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Comparison of calculation
procedures of primary productivity by aquatic macrophytes in a shallow
tropical coastal lagoon
SANTOS1,
A. M. dos & ESTEVES1, F. de A.
1
Federal University of Rio de Janeiro, Institute of Biology - Department
of Ecology, Laboratory of Limnology, Ilha do Fundão, ZIP CODE
21.941-590, Rio de Janeiro, Brazil - P. Box 68.020, e-mail:
s-anderson2003@ig.com.br;
festeves@biologia.ufrj.br.
ABSTRACT:
This research aimed to compare some of the most used harvested and
demographic methods to estimate net primary productivity
(NPP)
of aquatic macrophytes, with a recently new proposed method. Samplings
were carried out biweekly from June/1997 to June/1998 in the littoral
zone of Cabiúnas coastal lagoon (22o
and 22o 30' S and 41o 30' and 42o W)
located on the north coast of the State of Rio de Janeiro. All stems of
an emergent aquatic macrophyte Eleocharis interstincta,
were marked with numbered plastic labels in three study plots
(0.0625 m2) and their heights measured. The
marked stems at each visit were defined as a cohort that was followed
until the death of all stems. Biomass samples harvested with a quadrat
from the same area (0.0625 m2)
were also obtained at each visit. Regression equations were used to
relate biomass with the length of the stems. A modified method of Summed
Shoot Maximum method was developed for plants with clonal growth and, it
takes account the biomass lost by density dependent factors. Of all the
harvested methods evaluated in this research, the method proposed by
Symbula & Day (1988)
was the most appropriate since that it underestimates the net annual
primary productivity (NAPP) by
only 3.6%. However, it demands efforts of calculating the detritus
decomposition rate. Demographic methods like the Allen’s Curve and
Summed Shoot Maximum had the best performance in estimating NAPP of
E. interstincta in tropical environments. The Allen’s Curve was more
useful to estimate NPP due its accuracy and, being less sensitive to
density dependent effects, although it underestimated NAPP by 18.9%.
Key-words:
aquatic macrophytes; coastal lagoons; Eleocharis interstincta;
methods; primary production. |
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