We act as if they can. TRPA, to its credit, recently asked the same question, and hired a consultant to review the facts. The consultant, Toby Hanes of Hydro Science, was formerly a U.S. Forest Service hydrologist in the Tahoe Basin and has since worked on wetlands restoration projects around the lake. His report makes some unsettling observations on the effectiveness of mitigation measures.
Infiltration trenches are potentially valuable tools for eliminating dissolved phosphorus.
The dissolved portion of phosphorus, the phosphate ion, is the form that stimulates algal growth. And, fortunately, it s attracted to soil particles, where it sticks tightly. Yet, as Hanes explains in his report, phosphate ions are attracted to some soils, like fine clays, more than to coarser soils, like decomposed granite. Phosphate ions are cleaned out of water faster by fine silts and clay than by coarser decomposed granite. So, ideal conditions for removing dissolved phosphorus from runoff are lots of fine soils and long contact times.