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Monday, October 25, 2021

Ongoing battle Arboretum algae to end soon

ARIEL ROBBINS / AGGIE
ARIEL ROBBINS / AGGIE

Three phase renovation project plans to rid the waterway of algae and duckweed.

The UC Davis’ mile and a half long Arboretum is scheduled for a renovation project to begin this summer, alleviating the algae blooms that have monopolized its surface for the first time in 20 years. The project will introduce flowing water through a series of elevation changes to promote a natural cleaning system.

Michael Fan, senior engineering supervisor of UC Davis’ Facilities Department of Resource Recovery, explained that in the 1800s, Putah Creek naturally forked into  northern and southern flowing sections. The north end neared a developing area, so a dam was built to prevent flooding. In the 1950s, Army Corps engineers isolated the two sections, and the north became the stagnant pond we now know as our university’s Arboretum.

The stagnant water trapped by the dam, abundance of solar exposure, nutrients (due to inflow of organic matter) and high water temperature creates an optimal habitat for algae and duckweed.

“We basically had this problem from day one once we [installed] the dam,” Fan said.

Today, the Arboretum mainly serves to retain stormwater. The Arboretum is the lowest point on campus, so anything bound within the core of the campus, 113-west and Russell Boulevard eventually gets drained into the waterway.

The stormwater accumulation has led to the buildup of nutrients, such as fertilization in the creek, further exacerbating the growth of algae.

“The water has algae growing, fish dying and all this negative stuff [happening…] By the time of the ambient temperature drop during the end of fall, the water starts becoming clean,” Fan said. “Then, come the winter time until the beginning of summer, the cycle will start again.”

Due to the shallow depth of the Arboretum, once the plant material and the leaves decay, they both become ‘sludge,’ according to Fan. The sludge buildup in the waterway then provides a plethora of nutrients for algae.

The explosion of algae and duckweed has taken up the majority of the Arboretum’s nutrients. However, regardless of its ecological effects, many people, such as Fan, think “it just looks bad.”

“Duckweed is a simpleton. It’s fluffy and light, you can just scoop and clump them together,” Fan said. “But, to see change, you have to holistically address the [situation] of nutrients from wastewater, vegetation, the sludge and all the nutrient sources identified.”

In order to prevent the growth of algae and duckweed, the 2016 summer clean-up project intends to stop this cycle.

To change the artificially favored algae and duckweed ecosystem, assistant director of UC Davis Arboretum and one of the project heads, Andrew Fulks, aims to mold the Arboretum so that it looks similar to a natural creek of the Central Valley.

Beginning sometime late July or early August, the project will proceed into phase one of three, beginning with the section from east end to Mrak Hall “dry” bridge.

Phase one focuses on adding small weirs (small dams to raise water levels),  planting wetland plants and improving paths. According to Fulks, the weirs will “back up the water behind them.”

“We have a pipe that goes underneath and the pump at the lower end that recirculates water up the upper end, [which] fills up the weir,” Fulks said. “Then, it spills over a notch in the weir into the next segment and it does the same thing, each one dropping about three inches as it heads to the west.”  

By introducing elevation, recirculation will cause the surface of the water to flow. This will ultimately increase the amount of oxygen and prevent the growth of algae and duckweed.

Next, wetland plants will be planted around the weirs and along the edges of the water itself.

“There’s biofilms that grow around the stems around the wetland plants and those take up the nutrients and chemicals. It helps filter the water as the water’s moving through the waterway,” Fulks said.

Besides its cleaning effect, wetland plants are used to create a more pleasing visual appeal for Arboretum visitors.

“The aquatic plants intake the nitrogen and phosphorous for their growth, [and] after six days, a study shows that algae growth dropped quite a bit,” Fan said.

In addition, there are plans to make the pathways more “universally accessible,” Fulks said. This includes path improvements adjacent to the waterway and near the banks.

As stated by Ellen Zagory, director of horticulture education at UC Davis, a pilot project was conducted at the east end of the Arboretum and it worked as planned.

The east end of the Arboretum takes priority since a circulation system is already intact in the area of the Water Waste Treatment Plant to the west end.

At the Water Waste Treatment Plant, UC Davis focuses on treating the water coming in from all over campus. According to Fan, at the plant, water is treated to the highest degree the state of California permits. Under the permit, the water becomes usable for “irrigation, body contact and swimming inside.”

By spending a fairly small amount of money in 2007 on a pipeline starting at the Treatment Plant, the water cleaned at the Treatment Plant was sent into the south Putah Creek, and then back to the Arboretum waterway.

“Gravity flowed into that location,” Fan said. “The water flows west, then there’s a strong pump station that we pump the water from the waterway into the Putah Creek. So, we go in a circle.”

Because of this, the west side has been kept relatively clean while the east side has remained green.

The project’s decrease of nutrient concentration will benefit the environment. When the nutrients are removed from the Arboretum, the receiving stream, Putah Creek, will take in less nutrients, ensuring higher water quality.

“Putah Creek is full of nutrients, so they don’t need that much [more] nutrients,” Fan said. “It’s bad for the water quality, because if you have too much nutrients anywhere, they tend to grow algae.”

After the cleanup, the new environment will not be optimal to sustain the algae. However, even with elevation and flowing, clean water, it is impossible to prevent vegetation and leaves from forming sludge.

“It’s kind of like having a big house — it’s great with all this room, but you have to go through the trouble to clean each room,” Fan said.

To ensure results, the Arboretum requires active dredging, nutrient maintenance and moving water. Fan attributes the duckweed to changes in the environment.

“We used to have a lot of ducks, and the ducks would eat the duckweed,” Zagory said. “But, we now have river otters, and the river otters have scared the ducks.”

Due to the lack of its primary consumer, duckweed now has an uncontrolled density. Although the project focuses on ‘clearing’ the lake, the water will never reach perfect clarity.

The wildlife — ranging from alumni’s pet goldfish to the western pond turtle — is likely to stir up the sediment in the shallow waters.

“The carp in particular stir up a lot of the sediment at the bottom of the channel because they’re going around looking for things to eat,” Fulks said.

Phase two and three of the project will continue from the east to the west side of the Arboretum and make for a cleaner, more welcoming environment.

“[The project] will create a more visual look for folks because we’ll have some emerging marsh plants along the edges of the water that we don’t have right now,” Fulks said. “And, the small areas of water flowing across a weir and dropping few inches and making some noise. It’s going to be really nice for folks to go out there and visit.”

Written by: Sabrina Choi — science@theaggie.org

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