Phytoplankton Imbalance
What Is The Tipping Point That Causes the Food Web To Collapse?
The tipping point in eutrophication occurs when sediment nutrient recycling becomes self-sustaining because hypoxia becomes entrenched and the food web can no longer maintain nutrient clearance, leading to a fundamental transformation in the ecosystem.
When this happens, the water body not only loses the balance between vegetative and animal populations necessary to maintain nutrient clearance but the transformation to nutrient recycling also locks in feedback mechanisms that cause the lake to keep worsening its own condition.
Why Is The Eutrophication Tipping Point Important?
The impairment of the food web’s capacity to clear nutrients may not always be apparent through dramatic events like fish kills.
Instead, overt symptoms such as invasive weeds, excessive algae, and eventually toxic cyanobacteria Harmful Algal Blooms (HABs) become more noticeable.
Many people fall into the trap of reactively fighting these symptoms using potent chemical herbicides, algaecides, and chemical precipitants to remove phosphorus from the water column.
But, these treatments only exacerbate the problem by creating more organic sediment from decomposing weeds and algae, increasing the sediment nutrient stockpile available for recycling, and accelerating the decline of the ecosystem.
The Government Accountability Report on the failure to manage hypoxia and HABs specifically called out these practices as counterproductive.
Investing in these chemical treatments is essentially paying good money to make your lake worse.
How Do You Assess The Tipping Point?
While the food web can be assessed at many levels, including fish censuses, these assessments can be expensive.
Phytoplankton and zooplankton, which are foundation levels of the food web, are cheaper and easier to measure and gain insight from.
Collecting phytoplankton and zooplankton samples is relatively simple, and they are sent to a specialized laboratory for professional analysis that details:
Phytoplankton and Zooplankton Taxonomy and Biodiversity
This shows the extent to which beneficial algae species that provide good nutrition for the food web are present or have been displaced by toxic cyanobacteria species.
Phytoplankton and Zooplankton Biovolume
This shows how excessive phytoplankton levels have become. When combined with measurements of hypoxia, the eutrophic status of the water body can be easily inferred.
High phytoplankton levels and cyanobacteria predominance provide insight into the eutrophic status of the water body and help forecast its future trajectory.
Because cyanobacteria are poor nutrition for zooplankton, zooplankton numbers decrease as they get starved out and cyanobacteria become more dominant.
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