Answer:
Undercoverage bias
Explanation:
Undercoverage bias is a type of bias that occur in research during sampling, whereby the sample collected is unrepresentative of the target population under study. This occurs when an element of the population under study is not given equal chance of being selected in the sample process.
As stated in the question above, only soil samples from the land located at one side of the stream were collected while neglecting the soil samples from the other side of the land divided by running stream. The sample collected is unrepresentative of the target population, which is the plot of land. The potential source of bias that might result from the sampling method is undercoverage bias.