a) Cooler water holds less oxygen.
b) Warmer water holds more oxygen.
c) Cooler water holds more oxygen.
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c) Cooler water holds more oxygen.
In general, cooler water can hold more dissolved oxygen than warmer water. As the temperature of the water increases, the solubility of oxygen decreases, meaning that warmer water typically contains lower levels of dissolved oxygen. This is important for aquatic life, as many organisms require adequate oxygen levels to survive.
a) Photosynthesis
During the day, aquatic plants and phytoplankton perform photosynthesis, which produces oxygen as a byproduct. This process leads to increased levels of dissolved oxygen in the water, especially in well-lit areas. In contrast, decomposition and respiration consume oxygen, and sedimentation does not directly affect dissolved oxygen levels in a way that would increase them.
b) Agricultural runoff
Agricultural runoff often contains fertilizers and organic materials that can contribute to nutrient overload in water bodies. This nutrient enrichment can lead to algal blooms, which, when they die and decompose, consume significant amounts of dissolved oxygen, leading to hypoxic conditions (low oxygen levels) in the water. While deforestation and other activities can also impact water quality, agricultural runoff is a direct contributor to reduced dissolved oxygen levels through its effects on nutrient cycling and algal growth.
b) Cloudiness or clarity
Turbidity measures the cloudiness or clarity of water, which is caused by the presence of suspended particles, such as sediments, algae, and other organic materials. High turbidity can indicate poor water quality and can affect aquatic life by reducing light penetration and disrupting photosynthesis.
c) Secchi disk
A Secchi disk is a device used to measure turbidity in water by determining the depth at which the disk is no longer visible when lowered into the water. It helps assess the clarity of the water. Other more advanced instruments, like turbidity meters (nephelometers), can also be used, but the Secchi disk is a simple and widely recognized method for measuring turbidity. The other options mentioned (pH meter, Winkler titration kit, and thermometer) serve different purposes in water quality measurement.
c) Sediment runoff
Sediment runoff is a primary cause of high turbidity in water. When rainwater or runoff carries soil, silt, and other particles into rivers, lakes, or other bodies of water, it increases the concentration of suspended particles, resulting in higher turbidity. While excessive sunlight can promote algal blooms (which can also contribute to turbidity), and strong winds can stir up sediments and increase turbidity temporarily, sediment runoff is a more direct and common cause.
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