Longitudinal Patterns in Stream Channel Geomorphology and Aquatic Habitat in the Luquillo Mountains of Puerto Rico

Project Description: 

The hydrologic, geomorphic, and ecological dynamics of tropical montane
streams are poorly understood in comparison to many temperate and/or alluvial rivers.
Yet as the threat to tropical freshwater environments increases, information on the
dynamics of relatively pristine streams is important for understanding landscape
evolution, managing and conserving natural resources, and implementing stream
restoration. This dissertation characterizes the geomorphology and hydrology of five
adjacent watersheds draining the Luquillo Experimental Forest (LEF) in northeastern
Puerto Rico, and discusses implications on aquatic habitat. I performed several
interrelated studies, including: 1) formulating a geographic information systems (GIS)
framework to estimate hydrologic parameters from topographic information and
hydrologic records, 2) developing a method to determine active stream channel
boundaries (“bankfull” stage) that allows for comparison of channel geometry on the
basis of flow-frequency, 3) decoupling the relative influences of lithologic and hydraulic
controls on channel morphology using an extensive field-based stream survey and
analysis of stream profiles, channel geometry, and sediment dynamics, 4) linking
network- and pool-scale geofluvial dynamics to the abundance of migratory fish and
shrimp through a collaborative analysis combining geomorphic surveys and aquatic
faunal sampling. This research indicates that these streams have some properties
resembling both temperate montane and alluvial rivers. Similar to low-gradient rivers
where floodplains mark channel boundaries, the active channel stage in these streams is
defined by the incipient presence of woody vegetation and soil development. Systematic
basin-scale geomorphic patterns are well-developed despite apparent non-fluvial and
lithologic control on local channel morphology. This implies that strong fluvial forces are
sufficient to override channel boundary resistance; a feature common in self-forming
“threshold” alluvial channels. Migratory aquatic fauna abundances are influenced by a
variety of geomorphic factors such as barrier waterfalls and suitable headwater habitat,
and are consequently highly variable and patchy. These results stand in contrast to the
notion that aquatic communities mirror systematic geomorphic gradients, but rather
acknowledges the influences of multiscale geomorphic processes. Ultimately, this
research provides baseline information on physical and biological processes in relatively
unaltered tropical streams and can be used to inform further studies that document human
interactions with stream networks.

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Contact Information
Person(s) Completing This Form: 
Miguel Leon
Andrew Pike Fred N Scatena
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