Environmental Science
How Invasive Carp Alter Nutrient Cycling in Shallow Lakes
Quick fact
Invasive carp can increase water column phosphorus concentrations by up to 100% in shallow lakes, directly fueling harmful algal blooms and degrading water clarity.
Why this is interesting
You've probably seen a clear lake turn murky green almost overnight. But what if the cause wasn't a factory or farm, but a fish?
Read the full explanation
Understanding How Invasive Carp Alter Nutrient Cycling in Shallow Lakes
Shallow lakes are delicate. They often sit in a clear-water state, with abundant aquatic plants that keep the water transparent. When invasive carp—like the common carp (Cyprinus carpio) or Asian carp—appear, they act like underwater bulldozers. As they feed, they root through the sediment, stirring up fine particles and nutrients. Their constant swimming also keeps sediment suspended. This turbidity blocks sunlight, causing plants to die. Without plants, sediments become easier to resuspend, and nutrients that were trapped are now released into the water. The lake becomes turbid and green with algae. This is the beginning of a vicious cycle that can completely transform the ecosystem.
A deeper explanation
The mechanism lies in the carp's behavior and the lake's nutrient dynamics. Carp are benthivorous—they feed on bottom-dwelling organisms and organic matter. While doing so, they physically disturb the sediment. In shallow lakes, where the entire water column is mixed by wind, this disturbance has a big effect. Sediment contains a large reservoir of phosphorus, often stored in iron-bound forms that are insoluble under oxygen-rich conditions. When carp resuspend sediment, they expose it to varying oxygen levels, breaking the iron-phosphorus bond and releasing soluble phosphate into the water. Similarly, nitrogen compounds are mobilized. This nutrient pulse triggers explosive growth of phytoplankton and cyanobacteria, which can dominate the system. The algae block light, killing submerged plants that would otherwise stabilize the sediment and absorb nutrients. As plants decline, sediments become more easily resuspended, reinforcing the turbid state. The system shifts from a clear, plant-dominated state to a turbid, algae-dominated state. This is an example of a positive feedback loop that makes the lake resistant to recovery even if carp are removed. Understanding this mechanism is critical for lake management and for predicting how invasions can alter ecosystem function.