## 4 Discussion
### UAV Surveys as a Part of Multi-Platform Environmental Monitoring of the Lake Sevan Coastal Zone
Since the man-made forests and shrublands dominated by the area in a coastal zone (especially along the shoreline of Major Sevan), the structural transformation of coastal habitats has led to a high increase of living and dead biomass near the shores. The current degradation of eroded and submerged forested shores in some key sites (Norashen Peninsula, sites along Major Sevan coasts) is so heavy that it became impossible to detect accurately shoreline positions, even with the help of ultra-high spatial resolution UAV imagery. As a result of conducted highly detailed optical and thermal UAV surveys for key coastal sites, we propose monitoring of marsh shores and coastal wetlands by the following findings. 1. Research in the habitat structure and the state of vegetation cover. UAV survey data can identify the types of vegetation communities not only through their species composition but also through indirect indicators in the form of specific plants, which indicate the degree of water abundance in those cases when it is impossible to interpret ground features beneath thick vegetation cover. UAV-based optical survey data allow reliable interpretation of vegetation species' composition and habitat types, while thermal surveys additionally enable identifying the areas of different water abundance and determining species structure, spatial patterns, and the ecological status of forest plantations, shrubland, and grassland from their thermal images. 2. The monitoring of processes related to decay of macrobiota. The processes of biota decomposition at flooded coastal sites lead to heat emissions and irreversible chemical reactions. These exothermic reactions in coastal waters can contribute to eutrophication and, combined with high aerial temperatures especially during the spring-summer period, can also exacerbate algal blooms in surface waters. Locations of vegetation decay were identified from UAV-derived thermal surveys  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Thematic Task** & **Spatial Scope** & **Periodicity** & **Platforms** \\ \hline \multirow{4}{*}{ \begin{tabular}{c} Recreationally \\ developed areas in \\ coastal zone and adjacent \\ waters, nearshore waters \\ around river mouths \\ (3 m) \\ \end{tabular}  } & \multirow{4}{*}{Daily} & Multi-spectral data from \\  & & PlanetScope \\  & & microsatellite \\ \cline{1-1}  & & constellation \\ \hline \multirow{4}{*}{\ \begin{tabular}{c} Recreationally \\ coaestal zone and adjacent \\ waters, nearshore waters \\ around river mouths, \\ coastal wetlands \\ (better than 0.1 m) \\ \end{tabular}  } & \multirow{4}{*}{ \begin{tabular}{c} In cases of early warning \\ and prompt response up \\ to several times per day, \\ on request \\ \end{tabular}  } & UAV-derived data in the \\  & & visible, infrared, \\ \cline{1-1}  & and thermal bands \\ \cline{1-1}  
(Figure 11). Some uncertainties remain, however, regarding the interpretation of nadir thermal images as well as living and decaying vegetation on hillocks within marshes. Oblique aerial thermal and optical survey seems to be the only means of resolving this problem. 3. Monitoring of the hydrothermal regime. Research into hydrothermal regimes and representation of processes related to mixing of lagoon, marsh, or river waters with the lake waters are important constituents of water quality monitoring. UAV-based thermal images identified the main mixing areas of waters flowing out of marsh swamps and lagoons (Figure 11). In the coastal zone of the Norashen Peninsula, which is an extremely dynamic area among all key study sites, the thermal survey results helped to elucidate the complex structural dynamic system of nearshore waters, semi-closed and closed lagoons, foreshores, and marsh swamps of different types (reed and cattail species). Such a landscape is unique for Lake Sevan shores.