The current spring simulated flood of the inland Delta is occurring very early this year, with high flows set at its onset. For which species is this beneficial?
Higher flow implemented at the beginning of the spring flood is more beneficial as it fills the lateral wetlands, increasing water levels in the branches and wetlands at the beginning of the growing and nesting seasons. It is a period before the nesting of species that build nests on riverbanks, the water surface, or the lower layers of reed and sedge stands. Thus, there is no risk of nests being flooded or their eggs destroyed.
Shifting the spring flooding to an earlier date supports the reproduction and development of amphibian larvae utilizing wetlands for reproduction, which begins in March. Simultaneously, bird species are supported, as a later spring flood date would threaten their nests being washed away.
The spring flood is exceptionally important for creating a sufficient food base for many animal species that rely on habitats within the branch system and surrounding wetlands for nutrition. Early spring floods utilize a large quantity of small insects for their reproduction, which form a significant portion of the zooplankton. Zooplankton is one of the fundamental components of the food pyramid in the wetland ecosystem.
The spring flood also has a positive effect on young stands of riparian forest, which have insufficiently developed root systems and struggle during increasingly frequent dry spring periods (March-April). Due to the significantly altered regime in the branch system, the colmatation of the bottom of the branch system (clogging of gravel and soil pores with fine sediment) has led to significantly reduced soil moisture levels throughout the branch system, negatively affecting young stands of riparian forest in particular. Flooding of stands, or their vicinity, improves soil moisture levels and conditions for young trees during the spring period with insufficient rainfall.
Spring floods and water inundation in forests and meadows are also important for fish spawning. Following the peak flow of 120 m3/sec at certain locations, water in forest stands and wetlands will be maintained at higher levels for a longer period by barriers and will gradually recede.
Once naturally warmed to 10-12 degrees Celsius, spawning of cyprinid fish will begin, with individuals gathering in groups to spawn on vegetation. However, this discussion pertains to later flood stages and their impact on ecosystems, which we will address in the following article of our series – simulated floods, to be continued :).
