Additional Information Concerning DEP’s Wetlands Data

 

The impracticality of site-visiting all 5.3 million acres of land in New Jersey makes aerial photo interpretation an extremely useful tool in natural resource management, but some of the information required to make wetlands determinations for jurisdictional purposes requires on-site investigations.  DEP continues to reduce data disparities between the permitting program and the land use/land cover mapping project by improving both the mapping process and the permit and enforcement tracking process.  However, any deviations in these wetlands data sets are due to fundamental differences in the methodologies and purposes of these two processes.  When navigating or analyzing the land use/land cover data sets, consider the following:

 

• The land use/land cover mapped wetlands data is based upon interpretation of aerial photography, while the permitting program data are generated by on-site inspections.  Again, DEP cannot investigate each and every acre in the state, but some of the information required to make wetlands determinations for jurisdictional purposes requires on-site investigations—soil borings, depth to ground water, and other determinations obviously cannot be generated through photographic interpretation.  Soils maps and other types of existing collateral data are used whenever available to assist in the land use/land cover mapping process, but this information can never replace the precision of data gained from on-site investigations. 

 

• Classification may have changed, even if ground conditions have not.  The photos used to generate the land use/land cover data represent a fixed point in time, so the ground conditions captured in the photos—particularly the presence or absence of standing water or soil saturation, which are key photographic wetland indicators—may or may not be typical of the area being mapped over most years.  Consequently, there are areas mapped as wetlands in the land use/land cover data which will be determined not to be wetlands after all when an on-site jurisdictional determination is undertaken.  Due to the complex nature of wetlands, they are the most difficult land cover category to map from aerial photography. 

 

• Classification may have changed as a result of improved data from on-site investigation.  Development of certain sites can appear as a wetlands loss from the land use/land cover data, but it was determined through on-site field inspections conducted prior to development that these areas previously classified as disturbed wetlands were not, in fact, wetlands.  The land use/land cover mapped data include both naturally vegetated wetlands and several classes of disturbed wetlands.  Although these disturbed wetlands areas represent potential wetlands sites based on image saturation, location, and secondary data such as soils maps, they generally do not support typical wetlands vegetation or provide typical wetlands functions.

 

• Wetlands do transition naturally to other land use types, such as open water.  The land use/ land cover data set shows wetlands converting to water or barren land type which includes beaches, much of which is due to natural processes. The total wetlands loss number reported by the land use/land cover data reflects these natural changes, while natural wetlands changes do not appear in the permit data.

 

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