Atmospheric Contributions to Water Quality of Streams in the Hubbard Brook Experimental Forest, New Hampshire

Abstract

The balances of input in atmospheric precipitation and discharge in streams have been determined for selected mineral constituents in three small tributaries to Hubbard Brook in the White Mountains of New Hampshire. Inputs and discharge of sulfate, ammonium, and nitrate were calculated from hydrologic data, together with chemical analyses of weekly samples of precipitation and streamwater taken over a 2‐year period. The calculations show that precipitation provides most of the 30–50 kilograms of sulfate per hectare carried annually by the streams and that inputs exceed outflows of ammonium and of nitrate. Maximum effluent nitrate concentrations of 2 mg/l (milligrams per liter) are observed in early spring. Measurements of p H indicate that the hydrogen ion is one of the major cations in precipitation over the area. Determinations were made of the discharge of bicarbonate, silica, and aluminum in the streams. Annual stream loads of silica ranged from 20 to 40 kilograms per hectare. Effluent bicarbonate and silica concentrations vary directly with each other and inversely with aluminum.