| In order to explore the impact of the change of the dominant leaf litter source from broad leaf trees to a bamboo tree of Phyllostachys heterocycla on headwater stream ecosystem process and associated benthic macroinvertebrates, we analysed the leaf physical and chemical characters of Phyllostachys heterocycla, and two broad leaves of Lithocarpus glabra and Lindera glauca, and evaluated the breakdown rates of the above three litter and two mixture litter in coarse-mesh litter bags in a headwater stream of Xitiaoxi watershed, Zhejiang province, China. The concentrations of nitrogen concentration, phosphorus concentration and the thickness among the three categories of leaves varied significantly (P<0.05). The nitrogen concentrationof bamboo tree leaf (30.23g-Kg-’) was much higher than those of L. glabra (20.98g-Kg-1) and L. glauca (9.69g-Kg-1). Moreover, the leaves of Phyllostachys heterocycla (k=0.00592d-1) decomposed faster than those of Lithocarpus glabra (0.00297d-1) and Lindera glauca(0.00212d-1), however, the observed breakdwon rates of L. Glabra-L. Glauca (k=0.00531d-1) and L. Glabr-P. heterocycla (k=0.00586d-1) were significantly higher than predicted (P<0.05). No statistical differences were observed in macroinvertebrates abundance and biomass (P>0.05) among the three leaf types, however, the macroinvertebrate abundance and biomass varied significantly (P<0.05) during the sampling period. Proportions of the functional feeding groups showed that shredders was the most abundant group, accounting for49.7%of individuals, indicating it was an important component of fauna associated with litter breakdown. The dominant shredder taxon was Lepidostoma sp., which constructs nestsby broadleaves, accounting for37%of the total macroinvertebrate individuals. Because bamboo leaves are narrower, with higher concentrations of nitrogen and phosphorus, and defoliation occurs every two years. Furthermore, bamboo leaves can relatively accelerated the decomposition rates of the other two leaf species when mixtured. We considered that when the leaf litter source of headwater streams dominated by bamboo leaf, it might change the concentrations of nitrogen and phosphorus in stream water, the annual amount of leaf litter into stream, the retaining time, and the macrobenthos community structure.The selection of proper macroinvertebrate metrics was a key step in the successful construction of benthic-index of biotic integrity (B-IBI). In the context of lack of sufficient reference sites, the responses of biotic metrics to the stress gradients have been proved crucially important in metrics selection. We explored this using a data set (twenty-two sampling sites), where water environmental parameters, habitat quality index (HQI) and zoobenthos were measured and sampled using standardized methodology in the winter dry season (January,2010) within the Qinjiang Rvier basin, Guangxi. Water quality stress gradients were synthesized using principle component analysis. Twelve out of the38candidate metrics were excluded because of high co-linearity (|r|>0.80, P<0.05) with others. Multiple regression analysis of the rest twenty-six metrics, environmental gradients (PCI and PCII) and habitat quality index showed that thirteen macroinvertebrate metrics were significantly correlated (P<0.05) with the environmental stressors (PCs and HQI). Eight of these metrics, family richness, Ephemeroptera richness, Coleoptera richness; Ephemeroptera, Plecoptera and Trichoptera (EPT) abundance, proportion of dominant species; proportion of predators; Shannon-Weaver diversity index for genus; and Biotic index (BI), satisfied the selection criteria (e.g., operational simplicity) and are thus candidates for developing a multimetric system to assess river health in our study region. We suggest that the response of metrics to environmental gradient is a good alternative for the construction of benthic-index of biotic integrity in the context of no sufficient reference sites. |
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