Read the following passage and answer the items that follow. Your answers to these items should be based on the passage only.
The law in many parts of the world increasingly restricts the discharge of agricultural slurry in to water courses. The simplest and most economically sound practice returns the material to the land as semisolid manure or as sprayed slurry. This dilutes its concentration in the environment to what might have occurred in a more primitive and sustainable type of agriculture and converts pollutant into fertilizer. 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. The excess input of the nutrients, both nitrogen and phosphorus – based, from agricultural runoff (and human sewage) has caused many ‘healthy’ oligotrophic lakes (low nutrient concentrations, low plant productivity with abundant water weeds, and clear water) to change to eutrophic condition where high nutrient lead to high phytoplankton productivity (sometimes dominated by bloom-forming toxic species). This makes the water turbid, eliminates large plants and, in the worst situations, leads to anoxia and fish kills; so called cultural eutrophication. Thus important ecosystem services are lost, including the provisioning service of wild-caught fish and cultural service associated with recreation.
The process of cultural eutrophication of lakes has been understood for some time. But only recently did scientists notice huge ‘dead zones’ in the oceans near river outlets, particularly those draining large catchment areas such as Mississippi and North America and the Yangtze in China. The nutrient enriched water flows through streams, rivers and lakes and eventually to the estuary and ocean where the ecological impact may be huge, killing virtually all invertebrates and fish in areas up to 70,000 km2 in extent. More than 150 sea areas worldwide are now regularly starved of oxygen as a result of decomposition of algal blooms, fueled particularly by nitrogen from agricultural runoff of fertilizers and sewage from large cities. Oceanic dead zones are typically associated with industrialized nations and usually lie off countries that subsidize their agriculture, encouraging farmers to increase productivity and use more fertilizer.
The passage refers to the conversion of “pollutant to fertilizer”. What is the pollutant and what is the fertilizer in this context?
The passage explicitly states that agricultural slurry, when discharged into watercourses, acts as a pollutant. Conversely, when this material is returned to the land as semi-solid manure or sprayed slurry, soil microorganisms decompose its organic components. This process makes mineral nutrients available for absorption by vegetation, thereby converting the material into a fertilizer. Thus, discharged agricultural slurry is the pollutant, and its decomposed form in the soil functions as fertilizer.
Option (A) is incorrect because the passage identifies soil microorganisms as agents that decompose the organic components of slurry, making the mineral nutrients available. The microorganisms themselves are not the fertilizer; rather, the decomposed nutrients are.
Option (C) is incorrect. The passage describes watercourses as recipients of the pollutant (discharged slurry), not as fertilizer. The conversion to fertilizer occurs when the slurry is returned to the land and processed by soil microorganisms.
Option (D) is incorrect as option (B) accurately reflects the information provided in the passage regarding the conversion of pollutant to fertilizer.