Benthic insect assemblage abundance at two tropical headwater streams, La Selva Research Station, Costa Rica

Long-term monitoring of aquatic insects at two headwater streams at La Selva Research Station, Costa Rica. Samples were collected monthly from January 1997 to February 2004 and quarterly from May 2004 to September 2016. The sampling was paused in 2016, and then samples were collected monthly from July 2024 to June 2025. On each sampling date, three core samples (0.006 m² each) were collected from different locations within the 100 m study reach. The corer was inserted into the substrate to a depth of ~10 cm, cutting through leaf packs and debris. Samples were preserved in ~5% buffered formalin, and aquatic insects were subsequently sorted under a dissecting microscope at 40× magnification. Sampling and sample processing were performed by a single field technician during the entire study period. We used available keys for the Neotropics (Springer et al. 2010, Hamada et al. 2018). The STREAMS project is a long-term research program focused on the short- and long-term ecological effects of groundwater and surface-water interactions in neotropical streams at La Selva Research Station. La Selva is operated by the Organization for Tropical Studies (OTS). Streams at La Selva receive two types of groundwater: solute-rich groundwater associated with inter-basin geothermally-modified inputs and solute-poor groundwater originating with the local watershed. These groundwater inputs create riverscape heterogeneity in stream water chemistry, without differences in water temperature.