The Concept of Limiting Factor for Algae

The concept of a limiting factor is very old, summarized in Leibig’s Law of the Minimum, which used a bucket with staves of different lengths to show that the shortest stave controlled the depth water could attain in the bucket. The theory is simple, perhaps too simple to capture the variation induced by having multiple species present with varying optimal nutrient ratios, light requirements, and maximum growth rates. In reality, multiple factors control the growth of algae, with some species more impacted by one factor than others. There is therefore constant competition going on, with each species increasing in abundance to the extent possible before some species-specific limit is reached based on the relation of the individual species’ needs and available resources.

There are very few generalizations that apply to all algae with regard to limiting factors. Light is very important to photosynthesis, but some algae survive under very low light and some are “facultatively heterotrophic”, consuming organic compounds, bacteria, other algae, and even zooplankton to gain energy rather than depending on photosynthesis. Nitrogen is a key nutrient, but cyanobacteria with specialized cells called heterocytes can convert dissolved nitrogen gas into ammonium. Since our atmosphere is 78% nitrogen, it is virtually impossible to prevent these algae from acquiring some nitrogen. Phosphorus is the closest thing to a sure limiting factor, being relatively rare in the earth’s crust but critical to energy transfer. There is no substitute for phosphorus, and it can be controlled by multiple means in active management practices, so it is the logical target of choice in algae control programs that seek to prevent algae growth to bloom proportions.

Approaching algae management with multiple limiting factors is a good idea. In many cases, best management practices that control phosphorus also limit nitrogen and other nutrients. Increased flushing can reduce detention time such that growth rates are insufficient to generate blooms. Adjusting the fish community to encourage more and larger herbivorous zooplankton can increase algae consumption rates and funnel energy into desirable fish while limiting algae biomass. Yet control over planktonic algae will lead to deeper light penetration, which may provide benthic algae enough light to grow using nutrients available at the sediment-water interface during decomposition or other release mechanisms. Dredging can remove algae resting stages and nutrient reserves, limiting benthic production, but the cost is usually extreme.  

Using the concept of limiting factor(s) for algae is appropriate but more than a little complicated. The situation is far more complex that the simple bucket analogy suggests, and the more we can learn about the lake we want to manage the more successful we are likely to be in achieving our goals.

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