Correct Option (4)
The passage provides multiple reasons for restricting the discharge of agricultural slurry into watercourses. All three statements are supported by the text:
-
Statement 1: Losing nutrients in this way is not good practice economically. The passage explicitly states, "The simplest and most economically sound practice returns the material to the land as semisolid manure or as sprayed slurry." This implies that discharging slurry into water bodies is economically unsound, as it prevents the beneficial reuse of nutrients as fertilizer and represents a loss of valuable resources.
-
Statement 2: Water courses do not contain microorganisms that can decompose organic components of agricultural slurry. The passage notes, "Soil microorganisms decompose the organic components of sewage and slurry and most of the mineral nutrients become available to be absorbed again by the vegetation." This indicates that the primary environment for effective microbial decomposition and nutrient recycling of slurry is soil, not watercourses, which lack the necessary microbial communities for this process.
-
Statement 3: The discharge may lead to the eutrophication of water bodies. The passage details how "excess input of the nutrients, both nitrogen and phosphorus – based, from agricultural runoff" (which includes slurry) causes "cultural eutrophication." This process transforms healthy oligotrophic lakes into eutrophic conditions, leading to high phytoplankton productivity, water turbidity, elimination of large plants, anoxia, and fish kills. It also mentions the formation of oceanic "dead zones" due to nutrient-enriched water from such discharges.
Incorrect Options:
Options 1, 2, and 3 are incorrect because they only partially identify the reasons for restricting agricultural slurry discharge. The passage clearly supports all three statements as valid reasons, making option 4 the comprehensive and correct choice.