Lake water cleaner than St. Lucie basin runoff; lake water responsible for just 14 percent of phosphorus entering estuaries

OKEECHOBEE — Some Treasure Coast residents appear to be in denial when it comes to their own water pollution.

At a July 31 meeting, the Sewall’s Point Town Commission backed off a plan for septic to sewer conversion, despite the potential for funding help from the state. According to meeting reports, many Sewall’s Point residents continued to blame the Lake Okeechobee releases as the primary source of last year’s algae blooms.

Data compiled by South Florida Water Management District for the five-year period 2012-2016 tells a different story.

According to the Florida Department of Environmental Regulation, algal blooms require algae (which FDEP says is naturally present in all freshwater in Florida), hot weather, low salinity levels and a food source for the algae. The more nutrients you feed it, the bigger the algae bloom grows.

The data shows that from 2012-2016, local basin runoff accounted for about 79 percent of the freshwater flow, 86 percent of the total phosphorus load and 77 percent of the total nitrogen load to the St. Lucie Estuary.

In that five-year period, the much-maligned water from Lake Okeechobee made up 21 percent of the freshwater flow but only 14 percent of the phosphorus load.

The data shows the lake water is lower in phosphorus than most other sources of water in that basin. The SFWMD data and the University of Florida Water Institute studies both came to that same conclusion. Florida Department of Environmental Protection data agrees.

The 2012-2016 study shows:
• Ten Mile Creek contributes 10 percent of the freshwater and 11 percent of the total phosphorus load, with an annual average of 28 metric tons;
• The C-24 basin contributes 15 percent of the freshwater and 19 percent of the total phosphorus load, with an annual average of 50 metric tons;
• The C-23 basin contributed 12 percent of the freshwater and 24 percent of the total phosphorus load; with an annual average of 63 metric tons;
• Lake Okeechobee contributes 21 percent of the freshwater and 14 percent of the total phosphorus load, with an annual average of 35 metric tons;
• The C-44 basin contributes 14 percent of the freshwater and 19 percent of the total phosphorus load, at an average of 50 metric tons, 49 metric tons;
• The tidal basins contribute 28 percent of the freshwater and 13 percent of the total phosphorus load at an average of 34 metric tons.

Phosphorus levels in water are usually given in parts per billion or ppb.

During 2012-2016, the ppb averages for water from the various sources of flow to the St. Lucie estuaries were:
• C-23 basin, 487 ppb;
• C-24 basin, 310 ppb;
• C-44 basin 306 ppb;
• Ten Mile Creek – 249 ppb;
• Lake Okeechobee, 155 ppb;
• Tidal basins, 109 ppb.

It’s interesting to note that during that same time frame, water flowing from Lake Okeechobee to the Caloosahatchee River at Moore Haven averaged 87 pbb phosphorus. The water leaving the lake at Port Mayaca is significantly higher in phosphorus than the water leaving the lake at Moore Haven.

It is not unusual for phosphorus readings in the lake to vary in different parts of Big O. The source of 90 percent of the phosphorus coming into the lake is the watershed north of the lake.

The location of marshes, which help clean the water by absorbing nutrients, inside the Herbert Hoover Dike, also affects water quality.

According to SFWMD and FDEP data, the overall average phosphorus level in Lake Okeechobee is just above 100 ppb. In July 2017 it averaged 123 ppb.

FDEP has set the target goal for Lake Okeechobee at 40 ppb, but with the exception of rainfall, all of the water entering the lake is many times that 40 ppb goal. In addition, under certain conditions, the lake water absorbs phosphorus from the muck under the deep water near the lake center.

Because the marshes inside the Herbert Hoover Dike do clean some of the phosphorus out of the water and because the nutrient-rich inflows from the north are diluted by direct rainfall into the lake, the outflows from the lake are lower in phosphorus than the inflows.

Still, according to FDEP researchers, the only way to get the lake down to the 40 ppb goal is to clean up the water before it goes into the lake.

Also, just because the lake water is lower in phosphorus than the water from the St. Lucie basin does not mean it does not harm the estuaries. Researchers such as Dr. Brain Lapointe of Florida Atlantic University have pointed out that even if the water from the lake was as clean as rainwater, it would hurt the estuaries by lowering the salinity levels.

The freshwater flow from the lake contributes to the disruption of the salinity levels in the estuaries. When salinity levels are high, conditions do not favor algae growth. But algae blooms can — and do — happen on the Treasure Coast even without the extra freshwater from the lake.

The connection between the lake and the St. Lucie is man-made. One goal of Comprehensive Everglades Restoration Plan (CERP) is to restore more flow south and reduce the need for flow from the lake to the east and west.

Currently much of that flow south is blocked by the Tamiami Trail; projects are underway to restore more flow under the trail to Florida Bay.

But the data shows that eliminating the freshwater flow from the lake to the St. Lucie would not solve the problem of the pollution of the St. Lucie estuary.

Lake scientists say the algae blooms of 2016 were just a symptom of widespread ecological issues.

This year, no water from Lake Okeechobee has flowed into the St. Lucie.

Instead, because the lake level has been lower than the level in the C-44 canal, untreated, unfiltered phosphorus-laden water from the C-44 canal has been backflowing into Lake Okeechobee at Port Mayaca. Water from the C-44 is around 300 ppb, per the reports — nearly three times the lake’s average — and that extra nutrient load fed an algal bloom on the lake near Port Mayaca in July.

Hot weather + nutrients + low salinity + algae = algal bloom.

Search for the truth about Lake Okeechobee

Lake water lower in phosphorus than river basin runoff

OKEECHOBEE — Local basin runoff accounted for 68 percent of the freshwater flow and 75 percent of the phosphorus load to the Caloosahatchee River in the five-year period from 2012-2016, according to data released by the South Florida Water Management District.

Releases from Lake Okeechobee at Moore Haven made up 32 percent of the freshwater flow to the river, and contributed 25 percent of the total phosphorus, according to the data.

The lake water flowing through the Moore Haven lock averaged 87 ppb phosphorus. Water in the C-43 and S-4 basins west of Moore Haven accounted for 46 percent of the water and 60 percent of the total phosphorus load, and averaged 144 ppb. The tidal basin runoff accounted for 22 percent of the freshwater and 16 percent of the phosphorus, and averaged 82 ppb.

The nitrogen load in the freshwater was more evenly balanced. Lake Okeechobee water made up 32 percent of the water and 34 percent of the nitrogen load; C-43 and S-4 basin runoff was 46 percent of the water and 47 percent of the nitrogen load; tidal basin runoff contributed 22 percent of the freshwater and 20 percent of the total nitrogen.

Before man’s intervention, the Caloosahatchee River was connected to Lake Okeechobee by a series of marshes. During the dry season, it was not unusual for those marshes to dry up and for the Caloosahatchee River to get so low that residents joked about wading across it without getting their knees wet.

Since the river was connected to the lake by a channel, and then deepened and straightened for navigation and flood control, letting the river get that low is no longer an option. Pulse releases from Lake Okeechobee are needed in the dry season in order to prevent saltwater intrusion.

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