FRC Addresses pH Levels In the Fall River

pH Concerns in the Fall River

Over the summer months, the Fall River Conservancy heard concerns from Fall River residents and valley landowners regarding the pH levels in the Fall River. In order to determine the science behind these concerns, the Fall River Conservancy and California Trout have consulted with the USDA and UC Davis Watershed Sciences Center to determine what the pH levels looked like this summer in comparison to previous seasons. By looking at data collected from pH monitoring stations on the Upper Fall River, we can all learn more about pH and the current status of this water quality metric in the Fall River.

What is pH and why is it an important water quality metric?

pH is a water quality measure that describes how acidic or basic a given sample of water is. pH is reported on a scale of 0 to 14 – with values 0 to 6 representing relatively acidic samples and values 8 to 14 representing relatively basic samples. A value of 7 on the pH scale is considered neutral. A change of one unit on the pH scale represents a ten-fold change in the acid or base character of the sample. For example, a change in pH from 7 to 8 indicates that the water sample has become ten times more basic than it once was. pH is an important water quality metric because the pH of water determines the degree to which certain substances can dissolve in water. For example, carbon, nitrogen and phosphorous in water will dissolve at different rates under different pH conditions. Ultimately, changes in pH can result in different types and amounts of nutrients available to plants and animals.

Slider 3 Fall River Conservancy
Photo Credit: Val Atkinson

Current Status of pH In the Fall River

Currently there are four monitoring stations ran by the USDA located through-out the Upper Fall River that help to inform the discussion on pH.  By looking at pH from three of these stations for the 2013 season in comparison to 2012, we can help to better understand pH levels in the Fall River:

  • 2012 July averages from three monitoring sites had pH values of: 7.83, 8.07 and 8.85
  • 2013 July averages from three monitoring sites had pH values of: 8.31, 8.11, 8.89
  • 2012 August averages from three monitoring sites has pH values of: 7.86, 8.07, 8.85
  • 2013 August averages from three monitoring sites has pH values of: 8.32, 8.06, 8.94

By looking at the data, we can see that there are normal seasonal and daily variations in pH (as well as other water quality measures) in the Fall River. Further, the 2013 measurements do not seem to be unusually high nor do they differ greatly from measurements collected during 2012 with the same probes. These 2013 pH measures are near or have slightly exceeded the maximum pH values recorded in the 2012 year. Finally, only limited continuous monitoring data is available for the Fall River and assessing such values within the normal diurnal fluctuation of the water has never been assessed previously

Most importantly for the fish and those that value the health of the Fall River, the water at the monitored sites appear to have a relatively normal range of summer pH values for spring-fed rivers.  Although slightly higher levels have been recorded this past month, these pH levels are only fractionally higher than in previous seasons are not a cause for concern.

What is normal?

Most surface waters have a pH ranging between 7.5 and 8.5 ( However, spring-fed rivers tend to have higher pH levels due to their high baseline levels of geologically derived nutrients. It is not uncommon to detect summer pH levels in the range of 8 to low-to mid-9 values in spring-fed systems (Lawson 2003).

What causes variation in pH?

Daily and seasonal changes in pH are common and are usually buffered by the river’s natural water chemistry. Measurements of pH are often assessed in combination with measurements of alkalinity or Acid Neutralizing Capacity (ANC) that determines the water’s ability to buffer or resist changes in pH. Changes in pH can be a result of natural seasonal and/or diurnal changes in river conditions. For example, changing water temperatures, aeration, depth, addition of increased surface flows, and/or influxes of nutrients from natural sources or non-point sources associated with human activities (i.e. effluent from septic leach fields, urban runoff, fertilizers and sediments in tail waters or excrements from animals).

Normal plant photosynthesis uses up hydrogen molecules from the water, which causes the concentration of hydrogen ions to decrease during the day resulting in the pH increasing to a peak typically in midafternoon. For this reason, pH may be higher during daylight hours and during the growing season, when photosynthesis is at a maximum. It is unknown if the pH levels at these daily peak periods can be detrimental to crops nor what actually happens physically and chemically to these waters once impounded within agricultural fields where further nutrient and chemical alterations are expected to occur.

Final thoughts on the Fall River pH

Higher than average levels of nutrients in the water over long periods of time (not just small pulses) can results in excessive plant and algal production and can further negatively affect pH and dissolved oxygen levels in river waters. If long-term excess nutrients were present, the river would likely experience drastic changes in river plant productivity/algal blooms and consequently much higher pH levels and lower dissolved oxygen. Such changes would negatively affect fish and aquatic insects in the river. It does not, however, appear that the river water at the monitored sites has had such drastic impacts. Although elevated pH levels have been noted, they are not greatly different from general expectations nor previous measured levels. The water at the monitored sites appear to have a relatively normal range of summer pH values for spring-fed rivers although slightly higher levels have been recorded this past month, but with pH levels only fractionally higher than in previous seasons. Additionally, the monitored dissolved oxygen appears to be at healthy levels for all monitored areas.

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