Determining trends in water chemistry for two salmon rivers and their small tributaries, 1985-2006

Related projects
Final Report: A Systematic Survey of Water Chemistry for Downeast Area Rivers

Introduction
Atlantic Salmon are thought to be susceptible to changes in water quality caused by both natural fluctuations in chemical concentrations and climate as well as anthropogenic introduction of pollutants and land-use patterns. Non-point pollution is a factor as influenced by commercial logging operations in the salmon river watersheds. Acid rain has been implicated for both chronic acidification and for episodic acidification. Climate change is another potential factor, because salmon are at their southern limit already. Climate may also cause changes in organic acidity.

Unexplored factors are the trends in water chemistry variables such as acidity, aluminum, dissolved organic carbon, and base cations. We know that many lakes and streams in the northeast have become ‘softer’ in the past decade, based on analyses completed for trends related to acid rain in a major EPA report co-authored by the lead PI for this proposal (Stoddard et al. 2003). At the Bear Brook calibrated watershed (BBWM), an upland tributary of the Narraguagus, base cations have declined 30%, and sulfate 20%, in just the past 12 years (BBWM data, 1988-2001). This observation agrees with the observation that headwater lakes in Maine have become more dilute in the past 15 years (Kahl, 1999). We will evaluate the trends in chemistry from 6 salmon river tributaries, using data collected by the Mitchell Center during 1985-87. These are the only known historical data for this period against which to compare chemical measurements.

We also propose to use a flow-based sampling regime, akin to the techniques used at BBWM and the Narraguagus tributaries, to test hypotheses about the influence of episodic acidification. Data from East Bear Brook show a decrease in pH with an increase in stream flow, supporting observations of episodic acidification in the Narraguagus tributary watersheds and nearby streams at Acadia National Park (Figure 2). Higher acidity can affect nutrient and metal mobility, metal speciation, and acid neutralizing capacity of surface waters.

We have intensive stream chemistry for three tributaries on the Narraguagus River (Rocky, Baker, and Sinclair) and three on the Union (Halfmile, Indian Camp, and Spring) from 9/85 – 12/87 (Figure 1). We began re-sampling the Narraguagus tributaries again in 2000 and have continued until the present. We will continue this work, and add the three tributaries of the Union River. These data will be evaluated within the context of the water quality trend assessment research program of Kahl and co-workers that has been underway for the past 20 years.