Why are dissolved oxygen and temperature important? Understanding lake dissolved oxygen. (DO) and temperature patterns is important to lake management. By measuring dissolved oxygen and temperature, scientists can gauge the overall tance of temperature in relation to DO capacity of water. The three graphs show (from top to bottom) dissolved oxygen, water temperature, and chlorophyll concentration at a monitoring site in the Chesapeake Bay over.
Coral reefs are found in the euphotic zone where light penetrates the water — usually not deeper than 70 m.
Dissolved Oxygen Meters
Crustaceans such as crabs and lobsters are benthic bottom-dwelling organisms, but still require minimum levels of dissolved oxygen. Consequences of Unusual DO Levels If dissolved oxygen concentrations drop below a certain level, fish mortality rates will rise.
In the ocean, coastal fish begin to avoid areas where DO is below 3. It can be species-based or a water-wide mortality. Fish kills can occur for a number of reasons, but low dissolved oxygen is often a factor.
Dissolved oxygen depletion is the most common cause of fish kills When a body of water is overproductive, the oxygen in the water may get used up faster than it can be replenished. This occurs when a body of water is overstocked with organisms or if there is a large algal bloom die-off.
Fish kills are more common in eutrophic lakes: High levels of nutrients fuel algae blooms, which can initially boost dissolved oxygen levels. But more algae means more plant respiration, drawing on DO, and when the algae die, bacterial decomposition spikes, using up most or all of the dissolved oxygen available. This creates an anoxic, or oxygen-depleted, environment where fish and other organisms cannot survive. They occur when the water is covered by ice, and so cannot receive oxygen by diffusion from the atmosphere.
If the ice is then covered by snow, photosynthesis also cannot occur, and the algae will depend entirely on respiration or die off. In these situations, fish, plants and decomposition are all using up the dissolved oxygen, and it cannot be replenished, resulting in a winter fish kill. Gas Bubble Disease Sockeye salmon with gas bubble disease Just as low dissolved oxygen can cause problems, so too can high concentrations.
Extended periods of supersaturation can occur in highly aerated waters, often near hydropower dams and waterfalls, or due to excessive photosynthetic activity. This is often coupled with higher water temperatures, which also affects saturation. Dead Zones A dead zone is an area of water with little to no dissolved oxygen present. They are so named because aquatic organisms cannot survive there.
They can occur in large lakes and rivers as well, but are more well known in the oceanic context. Hypoxic and anoxic zones around the world photo credit: NASA These zones are usually a result of a fertilizer-fueled algae and phytoplankton growth boom. These anoxic conditions are usually stratified, occurring only in the lower layers of the water. Naturally occurring hypoxic low oxygen conditions are not considered dead zones.
Such naturally occurring zones frequently occur in deep lake basins and lower ocean levels due to water column stratification. Dissolved Oxygen and Water Column Stratification Stratification separates a body of water into layers. This layering can be based on temperature or dissolved substances namely salt and oxygen with both factors often playing a role. The stratification of water has been commonly studied in lakes, though it also occurs in the ocean.
It can also occur in rivers if pools are deep enough and in estuaries where there is a significant division between freshwater and saltwater sources. Lake Stratification Lake stratification The uppermost layer of a lake, known as the epilimnion, is exposed to solar radiation and contact with the atmosphere, keeping it warmer.
Within this upper layer, algae and phytoplankton engage in photosynthesis. The exact levels of DO vary depending on the temperature of the water, the amount of photosynthesis occurring and the quantity of dissolved oxygen used for respiration by aquatic life.
Below the epilimnion is the metalimnion, a transitional layer that fluctuates in thickness and temperature. Here, two different outcomes can occur. This means that the dissolved oxygen level will be higher in the metalimnion than in the epilimnion. The next layer is the hypolimnion. If the hypolimnion is deep enough to never mix with the upper layers, it is known as the monimolimnion. The hypolimnion is separated from the upper layers by the chemocline or halocline.
These clines mark the boundary between oxic and anoxic water and salinity gradients, respectively. While lab conditions would conclude that at colder temperatures and higher pressures water can hold more dissolved oxygen, this is not always the result. This organic material comes from dead algae and other organisms that sink to the bottom.
This turnover redistributes dissolved oxygen throughout all the layers and the process begins again. Ocean Stratification Stratification in the ocean Stratification in the ocean is both horizontal and vertical.
Dissolved Oxygen Meters FAQ
The littoral, or coastal area is most affected by estuaries and other inflow sources. The sublittoral, also known as the neritic or demersal zone, is considered a coastal zone as well. In this zone, dissolved oxygen concentrations may vary but they do not fluctuate as much as they do in the littoral zone. This zone is also where most oceanic benthic bottom-dwelling organisms exist.
Oceanic benthic fish do not live at the greatest depths of the ocean. They dwell at the seafloor near to coasts and oceanic shelves while remaining in the upper levels of the ocean. Beyond the demersal zone are the bathyal, abyssal and hadal plains, which are fairly similar in terms of consistently low DO. In the open ocean, there are five major vertical strata: The exact definitions and depths are subjective, but the following information is generally agreed upon.
The epipelagic is also known as the surface layer or photic zone where light penetrates. This is the layer with the highest levels of dissolved oxygen due to wave action and photosynthesis.
The epipelagic generally reaches to m and is bordered by a collection of clines. Dissolved oxygen levels decrease at the thermocline These clines can overlap or exist at separate depths.
Much like in a lake, the thermocline divides oceanic strata by temperature. Each of these clines can affect the amount of dissolved oxygen the ocean strata can hold. Within this strata, the oxygen minimum zone OMZ can occur. The OMZ develops because organisms use the oxygen for respiration, but it is too deep to be replenished by photosynthetic oxygen byproducts or aeration from waves.
The mesopelagic zone is bordered by chemoclines clines based on chemistry levels, e. Dissolved oxygen levels change with the pycnclines Below the mesopelagic is the aphotic zone s. These strata have lower dissolved oxygen levels than the surface water because photosynthesis does not occur but can have higher levels than the OMZ because less respiration occurs.
The bottom layer of the ocean is the abyssopelagic, which exists below m. Estuary Stratification Dissolved oxygen stratification in an estuary is dependent on salinity expressed in PSU. Estuary stratifications are based on salinity distributions. Because saltwater holds less dissolved oxygen than freshwater, this can affect aquatic organism distribution.
Species composition of the aquatic ecosystem. Many aquatic species can survive only within a limited temperature range.Effect of pH temperature and dissolved o2 in water ecosystem
Water density and stratification. Differences in water temperature and density between layers of water in a lake leads to stratification and seasonal turnover. Environmental cues for life-history stages. Changes in water temperature may act as a signal for aquatic insects to emerge or for fish to spawn. The most important source of heat for fresh water is generally the sun, although temperature can also be affected by the temperature of water inputs such as precipitation, surface runoff, groundwater, and water from upstream tributariesheat exchanges with the air, and heat lost or gained by evaporation or condensation.
Water temperature fluctuates between day and night diurnal temperature changes and over longer time periods e. In the spring, snowmelt running into rivers reduces the water temperature to below the ambient air temperature.
Water's the Matter--Lesson Presentation: Dissolved Oxygen
Permafrost also contributes to cold water runoff when it begins to thaw in June or July, and its meltwater seeps into the river. Water temperature varies along the length of a river with latitude and elevation, but can also vary between small sections only metres apart, depending on local conditions.
For example, a deep, shaded pool is cooler than a shallow, sunny area. In lakes, temperature can vary with depth, according to the level of solar radiation penetration and mixing characteristics. Human activities affecting water temperature can include the discharge of cooling water or heated industrial effluents, agriculture and forest harvesting due to effects on shadingurban development that alters the characteristics and path of stormwater runoff, and climate change.