By Ellie Van Os, Florida Oceanographic Society
Our estuaries have been in the media a lot lately and the news has not been good. As a result we are approached by many visitors to our Coastal Center who would like some clarification on what is going on. There are bad algae, there are dead manatees, there is too much fresh water – how are they connected? Are the Lake Okeechobee discharges killing the mammals and the pelicans? In an attempt to sort the mess, the following is a summary of what we know about the northern Indian River Lagoon and the southern Indian River Lagoon/St. Lucie River Estuary problems.
Estuaries, by definition, are delicately balanced ecosystems – not fresh water, not salt water but ideally somewhere in between, brackish. And if they are not somewhere in between, the system that by nature can compensate for small deviations from that definition can die if one or the other condition prevails. Th ink back to early science classes and the Water Cycle chart. Rain falls on the land and flows to the salty sea; rain forms over the water and moves over the land, looping the cycle. But once the water drops from the sky, it changes composition depending on where it flows: if it flows through vegetation it gets sucked up and put back into the atmosphere again as vapor; if it flows through soil it dissolves whatever is in the soil including pollutants like excess nutrients and carries them with it; if it flows too fast it scours the earth beneath it and carries a heavy sediment load often laden with toxic substances.
With that said, there is a good chance that the problems in the northern Indian River Lagoon – the dead manatees, the dead dolphins and the dead pelicans can be traced back to a break in the water cycle. A prolonged drought in that part of the state in the late 2000’s caused unusually high salinity in the northern lagoon. Then in January of 2010, temperatures in the Indian River Lagoon dropped to record breaking lows. That prolonged freeze event besides affecting many of our warm water fish and foraging sea turtles wreaked havoc with plants and animals at the base of the food webs in the lagoon, already stressed by being at the maximum limits of their salinity tolerances. On top of that another freeze in December of 2010 coupled with the continued drought-related high salinity seemingly halted the recovery of communities in the northern lagoon.
For years we have touted the Indian River Lagoon as North America’s most diverse estuary,and one of the reasons is because it straddles the temperate zone and the sub-tropical zone thereby hosting flora and fauna from both climates. Unfortunately because of the global climate change that we are currently experiencing, it is those edges, those areas that are in-between, that will demonstrate the widest extremes particularly of temperature and moisture, both culprits in the current calamity.
To arrive at the point we are now at in the northern Indian River Lagoon, some believe that the widespread die-off of naturally occurring drift algae during that frigid period released tons of nitrogen in the form of organic matter, to a system that had previously been able to deal with excess nutrients by their uptake by those very same plant tissues as well as in sediments stabilized by seagrass roots. Nutrients released from the die-off and from a myriad of unregulated nutrient sources including fertilizer and aging septic systems fueled a 130,000 acre algae bloom from just north of the Haulover Canal to Melbourne. A bloom of lesser intensity reached from Melbourne to Ft. Pierce. By the end of 2011 47,000 acres of seagrasses were lost, at least in part due to the algae bloom shading the necessary sunlight from the grassbeds. No good comes from the loss of primary producers like seagrass that provide food, shelter, stabilizing root structure and oxygen to the lagoon. The breakdown in the food web in the northern Indian River Lagoon is evidenced by the death of animals at all trophic (herbivore and carnivore) levels.
The saga of the St. Lucie River which merges with the southern Indian River Lagoon at the St. Lucie Inlet starts much the same way, with an imbalance in the water cycle. However the history of the imbalance goes back to the early 20th century when man’s drainage of our abundant wetlands was considered land reclamation. In order to reclaim the land and simultaneously open commerce through the middle of the state, the Okeechobee Waterway, connecting the east coast via the St. Lucie River with the west coast via the Caloosahatchee River through Lake Okeechobee, was opened with great fanfare. However in digging the canals that form the Okeechobee Waterway, and stabilizing Lake Okeechobee with a 35-foot berm, the Everglades suffered from a broken water cycle in that the natural flow south was blocked. Additionally the Okeechobee Waterway canals and others dug since then, cut through natural ridges that used to keep, for instance, the St. Lucie River drainage area, referred to as the watershed, far east of the current boundary at Lake Okeechobee. The tremendous increase in watershed area has effectively overwhelmed the water cycle balance in the St. Lucie River Estuary. The brackish water has been replaced by an overabundance of freshwater supplied by man-made canals. Fresh water is not necessarily bad – lakes and rivers are good, but the conversion of a brackish estuary to a fresh water system by the input of a devastating volume of fresh water destroys estuarine plant and animal communities. The speed of discharges to the estuary accelerates erosion of toxic sediments from the canals along the way. Furthermore the water coming from Lake Okeechobee is polluted with excess agricultural nutrients fueling a shift in nutrient uptake from seagrasses to planktonic algae, oft en toxic themselves, that thrive in systems with high dissolved nutrients. Oft en when algae blooms die, the bacteria that digest them use so much oxygen in respiration that they deplete it, forming a dead zone. It is a fact that the freshwater regime will not be the end product in the St. Lucie River estuary, so with the eventual restoration to a brackish system comes a serious lack of brood stock and unsuitable sediments for recolonization.
We have our work cut out for us, in both stopping the underlying causes and then restoring habitat and populations. September is recognized as Estuaries Month. Join us in showing solidarity for the goal of healthy estuaries by the Hands Across the Lagoon events being planned for various locations on the Indian River Lagoon on the morning of Saturday September 28th, and the Ais on the Lagoon event being planned for various locations on the Indian River Lagoon on the morning of Saturday September 28th, and the Ais on the Lagoon event being planned for Sunday morning September 29th, as an historical stewardship celebration.