Aluminum sulfate (alum) has been applied to hundreds of eutrophic (nutrient rich) lakes and storm water detention ponds worldwide for over 40 years in a popular remediation practice to control harmful algal blooms by removing excess phosphorous. The City of Madison is poised to begin aluminum sulfate applications in 2014 to several locations in the City and the Lake Wingra Watershed, including one or more storm water ponds in the UW-Madison Arboretum.
But a study in the journal Environmental Pollution, (Nogaro et. al., 2013) raises questions about the practice and concludes that the introduction of aluminum sulfate to ease the problem of excessive phosphorous in fresh water resources may create other problems with unintended consequences for parts of the environment not targeted by the treatment. These unintended effects in turn lead to negative impacts on key ecological and biogeochemical processes in lakes.
The Nogaro study followed the alum application in three bays and compared the results to three untreated control sites of Great Lake Saint Mary’s (GLSM) in Ohio. Nogaro and colleagues concluded that the aluminum sulfate applications increased the surface and pore water concentrations of free (dissolved) Aluminum (Al), sulfate (S04), and nitrous oxide (N20).
These changes are problematic because they can have untargeted and unintended negative consequences for ecological processes. For example, free (dissolved aluminum) is highly toxic to aquatic organisms (see review by Gensemer and Playle, 1999); nitrous oxide is a powerful greenhouse gas with about 300 times the global warming potential of carbon dioxide (CO2); and together the increase in Al and sulfate and altered nitrogen cycling can alter the makeup and functions of microbial and invertebrate communities that inhabit the bottom (benthic) zone of fresh water bodies. The activities of benthic communities play a critical role in many ecological processes such as nutrient cycling and sediment transport in fresh water lakes. The study also found that the aluminum sulfate application captured and inactivated an insufficient amount of phosphorous and that levels of P in the lake remained high.
Why Aluminum Sulfate Applications?
The alum application technique first was used in the early 1970’s and has become a popular short-term method to control harmful algal blooms through chemically altering the water and thus making unavailable the phosphorous (P) and other nutrients that feed the algae. When added to water with the correct pH range, aluminum sulfate (Al2(S04)3) absorbs phosphorous—and the sediment particles to which the nutrient clings—and forms a “floc” which sinks to the bottom of the water body, trapping the phosphorous, sediments, and metals. After several years of accumulation the sediment is dredged and spread on land designated to receive toxic substances.
City and Dane County officials and watershed protection advocates propose building Alum Dosing Facilities (ADP’s) at multiple sites throughout the city and county over the next several years. Proponents of phosphorous reduction through alum applications include the Clean Lakes Alliance in its “2012 Yahara Clean Plan for Phosphorous Reduction”; the Madison Metropolitan Sewerage District and partners in the Yahara WINs (watershed improvement network); and the City of Madison and Friends of Lake Wingra (FoLW) in their joint Lake Wingra Watershed management planning effort.
Until their study, the Nogaro researchers say, “only a few scientific research papers have examined the effects of alum on nutrient cycling and sediment and biogeochemical responses.” Instead, they say, most research until now has focused only on surface water changes, ignoring potential unintended effects on anything beyond that narrow focus. For example, the study says, few alum studies have looked at what goes on in the bottom sediments of treated water bodies, and most published studies of alum treatments have not used “concurrent replication within the study system, particularly in ecosystem scale studies.”
For more information
Gensemer, R. W. and Playle, R.C. 1999. The bioavailability and toxicity of aluminum in aquatic environments. Critical Reviews in Environmental Science & Technology 29: 315-450.
Nogaro, G. and A.J. Burgin, V. A. Schoepfer, M. J. Konkler, K. L. Bowman, and C.R. Hammerschmidt. 2013. Aluminum sulfate (alum) application interactions with coupled metal and nutrient cycling in a hypereutrophic lake ecosystem. Environmental Pollution. 176: 267-274.