Chlorophyll, primary productivity, and respiration in a lowland Costa Rican stream

Abstract

In situ nutrient enrichrnent bioassays were conducted in open and closed canopy sites of a third order stream draining primary rain forest and abandoned pasture land in northern Costa Rica. Artificial sand+agar substrata spiked with nitrogen, phosphorus, N+P, molybdenum, N+Mo, and a mix of manganese, zinc, and molybdenum were incubated for 15 and 21 days. The colonizing periphyton in the forested streamsites (4 mi chloroph:lll a m"2) showed extreme light limitation when compared with the open, pasture areas (14-45 mg chlorophyll a m- ) after 15 days of colonization. Chlorophyll a concentrations, oxygen production and consumption, and assimilation ratios did not show a significant nutrient addition effect indicating that ambient nutrient concentrations are at saturation levels for periphyton growth. Ten-to-fifteen day old periphyton was autotrophic (P!R>l) on al! trealrnents. Compared with other tropical streams, similar chlofophyll but lower Tates of primary productivity «300 mg 02 m-2 h-l) and respiratíon (70 mg 02 m-2 h-l) occurred in this stream.