A new report points to several worrying trends in the lower St. Johns River basin.
Salinity is increasing in the St. Johns River and its tributaries, according to the 2019 River Report, which was released Friday, and it’s largely due to sea level rise and river dredging, said Jacksonville University research scientist Gerry Pinto, the new report’s principal investigator.
“Salinity, if it changes, will cause a movement in transition zones in the river. So there'll be a redistribution of freshwater and saltwater fish and it may cause lifecycle disruptions,” Pinto said Friday as he shared the report’s findings with a crowd of people gathered at the University of North Florida for Jacksonville’s annual environmental symposium. “Many of our commercial fisheries that we depend on offshore have larval stages that live within the estuary. If conditions change within the estuary, it's not inconceivable to think that those would be affected. And then that, of course, has an economic effect.”
This saltwater intrusion is contributing to another issue highlighted in the report: loss of submerged aquatic vegetation.
“We have a lot of freshwater hardwood swamps that could be affected by salinity increasing, and are affected by it,” said Pinto. “You might go down the river and see a bunch of cypress trees that are dead. It's because salt water is probably killing those.”
Submerged aquatic vegetation like hardwood swamps and tape grass are considered critical habitats. They provide nursery areas for organisms, food for larger species like manatees, improve water quality, prevent erosion, and even trap and bury large amounts of carbon dioxide - the main greenhouse gas causing climate change.
Nutrient pollution is also causing concern for Pinto and his fellow report authors. Nitrogen levels are high, as they have been in past years. There was some improvement in the river’s mainstem between 2014 and 2018, but levels have gone up in the tributaries with a huge spike in 2017.
“We don't know if this is something that is just a discrepant data point or not. But also you have to remember that we've had some pretty bad weather in the last couple of years, a lot of storms, a lot of rainfall, that could be flushing a lot of this stuff and these nutrients into the waterways,” Pinto explained. “So it remains to be seen whether this is a trend that will increase or not.”
Phosphorus levels are similarly high, and they’ve been rising in the marine area of the river’s mainstem, especially over the last five years or so. Meanwhile, phosphorus levels in the tributaries have remained relatively stagnant (despite a spike in 2017) while levels in the mainstem’s freshwater have improved.
“That is somewhat worrisome, but something that we just need to keep an eye on, because we're not sure,” said Pinto. “Is this excessive water flushing out lands that were not normally submerged because of all this rain we've been having recently, or is it due to policies that are occurring in different parts of the basin where nutrient loads are being readjusted and moved around? This will all require some looking at in the next few years.”
These excess nutrients in the river are driving regular harmful algal blooms.
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Additionally, non-native aquatic species are growing in population.
“Because of the warming trends globally, those species’ ranges are increasing and so we tend to see more of them every year,” Pinto said. “The lionfish is a great example.”
A surprising new trend found in the report is elevated levels of metals, especially arsenic, cadmium, nickel, lead, and silver, predominantly in the saltwater portions of the St. Johns River mainstem.
Metals were decreasing throughout the river between 2009 and 2014, but since 2016 they’ve been increasing dramatically. Pinto believes this is largely due to recent storms like Hurricanes Matthew and Irma and the river dredging.
One of the most troubling trends, according to Pinto, is the ongoing loss of wetlands.
“Wetlands, of course, are very important. We all know that they're the kidneys of the ecosystem. They clean the air and the water. They also sequester carbon. They also help to add land back, because they trap sediments,” he said. “They are one of our keys to resiliency. They are one of the things that we must protect. We cannot continue destroying wetlands.”
This wetland loss is largely due to increased land development.
There is at least one piece of good news out of the report: threatened and endangered species like manatees, wood storks, and bald eagles are doing pretty well, despite recent storms and habitat loss.
Brendan Rivers can be reached at brivers@wjct.org, 904-358-6396 or on Twitter at @BrendanRivers.
