The Impacts of Alum Treatment on Waughop Lake, Pierce County

BY COLIN GLAZE

Some 12 thousand years ago, receding glaciers gouged and carved the Puget Sound landscape as Earth left its latest ice age. Ice blocks left behind during the retreat eventually melted and left depressions in the ground, called kettle lakes for their resemblance to filled pots of water. Waughop Lake, a small body of water located in Fort Steilacoom Park, Lakewood, is one of many of these in kettles in Washington, but it has a very scummy problem.

Waughop is a very peaceful lake, where many people come to walk with friends or to set up fishing stations on the beach to try for trout. Unfortunately, the lake has been struggling with hazardous algal blooms (HABs) for many years, and is therefore unsafe for swimming or drinking (a real worry for pet owners). HABs are caused by elevated levels of nutrients in the lake. The lake has no substantial inflows or outflows other than storm water runoff and percolation of groundwater around the lake. Therefore, problems like elevated nutrients that arise stay in the lake for much longer than other lakes with outflows.While they can form naturally, HABs are often initiated or exaggerated by anthropogenic sources, which is the case at Waughop.

ABOVE: Example of an algal bloom.

The history of Waughop Lake has been bumpy and, until recently, it was treated less like a lake and more like a waste lagoon. From 1870 until 1965 there was a hog farm located near the lake, and many of the buildings still remain. During this period of time, all animal and human waste from the farm was dumped directly into the lake, and there was even a slaughterhouse over one corner of the lake with a grated floor to allow blood and other animal products to fall easily into the water. While this practice has since been discontinued, the negative impact of humans on the lake has not stopped there. In more recent years, it was discovered that a sewage pipe from the nearby Pierce College had broken and the waste from the campus was running directly into the lake. Together, these events have thrown the nutrient levels in the lake out of balance and have fueled the HABs, which seem to get larger and larger each year.

ABOVE: “Farm at Fort Steilacoom Park” by Jett Brooks, licensed under CC BY 2.0 (2)

In the summer of 2020, the City of Lakewood hired a company to apply a treatment of aluminum sulfate (alum) to the lake in the hopes of stopping the algal blooms. Alum works by binding the aluminum to free phosphorus in the lake. With the phosphorus bound to the aluminum, it is no longer free to fuel the algal blooms and thus the alum cuts off the HAB cycle. In order to do this effectively, 21,477 gallons of aluminum sulfate were added to the lake. This is a lot of alum, which means a lot of sulfur. Once the aluminum in the alum binds with the phosphorus in the lake, the sulfur, having no other purpose, is left free in the lake. Since there is no outflow from Waughop, there is no way for the excess sulfur to leave the system.

Over the summer of 2020, Professor Jeff Tepper and I spent just under ten weeks monitoring the lake. For comparison, we collected regular lakewater samples from before and after the alum application at one and two meter depths. Other field methods included profiling the water column with an Insitu sonde (a device that can transmit data such as temperature and pH from underwater), taking onsite sulfide concentrations with a portable spectrophotometer, and coring samples of the lake sediment. In the lab we extracted pore water from the cores at two centimeter intervals and analyzed them for elemental composition. Specifically we looked for aluminum, iron, copper, and of course, sulfur. We also analyzed the samples for phosphorus, but the method we utilized is not very accurate for recording phosphorus levels, so those data are inconclusive.

The data collected about sulfur, on the other hand, were very interesting. We found that after the addition of the alum, sulfur concentrations increased by over fifteen times in the pore water, and by over 60 times in the water column. This large increase in sulfur has appeared to have had very negative effects on the lake, including the disappearance of all the lakebed plants. A GoPro video taken of the lakebed revealed that there were no longer plants in sight, and the bottom of the lake looked completely bare.

ABOVE: Levels of sulfide in Waughop pore water with depth. Note that after alum treatment (orange line) sulfide levels in the shallow lake bed subsurface spiked well above the threshold at which plants can survive.

ABOVE: Sulfur concentrations in Waughop lake water over time. Levels increased significantly post-alum treatment.

That being said, the idea that this destruction is an effect of the sulfur is only speculation, as we did not collect more specific data on the effects of sulfur on plant life. Due to these findings, this upcoming summer Jeff and I will be conducting more follow up research at Waughop to determine what exactly has happened to the sulfur, and how it affects the lake. Hopefully this continued research will shed some light on the full effects of alum treatment, and help revive this little lake so that everyone, including pets, can enjoy it.