Benthic community structure

Day, C. Dutka, B.J. Kwan, K.K. Batista, N. Reynoldson, T.B. Metcalfe-Smith, J.L. Correlations between sohd-phase microbial screening assays, whole-sediment toxicity tests with macroinvertebrates and in situ benthic community structure. J. Great Lakes Res. 1995, 21, 192-206. 

The purpose of this paper is to describe the SED-TOX index for the toxicity assessment of contaminated solid matrices, particularly sediments, demonstrate its discriminative potential, and show its correlation with chemical analyses derived data and indices of benthic community structure. 

Finally, as for all single and dimensionless indices that integrate a number of different measurements, there is a loss of information in the final score. This again argues for the need to consider, in the decision-making process, other parameters of sediment quality such as benthic community structure and sediment chemistry. 

It is assumed that the measurement endpoints for biological effects (toxicity tests, benthic community structure) are appropriate relative to the assessment endpoints. 

Maintenance of soft-bottom benthic invertebrate communities capable of supporting local fish populations. COPC concentrations in sediment will not result in toxicity to the soft-bottom benthic community. Assess the effect of COPCs in sediment on the survival of two amphipod species (Eohaustorius estuarius and Rhepoxynius abronius). Assess the effect of COPCs in sediment on survival and growth of the polychaete, Neanthes arenaceodentata. Assess in situ changes in benthic community structure (diversity and abundance). 

V. Algal Chemical Defenses and Benthic Community Structure.247... 

V. ALGAL CHEMICAL DEFENSES AND BENTHIC COMMUNITY STRUCTURE... 

To illustrate the WoE approach we will apply it to the evaluation of toxicity as a cause or risk factor in the alteration of benthic community structure in a waterway (Figure 12.11). Extensive data on chemical concentrations in sediments are obtained at the site under investigation (A). Data on the chemical contaminants are matched with laboratory tests of sediment toxicity to the chemicals (B). A comparison of the chemical concentrations to the toxicity data indicates that the materials are toxic under laboratory conditions (C). A hypothesis is then generated that identifies the sediment under consideration as likely to be toxic. Sediment bioassays of the sediment can confirm the hypothesis (D). Since the assessment endpoint is the preservation of benthos, measurements are made of the benthic community structure in the region (E). Chemical concentrations and toxicity results are also compared to measures of benthic community structure. Chemicals that are positively associated... 

Although bottom-water masses are relatively old in the NEPAP, bottom-water oxygen concentrations remain well above 2mil-1 and hence they probably do not influence benthic community structure (Levin Gage, 1998). In the eastern tropical Pacific, oxygen-minimum zones appear in mid-water (100-1000m) due to intense water column decomposition but they do not extend to abyssal depths (Wishner etal., 1990). 

In contrast, benthic community structure and processes in the NEPAP region are likely to be both extremely sensitive to, and have very little resistance to, physical perturbations (e.g. mining disturbance). This is because the natural ecosystem is relatively very stable (compared to virtually all other ecosystems), most animals are small and/or very delicately constructed, and critical habitat structure for the entire benthic fauna is concentrated within a few centimeters of the sediment-water interface. Thus, it would require very little physical energy to disrupt the animals and the thin veneer of surface sediments that define this ecosystem. The extremely low sediment accumulation rates, biotur-bation rates, nodule growth rates and macrofaunal recolonization rates of the NEPAP seafloor ecosystem, compared to other seafloor habitats (Smith Demopoulos, 2003), suggest that recovery from physical disturbance is likely to be extremely slow relative to other ecosystems. 

Biological/chemical approach. In a comprehensive sediment-assessment approach, five basic components should be considered (Krantzberg et al., 2000) i) benthic community structure, ii) laboratory bioassays for evaluating the toxicity of in-place pollutants, iii) bioaccumulation information, iv) knowledge of site stability, and v) physico-chemical sediment properties. 

This part of the Danube also showed the unfavourable effects of pollution on the structure of river bottom fauna. The leakage of pollutants into the canal had a lethal effect on the biota. Downstream from the canal, at location 11, changes in the benthic community structure were noted possibly caused by pollutants. The macrozoobenthos community in this site was considerably less dense with as much as a 95.7% deaease in the abundance of T. tubifex compared to the control sample. 

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