SOURCING ELEMENTAL ALUMINUM IN SURFACE WATERS IN THE SWIFT RIVER WATERSHED, NEW HAMPSHIRE: A PRELIMINARY REPORT

Aluminum is the third most abundant element in the Earth’s crust with high reactivity under conditions of the Earth surface and not found in elemental form naturally. It is also insoluble at the pH range of natural waters. High Al concentrations in aquatic systems pose a serious threat to environmental and human health. Elevated concentrations of Al are thought to cause irregular functions of gills in aquatic animals, metabolic irregularities in terrestrial animals, disruption of root processes in plants, and are linked to several human diseases. High Al concentrations in surface water were reported from areas affected by acid rain in the Northeastern US. The goals of this ongoing project are 1) to determine the Al concentrations of the Swift River and its tributaries (White Mountains National Forest, NH, US), and 2) to find the sources of the Al entering the aquatic system. Anthropogenic sources of Al are unknown in this watershed. We hypothesize elevated Al levels result from acidic dissolution of the bedrock and soil minerals. To test the hypothesis, water and soil samples were collected at 22 locations from the river and its tributaries. Also, weathered regolith was sampled at each location from the bottom of the soil profiles. An ammonium acetate extraction method was employed to extract exchangeable Al from the soil samples. The Al concentrations of water samples and soil extracts were determined by atomic absorption spectroscopy. The regolith samples were prepared for thin section analyses to evaluate the contribution of rock weathering to Al content of the system. Even though the water had relatively high pH values (5.5-6.4), the Al concentrations of the water were high between 32 and 502 ppb with most lying between 100 and 220 ppb. The water was nearly at flood stage during sampling in May due to snow melt and the higher pH values could have been caused by quick mixing of snow melt and more acidic base flow. The exchangeable Al concentrations of soil samples were an order of magnitude higher than water samples. This indicates that the soil exchangeable Al pool is large and may easily be mobilized by acid rain waters percolating through the soil profiles.