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The evolution of the shoals and vegetation plays an important role in maintaining the stability of the river regime and the estuarine ecosystem. However, the interaction between the evolution of shoals and vegetation dynamic has rarely been reported. In this study, we determined the interaction between the shoal and vegetation evolution of Jiuduansha in the Changjiang River Estuary in the last 30 years. We did this through the collection and summarization of the existing data of the regional hydrological processes, wading engineering, and vegetation, and combined it with the analysis of nautical charts and remote sensing images. During the past 30 years, the expansion of the shoals within the 0 m isobath in Jiuduansha was obvious, with an increase of 176.5%, while the expansion of the shoals within the 5 m isobath was relatively slow. The regional hydrological characteristics in the Jiuduansha area changed dramatically, especially the sediment discharges. The area of vegetation in Jiuduansha increased from 9.1 km2 in 1990 to 65.68 km2 in 2015, while the variations in the different vegetation types were different. The best combination of environmental factors with a significant correlation on the shoals within the 0 m isobath is the area of Spartina alterniflora and Phragmites australis. The evolution of Jiuduansha shoals was significantly affected by the variations in hydrological characteristics. Meanwhile, on a long-term scale, the expansion of the shoals could promote the regional vegetation expansions due to the suitable elevation and environmental conditions it provides. The interaction between the shoal and vegetation evolution varied in the different vegetation types and different elevations. In the future, long-term monitoring and detailed data are needed to the systematical analysis of the interaction between the hydrological processes and the evolution of the shoal and vegetation.

Urban green spaces are among the relatively few places to connect with nature in cities and represent locations where city dwellers can experience a variety of critical ecosystem services. As urbanization increases, deepening our understanding of the connections between city dwellers and the natural environment has become critical. In this study, we investigated the social values for ecosystem services by demonstrating an approach that combines a visitor-employed photography (VEP) method with the Social Values for Ecosystem Services (SolVES) mapping tool and applying this method to an urban wetland park. As a result, a quantified value index (VI) informs managers of the type and extent of urban ecosystem services (UESs) acknowledged by the public. Social values for each UES and environmental variable are delineated in a quantitative and spatially explicit manner. These outcomes could help planners and managers target specific areas in need of construction or improvement. Notably, public perceptions in this study are derived from photographs taken by invited park visitors. Real-time and on-site visiting experiences tend to be more effective and robust than recalling points of interest after visiting and manually marking them on maps via questionnaires. All the data used in this study are likely available in other green spaces. This approach can be generally extended to UES assessments elsewhere.

Shallow lakes have a tendency to settle into turbid or clear-water states, the latter having lower concentrations of total phosphorus (TP). However, how P-cycling is affected by and perhaps contributes to maintaining the different states is not well understood, in part because quantifying the processes involved by traditional methods is difficult. To elucidate these processes, we conducted experiments using 32P-PO4 as a tracer on samples collected from the unrestored, unvegetated sections of Huizhou West Lake where turbid water prevails as well as the restored, clear-water, macrophyte-rich waters of the lake. We measured PO4 uptake rates, 32P-PO4 accumulation by various plankton size-fractions (picoplankton (0.2–2 μm), nanoplankton (2–20 μm) and microplankton (>20 μm)) as well as release rates of 32P-PO4 by labelled plankton. Our results revealed slow PO4 uptake in the turbid state due to low PO4 concentration, slow recycling of the high particulate P, and high levels of particulate 32P which may allow for continuous high growth and biomass of phytoplankton. In contrast, in the clear water state, the uptake of PO4 was rapid due to a higher PO4 concentration, the recycling rates of particulate 32P were high and the levels of particulate 32P were low, potentially constraining the phytoplankton growth. A greater proportion of particulate 32P was in the microplankton fraction in clear waters, suggesting that grazing by microplankton may play an important role in the rapid P recycling in clear-waters. Our results provide some evidence for a reinforcement of the turbid conditions (low recycling rate) when the lake is in a turbid state and vice versa when in the clear water state. The results add new knowledge to the understanding of P cycling in shallow lakes and illustrate the utility of using P-kinetics in contrasting states in plankton communities.

This study investigated the polycyclic aromatic hydrocarbons (PAHs) occurrence, and their impact on the microbial community and PAH-degrading genera and genes in the Knysna Estuary of South Africa. The results reveal that the estuary exhibits low PAH levels (114.1–356.0 ng g−1). Ignavibacteriae and Deferribacteres, as well as Proteobacteria and Bacteroidetes, are keystone phyla. Among measured environmental factors, total organic carbon (TOC), nutrients such as nitrite and nitrate, metals as Al, Cr, Cu, Ni, Pb and Zn, and environmental properties (pH and salinity) are primary contributors to structuring the bacterial community assemblage. The abundance of alpha subunit genes of the PAH-ring hydroxylating dioxygenases (PAH-RHDα) of Gram-negative bacteria lies in the range of (2.0–4.2) × 105 copies g−1, while that of Gram-positive bacteria ranges from 3.0 × 105 to 1.3 × 107 copies g−1. The PAH-degrading bacteria account for up to 0.1% of the bacterial community and respond mainly to nitrate, TOC and salinity, while PAHs at low concentration are not significant influencing factors. PAH degraders such as Xanthomonadales, Pseudomonas, and Mycobacterium, which play a central role in PAH-metabolization coupled with other biogeochemical processes (e.g. iron cycling), may contribute to maintaining a healthy estuarine ecosystem. These results are important for developing appropriate utilization and protection strategies for pristine estuaries worldwide.

Microplastics are small, degrade slowly, and easily persist in the water column because they are close to neutrally buoyant. Understanding the distribution of microplastics is fundamental to evaluating the ecological risks that they cause and to identifying ways to control microplastics pollution. Most of the existing research on the distribution of microplastics in the coastal zone has focused on large spatial and temporal scales. To build on past work, we investigated variation in microplastics in a tidal flat of the Yangtze Estuary on small spatial (sediment depth, mudflat vs. vegetation zone) and temporal (fortnightly and semidiurnal) scales. Microplastics were more abundant in surface (0–2 cm) sediments during neap versus spring tide cycles, likely indicating increased deposition during periods with calm waters and increased suspension when water was more turbulent, but did not vary at greater depths in the sediment. Individual microplastics particles were also larger during neap versus spring tide periods. In contrast to the variation between spring and neap tide periods, we found no variation in the abundance of microplastics on the semidiurnal scale. Microplastics were also more abundant in the transect in the vegetation than at slightly lower elevations in the adjacent mudflat. Across all samples, the abundance of microplastics was negatively correlated with the strength of hydrological processes such as submergence time and flow velocity. Our results showed that sampling of microplastics in the intertidal environment needs to consider variation among spring and neap tide cycles, and also among different intertidal habitats that may differ only slightly in elevation. We encourage coupling sampling with direct measures of hydrological processes so that variation in microplastics abundance and size can be rigorously linked to hydrological processes.

Common carp (Cyprinus carpio) have been introduced into aquatic systems across the world, where their benthivorous feeding behavior has resulted in serious water quality problems. A 12-week mesocosm experiment was set up to test the hypotheses that common carp increase water column nutrient levels and decrease water clarity in aquatic ecosystems dominated by submerged plants. Further, we tested whether the effect of common carp on macrophytes depended on the species of plants. Relative to the controls, the presence of carp decreased water clarity by increasing total suspended solids (TSS) and light attenuation. However, levels of total nitrogen (TN) and total phosphorus (TP) in the water column were reduced. No significant change in phytoplankton biomass (measured as chlorophylla) and the biomass ofHydrilla verticillatawas observed between common carp treatment mesocosms and controls, but the common carp did reduce the biomass of the submerged macrophyteVallisneria denseserrulata. We conclude that removal of common carp is likely to improve water clarity in aquatic ecosystems dominated by submerged plants primarily by decreasing TSS and that the effect of common carp on macrophytes is stronger for the meadow formingVallisneriathan for the canopy formingHydrilla.