On January 17, 2014 Governor Brown declared a state of emergency due to the drought. After more than five years of drought in California, Water Year 2017 (beginning Oct 1, 2016) has received above average precipitation and snowpack-estimated at 200% of average. See the Summary of Water Conditions in California, provided by CDEC, and check out the Snowpack Update Report from USDA Natural Resource Conservation Service for Tahoe ski areas. On April 7, 2017 Gov. Brown officially ended the drought in all California counties, with the exception of Fresno, Kings, Tulare and Tuolumne.
At SYRCL, citizen scientists prevailed through the drought and continued to collect monthly water quality data that we use to understand the health of the Yuba River watershed. SYRCL began collecting water quality data across the Yuba River watershed in 2000 and uses this data to ask key questions about how water quality changes due to a variety of factors, including looking at differences between drought years, wet years, and normal years. The water quality parameters monitored include water and air temperature, pH, conductivity, dissolved oxygen and turbidity. We have taken a subset of this data to understand the influence of the drought on the main stem of the Yuba River and its tributaries. Table 1 shows the wet to dry index created for the Sacramento River watershed.
(1) Is the main stem of the Yuba River less affected by drought conditions than its tributaries, since it has a larger volume of water; and
(2) Will there be a larger number of water quality violations, according to water quality standards set by The Central Valley Regional Water Quality Control Board, during drought conditions?
To understand whether the quantity of water in the main stem buffers against changes in water chemistry, we evaluated water temperature data from four sites (Table 2) along the main stem of the Yuba River and five sites along tributaries during 2006 (wet) and 2014 (critically dry). Main stem sites included: Edwards Crossing, Purdon Crossing, Bridgeport Crossing, and Above Oregon Creek. Tributary sites included: Oregon Creek, Lower Rock Creek, Shady Creek, Lower Rush Creek, and Lower Kentucky Creek.
Water temperature is a significant water quality indicator as warm water temperatures reduce aquatic species ability to complete their life cycles. Increased temperatures decrease dissolved oxygen levels, starving organisms of essential oxygen, at the same time as elevating metabolism, respiration and oxygen demand of fish and other aquatic life. In addition, the solubility of many toxic substances (including cyanide, phenol, xylene, zinc) is intensified as temperatures rise, which can also impact organisms. Optimal water temperatures depend on each species. If water temperatures are outside the optimal range for a prolonged period, organisms become stressed and can die.
We found that the mainstem does not provide a significant buffering effect for water temperature in dry vs. wet years. For example, 2006 is was a wet year (Table 1), and there was little variance in water temperature throughout the year at both mainstem and tributary sties (Figure 1a and 1b). In 2014, a “critical” year for drought, there was a strong pattern of rising temperatures in the summer months at both mainstem and tributary sites (Figures 1c and 1d). These findings indicate that drought conditions impact the entire watershed, from the smallest creeks to the mainstem. Water temperature (and potentially other water quality parameters) become inhospitable to some aquatic species during the summer months. After multiple years of drought, we can hypothesize that species that were already struggling might find it difficult to persist without the cooler water they need to complete their life cycles.
To understand whether drought years resulted in an increase in water quality violations we calculated the percentage of data points where water quality violations occurred for water temperature, dissolved oxygen, and pH in the 2006 and 2014 water years. As stated above, temperature has rippling effects on aquatic life and changes the availability of dissolved oxygen. The acidity or alkalinity of water is measured by pH. While different species have optimal ranges, the largest variety of aquatic organisms thrive at a range of 6.5-8.5, and values outside this range reduce biodiversity. Low pH can also allow toxic elements and compounds to mobilize and become available for uptake by plants and animals.
Water temperature violations (>20°C) were greater in drought years than wet years in both tributary and mainstem data. Both dissolved oxygen violations (<7 mg/L) and pH violations (<6.5 and >8.5) were greater in the dry year compared to the wet year, shown in Table 3. We plan to do further analysis to look at more than one wet or dry year to see if we can establish a stronger trend in water quality violations.
Main stem and tributary monitoring locations throughout the Yuba River watershed showed a pattern throughout the year of warming temperatures in summer months (Figure 2). These conditions could have impacted habitat and affected life cycles of aquatic species. Population studies have not been assessed as part of this article.
After a winter with such plentiful precipitation, we are eager to study how our watershed has changed and how water quality parameters compare to past years. Monthly water quality monitoring across the Yuba watershed (Figure 3) will continue to provide quality data, all thanks to our dedicated citizen scientist River Monitor volunteers!