Climate change is already impacting the quality of drinking water supply reservoirs and impoundments. More erratic precipitation patterns, increasingly heavy precipitation events, and changing stream flow patterns are occurring. How are these weather changes impacting water quality? How can we monitor our water supplies to plan ahead for changes that may be needed to our treatment facilities?
Tracking Changes and Trends
Identifying key water quality indicators and tracking changes and trends over time is the best predictive tool to understand if your source of supply is at risk from climate change. For example, tracking mercury concentrations in your reservoir water column is one such indicator. Methyl mercury is an organometallic cation that accumulates in the environment in fish, algae and plankton. Methyl mercury is an environmental toxicant derived from burning fossil fuels which enters water supply reservoirs from precipitation. Methyl mercury bioaccumulates and concentrates more intensively when reservoirs fluctuate from pronounced and fast changes in water depth. Mercury concentrations have been observed to be increasing in some reservoirs in Maine where water levels are widely fluctuated for hydropower and potable water-use. Tracking mercury concentrations at the source can help a water supplier understand if this phenomenon is occurring in a reservoir.
Sea Level Rise Pushing “Salt Lines” Upstream
Salinity can also be a good indicator of water quality concerns in fresh water estuaries of large rivers used for water supplies. The “salt line” is the most upstream extent that saline water ebbs and flows in coastal estuaries during tidal events. Movement of the salt line further upstream in river systems will occur with sea levels rise. Studies conducted by the City of Philadelphia have shown that a sea level rise of about 0.7 meters will push the salt line far enough upstream to render its major supply on the Delaware River unusable without desalination. In a large urban center such as Philadelphia, alternative large sources of supply are limited. Here in New England, many large communities also rely on river systems as water supplies. Intensive tracking of the salt line may make sense as a predictive tool for water systems using tidally influenced rivers as water supplies.
Algae Outbreaks on the Rise
Erratic weather is causing unprecedented algae outbreaks in the Great Lakes and in New England. Algae can present a serious challenge for some types of water filtration such as pressure filters or slow sand filters. Blue-green algae in particular are a concern for water suppliers because some species produce cyanotoxins, which are regulated and a threat to human health.
In the past 5 years, several outbreaks of golden algae (Uroglena sp., et. al) have occurred in ice covered water reservoirs during cold winter months in Northern New England. This type of algae normally remains dormant in lake sediments but can bloom from concentrated light under ice covered lakes or during turnover events in reservoirs. Often these events are triggered by aggressive water circulation from extreme rainfall events. Some utilities are now tracking water quality (algae and plankton concentrations) in their reservoirs in order to anticipate events and to prepare emergency response plans should an event occur.
Similarly, the City of Toledo, Ohio was forced to institute a boil water order in response to a major algae event in its Lake Erie source of supply. The algal toxin microsystin, which can cause cramping, skin rashes and vomiting, was found in the water supply as a result of an extensive algae outbreak.
Algae outbreaks in the Great lakes are becoming more and more common. Researchers have identified warmer lake temperatures related to climate change and the presence of zebra mussels as the two primary impacts changing how the lakes respond to and cycle nutrients. Management of phosphorus entering the lakes from non-point sources and wastewater discharges is only part of the problem. Water systems on the Great Lakes are now incorporating strategies in their water treatment processes to account for more frequent and more intense algae events.
Water utilities can mitigate risk and future exposure to climate change impacts by identifying and tracking key indicator water quality parameters specific to the region, type of water supply source (river, lake or well), risk to treatment processes and local conditions. Development of a plan can be done cost effectively and can be incorporated into a utility’s routine water quality sampling program to begin to develop an understanding of climate change impacts.