How do the variations of water and sediment fluxes into the estuary influence the ecosystem?

The water and sediment fluxes into the estuary from upstream highly influence the estuarine ecosystem. The lack of method to evaluate the impact of daily water and sediment fluxes on ecosystem has limited the ecological management of estuary. Therefore, it is important to find a quantitative method for analysing the response of estuarine ecosystem to daily water and sediment fluxes into the estuary. Based on long time sequenced data, we aim to determine the dynamic response of fish communities to the interannual and seasonal variations of water and sediment fluxes, providing a novel method for the regulation of water and sediment process in dammed rivers. We establish a functional regression model and improve Functional Linear Regression That is Interpretable (FLiRTI) method to quantify the dynamic response relationship between the annual catch per unit effort (CPUE) and the daily water and sediment fluxes into the Yellow River Estuary from 1980 to 2011. The results showed that the water and sediment fluxes into the estuary explained 56% of the variability in the CPUE. Low fluxes during the spawning period (April-May) and high fluxes during the dam discharge period (June-July) were not conducive to estuarine fisheries. By increasing freshwater inflow in spring to 3.1 or 4.3 billion m³, the cumulative effect on estuarine fish communities can be increased by 20% and 44%, respectively. We propose a functional regression method to quantify the response of estuarine fish communities to water and sediment fluxes into the estuary. We suggest that advancing the discharge time of dam to spring, a suitable spawning environment for fish can be provided, thus effectively increasing fish production in the estuary. This study overcomes the limitation of number of species as well as the disunity of hydrological and ecological data on time scale, providing new idea for estuarine ecology research.