The nitrogen dynamics of Deer Cave, Sarawak, and the role of bat caves as biogeochemical sinks in Tropical Moist Forests

A better understanding of the role of bat caves as nitrogen sinks in tropical moist forest ecosystems can be expected to shed light on regional and spatial variability in nutrient recycling studies. We measured the nitrogen flux (in air and water) associated with a very large Chaerephon plicata bat colony in Deer Cave, Borneo, in the process generating a new, quantitative, estimate of the total bat population (774,828 ±48,320), and the first detailed modelling of an ammonia plume in a cave. Long-term storage of N does not occur in this wet cave. Our final budget numbers indicate that, of the daily input of N (i.e., ecologically-useful fixed-N in guano) to this cave, ammonia production is minor (and most of it is exported in water rather than air). The conclusion is that the export budget is dominated (perhaps as large as 94.4%) by microbial denitrification of fixed-N to diatomic N exported in air. Deer Cave thus acts as a nitrogen sink, potentially removing up to 39% of the ecologically-useful fixed-N from the total forest nitrogen budget over an area of hundreds of square kilometers.