Using pigment level as a primary production indicator to assess organic matter variability in two linked wetland systems with different disturbance levels and its effect on secondary communities

Abstract

In a mesocosm experiment, pigment levels, organic matter and the structure of macroinvertebrate community were compared in two linked wetland systems encompassing fish-farm pond and natural reservoir. A stratified sampling design was applied, and treated experimental azoic sediment was placed in suspended boxes. The set of box was used to follow cumulative colonization period and single-month colonization approach for the study of macrofauna and biochemical parameters (organic matter, chlorophyll a and phaeopigments). There were significant differences between systems for the abiotic and community variables and polychaete diversity. Regarding the structure of macroinvertebrate community, the pond system appears to have higher abundance than the natural system. Monthly fluctuation was observed for abiotic variable and community variables in both systems, but polychaete diversity indices did not vary monthly in the pond system, which suggests that diversity indices in disturbed systems do not follow the organic matter variation. The correlation coefficient was also tested within abiotic and community variables for both systems. In the pond system, the organic matter was strongly related with chlorophyll a, carotenoid and phaeopigments. Due to the fact that the source of OM in the pond system is allochthonous, phaeopigments level is likely not to be directly affected by organic matter enrichment, but organic matter inputs create the high primary production and consequently affect the phaeopigments level. Polychaete abundance was positively correlated with the load in organic matter for both reservoir and pond systems, but the correlation coefficient between organic matter and polychaete diversity indices was higher in reservoir than in the pond system. The Moss index was used to indicate the production and degradation state of the systems, and it represented the natural reservoir in a higher production phase than the fish pond, and later on, the monthly variation of the percentage of degradation confirms the pond system in a more decayed state than the natural reservoir system. This study shows that although the organic matter and phaeopigments level tend to be higher in disturbed system, this does not necessarily favor all species, and more sensitive species are endangered of getting displaced by opportunistic species in systems with anthropogenic impact.