Transcript Slide 1
Eutrophication : a major issue - What is eutrophication? - Step by step eutrophication process - Effects on water quality, treatment costs, compliance and recreational activities - What is the situation in Puerto Rico? - Can the eutrofication be reversed? - actual lake restoration process - how soon can we see results? - what are the benefits? - How much is the cost? - funding option - is there a lease option? - Do all this makes sense ? What is Eutrophication? Eutrophication is a process whereby water bodies, such as lakes, estuaries, or slow-moving streams receive excess nutrients that stimulate excessive plant growth (algae, periphyton attached algae, and nuisance plants weeds). This enhanced plant growth, often called an algal bloom, reduces dissolved oxygen in the water when dead plant material decomposes and can cause other organisms to die. Nutrients can come from many sources, such as fertilizers applied to agricultural fields, golf courses, and suburban lawns; deposition of nitrogen from the atmosphere; erosion of soil containing nutrients; and sewage treatment plant discharges. Step by step eutrophication process Oligotrophic lake with a low level of nutrients. Artificial input of nutrients from run-off and discharge of effluent. Eutrophic lake with a high level of nutrients. Phosphorus is usually the bio-limiting element in freshwater lakes. Rapid growth of algae and other biomass resulting in a decrease in the concentration of dissolved oxygen. Turbidity (cloudiness) of water increases as does rate of sedimentation. Increased growth of rooted plants such as reeds. Algal blooms during the Summer months. Note that dissolved oxygen levels are at their lowest at night when plants respire rather than photosynthesis. Development of anoxic conditions and release of noxious gases such as hydrogen sulphide, thioalcohols and ammonia. Eutrophication process, the movie summary Effects on water quality, treatment costs, compliance and recreational activities Effects on water quality • Bad taste and odor : some of the algal species that "bloom" produce toxins (geosmin, MIB), water taste and odor deteriorates. • Oxygen depletion: penetration of light into the water is diminished. This occurs because the algae forms mats as a result of being produced faster than they are consumed. Diminished light penetration decreases the productivity of plants living in the deeper waters and hence their production of oxygen. • DBP precursors : As the water becomes depleted in oxygen, the abundant algae and fish die and decompose, further oxygen is consumed by this process. • Under anoxic conditions iron, manganese, ammonia and phosphorous are released into the water column, anaerobic bacteria flourish, producing hydrogen sulfide. Effects on treatment costs and compliance • Bad taste, odor, and high organics increase operational costs • Compliance with local and federal regulations becomes more difficult to achieve Effects on recreational activities • Recreation : Lowered oxygen results in the death of fish that need high levels of dissolved oxygen "DO"), such as trout, salmon and other desirable sport fish. The community composition of the water body changes, with fish that can tolerate low DO, such as carp predominating. • Changes in fish communities have ramifications for the rest of the aquatic ecosystem like the explosion of mosquitoes. What is the situation in Puerto Rico? EQB Report 2002 Can the eutrophication be reversed? actual lake restoration process, how soon can we see results?, what are the benefits? How much is the cost? - funding option - is there a lease option? How much is the cost? • size and depth of lake • how fast we want to achieve goals • need of biological treatment • available water quality data • bathymetric study • cheaper than dredging • more effective than inflow control • reduce operational costs • more than 2,000 installations Funding options, is there a lease option? Do all this makes sense?