Empirically Speaking

Addressing Severe and Chronic Cyanobacterial Blooms

By Dr. Wes Neal

             Like most college campuses, water quality and fish health at Mississippi State University do not rank very high on the totem pole of groundskeeping importance. Emphasis is largely placed on healthy turf grass and sporting fields, as well as lovely flower gardens, and little consideration is given to waterbodies around campus. We replace the sod in the Junction almost every year so that tailgaters will have a perfect lawn to trample and spill beer on; meanwhile, ducks and geese pull every blade of grass from the campus shorelines.

This perspective changes when water quality issues become so severe that the public outcry reaches administrators. Even then, convincing administrators to invest financial resources to address water quality issues is no easy task – treatment costs money, and boosters send money for football, not lake management.

            Chadwick Lake is a 12-acre impoundment strategically located on campus beside many of our important athletic centers and sports stadiums. The lake is a focal point for many users, and the university recently installed a $1 million walking path around the lake. Students, faculty, and the public enjoy the lake and surrounding terrain, use the walking trail, and some even fish during the spring when it is permitted.

For years, runoff from the manicured landscape, the football and baseball fields, and asphalt parking lots has been draining into the lake, carrying all the excess nutrients from turf management with it. The result is eutrophication, or the nutrient enrichment of the lake. Most of the year, the lake is just a little too green. However, when the Dawg Days of summer arrive and temperatures soar, cyanobacteria thrive. Thrive might not be the best word here. Maybe explode? Go viral? Big bang? Trust me, it can be bad.

            If you have ever been around a severe cyanobacterial bloom, there are two characteristics you cannot miss. First are the unnatural colors of the decomposing mats. Cyanobacteria start off green and can be confused with healthy green algae. It will then start to clump up on the surface and appear as if someone dumped bright green paint in the pond. As it accumulates in thick mats, it starts to decompose and can take on a peculiar light blue color (hence, cyano) that looks oily, mixed with red, brown, white, and nuclear, if that was a color. The second characteristic is the smell. Oh boy, what a smell. And when the wind blows it all into a small corner of the lake, the smell will really hit you.

            It’s a cross between mild skunk and mildew from grandma’s broom closet.

This is not a new problem in Chadwick Lake. For more than a decade I have been fielding complaints from users and offering recommendations to administrators. Fish kills really get their attention, as do complaints from John Q. Public. While administrators tend to avoid expensive long-term solutions, they are receptive to short-term remedial approaches when problems arise. Although they are eager to fix the issues when conditions are bad, the momentum is always short-lived as the problem goes away with cooler weather. Out of sight, out of mind.

            In late summer 2020 calls began coming in. It all began in September and really came to a head in October. “The lake smells terrible!” they cried. One faculty member told me that he had developed a strong allergic reaction immediately after exposure to just the air around the lake. A grad student reported fish were dying. Everyone commented on the unusual color, and of course, the smell.

            It wasn’t Covid.

As usual, I told administrators that the lake was just a symptom, and the issue is what is happening outside of the lake in the watershed. I reminded them that we have this conversation every year. I told them not to waste my time if they were not going to listen (just kidding, I like my job). This time, however, something was different. Maybe it was the increased severity of the lake’s issues, but finally people seemed to be willing to come to the table.

The first recommendation was to deal with the immediate problem – the ongoing bloom. For cyanobacteria, I usually recommend that you let it run its course. Treating the bloom will kill the cyanobacteria, which likely will lead to an oxygen depletion in the heat of summer. Another risk is that dying cyanobacterial cells can release any cyanotoxins that might be present. So, I usually steer most landowners away from treating the lake.

However, this is a high-visibility situation and the risk to fish is not nearly as important as other impacts. In this scenario, I like to use a chelated copper complex with surfactant. The surfactant helps the chemical get through the cyanobacteria’s jelly-like outer layers and into the cell. For Chadwick Lake, we decided to go with the maximum rate of 1.0 ppm, or 3 gallons per acre-foot. Of course, when full, this lake has about 72 acre-feet of water, so that’s an expensive diagnosis. Nonetheless, some things at the university take time, and purchases are often one of them. By the time the chemicals were on hand, the bloom had largely dissipated, and we made the decision to hold on to the herbicide and save it for future use.

My next recommendation was to reduce the rampant use of lawn fertilizer. That was quickly vetoed – not officially, of course, but there was a certain understood agreement that grass must be perfect. So instead, I suggested intercepting the nutrients before reaching the lake. Ideally, terrestrial vegetation could filter the overland flow and remove the nutrients, but that blocks views and access, or at the very least gives the campus a less-than-manicured appearance, so that is a no-go. I heard there used to be a buffer strip at the lake, but someone spotted a snake, and apparently one nope-rope is one too many. Further, much of the runoff travelled to the lake via a pipe, so overland interception would be less effective.

Wetlands are excellent at taking up nutrients, so I suggested that the upper lake be converted into a wetland. Much of the upper end was already very shallow, so a levee could be constructed to separate the upper and lower lake, and native vegetation could be established in the shallow water to intercept and turn the nutrients into biomass. The walking trail has a causeway that loops over the upper end; why not have it saunter through a wetland of spider lilies, pickerelweed, and swamp rose mallow?

This idea was not officially rejected, although no progress has been made to date. The one exception is they did build a very small berm on one of the incoming drainages to capture storm water runoff temporarily to reduce sediment and nutrients prior to entering the lake. I am not sure it does anything at all.

Finally, I recommended aeration. Aeration can certainly help prevent the fish kills caused in summer, but it also maintains oxygen down to the sediment, which helps control nutrients. When there is no oxygen down deep, phosphorus will usually release from the sediment where it was bound to iron and become bioavailable once fall mixing occurs. By keeping the sediments aerated, I hoped more phosphorus would bind with iron in the bottom muck and remain unavailable to cyanobacteria.

I was very clear that we needed deep aeration, particularly destratification, not pretty fountains. Destratification systems can move and aerate water efficiently from the deep areas. Most fountains, on the other hand, mostly pull water from shallow layers and do not provide adequate mixing or aeration. But universities love fountains, and I just knew they would opt for fountains.

Luckily, the administration decided to install both fountains and subsurface diffusers underneath them. In fact, the fountains are large capacity, sending water high into the air with more mixing effect than standard fountains. But they are brightly lit up at night, so I stand by my “fountains are just pretty” comment. However, the destratification really seems to be helping. I have not had a single call since the installation occurred, and although the water is still green, excessive cyanobacterial blooms seem to have subsided. The past two summers, no mats have formed in the upper end. 

Time will tell if this is a permanent solution. But 2023 was the hottest year in human history and the warmest in 100,000 years of fossil records. If cyanobacterial blooms are a temperature-related phenomenon, I would have expected major problems this past fall. I am still hopeful that we can make a wetland in the upper end to help filter nutrients and provide habitat for wildlife, but mostly I am just glad I don’t have to field complaints.