How much dissolved oxygen in water

Emergency Management. Survey Manual. Dissolved oxygen DO is a measure of how much oxygen is dissolved in the water - the amount of oxygen available to living aquatic organisms. The amount of dissolved oxygen in a stream or lake can tell us a lot about its water quality. The USGS has been measuring water for decades. Some measurements, such as temperature , pH , and specific conductance are taken almost every time water is sampled and investigated, no matter where in the U.

Another common measurement often taken is dissolved oxygen DO , which is a measure of how much oxygen is dissolved in the water - DO can tell us a lot about water quality. Although water molecules contain an oxygen atom, this oxygen is not what is needed by aquatic organisms living in natural waters. A small amount of oxygen, up to about ten molecules of oxygen per million of water, is actually dissolved in water. Oxygen enters a stream mainly from the atmosphere and, in areas where groundwater discharge into streams is a large portion of streamflow, from groundwater discharge.

This dissolved oxygen is breathed by fish and zooplankton and is needed by them to survive. A eutrophic lake where dissolved-oxygen concentrations are low. Algal blooms can occur under such conditions. Rapidly moving water, such as in a mountain stream or large river, tends to contain a lot of dissolved oxygen, whereas stagnant water contains less.

Bacteria in water can consume oxygen as organic matter decays. Thus, excess organic material in lakes and rivers can cause eutrophic conditions, which is an oxygen-deficient situation that can cause a water body to "die. Water near the surface of the lake— the epilimnion— is too warm for them, while water near the bottom—the hypolimnion— has too little oxygen.

Conditions may become especially serious during a period of hot, calm weather, resulting in the loss of many fish. You may have heard about summertime fish kills in local lakes that likely result from this problem. Water temperture affects dissolved-oxygen concentrations in a river or water body. As the chart shows, the concentration of dissolved oxygen in surface water is affected by temperature and has both a seasonal and a daily cycle.

Cold water can hold more dissolved oxygen than warm water. In winter and early spring, when the water temperature is low, the dissolved oxygen concentration is high. In summer and fall, when the water temperature is high, the dissolved-oxygen concentration is often lower. Dissolved oxygen in surface water is used by all forms of aquatic life; therefore, this constituent typically is measured to assess the "health" of lakes and streams. Oxygen enters a stream from the atmosphere and from groundwater discharge.

The contribution of oxygen from groundwater discharge is significant, however, only in areas where groundwater is a large component of streamflow, such as in areas of glacial deposits. You may have heard about a Gulf of Mexico "dead zone" in areas of the Gulf south of Louisiana, where the Mississippi and Atchafalaya Rivers discharge.

A dead zone forms seasonally in the northern Gulf of Mexico when subsurface waters become depleted in dissolved oxygen and cannot support most life.

The zone forms west of the Mississippi Delta over the continental shelf off Louisiana and sometimes extends off Texas. The oxygen depletion begins in late spring, increases in summer, and ends in the fall. Orange and red colors indicate lower dissolved oxygen concentrations.

In the graph below you can see the percentage levels of Oxygen dissolved in the river "The Thames" in the period , The New York harbor in the period , and the river "The Rhine" in the period Here we can see how the oxygen levels for some of the majors rivers have returned to the previous high levels after decades of low levels.

This has consequences for both marine organisms and humans. The increased levels of percentage of dissolved oxygen have improved the possibilities of aquatic live. Source: The Skeptical environmentalist; measuring the real state of the world. Author: Bjorn Lomborg. A high DO level in a community water supply is good because it makes drinking water taste better.

However, high DO levels speed up corrosion in water pipes. For this reason, industries use water with the least possible amount of dissolved oxygen. Water used in very low pressure boilers have no more than 2. Toggle navigation. Why oxygen dissolved in water is important Why Dissolved Oxygen is Important Dissolved oxygen The dissolved oxygen DO is oxygen that is dissolved in water.

The temperature effect If water is too warm, there may not be enough oxygen in it. This test relates to the amount of potential decomposable organic material or food in the water. If the 5-day BOD is ten, the corresponding Q-value would be approximately 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; cloudy days will also reduce photosynthesis.

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. 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. The increased DO is needed to support an increase in metabolic activity - a phenomenon shared by other cold-blooded aquatic animals. Because of these differences, river water weighs less than ocean water and floats on top of it—although wind and other strong mixing forces may change this pattern.

The boundary where the fresh water layer meets the salt water layer below is called the pycnocline. The pycnocline acts as a physical barrier that prevents the two layers from mixing together.

During the summer, when algae-consuming bacteria are most active, the pycnocline cuts off oxygen-deprived bottom waters from oxygen-rich surface waters. This can create large areas of low- or no-oxygen at the bottom of the Bay. The bottom of the Bay is not flat—rather, it has varying shallow and deep areas.