Characterizing a tropical dry forest stream: Parallels and deviations from tropical streams of the Luquillo Mountains and implications for the STREON experiment

Decades of research at the Luquillo LTER site in Puerto Rico has shed light on ecosystem dynamics important for understanding the structure and function of subtropical wet forest ecosystems. Research efforts have included ecosystem response to disturbance and land use change, community and system response to migratory barriers, and how each of these controls the ecosystem services available to a densely populated island landscape. Despite these advances in tropical research, there remains a lack of data describing tropical dry forests, most notably the streams that drain them. Our recent work within the Luquillo LTER attempts to bring these systems into our research focus because not only are they susceptible to the same threats as tropical wet forest streams (e.g. alterations to nutrient cycling and biodiversity loss), but they likely also represent specificity in their ecology and response to land use and climate change within the tropical biome.

The Rio Cupeyes is a dry forest stream in SW Puerto Rico, and has been identified as the STREON site for the Atlantic Neotropical domain of NEON. As a result of our lack of baseline data and understanding of this stream type, we attempt to characterize the ecology of the Rio Cupeyes in order to answer the following research questions:

1. How do tropical dry forest streams agree with or deviate from known ecological drivers and processes found in the tropical wet forest streams of the Luquillo Mountains?
2. How does a complex landscape (i.e. patchiness in basin geology, multiple land uses within the watershed) contribute to our ability to scale process rates in streams?
   1. Do tributaries to the Rio Cupeyes that drain different landscapes create hotspots in ecosystem processes (i.e. nutrient uptake and metabolism)?

In order to address these questions, our ongoing study has employed synoptic sampling for a suite of physicochemical and biological variables, and also quantified process rates upstream and downstream of tributary junctions. These results have important implications for our ability to scale processes in streams and, specifically in the Rio Cupeyes, to interpret results from the reach-scale STREON experiment.