On the other hand, soil under a snow pack is frozen, so rain and melted snow can t soak into the ground. When rain falls directly on coarse Tahoe Basin soils, it s likely to soak in. That water then flows underground to streams, dissolving phosphorus, carrying it to streams, and producing higher phosphate concentrations. Similar processes occur during snowmelt periods. Hatch also correlated stream-phosphorus loads with various watershed characteristics.
Some correlations seem obvious.
For example, because of the Sierra rain shadow effect, precipitation is higher along the west shore of the Tahoe watershed than it is along the east shore. And watersheds with higher precipitation have higher stream discharges and phosphorus loadings. Similarly, watersheds with larger drainage areas, steeper terrain and long channel lengths have larger phosphorus loads. Higher phosphorus loads are also found in watersheds with more roads and other impermeable coverage. That seems rational because more roads and impermeable coverage means more runoff channeled to streams, and more pulses of high flow.