The following information was gathered by Kate Warner, PhD, the Source Water Program Manager for the Maine Rural Water Association and was used with her permission.
Across the world and particularly throughout the northeastern United States, extreme precipitation events have increased in frequency by 60 to 70% since the 1950s. These events can change the flow paths of water and cause saturated soils to leach into lakes. Since lakes are one of Maine’s primary drinking water sources, this could impact the water quality, and in turn, our drinking water.
An extreme precipitation event is generally defined as a set amount of rain occurring over a 24-hour period. In Maine, rain events are broken down into occurrences of 1, 2, 3, or 4 inches or more of rain in a timeframe. The one-inch events are common, but the higher rainfall amounts are also occurring more often and are expected to continue to increase in frequency and intensity.
These extreme rainfall events can cause flooding, increased risk of landslides, and as mentioned previously, degrade water quality. Through experience, water utilities know that changes may need to be made in how they treat their water based on if the weather has been wet or dry and specific water quality metrics are becoming increasingly studied as weather patterns change. Increased precipitation can lead to changes in water chemistry, increases in dissolved organic carbon, nutrient loading, and increased particulates. Kate Warner, PhD, set out to investigate how water quality in some of Maine’s drinking water lakes responds to extreme precipitation with a focus on changes in dissolved organic carbon.
Dissolved organic carbon (DOC) comes from the breakdown or decomposition of plant and animal material. It is present in the soil and flows into lakes and streams via surface, ground, and soil waters and is essential for helping to regulate aquatic ecosystem structure and function. Changes in DOC can have subsequent implications on treatment of drinking water by increasing nuisance of algae, leading to taste and odor problems, altering disinfection by-products, and contributing to food resources for certain types of bacteria. Dr. Kate Warner measured DOC concentrations 24 hours before, 24 to 48 hours after, five to seven days after, and three weeks after five different extreme precipitation events. DOC response showed three different patterns that occurred because of an extreme event: an immediate spike in DOC concentrations followed by a return to pre-storm conditions, a sustained increase in DOC after an event, and no change in DOC.
DOC can play an important role in water quality and can impact the treatment process for water utilities. Identifying how DOC might change because of increased extreme precipitation events may allow for better preparation when storm events are predicted and allow utilities to continue to provide for their customers as they always do. Research shows that extreme rainfall will increase by as much as 10% in Maine by 2050. Identifying these changes can also aid in reducing economic costs to water utilities and it may aid in mitigation or management strategies.
