## 4 Discussion  
The results of the present study confirmed the capability of Sentinel-2-derived products in tracking the bottom coverage of optically shallow waters and demonstrated the existence of striking inter- and intra-annual variations in the spatial cover patterns of macrophytes. In this context, remote sensing has proven to be a valid tool for investigating seasonal variation in macrophytes over a wide study area (3.97 km\({}^{2}\)); processes that would be impossible to adequately assess using classical immunological approaches (e.g., by macrophyte survey along transects, as implemented under the Water Framework Directive) [9; 87]. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multicolumn{1}{c}{**Year**} & \multicolumn{1}{c}{**Potential Drivers**} & \multicolumn{1}{c}{**Response**} & \multicolumn{1}{c}{**Implication for**} & \multicolumn{1}{c}{**Herbivore/Macrophyte**} \\  & & & **Following Year** & **Change** \\ \hline \multirow{4}{*}{2015} & \multirow{4}{*}{Herbivore bird population 7589. Winter wind mostly calm. Summer Chl–a was 2.6 mg m\({}^{-3}\). Spring lake level was 1.06 m.} & \multirow{4}{*}{Macrophyte cover normal. Spring lake level was 1.03 m.} & Lower herbivore bird grazing earlier in the year may have allowed an increase in macrophyte growth in subsequent months and lead to more foraging the following year. \\ \hline \multirow{4}{*}{2016} & \multirow{4}{*}{Herbivore population increases to 13,908. High winter wind speed recorded (red in Figure S3). Summer Chl–a increases to 4.3 mg m\({}^{-3}\). Spring lake level was 1.03 m.} & \multirow{4}{*}{Lowest total macrophyte cover in timeseries for MAM, JJA, SON recorded. Spring lake level was 1.03 m.} & Lower macrophyte cover and lower density in SON \\  & & & & \\ \hline \multirow{4}{*}{2017} & \multirow{4}{*}{Herbivore population declines to 10,327. Winter wind mostly calm. Summer Chl–a was 1.9 mg m\({}^{-3}\). Spring lake level was 1.08 m.} & \multirow{4}{*}{Macrophytes remain at similar or slightly lower levels.} & \multirow{4}{*}{Normal. \(\uparrow\rightarrow\)} \\  & & & & \\ \hline \multirow{4}{*}{2018} & \multirow{4}{*}{Herbivore population continues recovery and reaches highest level of 15,074. Winter wind mostly calm but storm in May. Spring had higher water levels (1.29 m). Summer Chl–a increases to highest for the timeseries of 4.8 mg m\({}^{-3}\). Spring lake level was 1.07 m.} & \multirow{4}{*}{Area of dense macrophytes is reduced to minimum of the timeseries. Total macrophytes may have implications for foraging.} & \multirow{4}{*}{\(\uparrow\downarrow\)} \\  & & & & \\ \hline \multirow{4}{*}{2019} & \multirow{4}{*}{Herbivore population declines to 11,326. Winter wind mostly calm. Spring lake level was 1.06 m.} & \multirow{4}{*}{Area of dense macrophytes recovers. Total macrophytes in summer return to higher levels.} & \multirow{4}{*}{\(\uparrow\downarrow\)} \\  & & & & \\ \cline{1-1} \cline{4-5}  & & & & \\ \cline{1-1} \cline{4  
The comparison between our seasonal maps and those of the two previous works [6; 33] shows that 1997 was the most favorable year for macrophtye growth (the RM class covered 72% of the entire mask), especially for the D\({}_{\rm RM}\) class (69%) that was located mainly near the coast. These percentages of vegetation coverage were also reached in other years (e.g., 2010, 2015, 2017, 2018, and 2020), but the substantial difference concerns the D\({}_{\rm RM}\) class, which after 1997 never reached 50%, even in the most favorable years. In addition, when present, it is mostly located far from the coast. As a result, a gradual change in macrophtye quality/density is observable from 1997 to the present day, and a shift of dense macrophytes to deeper areas. This is in line with previous works highlighting high intrinsic dynamic rates of macrophytes in deep lakes [4; 39].