Caption: Photo from eastern Pennsylvania (book illustrated in centimeters) shows black alluvium deposited from industrial coal mining (60 cm at the top). The darkest area settled on the soil of the previously fertile brown and red native floodplains. This soil is located almost 100 km downstream of active mines, which shows how knowing the characteristics of watersheds is essential to understanding the alluvial properties of soils. Alluvial soils are formed by floods and are generally considered fertile, but this is not always the case. The amount and type of sediment brought by rivers is influenced by many human activities such as deforestation, various construction and agricultural activities. These human activities increase the rate of erosion and therefore a large number of sediments are brought downstream. These eroded soils and nutrients can sometimes be good. But there are occasions when these flood deposits involve contamination by pollution of the highlands. Alluvial soils are soils that are deposited by surface water. They are often found along rivers, floodplains and deltas. The alluvial lands of the coastal regions are known as riverine.
Alluvial land is considered an important soil type because it plays an important role in our ecosystem. Alluvial soils are one of the most fertile soils for cultivation. In addition, it removes nutrients and other sediments from running water, improving water quality for downstream areas. Alluviium (from the Latin alluvius, from alluere, „to wash against it”) is loose clay, silt, sand or gravel deposited by running water in the bed of a stream, in a floodplain, in an alluvial fan or beach or in similar environments. [1] [2] [3] Alluvium is sometimes called alluvial deposits. [4] [5] Alluvium is generally geologically young and is not solidified into solid rock. Sediments that settle underwater, in seas, estuaries, lakes or ponds are not called alluvium. [1] All alluvial soils are formed by flooding. Because floods regularly deposit new sediments on the surface, alluvial soils can have a unique stratified appearance. Dark and light colors alternate, as well as different sizes of gravel particles. This unique stratification process is called stratification.
Alluvium consists of silt, sand, clay, gravel and a good amount of organic matter. Alluvial soils are of more recent origin and therefore have weak profiles. Alluvial soils have a unique stratified appearance, as the flood continues to lay new layers compared to the previous one. This process of stratification, called stratification, is evident in many floodplains. Alluvial soils are considered immature soils because their soil profile remains incomplete. The texture of the alluvial soil is silty; It contains a mixture of sandy and loamy soils. Alluvial soils vary in texture because they have been formed by erosion, transport and river deposition activities. The texture makes it a porous soil with good drainage. The river or stream frequently replenishes the soil, making it one of the most fertile soils for crops. Most alluvium is Quaternary and is often called „cover” because these sediments obscure the underlying bedrock.
Most sediments that fill a basin („basin filling”) that is not lithified are usually grouped as „alluvial”. [9] Pliocene alluvium, for example, occurs in parts of Idaho. [10] Late Miocene alluvium, for example, is found in the San Joaquin River Valley in California. [11] These soils have a different shape from many other soils created by the long process of rock transformation, which often takes millennia. You can read more about this process on this blog. In these cases, urban soils trap harmful pollution and prevent it from entering downstream areas. In other cases, flood deposits can also lead to contamination by pollution of the highlands. Urban and industrial watersheds present an increased risk of floodplains containing chlorinated compounds and potentially harmful trace metals. Sometimes the pollution is very obvious, with dead plants and waste on the surface of the soil. In other areas, however, contamination is not visible. In these cases, a soil analysis is necessary.
Follow SSSA on Facebook in www.facebook.com/SSSA.soils, Twitter in SSSA_Soils. SSSA has www.soils4kids.org basic information about www.soils.org/discover-soils, for www.soils4teachers.org teachers and for students up to Grade 12. Alluvial soils generally have a low nitrogen content, but contain a good amount of alkalis, potash and phosphoric acid. The proportion of iron oxide and lime varies over a wide range. Much of the world`s supply of tin ore comes from alluvial lands. In some parts of the world, alluvial deposits also contain gold, platinum and precious stones. The color of alluvial soils varies from light gray to ash gray, depending on the depth of the deposit, the texture of the materials and the time it takes to reach maturity. All alluvial soils are formed by floods.
The new sediments added come from the creek watershed. And this is sensitive to changes in land use. Examples could be deforestation, ploughing for agriculture or disturbances during construction. These human activities can increase upland erosion, and the resulting sediments then flow downstream and settle. Caption: Photo from eastern Pennsylvania showing flood deposits from three different stages of watershed use (book illustrated in centimeters). The lowest material (less than 60 cm) is the ancient fertile alluvium, which has a thick layer of plow from agriculture in the 19th century. In addition, there are industrial coal washes in layers (20-60 cm) from the early 20th century, which buried this once fertile farmland in industrial waste. The northernmost sandy material (0-20 cm) is man-made material from the construction of a nearby road over the past decade.
This soil profile clearly shows evidence of human influences from agriculture, industrial coal mining, and more modern suburban construction over the past 300 years. To learn more about alluvial soils and their benefits to society, read the full blog post: soilsmatter.wordpress.com/2020/02/15/what-are-alluvial-soils. In many parts of the world, there are distinct soil colors, chemical properties, and human artifacts buried in floodplains. These allow scientists to reconstruct the history of human settlement and land use. Urban and industrial areas have increased the risk of floodplains containing chlorinated compounds and potentially harmful trace metals. Soil contamination is not always visible and can only be detected by soil tests. In many parts of the world, there are distinct soil colors, chemical properties, and human artifacts buried in floodplains. These allow scientists to reconstruct the history of human settlement and land use. In modern urban areas, alluvial soils contain discarded waste that has been washed away and buried by flooding. The most recent deposits on the surface usually contain abundant plastics. Deeper deposits contain older manufactured materials such as glass, brick and stone. Therefore, alluvial soils are also of crucial importance to archaeologists and soil scientists for the dating of human settlements.
The next time you are in a floodplain, remember that the unique alluvial soils that form there provide many useful values for society: agricultural production, the capture of pollutants and the preservation of evidence of our own human history. The current consensus is that the term „alluvium” refers to loose sediments of all kinds deposited by water flowing in floodplains or in alluvial fans or related landforms. [1] [7] [8] However, the meaning of the term has changed considerably since it was first defined in Antoine Furetière`s French dictionary, published posthumously in 1690. Following the concepts of Roman law, Furetière defined alluvium (the French term for alluvium) as a new land formed by the deposit of sediments along rivers and seas. In the 19th century, the term referred to younger sediments deposited by rivers on older diluviums, which were similar in nature but interpreted as sediments deposited by Noah`s flood. With geologists rejecting the concept of an original universal flood, the term „diluvium” fell out of favor and was replaced by „older alluvium.” At the same time, the term „alluvium” referred to all sediment deposits due to running water in the plains.