# Risk Assessment of a Coastal Ecosystem from SW Spain
## 3 Results and Discussion
### Tabular Matrix  
Statistically significant differences (\(p<0.05\)) between the reference treatment (RSP sediment, pH 8.0--no CO\({}_{2}\) added) and the other treatments and stations are presented as showing a positive response in contamination, toxicity, integrity, or bioaccumulation (Table 3).  
In general, the metal concentration in sediment was not significantly affected by acidification for RSP sediment. Nevertheless, significant differences (\(p<0.05\)) were found between the metal concentration in the TRO and the control. These results were expected since the metal contamination in the TRO station was higher than in the RSP station. These results agreed with those reported by [16], which characterized the RSP as a low metal-concentration station and, the TRO as a station with moderate metal concentration. On the other hand, the results obtained in the mobility index showed significant differences (\(p<0.05\)) between the reference case and pH 6.5 and 6.0 for the RSP and starting at pH 7.5 for the TRO. These findings indicated that acidification could increase the mobility of metals from the sediment samples to the water column, which might cause toxic effects on marine organisms. Previous studies reported the pH as a variable that mostly might influence the availability of elements from sediments [17]. Furthermore, it can be suggested that the  
\begin{table}
\begin{tabular}{l l l l l l l} \hline \hline
**Cases** & **Metals** & \multicolumn{3}{c}{**Toxicity**} & \multicolumn{3}{c}{**Bioaccumulation**} & **Benthic** \\ \cline{2-7}
**Site, pH Treatment** & **Sediment** & **Mobility** & **Acute** & **Chronic** & & \\ \hline RSP, pH 8.0 & – & – & – & – & – & – \\ RSP, pH 7.5 & – & – & – & +/\(-\) & – & – \\ RSP, pH 7.0 & – & – & + & + & +/\(-\) & +/\(-\) \\ RSP, pH 6.5 & – & + & + & + & + & +/\(-\) \\ RSP, pH 6.0 & – & + & + & + & + & + \\ \hline TRO, pH 8.0 & + & +/\(-\) & +/\(-\) & +/\(-\) & +/\(-\) & + \\ TRO, pH 7.5 & + & + & +/\(-\) & + & +/\(-\) & + \\ TRO, pH 7.0 & + & + & + & + & +/\(-\) & + \\ TRO, pH 6.5 & + & + & + & + & + & + \\ TRO, pH 6.0 & + & + & + & + & + & + \\ \hline \hline \end{tabular}
\end{table}
Table 3: Matrix results for the different pH treatments used and sediment samples, representing significant differences (\(p<0.05\)) were found when compared to the reference case (RSP, pH 8.0). Responses are shown as either positive (+), negative (\(-\)), and (+/\(-\)) when the result was close to being positive, but not, showed a significant difference.  
significant difference found in the toxicity indexes at pH 7.0, using the RSP sediment, could also be related to the increase in metal mobility. Nevertheless, a significant toxic effect at pH 7.5 was observed, and, according with previous results, showed significant effects on the larval development inhibition of mussels and amphipods, and clam mortalities associated with acidification [7; 22; 34; 35].  
The results of the integrity of the benthic community showed significant (\(p<0.05\)) differences for all treatments tested using the TRO sediment. These results were expected since the TRO sediment sample presented higher contamination than the RSP sample and the lowest value of total abundance of macrobethic found in the study. On the other hand, the results of the bioaccumulation of metals in the tissues of mussels showed a significant (\(p<0.05\)) increase in the concentration of metals at pH 6.5 for both sediment samples.