During the water cycle, when rainwater flows over mountain surfaces, which type of cycle's elements can it mobilize into aquatic ecosystems?

Correct answer: Elements of sedimentary biogeochemical cycles

Direct answer: B. Rainwater flowing over rock and soil causes weathering and erosion. In this process, dissolved ions and fine sediment can be carried into streams, lakes and eventually oceans. This is especially important for sedimentary nutrient cycles, in which the main reservoirs are rocks, soil and sediments rather than the atmosphere. Phosphorus is a standard example: weathering releases phosphate from rocks, runoff transports it, and aquatic organisms may take it up. A is too narrow because nitrogen has important gaseous pathways and is not represented only by runoff. C is wrong because the process is not limited to oxygen and hydrogen. D is plainly incorrect because runoff does transport dissolved and suspended materials. The exact amount transported depends on rock type, soil, slope and rainfall, but the broad classification is sedimentary cycling.