Limnology & Oceanography Methods

Instructor: Fawn Goodberry

Fawn has taught as a brain training instructor with the Learning Rx. In graduate school served as a teaching assistant for Introduction to Evolution and Ecology and Population Genetics. She received her masters degree in biology in 2013.

In the fields of oceanography and limnology, there are many areas to study— the biological, the physical/chemical, and the geological. Many tools and methods help scientists answer a variety of questions and study these certain components. In this lesson, we will discuss some of the major areas to study in freshwater and oceans and some of the methods that are widely used.

Studying Oceans and Lakes

Have you ever gone to the beach whether it be at the ocean or a lake? If so, you probably thought, ''Wow, I wish this were my day job!'' Well, some people do just that. They spend their days at work on boats or on the beaches studying lakes, rivers, streams or the ocean. Let's learn a little more about what they study.

Limnology & Oceanography

The fields of limnology and oceanography are quite similar. Limnology is the study of inland waters including lakes ponds, rivers, springs, streams and wetlands. Oceanography is the study of the ocean— its currents, waves, the geology of the sea floor and the various physical and chemical properties. Both fields have various aspects of what to study. Let's look at the various methods that both would use.

Biological Methods

Those who study the plants and animals in oceans and inland water would be studying the biological component of these fields. Biologists would be interested in the numbers of plants and animals in a certain area or of a certain species. Where they live for certain parts of their lives, how they reproduce, how often and where and how these animals interact with each other and the environment around them.

Methods used to study the biological areas involve field work, laboratory experiments and computer models.

In the field, biologists would use a variety of tools. Let's look at the tools biologists would use, starting at the bottom of the food chain.

Plankton net

Plankton Nets (as seen above) which come in a variety of mesh sizes, to capture 'phyto plankton' (microscopic plants, think of algae) and zooplankton (microscopic animals, think of sea monkeys) of varying sizes.

To capture and record what kinds and how many fish are in the ocean or a body of water there are a few ways to accomplish this.

Electrofishing by back pack or by boat, is when a probe is put into the water by someone on a boat or by a person who is walking through the water wearing the device as a back pack. A shock is sent to the water which does not kill the fish but causes a response that makes the fish swim towards the shocking instrument known as the anode.

Backpack electro fishing

Other methods to catch fish and document the data needed for what a particular study is looking at include:

Seine nets which are nets equipped with sinkers on the bottom of the nets and small buoys on the top of the net. Two or more people will walk the nets out into the water, deploy the net which essentially herds the fish into one area.

Other nets are deployed from boats to catch fish in different parts of the water column. Dredge nets essentially are dragged along the bottom of the water to catch fish in the deepest waters. Trawl nets are deployed at a pre-determined depth to target a certain specie or species of fish. Drift nets are nets that are allowed to free flow with the currents of the water and target a wide variety of fish.

Physical/Chemical Methods

Another component that oceanographers and limnologists study is the physical component of the waters. This involves looking at the temperature throughout the different depths of the water column. The clarity or how far light can penetrate, the pH (how acidic or basic), turbidity (how cloudy the water is), salinity (salt content) and conductivity (the ability to conduct electricity). Here are some methods that they use:

Secchi disk: measures clarity of a body of water and what is known as secchi depth. A black and white disk is lowered into the water by a rope that has marked measurements, once the disk is no longer visible the depth is measured.

Secchi disk

There a variety of probes that can measure multiple parameters at one time, one such probe is known as a data-sonde probe. Depending on funds available to the scientist, they may purchase one of these to be able to measure pH, salinity, turbidity, temperature and a variety of other parameters at one time. These types of probes are calibrated with stock solutions and log all the data on a hand-held device or computer.

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