The Effects of Nitrogen on Estuaries

Complied by
Bernadette Pate Holt

WFSC 611
Fall 1997

Summary:

The majority off the water that covers our planet is sea water. The ability to understand the aquatic ecosystem and its basic features of productivity, nutrient limitation, nutrient cycling and the food web structure are important to maintaining and preserving this precious resource. The availability of nitrogen plays an important part in the health of this ecosystem.

Nitrogen is the key element for all living processes. It is at the heart of all protein diversity. Proteins are built up of amino acids, all dependent on nitrogen. Although nitrogen is very abundant it the atmosphere (78%) of the Earth it must be "fixed" into organically usable nitrates, nitrites and ammonia before it is usable by animals and most plants. Nitrate and nitrite are organic icons occurring naturally as a part of the nitrogen cycle. The nitrogen cycle is made up of four processes: fixation, ammonification, nitrification and denitrifications.

Nitrogen fixation:

Nitrogen fixation occurs in two ways; high energy fixation and biological fixation. Nitrate is the product of high energy fixation by lightening, cosmic radiation and meteorite trails. The nitrate is then carried to the earth’s surface in rainfall as nitric acid. This type of fixation accounts or only 10% of the nitrate entering the nitrogen cycle, whereas, biological fixation accounts for 90% of the fixed nitrogen in the cycle. In biological fixation molecular nitrogen (N2) it split into two free N molecules. The N molecules combine with hydrogen (H) molecules to produce ammonia (NH3).

The fixation process is accomplished by a series of different organisms. In the water, blue green algae (cyanobacteria) like Nostoc and Calothrix can fix nitrogen yielding ammonia as a stable end product. Recent research done by Jon Zehr, Ph.D. has found that the marine filamentous momheterocystous cyanobacterium Trichodesmium is also capable of fixing nitrogen. It fixes nitrogen in aerobic waters at the same time as involving oxygen through photosynthesis. This is viewed as unusual since the enzyme responsible for nitrogen fixation is rapidly inactivated by oxygen. Most organisms have developed means to separate nitrogen fixation and photosynthesis temporally or spatially.

Resource:

http://www.nap.edu/readingroom/

The oceans’ depths contain an inexhaustible supply of organic nitrogen. In estuarine systems, nitrogen is the primary limiting nutrient. Thus, nitrogen levels control the rate of primary production. Excessive aquatic plant production may negatively impact estuarine environments in several ways.

• Algal mats, decaying algal clumps, odors, and discoloration of the water will interfere with recreational and aesthetic water uses.

• Extensive growth of rooted aquatic macrophytes will interfere with navigation, aeration, and channel capacity.

• Dead macrophytes and phytoplankton settle to the bottom of a water body, stimulating microbial breakdown.

• Aquatic life uses may be hampered when the entire water body experiences daily fluctuation in dissolved oxygen levels an a result of nightly plant respiration. Extreme oxygen depletion can lead to death of desirable fish species.

• Toxic algae (Red Tide) have been associated with eutrophication in coastal regions and may result in paralytic shellfish poisoning.

• Algae blooms shade submerged aquatic vegetation, reducing or eliminating photosynthesis and productivity.

Resource:

http://h2osparc.wq.ncsu.edu/info/no3.html

There are several sources of the nitrogen that finds its way into the estuaries. Some of the nonpoint sources are agriculture, residential and urban sources, fossil fuels, and aerosols. The point sources of nitrogen can be found in industries that use nitrites in manufacturing releasing nitrate in the effluent water. Industries that use nitrate in their processes include meat curing, fertilizer production, explosives, glass, and heat-transfer and storage for solar-heating applications. One of the greatest contributors of nutrients is offshore sewage pipe outfalls. Nitrogen is a significant factor in the health of estuaries. However, unchecked addition of nitrogen rich effluents into our coastal waters can produce unfavorable results. In order to maintain the viability of our estuaries, protection against an overabundance of nitrogen is important.

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