Passage II

Scientists noted an increase in plant growth in a lake. Increased growth of lake weeds and algae is usually the result of an increased input of nutrients, especially phosphates and nitrates. Nitrates are easily carried by water moving through the soil (groundwater) or streams. Phosphates can attach to soil or stream sediment particles.To determine the primary source of nutrients entering the lake, scientists conducted the following experiments.

Experiment 1

Scientists deduced that one source of phosphates and nitrates was seepage from wastewater systems buried in the soil near houses adjacent to the lake. Sampling wells were placed in locations where samples of groundwater, flowing from houses toward the lake, could be obtained daily. The results are presented in Table 1.

Experiment 2

Scientists suspected that another source of nutrients where fertilizers was the runoff from nearby farm lands were applied.Water and suspended-sediment samples were obtained from two streams that flowed into the lake.These streams intercept surface runoff from the farm lands during rainfall and snowmelt.The results are depicted in Table 2.