Nutrient Reduction

During the December 2020 public meeting, the public was informed that the Cullen Park wetland is projected to remove 10-40 tons of phosphorous on an annual basis. Based on the Ohio EPA Nutrient Mass Balance Study for 2020, the 2019 phosphorous load entering Lake Erie from Ohio Rivers was 3,897 tons. 10 tons is only 67/100,000ths of that load and 40 tons is only 27/10,000ths of the load.

As miniscule as this is, it still exaggerates the phosphorous retention potential of the Cullen Park wetland because:

First, it must be noted that repeated requests for information regarding how the 10-40 ton estimate was calculated went unanswered.   The Port Authority was sent a public records request seeking this information. The Port responded that it didn’t have any records it could provide. (Port Authority response to public records request). Despite this lack of information, we were able to derive the source of the estimates.

A Cullen Park wetland consultant estimated that one percent of the Maumee River will flow into the bay in Cullen Park. One percent of the phosphorous load in the Maumee River Between 2013 and 2019 ranged from 12.68 to 38.97 tons (Nutrient Mass Balance Study for Ohio’s Major Rivers 2020). Rounding up and down to the nearest 10th, that range goes from 10 to 40 tons.

In other words, the Cullen Park wetland’s nutrient reduction projection assumes that: 1) all of the water entering the Cullen Park area will flow through the wetland and 2) the Cullen Park wetland will remove 100% of phosphorous from the water that enters it. Both of these assumptions are faulty.

10-40 Tons Of Phosphorus Will Not Enter The Wetland

The project consultants estimate that the wetland will remove 10-40 tons of phosphorous. Based on the above, one hundred percent of the water entering the bay in Cullen Park will need to flow through the wetland for this to happen.  According to the most recent designs, a dike will surround the wetland and water entering it from the bay will be limited to what can flow in and out of 5×5 foot box culverts.  One look at the wetland design should make it obvious that one hundred percent of the water entering Cullen Park will never be able to enter the wetland.

Even if one hundred percent of the water could flow through the wetland, it still would not be able to remove 10-40 tons of phoshorous.

Plants Do Not Retain One Hundred Percent of the Phosphorous They Remove

Wetlands cannot retain 100% of the phosphorous they remove from a water supply because some of what they remove is later released back into that water.

“Phosphorus in the water column may be used by beneficial algae. However, when the plants and algae die, a portion of the phosphorus is released back into the water.”

Working Wetlands: A Collaborative Study About Wetland’s Capacity for Removing Nutrients. National Estuarine Research Reserve Science Collaborative January 16, 2020

Wetlands also do not have an unlimited ability to remove nutrients from the water supply. Too many nutrients will overload, overwhelm, or destroy a wetland, causing it to send more phosphorous back into the water supply.

“The nice thing about wetlands is that they can CLEANSE and FILTER water as it MOVES through. But too much can OVERWHELM this natural filtering system and DESTROY it.” Thomas Miller

Working Wetlands

The maximum amount of phosphorus a wetland can retain before it becomes overloaded or overwhelmed is called the threshold. If the threshold is exceeded, the result can be harmful algal blooms in the water around the wetland.

Working Wetlands Infographic

In 2016, the Environmental Evidence Journal published How effective are created or restored freshwater wetlands for nitrogen and phosphorus removal? A systematic review. This review evaluated 93 scientific studies of wetland nutrient removal efficiencies.

The nutrient removal rates of the studied wetlands ranged from a high of 70% to a low of -36% (this wetland discharged 36% more phosphorous than it took in). With wetlands having such widely varying efficiencies, it is categorically impossible for the Cullen Park wetland to have the predicted 100% efficiency rate. Further, estimating how much phosphorous the Cullen Park wetland will remove is pure speculation because the necessary science to make such calculations does not exist.

Wetland Science Has Not Advanced To The Point Where The Nutrient Reduction Capacity Of Constructed Wetlands With Multiple Entrance And Exit Points and Bi-directional Flow can be Measured

The National Estuarine Research Reserve Science Collaborative (NERRSC) recently studied the nutrient reduction capabilities of wetlands. Among the wetlands in the study were the Old Woman Creek open coastal wetland and the Crane Creek diked wetland.

The Old Woman Creek wetland is a flow through wetland with a one directional flow between entrance and exit points. The study calculated that the Old Woman Creek wetland was able to effectively remove only 1.88 tons on phosphorous before it reached its threshold level and began releasing phosphorous back into the water. At this level, Old Woman Creek would need to be 26 times larger than it is now to remove the 40 tons that the Cullen Park wetland is projected to remove.

The Cullen Park wetland, however, is not a one directional flow through wetland. It is a diked wetland like the Crane Creek wetland. The significant difference between the two is that Crane Creek wetland has only one bi-directional entrance and exit point and the Cullen Park wetland has multiple bi-directional entrance and exit points.

The NERRSC study could not calculate an accurate nutrient reduction level or threshold for Crane Creek:

Our procedure doesn’t seem to work well for diked wetlands like Crane Creek, where water flows in and out of the same location, as opposed to flowing through the wetland. This is because the amount of water flowing into the wetland and how far it flows into the wetland can differ a lot. As a result, our estimates from one year to the next differ a lot and are not very accurate. 

Working Wetlands

If the wetland experts at the National Estuarine Research Reserve Science Collaborative could not calculate or accurately estimate the phosphorus retention capacity of the Crane Creek working wetland, the ODNR and Port Authority project consultants cannot calculate or accurately estimate the phosphorous retention capacity of the Cullen Park wetland, which is not yet constructed much less working.