Suspended Particulate Matter (SPM) refers to small particles, both organic and inorganic, that are suspended in a liquid medium such as water. These particles remain dispersed in the water column due to turbulence, currents, or their small size and low density. SPM plays a critical role in aquatic ecosystems and is a key parameter in water quality assessments.
Composition of SPM
SPM consists of two main types of particles:
- Inorganic Particles:
- Minerals: Sand, silt, and clay particles eroded from land or riverbeds.
- Sediments: Particles introduced into the water by weathering, runoff, or resuspension from the bottom of a water body.
- Organic Particles:
- Detritus: Decomposed plant and animal matter.
- Phytoplankton: Microscopic algae and photosynthetic organisms.
- Zooplankton: Tiny animals or their fragments.
Sources of SPM
- Natural Processes:
- Erosion and runoff from land surfaces.
- River and stream input carrying sediments.
- Resuspension of bottom sediments due to currents or waves.
- Human Activities:
- Agricultural runoff carrying soil and organic material.
- Urban and industrial discharges.
- Construction and dredging activities.
- Deforestation and land use changes.
Key Characteristics
- Size: SPM particles vary in size from fine colloidal particles (<1 micrometer) to larger sand grains (>100 micrometers).
- Concentration: The amount of SPM in water can range from very low (in clear lakes or open oceans) to very high (in rivers, estuaries, or during storms).
- Light Interaction:
- SPM scatters and absorbs light, reducing water clarity and affecting how light penetrates through the water column.
Importance of SPM
- Water Quality:
- High concentrations of SPM can decrease water transparency, affect photosynthesis in aquatic plants, and influence dissolved oxygen levels.
- It can act as a carrier for nutrients, contaminants, and pathogens.
- Ecosystem Health:
- SPM affects the habitat of aquatic organisms. For instance, it can smother benthic organisms (organisms living at the bottom) or clog fish gills.
- Nutrient Cycling:
- Organic SPM contributes to the cycling of nutrients in aquatic ecosystems by providing food for microorganisms and other aquatic life.
- Remote Sensing:
- SPM concentration is often estimated using satellite imagery by analyzing the scattering of light in water.
- Sediment Transport:
- SPM is a crucial part of sediment transport in rivers and coastal areas, influencing erosion, sediment deposition, and the morphology of water bodies.
Measurement of SPM
SPM is typically measured by:
- Filtration: Water is filtered, and the retained particles are dried and weighed.
- Turbidity: Optical instruments estimate SPM indirectly by measuring water clarity.
- Remote Sensing: Satellites detect SPM by analyzing the optical properties of water.