Lake Ecology: The Complex World Within Water

Updated: Aug 30

By Julie Kucks


Perhaps you’ve seen a Rube Goldberg Machine in action. Rube Goldberg, a cartoonist and inventor, became famous for sketches he created of complicated cause-and-effect machines that achieved a very simple task by the end, such as folding a napkin. These cartoon machines sparked the imagination of engineers who soon began building real-life models to study the complexities of cause-and-effect in the physical realm.


Our natural world is a complex, organic system of pushes and pulls that are all interconnected and dependent upon one another. This incredible system works at a very delicate balance and ultimately achieves what we often ignorantly perceive as a “simple” result. What we often don’t remember is that when we pour ourselves a simple glass of water, there is actually an entire ecosystem’s process that has gone into creating that one glass of H2O.


This week, we here at NJIN had the desire to dive into a fundamental understanding of the complex world of lake ecology and better understand how climate change is threatening the livelihood of these essential ecosystems worldwide.


Let’s dig in!


The Basics


Lake ecology, or limnology as it’s more officially called, truly has myriad depths and corners of fascination. We decided to take a look at four elemental areas, the interrelation of which can be seen as the foundation for the wellbeing of lake habitats.


Turbidity

Turbidity is defined as the clarity of water – an optical measurement that is directly correlated with the amount of scattered light which bounces off material in lake water. Higher turbidity makes for higher levels of scattered light which decreases light’s intensity. Turbidity is caused by TSS or total suspended solids in water. Materials such as silt, clay, organic/inorganic matter, algae, compounds, and microscopic organisms make up these solids.

Excess turbidity negatively impacts life within the lake ecosystem as it decreases light penetration which in turn decreases photosynthetic capabilities. This has an adverse effect on plant life and food sources and it also affects the levels of dissolved oxygen in the water which fish need to survive.

Turbidity is also affected by land use by humans – ineffective pasture, woodland, and cropland management will affect erosion levels as well as chemical interferences within the water’s ecosystem.

A simple way to measure lake turbidity is through use of a secchi disk which is a black and white colored disk 8 inches in diameter that is lowered into the water by an attached rope. The point at which the secchi disk goes out of sight determines the amount of turbidity in the body of water. It is also effective to use higher tech measurements that determine the degree which turbidity has on the amount of scattered light bouncing off particles in the water. [1]


Climate change & turbidity

With climate change has come an increase in the number and ferocity of storms around the world. This increase in amount and intensity of rainfall is causing widespread erosion. Erosion then increases sediment and soil in rivers, streams, and lakes thereby increasing turbidity levels. [1] Since the more turbid a lake is, the less animal and plant life it will be able to support, this a serious threat to lake livelihood.

Light

Light. It is a critical element for life and that is no different with aquatic life. The amount that lake water is able to absorb light affects temperature and photosynthetic abilities of aquatic plants. Light is directly affected by turbidity in the lake. Increased turbidity means decreased light, thereby affecting photosynthesis and food production within the lake. Temperature and photosynthesis both provide sources of livelihood for aquatic life by determining water circulation, alkalinity, and dissolved oxygen levels under the water necessary for fish and other organisms. The heat absorbed with the light is also a critical element to maintaining the water’s temperature levels and determining wind patterns.


Climate change & light:

The effects of climate change on turbidity mentioned above directly affect the amount of light available to the lake’s ecosystem. Increased turbidity diminishes light absorption which affects plant growth and oxygen levels.

Temperature & Climate

The temperature of lake water strongly affects the makeup and life within its habitat. One of the biggest components of temperature within a lake is how it determines the water stratification. Lake stratification is when a lake’s water divides into different sections based on differences in temperature and density. Water density operates differently than that of other substances – water becomes less dense as a solid, yet becomes denser the cooler the water’s temperature becomes. It is its densest at around 4 º C, a few degrees before freezing.

Stratification in a lake occurs when the water levels separate from each other due to temperature and, consequently, density. Ultimately, the temperature of a lake’s water depends on its climate, depth, and turbidity. This element is so important in lake ecology that lakes are actually classified into six lake types based on temperature and how their waters do or do not stratify. [1]



Six Types of Lakes:

Amictic: coldest lakes which exist in climates that keep their waters permanently frozen, thereby never allowing for stratification

Holomictic: circulation of water layers occur at points throughout the year – freezing may occur but is not permanent

Dimictic: lakes experience seasonal temperature levels that allow for mixing of water levels – water circulates only in Fall and Spring

Polymictic: stratification occurs at random, irregular times – these can be lakes existing in either cold or warm climes

Meromictic: these lakes never experience full circulation due to chemicals causing the water to continually hold their stratification

Both stratification and circulation of water in dimictic lakes are perfect examples of the fascinating, important process temperature plays in the lake’s livelihood. Seasonal stratification is a process that occurs in a majority of lakes worldwide as most of the world’s lakes exist in the Northern Hemisphere and experience this seasonal climatic process.[2]

Seasonal stratification is important as it allows fish and other organisms to live through the winter months at the warmer water temps below the icy surface of the lake. Stratification has a huge role to play in availability of dissolved oxygen throughout the lake as well as the chemical balances and aquatic population support.

Seasonal circulation, a.k.a. the absence of stratification, is also important for maintaining life in the lake. While during the transition point from winter into spring, the surface of the water is cooler than the water at the bottom of the lake, as the ice begins to melt and the surface of the water begins to heat, the water becomes less dense and approaches temperatures closer to that of the bottom of the lake. At this point, “turnover” occurs where very light winds and the tender tip of water density causes the lake water to turn over and circulate itself. This seasonal water circulation within a lake is important to provide renewed plant material and dissolved oxygen levels to the bottom of the lake.


Climate change & temperature:

Studies funded by NASA and National Science Foundation took over 25 years of satellite temperature data of lakes around the world and revealed that lakes have been warming by 0.61 ° F each decade. Another study by Nature Communications revealed that lake stratification periods could extend by up to two weeks by the end of the century, with stratification beginning earlier and lasting longer. Studies have also shown that ice covers of lakes are diminishing due to climate change. [3] All of this warming in temperature will affect the natural balance within the ecosystem, causing irreversible damage to aquatic life.


Alkalinity

Whenever we discuss water quality, alkalinity is at the top of the list of factors to consider. It is important because a water’s alkalinity interacts directly with the health of aquatic life.


Alkalinity is defined as water’s ability to neutralize acids and bases, thereby maintaining a stable pH.[1] An alkaline environment is considered to have a pH of 7 or higher. Before modern-day man’s inventions, lakes were much more likely to maintain a stable pH. Now, however, due to chemical spills, acid rain, wastewater, and pollution in general, it is much easier for the pH levels within a lake to shift dramatically which can be damaging or fatal to aquatic life. The higher a lake’s alkalinity levels, the better chance it has to counteract a sudden shift in pH levels.


While pH levels are affected by external forces, the pH levels within a lake are also always naturally in flux as there is a cyclic relationship between photosynthetic processes and carbon dioxide levels. During the day, aquatic plants’ photosynthesis naturally depletes levels of carbon dioxide in the lake, thereby increasing pH levels. At night, photosynthesis stops, giving time for aquatic life’s respiration to replenish carbon dioxide levels and bring the pH back to an equilibrium. This process obviously depends on a balance between aquatic plant and animal life which is dependent on overall alkalinity.


Climate change & alkalinity:

One of the major ways alkalinity is affected by climate change is the amount of soil erosion and surface runoff that’s occurring which picks up pollutants and other undesirables, eventually dumping them into lakes and affecting the delicate pH balance. These runoffs also have an adverse effect on turbidity, they jeopardize aquatic life’s health, and they make the process of cleaning water more arduous and expensive.

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The more we explore lake ecology, the more we see how tender the balance is within the lake’s ecosystem and how interrelated everything is – effective water circulation in a dimictic lake depends on climate and water temperature; water temperature is dependent on turbidity; aquatic life is dependent on turbidity and light which is reliant upon cleanliness of water and healthy levels of bacterial populations.

The health of each element within limnology is reliant upon the other elements. Like an effective Rube Goldberg Machine, it is critical for each portion of the system to be operating at its peak so as to maintain life.

The more knowledge we have of how climate change affects the planet, the more knowledge we have of how intimately connected we all are to these effects. Let’s keep gaining knowledge and spreading news about how our planet functions so we can help keep it healthy!

Julie Kucks is a freelance content writer for New Jersey Institute of Nature and Cedar Hill Prep. Her work has also been featured in Fine Living Lancaster. Julie's writing interests include sustainable living practices, permaculture, mental health, and the power of breathwork. She also enjoys piano tuning, singing and songwriting, playing mountain dulcimer, hiking, and carousing with her kittens, Nike & Lionne.


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