Date of Award

2006

Level of Access

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Earth Sciences

Advisor

Stephen A. Norton

Second Committee Member

Ivan J. Fernandez

Third Committee Member

Aria Amirbahman

Abstract

A longitudinal study of first order streams in three forested watersheds was conducted to determine spatial and temporal trends in geochemistry during high discharge acidic episodes. The watersheds were East Bear Brook and Hadlock Brook (Maine, USA), and Fernow WS3 (West Virginia, USA). Watersheds were selected based on soil type, stream pH, and historical chemistry. Stream sampling sites were distributed along an elevational gradient and sampled simultaneously during a high discharge episode. Base flow samples were collected prior to the start of the hydrological event. The Maine watersheds, East Bear Brook and Hadlock Brook, were sampled during fall 2005 rain events. Fernow WS3 was sampled during a December 2005 snowmelt event. All watersheds experienced a temporal decline in pH and ANC during the hydrologic event. Temporal decline in pH at East Bear Brook resulted from increased organic acids, cation exchange in soils releasing hydrogen (H ), and high PCO2 in soil water. Organic acids also contributed to pH depression at Hadlock Brook along with direct inputs of acid precipitation and addition of NO3". At Fernow WS3, pH declined in response to increased NO3" and SO4 " during the hydrologic event. Acid neutralizing capacity and pH increased downstream in all streams. As water moved downstream neutralization mechanisms such as water column-stream sediment ion exchange, degassing of CO2, and mixing with higher pH groundwater caused the pH to increase. The temporal decline in ANC at East Bear Brook and Hadlock Brook resulted from increased organic acid and greater dilution of base cations than anions by groundwater. As with pH, ANC generally increased downstream at East Bear Brook and Hadlock Brook due to neutralization and dilution by higher ANC groundwater. The temporal decrease in ANC at Fernow WS3 was due to a slight increase in acid anions. There was no evident spatial trend in ANC at Fernow WS3. Soil water draining the low alkalinity upper soil horizons was a major influence on event stream chemistry at East Bear Brook and Hadlock Brook. Increased DOC, K, Al, Fe, and trace metals were typically positively correlated with flow. Calcium, Mg, and Na were diluted with increasing discharge over time but generally increased downstream due to thicker soils and deeper flow paths of discharging groundwater. Event chemistry was well buffered by the Fernow WS3 soils with no significant change in base cations and little change in acid anions. Aluminum (Al) was oversaturated with respect to gibbsite in all streams but undersaturated with respect amorphous Al(OH)3. Concentrations of total and dissolved Al, as well as dissolved Fe, increased with increasing stream flow at all sampling locations. Total and dissolved Al typically decreased downstream as a result of dilution or precipitation of Al(OH)3. Particulate Al and particulate Fe covaried at all three research sites, implying that they are from similar sources. Phosphorus (P) was low, <1.0-5.0 |ig/L in all research streams. Other trace metals were low and typically influenced by changes in flow path, not pH.

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Geochemistry Commons

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