Effects of Microscopic Hydrodynamic Conditions and Exposure Time on the Biomass of Benthic Diatoms

Abstract Background: Benthic algae are at the bottom of the nutrient chain in the river ecosystem and are the basic guarantee to maintain the health of the river ecosystem. Human activities lead to changes in the hydrology and hydrodynamics of many rivers, which affect the growth of benthic diatoms. However, there is a lack of relevant studies on the effects of hydrodynamic conditions and exposure time on the growth of benthic diatoms, so the protection of benthic diatoms and other bait resources is difficult to be realized. Methods: Based on this, a continuous field observation was carried out to study the growth situation of benthic diatom on pebbles under different flow patterns. The three-dimensional hydrodynamic numerical simulation was used to further analyze the flow field surrounding the pebble. And then, the effects of hydrodynamic conditions and exposure time on the biomass of benthic diatoms were studied. Result: The research results show that (1) the species composition and dominant species of benthic diatoms are different at different growth stages; (2) there is an appropriate velocity range for the growth of benthic diatoms, and too low and too high flow rates are not conducive to the growth of benthic diatoms; (3) the growth suitability at different parts on the pebble for benthic diatoms from high to low is the rear part of the pebble (without direct erosion), the side parts of the pebble, the upper part of the pebble and the front part of the pebble (direct erosion); (4) most benthic diatoms die if exposed to air for more than four hours. Conclusion: The effects of hydrodynamic conditions on the biomass of benthic diatoms are obvious on the microscopic scale. The research results in this paper are helpful to further understand the growth status of benthic diatoms in microscopic environment and provide reference and information for the restoration of the hydraulic habitat of benthic diatoms in the reach affected by human activities.