Name: microbes in streams, lakes, and rivers
Uploaded: 2026-03-12T13:57:36.000Z
Duration: 1 min 24 s
Channel: JoVE

K12 Standards

Alabama Course of Study Science

9-12

Environmental Science

Unity and Diversity

9-12.EVS.2.3.b

Freshwater Microbial Ecology

L’écologie microbienne des eaux douces est façonnée par la disponibilité du carbone organique, des nutriments, de l’oxygène et de la lumière.Près de la surface, le phytoplancton utilise la lumière du soleil pour convertir le dioxyde de carbone en carbone organique.Dans les eaux peu profondes, les diatomées contribuent à la production de carbone organique, tandis que les microbes hétérotrophes décomposent ce carbone organique, libérant du dioxyde de carbone et recyclant les nutriments dans l’eau.Les biofilms sur les surfaces submergées piègent la matière organique de l’eau, où bactéries, champignons et protistes travaillent ensemble pour la décomposer et libérer du dioxyde de carbone.Les zones benthiques reçoivent généralement du carbone provenant de la litière de feuilles et de la matière organique submergée, qui est dégradé par des microbes hétérotrophes.Ces microbes libèrent du carbone organique dissous dans l’eau, soutenant ainsi les communautés microbiennes voisines.Le ruissellement urbain et agricole peut introduire des déchets organiques dans l’eau douce, entraînant l’eutrophisation.Cela favorise des proliférations cyanobactériennes à la surface et une déplétion subséquente de l’oxygène, car les microbes hétérotrophes décomposent l’excès de biomasse, affectant la structure globale de la communauté microbienne.

Écologie microbienne des eaux douces

Les systèmes d’eau douce tels que les ruisseaux, rivières et lacs présentent des caractéristiques physiques et biologiques distinctes qui influencent leurs communautés microbiennes. Ces environnements sont globalement catégorisés en systèmes lotiques — ceux dont les eaux courantes comme les ruisseaux et la plupart des rivières — et systèmes lentiques, qui incluent des eaux calmes ou à courant lent comme les lacs, les étangs et les marais.Dans les systèmes lentiques, le phytoplancton alimente la production primaire, générant du carbone organique autochtone. En revanche, les systèmes lotiques subissent des turbulences, une faible luminosité et un mélange rapide, ce qui limite la croissance du plancton. Ces eaux courantes dépendent plutôt des apports de carbone allochtone—dissous ou particulaires—provenant de la végétation environnante et des activités humaines, soutenant ainsi la colonisation microbienne.Les ruisseaux et rivières soutiennent souvent des communautés microbiennes benthiques dynamiques, avec des biofilms composés à la fois d’organismes photosynthétiques et d’hétérotrophes. Ces biofilms jouent un rôle crucial dans le recyclage des nutriments et la décomposition de la matière organique. Cependant, les perturbations causées par le ruissellement urbain ou l’activité agricole peuvent perturber cet équilibre, entraînant une diminution des niveaux d’oxygène, appelée « sac » de l’oxygène, et une potentielle anoxie. La pollution ponctuelle, comme les rejets d’eaux usées, et la pollution diffuse, comme le ruissellement des fermes, peuvent modifier la dynamique microbienne et réduire la qualité de l’eau.Les lacs diffèrent considérablement en raison de leur nature lentique. Leur structure microbienne est influencée par la profondeur, la disponibilité des nutriments et la stratification thermique. Les lacs peu profonds peuvent accueillir des autotrophes benthiques tout au long de la colonne d’eau, tandis que les lacs plus profonds développent des couches thermiques distinctes en été. L’épilimnion supérieur est riche en oxygène et productif, tandis que l’hypolimnion plus profond devient souvent anoxique en raison d’un mélange et d’une respiration limités qui dépassent la diffusion de l’oxygène. Les retournements saisonniers en automne et au printemps peuvent redistribuer les nutriments, entraînant des floraisons transitoires.Les lacs tropicaux, bien qu’ils soient similaires aux lacs tempérés en été, bénéficient de chaleur toute l’année et d’une dynamique due aux précipitations. Cela favorise une productivité continue et des proliférations fréquentes, notamment par les cyanobactéries fixatrices d’azote. Les lacs varient également en termes de nutriments, allant de systèmes oligotrophes pauvres en nutriments, qui restent oxygénés toute l’année, à des lacs eutrophes riches en nutriments qui soutiennent de grandes populations de cyanobactéries. Ces microbes prospèrent dans des eaux alcalines et chaudes et peuvent surpasser les algues eucaryotes, produisant parfois des toxines et modifiant la qualité de l’eau.

Freshwater systems such as streams, rivers, and lakes exhibit distinct physical and biological characteristics that influence their microbial communities. ...

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Education

Enseignement

JoVE Core

Microbiology

Microbiologie

Unit

Unité

Microbial Ecology

Écologie microbienne

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

microbes in streams, lakes, and rivers

Freshwater microbes live in streams, rivers, lakes, ponds, and marshes, but their communities change with water movement, light, depth, and nutrients. These systems are often grouped into lotic waters, which flow, and lentic waters, which are still or slow-moving. The physical setting shapes where microbes grow and how they get energy.

In lentic systems, phytoplankton are the main producers. They make autochthonous organic carbon, which means carbon made within the water body. In lotic systems, rapid mixing, low light, and turbulence limit plankton growth. These flowing waters depend more on allochthonous carbon, which is material that comes from outside the water, such as vegetation and human activity.

Streams and rivers often have active benthic microbial communities on the bottom. Their biofilms include photosynthetic organisms and heterotrophs, which must obtain energy from organic matter. These biofilms help recycle nutrients and break down organic matter. Urban runoff or agricultural activity can disturb this balance and lower oxygen levels, a pattern called oxygen sag, which can lead to anoxia, or very low oxygen.

Pollution also changes freshwater microbes. Point source pollution, such as wastewater discharge, and nonpoint source pollution, such as farm runoff, can shift microbial communities and reduce water quality. Lakes show another set of patterns because depth and thermal stratification, or layering by temperature, strongly affect them. Shallow lakes may support benthic autotrophs through much of the water column, while deeper lakes form separate layers in summer.

In deep lakes, the upper epilimnion is oxygen-rich and productive. The lower hypolimnion often becomes anoxic because mixing is limited and respiration uses oxygen faster than it can diffuse downward. Seasonal overturn in autumn and spring can move nutrients through the water and trigger short-lived blooms. Tropical lakes also support frequent blooms, but they stay warm year-round and respond strongly to rainfall, especially when nitrogen-fixing cyanobacteria grow.

Lakes also vary in nutrient level. Oligotrophic lakes are nutrient-poor and usually stay oxygenated throughout the year. Eutrophic lakes are nutrient-rich and can support large cyanobacterial populations. These microbes do well in warm, alkaline water and may outcompete eukaryotic algae. Some can also produce toxins and change water quality.

Microbes in Streams, Lakes, and Rivers

introduction to microbial ecology

Microbial Communities in Soil and Extremes

Microbial ecology looks at how microorganisms live, interact, and adapt in different ecosystems. It also shows how these tiny organisms help shape nutrient cycling, energy flow, and environmental balance. An ecosystem includes living parts and non-living parts, and microbes respond to both. Microorganisms can form populations, which are groups of the same species living together at the same time. When populations from different species live and interact in the same place, they form a microbial...

ecological niche

Microbial Niches in Ecosystems

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methods to assess microbial populations

Measuring Microbes in Samples

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methods to assess microbial communities

Measuring Microbial Diversity and Activity

Microbial communities include bacteria, archaea, and eukaryotic microorganisms. They live in many ecosystems and affect important environmental and biological processes. Scientists study these communities by looking at how many species are present, how many individuals each species has, and how evenly the species are spread out. Species richness is the number of different species in a sample. Species abundance is the relative amount of each species. Species evenness describes how uniformly the...

the winogradsky column

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microbial mats

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microbial interactions: mutualism

Mutualistic Partnerships in Nature

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microbial interactions: cooperation

Microbial Cooperation in Soil and Hosts

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microbial interactions: predation

How Microbes Hunt and Defend

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microbial interactions: competition

Microbial Competition and Niche Partitioning

Microbial competition shapes how bacteria and other microbes share space and resources. In shared environments, they compete for nutrients, space, or light. The strength of this competition depends on the environment, including nutrient levels, space limits, and how many microbial species are present. These interactions help determine the structure, function, and resilience of microbial communities. Microbial competition is usually grouped into exploitative competition and interference...

microbial interactions: parasitism

Microbial Parasites and Host Dependence

Microbial parasites depend on a host for nutrients and shelter, and this dependence often harms the host. In parasitism, only the parasite benefits. This is different from mutualism, where both organisms gain from the relationship. Microbial parasites are classified by where they live in or on the host. Ectoparasites stay on the host’s surface, such as the skin or outer tissues, and take in nutrients from outside. Endoparasites live inside the host’s body and invade tissues or organs.

microbe-plant interactions

How Plant Microbes Affect Growth

Plant microbes can help, harm, or simply live alongside their hosts. These microbe-plant interactions shape plant growth, health, and ecosystem function. The plant microbiome includes bacteria, fungi, archaea, protists, and viruses, and these organisms may live on the plant surface, inside plant tissues, or in symbiosis throughout the plant. Some of the most important beneficial partnerships involve mycorrhizal fungi. These fungi form close connections with roots and are grouped as arbuscular...

microbes and the carbon cycle

How Microbes Move Carbon Through Earth

Microbes move carbon through Earth’s major reservoirs and help drive the carbon cycle. Carbon shifts among the biosphere, lithosphere, atmosphere, and hydrosphere, where it supports life and helps regulate climate. It commonly cycles as carbon dioxide (CO2), the oxidized form of carbon, but methane (CH4) and organic compounds also matter. Photosynthetic microbes take in atmospheric CO2 and turn it into organic carbon. Cyanobacteria are especially important because they carry out oxygenic...

microbes and methanogenesis

How Microbes Produce Methane

Methane production in anaerobic ecosystems depends on methanogenic archaea and the microbes that work with them. This process happens where oxygen is absent, such as wetlands, sediments, and animal gastrointestinal tracts. In these anoxic habitats, aerobic respiration cannot run, so microbes use other pathways to break down organic matter. Anaerobic decomposition starts when cellulolytic bacteria, or cellulose-digesting bacteria, hydrolyze dead organic material into simple sugars. Other...

microbes and the nitrogen cycle

Microbial Steps in the Nitrogen Cycle

Microbes drive the nitrogen cycle by changing nitrogen into forms that plants and other organisms can use. This biogeochemical cycle keeps nitrogenous compounds balanced in ecosystems. It also supports plant growth and microbial growth. Nitrogen fixation begins the cycle by converting inert atmospheric nitrogen gas, N2, into ammonia, NH3. This step depends on nitrogenase enzymes. Free-living diazotrophs do this on their own. Aerobic bacteria such as Azotobacter spp. and anaerobic bacteria such...

microbes and the sulfur cycle

Sulfur Cycling Through Microbial Reactions

Sulfur cycling depends on microbial reactions that move sulfur through rocks, water, soil, and the air. In Earth systems, sulfur shifts among inorganic forms such as sulfate, elemental sulfur, and sulfide. These changes happen through both abiotic processes and biological activity in oxic and anoxic environments. Sulfate is the most oxidized form of sulfur. It is stored mainly in rocks, marine sediments, and ocean water, where it acts as a long-term reservoir in the global sulfur cycle. In...

microbes and other elemental cycles

Microbes Driving Iron and Manganese Cycles

Microbes drive iron and manganese cycling in aquatic environments by changing these metals between reduced and oxidized forms. These reactions are especially important along redox gradients, where oxygen levels shift across stratified water layers. The microbes use these metals for energy, growth, and structural needs. In oxygen-rich surface waters, iron is usually present as insoluble ferric iron, Fe(III). Some bacteria release siderophores, which are small organic molecules that bind ferric...

marine microbial ecology

Microbial Life in the Ocean

Marine microbial life is shaped by salinity, low nutrients, and changing oxygen levels. These physical and chemical limits influence which microbes can survive and how they function. They also affect how ocean microbes help drive nutrient and carbon cycling. Small cell size is common in these environments because it gives microbes a larger surface-to-volume ratio. That helps them take up nutrients more efficiently when nutrients are scarce. In estuaries, where salinity changes often,...

deep sea microbial ecology

Deep Sea Microbes and Extreme Conditions

Deep sea microbes live in one of Earth’s harshest environments. The deep ocean is far below the sunlit photic zone, which usually reaches the upper 100 to 200 meters of open water. Below that layer, the bathypelagic and abyssal zones stretch from about 1,000 to 6,000 meters, and hadal trenches go even deeper. This region is dark, cold, and highly pressurized. Temperatures are usually around 2 to 3°C, although hydrothermal vents can be slightly warmer. Pressure rises by about 1 atmosphere for...

freshwater microbial ecology

Freshwater microbes live in streams, rivers, lakes, ponds, and marshes, but their communities change with water movement, light, depth, and nutrients. These systems are often grouped into lotic waters, which flow, and lentic waters, which are still or slow-moving. The physical setting shapes where microbes grow and how they get energy. In lentic systems, phytoplankton are the main producers. They make autochthonous organic carbon, which means carbon made within the water body. In lotic...

soil microbial ecology

How Soil Microbes Cycle Nutrients

Soil microbes drive nutrient cycling, organic matter turnover, and ecosystem stability. A gram of soil can contain thousands of bacterial and archaeal taxa, but their shared job is what helps sustain land ecosystems. Their activity changes the way carbon, nitrogen, and other nutrients move through soil. Soil is a patchwork of minerals, organic matter, water, and air. Microbes live in tiny microhabitats shaped by pore size, moisture, oxygen, and nutrients. Sandy soils drain fast and tend to...

key terms and concepts

Explore how water flow, depth, nutrients, and pollution shape freshwater microbes in streams, rivers, lakes, and cyanobacteria blooms.

Microbes in Streams, Lakes, and Rivers | JoVE K12

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Microbes in Streams, Lakes, and Rivers

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