Issues of Concern Eutrophication Drought Urbanization Response to disturbance (e.g. Rodeo/Chedeski fire) Perchlorate in Colorado River and offshoots (CAP canal, Lake Pleasant) Algal toxins Narrative Nutrient Criteria Biocriteria for reservoirs
Ongoing Drought According to some climate experts, the most recent drought began in 1996. Dry conditions have been worsening over the past four years; by the summer of 2002 most of Arizona and New Mexico were considered to be in "extreme" drought.
Long-term Climatic Trends and the Pacific Decadal Oscillation (PDO) PDO is not a ten-year La Niña. Regular (20 – 30 year) pattern of high and low pressure systems over the northern portions of the Pacific Ocean. Correlates with relatively wetter or drier periods in the western portion of North America.
What does it mean for Watersheds in the Southwest? Positive PDO phases tends to enhance El Niño conditions and weaken the effects of La Niñas. Negative PDO phases enhance the effects of La Niñas and weaken the effects of El Niños
Negative PDO phase starting around 1995. This may result in drier La Niña winters. An extended period of drier than usual winters would likely produce a decrease in renewable water supplies in the desert southwest.
Although winter precipitation accounts for only 50 to 60% of our annual precipitation, it is responsible for 80 to 95% of the annual streamflow.
The UA’s Climate Assessment Project for the Southwest (CLIMAS), conducted an analysis of the effects of prolonged drought in the Phoenix and Tucson Active Management Areas (AMAs). Impact of Severe Drought on Water Resources
The research team assumed a ten-year drought of the magnitude that occurred in the 1950s and demand levels projected by ADWR for 2025. Even assuming full availability of CAP water, the Phoenix AMA could well exceed its renewable water supply by 39 percent.
The greater Phoenix metro area has experienced explosive growth in the past 20-30 years, an era when climate has been relatively wet.
Assuming that relatively wet conditions will continue into the indefinite future is unwise given all that we have learned about the climate history of the southwest.
Rodeo/Chedeski Fire and it’s Effect(s) on the Salt River Reservoirs
Salt River Above Roosevelt Nutrient Levels by Sampling Period
Nutrient Loading via the Salt River by Year (all data from late August/early September)
Mean Chlorophyll Levels (mg/m 3 ) in Roosevelt for Summer 2002 and Summer 2003.
Conclusions There is no single “slug” of water from the fire. Episodic events, especially during monsoons, will continue to bring heavy nutrient and sediment loads to Roosevelt. These events will, hopefully, diminish over time as vegetation becomes established in the watershed. The long-term, chronic effects of the fire on downstream water quality are unknown.
Hypolimnetic Anoxia within Lake Pleasant Complaints of H 2 S at Waddell Dam. Complaints of dissolved Mn at downstream municipalities.
Why Bottom Release? Implemented since 1997 to alleviate taste and odor problems in the CAP canal. Recommendation was made not because it was believed that MIB/geosmin produced within Pleasant was problematic to receiving cities. Recommended to withdraw anoxic hypolimnetic water as soon as possible in the year. Oxygenated water over the sediments as soon as possible in the year = decreased phosphorous, Mn, and H 2 S accumulation within the hypolimnion.
Did it Work? Divisional shift from periphytic cyanobacteria to green filamentous algae and diatoms (non taste and odor producing species). Taste and odors are no longer a significant problem in the CAP canal.
Two things that will hinder the original plan of hypolimnetic withdraw are; –Decreased amount of water released from the hypolimnion and, –Increased amount of time sediments are exposed to anoxic conditions.
Both may occur due to increased amount of bypass pumping of Colorado River water, delay of release from Pleasant until later in the year, etc.