Balancing the Nutrients: The Eutrophication Quiz

If we identify the chemical triggers for algae growth, then we look for limiting nutrients in freshwater; if nitrogen and phosphorus are added via runoff, then they stimulate rapid plant growth; therefore, these two are the primary causes of eutrophication.

If we examine the definition of eutrophication, then we see it is a natural aging process of lakes; if human activity accelerates it, then it is called cultural eutrophication; therefore, the statement that it only occurs in man-made ponds is false.

If a thick layer of algae forms on the water's surface, then sunlight cannot penetrate to deeper levels; if sunlight is blocked, then submerged plants cannot perform photosynthesis; therefore, the immediate result is the shading of bottom-dwelling plants.

If algae die, then bacteria begin to decompose the organic matter; if bacteria use up the available oxygen during this process, then oxygen levels drop significantly; if oxygen levels are critically low, then the condition is specifically defined as hypoxia.

If the algae bloom dies and sinks, then decomposers break them down; if these decomposers consume the dissolved oxygen, then there is insufficient oxygen for fish; therefore, the fish die from a lack of breathable oxygen (suffocation).

If we track where excess nitrogen and phosphorus come from, then we find them in farm fertilizers, household soaps, and waste; if these enter the watershed, then they cause eutrophication; therefore, fertilizers, detergents, and sewage are correct sources.

If nutrient levels (physical component) change, then the algae population (biological component) spikes; if the oxygen levels subsequently drop, then fish populations decrease; therefore, this demonstrates that changes to ecosystem components affect populations.

If a large volume of organic matter (dead algae) becomes available, then the population of decomposers increases; if these bacteria respire while breaking down the matter, then they use up dissolved oxygen; therefore, decomposers are a major cause of oxygen depletion.

If animal waste is concentrated in one area, then it contains high levels of nitrogen; if rain washes this waste into nearby lakes, then it triggers algae blooms; therefore, feedlots or industrial farms are the primary source in this context.

If a lake has very few nutrients, then it supports little plant growth; if there is little plant growth, then the water remains clear and oxygen-rich; therefore, the scientific term for this healthy, low-nutrient state is oligotrophic.

If there is a large amount of organic matter to be decomposed, then the organisms doing the breaking down require more oxygen; if the demand for oxygen rises, then the BOD increases; therefore, eutrophication leads to a high BOD.

If we reduce the input of nutrients, then we slow the process; if buffer zones trap nutrients before they reach the water, then the lake stays cleaner; therefore, using P-free detergents, planting buffers, and reducing runoff are effective.

If an algal bloom covers the surface, then sunlight is blocked from reaching the bottom; if plants cannot receive sunlight, then they cannot photosynthesize regardless of nutrient levels; therefore, submerged plants actually die rather than thrive.

If oxygen levels drop below what is required for survival, then organisms must leave or they will perish; if a large area lacks enough oxygen to support life, then it is characterized as a Dead Zone; therefore, hypoxia is the direct cause of these zones.

If nutrients like nitrogen and phosphorus accumulate in a lake, then the biological productivity increases; if this enrichment leads to structural changes in the ecosystem, then the process is defined as eutrophication.

If we evaluate human activities for nutrient output, then fertilizer application is the highest; if these chemicals wash into the water, then they accelerate the natural aging of the lake; therefore, fertilizer use is the most impactful activity listed.

If a population spikes rapidly (a bloom), then it often indicates a nutrient imbalance; if this spike leads to the eventual death of other species via oxygen depletion, then it is not a sign of health; therefore, the statement is false.

If plants need multiple nutrients to grow, then they will grow only as much as the scarcest nutrient allows; if phosphorus is naturally rare in freshwater, then adding it causes a massive growth explosion; therefore, it is considered the limiting factor.

If there is a high concentration of algae (phytoplankton), then the chlorophyll in the organisms reflects green light; if the water is full of these organisms, then its clarity decreases; therefore, the water typically appears green.

If submerged plants die, then fish lose their nursery and hiding spots; if the plants are no longer photosynthesizing, then they stop producing oxygen; therefore, their death removes habitat and worsens the chemical imbalance.