Temporal and spatial evolution of hydrological connectivity in River-Lake-Swamps in high efficiency eco-economic zone at the Yellow River Delta from 1970-2015

Hydrological connectivity is essential for hydrological and ecological functions of river, lake and marsh systems．The connectivity is mediated largely by water to transfer materials, energy and organisms with major impacts from human activities and climate changes．Four remote sensing images of river, lake and marsh system in High Efficiency Eco-economic Zone of the Yellow River Delta in the past 46 years were interpreted to reflect changes in water system structure．The structural connectivity was evaluated at the grid scale by graph theory．Annual runoff and sediment data reflected changes in functional connectivity．It was found that the ditch grew at a rate of 25%, the reservoir increased 11.65 times．The average value of β connectivity from 1970-2015 was found to be 0.38, 0.41, 0.41, and 0.42, the average value of γ connectivity 0.14, 0.16, 0.16, 0.17．The average value of Q connectivity from 1970-2015 was found to be 0.31, 0.19, 0.10, 0.12, average value of S connectivity 0.36, 0.21, 0.13, and 0.16．The structural connectivity of the whole basin was found weakly correlated with GDP in 2005．The correlation between Q and GDP was 0.335, between S and GDP 0.287．The structural connectivity of the whole basin was found correlated weakly with GDP in 2015．The correlation between Q and GDP was found to be −0.010, between S and GDP 0.084．In general, water conservancy construction in the Delta has gradually increased, water system structure changed significantly, with structural connectivity showing an increasing trend, and functional connectivity showing a trend of first decline and then a small increase, closely related to the impact of human activities．This study supports the concept of major impact of human activities on the structure and function of regional water systems．