# Integrative Assessment of Sediment Quality in the Sao Francisco River (Mina Gerais, Brazil)
## 3 Results
### Benthic Community Structure  
Concerning benthic community structure analysis, a total of 3915 individuals were identified in the benthic fauna in sediments from the five sampling stations and along the river. They were classified into 60 species (1 hirudinean, 12 oligochaetes, 1 crustacean, 43 insects, 3 mollusks, and 1 nematode), and 4 species were not fully identified (17 _hirudinean_) annelids, 14 _conchostracan_ crustaceans, _2 dryiopidae_ beetles, and 63 individuals classified as _hematode_). Figure 2 shows a relative abundance of different taxonomic groups (hirudinea, oligochaeta, mollusca, and nematoda) observed at each sampling station. Therefore, the benthic community at BG4 clearly differed from the rest of the stations; it was dominated by nematodes (around 68%), unlike the communities from the rest of the stations, where insects were the dominant group (60-77%). Relative nematode abundance \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **SF1** & **BG4** & **SF2** & **SF3** & **ZM2** \\ \hline Fines (\%) & 7.37 & 50.16 & 26.28 & 37.82 & 27.81 \\ TOC (\(\mu\)g/g) & 20,970 & 10,590 & 11,960 & 12,430 & 17,590 \\ Nitrate (\(\mu\)g/L) & 83.46 & 617.32 & 50.87 & 24.52 & 35.28 \\ Ammonium (\(\mu\)g/L) & 1511 & 8760 & 1210 & 1432 & 1424 \\ Ammonia (\(\mu\)g/L) & 33.99 & 35.18 & 4.86 & 8.65 & 8.59 \\ Ammoniacal nitrogen (\(\mu\)g/L) & 1545 & 8795 & 1215 & 1441 & 1432 \\ SEM-AVS (\(\mu\)mol/g) & 58.7 & 3687 & 2720 & 2947 & 96.1 \\ Al (\(\mu\)g/g) & 2197 & 3993 & 2596 & 4558 & 32,767 \\ As (\(\mu\)g/g) & 5.51 & 1.36 & 1.48 & 2.56 & 8.83 \\ Co (\(\mu\)g/g) & 6.83 & 3.48 & 8.36 & 8.27 & 5.91 \\ Cr (\(\mu\)g/g) & 15.78 & 10.55 & 14.63 & 11.99 & 12.50 \\ Cu (\(\mu\)g/g) & 4.76 & 14.50 & 21.19 & 43.64 & 16.41 \\ Fe (\(\mu\)g/g) & 22,017 & 13,059 & 8030 & 14154 & 12,307 \\ Ni (\(\mu\)g/g) & 5.15 & 3.56 & 5.64 & 4.56 & 4.71 \\ Pb (\(\mu\)g/g) & 4.28 & 14.5 & 36.7 & 132 & 15.3 \\ Zn (\(\mu\)g/g) & 25.1 & 958 & 1239 & 3676 & 639 \\ Hg (\(\mu\)g/g) & 0.02 & 0.02 & 0.09 & 0.17 & 0.12 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Summarized results of physicochemical parameters analyzed in sediments from the San Francisco River (SFR): percentage of fines, total organic content (TOC), nitrogen species (nitrate, ammonium, ammonia, and ammoniacal nitrogen), SEM-AVSs, and metal(loid) concentrations (Al, As, Co, Cr, Cu, Fe, Ni, Pb, Zn, and Hg). varied from 5% (at the SF1 station) to 0% (at the SF3 and ZM2 stations), and relative insect abundance was 2% at the BG4 station. The univariate metrics of the community structure for all the sampling stations are shown in Table 2. According to the BMWP results, all stations showed a bad ecological status. The BMWP score showed significant (\(p<0.05\)) differences among sampling sites (BG4 and SF2), close to the affluent, and the control site (SF1). As expected, the SF1 site presented the best BMWP results, which were still considered 'bad' but just at the limit between degraded and regular. Conversely, BG4 showed the lowest BMWP score, defined by the abundance, number of individuals, richness, and diversity values, and the SF2 station showed the lowest Pielou evenness values. The benthic community structure at the SF2 station showed the highest Pielou evenness, while BG4 showed the lowest values. Figure 3 shows the results of clustering the different stations using the Bray-Curtis index for abundance similarities. Cluster analysis distinguished three main groups of sites (BG4, SF1, and the rest of the sites), which were considered to represent different communities on the basis of their geometric means. As mentioned above, BG4 was clearly different from the other stations, and the control site (SF1) was different from the other stations but closer than BG4. The SF2, SF3, and ZM2 stations showed similar communities among them.