beforeafter eutrophication. eutrophication – nutrient enrichment of waters major nutrients...

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