Abstract
Biomonitoring programs to access the ecological integrity of freshwaters tend to rely exclusively on structural parameters. Here we evaluated stream ecological integrity using (a) benthic macroinvertebrate derived metrics and a biotic index as measures of structural integrity and (b) oak litter decomposition and associated fungal sporulation rates as measures of functional integrity. The study was done at four sites (S1, S2, S3 and S4) along a downstream increasing phosphorus and habitat degradation gradient in a small stream. The biotic index, invertebrate metrics, invertebrate and fungal communities' structure and sporulation rates discriminated upstream and downstream sites. Decomposition rates classified sites S4 and S2 as having a compromised ecosystem functioning. Although both functional and structural approaches gave the same results for the most impacted site (S4), they were complementary for moderately impacted sites (S2 and S3), and we therefore support the need for incorporating functional measures in evaluations of stream ecological integrity.
Highlights
High human densities in coastal zones with large urban and industrial settlements and intensive agriculture causes great pressure on surface water bodies and consequent deterioration of water quality (Ferreira et al, 2004; Martınez Mas et al, 2004) and changes in riparian vegetation (Urban et al, 2006; Wooster and DeBano, 2006)
The Iberian Biological Monitoring Working Party (IBMWP) biotic index indicated that sites S1 and S2 had very good water quality, site S3 had good water quality and site S4 had moderate water quality
These alterations were reflected in the IHF and QBR indices scores, which decreased from site S1 to S4, identifying a downstream degradation gradient. The effect of these differences among sites in the stream ecological integrity was evaluated by the assessment of both structural integrity, by means of a biotic index and benthic macroinvertebrates derived metrics, and functional integrity, by the use of litter decomposition rates
Summary
High human densities in coastal zones with large urban and industrial settlements and intensive agriculture causes great pressure on surface water bodies and consequent deterioration of water quality (Ferreira et al, 2004; Martınez Mas et al, 2004) and changes in riparian vegetation (Urban et al, 2006; Wooster and DeBano, 2006). Castela et al / Environmental Pollution 153 (2008) 440e449 litter mass loss rates with increasing dissolved nutrients, resulting from both cultural activities (Suberkropp and Chauvet, 1995; Niyogi et al, 2003; Gulis et al, 2006) and experimental enrichment (Elwood et al, 1981; Gulis and Suberkropp, 2003a; Ferreira et al, 2006) This stimulatory effect is mostly carried out through the stimulation of the activity of aquatic hyphomycetes (Gulis and Suberkropp, 2003a; Ferreira et al, 2006), which are the major microbial players in litter processing (Pascoal and Cassio, 2004). This co variation of factors can create confounding effects in the use of litter decomposition to assess ecosystem functional integrity in lowland streams (Niyogi et al, 2003; Hagen et al, 2006)
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