I suppose there is no perfect strategy for lake remediation programs. In the case of nutrient impaired lakes – those lakes with excess phosphorus resulting from land development, causing algae blooms – each approach has its pros and cons.
In previous columns and in national publications, I have made the case that for most phosphorus impaired lakes, watershed management is insufficient. There are two reasons for this. First, the underlying land use that causes polluted runoff is hard-wired in such a way that we cannot “undo” the development overlay. The best we can do with our best management practices is small tweaks. Look at the case of the Yahara River Watershed (Madison, WI). Several millions dollars have been spent spanning 50 years and there has been no measurable decrease in phosphorus inputs to the downstream lakes. Another $128 million is proposed for at least 20 more years.
The second reason watershed management has been insufficient is that most phosphorus-impaired lakes are unresponsive to phosphorus reductions. A substantial cause of their impairment is phosphorus that has built up in the lake sediments and recycles back into the water.
Patience will (probably) work. Theoretically, if we reduce the runoff phosphorus inputs by a large enough amount (my modeling indicates 80+%) and if we wait long enough (in most cases it is probably several decades or centuries), lakes will improve.
The internal phosphorus recycling that sustains the impaired condition can be treated. Some people refer to this recycling as a symptom, although I think of it more as a reality of an altered state. In previous columns, I have described alum applications as a method that arrests the internal recycling and in most cases will restore the lake. Alum is safe and inexpensive (usually less than 10% the cost of watershed management). Alum is also quick (days).
Treating symptoms works. When using alum, this method is safe, quick and inexpensive. Retreatments are required periodically, so this strategy should be considered as a maintenance program.
There are many cases in Florida where watershed management is impractical or expensive, but the lakes are responsive to substantial phosphorus reductions. A workaround used there involves collecting inflowing runoff streams and treating the water to remove phosphorus in a shore-based treatment plant, akin to sewage treatment plants.
Workarounds may work elsewhere. The kind of out-of-the-box approach used in Florida has proven to be effective and affordable. In cases where we may not have sufficient patience or may be philosophically opposed to treating symptoms, we should think outside those boxes.
We can fix phosphorus-impaired lakes using different strategies. All should be explored to find the best one for every lake.