## 3 Results and Discussion
### Influence of Grain Size Distribution, Land Use, and Total Organic Carbon on Heavy Metal Content
Land use is one of the main factors governing the accumulation of heavy metals in sediments; indeed, previous research has shown that their increase is related to predominantly urban land use [35; 59; 60]. In the examined scenario, regarding the correlation between land use and the presence of heavy metals in the analyzed sampling points, the distribution of land use was evaluated for each sub-basin subtended by the closure section represented by each sampling point. For the San Giuliano reservoir (Table 13), almost all the area of each sub-basin is characterized by a land use referred to as 'non-irrigated arable land,' for an average percentage of 95%, which reaches 99% in the case of the sub-basin subtended by sampling station SG_S11. Other land-use categories are limited to small percentages and irrelevant to the assessments. Similarly, in the case of the Camastra reservoir (Table 14), land use is predominantly characterized by 'forest', which in the sub-basins covers an area of between 20% and 100% of the total surface area, and by 'non-irrigated arable land,' which is not present everywhere, with percentages averaging 20%. Urban-type land use is only found in the sub-basins belonging to the closure sections C_B1, C_B3, and C_B4, although the percentage of total area covered is less than 1%. On average, although only in some sub-basins considered, agricultural areas currently cover 15% of the total area are essential. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multirow{2}{*}{**Forest \%**} & \multirow{2}{*}{**Urban \%**} & \multicolumn{2}{c}{**Non-Irrigated**} & \multirow{2}{*}{**Farm Areas \%**} & \multirow{2}{*}{**Water Bodies \%**} & \multirow{2}{*}{**Other Areas \%**} \\  & & & & **Arable Land \%** & & \\ \hline SG\_S1 & 3.45 & 0.12 & 94.88 & 0.41 & 1.02 & 0.12 \\ SG\_S2 & 3.45 & 0.12 & 94.88 & 0.41 & 1.02 & 0.12 \\ SG\_S3 & 3.41 & 0.19 & 94.99 & 0.27 & 1.03 & 0.12 \\ SG\_S4 & 3.41 & 0.19 & 94.99 & 0.27 & 1.03 & 0.12 \\ SG\_S5 & 3.41 & 0.19 & 94.99 & 0.27 & 1.03 & 0.12 \\ SG\_S6 & 3.38 & 0.19 & 95.01 & 0.27 & 1.03 & 0.12 \\ SG\_S7 & 3.38 & 0.19 & 95.01 & 0.27 & 1.03 & 0.12 \\ SG\_S8 & 3.41 & 0.19 & 95.83 & 0.28 & 0.17 & 0.12 \\ SG\_S9 & 3.38 & 0.15 & 95.04 & 0.27 & 1.03 & 0.12 \\ SG\_S10 & 3.45 & 0.12 & 94.88 & 0.41 & 1.02 & 0.12 \\ SG\_S11 & 0.22 & 0.01 & 99.47 & 0.30 & 0.00 & 0.00 \\ SG\_S12 & 3.40 & 0.12 & 94.93 & 0.41 & 0.00 & 0.12 \\ \hline \hline \end{tabular}
\end{table} 
Table 13: Land use percentage of the sub-basin for each San Giuliano reservoir sampling site. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multirow{2}{*}{**Forest \%**} & \multirow{2}{*}{**Urban \%**} & \multicolumn{2}{c}{**Non-Irrigated**} & \multirow{2}{*}{**Farm Areas \%**} & \multirow{2}{*}{**Water Bodies \%**} & \multirow{2}{*}{**Other Areas \%**} \\  & & & & **Arable Land \%** & & \\ \hline C\_B1 & 64.88 & 0.41 & 19.14 & 14.97 & 0.57 & 0.00 \\ C\_B2 & 98.22 & 0.00 & 0.00 & 0.00 & 1.77 & 0.00 \\ C\_B3 & 64.81 & 0.41 & 19.13 & 14.93 & 0.70 & 0.00 \\ C\_B4 & 64.90 & 0.40 & 19.02 & 14.79 & 0.87 & 0.00 \\ C\_S1 & 81.32 & 0.00 & 18.67 & 0.00 & 0.00 & 0.00 \\ C\_S2 & 97.66 & 0.00 & 2.33 & 0.00 & 0.00 & 0.00 \\ C\_S3 & 78.06 & 0.00 & 19.46 & 2.47 & 0.01 & 0.00 \\ C\_S4 & 89.31 & 0.00 & 0.00 & 10.26 & 0.42 & 0.00 \\ C\_S5 & 99.99 & 0.00 & 0.00 & 0.00 & 0.00 & 0.00 \\ C\_S6 & 43.79 & 0.00 & 44.83 & 10.01 & 1.34 & 0.00 \\ C\_S7 & 89.44 & 0.00 & 0.00 & 0.00 & 10.55 & 0.00 \\ C\_S8 & 100.00 & 0.00 & 0.00 & 0.00 & 0.00 & 0.00 \\ C\_S9 & 63.83 & 0.00 & 18.37 & 17.78 & 0.00 & 0.00 \\ C\_S10 & 66.58 & 0.00 & 33.38 & 0.00 & 0.02 & 0.00 \\ C\_S11 & 19.71 & 0.00 & 79.63 & 0.00 & 0.65 & 0.00 \\ C\_S12 & 80.77 & 0.00 & 6.93 & 0.00 & 12.28 & 0.00 \\ C\_S13 & 89.25 & 0.00 & 10.74 & 0.00 & 0.00 & 0.00 \\ \hline \hline \end{tabular}
\end{table} 
Table 14: Land use percentage of the sub-basin for each Camastra reservoir sampling site.