Decaying Vegetation Removal
The largest uncertainty noted on the Hardy (2011) report is the potential effect of extended low-flow periods on aquatic vegetation dynamics within the Comal system as neither the hydraulic and habitat modeling, nor water quality modeling conducted addresses this issue. The main concern is that under extremely low-flow conditions, aquatic vegetation may start to die, and subsequently decay, consuming a large amount of dissolved oxygen (DO) during the decay process. This in turn could cause large swings in the DO concentration within Landa Lake, which depending on the severity, could affect the biological community including the fountain darter. The concern is probably limited to the lake portions of the system as the culverts and weirs present at the uppermost portions of the Old and New Channels would likely provide sufficient re-aeration to compensate for most events. However, within the lake environment, problems will occur.
To minimize and mitigate the impact of incidental take from low-flow events, upon receipt of DO data indicating a water quality concern created by decaying vegetation and the total Comal springflow drops below 80 cfs, the City of New Braunfels will implement a dissolved oxygen management program. The program will be focused on ensuring adequate DO levels for the ecosystem. Techniques to accomplish this objective may include artificial aeration of area of Landa Lake or other solutions. If appropriate, the program may include removal of decaying vegetation. Removal techniques for decaying vegetation, if necessary, may include using rakes/pitch forks and a jon boat to transfer material to the banks for subsequent removal. In this way, greater dissolved oxygen will remain available for the living aquatic ecology, rather than be consumed in the decay process.