Ecosystem metabolism in tropical streams and rivers: a review and synthesis

Ecosystem metabolism of freshwater ecosystems has been studied for several decades, with theory and synthesis largely derived from temperate streams and rivers in North America and Europe. Advances in sensor technology and modeling have opened a wider range of streams to be included to test theories beyond temperate streams. In this paper, we review and synthesize ecosystem metabolism data from tropical streams and rivers to determine to what extent the constraints of metabolism measured in temperate streams are similar in tropical streams. We compiled 202 measurements of gross primary productivity (GPP) and ecosystem respiration (ER) from 83 tropical streams spanning 22.2 degrees S to 18.4 degrees N. Overall, tropical streams were heterotrophic (ER > GPP), with GPP ranging from 0.01 to 11.7 g O-2 m(-2) d(-1) and ER ranging from -0.2 to -42.1 g O-2 m(-2) d(-1), similar on average to rates reviewed from temperate streams, but with higher maximum ER in tropical streams. Gross primary productivity increased with watershed area; a result also observed in temperate streams. ER decreased with elevated phosphorus and higher annual rainfall. We constructed a structural equation model that explained greater variation of ER (74%) than GPP (26%), and reflects similar drivers, such as land-use and watershed area, as in temperate streams. We conclude that tropical stream ecosystem metabolism has similar drivers as temperate streams, and a warmer and wetter climate and human use of tropical lands will influence metabolic rates in streams.

Automated summary

In this paper, ecosystem metabolism data from tropical streams and rivers were reviewed to determine the similarities and differences with temperate streams. The study found that tropical streams exhibit similar metabolic constraints and drivers as temperate streams, with factors such as watershed area and land use influencing rates of gross primary productivity and ecosystem respiration. A structural equation model explained greater variation in ecosystem respiration than gross primary productivity, highlighting the key role of environmental factors in shaping metabolic rates in tropical streams.