A soil horizon is a layer parallel to the soil surface, whose physical and biological characteristics differ from the layers above and beneath. Horizons are defined in many cases by obvious physical features colour and texture; these may be described both in absolute terms and in terms relative to the surrounding material, i.e. ‘coarser’ or ‘sandier’ than the horizons above and below. The identified horizons are indicated with symbols, which are used in a hierarchical way. Master horizons are indicated by capital letters. Suffixes, in form of lowercase letters and figures, further differentiate the master horizons. There are many different systems of horizon symbols in the world, it should be emphasised that no one system is more correct – as artificial constructs, their utility lies in their ability to describe local conditions in a consistent manner. Due to the different definitions of the horizon symbols, the systems cannot be mixed. Below, some of these systems will be described. In most soil classification systems, horizons are used to define soil types.
Some systems use entire horizon sequences for definition. Other systems pick out certain horizons, the “diagnostic horizons”, for the definition, e.g. the World Reference Base for Soil Resources, the USDA soil taxonomy and the Australian Soil Classification. Diagnostic horizons are indicated with names, e.g. the “cambic horizon” or the “spodic horizon”. The WRB, e.g. lists 37 diagnostic horizons. Of course, besides these diagnostic horizons, some other soil characteristics may be needed to define a soil type; some soils don’t have a clear development of horizons. A soil horizon sensu stricto is a result of soil-forming processes. Layers that do not have undergone such processes may be called “layers”; some soil scientists use the word layer in a more general way, including the horizons sensu stricto. Many soils have an organic surface layer, denominated with a capital letter; the mineral soil starts with an A horizon. If a well-developed subsoil horizon as a result of soil formation exists, it is called a B horizon.
An underlying loose, but poorly developed horizon is called a C horizon. Hard bedrock is denominated R. Most individual systems defined more layers than just these five. In the following, the horizons and layers are listed more or less by their position from top to bottom within the soil profile. Not all of them are present in every soil. Soils with a history of human interference, for instance through major earthworks or regular deep ploughing, may lack distinct horizons completely; when examining soils in the field, attention must be paid to the local geomorphology and the historical uses, to which the land has been put, in order to ensure that the appropriate names are applied to the observed horizons. O horizon The "O" stands for organic matter, it is a surface layer, dominated by the presence of large amounts of organic matter in varying stages of decomposition. In the Australian system, the O horizon should be considered distinct from the layer of leaf litter covering many vegetated areas, which contains no weathered mineral particles and is not part of the soil itself.
O horizons may be divided 3 categories: fibric and sapric. Oi horizons contain decomposed matter whose origin can be spotted on sight, Oe horizons contain intermediately decomposed organic matter, Oa horizons contain only well-decomposed organic matter, the origin of, not visible; the O horizon is greater than 20% organic matter by weight. P horizon These horizons are heavily organic, but are distinct from O horizons in that they form under waterlogged conditions; the "P" designation comes from peats. They may be divided into P2 in the same way as O horizons. A horizon The A horizon is the top layer of the mineral soil horizons referred to as'topsoil'; this layer contains dark decomposed organic matter, called "humus". The technical definition of an A horizon may vary between the systems, but it is most described in terms relative to deeper layers. "A" horizons may be darker in colour than deeper layers and contain more organic matter, or they may be lighter but contain less clay or pedogenic oxides.
The A is a surface horizon, as such is known as the zone in which most biological activity occurs. Soil organisms such as earthworms, arthropods, nematodes and many species of bacteria and archaea are concentrated here in close association with plant roots. Thus, the A horizon may be referred to as the biomantle. However, since biological activity extends far deeper into the soil, it cannot be used as a chief distinguishing feature of an A horizon; the A horizon may be further subdivided into A1, A2 and A3. E horizon “E”, being short for eluviated, is most used to label a horizon, leached of its mineral and/or organic content, leaving a pale layer composed of silicates or silica; these are present only in older, well-developed soils, occur between the A and B horizons. In systems where this designation is not employed, leached layers are classified firstly as an A or B according to other characteristics, appended with the designation “e”. In soils that contain gravels, due to animal bioturbation, a stonelayer forms near or
The Dust Bowl was a period of severe dust storms that damaged the ecology and agriculture of the American and Canadian prairies during the 1930s. The drought came in three waves, 1934, 1936, 1939–1940, but some regions of the high plains experienced drought conditions for as many as eight years. With insufficient understanding of the ecology of the plains, farmers had conducted extensive deep plowing of the virgin topsoil of the Great Plains during the previous decade; the rapid mechanization of farm equipment small gasoline tractors, widespread use of the combine harvester contributed to farmers' decisions to convert arid grassland to cultivated cropland. During the drought of the 1930s, the unanchored soil turned to dust, which the prevailing winds blew away in huge clouds that sometimes blackened the sky; these choking billows of dust – named "black blizzards" or "black rollers" – traveled cross country, reaching as far as the East Coast and striking such cities as New York City and Washington, D.
C. On the plains, they reduced visibility to 3 feet or less. Associated Press reporter Robert E. Geiger happened to be in Boise City, Oklahoma, to witness the "Black Sunday" black blizzards of April 14, 1935. While the term "the Dust Bowl" was a reference to the geographical area affected by the dust, today it refers to the event itself; the drought and erosion of the Dust Bowl affected 100,000,000 acres that centered on the panhandles of Texas and Oklahoma and touched adjacent sections of New Mexico and Kansas. The Dust Bowl forced tens of thousands of poverty-stricken families to abandon their farms, unable to pay mortgages or grow crops, losses reached $25 million per day by 1936. Many of these families, who were known as "Okies" because so many of them came from Oklahoma, migrated to California and other states to find that the Great Depression had rendered economic conditions there little better than those they had left; the Dust Bowl has been the subject of many cultural works, notably the novel The Grapes of Wrath by John Steinbeck, the folk music of Woody Guthrie, photographs depicting the conditions of migrants by Dorothea Lange.
The Dust Bowl area lies principally west of the 100th meridian on the High Plains, characterized by plains which vary from rolling in the north to flat in the Llano Estacado. Elevation ranges from 2,500 feet in the east to 6,000 feet at the base of the Rocky Mountains; the area is semiarid. The region is prone to extended drought, alternating with unusual wetness of equivalent duration. During wet years, the rich soil provides bountiful agricultural output, but crops fail during dry years; the region is subject to high winds. During early European and American exploration of the Great Plains, this region was thought unsuitable for European-style agriculture; the lack of surface water and timber made the region less attractive than other areas for pioneer settlement and agriculture. The federal government encouraged settlement and development of the Plains for agriculture via the Homestead Act of 1862, offering settlers 160-acre plots. With the end of the Civil War in 1865 and the completion of the First Transcontinental Railroad in 1869, waves of new migrants and immigrants reached the Great Plains, they increased the acreage under cultivation.
An unusually wet period in the Great Plains mistakenly led settlers and the federal government to believe that "rain follows the plow" and that the climate of the region had changed permanently. While initial agricultural endeavors were cattle ranching, the adverse effect of harsh winters on the cattle, beginning in 1886, a short drought in 1890, general overgrazing, led many landowners to increase the amount of land under cultivation. Recognizing the challenge of cultivating marginal arid land, the United States government expanded on the 160 acres offered under the Homestead Act – granting 640 acres to homesteaders in western Nebraska under the Kinkaid Act and 320 acres elsewhere in the Great Plains under the Enlarged Homestead Act. Waves of European settlers arrived in the plains at the beginning of the 20th century. A return of unusually wet weather confirmed a held opinion that the "formerly" semiarid area could support large-scale agriculture. At the same time, technological improvements such as mechanized plowing and mechanized harvesting made it possible to operate larger properties without increasing labor costs.
The combined effects of the disruption of the Russian Revolution, which decreased the supply of wheat and other commodity crops, World War I increased agricultural prices. For example, in the Llano Estacado of eastern New Mexico and northwestern Texas, the area of farmland was doubled between 1900 and 1920 tripled again between 1925 and 1930; the agricultural methods favored by farmers during this per
Erosion control is the practice of preventing or controlling wind or water erosion in agriculture, land development, coastal areas, river banks and construction. Effective erosion controls handle surface runoff and are important techniques in preventing water pollution, soil loss, wildlife habitat loss and human property loss. Erosion controls are used in agricultural settings or urban environments. In urban areas erosion controls are part of stormwater runoff management programs required by local governments; the controls involve the creation of a physical barrier, such as vegetation or rock, to absorb some of the energy of the wind or water, causing the erosion. They involve building and maintaining storm drains. On construction sites they are implemented in conjunction with sediment controls such as sediment basins and silt fences. Bank erosion is a natural process: without it, rivers would not meander and change course. However, land management patterns that change the hydrograph and/or vegetation cover can act to increase or decrease channel migration rates.
In many places, whether or not the banks are unstable due to human activities, people try to keep a river in a single place. This can be done for environmental reclamation or to prevent a river from changing course into land, being used by people. One way that this is done is by placing riprap or gabions along the bank. Examples of erosion control methods include: Since the 1920s and 1930s scientists have been creating mathematical models for understanding the mechanisms of soil erosion and resulting sediment surface runoff, including an early paper by Albert Einstein applying Baer's law; these models have addressed both gully and sheet erosion. Earliest models were a simple set of linked equations. By the 1970s the models had expanded to complex computer models addressing nonpoint source pollution with thousands of lines of computer code; the more complex models were able to address nuances in micrometeorology, soil particle size distributions and micro-terrain variation. Bridge scour Burned area emergency response Certified Professional in Erosion and Sediment Control Coastal management Dust Bowl Natural Resources Conservation Service Universal Soil Loss Equation Vetiver System "Saving Runaway Farm Land", November 1930, Popular Mechanics One of the first articles on the problem of soil erosion control Erosion Control Technology Council - a trade organization that mission is to educate and standardize the erosion control industry International Erosion Control Association - Professional Association, Training WatchYourDirt.com - Erosion Control Educational Video Resource Soil Bioengineering and Biotechnical Slope Stabilization - Erosion Control subsection of a website on Riparian Habitat Restoration
Peat known as turf, is an accumulation of decayed vegetation or organic matter. It is unique to natural areas called peatlands, mires, moors, or muskegs; the peatland ecosystem is the most efficient carbon sink on the planet, because peatland plants capture CO2 released from the peat, maintaining an equilibrium. In natural peatlands, the "annual rate of biomass production is greater than the rate of decomposition", but it takes "thousands of years for peatlands to develop the deposits of 1.5 to 2.3 m, the average depth of the boreal peatlands". Sphagnum moss called peat moss, is one of the most common components in peat, although many other plants can contribute; the biological features of Sphagnum mosses act to create a habitat aiding peat formation, a phenomenon termed'habitat manipulation'. Soils consisting of peat are known as histosols. Peat forms in wetland conditions, where flooding obstructs the flow of oxygen from the atmosphere, slowing the rate of decomposition. Peatlands bogs, are the primary source of peat, although less-common wetlands including fens and peat swamp forests deposit peat.
Landscapes covered in peat are home to specific kinds of plants including Sphagnum moss, ericaceous shrubs, sedges. Because organic matter accumulates over thousands of years, peat deposits provide records of past vegetation and climate by preserving plant remains, such as pollen; this allows humans to reconstruct past environments and study changes in human land use. Peat is harvested as an important source of fuel in certain parts of the world. By volume, there are about 4 trillion cubic metres of peat in the world, covering a total of around 2% of the global land area, containing about 8 billion terajoules of energy. Over time, the formation of peat is the first step in the geological formation of other fossil fuels such as coal low-grade coal such as lignite. Depending on the agency, peat is not regarded as a renewable source of energy, due to its extraction rate in industrialized countries far exceeding its slow regrowth rate of 1 mm per year, as it is reported that peat regrowth takes place only in 30-40% of peatlands.
Because of this, the UNFCCC, another organization affiliated with the United Nations classified peat as a fossil fuel. However, the Intergovernmental Panel on Climate Change has begun to classify peat as a "slowly renewable" fuel; this is the classification used by many in the peat industry. At 106 g CO2/MJ, the carbon dioxide emission intensity of peat is higher than that of coal and natural gas. Peat forms when plant material does not decay in acidic and anaerobic conditions, it is composed of wetland vegetation: principally bog plants including mosses and shrubs. As it accumulates, the peat holds water; this creates wetter conditions that allow the area of wetland to expand. Peatland features can include ponds and raised bogs. Most modern peat bogs formed 12,000 years ago in high latitudes after the glaciers retreated at the end of the last ice age. Peat accumulates at the rate of about a millimetre per year. Peat material is either hemic, or sapric. Fibric peats are the least consist of intact fibre.
Hemic peats are decomposed and sapric are the most decomposed. Phragmites peat are composed of reed grass, Phragmites australis, other grasses, it is denser than many other types of peat. Engineers may describe a soil as peat which has a high percentage of organic material; this soil is problematic because it exhibits poor consolidation properties – it cannot be compacted to serve as a stable foundation to support loads, such as roads or buildings. In a cited article and Clarke defined peatlands or mires as...the most widespread of all wetland types in the world, representing 50 to 70% of global wetlands. They cover over 3 % of the land and freshwater surface of the planet. In these ecosystems are found one third of the world’s soil carbon and 10% of global freshwater resources; these ecosystems are characterized by the unique ability to accumulate and store dead organic matter from Sphagnum and many other non-moss species, as peat, under conditions of permanent water saturation. Peatlands are adapted to the extreme conditions of high water and low oxygen content, of toxic elements and low availability of plant nutrients.
Their water chemistry varies from alkaline to acidic. Peatlands occur on all continents, from the tropical to boreal and Arctic zones from sea level to high alpine conditions. Peatlands are areas of land with formed layers of peat, they can cover around 4 million square kilometres. In Europe, peatlands extend to about 515,000 km2. About 60% of the world's wetlands are made of peat. Peat deposits are found in many places around the world, including northern Europe and North America; the North American peat deposits are principally found in the Northern United States. Some of the world's largest peatlands include the West Siberian Lowland, the Hudson Bay Lowlands, the Mackenzie River Valley. There is less peat in part because there is less land; that said, the vast Magellanic Moorland in South America is an extensive peat-dominated landscape. Peat can be found in New Zealand
Desertification is a type of land degradation in which a dry area of land becomes a desert losing its bodies of water as well as vegetation and wildlife. It is caused by a variety of factors, such as through climate change and through the overexploitation of soil through human activity; when deserts appear automatically over the natural course of a planet's life cycle it can be called a natural phenomenon. Desertification is a significant global ecological and environmental problem with far reaching consequences on socio-economic and political conditions. Considerable controversy exists over the proper definition of the term "desertification" for which Helmut Geist has identified more than 100 formal definitions; the most accepted of these is that of the Princeton University Dictionary which defines it as "the process of fertile land transforming into desert as a result of deforestation, drought or improper/inappropriate agriculture". Desertification has been neatly defined in the text of the United Nations Convention to Combat Desertification as "land degradation in arid, semi-arid and dry sub-humid regions resulting from various factors, including climatic variations and human activities."Another major contribution to the controversy comes from the sub-grouping of types of desertification.
Spanning from the vague yet shortsighted view as the "man-made-desert" to the broader yet less focused type as the "Non-pattern-Desert". The earliest known discussion of the topic arose soon after the French colonization of West Africa, when the Comité d'Etudes commissioned a study on desséchement progressif to explore the prehistoric expansion of the Sahara Desert; the world's most noted deserts have been formed by natural processes interacting over long intervals of time. During most of these times, deserts have shrunk independent of human activities. Paleodeserts are large sand seas now inactive because they are stabilized by vegetation, some extending beyond the present margins of core deserts, such as the Sahara, the largest hot desert. Desertification has played a significant role in human history, contributing to the collapse of several large empires, such as Carthage and the Roman Empire, as well as causing displacement of local populations. Historical evidence shows that the serious and extensive land deterioration occurring several centuries ago in arid regions had three epicenters: the Mediterranean, the Mesopotamian Valley, the Loess Plateau of China, where population was dense.
Drylands occupy 40–41% of Earth’s land area and are home to more than 2 billion people. It has been estimated that some 10–20% of drylands are degraded, the total area affected by desertification being between 6 and 12 million square kilometres, that about 1–6% of the inhabitants of drylands live in desertified areas, that a billion people are under threat from further desertification; as of 1998, the then-current degree of southward expansion of the Sahara was not well known, due to a lack of recent, measurable expansion of the desert into the Sahel at the time. The impact of global warming and human activities are presented in the Sahel. In this area, the level of desertification is high compared to other areas in the world. All areas situated in the eastern part of Africa are characterized by a dry climate, hot temperatures, low rainfall. So, droughts are the rule in the Sahel region; some studies have shown that Africa has lost 650,000 km² of its productive agricultural land over the past 50 years.
The propagation of desertification in this area is considerable. Some statistics have shown that since 1900 the Sahara has expanded by 250 km to the south over a stretch of land from west to east 6,000 km long; the survey, done by the research institute for development, had demonstrated that this means dryness is spreading fast in the Sahelian countries. 70% of the arid area has deteriorated and water resources have disappeared, leading to soil degradation. The loss of topsoil means that plants cannot take root and can be uprooted by torrential water or strong winds; the United Nations Convention says that about six million Sahelian citizens would have to give up the desertified zones of sub-Saharan Africa for North Africa and Europe between 1997 and 2020. Another major area, being impacted by desertification is the Gobi Desert; the Gobi desert is the fastest moving desert on Earth. This has destroyed many villages in its path. Photos show that the Gobi Desert has expanded to the point the entire nation of Croatia could fit inside its area.
This is causing a major problem for the people of China. They will soon have to deal with the desert. Although the Gobi Desert itself is still a distance away from Beijing, reports from field studies state there are large sand dunes forming only 70 km outside the city; as the desertification takes place, the landscape may progress through different stages and continuously transform in appearance. On sloped terrain, desertification can create larger empty spaces over a large strip of land, a phenomenon known as "Brousse tigrée". A mathematical model of this phenomenon proposed by C. Klausmeier attributes this patterning to dynamics in plant-water interaction. One outcome of this observation suggests an optimal plan
A microorganism, or microbe, is a microscopic organism, which may exist in its single-celled form or in a colony of cells. The possible existence of unseen microbial life was suspected from ancient times, such as in Jain scriptures from 6th century BC India and the 1st century BC book On Agriculture by Marcus Terentius Varro. Microbiology, the scientific study of microorganisms, began with their observation under the microscope in the 1670s by Antonie van Leeuwenhoek. In the 1850s, Louis Pasteur found that microorganisms caused food spoilage, debunking the theory of spontaneous generation. In the 1880s, Robert Koch discovered that microorganisms caused the diseases tuberculosis and anthrax. Microorganisms include all unicellular organisms and so are diverse. Of the three domains of life identified by Carl Woese, all of the Archaea and Bacteria are microorganisms; these were grouped together in the two domain system as Prokaryotes, the other being the eukaryotes. The third domain Eukaryota includes all multicellular organisms and many unicellular protists and protozoans.
Some protists are related to some to green plants. Many of the multicellular organisms are microscopic, namely micro-animals, some fungi and some algae, but these are not discussed here, they live in every habitat from the poles to the equator, geysers and the deep sea. Some are adapted to extremes such as hot or cold conditions, others to high pressure and a few such as Deinococcus radiodurans to high radiation environments. Microorganisms make up the microbiota found in and on all multicellular organisms. A December 2017 report stated that 3.45-billion-year-old Australian rocks once contained microorganisms, the earliest direct evidence of life on Earth. Microbes are important in human culture and health in many ways, serving to ferment foods, treat sewage, produce fuel and other bioactive compounds, they are essential tools in biology as model organisms and have been put to use in biological warfare and bioterrorism. They are a vital component of fertile soils. In the human body microorganisms make up the human microbiota including the essential gut flora.
They are the pathogens responsible for many infectious diseases and as such are the target of hygiene measures. The possible existence of microorganisms was discussed for many centuries before their discovery in the 17th century. By the fifth century BC, the Jains of present-day India postulated the existence of tiny organisms called nigodas; these nigodas are said to be born in clusters. According to the Jain leader Mahavira, the humans destroy these nigodas on a massive scale, when they eat, breathe and move. Many modern Jains assert that Mahavira's teachings presage the existence of microorganisms as discovered by modern science; the earliest known idea to indicate the possibility of diseases spreading by yet unseen organisms was that of the Roman scholar Marcus Terentius Varro in a 1st-century BC book titled On Agriculture in which he called the unseen creatures animalcules, warns against locating a homestead near a swamp: … and because there are bred certain minute creatures that cannot be seen by the eyes, which float in the air and enter the body through the mouth and nose and they cause serious diseases.
In The Canon of Medicine, Avicenna suggested that tuberculosis and other diseases might be contagious. Akshamsaddin mentioned the microbe in his work Maddat ul-Hayat about two centuries prior to Antonie Van Leeuwenhoek's discovery through experimentation: It is incorrect to assume that diseases appear one by one in humans. Disease infects by spreading from one person to another; this infection occurs through seeds that are so small they are alive. In 1546, Girolamo Fracastoro proposed that epidemic diseases were caused by transferable seedlike entities that could transmit infection by direct or indirect contact, or without contact over long distances. Antonie Van Leeuwenhoek is considered to be the father of microbiology, he was the first in 1673 to discover, describe and conduct scientific experiments with microoorganisms, using simple single-lensed microscopes of his own design. Robert Hooke, a contemporary of Leeuwenhoek used microscopy to observe microbial life in the form of the fruiting bodies of moulds.
In his 1665 book Micrographia, he made drawings of studies, he coined the term cell. Louis Pasteur exposed boiled broths to the air, in vessels that contained a filter to prevent particles from passing through to the growth medium, in vessels without a filter, but with air allowed in via a curved tube so dust particles would settle and not come in contact with the broth. By boiling the broth beforehand, Pasteur ensured that no microorganisms survived within the broths at the beginning of his experiment. Nothing grew in the broths in the course of Pasteur's experiment; this meant that the living organisms that grew in such broths came from outside, as spores on dust, rather than spontaneously generated within the broth. Thus, Pasteur supported the germ theory of disease. In 1876, Robert Koch established, he found that the blood of cattle which were infected with anthrax always had large numbers of Bacillus anthracis. Koch found that he could transmit anthrax from one animal to another by taking a small sample of blood from the infected animal and injecting it into a healthy one, this caused the healthy animal to become sick.
He found that he could grow the bacteria in a nutrient broth inject it into a heal
Water pollution is the contamination of water bodies as a result of human activities. Water bodies include for example lakes, oceans and groundwater. Water pollution results. For example, releasing inadequately treated wastewater into natural water bodies can lead to degradation of aquatic ecosystems. In turn, this can lead to public health problems for people living downstream, they may use the same polluted river water for bathing or irrigation. Water pollution is the leading worldwide cause of death and disease, e.g. due to water-borne diseases. Water pollution can be grouped into surface water pollution. Marine pollution and nutrient pollution are subsets of water pollution. Sources of water pollution are either non-point sources. Point sources have one identifiable cause of the pollution, such as a storm drain, wastewater treatment plant or stream. Non-point sources are more diffuse, such as agricultural runoff. Pollution is the result of the cumulative effect over time. All plants and organisms living in or being exposed to polluted water bodies can be impacted.
The effects can damage individual species and impact the natural biological communities they are part of. The causes of water pollution include a wide range of chemicals and pathogens as well as physical parameters. Contaminants may include inorganic substances. Elevated temperatures can lead to polluted water. A common cause of thermal pollution is the use of water as a coolant by power plants and industrial manufacturers. Elevated water temperatures decrease oxygen levels, which can kill fish and alter food chain composition, reduce species biodiversity, foster invasion by new thermophilic species. Water pollution is measured by analysing water samples. Physical and biological tests can be done. Control of water pollution requires appropriate management plans; the infrastructure may include wastewater treatment plants. Sewage treatment plants and industrial wastewater treatment plants are required to protect water bodies from untreated wastewater. Agricultural wastewater treatment for farms, erosion control from construction sites can help prevent water pollution.
Nature-based solutions are another approach to prevent water pollution. Effective control of urban runoff includes reducing quantity of flow. In the United States, best management practices for water pollution include approaches to reduce the quantity of water and improve water quality. Water is referred to as polluted when it is impaired by anthropogenic contaminants. Due to these contaminants it either does not support a human use, such as drinking water, or undergoes a marked shift in its ability to support its biotic communities, such as fish. Natural phenomena such as volcanoes, algae blooms and earthquakes cause major changes in water quality and the ecological status of water. Water pollution is a major global problem, it requires ongoing revision of water resource policy at all levels. It has been suggested. Water pollution accounted for the deaths of 1.8 million people in 2015. India and China are two countries with high levels of water pollution: An estimated 580 people in India die of water pollution related illness every day.
About 90 percent of the water in the cities of China is polluted. As of 2007, half a billion Chinese had no access to safe drinking water. In addition to the acute problems of water pollution in developing countries, developed countries continue to struggle with pollution problems. For example, in a report on water quality in the United States in 2009, 44 percent of assessed stream miles, 64 percent of assessed lake acres, 30 percent of assessed bays and estuarine square miles were classified as polluted. Surface water pollution includes pollution of rivers and oceans. A subset of surface water pollution is marine pollution. One common path of entry by contaminants to the sea are rivers. An example is directly discharging sewage and industrial waste into the ocean. Pollution such as this occurs in developing nations. In fact, the 10 largest emitters of oceanic plastic pollution worldwide are, from the most to the least, Indonesia, Vietnam, Sri Lanka, Egypt, Malaysia and Bangladesh through the rivers Yangtze, Yellow, Nile, Pearl, Amur and the Mekong, accounting for "90 percent of all the plastic that reaches the world's oceans."Large gyres in the oceans trap floating plastic debris.
Plastic debris can absorb toxic chemicals from ocean pollution poisoning any creature that eats it. Many of these long-lasting pieces end up in the stomachs of marine animals; this results in obstruction of digestive pathways, which leads to reduced appetite or starvation. There are a variety of secondary effects stemming not from the original pollutant, but a derivative condition. An example is silt-bearing surface runoff, which can inhibit the penetration of sunlight through the water column, hampering photosynthesis in aquatic plants. Interactions between groundwater and surface water are complex. Groundwater pollution referred to as groundwater contamination, is not as classified as surface water pollution. By its nature, groundwater aquifers are susceptible to contamination from sources that may not directly affect surface water bodies; the distinction of point vs. non-point source may be irrelevant. Analysis of groundwater contamination may focus on soil characteristics and site