Seasonal Patterns in the Relative Importance of Organic Acids and Sulfate in Episodic Acidification of Downeast Salmon Rivers By Mark Whiting, Maine DEP & William Otto, U of Maine at Machias

Summary of GMC Hypothesis These river are naturally acidic The important acidity is natural organic acidity (Dissolved Organic Carbon, or DOC), this drives day to day pH and our episodic acidification events Salmon recovery may be hindered by low pH, but since it is natural, the original salmon decline must be from other causes

How do you tell which acids are the important ones?

Review available data 700 total samples from all rivers, from 1999 – 2002 Water samples were taken by volunteers from salmon river watershed councils Analysis done by George Mitchell Center Samples ranged from N = 19 (Tunk Stream) to N = 142 (Sheepscot R.)

Episodic acidification occurs in all downeast salmon rivers Low pH is driven by rain events and especially runoff and snowmelt Low pH events occur October - May pH will respond to either changes in the concentration of acids or bases, this report concentrates on the sources of acidity

The role of CO2 Carbon dioxide concentrations vary diurnally, with a low at night and a high in the afternoon, following the relative amounts of photosynthesis and respiration pH varies ± 0.2 pH unit around the daily mean in the peak of the summer season due to CO2

Pleasant River, All Samples

Narraguagus, Stormwater Only

Seasonal scale pH variation Regressions are variable, different acids are important at different times and places Two acids, DOC often important overall and in some stormwater data sets Sulfate is sometimes more important than DOC in specific stormwater data sets (i.e., depending on the river, specific storms, during acidic episodes, etc)

Analysis of low pH events Plot pH by month for each river, include plots of the acidic anions by month, which acid source accounts for pH minima? One ueq/l of an acid is needed to neutralize one ueq/l of a base, so the dominant anion is the one with the most ueq’s above baseflow values

Summary Overall Sulfate and DOC are about equal when measured in ueq/L Sulfate, DOC and combinations of the two are apparently the acids responsible for low pH events In this data set, during low pH events Sulfate dominates in Tunk, the Narraguagus, and Pleasant Rivers

Summary (continued) Sulfate and DOC both play a role in acidic episodes on the Machias, E Machias and Dennys Only in the Dennys is DOC more abundant during low pH events than Sulfate Nitrate often peaks in high flow periods, but the concentration are still very low

Conclusions Acid rain is our oldest, best known, and most studied problem affecting salmon survival downeast Our low pH events are classic episodic acidification with acid rain components, esp. sulfate the primary driver DOC is important in baseflow, and sometimes in stormwater acidity