The Issues

Assessment of Stressor Impacts to the Estuaries and Coast

To ensure the new CCMP is based on sound science, the MBNEP Science Advisory Committee determined what areas of our coastal environment are most stressed adn from what cause(s). Over thirty scientists and resource managers from various disciplines evaluated ecosystem services provided by a set of coastal habitats to determine levels of impact from a suite of stressors.

The Coastal Habitats

Alabama’s extraordinary species diversity is a product of the mosaic of distinct coastal habitats  characterizing our region:  They include the remnants of vast long leaf pine forests once dominating our landscape to the sea grass beds and oyster reefs fringing our coastlines. The mixture of habitats found here provides ecosystem services which support more different species than found in any state east of the Mississippi River.

The Ecosystem Services

Ecosystem services are the processes by which the environment produces the resources we value.  The most obvious examples are the services provided by plants - they use the energy of the sun to convert carbon dioxide to the food we eat and the oxygen we breathe.  They stabilize soil and prevent erosion and provide habitat for the fish, birds, and wildlife we value.  Other examples are less obvious.  Wetlands reduce excess nutrients, buffer shorelines from the erosive energy of storms, promote species diversity, and contribute to groundwater replenishment.  While we often take these natural processes for granted, ecosystem services have monetary value which would become more apparent if it became necessary to replace them.

The Environmental Stressors

Environmental stressors are factors or phenomena negatively impacting habitats, reducing their ability to provide ecosystem services.  Some stressors, like hurricanes, droughts, and cold snaps may be naturally occurring and independent of human activity.  The stressors evaluated by MBNEP’s Science Advisory Committee are those related to anthropogenic or, human-caused, factors.

The Methodology

Understanding which of the different coastal habitats providing critical ecosystem services most threatened by anthropogenically-, or human-, related stressors was a target of MBNEP’s Science Advisory Committee.  In June, 2011 over 30 scientists and ecologists were recruited to evaluate the impact of each of a suite of common anthropogenic stressors on provision of important ecosystem services by the various coastal habitat types.  For each of the 10 coastal habitat types, each of 13 stressors was rated numerically between zero, for those having absolutely no negative impact, and three for those having the most direct negative impact for each of the 14 recognized ecosystem services.  All this information was compiled onto a spreadsheet containing a total of 1,820 cells.  In cases where a stressor was unrelated to the provision of a service by a habitat, or where an evaluator felt unqualified to judge, respondents were instructed to leave cells blank.  Any blank cells were not incorporated into the analysis. 

Data from the respondents were combined and analyzed to provide average scores for each stressor/ecosystem service/coastal habitat type cell.  With subsequent concern some averages might represent a small number of responses, the standard deviation of each determined average and number of responses were added and reviewed.  This information provided an indication of the level of confidence and the variability for an average response.  Where cells contained less than 7 responses for averaging purposes, MBNEP recruited additional respondents with that type of expertise to round out the averages. 

The SAC determined any tabulated value of 2.2 or higher indicated significant stress.  Response frequency histograms were subsequently generated to tease the validity of cells calculated on a small number of responses..  Where those occurred, the SAC sought input from additional experts to resolve questions with confidence.

From this effort, three habitat types - freshwater wetlands, streams, rivers and riparian buffers, and intertidal marshes and flats - were identified as most stressed from dredging and filling, fragmentation, and sedimentation, all related to land use change.  As you can see from the accompanying table, these three habitat types and the ecosystem services they provide are related to several, if not all, of the things people value about living in coastal Alabama.