Aquatic Ecology - Limiting Factors Study Guide

What does alkalinity measure? What are the optimal levels?

Alkalinity is a measure of carbonate and bicarbonate ions which buffer changes in pH.

• optimal levels: 100-400ppm

  • Below 50 ppm results in rapid pH fluctuations which can be detrimental to aquatic life?

What is ammonia? When does ammonia become limiting?

Ammonia is the result of protein metabolism

• Total ammonia starts to become limiting around 1 ppm

What are optimal levels of carbon dioxide? When does it come limiting? 

• Optimal carbon dioxide levels are 5-10 ppm 

• Levels become limiting above 10 ppm 

What does conductivity measure? What is the optimal range?

Conductivity is the measure of how well electricity conducts through water. Therefor conductivity is a crude measurement of dissolved soils or nutrient level 

• Optimal rangers are 100-300 umhos 

What is current velocity? How is it a limiting factor?

Current velocity is a limiting factor for stream living fish. 

• Fish adapted for high current velocities have a flattened head, large pectoral fins (gill fins) and streamline body 

• It is a limiting factor as it impacts distribution of fish (for example margined madtoms prefer swift waters, tadpole madtoms prefer stagnant water) 

How is depth a limiting factor?

• Most aquatic organisms prefer specific depths (ex. sunfish and pickerel are only found in shallow water)

• As depth increases, biomass and productivity decreases 

• In NY, ponds should be at least 10ft deep to reduce winter kill 

How is elevation a limiting factor?

• Trout don’t occur below 1500ft. this is CORRELATED WITH TEMPERATURE 

• Impacts growing season: high elevation  lakes have shorter growing seasons and is fed by rainwater (which is low in nutrients) 

  • Therefor because of the short growing season high elevation lakes have low productivity, colder water, low PH and low nutrients. 

What is embeddedness?

Embeddedness measures how deeply rocks are buried in stream substrate.

• some fish need space under rocks to spawn

• AS embeddedness increases, spawning areas (and therefor production and biomass) decrease

How does habitat impact limiting factors?

• Riffle habitat has a high biomass of inverts and low biomass of fish 

What is hardness? What are optimal levels? What are marginal and limiting levels?

Hardness is the measure of magnesium and calcium ions.

• Optimal levels are 100-400ppm

• Marginal is 50-100ppm

• Limiting is below 50ppm 

What are some heavy metals? What are toxic levels?

Heavy metals are cadmium, copper, lead, mercury, and zinc

• It becomes toxic at 0.002ppm 

• Acid waters leach heavy metals from the substrate

Why is hydrogen sulfide an issue? What levels are lethal? Under what conditions is it extremely harmful? 

• Hydrogen sulfide is toxic to aquatic organisms 

• Continuous exposure to levels as low as 0.002ppm is lethal to many fish 

• Hydrogen sulfide is more toxic at low temperature and pH 

What does instream cover provide?

Instream cover provides feeding station and protection for trout

• Instream cover results in increased biomass and density 

How is light a limiting factor?

Light is a limiting factor as it is required for primary production. 

• Trout streams are most productive when they are half shaded and half sunlight 

• Too much or too  little light reduced productivity 

When does oxygen become a limiting factor?

Oxygen is required for metabolism by most aquatic organisms.

• It becomes limiting for most fish at 5 ppm

What is pH? What are optimal levels?

PH is a measure of hydrogen ion concentration.

• 6.5-8.5 is optimal levels 

• Brief exposure to high and low levels are not limiting 

What is the optimal range of phosphorous?

Phosphorous is the most limiting nutrient in standing waters.

• Optimal range is 0.01-3.0ppm

Describe salinity tolerance. What is it especially important for?  

Salinity is limiting for euryhaline organisms.

What do shoreline curves impact?

Shoreline curves increase edge/ecotone effect and therefor increase productivity. 

• round standing bodies of water are less productive 

What does sinuosity measure? 

Sinuosity measures how many curves a stream has in a given length 

• as sinuosity increases the diversity and biomass of fish increases 

Do all living things require space?

Yes! (different levels)

How does stream gradient impact other things?

High gradient streams have lower productivity and limited species diversity because of their high velocity and low sinuosity (curves) 

How are streams ordered? 

Stream order is classified based on the number of tributaries covering on a stream. 

• As stream order increases, biomass and productivity increases 

• First order streams are the least productive, they have the lowest diversity and inverts + fish 

What does structure include? 

structure includes shoals, submerged trees, and artificial reefs. 

• productivity is highest around structures 

• fish population depends on what structures are present 

How is substrate a limiting factor?

Substrate has multiple impacts on distribution and production of aquatic organisms

• fish production may be impacted by amount of spawning gravel

• rooted plants only occur in presence of fine sediments (sand + silt), while marine algae only occurs in the presence of course sediments (cobblers and boulders)

How does temperature impact limiting factors?

same species can have different temp presferences for life and functions

What is turbidity? What are optimal levels?

Turbidity is the measure of suspended solids. High turbidity reduces photosynthesis, makes it difficult for aquatic animals to find food and breath.

• optimal turbidity of standing waters is 0-2 JTU NTU or FTU

  • 0-10 JTU for standing waters