Answer:
Step-by-step explanation:
(a) Reasons that can cause heterogeneity in obtaining representative samples from surface water (river, stream, lake) include:
1. Flow dynamics: Surface water bodies are constantly in motion, with different currents and turbulence. This movement can result in variations in water composition, temperature, and nutrient levels, making it challenging to obtain a truly representative sample.
2. Spatial variability: Surface water bodies often exhibit spatial heterogeneity, meaning that different areas within the water body may have varying characteristics. For example, one part of a river might have higher levels of pollutants due to nearby industrial activities, while another part may be cleaner. Obtaining a representative sample requires careful consideration of these variations.
3. Seasonal changes: Surface water bodies can undergo significant seasonal changes, such as variations in temperature, precipitation, and biological activity. These changes can impact the composition of the water, making it difficult to obtain a representative sample that accurately represents the overall condition of the water body.
4. Mixing of water sources: Rivers and streams can receive inputs from multiple sources, such as tributaries, groundwater, and runoff from surrounding land. The mixing of these different water sources can lead to heterogeneity in terms of nutrient levels, pollutants, and other dissolved substances.
(b) Reasons that can cause heterogeneity in obtaining representative samples from the atmosphere include:
1. Vertical stratification: The atmosphere is stratified into different layers with varying properties. For example, the troposphere is the layer closest to the Earth's surface and contains the majority of weather phenomena. As we move higher into the atmosphere, we encounter the stratosphere, mesosphere, and thermosphere, each with distinct characteristics. Obtaining representative samples from these different layers can be challenging due to their stratification.
2. Wind patterns: The movement of air masses and prevailing wind patterns can cause spatial heterogeneity in the composition of the atmosphere. For example, pollutants emitted from industrial areas may be carried by prevailing winds to certain regions, leading to higher concentrations of pollutants in those areas. Sampling efforts need to consider these wind patterns to obtain representative samples.
3. Localized sources of pollution: Certain areas may have localized sources of pollution, such as industrial zones or densely populated cities. These localized sources can lead to higher concentrations of pollutants in the immediate vicinity, resulting in heterogeneity in air quality. Sampling strategies should account for these localized sources to ensure representative samples.
4. Temporal variability: Atmospheric conditions can vary over time due to factors such as diurnal cycles, seasonal changes, and weather patterns. For example, temperature, humidity, and pollutant levels can fluctuate throughout the day. Obtaining representative samples requires careful consideration of these temporal variations.
It is important to note that these reasons for heterogeneity are not exhaustive, as each surface water body and atmosphere can have unique characteristics and factors that contribute to heterogeneity.