ROXBURY, NJ – Only a fraction of the weeds normally yanked from Lake Hopatcong each summer were removed in 2020 due to the pullback of the program after harvester operator Curtis Mulch died when his machine capsized, according to a report.
One of the goals of weed harvesting is to remove phosphorus from the lake. Scientists say phosphorus reduction is important when it comes to battling harmful algal blooms (HABs) like those that plagued the lake in 2019.
But weed removal largely came to a halt after the June incident that “horrendously resulted in the death of” Mulch, a Roxbury resident, noted Princeton Hydro in its recently published 2020 Lake Hopatcong Water Quality Report.
This meant that only about 35 cubic yards of “plant biomass” were mechanically removed from the lake last year, the report said.
Princeton Hydro noted that 35 cubic yards equals about 16 tons of weeds. That might sound like a lot, but the scientists said pulling out 16 tons of weeds equals the removal of only about six pounds of phosphorus.
“This was less than 0.1 percent of the TP (total phosphorus) load targeted for removal,” said the report.
The state’s goal for Lake Hopatcong is to attain an average total phosphorus concentration, during “growing season,” of 0.03 mg/L (micrograms per liter), said Princeton Hydro. “Based on Princeton Hydro’s in‐house database on northern New Jersey lakes, TP concentrations equal to or greater than 0.03 mg/L have an increasing change of developing of algal blooms / mats,” said the company.
Although there were some peak season spikes, the monthly average total phosphorus concentrations in the lake last summer ranged 0.034 mg/L during May to 0.046 mg/L during August, said the report.
While mechanical weed removal is important, “near-shore septic systems” and stormwater runoff likely play a big part in the lake’s phosphorus loads, noted the scientists.
“It has been well documented that phosphorus is the primary limiting nutrient in Lake Hopatcong,” wrote Princeton Hydro. “That is, a slight increase in phosphorus will result in a substantial increase amount of algal and/or aquatic plant biomass.”
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