Bottom deposits and particles suspended in water

The aquatic environment is influenced not only by physical and chemical factors but also by the nature of solid materials present in it — these include bottom deposits (sediments) and suspended particles.
Both play vital roles in determining water quality, nutrient availability, and the living conditions for aquatic organisms, especially fish and microorganisms.

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1. Bottom Deposits (Sediments):Bottom deposits are the materials that settle down and accumulate on the floor of aquatic environments such as rivers, lakes, ponds, and oceans.
They consist of inorganic particles, organic matter, and biological remains.

Composition of Bottom Deposits

Bottom deposits vary depending on the origin of the water body and may include:

1. Inorganic Materials
   1. Sand, silt, clay particles, and mineral fragments (silica, calcium carbonate, iron, etc.)
   1. Originating from weathering and erosion of rocks and soils.
2. Organic Materials
   1. Decomposed remains of plants, animals, and microorganisms.
   1. Detritus from aquatic vegetation, algae, and fish excreta.
3. Chemical Precipitates
   1. Compounds like calcium carbonate, iron oxide, or manganese dioxide that settle due to chemical reactions in water.
4. Biological Components
   1. Shells, skeletons, and remains of aquatic organisms (benthic fauna and flora).

Formation of Bottom Deposits

• Erosion and Transport:
  Particles from surrounding land enter the water through rainfall, runoff, and river flow.
• Sedimentation:
  Heavier particles settle at the bottom as the water velocity decreases.
• Decomposition:
  Organic matter decomposes under the influence of bacteria, forming nutrient-rich mud.
• Chemical Precipitation:
  Changes in temperature, pH, or oxygen cause dissolved substances to precipitate and settle.

Types of Bottom Deposits

1. Sandy Bottoms:
   1. Found in areas with strong water currents.
   1. Well-aerated but poor in nutrients.
   1. Favors burrowing animals and bottom-dwelling fishes.
2. Muddy Bottoms:
   1. Common in ponds and lakes with slow-moving or stagnant water.
   1. Rich in organic matter and nutrients.
   1. Supports bacterial growth and benthic fauna (worms, mollusks, etc.).
3. Rocky or Gravel Bottoms:
   1. Common in mountain streams and coastal regions.
   1. Provides attachment surfaces for algae, sponges, and sessile organisms.
4. Calcareous or Lime-Rich Bottoms:
   1. Formed by calcium carbonate deposits.
   1. Found in hard water areas or coral reefs.

Biological Significance of Bottom Deposits

• Habitat for Benthos:
  Provides living space for bottom-dwelling organisms like worms, mollusks, crustaceans, and certain fish species (e.g., catfish).
• Nutrient Source:
  Rich in nitrogen, phosphorus, and organic matter — nutrients that support primary productivity (phytoplankton and aquatic plants).
• Role in Decomposition:
  Microbes in sediments decompose organic waste, releasing nutrients back into the water (a process known as mineralization).
• Indicator of Pollution:
  Accumulation of heavy metals, pesticides, and industrial waste in sediments can indicate the degree of water pollution.

2. Particles Suspended in Water (Suspended Load)

Definition

Suspended particles are minute solid or colloidal materials that remain floating or dispersed in water due to low settling velocity.
These particles contribute to the turbidity of water.

Composition of Suspended Particles

• Inorganic Suspended Solids: Clay, silt, fine sand, mineral particles.
• Organic Suspended Solids: Detritus, plankton, fecal matter, bacteria, algae.
• Colloidal Particles: Proteins, humic substances, and fine organic molecules that do not settle easily.

Sources of Suspended Particles

1. Natural Sources:
   1. Erosion of soil and rocks.
   1. Runoff from agricultural lands.
   1. Decomposing vegetation.
   1. Biological activity (plankton growth).
2. Anthropogenic (Human-Induced) Sources:
   1. Domestic sewage.
   1. Industrial effluents.
   1. Deforestation and construction activities.
   1. Dredging and mining operations.

Effects of Suspended Particles on Aquatic Life

• Reduced Light Penetration:
  • Limits photosynthesis of aquatic plants and phytoplankton.
  • Affects the oxygen production in water.
• Reduced Visibility:
  • Hinders fish feeding and predator-prey interactions.
  • Especially affects visually oriented species (e.g., perches, trouts).
• Respiratory Stress:
  • Suspended silt can clog fish gills, reducing oxygen uptake.
  • Leads to respiratory distress or suffocation.
• Deposition and Habitat Alteration:
  • When suspended particles settle, they smother benthic habitats and fish eggs.
  • Reduces breeding success of bottom spawners (e.g., carps).
• Transport of Pollutants:
  • Suspended particles adsorb toxic metals, pesticides, and organic contaminants.
  • These are later deposited in sediments, leading to bioaccumulation in aquatic food chains.

Measureme4nt of Suspended Solids

• Measured as Total Suspended Solids (TSS) in mg/L.
• Also expressed as Turbidity in Nephelometric Turbidity Units (NTU).
• High TSS indicates pollution, erosion, or eutrophication.

3. Relationship Between Bottom Deposits and Suspended Particles

• Dynamic Exchange:
  Sediments and suspended particles constantly interact — suspended materials settle to form deposits, while turbulence and currents resuspend them.
• Nutrient Recycling:
  Sediments act as nutrient reservoirs; when disturbed, nutrients are released back into the water, promoting algal blooms.
• Indicator of Ecosystem Health:
  Clean, stable bottoms with balanced suspended particles indicate a healthy aquatic system. Excessive turbidity or sedimentation reflects environmental stress or pollution.

4. Ecological Importance

5. Impact on Fisheries

• Positive Effects:
  • Moderate organic sediments enhance plankton growth and fish productivity.
  • Nutrient-rich mud is favorable for bottom feeders.
• Negative Effects:
  • Excessive siltation can destroy spawning beds.
  • High turbidity limits feeding and growth.
  • Accumulation of toxins in bottom deposits may cause fish mortality.

6. Management and Control

Monitoring of TSS and sediment quality for sustainable aquatic management.

Erosion control through vegetation and soil conservation.

Sediment traps and filters in inflowing streams.

Regular dredging to remove excess deposits.

Treatment of effluents before discharge into natural water bodies.