To study metal enrichment and identify the influencing factors, 106 surface soils were collected in the Yellow River delta, including ten vegetation types. Concentrations of 10 different metals, including As, Cd, Cr, Ni, Cu, Pb, Zn, Mn, Al, Fe, and physicochemical properties pH, salinity, particle size were detected. The pH value was 7.35~9.17, and the salinity was in the range of 0.01~2.00%. The average value of silt was 76.18%, which was the main particle size for 99% of the samples. The mean concentrations of As, Cd, Cr, and Ni were higher than the background value of Shandong Province or the background value of yellow soil in China. A higher concentration of Fe occurred in Phragmites australis (mean concentration 2.50%) and paddy field. The concentrations of Cd, Cr, Ni, Cu, Pb and Zn were lower in the Suaeda salsa soil. The Nemerow pollution index indicated that 79% of all samples showed low-level metal pollution, and 7% of all samples showed moderate-level metal pollution. In the areas with higher salinity, the concentrations of As were higher, while the concentrations of Cd and Ni were lower. The correlation analysis showed that with increasing pH, the concentrations of As and Zn decreased significantly. The metal concentrations had a significant positive correlation with clay, except for As.

Nested Delft 3D and Hydrus 1D models were applied to simulate variations in the hydrological process of tidal creeks, soil water, and salt transport in the soil profile of the reconstruction area in the Yellow River Delta under six gate dam scenarios. The results showed that the gate dam set up near the sea area was more conducive to reducing the variation range of water depth in the reconstruction area. The water depth changes in scenarios with 6 m gate valves were higher than those with 3 m sluice valves in the same gate dam location. The variations in surface water salinity, cumulative flooding time, flooding frequency, and cumulative infiltration in each scenario were similar to those for water depth. Rapid changes in soil water and salt content occurred in each scenario in periods without flooding. The fluctuation of soil salt content in different soil layers was contrary to the changes in soil water content. The overall difference in the soil salt contents and soil water content of the soil profile in scenarios with a gate dam near the sea was relatively larger than that of those with a gate dam near the shore. Obvious differences in both the soil water content and soil salt content between scenarios with 3 m and 6 m gate valves were not observed. Our results contribute to the understanding of the function of gate dams in controlling soil water and salt content in coastal wetlands.

The concentration and speciation of heavy metals in the intertidal zone play an irreplaceable role in protecting biodiversity. However, it could be changed by the constantly changing hydrological regimes and salinity. To identify the change and mechanisms of these phenomena, an incubation experiment was conducted under three hydrological regimes (no flooding, periodic flooding, and long-term flooding) and five salinities (0‰, 5‰, 10‰, 20‰, and 30‰). The concentration and speciation of Cd, Cr, Cu, Pb, and Zn in sediment cores collected at the first, third, fifth, seventh, and ninth week were detected. The results indicated that as the incubation time increased, the concentrations of Cr, Cu, and Pb decreased while the concentrations of Cd and Zn increased. The primary speciation for Cd was acid-soluble fraction, whereas the residual fraction was the dominant form for Cr, Cu, Pb, and Zn. The acid-soluble fraction of Cd was lowest in freshwater conditions. The oxidizable fraction of Cd generally increased under long-term flooding and was higher than that under no-flooding or periodic-flooding conditions. The speciation of Cr under freshwater and 5‰ salinity conditions was similar but distinctly different from that under other salinity levels. Cu was easily combined with organic matter, and the oxidizable fraction of Cu was the predominant form, aside from the residual fraction. The residual fraction of Pb observably increased in the ninth week. The general linear model revealed that hydrological regimes, salt conditions, and incubation time had an obvious influence on metal speciation. Throughout the incubation experiment, Cd posed a higher risk (ranging from 21.91% to 71.91%) and should be closely monitored. The risks associated with Cr and Zn also increased during the incubation period.

The rapid economic and urban development in the Yellow River Delta Efficient Ecological Economic Zone (YRDEEZ) has intensified land use changes and aggravated ecological patch fragmentation. Constructing ecological networks (ENs) can reconnect fragmented patches and enhance ecosystem services. This study simulated land use patterns for 2040 under three scenarios: Natural Development (NDS), Ecological Protection (EPS), and Urban Development (UDS). Results indicated a consistent decline in agricultural land and an expansion of urban land across all scenarios, with the most pronounced urban growth under UDS (6.79%) and the largest ecological land area under EPS (5178.96 km²). Since 2000, the number of EN sources and corridors had decreased, with sources mainly concentrated along coastal areas. The source and corridor under UDS exhibited the highest area ratio (20.08%), while NDS showed the lowest (18.72%), with UDS demonstrating the strongest resilience. Through community detection, the UDS EN was divided into five ecological clusters, encompassing 127 intra-cluster corridors (2285.95 km) and 34 inter-cluster corridors (1171.32 km), among which the cluster near the Yellow River estuary was determined to be the most critical (Level 1). These findings will provide valuable insights for managing landscape fragmentation and biological habitat protection in YRDEEZ. Meanwhile, the multi-scenario simulations of ENs could play an important role in constructing ecological security patterns and protecting ecosystems.

As a key part of coastal wetlands, the accurate distribution data of tidal flats is of great significance for the protection and management of coastal ecosystems. Current techniques for extracting tidal flats from remote sensing imagery predominantly focus on detecting the distribution range of temporary water bodies. This requires a higher degree of synchronicity between high and low tides and satellite transit time, so the existing extraction methods often result in low spatial accuracy in irregular tidal areas. To address these limitations, we selected the Yellow River Delta (YRD) as our study area and utilized the Google Earth Engine (GEE) cloud computing platform combined with time-series Landsat images to propose a new method for extracting tidal flats affected by irregular tides based on surface humidity differences. This method successfully identified the tidal flats of the YRD and was validated temporally within the study area. Additionally, promotion verification was carried out in other coastal areas affected by irregular tides, revealing strong levels of universality and robustness. Notably, in the study area, the extraction method’s accuracy improved by about 25% compared with other methods. Consequently, tidal flat mapping based on this method can provide critical data support for ecological protection of coastal zones and assist in the formulation of sustainable coastal zone management policies.

Soil salinization severely threatens global agricultural productivity. Arbuscular mycorrhizal fungi (AMF) and straw incorporation are promising biological amendments for salt-affected soils, but their interactive effects on crop growth and soil biological processes remain poorly understood. In this study, a sterilized-soil pot experiment was conducted to evaluate the individual and interactive effects of a native AMF strain (Claroideoglomus sp., AM5) inoculation and straw incorporation (SI) on maize performance traits, soil properties, and bacterial communities in saline soil. Four treatments were established, including control (CK), AM5, SI, and AM5 + SI. The combined treatment exerted significant synergistic effects. AM5 successfully colonized maize roots with a 72% mycorrhizal infection rate (MIR) and 106% mycorrhizal dependence, and SI further enhanced colonization (80% MIR, 127% MD). Compared with CK, AM5 + SI increased aboveground fresh and dry weights by 61.5% and 48.7%, and Chlorophyll a and net photosynthetic rate by 35.4% and 147.3%, respectively. Soil physicochemical and biological conditions were improved, as evidenced by reduced topsoil and subsoil electrical conductivity (55.2% and 40.6%, respectively), increased nutrient availability (e.g., available phosphorus and potassium contents), and enhanced soil hydrolase activities (sucrase, urease, and alkaline phosphatase), particularly in subsoil. The combined treatment also restructured the soil bacterial community in both layers, increasing microbial diversity and selectively enriching beneficial phyla (e.g., Pseudomonadota, Actinomycetota), whose abundances were closely correlated with improvements in soil properties. These results confirm our hypothesis that the co-application of native AM5 and straw incorporation exerts synergistic effects on soil biological functions, leading to enhanced maize growth and soil fertility in saline soil. Random forest and PLS-SEM revealed that these soil-microbe changes were accompanied by greater maize biomass accumulation, photosynthetic capacity, and antioxidant defense, with distinct regulatory pathways between topsoil and subsoil. These findings indicate that co-application of native AMF and straw incorporation may effectively improve soil biological functions and maize performance in coastal saline soil, providing mechanistic insights for biological remediation using native AMF and organic residues.