Nitrate levels in ephemeral streams. On 10 June 2006, I collected water samples from two ephemeral streams within my study site on Niwot Ridge. Each value shows the nitrate concentration (mg/L) in one of the streams. The two uppermost values were collected right at the edge of melting snowbanks. Water flows downhill from the top toward the bottom of the photo. This graphic suggests that the nitrate is rapidly absorbed by the ecosystem as the water flows away from the snow.