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Related Concept Videos

Coagulation01:06

Coagulation

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Colloidal solids are solid particles suspended in solution. They are usually negatively charged, attracting a compact primary layer of positively charged ions, which attract more counterions to form an electrical double layer. Electrostatic repulsion between the charged double layers prevents the particles from colliding, stabilizing the colloids. These solids are often undesirable because they can contain toxins that are difficult to remove. Coagulation is a technique that helps aggregate and...
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Children at play often make suspensions such as mixtures of mud and water, flour and water, or a suspension of solid pigments in water known as tempera paint. These suspensions are heterogeneous mixtures composed of relatively large particles visible to the naked eye or seen with a magnifying glass. They are cloudy, and the suspended particles settle out after mixing. The suspended particles in a suspension settle out after some time of mixing. The separation of particles from a suspension is...
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The high insolubility of some precipitates can result in an unfavorable relative supersaturation. This can lead to colloidal particles with a large surface-to-mass ratio, where adsorption is promoted. For instance, in the precipitation of silver chloride, silver ions are adsorbed on the surface of the colloidal particles, forming a primary layer. This layer attracts ions of opposite charge (such as nitrate ions), forming a diffuse secondary layer of adsorbed ions. This electric double layer...
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Colloids03:22

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Red Algae01:23

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Red algae, also known as rhodophytes, are primarily found in marine environments, though some species inhabit freshwater and terrestrial ecosystems. These organisms exist in both unicellular and multicellular forms, with some multicellular varieties reaching macroscopic sizes.As phototrophic organisms, red algae contain chlorophyll a; however, their chloroplasts lack chlorophyll b. Instead, they possess phycobiliproteins, which serve as major light-harvesting pigments, similar to those found in...
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Redox Equilibria: Overview01:23

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A reduction-oxidation reaction is commonly called a redox reaction. In a redox reaction, electrons are transferred from one species to another rather than being shared between or among atoms. The reducing agent or reductant is the species that loses electrons and gets oxidized in the process. The species that gains electrons and gets reduced in the process is the oxidizing agent or oxidant. Redox reactions are represented as two separate equations called half-reactions, where one equation...
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Related Experiment Video

Updated: Feb 20, 2026

Soil Lysimeter Excavation for Coupled Hydrological, Geochemical, and Microbiological Investigations
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Soil Lysimeter Excavation for Coupled Hydrological, Geochemical, and Microbiological Investigations

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Organic colloid composition in variable-redox porewaters within a mountainous floodplain.

Brandy D Stewart1, Sharon E Bone2, Eleanor Spielman-Sun1

  • 1Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, CA, 94025, USA.

Water Research
|February 18, 2026
PubMed
Summary
This summary is machine-generated.

Organic matter in soil porewater changes with depth along redox gradients. Carboxylate-rich organic matter, associated with iron, was found at deeper, reducing soil layers, suggesting potential transport to surface waters.

Keywords:
Alpine floodplainOrganic matterScanning transmission X-ray microscopyTransmission electron microscopy

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Sediment Core Sectioning and Extraction of Pore Waters under Anoxic Conditions
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Area of Science:

  • Environmental Science
  • Geochemistry
  • Soil Science

Background:

  • Redox gradients in groundwater systems influence colloid production and transport.
  • The organic composition of colloids is less understood than inorganic components.
  • Organic matter in colloids plays roles in mineral association, metal complexation, and microbial respiration.

Purpose of the Study:

  • To examine the composition of porewater organic matter along a redox gradient in riparian soil.
  • To understand how organic matter chemistry changes with depth and redox conditions.

Main Methods:

  • Analysis of porewater organic matter composition at various depths (90-350 cm) in riparian soil.
  • Utilized correlated scanning transmission X-ray microscopy and transmission electron microscopy.
  • Radiocarbon dating of porewater carbon.

Main Results:

  • Observed a shift in organic matter chemistry from carboxylate-rich at 200 cm (oxic to suboxic with iron/sulfate reduction) to phenol- and substituted-aromatic-rich at other depths.
  • Found younger carbon in porewater at 200 cm compared to shallower and deeper samples.
  • Increased dissolved/colloidal organic matter, pH, alkalinity, and conductivity were noted at 200 cm.

Conclusions:

  • Riparian soil porewater organic matter chemistry varies significantly with redox conditions and depth.
  • The presence of iron- and carboxylate-rich organic colloids at reducing depths suggests a potential mechanism for transport to surface waters via groundwater flow.