In support of Maryland's efforts
to develop statewide water-quality management
plans, a statistical analysis was performed
to identify a set of representative and relatively
homogeneous areas referred to as Hydrochemical
Response Units (HRUs). The State intends to
select representative areas within each hydrochemical
response unit for monitoring and model development,
and then apply the model to the entire unit.
To identify hydrochemical response units, cluster
analysis was applied to 1,136 digitally defined
watershed units. Basin characteristics including
land cover, soil type, slope, and geology were
determined for each watershed unit and a clustering
algorithm was applied to the data sets. A total
of 11 hydrochemical response units were identified
by the analysis. Major features that were important
in distinguishing different areas of the state
include: 1) upland and lowland Coastal Plain
settings, 2) igneous, shale, and carbonate geology;
and 3) urban land cover. The hydrochemical response
units described in this report are considered
to be an initial classification of watersheds
in Maryland that can be refined as geographic
data sets are improved and additional hydrologic
data are collected.