A multi agency project funded by US EPA's STAR Program
 
Developing stressor indicators

Many human activities can cause "stress" to coastal margin ecosystems.
For convenience, the types of stresses caused by human activities are grouped into five major categories;
click on a category to see the human activities that are associated with each type of stress.

Major Stressor Category Types of Stress
Habitat Alteration:

Fragmentation of habitat
Dredging and filling
Erosion
Conversion of land use

Chemical Disturbance:

Toxic contaminants
Nutrient additions
Salinity increases
Sediment additions
Atmospheric deposition of chemicals

Alteration of Biotic Processes:

Exotic species introductions
Changes in predation or grazing amounts
Overharvest of animals or plants

Alteration of Physical Processes:

Sediment additions
Temperature alterations

Hydrologic Disturbance:

Water level alteration
Stream flow alteration
Water table lowering


Stressor = Habitat Alteration

Human Activity Habitat Fragmentation Dredging or Filling Erosion Land Conversion
Agriculture X   X X
Energy Production X     X
Mining X   X X
Recreational Activities X   X  
Forestry X    X  
Transportation X X X X
Urbanization X X X X
         
Example stressor indicator: Change in amount of habitat Change in water depth Amount of sediment deposited Change in land use

Within the category of Habitat Alteration, the human activity of agriculture can lead to fragmentation of habitat, erosion of the land, and conversion of land from its natural habitat to agricultural fields. These types of changes can be measured; for example, habitat fragmentation can be measured as the loss in amount of a habitat type such as forests.

Top

Stressor = Chemical Disturbance

Human Activity Contaminants Nutrients Salinity Sediments Atmospheric Deposition
Agriculture X X X X X
Energy Production X      X
Mining X     X X
Recreational Activities X X   X  
Forestry    X   X
Transportation X X X X
Urbanization X X X X  
   
Example stressor indicator: Amount of pesticide use Nitrogen & phosphorus levels Salinity levels Suspended solids levels Mercury deposition amounts

In terms of Chemical Disturbances to aquatic systems, agriculture can introduce contaminants (pesticides and herbicides) and nutrients, can lead to increased salinity through salinization of farm fields, can cause increased levels of sediment in the water due to erosion, and can introduce pollutants into the atmosphere that are deposited in aquatic systems in other areas. The threat from these stressors can be measured or estimated; for example, the amount of pesticide or herbicide used on fields per acre is often used as an indicator of the threat these chemicals pose to nearby water bodies.

Top

Stressor = Disruption of Biotic Processes

Human Activity Exotic Species Introduction Altering Predation or Grazing Amounts Overharvest of Plants or Animals
Agriculture   X  
Energy Production       
Mining      
Recreational Activities X   X
Forestry      X
Transportation X    
Urbanization   X  
 
Example stressor indicator: Distribution of exotics Food web alteration Fish population size

Recreational activities have the potential to disrupt biotic processes in aquatic systems. For example, boaters can unwittingly spread invading aquatic species from one lake to another, and fishing activities can lead to the overharvest of popular fish species.

Top

Stressor = Disruption of Physical Processes

Human Activity Increased Sedimentation Altered Temperatures
Agriculture X X
Energy Production    X
Mining X X
Recreational Activities X X
Forestry X  X
Transportation X  
Urbanization X X
 
Example stressor indicator: Changes in sediment loads Temperature change over time

Most human activities can lead to increased amounts of erosion which causes increased sedimentation in streams and lakes. In addition, most human activities can either raise or lower lake and stream water temperatures; for example, power plants release heated water while dams often release cold water from the lake bottom into downstream receiving waters.

Top

Stressor = Hydrologic Disturbance

Human Activity Water Level Alteration Stream Flow Alteration Water Table Lowering
Agriculture   X X
Energy Production      X
Mining   X  
Recreational Activities     X
Forestry    X X
Transportation X X  
Urbanization   X X
 
Example stressor indicator: Number of Dams Stream Gauge Data Lake Level Changes

Hydrology is the study of water's physical properties and movement. A dam creates an obvious hydrologic disturbance by altering stream flow and greatly raising water levels. However some hydrologic disturbances are more subtle. For example, water demands on an aquifer by an urban area can lower the water table enough to decrease lake levels in the area.

Top