## 3 Results
### Physical, Chemical, and Phytoplankton Properties (In Situ)
In November 2009 and January 2010, phytoplankton responded differently to HA addition depending on size class and location (Figure 3 and Table 3). In November 2009, total and net-sized chl \(a\) increased significantly at St. A with HA addition, whereas total and nanosized chl \(a\) increased at St. B. Total chl \(a\) increased significantly at Sts. B and C, whereas nanosized chl \(a\) increased at Sts. A and C in January 2010. In March 2010, total and nanosized chl \(a\) increased significantly (_p_ < 0.05) with HA addition (Figure 4 and Table 3). \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Sampling**} & \multirow{2}{*}{**Station**} & \multicolumn{4}{c}{**Total**} & \multicolumn{4}{c}{**Net-sized**} & \multicolumn{4}{c}{**Nanosized**} \\ \cline{3-10}  & & \multicolumn{1}{c}{**Time**} & \multicolumn{1}{c}{**Trt**} & \multicolumn{1}{c}{**T\({}^{\star}\)Trt**} & \multicolumn{1}{c}{**Time**} & \multicolumn{1}{c}{**Trt**} & \multicolumn{1}{c}{**T\({}^{\star}\)Trt**} & \multicolumn{1}{c}{**Time**} & \multicolumn{1}{c}{**Trt**} & \multicolumn{1}{c}{**T\({}^{\star}\)Trt**} \\ \hline \multirow{3}{*}{May 2009} & A & 0.002 & 0.028 & 0.178 & 0.014 & 0.645 & 0.205 & 0.003 & 0.026 & 0.279 \\  & B & \(<\)0.001 & 0.016 & 0.019 & 0.089 & 0.734 & 0.199 & 0.003 & 0.168 & 0.060 \\  & C & \(<\)0.001 & 0.001 & 0.004 & 0.073 & 0.021 & 0.281 & \(<\)0.001 & \(<\)0.001 & 0.005 \\ \cline{2-10}  & A & 0.001 & 0.023 & 0.133 & 0.052 & 0.716 & 0.430 & 0.011 & 0.014 & 0.296 \\  & B & 0.003 & 0.018 & 0.227 & 0.017 & 0.974 & 0.445 & 0.003 & 0.049 & 0.157 \\  & C & 0.001 & 0.019 & 0.200 & 0.052 & 0.194 & 0.514 & 0.001 & 0.133 & 0.165 \\ \cline{2-10}  & A & \(<\)0.001 & 0.006 & 0.039 & 0.130 & 0.001 & 0.424 & 0.001 & 0.066 & 0.169 \\ \cline{2-10}  & B & 0.006 & 0.015 & 0.139 & 0.130 & 0.827 & 0.446 & 0.001 & 0.001 & 0.016 \\  & C & 0.008 & 0.587 & 0.317 & 0.123 & 0.976 & 0.391 & 0.009 & 0.223 & 0.388 \\ \cline{2-10}  & A & 0.003 & 0.062 & 0.165 & 0.026 & 0.096 & 0.122 & 0.006 & 0.034 & 0.223 \\ \cline{2-10} Jan 2010 & B & 0.002 & 0.009 & 0.178 & 0.068 & 0.985 & 0.426 & 0.037 & 0.161 & 0.401 \\  & C & 0.002 & \(<\)0.001 & 0.006 & 0.073 & 0.098 & 0.196 & 0.003 & \(<\)0.001 & 0.007 \\ \cline{2-10}  & A & 0.001 & \(<\)0.001 & 0.017 & 0.066 & 0.381 & 0.541 & \(<\)0.001 & \(<\)0.001 & 0.011 \\ \cline{2-10}  & C & \(<\)0.001 & \(<\)0.001 & 0.002 & 0.050 & 0.031 & 0.354 & \(<\)0.001 & \(<\)0.001 & 0.004 \\ \cline{2-10} Feb 2011 & A & 0.022 & 0.090 & 0.093 & 0.261 & 0.956 & 0.371 & \(<\)0.001 & 0.052 & 0.077 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Results of the RM-ANOVA analyses on HA addition treatments for total, net-, and nanosized phytoplankton at a significance level of 0.05. Time and Trt (treatment) represent the differences over time and between the treatments (control vs. HA (5 ppm) addition), respectively and T\({}^{\star}\)Trt represents differences between the treatments and over time. Significant _p_-values (<0.05) are highlighted in gray. Figure 4: Size-fractionated chl \(a\) concentration (\(\mu\)g L\({}^{-1}\)) and contribution percentage (%) of nanosize class during the mesocosm experiments for water samples collected at Sts. A and C in March 2010 and at St. A in February 2011. Treatments of 2.5, 5, and 10 ppm HA (Sigma-Aldrich®) and 5 ppm HA obtained from IHSS were designed for the experiments in March 2010 and February 2011, respectively. Higher chl \(a\) levels were observed in the HA 10 ppm treatment compared to the 5 ppm treatment, which in turn had higher chl \(a\) levels than the 2.5 ppm treatment (Figure 4). In February 2011, total and nanosized chl \(a\) also increased with HA addition, especially after 5 days of incubation (Figure 4), although the increase was not statistically significant (_p_ < 0.1; Table 3). The pattern of response was similar between the treatments of HA from IHSS and from Sigma-Aldrich(r) (Figure 4).