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Related Concept Videos

Inorganic Nitrogen Assimilation01:22

Inorganic Nitrogen Assimilation

356
Nitrogen is an essential element in biological systems, forming a crucial component of proteins, nucleic acids, and other cellular constituents. Many bacteria and archaea acquire nitrogen in the form of nitrate (NO₃⁻) or ammonia (NH₃), which are then assimilated into biomolecules through specific enzymatic pathways.Assimilatory Nitrate ReductionWhen nitrate enters the cell, it undergoes a two-step reduction process known as assimilatory nitrate reduction. Initially, the enzyme...
356
The Nitrogen Cycle01:49

The Nitrogen Cycle

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Nitrogen atoms, present in all proteins and DNA, are recycled between abiotic and biotic components of the ecosystem. However, the primary form of nitrogen on Earth is nitrogen gas, which cannot be used by most animals and plants. Thus, nitrogen gas must first be converted into a usable form by nitrogen-fixing bacteria before it can be cycled through other living organisms. The use of nitrogen-containing fertilizers and animal waste products in human agriculture has greatly influenced the...
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Overview of Nitrogen Metabolism01:20

Overview of Nitrogen Metabolism

10.8K
Nitrogen is a very important element for life because it is a major constituent of proteins and nucleic acids. It is a macronutrient, and in nature, it is recycled from organic compounds and stored in the form of  ammonia, ammonium ions, nitrate, nitrite, or  nitrogen gas by many metabolic processes. Many of these metabolic processes are carried out only by prokaryotes.
The largest pool of nitrogen available in the terrestrial ecosystem is gaseous nitrogen (N2) from the air, but this...
10.8K
Metabolism of Chemolithotrophs01:15

Metabolism of Chemolithotrophs

598
Chemolithotrophs are microorganisms that obtain energy by oxidizing inorganic molecules such as hydrogen gas (H₂), ammonia (NH₃), reduced sulfur compounds (H₂S, S²⁻), and ferrous iron (Fe²⁺). Unlike heterotrophic organisms that rely on organic carbon, chemolithotrophs transfer electrons from these inorganic donors to the electron transport chain (ETC), generating a proton motive force (PMF) that drives ATP synthesis through oxidative phosphorylation.
598
Primary Production01:06

Primary Production

24.9K
The total amount of energy acquired by primary producers in an ecosystem is called gross primary production (GPP). However, of this energy, producers use some for metabolic processes, and some is lost as heat, decreasing the amount of energy available to the next trophic level. The remaining usable amount of energy is called the net primary productivity (NPP). In terrestrial ecosystems, NPP is driven by climate, while light penetration and nutrient availability drive NPP in aquatic ecosystems.
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Key Elements for Plant Nutrition02:35

Key Elements for Plant Nutrition

23.7K
Like all living organisms, plants require organic and inorganic nutrients to survive, reproduce, grow and maintain homeostasis. To identify nutrients that are essential for plant functioning, researchers have leveraged a technique called hydroponics. In hydroponic culture systems, plants are grown—without soil—in water-based solutions containing nutrients. At least 17 nutrients have been identified as essential elements required by plants. Plants acquire these elements from the...
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Related Experiment Video

Updated: Dec 16, 2025

Measurement of the Potential Rates of Dissimilatory Nitrate Reduction to Ammonium Based on 14NH4+/15NH4+ Analyses via Sequential Conversion to N2O
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Measurement of the Potential Rates of Dissimilatory Nitrate Reduction to Ammonium Based on 14NH4+/15NH4+ Analyses via Sequential Conversion to N2O

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[Identifying Nitrate Sources in a Typical Karst Underground River Basin].

Ran Zhao1, Zhi-Wei Han1,2, Chun-Hua Shen1

  • 1College of Resource and Environmental Engineering, Guizhou University, Guiyang 550025, China.

Huan Jing Ke Xue= Huanjing Kexue
|July 2, 2020
PubMed
Summary

Nitrate pollution in karst underground rivers originates mainly from fertilizers and soil. Stable isotope analysis revealed seasonal variations in pollution sources, crucial for watershed management.

Keywords:
SIAR modelkarst underground rivermulti-isotopenitrate pollutionsource analysis

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Estimating Sediment Denitrification Rates Using Cores and N2O Microsensors
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Understanding Dissolved Organic Matter Biogeochemistry Through In Situ Nutrient Manipulations in Stream Ecosystems
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Related Experiment Videos

Last Updated: Dec 16, 2025

Measurement of the Potential Rates of Dissimilatory Nitrate Reduction to Ammonium Based on 14NH4+/15NH4+ Analyses via Sequential Conversion to N2O
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Estimating Sediment Denitrification Rates Using Cores and N2O Microsensors
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Understanding Dissolved Organic Matter Biogeochemistry Through In Situ Nutrient Manipulations in Stream Ecosystems
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Understanding Dissolved Organic Matter Biogeochemistry Through In Situ Nutrient Manipulations in Stream Ecosystems

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Area of Science:

  • Environmental Science
  • Hydrogeology
  • Isotope Geochemistry

Context:

  • Karst underground rivers are vital groundwater sources.
  • Nitrate pollution poses a significant threat to these ecosystems.
  • Understanding pollution origins is critical for effective management.

Purpose:

  • To identify and quantify nitrate sources in the Guancun karst underground river basin.
  • To apply stable isotope techniques (δ15N-NO3-, δ18O-NO3-, and δ18O-H2O) for source apportionment.
  • To assess the influence of land use on nitrate distribution and sources.

Summary:

  • Stable isotope analysis indicated that nitrate primarily originates from fertilizers, soil organic nitrogen, and manure/sewage.
  • Nitrification was identified as the dominant nitrate formation process, with minimal isotopic fractionation.
  • The Stable Isotope Analysis in R (SIAR) model revealed seasonal variations in source contributions, with fertilizers being dominant in the wet season and manure/sewage in the dry season.

Impact:

  • Provides a quantitative assessment of temporal variations in nitrate sources.
  • Offers a theoretical basis for non-point source pollution control and watershed management in karst areas.
  • Highlights the significant contribution of non-point sources to nitrate pollution in karst groundwater rivers.