Organic Matter Dynamics in Tropical Island Streams: Allochthonous Inputs, Particulate Exports, and Benthic Standing Stocks

Fifteen years ago a special issue of JNABS highlighted the ecological relevance of organic matter budgets in streams. Consequently, the authors contributing to the issue illustrated the benefits of long-term assessments and the importance of these contributions to the conservation and management of lotic systems. Although such studies have increased throughout the years, tropical streams remain under-represented in this category. As part of an ongoing long-term study assessing organic matter dynamics of tropical island streams we studied allochthonous litter inputs, benthic standing stocks and fine particulate exports in two headwater reaches in the Luquillo Experimental Forest. Allochthonous inputs measured as direct litterfall ranged from 4.5±0.7 to 5.4±0.6 g m-2 d-1 or 1,731 to 1,977 g m-2 yr-1. Mean monthly standing crop ranged from 28.4±4.6 to 40.4±11.5 g/m2 as coarse (>1mm); 6.8±1.6 to 13.9±1.7 g/m2 as fine (<1mm and >250µm); and 42.2±7.0 to 115.5±17.8 g/m2 as very fine (<250µm) benthic organic matter. Fine particulate exports (seston) ranged from 302,190±33,232 to 833,546±391,274 kg/yr. This study represents a continuous effort to understand the dynamics of tropical streams in relation to their temperate counterparts.