EXERCISE 4C

• Slope, water depth, and nature of the stream bed impart physical character to the flowing water.
• Steep slope increases flow velocity

  Deeper water has a calmer flow than shallow water
• Rumbling waters are the result of obstruction such as rocks and boulders on the stream bed.
• Rumbling results in higher oxygen content than calmer waters.
• Light penetration in stream waters is affected by the presence of suspended turbidity-causing materials which may be organic or inorganic
• Inorganic turbidity: caused by suspended silt that increases in amount during or after heavy rain

  Organic turbidity: caused by suspended organisms primarily microscopic algae
• Algae tend to be plentiful in nutrient-rich water exposed to strong sunlight.
• Algal growth in streams generally increases after the water has been cleared its turbidity brought by rain
• Since water flows, and with it the floating organisms, there are no true plankton community in a stream. Floating organisms are just transient inhabitants but the physical and chemical characteristics of the stream influence the kind and abundance of organisms that live there
• Organisms inhabiting a stream may be grouped as follows:

  • Phytoplankton: microscopic floating algae
  • Zooplankton: small, floating animals
  • Periphyton: attached to microscopic algae on any type of material together with their associated minute animals
  • Nekton: animals that swim on their own even against current
  • Benthic macrophytes: rooted macrophytes
  • Benthos: bottom dwelling animals
• Regardless of the length of stay in any portion of the stream, each biological entity contributes to the development of the measurable properties of the water.

  For example, physical property of water transparency to sunlight and chemical property expressed in terms of dissolved oxygen (DO)

  Each organism also participates in energy flow and nutrient cycling by being a part of the food chain.
• The nature of the medium in which the primary producers grow in the open water requires that the rate of photosynthesis be measure in a known volume of water

  In this case, photosynthesis is expressed as the amount of carbon fixed per unit volume of the water per unit time (e.g. mg C/L/day)
• Light-and-dark-bottle method is a common way of measuring photosynthesis in water. It is an indirect means of determining the amount of organic matter formed as it makes use of the oxygen given off by algae in a known volume of water sample within the time of incubation, and then converts this into the equivalent amount of carbon fixed.

  Assumption:

  • Initial amount of oxygen is known
  • Final amount of oxygen could also be known
• Difference between initial and final amount of oxygen sample represents the net amount of oxygen fixed
• Light-and-dark-bottle method allows for an estimation of the amount of oxygen consumed during respiration and this is designated as community respiration
• Community respiration includes not only algae but also animals and aerobic bacteria that are consuming the oxygen in the water sample during the incubation period
• Environmental factors like light intensity, water temp, and the amount of dissolved CO2 and nutrient influence the process.

  Biologically, the rate of photosynthesis is affected by the phytoplankton density, the composition of the community, and whether the community is young or old