Water Research Center
Dissovled Oxygen in Water

 

by:
Mr. Brian Oram, PG
B.F. Environmental Consultants Inc.

 

What is Dissolved Oxygen?

Dissolved Oxygen in a stream may vary from 0 mg/l to 18 mg/l. Readings above 18 mg/l are physically impossible. Dissolved oxygen gets into the water by diffusion from the atmosphere, aeration of the water as it tumbles over falls and rapids, and as a waste product of photosynthesis.

What factors affect the DO level?

 

 

Water Quality Index Chart- Based on Dissolved Oxygen

 


Water Quality Index and BOD - Biological Oxygen Demand

 

 

Students should be aware that plants, in general, only produce oxygen when light is available for photosynthesis. Rooted aquatic plants are more abundant in lakes and impounded rivers than in rivers with significant current or in streams. Large daily fluctuations in dissolved oxygen are characteristic of bodies of water with extensive plant growth. DO levels rise from morning through the afternoon as a result of photosynthesis, reaching a peak in late afternoon. Photosynthesis stops at night, but plants and animals continue to respire and consume oxygen. As a result, DO levels fall to a low point just before dawn. Dissolved oxygen levels may dip below 4 mg/l in such waters - the minimum amount needed to sustain warm water fish like bluegill, bass, and pike.

How dissolved oxygen affects aquatic life

The amount of DO an aquatic organism needs depends upon its species, the temperature of the water, pollutants present, and the state of the organism itself (adult or young, active or dormant).

 

A trout needs five to six times more DO when the water temperature is 24 degrees C (75 degrees F) as compared to when the water temperature is 4 degrees C (41 degrees F). The increased DO is needed to support an increase in metabolic rates - a phenomenon shared by other cold blooded aquatic animals.

The generally accepted minimum amount of DO that will support a large population of various fishes is from 4 to 5 mg/l. When the DO drops below 3 mg/l, even the hardy fish die. Keep in mind that even though there may be enough DO to keep an adult alive, reproduction may be hampered by the need for higher DO for eggs and immature stages. Depletion in DO can cause major shifts in the kinds of aquatic organisms found in water bodies. Species that cannot tolerate low levels of DO - mayfly nymphs, stonefly nymphs, and beetle larvae - will be replaced by a few kinds of pollution-tolerant organisms, such as worms and fly larvae. Nuisance algae and anaerobic organisms (that live without oxygen) may also become abundant in waters with low levels of DO.

The following will give you some idea of how various fish species differ in their DO requirements:

Lowest DO at which fish survived for 24 hours (Summer)

Northern Pike - 6.0 mg/L

Black Bass - 5.5 mg/L

Common Sunfish - 4.2 mg/L

Yellow Perch - 4.2 mg/L

Black Bullhead - 3.3 mg/L

Certain pollutants interfere with oxygen uptake and metabolism so that some species of aquatic animals may need higher DO levels when these pollutants are present.

Back to Main Watershed Page

For More information about the Water Research Center, 
please contact:

 Attn: Mr. Brian Oram, Professional Geologist (PG)
Water Research Center
B.F. Environmental Consultants Inc.
15 Hillcrest Drive
Dallas, PA 18612

Visit Our Online Blog- My 2 cents - Ok May a Quarter
Titled:  Pennsylvania Environmental Solutions

water testing kits, water research laboratory, drinking water laboratory
Webmaster

Home |  Drinking Water Help Guides | Contact Us
 Available Test Parameters   
 Research Interests, Funded Research and Applied Research 
  Homeowner Information Water Testing
 Environmental Topics - Infiltration, Permeability, Soil Science, 
 Wellhead Protection, Groundwater, Watersheds
 PowerPoint Presentations


Continuing Education Courses - OSHA Training, Engineers, Geologists,
Sustainability, Architects, LEED Professionals

Watershed Monitoring, Research, Training,
Lake and Watershed Studies, Citizen Monitoring, Volunteer Monitoring Programs


 The Water Library - Pdf files on Water Issues and Topics
 Tools for Environmental Professionals, Citizens, and Students
 Field Training and Workshops in Earth Science
 Affiliations and Hot Links  

Search Our Site

part of the Web Design Pros Network
"specializing in Education and Training of Professions and Sustainability"

eXTReMe Tracker