Seasonal pools are often not identified as wetlands due to their temporary nature.  Pools that are not identified cannot be protected during development activities that would alter or destroy them.  Some estimates state that more than 50 percent of the wetlands in the United States have been lost since European settlement (Vileisis, 1997).

The rate at which seasonal pools have been lost is likely even greater considering that these areas are often overlooked.  Filling seasonal pools, and disturbances to the vegetation and soil around pools from building and road construction, quarries, and logging operations lead to direct mortality of animals and habitat destruction or degradation.

Habitat Fragmentation

Fragmentation of the landscape by various human activities destroys or reduces the amount of habitat available to seasonal pool animals and reduces their ability to find and colonize new habitats.  Roads are a common form of habitat fragmentation, even in relatively undeveloped areas.  And roads near seasonal pools present a physical obstacle to animals moving from their upland feeding habitats to their seasonal pool breeding habitats.  Many animals are killed as they attempt these crossings.  The presence of roads also provides opportunities for undesirable elements to get into the pools.  Roads bring invasive plant species, sediments, and contaminants to pools through runoff.  During the winter the application of road salt poses a problem for pools located near roads.  As the snow melts, salt-laden water flows into these pools and increases the salinity of the water, making the water less hospitable to wildlife.

Development of extensive agricultural, urban and suburban areas also creates biological “islands” of isolated natural areas.  It can be difficult for animals to move long distances across unsuitable habitat such as open lawns and parking lots and to navigate large obstacles such as highways and fences.  Some highly mobile animals are able to disperse over these obstacles.  Other more sessile animals are unable to move great distances from their preferred habitat.  For those species that can travel large distances, there is increased risk that they will not be able to find suitable habitat at the end of their journey in a fragmented landscape with diminished habitat.

Just as habitat fragmentation isolates a group of animals on an island of habitat; it also isolates the gene pool collectively held by that group of animals.  When animals cannot make contact with other populations, inbreeding within one population takes place.  This means there is no gene flow between populations and genetic diversity is lost.  As genetic diversity is lost, the ability of that population to adapt to changes in the environment is reduced.  This increases the chances that the population will not be able to survive over the long-term.

Alteration of Hydrology

Alterations to the natural water regime change many habitat parameters such as inundated area and depth, length of inundation, temperature, dissolved oxygen levels, and types and amounts of vegetation in and around the aquatic habitat.  All of these factors are important in proper development of aquatic eggs and larvae.  Heavy water demand can lead to decreased water tables and decreased water retention in seasonal pools.  Deepening of pools can increase their water retention and can change them from seasonal to permanent aquatic habitats.

Alteration of Water Chemistry

Many human activities have degraded water quality in aquatic habitats.  Agricultural runoff is a major source of pollutants in Pennsylvania where there are abundant farmlands.  Agricultural runoff is generated as rainwater flows through fields that have been treated with fertilizers, herbicides, and insecticides, and through livestock pastures and feedlots, washing the waste into local aquatic systems.

Suburban and urban runoff comes from rainwater that flows off rooftops, down streets and parking lots, through industrial zones and garbage disposal sites, and through lawns and golf courses treated with various chemicals.  This runoff contains sediments, garbage, road salt, oil, pesticides, herbicides, and a whole mixed bag of other household and industrial chemicals.

Testing for a variety of synthetic chemicals and heavy metals that can be toxic to wildlife is an important part of water quality monitoring.  Other important variables used to monitor water quality include temperature, pH, dissolved oxygen, sediment load, nutrient levels such as nitrates and phosphates, and bacterial and algal levels.  The types of plants and animals found living at a site can also be used to evaluate water quality.  Certain species are very tolerant of poor water quality, while others will only be found in clean habitats.  The types of plants and animals living at a site can be monitored for change over time.  If species intolerant of pollution disappear from a site, and species tolerant of pollution increase, this is an indication that there is a problem with water quality.

Seasonal pool animals are adapted to the relatively high acidity levels naturally found in seasonal pools, but they have tolerance limits.  Increased acidification of seasonal pools takes place due to acid rain.  In a review of literature, Hulse (2001) describes one study that showed that embryos living inside eggs of spotted and Jefferson salamanders experience higher mortality at lower (more acidic) pH values.  In a lab setting, no hatching occurred at pH values below 4.5.  Another study showed that natural pools that supported Jefferson salamanders had significantly higher (less acidic) pH values than pools that did not.  Other studies on spotted salamanders found that increased acidity can deform egg membranes and developing embryos and produce a decrease in hatching success and higher levels of larval mortality (Hulse, 2001).

Alteration of Substrate

The term substrate is used here to refer to the environment at the bottom of a seasonal pool.  Substrate requirements can be quite specific for seasonal pool animals.  The amount and composition of materials such as leaves, woody debris, and muck are important factors.  The substrate can be altered by activities such as dumping, dredging and filling.  Gradual non-point effects from runoff can also change substrate.  For example, surface runoff from agricultural fields carries fine sediments.  The silt gets deposited into nearby seasonal pools, eventually filling in the pool basin.

Loss of Vegetation

In-pool and upland vegetation are an important part of the seasonal pool habitat.  Removal or change in composition of vegetation in and around a pool affects which species can use the pool.  For species that lay their eggs in plant material, loss of vegetation eliminates egg-laying sites.  For species that lay their eggs in the water, removal of vegetation reduces shade.  This causes water temperatures and evaporation rates to increase.  These effects are particularly noticeable in small wetlands like seasonal pools.  One cause of mortality of odonate eggs is prolonged high temperatures or periods of drought (Brooks, 2003).

Climate Change

All aspects of life in a seasonal pool, from amphibian migration to egg and larval development to adult feeding, thermoregulation, and reproductive success, depend on certain environmental cues and conditions.   For example, the migration of salamanders to seasonal pools is in response to environmental cues.  One study showed that salamander migrations started when evening rains occurred with moderate temperatures over 44.6 F during the day and over 40 F at night (Hulse 2001).  In Pennsylvania, migrations can start as early as the end of February and as late as the beginning of April depending on local temperatures and rainfall.

While predictions of climate change do not agree on the details, evidence shows that changes in average yearly temperatures, minimum and maximum temperatures, rainfall amounts, and other environmental changes are occurring.  These changes are having an effect on wildlife, which respond more quickly to environmental changes than humans, who are able to create a favorable environment inside their home.

There is already evidence that the geographic ranges of plant and animals have been shifting in response to changes in climate.  Climate change is of increasing concern for species of special concern, especially in regard to species that are geographically restricted (Westfall and May 1996).

Global Warming – Early Warning Signs – References:  http://www.climatehotmap.org/references.html

U.S. Environmental Protection Agency:  Global Warming – Impacts Bibliography http://yosemite.epa.gov/oar/globalwarming.nsf/content/ImpactsImpactsBibliography.html