) in length, 13
meters deep, and 60 meters wide. Along with this great feat of nature came the Roman network of
approximately 300,000 km (186,411 miles) of major highways and roads.
5 Anthroturbation and the Anthropocene: a review of human influence on the Earth’s geomorphology
While a vast range of additional activities degraded the environment during this era, the next focus
of major anthroturbation marks the beginning of the Industrial Revolution. In the early 1800s,
steam power changed modern society. By then, the entire configuration of the human population
had transformed with migration, wars, diseases, medical improvement, and had become a highly
evolved and global civilization. Steam power soon replaced human and domesticated animal
power. Initially, the power was fueled through the combustion of wood. Shortly, the wooden fuel
was replaced with hydrocarbons in the form of coal. Obtaining coal through surface mining and
deep underground mining modified the stratigraphy to such an extent that this boundary may be
used to mark a new geologic
epoch. Coal mining is still a
substantial portion of human
endeavors to extract resources
in lesser developed countries.
However, for the first time in
nearly 20 years coal production
slightly decreased in the United
States by ~3% (U.S. Energy
Information Administration
2012). Other hydrocarbons,
such as oil and natural gas, are
now extracted more frequently
in replace of coal. Although the
consumption of coal has
Figure 1. Timeline of human advancement until the Industrial
Revolution (Braje & Erlandson, 2014).
6 Anthroturbation and the Anthropocene: a review of human influence on the Earth’s geomorphology
diminished marginally among developed countries, there is still exploitation of non-renewable
resources on a global scale.
Land-use Modifications
Our history of technological and cultural advances have led to the comprehension that human
population and practices have reformed the bulk of suitable land beyond recognition. George
Perkins Marsh was one of the first geographers to document the extensive unsustainable land-use
practices in 1864 with his book Man and Nature; or Physical Geography as Modified by Human
Action. Since his landmark publication, the population has grown from a little over 1 billion to 7.2
billion today. Using these current population trends, Hooke (2012) has estimated that humans thus
far have modified above 50% of the Earth’s ice-free surface. Urban developments are the leading
causes of the loss of ecosystem
function and productivity. This has
led to a 24% global decline (Bai, Z.
G., et al. 2008). The two imperative
land-use practices for human
survival: urban and agriculture,
also happen to be the most
destructive to the ecosystem and
the environment. Urbanization can
account for 0.-3 to 3.5Mkm2
of the
global area (Potere & Schneider
2007). The reason for the immense
range of area is based on the
Figure 2. Land area modified by humans calculated from data
up to 2007 (Hook 2012).
7 Anthroturbation and the Anthropocene: a review of human influence on the Earth’s geomorphology
differing terminology of urban area. In a basic sense, an urban area is defined as one which a
population density exceeds a minimum value. As this can be projected onto or overlook any
population, researchers have used additional data, such as population density provided by the
United Nations Population Division to enforce their statistical evidence towards the greater amount
of the two spectrums (3.5Mkm2). Cropland is the second most desired and depleted land use with
an area around 16.7 Mkm2
(Hooke 2012). Poor agricultural practices worldwide have been
responsible for the degradation of up to 40% of the top soil. Out of this number, it must also be
presented that about 75% of the Earth’s area is unsuitable for agricultural due to poor nutrients,
topography, and climate. Account for actual agricultural land area in the recent past and future can
be uncertain due to the increase of multi-use land i.e., agriculture in urban settings. Figure 2
demonstrates the area involved as well as the percent of the Earth’s land surface that has been
modified by humans.
Anthropocene
Constructing a Definition
The Anthropocene or age of the humans is here, according to most scientists. Debates on the actual
start of the new geologic epoch have been vast and offer an assortment of explanations. Dates for
the boundary of the Anthropocene have been proposed ranging from 40,000 years ago to the early
1800s. However, no beginning or geologic epoch has been officially created. An Italian geologists,
Antonio Stoppani was first to document the probable new epoch, “anthropozoic era” in 1837 (Braje
& Erlandson 2014). Over 140 years later, scientists are still discussing the fate of the term. The
Stratigraphy Commission of the Geological Society of London has been given the task. The team
is composed of 23 scientists including geoscientists, paleoclimatologists, an environmental
8 Anthroturbation and the Anthropocene: a review of human influence on the Earth’s geomorphology
historian, a journalist, and an archaeologists. Together, they must collaborate to determine the
exact “Golden spike.” That is the term used by the Stratigraphy Commission of the Geological
Society of London to determine the physical boundary of a new, anthropogenic, geological epoch.
Thus far, there are 5 suggestions for the Anthropocene: 1) Merging Holocene and Anthropocene,
Holocene is already the shortest geological epoch to date with ~11,700 years; 2) Completely
replace the Holocene with the Anthropocene; 3) create the Anthropocene at AD 1500 with the
beginning of the Columbian Exchange; 4) Anthropocene starting at AD 2000 when the human
effects were recognized and accepted by geoscientists; or 5) Discard the idea of creating an
Anthropocene epoch, but use it as an informal term. This would be due to the fact that the spatial
distribution of human impact is extremely difficult to be linked globally.
Amendments of Geologic Principle
In terms of defining the next epoch of the Anthropocene, the issues of spatial and timescales arise
as the Stratigraphy Commission of the Geological Society of London have revealed with option 5.
Persisting with the concept of humans now being the most intensive geomorphic agent on the
planet, Knight and Harrison (2014) have proposed to drop the Principal of Uniformitarianism.
They maintain that the Anthropocene era is of post-normal science. This is due to the ongoing and
extensive anthroturbation of the Earth’s surface. They believe that we have come to a point in
which the geological record cannot be thought of as a preservation of natural history, but as a
distorted image of a mixture of phenomena. Upcoming Earth science students must now deal with
this issue in interpretation. “We argue that all geoscientists need to critically reconsider whether
the long-held assumptions of uniformitarianism are useful in the Anthropocene era” (Knight &
Harrison 2014, 71). The definition of uniformitarianism provides a method for interpreting past
geological events based on the idea that the present is the key to the past along with the assumption
9 Anthroturbation and the Anthropocene: a review of human influence on the Earth’s geomorphology
that the Earth has been acting under the same natural forces since its origin. Knight and Harrison
are not alone in their approach. Other studies such as Is Uniformitarianism Necessary? (Gould
1965) and Twelve Fallacies of Uniformitarianism (Shea 1982) that have looked at the Principle of
Uniformitarianism have also agreed it cannot continue to be applied to geology and geography.
This is due to the constraint on the interpretation of the past because of the alteration of the
dynamics and land surface systems since the beginning of the Anthropocene.
Definite Anthropogenic Mark in the Record
The latest addition of evidence to
the Anthropocene epoch case is
that of a new type of rock
formation referred to as
“plastiglomerate.” This term was
created to describe an
intermingling of basaltic lava
fragments, melted plastic, and
beach sediment. Found on
Kamilo Beach, Hawaii, Corcoran
(2014) describes the formation of the features in detail and states the “results indicate that this
anthropogenically influenced material has great potential to form a marker horizon of human
pollution, signaling the occurrence of the informal Anthropocene epoch.” Corcoran’s research may
aid in the argument of the Anthropocene, as it is a definite mark, or “golden spike,” in the geologic
record for the team of scientists at the Stratigraphy Commission of the Geological Society in
London. The new plastiglomerate, with the evidence that human activity has pressed the behavior
Figure 3. Four examples of a “Plastiglomerate” found in Kamilo
Beach, Hawaii (Corcoran 2014).
10 Anthroturbation and the Anthropocene: a review of human influence on the Earth’s geomorphology
of many Earth systems beyond limits of their natural variability, will also correspond with the end
of uniformitarianism as Knight and Harrison (2014) have anticipated.
Anthroturbation
Bioturbation, meaning the natural reworking of sediments and soils, can easily be applied to human
influences of these same properties with the term anthroturbation. For the purposes of this broad
paper, anthroturbation is applied to the surface, shallow, and deep mixing of the soils, sediment,
and stratigraphy. The order of magnitude of anthroturbation is greater than any plant or animal
bioturbation in Earth’s history (Zalasiewicz et al. 2014). As a reference, sea creatures usually do
not burrow more than 2.5 meters and land animals, such as wolves, typically burrow around 4
meters. Human interference has led to the depletion of underground resources (up to several
kilometers in depth from the Earth’s surface) that have caused topographic subsidence or collapse.
The result is a long-lasting, possibly permanent modification of the landscape, both above as well
as below ground. Hence, the subterranean alteration most likely has the highest long-term
preservation rate of anything constructed by humans above ground. As with the issue of the
“golden spike” in determining the Anthropocene, animal burrows in the fossil record were used to
define the Cambrian (~542 Mya). In a sense, humans now are also like the trace fossils with the
exception of human’s ability to leave more than one imprint with a single skeleton. This can be
expressed through one individual human living in multiple homes, driving various roads with more
than one vehicle, and all material possessions derived from the Earth’s crust.
11 Anthroturbation and the Anthropocene: a review of human influence on the Earth’s geomorphology
Surface Anthroturbation
Legacy Sediment
Quarries for surface mining, construction, urban development, agricultural practices, and deep-sea
trawling, can all be denoted as surface anthroturbation (Zalasiewicz et al. 2014). While surface
anthroturbation has generally been detected and described as sediments moved around by humans,
the term legacy sediment has recently gained attention. Anthropogenic sediment does not occur
uniformly across the landscape, rather in concentrated areas where it then produces landforms.
Some examples are: colluvium drapes on hill sides, fans and aprons at the base of hill slopes,
alluvial depositional features in channels, deltas, flood plains, and lakes. It can then be defined as
sediment that is deposited and preserved where sediment delivery exceeds transport capacity. As
with the Anthropocene, the definition and usage of legacy sediment is not official but widely
accepted in the literature.
History
In the 1970s, geomorphologists theorized that rivers were out of equilibrium due to sediment
storage and delivery. As an example, streams in the Atlantic Coastal Plain had an overwhelming
amount of sediment load that was eventually contributed to anthropogenic sediment from
upstream land use. Historically, there has been documented knowledge of anthropogenic
sediment. However, the issues lies with inconsistent terminology. The term “legacy sediment”
first appeared in the literature in 2004, and was used in referring to the effects of copper
contamination in water quality from legacy sediment. Within a few years, it gained popularity
and was appearing more along with similar terms like “legacy pollution” and “legacy
contaminants” as detailed in figure 4 (James 2013).
12 Anthroturbation and the Anthropocene: a review of human influence on the Earth’s geomorphology
Definition and Concerns
Formulating a proper definition for legacy sediment to ensure its appropriate usage and
understanding has proved difficult for the following reasons. The term legacy refers to something
that has been transmitted through an ancestor or from the past. This poses a concern for the
definition because all sediment has occurred from something in the past, i.e. geological and
geomorphic processes. Measuring legacy sediment as a stratigraphic unit poses issues such as 1)
the minimum and maximum thickness of sediment, 2) determining the actual amount of sediment
that has been produced by humans rather than natural sources, and 3) the legacy sediment may be
mixed with sediment that has transpired in a natural geomorphic manner. Under the typical
stratigraphy classification standards, legacy sediment could be categorized as a lithostratigraphic
unit (LSU) or a chronostratigraphic unit (CSU). A lithostratigraphic unit (LSU) which is identified
on the distinctive lithic characteristics of a unique rock formation and adheres to the Law of
Superposition; older material is beneath younger material. Legacy sediment is typically assorted
with naturally produced sediment and therefore not chemically or compositionally similar. A
Chronostratigraphic Unit (CSU) is based on the time of deposition and therefore may be
Figure 4. An internet search results of studies that refer to ‘legacy sediment’ (James 2013).
13 Anthroturbation and the Anthropocene: a review of human influence on the Earth’s geomorphology
challenging to determine because of the time progression of erosion
spatially but could also serve as an indicator of the Anthropocene.
Overall, there is a need for a universal term that can encompass all
aspects of the legacy sediment produced by a mixture of anthropogenic
activities outside of agricultural uses such as mining, logging,
urbanization, and other land use practices. One researcher generates a
broader definition of LS (James 2013, 19):
“Legacy sediment: Earth materials- primarily alluvium [or
colluvium]-deposited following human disturbances such as
deforestation, agricultural land use, or mining. The phrase is often
used to describe post-European floodplain settlement, also known
as post settlement alluvium. Awareness of legacy sediment has
grown in response to the importance it plays in sediment budgets,
water quality, river restoration, toxicity, lateral channel
connectivity, and Geomorphic theory…”
Subsurface Anthroturbation
Subsurface anthroturbation can be placed in two categories based on depth: shallow
anthroturbation and deep anthroturbation. Shallow anthroturbation has been defined as human
bioturbation occurring meters to tens of meters below the Earth’s surface (Zalasiewicz et al. 2014).
This subsurface anthroturbation includes structures such as tunnels, sewage piping, electricity
lines, gas piping, and metro systems. The importance of shallow anthroturbation over surface is
preservation time. With surface and legacy sediment, it can be misunderstood as a natural
phenomenon. Shallow anthroturbation has a much higher chance of being preserved over surface
Figure 5. Contact of
Legacy Sediment
overlying pre-
settlement alluvium at
black arrow in Clarks
Fork, South Carolina
(James 2013).
14 Anthroturbation and the Anthropocene: a review of human influence on the Earth’s geomorphology
structures, especially the subsurface structures near subducting crust or coastal plains. These may
be held below the surface for some time then be uplifted at which time weathering and erosional
forces will degrade them. As previously stated, other structures may be located on a stable or
descending crust. Wherein they will be preserved below the surface for a longer period or
permanently.
Deep anthroturbation extends from hundreds to thousands of
meters below the Earth’s surface. Mining, boreholes, and
underground storage facilities can all be placed under this
category and will be further discussed. The possible
preservation is higher than both surface and shallow
anthroturbated structures. The deeply disturbed regions may
only be altered through intense geologic occurrences such as
an igneous intrusions and/or high-grade metamorphism.
Mining
The beginning of mining dates as far back as the Neolithic
(~7,000 years ago) with the discovery of flint as a tool.
Primitive humans would excavate shallow pits for this, and
as we have seen, many more resources have now been sought
after through mining. Mining, therefore, involves the
extraction of underground material. The geomorphological
results are a void left in the strata from which the ore
previously was embedded. A subsequent collapse will typically follow, the void will then be
packed with deposits of fragmented and unsorted debris of the surrounding lithology rather than
Figure 6. Patterns of underground
rock removal resulting from coal
mining (Zalasiewicz et al. 2014).
15 Anthroturbation and the Anthropocene: a review of human influence on the Earth’s geomorphology
the original stratigraphic layer. The depth of mines can vary, a few hundred meters in depth to an
extremity of 4 km (~2.5 miles) as seen in a South African gold mine. Preservation of the
anthroturbation in the geologic record varies with the depth and type of ore being mined. For coal
mines that exploit stratabound minerals, the subsequent stratigraphy will demonstrate associated
patterns of events correlating to the replacement by collapse of overlying strata as well as contact
of the underlying strata with minimal remnants of coal (Figure 5). Also, the geologic record will
show evidence of penetration by boreholes and small places of excavations in the nearby unaltered
strata.
Boreholes
Boreholes can be thought of as an additional form of mining. Instead, boreholes are deeper than
traditional mines and aim to retrieve a liquid resource. Boreholes are typically several kilometers
in depth. An extreme case, however, is the Kola Superdeep Borehole located in Russia. With a
depth of 12,262 meters (~7.6 miles), it is the deepest borehole in the world. These vertical
structures are found globally and so abundant that adding the total length of them would equate to
the distance of Earth to Mars. This also parallels to 7 meters of borehole per every human on the
planet. While these are probably the most plentiful structure, there slender vertical composition
barely punctures the strata of the geologic record. However, they still produce evidence of
anthroturbation occasionally when caving-in of the surrounding softer sediment enters the
borehole. Furthermore, deviations in surface topography occur due to the alteration of the pore
fluid composition by the addition of drilling liquids. The alteration of the subterranean landscape,
both shallow and deep, presents a difficulty for naming a new geological time “Anthropocene.”
This is because it is untraditional deposition. The relationships are cross-cutting rather than super
16 Anthroturbation and the Anthropocene: a review of human influence on the Earth’s geomorphology
positional as natural geologic strata. Also, there is a lack of new natural strata at the surface because
of the vast amount of terranean erosion and legacy sediment erosion.
Fluvial System Alteration
During the discussion of anthropogenic impact regarding the geomorphology of the planet, it
would be unjust to not mention fluvial geomorphology. Here, a brief overview of the human
impacts on the fluvial systems will be presented as extended confirmation of the Anthropocene.
River systems have been influenced directly through in-stream modification and indirectly with
changes in land-use. A few examples of within stream reform come from the following: dams,
beaver trapping, bank stabilization, and channelization through transportation. Indirect influences
as a result of landscape change are logging, agriculture, and urban development. The morphology
of the river systems is altered through the increase or decrease of sediment yield. This can serve
as an example of legacy sediment.
Dam placement and wood removal
The placement of dams for water resources allegedly began in 2800 BC in Egypt (Smith 1971).
The usage of dams is global and is mostly evident in developed countries such as the United States.
For the purposes of this paper, I will use the United States as a significant example of the effects
of human population on stream morphology. The US
experienced a boom of dam construction from 1950 to the
1970s. A dam’s typical lifespan is a mere 50 years. Therefore,
most of these dams have reached their maximum, and are now
posing other environmental hazards. Although the bulk of
these dams are categorized as small (> 25 feet in height), they
Figure 7. Dam distribution and
height across the United States
(National Inventory of Dams
2015).
17 Anthroturbation and the Anthropocene: a review of human influence on the Earth’s geomorphology
still produce morphological effects to the streams. The major impact of small dams is the
fragmentation of river landscape, resulting in degradation of stream habitat and reduction of the
transportation of sediment (Chin et al. 2007).
The addition of dams is now trending in other
countries, as shown in figure 9, due to a
changing global economy and climate. Figure 8
shows the dams being constructed or future dam
sites. Most of these are in developing countries
or are a result of glacial meltwaters. Along with
the high number of dams, the US has a history
of adding and removing wood in streams for different reasons. This has intensively transformed
the hydraulics of streams across the United States. Wohl (2014) documented these changes in river
corridors by human activity since European Settlement primarily through steamboat navigation
and timber rafting. Prior to railroad development, the steamboat was the United States’ main
source of transporting commodities in the 19th
century. Steamboat navigation involves the removal
of wood along with other in-stream obstacles. Snagging of Large Woody Debris (LWD), dredging,
and rock removal were all incorporated into the stream bed management for easier steamboat
navigation. Steamboat routes were engineered this way for decades, creating channelized canals
and reducing natural variation and complexity. Changing channels and steamboat accessibility also
resulted in the decrease of natural mobilization of wood to rivers. Firstly, steamboats were fueled
by wood and therefore the riparian forest was harvested for this purpose. The second effect was
population density increase through settlement and the practice of logging as their income through
commercial production.
Figure 8. Newly constructed and future
constructed sites of dams (Lewis & Maslin
2015).
18 Anthroturbation and the Anthropocene: a review of human influence on the Earth’s geomorphology
Commercial logging then reformed the rivers in a new way with the addition of materials to the
stream, also called timber rafting. Timber rafting was the transportation of logs by means of
floating downstream to collection points. This process became so widespread that the state of New
York occupied every one of its large rivers with timber rafting (Wohl 2014). The rivers were then
declared public highways for log transport, and it was illegal to obstruct the timber moving
downstream. Additional modifications to channels for the enhanced passage of timber further
congested the natural rivers in the US.
Indirect Long-term Effects
To condense the intensity of river
modification, figure 9 illustrates a time-lapse
diagram of change throughout the settlement of
the United States. The stages of the alluvial
floodplain begin with A) Pre-settlement
period. In this stage, rivers were able to
meander leading to the production of gravel
beds and fine-grained banks. B) During the
agricultural era, extreme upland erosion and
downstream legacy sediment deposition
caused rapid aggradation and incising. C)
Stream attempts to readjust to pre-settlement
period with a decrease in unsustainable
agricultural practices and an increase in
urbanization. “A” represents legacy sediments
Figure 9. Diagram demonstrating long-term
changes in stream morphology due to indirect
human activities (Wohl 2014.)
19 Anthroturbation and the Anthropocene: a review of human influence on the Earth’s geomorphology
as post-settlement deposition. “VR” stands for very recent, as seen as coarse sediment on the river
bed, and “PS” for pre-settlement sediment. Lastly, D) Representation of current conditions of a
highly modified stream with numerous small dams upstream. The dams have caused aggradation
through the buildup of fine-grain alluvium as seen with the “VR” arrow pointing to the new
deposition. The ultimate outcome is a change in stream structure with an unnatural variation.
Conclusion
Through examining the modifications on both a global scale with human population explosion
leading to extraction of subterranean resources, and a more local scale of long-term river channel
morphology, the overview of the appearance of the Anthropocene is recognizable. Humans have
altered a great quantity of the planet and researchers are still attempting to quantify the extent. As
the literature has displayed, many academics believe we are now in the Anthropocene and need to
adjust the teachings of Earth Science to reflect this change. Others may also hope to provide this
indication as a turning point for society to more sustainable practices and population control.
Furthermore, the evidence of humans as the primary geomorphic force on the planet is s, widely
accepted throughout the literature, and can serve as an active branch of study in the field of
biogeomorphology.
20 Anthroturbation and the Anthropocene: a review of human influence on the Earth’s geomorphology
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Anthroturbation;biogeomorphologyFINAL

  • 1. Anthroturbation and the Anthropocene: areview of human influence on the Earth’s geomorphology Texas State University Department of Geography Biogeomorphology Spring 2015 Christina Lopez April 28, 2015
  • 2. 1 Anthroturbation and the Anthropocene: a review of human influence on the Earth’s geomorphology Anthroturbation and the Anthropocene: a review of human influence on the Earth’s geomorphology Abstract As the field of biogeomorphology develops, the acknowledgement of the human influence on the planet emerges as a realization of utmost importance. Human population and evolution on the Earth are making a visible impact on the landscape nearly inescapable. This has led academics and researchers to debate the creation of a new geologic epoch “the Anthropocene” or the “Age of the Humans.” Taking this recognition further, some scientists are now refuting a founding principle of Earth science because of this human influence. The history of human impact as a geomorphic agent will be reviewed through the expression of the fruition of human development. Defining the “Anthropocene epoch” within the differing scales of anthroturbation, and the systems of fluvial geomorphology modifications, generates an overview of the inevitable conclusion that humans are now the largest geomorphic agent on the planet and have been the dominate force for some time. Keywords: Anthropocene, Legacy sediment, Human impacts, Fluvial geomorphology Introduction Humans have modified their physical environment to improve the quality of life. An indirect effect of this is the change of land use, which rids the environment of its native species, as well as alters the geomorphic processes based on the destruction or construction of various structures. The impacts of wildlife have been well noted throughout the literature. The cultural view of most humans is to clear their territory of predators. Therefore it is easily recognized that strong associations between the decline of carnivore populations and high human population density
  • 3. 2 Anthroturbation and the Anthropocene: a review of human influence on the Earth’s geomorphology exists (Woodroffe 1999). As predators decrease, more people settle into the “safe territory” and make further modifications to create an urban environment. Consequently, urbanization is the leading cause of species extinction (McKinney 2005). Urbanization has offered an interesting outcome to the few species that remain. A phenomenon termed “urban-adaptable” has created a biological homogenization in major cities worldwide. This has allowed the same few species to thrive in these urban environments while approximately 785 species have become extinct, with an additional 16,300 becoming endangered around the globe. (IUCN 2015). A shift to the majority of humans residing in urban areas has also caused biogeomorphic instabilities with the grouping of domesticated animals in a managed environment. Impacting most of the world’s wildlife, severe environmental issues have arisen: soil erosion, overgrazing, soil compaction (resulting in increased runoff), and surface water quality contamination (Butler 2013). With a global population of 7.2 billion, human dominance over the landscape has imposed multiple challenges to the Earth’s ecosystem, atmosphere, and geomorphic equilibrium. This paper’s focus is to expose evidence in support of the proposition that human beings are the greatest geomorphic agents this planet has yet to support. Through the history of human existence, the consequences of biogeomorphological progress of humans is evident. There has been an alteration to one of the largest geomorphic forces of sediment transportation, and stratigraphic disturbances, as well as geological formations, with human mishaps embedded which form our recent anthroturbated history. History Through population increase and the establishment of civilization, the Earth’s surface and subterranean landscape, have become a resource for a society with never-ending needs. All through the planet’s history, plants and animals have bioturbated the Earth but not to the extent of humans. Geologists used the presence of animal burrows in the fossil record to define the Cambrian epoch
  • 4. 3 Anthroturbation and the Anthropocene: a review of human influence on the Earth’s geomorphology (Zalasiewicz et al. 2014) and may now be adding another epoch based on human bioturbation also referred to as anthroturbation. Human progression as geomorphic agents Paleolithic There has been little evidence of dinosaur burrowing or primate burrowing (Hooke 2000). The assumed beginning of landscape modification in various forms through the Homo erectus species may have begun in the early to middle Paleolithic. The Paleolithic was characterized by the Pleistocene epoch of geologic time (~2.6 Mya -12,000 years ago). It has also been denoted as the Stone Age, as well as the time modern humans began moving out of Africa, according to the Out of Africa Hypothesis. It has been discovered that this now-extinct species of hominid had been creating sizeable dwellings with the movement of small boulders for walls and stone rubble serving as foundations. As the name Stone Age implies, during the later period of the Paleolithic, humans found stones to be useful as simple tools. More specifically, rocks such as flint were mined on the shallow surface through digging with bones. By the end of the Paleolithic, mining activity had produced depressions over 10 meters in depth and 10 meters in length (Bromehead 1954) Mesolithic through the Bronze Age With the settlement of the hunter gathers in the middle Mesolithic, humans began farming. This circumstance may have changed due to the increase in population. Alternatively, population increase may have been the result of farming because of warmer climatic conditions. The Pleistocene glaciers began to retreat, sea level rose, and an extinction of many large-bodied animals could have promoted this change in cultural structure and expansion of civilizations. Notable anthroturbation occurred with the excavating of mud for bricks, tilling the soil for croplands, and
  • 5. 4 Anthroturbation and the Anthropocene: a review of human influence on the Earth’s geomorphology displacement of soils on a larger scale with small canal construction for water consumption. The practice of melting copper in the late Mesolithic eventually led to the addition of tin to copper, thus composing a stronger alloy in the Neolithic about 7,000 years ago. Just as in the early days of mining flint, history repeated itself as humans used these metallic resources as weaponry and then advanced to quarrying large amounts for stone structures. Lastly, the most vital concept in human history transpired during this period (about 5,000 years ago). The development of the wheel led to increased ability to transport geologic materials as well as human mobility. As people rapidly learned, a wheel revolves with more ease and speed on paved terrain. Thus more modification and anthroturbation followed as infrastructure emerged. Iron Age through the Industrial Revolution Throughout the dramatic improvements of human progress as geomorphic agents, this age has altered the surface of the Earth more than the past ages of humanity combined. Nearly 2500 years ago, the use of iron as a tool increased human’s ability to move Earth with the incorporation of hammers, chisels, and picks. Iron was readily accessible, making a less expensive resource available to the common people. An example of the improved technology was the construction of the first large-scale canal ~2,600 years ago in 600 B.C. The canal diverted water from the Mediterranean to the Red Sea, and was approximately 160 km (almost 100 miles) in length, 13 meters deep, and 60 meters wide. Along with this great feat of nature came the Roman network of approximately 300,000 km (186,411 miles) of major highways and roads.
  • 6. 5 Anthroturbation and the Anthropocene: a review of human influence on the Earth’s geomorphology While a vast range of additional activities degraded the environment during this era, the next focus of major anthroturbation marks the beginning of the Industrial Revolution. In the early 1800s, steam power changed modern society. By then, the entire configuration of the human population had transformed with migration, wars, diseases, medical improvement, and had become a highly evolved and global civilization. Steam power soon replaced human and domesticated animal power. Initially, the power was fueled through the combustion of wood. Shortly, the wooden fuel was replaced with hydrocarbons in the form of coal. Obtaining coal through surface mining and deep underground mining modified the stratigraphy to such an extent that this boundary may be used to mark a new geologic epoch. Coal mining is still a substantial portion of human endeavors to extract resources in lesser developed countries. However, for the first time in nearly 20 years coal production slightly decreased in the United States by ~3% (U.S. Energy Information Administration 2012). Other hydrocarbons, such as oil and natural gas, are now extracted more frequently in replace of coal. Although the consumption of coal has Figure 1. Timeline of human advancement until the Industrial Revolution (Braje & Erlandson, 2014).
  • 7. 6 Anthroturbation and the Anthropocene: a review of human influence on the Earth’s geomorphology diminished marginally among developed countries, there is still exploitation of non-renewable resources on a global scale. Land-use Modifications Our history of technological and cultural advances have led to the comprehension that human population and practices have reformed the bulk of suitable land beyond recognition. George Perkins Marsh was one of the first geographers to document the extensive unsustainable land-use practices in 1864 with his book Man and Nature; or Physical Geography as Modified by Human Action. Since his landmark publication, the population has grown from a little over 1 billion to 7.2 billion today. Using these current population trends, Hooke (2012) has estimated that humans thus far have modified above 50% of the Earth’s ice-free surface. Urban developments are the leading causes of the loss of ecosystem function and productivity. This has led to a 24% global decline (Bai, Z. G., et al. 2008). The two imperative land-use practices for human survival: urban and agriculture, also happen to be the most destructive to the ecosystem and the environment. Urbanization can account for 0.-3 to 3.5Mkm2 of the global area (Potere & Schneider 2007). The reason for the immense range of area is based on the Figure 2. Land area modified by humans calculated from data up to 2007 (Hook 2012).
  • 8. 7 Anthroturbation and the Anthropocene: a review of human influence on the Earth’s geomorphology differing terminology of urban area. In a basic sense, an urban area is defined as one which a population density exceeds a minimum value. As this can be projected onto or overlook any population, researchers have used additional data, such as population density provided by the United Nations Population Division to enforce their statistical evidence towards the greater amount of the two spectrums (3.5Mkm2). Cropland is the second most desired and depleted land use with an area around 16.7 Mkm2 (Hooke 2012). Poor agricultural practices worldwide have been responsible for the degradation of up to 40% of the top soil. Out of this number, it must also be presented that about 75% of the Earth’s area is unsuitable for agricultural due to poor nutrients, topography, and climate. Account for actual agricultural land area in the recent past and future can be uncertain due to the increase of multi-use land i.e., agriculture in urban settings. Figure 2 demonstrates the area involved as well as the percent of the Earth’s land surface that has been modified by humans. Anthropocene Constructing a Definition The Anthropocene or age of the humans is here, according to most scientists. Debates on the actual start of the new geologic epoch have been vast and offer an assortment of explanations. Dates for the boundary of the Anthropocene have been proposed ranging from 40,000 years ago to the early 1800s. However, no beginning or geologic epoch has been officially created. An Italian geologists, Antonio Stoppani was first to document the probable new epoch, “anthropozoic era” in 1837 (Braje & Erlandson 2014). Over 140 years later, scientists are still discussing the fate of the term. The Stratigraphy Commission of the Geological Society of London has been given the task. The team is composed of 23 scientists including geoscientists, paleoclimatologists, an environmental
  • 9. 8 Anthroturbation and the Anthropocene: a review of human influence on the Earth’s geomorphology historian, a journalist, and an archaeologists. Together, they must collaborate to determine the exact “Golden spike.” That is the term used by the Stratigraphy Commission of the Geological Society of London to determine the physical boundary of a new, anthropogenic, geological epoch. Thus far, there are 5 suggestions for the Anthropocene: 1) Merging Holocene and Anthropocene, Holocene is already the shortest geological epoch to date with ~11,700 years; 2) Completely replace the Holocene with the Anthropocene; 3) create the Anthropocene at AD 1500 with the beginning of the Columbian Exchange; 4) Anthropocene starting at AD 2000 when the human effects were recognized and accepted by geoscientists; or 5) Discard the idea of creating an Anthropocene epoch, but use it as an informal term. This would be due to the fact that the spatial distribution of human impact is extremely difficult to be linked globally. Amendments of Geologic Principle In terms of defining the next epoch of the Anthropocene, the issues of spatial and timescales arise as the Stratigraphy Commission of the Geological Society of London have revealed with option 5. Persisting with the concept of humans now being the most intensive geomorphic agent on the planet, Knight and Harrison (2014) have proposed to drop the Principal of Uniformitarianism. They maintain that the Anthropocene era is of post-normal science. This is due to the ongoing and extensive anthroturbation of the Earth’s surface. They believe that we have come to a point in which the geological record cannot be thought of as a preservation of natural history, but as a distorted image of a mixture of phenomena. Upcoming Earth science students must now deal with this issue in interpretation. “We argue that all geoscientists need to critically reconsider whether the long-held assumptions of uniformitarianism are useful in the Anthropocene era” (Knight & Harrison 2014, 71). The definition of uniformitarianism provides a method for interpreting past geological events based on the idea that the present is the key to the past along with the assumption
  • 10. 9 Anthroturbation and the Anthropocene: a review of human influence on the Earth’s geomorphology that the Earth has been acting under the same natural forces since its origin. Knight and Harrison are not alone in their approach. Other studies such as Is Uniformitarianism Necessary? (Gould 1965) and Twelve Fallacies of Uniformitarianism (Shea 1982) that have looked at the Principle of Uniformitarianism have also agreed it cannot continue to be applied to geology and geography. This is due to the constraint on the interpretation of the past because of the alteration of the dynamics and land surface systems since the beginning of the Anthropocene. Definite Anthropogenic Mark in the Record The latest addition of evidence to the Anthropocene epoch case is that of a new type of rock formation referred to as “plastiglomerate.” This term was created to describe an intermingling of basaltic lava fragments, melted plastic, and beach sediment. Found on Kamilo Beach, Hawaii, Corcoran (2014) describes the formation of the features in detail and states the “results indicate that this anthropogenically influenced material has great potential to form a marker horizon of human pollution, signaling the occurrence of the informal Anthropocene epoch.” Corcoran’s research may aid in the argument of the Anthropocene, as it is a definite mark, or “golden spike,” in the geologic record for the team of scientists at the Stratigraphy Commission of the Geological Society in London. The new plastiglomerate, with the evidence that human activity has pressed the behavior Figure 3. Four examples of a “Plastiglomerate” found in Kamilo Beach, Hawaii (Corcoran 2014).
  • 11. 10 Anthroturbation and the Anthropocene: a review of human influence on the Earth’s geomorphology of many Earth systems beyond limits of their natural variability, will also correspond with the end of uniformitarianism as Knight and Harrison (2014) have anticipated. Anthroturbation Bioturbation, meaning the natural reworking of sediments and soils, can easily be applied to human influences of these same properties with the term anthroturbation. For the purposes of this broad paper, anthroturbation is applied to the surface, shallow, and deep mixing of the soils, sediment, and stratigraphy. The order of magnitude of anthroturbation is greater than any plant or animal bioturbation in Earth’s history (Zalasiewicz et al. 2014). As a reference, sea creatures usually do not burrow more than 2.5 meters and land animals, such as wolves, typically burrow around 4 meters. Human interference has led to the depletion of underground resources (up to several kilometers in depth from the Earth’s surface) that have caused topographic subsidence or collapse. The result is a long-lasting, possibly permanent modification of the landscape, both above as well as below ground. Hence, the subterranean alteration most likely has the highest long-term preservation rate of anything constructed by humans above ground. As with the issue of the “golden spike” in determining the Anthropocene, animal burrows in the fossil record were used to define the Cambrian (~542 Mya). In a sense, humans now are also like the trace fossils with the exception of human’s ability to leave more than one imprint with a single skeleton. This can be expressed through one individual human living in multiple homes, driving various roads with more than one vehicle, and all material possessions derived from the Earth’s crust.
  • 12. 11 Anthroturbation and the Anthropocene: a review of human influence on the Earth’s geomorphology Surface Anthroturbation Legacy Sediment Quarries for surface mining, construction, urban development, agricultural practices, and deep-sea trawling, can all be denoted as surface anthroturbation (Zalasiewicz et al. 2014). While surface anthroturbation has generally been detected and described as sediments moved around by humans, the term legacy sediment has recently gained attention. Anthropogenic sediment does not occur uniformly across the landscape, rather in concentrated areas where it then produces landforms. Some examples are: colluvium drapes on hill sides, fans and aprons at the base of hill slopes, alluvial depositional features in channels, deltas, flood plains, and lakes. It can then be defined as sediment that is deposited and preserved where sediment delivery exceeds transport capacity. As with the Anthropocene, the definition and usage of legacy sediment is not official but widely accepted in the literature. History In the 1970s, geomorphologists theorized that rivers were out of equilibrium due to sediment storage and delivery. As an example, streams in the Atlantic Coastal Plain had an overwhelming amount of sediment load that was eventually contributed to anthropogenic sediment from upstream land use. Historically, there has been documented knowledge of anthropogenic sediment. However, the issues lies with inconsistent terminology. The term “legacy sediment” first appeared in the literature in 2004, and was used in referring to the effects of copper contamination in water quality from legacy sediment. Within a few years, it gained popularity and was appearing more along with similar terms like “legacy pollution” and “legacy contaminants” as detailed in figure 4 (James 2013).
  • 13. 12 Anthroturbation and the Anthropocene: a review of human influence on the Earth’s geomorphology Definition and Concerns Formulating a proper definition for legacy sediment to ensure its appropriate usage and understanding has proved difficult for the following reasons. The term legacy refers to something that has been transmitted through an ancestor or from the past. This poses a concern for the definition because all sediment has occurred from something in the past, i.e. geological and geomorphic processes. Measuring legacy sediment as a stratigraphic unit poses issues such as 1) the minimum and maximum thickness of sediment, 2) determining the actual amount of sediment that has been produced by humans rather than natural sources, and 3) the legacy sediment may be mixed with sediment that has transpired in a natural geomorphic manner. Under the typical stratigraphy classification standards, legacy sediment could be categorized as a lithostratigraphic unit (LSU) or a chronostratigraphic unit (CSU). A lithostratigraphic unit (LSU) which is identified on the distinctive lithic characteristics of a unique rock formation and adheres to the Law of Superposition; older material is beneath younger material. Legacy sediment is typically assorted with naturally produced sediment and therefore not chemically or compositionally similar. A Chronostratigraphic Unit (CSU) is based on the time of deposition and therefore may be Figure 4. An internet search results of studies that refer to ‘legacy sediment’ (James 2013).
  • 14. 13 Anthroturbation and the Anthropocene: a review of human influence on the Earth’s geomorphology challenging to determine because of the time progression of erosion spatially but could also serve as an indicator of the Anthropocene. Overall, there is a need for a universal term that can encompass all aspects of the legacy sediment produced by a mixture of anthropogenic activities outside of agricultural uses such as mining, logging, urbanization, and other land use practices. One researcher generates a broader definition of LS (James 2013, 19): “Legacy sediment: Earth materials- primarily alluvium [or colluvium]-deposited following human disturbances such as deforestation, agricultural land use, or mining. The phrase is often used to describe post-European floodplain settlement, also known as post settlement alluvium. Awareness of legacy sediment has grown in response to the importance it plays in sediment budgets, water quality, river restoration, toxicity, lateral channel connectivity, and Geomorphic theory…” Subsurface Anthroturbation Subsurface anthroturbation can be placed in two categories based on depth: shallow anthroturbation and deep anthroturbation. Shallow anthroturbation has been defined as human bioturbation occurring meters to tens of meters below the Earth’s surface (Zalasiewicz et al. 2014). This subsurface anthroturbation includes structures such as tunnels, sewage piping, electricity lines, gas piping, and metro systems. The importance of shallow anthroturbation over surface is preservation time. With surface and legacy sediment, it can be misunderstood as a natural phenomenon. Shallow anthroturbation has a much higher chance of being preserved over surface Figure 5. Contact of Legacy Sediment overlying pre- settlement alluvium at black arrow in Clarks Fork, South Carolina (James 2013).
  • 15. 14 Anthroturbation and the Anthropocene: a review of human influence on the Earth’s geomorphology structures, especially the subsurface structures near subducting crust or coastal plains. These may be held below the surface for some time then be uplifted at which time weathering and erosional forces will degrade them. As previously stated, other structures may be located on a stable or descending crust. Wherein they will be preserved below the surface for a longer period or permanently. Deep anthroturbation extends from hundreds to thousands of meters below the Earth’s surface. Mining, boreholes, and underground storage facilities can all be placed under this category and will be further discussed. The possible preservation is higher than both surface and shallow anthroturbated structures. The deeply disturbed regions may only be altered through intense geologic occurrences such as an igneous intrusions and/or high-grade metamorphism. Mining The beginning of mining dates as far back as the Neolithic (~7,000 years ago) with the discovery of flint as a tool. Primitive humans would excavate shallow pits for this, and as we have seen, many more resources have now been sought after through mining. Mining, therefore, involves the extraction of underground material. The geomorphological results are a void left in the strata from which the ore previously was embedded. A subsequent collapse will typically follow, the void will then be packed with deposits of fragmented and unsorted debris of the surrounding lithology rather than Figure 6. Patterns of underground rock removal resulting from coal mining (Zalasiewicz et al. 2014).
  • 16. 15 Anthroturbation and the Anthropocene: a review of human influence on the Earth’s geomorphology the original stratigraphic layer. The depth of mines can vary, a few hundred meters in depth to an extremity of 4 km (~2.5 miles) as seen in a South African gold mine. Preservation of the anthroturbation in the geologic record varies with the depth and type of ore being mined. For coal mines that exploit stratabound minerals, the subsequent stratigraphy will demonstrate associated patterns of events correlating to the replacement by collapse of overlying strata as well as contact of the underlying strata with minimal remnants of coal (Figure 5). Also, the geologic record will show evidence of penetration by boreholes and small places of excavations in the nearby unaltered strata. Boreholes Boreholes can be thought of as an additional form of mining. Instead, boreholes are deeper than traditional mines and aim to retrieve a liquid resource. Boreholes are typically several kilometers in depth. An extreme case, however, is the Kola Superdeep Borehole located in Russia. With a depth of 12,262 meters (~7.6 miles), it is the deepest borehole in the world. These vertical structures are found globally and so abundant that adding the total length of them would equate to the distance of Earth to Mars. This also parallels to 7 meters of borehole per every human on the planet. While these are probably the most plentiful structure, there slender vertical composition barely punctures the strata of the geologic record. However, they still produce evidence of anthroturbation occasionally when caving-in of the surrounding softer sediment enters the borehole. Furthermore, deviations in surface topography occur due to the alteration of the pore fluid composition by the addition of drilling liquids. The alteration of the subterranean landscape, both shallow and deep, presents a difficulty for naming a new geological time “Anthropocene.” This is because it is untraditional deposition. The relationships are cross-cutting rather than super
  • 17. 16 Anthroturbation and the Anthropocene: a review of human influence on the Earth’s geomorphology positional as natural geologic strata. Also, there is a lack of new natural strata at the surface because of the vast amount of terranean erosion and legacy sediment erosion. Fluvial System Alteration During the discussion of anthropogenic impact regarding the geomorphology of the planet, it would be unjust to not mention fluvial geomorphology. Here, a brief overview of the human impacts on the fluvial systems will be presented as extended confirmation of the Anthropocene. River systems have been influenced directly through in-stream modification and indirectly with changes in land-use. A few examples of within stream reform come from the following: dams, beaver trapping, bank stabilization, and channelization through transportation. Indirect influences as a result of landscape change are logging, agriculture, and urban development. The morphology of the river systems is altered through the increase or decrease of sediment yield. This can serve as an example of legacy sediment. Dam placement and wood removal The placement of dams for water resources allegedly began in 2800 BC in Egypt (Smith 1971). The usage of dams is global and is mostly evident in developed countries such as the United States. For the purposes of this paper, I will use the United States as a significant example of the effects of human population on stream morphology. The US experienced a boom of dam construction from 1950 to the 1970s. A dam’s typical lifespan is a mere 50 years. Therefore, most of these dams have reached their maximum, and are now posing other environmental hazards. Although the bulk of these dams are categorized as small (> 25 feet in height), they Figure 7. Dam distribution and height across the United States (National Inventory of Dams 2015).
  • 18. 17 Anthroturbation and the Anthropocene: a review of human influence on the Earth’s geomorphology still produce morphological effects to the streams. The major impact of small dams is the fragmentation of river landscape, resulting in degradation of stream habitat and reduction of the transportation of sediment (Chin et al. 2007). The addition of dams is now trending in other countries, as shown in figure 9, due to a changing global economy and climate. Figure 8 shows the dams being constructed or future dam sites. Most of these are in developing countries or are a result of glacial meltwaters. Along with the high number of dams, the US has a history of adding and removing wood in streams for different reasons. This has intensively transformed the hydraulics of streams across the United States. Wohl (2014) documented these changes in river corridors by human activity since European Settlement primarily through steamboat navigation and timber rafting. Prior to railroad development, the steamboat was the United States’ main source of transporting commodities in the 19th century. Steamboat navigation involves the removal of wood along with other in-stream obstacles. Snagging of Large Woody Debris (LWD), dredging, and rock removal were all incorporated into the stream bed management for easier steamboat navigation. Steamboat routes were engineered this way for decades, creating channelized canals and reducing natural variation and complexity. Changing channels and steamboat accessibility also resulted in the decrease of natural mobilization of wood to rivers. Firstly, steamboats were fueled by wood and therefore the riparian forest was harvested for this purpose. The second effect was population density increase through settlement and the practice of logging as their income through commercial production. Figure 8. Newly constructed and future constructed sites of dams (Lewis & Maslin 2015).
  • 19. 18 Anthroturbation and the Anthropocene: a review of human influence on the Earth’s geomorphology Commercial logging then reformed the rivers in a new way with the addition of materials to the stream, also called timber rafting. Timber rafting was the transportation of logs by means of floating downstream to collection points. This process became so widespread that the state of New York occupied every one of its large rivers with timber rafting (Wohl 2014). The rivers were then declared public highways for log transport, and it was illegal to obstruct the timber moving downstream. Additional modifications to channels for the enhanced passage of timber further congested the natural rivers in the US. Indirect Long-term Effects To condense the intensity of river modification, figure 9 illustrates a time-lapse diagram of change throughout the settlement of the United States. The stages of the alluvial floodplain begin with A) Pre-settlement period. In this stage, rivers were able to meander leading to the production of gravel beds and fine-grained banks. B) During the agricultural era, extreme upland erosion and downstream legacy sediment deposition caused rapid aggradation and incising. C) Stream attempts to readjust to pre-settlement period with a decrease in unsustainable agricultural practices and an increase in urbanization. “A” represents legacy sediments Figure 9. Diagram demonstrating long-term changes in stream morphology due to indirect human activities (Wohl 2014.)
  • 20. 19 Anthroturbation and the Anthropocene: a review of human influence on the Earth’s geomorphology as post-settlement deposition. “VR” stands for very recent, as seen as coarse sediment on the river bed, and “PS” for pre-settlement sediment. Lastly, D) Representation of current conditions of a highly modified stream with numerous small dams upstream. The dams have caused aggradation through the buildup of fine-grain alluvium as seen with the “VR” arrow pointing to the new deposition. The ultimate outcome is a change in stream structure with an unnatural variation. Conclusion Through examining the modifications on both a global scale with human population explosion leading to extraction of subterranean resources, and a more local scale of long-term river channel morphology, the overview of the appearance of the Anthropocene is recognizable. Humans have altered a great quantity of the planet and researchers are still attempting to quantify the extent. As the literature has displayed, many academics believe we are now in the Anthropocene and need to adjust the teachings of Earth Science to reflect this change. Others may also hope to provide this indication as a turning point for society to more sustainable practices and population control. Furthermore, the evidence of humans as the primary geomorphic force on the planet is s, widely accepted throughout the literature, and can serve as an active branch of study in the field of biogeomorphology.
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