How have Total Phosphorus (Total P) levels changed from 1975 to 2019?

• A. They increased dramatically.
• B. Total P levels have remained steady throughout the same period.
• C. They decreased to almost zero.
• D. They varied unpredictably with no pattern.

Answer: (B)

Total phosphorus in a watershed tends to reflect a balance between inputs (like fertilizer, manure, and wastewater) and losses (such as uptake by plants, sedimentation, and drainage). When those inputs and losses settle into that balance, the long-term average stays about the same, even if year-to-year values bounce up or down due to weather or management changes.

From 1975 to 2019, the data show no significant long-term change in Total P; the average level remains roughly constant, with short-term fluctuations tied to rainfall, floods, or seasonal factors. That pattern—stable long-term means with variability from year to year—is why the answer describes the levels as steady over the period. If it were rising dramatically, falling to near zero, or varying without any pattern, the trend would look very different.