Net ecosystem exchange of carbon dioxide in a temperate poor fen: a comparison of automated and manual chamber techniques

We used five analytical approaches to compare net ecosystem exchange (NEE) of carbon dioxide (CO2) from automated and manual static chambers in a peatland, and found the methods comparable. Once per week we sampled manually from 10 collars with a closed chamber system using a LiCor 6200 portable photosynthesis system, and simulated four photosynthetically active radiation (PAR) levels using shrouds. Ten automated chambers sampled CO2 flux every 3 h with a LiCor 6252 infrared gas analyzer. Results of the five comparisons showed ( 1) NEE measurements made from May to August, 2001 by the manual and automated chambers had similar ranges: - 10.8 to 12.7 mu mol CO2 m(-2) s(-1) and - 17.2 to 13.1 mu mol CO2 m(-2) s(-1), respectively. ( 2) When sorted into four PAR regimes and adjusted for temperature ( respiration was measured under different temperature regimes), mean NEE did not differ significantly between the chambers ( p < 0.05). ( 3) Chambers were not significantly different in regression of ln( - respiration) on temperature. ( 4) But differences were found in the PAR vs. NEE relationship with manual chambers providing higher maximum gross photosynthesis estimates (GP(max)), and slower uptake of CO2 at low PAR ( a) even after temperature adjustment. ( 5) Due to the high variability in chamber characteristics, we developed an equation that includes foliar biomass, water table, temperature, and PAR, to more directly compare automated and manual NEE. Comparing fitted parameters did not identify new differences between the chambers. These complementary chamber techniques offer a unique opportunity to assess the variability and uncertainty in CO2 flux measurements.