Canals not polluting lagoon as much as thought
The conventional wisdom of the past few years that Indian River County drainage canals are a main culprit in the ecological collapse of the lagoon may be faulty, according to a review of independent laboratory tests.
The tests show low levels of nutrients in the three main drainage canals that empty into the estuary, according to David Gunter, superintendent of the Indian River Farms Water Control District.
“Looking at our quarterly tests and going by what I see in the field, I think nutrient levels in the canals have been going down for years,” says Gunter, whose agency maintains and operates 227 miles of canals in the county.
Nutrients, mainly nitrogen and phosphorus, feed algae blooms that consume oxygen and make the lagoon murky, cutting off light to seagrass beds and smothering marine life.
Until this review of test results by Vero Beach 32963, it was commonly assumed the canals must be a pollution villain, dumping high levels of nutrients into the estuary: They drain a large basin occupied by homes – including many on nutrient-producing septic systems – and by agricultural operations that employ nitrogen fertilizers and generate animal waste.
For the past year or so, dire pronouncements about nutrient pollution from the canals have been voiced repeatedly at scientific conferences and county government meetings.
District 5 County Commissioner Bob Solari has even been promoting the idea of reversing the flow of the canals – a project Gunter says would cost at least $360 million – in part to keep nutrients out of the lagoon.
But tests done by Flowers Chemical Laboratories, Inc., an independent lab certified by the state of Florida and the National Environmental Laboratory Accreditation Conference, show total nitrogen levels in the main relief canal have been cut by more than half in the past 20 years.
The nitrogen levels in the canals are now much lower than in the lagoon itself – meaning the 480 million gallons of water that pours into the lagoon from the canals each day could actually be flushing pollution out the inlets to the ocean. The same tests show only miniscule levels of phosphorous, the other main nutrient pollutant plaguing the lagoon.
Last fall the county hired ORCA – the Ocean Research and Conservation Association – to install devices called Kilroys near the outfalls of the north, south and main relief canals to measure nitrogen levels and other environmental factors.
The county’s first-year cost for three Kilroys was $72,000, according to ORCA Managing Director Warren Falls and County Public Works Director Chris Mora. That includes the cost of permitting, installation and weekly maintenance along with $52,500 for the nitrogen sensor upgrades.
Concern about nutrients in the canals became more acute and ended up in the news in November when the newly-installed Kilroys showed dramatic spikes in nitrogen levels that took government officials and environmental scientists by surprise.
The spikes were so extreme, showing levels as high as 9 parts per million, they were questioned by county staff.
“We were getting what seemed like suspicious readings, so we took grab samples right next to the Kilroy on the main relief canal for three days and compared analysis of that water with the Kilroy reading,” says Mora. “They didn’t match.”
The county tests showed steady low levels of nitrogen during a period when the Kilroy continued to show dramatic spikes.
ORCA CEO and Senior Scientist Edie Widder says she is consulting the German manufacturer of the nitrogen sensors and conducting tests to try and figure what went wrong with readings.
She believes there were pulses of nitrogen, likely connected with rain events that fill the canals with dirty water, but says she isn’t convinced the spikes were as great as the sensors showed. Widder says she “would be inclined to agree” the canals have relatively low levels of nutrients overall.
One reason for uncertainty about the chemical contents of canal water is that the canals are Class 4 waterways, intended for agricultural drainage and irrigation. As such, they are subject to far fewer regulations and testing requirments than Class 3 waterways like the lagoon, which are supposed to be clean enough for swimming and fishing.
Gunter says the independent lab tests his district pays for are required by his blanket consumptive use permit that allows him to authorize agricultural discharges into and withdrawals from the canals.
“The tests have been conducted quarterly and submitted to St. Johns River Water Management District since the 1980s,” Gunter says.
Test results examined by Vero Beach 32963 show TKN, or total nitrogen, at the test site on the south relief canal has dropped from 1.86 parts per million in 1990 to 1.12 ppm in late 2013. Total nitrogen at the test site on the main relief canal has plummeted from 1.42 ppm to 0.60 ppm during the same period, while total nitrogen in the north relief canal has fallen more than 70 percent, from 2.67 ppm to 0.74 ppm.
Nitrogen levels in the lagoon are much higher than in the canals, with dry-season readings of 9 ppm and wet-season levels of 14 or 15 parts per million.
Gunter sites several reasons for the decline in nutrients in the canals.
“There is less agriculture in the basin than there used to be, which reduces the nutrient load, and since the early 1990s at least, new subdivisions and other developments have has had to have stormwater retention ponds.”
Mandated by the Florida Legislature in the 1980s, stormwater retention ponds catch nutrient-bearing runoff that used to flow directly into drainage ditches and canals and allows the nutrients and sediment to settle and be filtered out before the water reaches the lagoon.
For the past four years Gunter and his handful of employees have been removing nitrogen-rich water lettuce from the canals and composting it on district right-of-ways that follow the canals.
“We have removed 30,000 pounds of nitrogen and 2,600 to 3,000 pounds of phosphorous each year for the past several years,” he says.
The network of main, secondary and tertiary canals in the Indian River Farms Water Control District was completed more than 90 years ago to drain the eastern marsh and create agricultural land. The waterways have been emptying into the lagoon ever since.
“The flow of water from the canals fluctuates according to rainfall but overall it hasn’t changed since the 1920s, but the problems in the lagoon have occurred recently,” Gunter says.
He says the biggest change he has seen, and the one most likely responsible for increased nutrient loads and ecological problems in the lagoon, is development on or near the shore of the estuary.
“When I was a kid running up and down [the lagoon] like a little river rat in an outboard boat, you could count on one hand the number of homes that were directly on the lagoon before Vero Isles went in. On the East Shore, there was nothing from the Sebastian Inlet all the way south to the St. Lucie County line.
“Then development came on strong and there are more houses than you can count. Some are on septic and some are on sewer, but all of them have a nice pretty yard. If they are not in a seawall area, the back lots slope down to the lagoon and the fertilizer residue and other nutrients are running down the bank into the water.”
Meanwhile, Gunter says his canals are as clean as Class 3 waters 90 percent of the time. “I have eaten fish from these canals and you can see by looking at me I don’t have third eyeball in the middle of my forehead.”