Sentinel responses to droughts, wildfires, and floods: effects of UV radiation on lakes and their ecosystem services

Abstract

Environmental drivers such as climate change are responsible for extreme events that are critically altering freshwater resources across the planet. In the continental US, these events range from increases in the frequency and duration of droughts and wildfires in the West, to increasing precipitation and floods that are turning lakes and reservoirs brown in the East. Such events transform and transport organic carbon in ways that affect the exposure of ecosystems to ultraviolet (UV) radiation and visible light, with important implications for ecosystem services. Organic matter dissolved in storm runoff or released as black carbon in smoke selectively reduces UV radiation exposure. In contrast, droughts generally increase water transparency, so that UV radiation and visible light penetrate to greater depths. These shifts in water transparency alter the potential for solar disinfection of waterborne parasites, the production of carcinogenic disinfection byproducts in drinking water, and the vertical distribution of zooplankton that are a critical link in aquatic food webs.

Climate change-induced increases in precipitation are reducing the potential for solar ultraviolet radiation to inactivate pathogens in surface waters

“…For example, 1% of incident 320 nm UV reaches depths of tens of meters in some of the most transparent lakes and drinking water reservoirs in the world, but only a few centimeters in less transparent lakes 35 . DOM and other dissolved and particulate compounds reduce water transparency and thus exposure to disinfecting solar UV as well.…”

“…This phenomenon, known as browning, can substantially reduce water clarity on time scales ranging from individual storm events to seasonal, inter-annual, and inter-decadal time periods 35 . The causes of browning are multiple and include recovery from acidification 37 , and increased precipitation related to climate change 35,38 .…”

“…This phenomenon, known as browning, can substantially reduce water clarity on time scales ranging from individual storm events to seasonal, inter-annual, and inter-decadal time periods 35 . The causes of browning are multiple and include recovery from acidification 37 , and increased precipitation related to climate change 35,38 . The increases in the quantity as well as darker color of terrestrially-derived DOM associated with browning result in greatly increased absorption of UV and reduce SIP, fostering increased survival of waterborne pathogens.…”

“…The penetration of UV into water bodies is controlled in large part by input of terrestrially-derived DOM to surface waters 35,39 and therefore by precipitation and hydrologic conditions 38 . Increases in precipitation lead to water-saturated wetlands and soils with lower oxygen that produce greater amounts of DOM, ultimately transported by increased runoff to rivers, lakes, and coastal oceans.…”

“…Increases in precipitation lead to water-saturated wetlands and soils with lower oxygen that produce greater amounts of DOM, ultimately transported by increased runoff to rivers, lakes, and coastal oceans. This leads to higher concentrations of DOM and reduced UV transparency 35,39 . In regions such as the northeastern USA, extreme precipitation events have increased by as much as 71% between 1958 and 2012 1 .…”