Passage I

Two measures of water quality are the number of Escherichia coli bacteria present and the biotic index, BI (a numerical value based on the type，diversity, and pollution tolerance of aquatic invertebrate animals). Both of these measures can be affected-by water flow.

E.coli levels that are above 100 colonies formed per 100 mL of water indicate reduced water quality. Figure 1 shows the E. coli levels on 5 collection days at Sites l and 2 in a river.

Table 1 shows how water quality rating varies with BI. Table 2 shows the average BI of each site during the collection period.

Figure 2 shows the water flow at each site on the 5 collection days.

5. Suppose large amounts of fertilizer from adjacent fields begin to enter the river at Site 1. The BI of this site will most likely change in which of the following ways? The BI will:

Answer and Explanation

Your Answer is

Correct Answer is D

Explanation

General knowledge questions.

A large amount of organic fertilizers entering the water source will cause algae, bacteria, and molluscs living at the bottom to proliferate, resulting in a decline in water quality. According to table 1, it can be seen that the higher the BI value, the better the water quality, and the BI value measured by the water quality decline must also decrease.