Before After
Eutrophication
Eutrophication – nutrient enrichment of waters
Major nutrients - phosphorus andnitrogen
Consequences - increased plantgrowth
- decreased waterquality
Eutrophication of lakes, reservoirs and rivers ranks as one of the most widespread environmental problems.
Eutrophication can have significant negative ecological, health, social and economic impacts on use of a primary and finite resource, water.
Decreased water quality
• Algal blooms– Decreased transparency– DOC and chlorination disinfection products– Toxic cyanobacteria and dinoflagellate
• Growth of aquatic plants
• Anoxia
Effects of Eutrophication
Source: Issues in Ecology #2 (1998)
Laguna de Bay, Philippines
Decreased water quality
Elevated nitrate concentrations
Species changes
Increased incidence of water-related diseases
Positive features of eutrophication
- increased fish yield
- increased plant production and nutrient reuse
Indicators of eutrophication
Secchi disk transparency
Chlorophyll concentration
Phosphorus concentrations
Nitrogen concentrations
Experimental Lakes Area
Lake 227
Lake 226C, N, PEutrophic algal blooms
C, N
Effects of Eutrophication
Source: Issues in Ecology #2 (1998)
Source: Issues in Ecology #2 (1998)
Classification of Lakes
Source: Principles Env. Sci. & Eng. (Davis & Masten)
Total P vs. Chlorophyll a
Source: Principles Env. Sci. & Eng. (Davis & Masten)
Meybeck, 1982
N fixation• N2 reactive N
– (e.g. NH3 , NH4+)
• Mostly biological
free- living bacteria (asymbiotic)
symbiotic
Synthetic fertilizer
• production is consideredN fixation
• takes N2, reacts it withnatural gas, producing NH3and CO2
Agriculture…
(Townsend et al. Frontiers Ecol. Environ. 2003)
(Tilman et al. Nature, 2002)
Percent Increase in Nitrogen Fluxes in Rivers
Source: Millennium Ecosystem Assessment
Gulf of Mexico Dead Zone
Source: NOAA
US East Coast
Source: Issues in Ecology #2 (1998)
Fish Kills and Anoxia in the Chesapeake
(Townsend et al. Frontiers Ecol. Environ. 2003)
Is N or P limiting? – Assessment
Concentration ratiosExperimental enrichmentsSupply and recycling ratiosPhysiological assays
Analysis of Cause and Effect
Low Nutrient Supply
Low N & P conc. in lake
Low algae productivity
Low chlorophyll a
Lake more transparent
Greater Secchi disc depth
High Nutrient Supply
High N & P conc. in lake
High algae productivity
High chlorophyll a
Lake less transparent
Smaller Secchi disc depth
Gradient of Conditions
Toxicinflow
HighSediment
HighFlowrate
Within-lake factors which moderate degree of eutrophication
* food web structure* sediment regeneration* basin morphology* hydrodynamics
Technically effective control of eutrophication is possible but not always economically feasible
Solutions…• Source Reduction
– Eliminate excess fertilization– Wastewater treatment plants
• In Lake Control:– Mechanical harvesting of aquatic plants– Chemical control (algaecides)– Biological control (increase grazing)– Flow augmentation– Deep water aeration– Selective removal of deep water– Sediment removal
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