PRINCIPLES OF POLLUTION ECOLOGY

ENVIRONMENT:

ORGANISMS:


General effects of pollutants:

  1. Degradation of habitat quality for naturally adapted species.
  2. Detrimental impact on certain species and groups related to intensity, duration and type of pollution.
  3. Community structure altered. Generally, number of species declines.
  4. Flow of matter and energy in ecosystem altered.
  5. Removal of larger organisms with longer life spans (K-selected).
  6. Increase in small, opportunistic species with short life spans, adapted to rapidly changing environments (r-selected).
  7. Patterns of changes in community and ecosystem folow gradient from point of discharge.

Effects of pollutants can be related to three environmental factors:

  1. Excess plant production (aquatic).
  2. Deoxygenation (aquatic)
  3. Physiological effects (eg. toxic; all environs.)

Pollutants can be classified under this scheme in related groups:

  1. Organic matter
  2. Plant nutrients
  3. Toxic substances
  4. Suspended solids
  5. Energy-related (thermal)
  6. Pathogenic organisms


A LAW OF ECOLOGY RELATED TO POLLUTION ECOLOGY:

LEIBIG'S LAW OF THE MINIMUM (1840): The growth of an organism is dependent on the amount of essential material which is presented to it in minimum quantity. Applicable only under steady-state conditions (i.e. when matter and energy inflows and outflows are balanced and the material that is "limiting" does not change from one material to another)

Leibig's Law was extended by Shelford (1913) to describe not only the lower limit required of essential materials, but also the upper limit of tolerance to these materials. Organisms have an ecological minimum and maximum with a range in between which represents the limits of tolerance.


DEOXYGENATING SUBSTANCES:

Processes affecting oxygen concentration in water. Oxygen cycle and carbon cycle are intimately related (i.e., 6CO2 + 6H2O <------> 6CH2O + 6O2 )

Deoxygenation mechanisms:

1. Respiration:

aerobic: 6CH2O + 6O2 ---------> 6CO2 + 6H2O

anaerobic: 6CH2O ---------> 3CH4 + 3CO2

2. Nitrification:

NH4+ + 2O2 ------> NO3- + 2H+ + H2O

3. Sulfur oxdiation:

(organic sulfur) + O2 -------> SO42-

GENERAL CONCLUSION:

Organic loading to aquatic system is directly proportional to oxygen demand.

Oxygen demand can be measured:


Environmental Factors affecting oxygen solubility in water:

A. Solubility inversely proportional to temperature:

B. Solubility directly proportional to pressure

C. Solubility inversely proportional to salinity


Concept of Oxygen SATURATION:

%Saturation = 100 * (Oxygen[actual]/Oxygen[max])


EFFECTS OF DEXOYGENATING SUBSTANCES ON BODIES OF WATER:

Examination must consider two factors:

  1. Loss of oxygen due to BOD
  2. Gain of oxygen due to:

Use first-order kinetics to examine processes:

A. Loss Mechanisms:

where: D = Csat - Cact (i.e. oxygen deficit)


Loss mechanism is, therefore, a negative exponential decay function. Empirically, k1 has been found to equal ca. 0.230 day-1 at 20 degrees C. Therefore, the half-time for loss of most deoxygenating substances is ca. 3 days (i.e. (ln(2)/0.230) ).

A general relationship for k1 relative to temperature has also been derived:

k1(T) = 0.434(K1(20)) * (1.047(T - 20))

 

It can be seen, therefore, that the half-time for elimination of dexoygenating substances is strongly dependent on temperature:


Temp (deg.C)

t1/2 (days)

4
6.3

10
4.8

20
3.0

30
1.9


B. Gain Mechanisms:

For simplicity, only consider gains due to reaeration. In this case, gain of oxygen is proportional to the magnitude of the oxygen deficit:

This consideration of gain mechanisms is described by a sigmoidal (s-shaped) function. Values of K2 can be estimated under a variety of conditions using numerous methods (cf. Connell and Miller, p.104).

C. Net reaction :

The (loss-gain) due to inputs of deoxygenating systems where photosynthesis is of little importance to oxygen-gain mechanism (eg. most rivers and streams, and in surface waters of nonproductive [i.e. oligotrophic, mesotrophic] lakes):

Most appropriate use of this treatment is in a river or stream and where the x-axis above is in units of distance.


CYCLING OF OXYGEN

The cycling of oxygen (as well as other chemicals) in lakes is closely related to seasonal temperature changes and to the unique temperature-density relationsip of water:

In temperate zone lakes, this relationship causes stratification of layers in the lake due to density gradients. Stratification effectively isolates the surface layer of the lake from the bottom layer of the lake. As seasons change, the lake temperature becomes isothermal, allowing the layers to mix:


RELATIONSHIP OF TEMPERATURE AND OXYGEN CYCLING:

A. Dependent on isolation from mixing (stratification) of layers of water at depth.

B. Dependent on relative rates of: Respiration, photosynthesis, reaeration.


Dissolved oxygen quality criteria:

Numerical Categories:

Criteria to maintain designated use:

Designated Use          Lowest acceptable DO levels (mg/l)*

Aquatic life Warm water fish 5.0 Cold water fish 6.0 Spawning season 7.0 Estuarine biota 5.0 Recreation Primary Contact 3.0 Secondary Contact 3.0 *Summary of state standards
(Table taken from NCSU's Water Quality Education Web Site)


NITROGEN CYCLING:

A. Sources:

B. Concentrations:

C. Simplified Nitrogen Cycle:


PHOSPHOROUS CYCLING:

Most common limiting nutrient for biological productivity.

A. Sources (combo of autocth and allocth.): Three forms:

1. Orthophosphate (PO43-): Form mainly used by autotrophs. Rocks, bird guano, animal wastes (feedlots, STPs), runoff and groundwater (fertilizers).

2. Metaphosphate (poly-): Soluble organic form utlilized mainly by bacteria. Detergents.

3. Particulate: Detrital remnants of animals and plants. Approx. 70% of total phosphorous in a lake is particulate.

B. Concentrations:

C. Simplified phosphorous cycle:

[PO4] high in hypo relative to epi; Held in hypo until turnover (Spring and Fall "blooms")

D. Phosphorous cycling is intimately related to Iron cycling ("phosphate trap"):

  • Iron cycle dictated by redox reactions: Fe2+ <-------> Fe3+ + e-

  • Fe2+ (reduced; soluble)

  • Fe3+ (oxidized; ppt) Fe3+ + 3OH- ---> Fe(OH)3 (s)

    PO43- has strong affinity for Fe(OH)3 and coprecipitates as (Fe(OH)3 *PO43-). Also, some FePO4(s) formed.

    Requirements for phosphate trap:

    1. High oxygen in hypolimnion at turnover

    2. [Fe] > [S] (FeS ppts at higher oxid potential)


    CULTURAL EUTROPHICATION:

    Increasing rate of ontogeny of lake or river system from low productivity to high. Natural process. Human inputs greatly increase rates. In MOST NATURAL systems, phosphorous is limiting nutrient.

    1669 - Hennig Brand of Hamburg (alchemist) (discovered, named phosphorous). Of note is that Brand extracted phosphorous from a large amount of URINE.

    Cultural Sources:

    In 1969, IJC identified phosphorous as major culprit in Great Lakes pollution. At that time, 50% of phosphorous in Lakes came from detergents. Detergent companies attempted to disprove P as limiting nutrient.

    D. Schindler (1974) Experimental Lakes Area (ELA) experiments, among other evidence supported that abatement of phosphorous would decrease rates of eutrophication.

    IJC referral: 1 mg/L in effluent of large producers of effluent.

    Canada (federal legist.): detergents < 2.2% by weight

    U.S. (by state): < 0.5% by weight (Ohio and Penna. lagged behind)

    Not only is the amount of phosphorous important, but also is the relative amount of nitrogen:


    NUTRIENT CYCLING IN AQUATIC SYSTEMS:



    OXYGEN DEPLETION AND NUTRIENT ENRICHMENT EFFECTS ON ORGANISMS:


    Biotic Indexes:

    1. Saprobic Index: relates stages of organic pollution to numbers and kinds of organisms. Useful for organic pollution only.

    2. Diversity Indexes: assess community diversity. Idea that more diverse communities are more healthy, clean and stable. Composite score indexes (ICI, IBI) can be used to tentatively identify types of pollution. Ohio EPA provides model for use of Biotic Indexes.

    Values Compared to Those Expected in Various EcoRegions:


    3. Habitat Suitability Indexes: