Dynamics and integrity of wetland network in estuary

Hydrological connectivity improves soil nutrients and root architecture at the soil profile scale in a wetland ecosystem

Hydrological connectivity is an essential driver of the stability, structure, and function of wetland ecosystems. Small-scale hydrological connectivity restricts large-scale hydrological cycle processes. This study aimed to investigate the response of soil and root properties to hydrological connectivity at the soil profile scale. Tamarix chinensis, which is a typical plant of the Yellow River Delta wetland, was sampled for analysis. We investigated soil and root properties in the three study plots where T. chinensis distributed and compared them at different soil depths and under different hydrological connectivity conditions. We found that the soil organic carbon (SOC), soil organic matter (SOM), and soil total nitrogen (STN) were significantly higher in shallow soil (0-10 cm deep), and that root architecture parameters such as root length and width at soil depth of 0-10 cm were also significantly higher than at other soil depths. Both the soil nutrients and root architecture parameters were significantly influenced by hydrological connectivity. Specifically, SOC, SOM, and STN were significantly higher in regions of high hydrological connectivity than in regions of low hydrological connectivity. Additionally, root length, root surface area, root projected area, and root volume were markedly higher in regions of high hydrological connectivity. Furthermore, root length and width had significant positive correlations with both SOC and SOM in regions of high hydrological connectivity. Taken together, these results indicate that higher hydrological connectivity promotes soil nutrients and root architecture at the soil profile scale. In the process of wetland protection and restoration, we should not only pay attention to hydrological connectivity at a watershed scale, but also to improving hydrological connectivity at smaller scales so as to restore soil nutrients and promote plant growth.

Tides affect plant connectivity in coastal wetlands on a small-patch scale

Coastal wetlands are ecologically and economically important; however, they are currently faced with fragmentation and loss. Plants are a fundamental element of wetlands and previous researches have focused on wetland plant connectivity; however, these researches have been conducted at the landscape but not species level. Here, given that tidal flats are important areas in coastal wetlands, we investigated the connectivity characteristics of typical plant species and environmental factors in different wetland regions influenced by various tidal conditions to reveal vegetation connectivity and its relationship with environmental factors on a small-patch scale. We found that tides negatively affect plant connectivity because both the Tamarix chinensis and Suaeda salsa have the highest connectivity on river banks, which are not influenced by tides. Of two tidal regions, different tides conditions have different influence on two plant species. T. chinensis had higher connectivity in the supratidal zone, whereas S. salsa had higher connectivity in the intertidal zone. Besides, the soil water content and soil salinity were significantly different in the three regions, but the soil total nitrogen and phosphorous were not. Soil water content and soil salinity were two factors that significantly affected plant connectivity. Specifically, soil water content positively affected the connectivity of T. chinensis and S. salsa, whereas soil salinity negatively affected the connectivity of T. chinensis. Taken together, these results indicate that tidal conditions affect plant connectivity on a small-patch scale. River banks and supratidal zone are beneficial for the recovery and growth of T. chinensis, intertidal zone and river banks are more conducive to the recovery and growth of S. salsa. Based on the above research, this study provides insights that could be applied to vegetation restoration in coastal wetlands.

Methodologies and Management Framework for Restoration of Wetland Hydrologic Connectivity: A Synthesis

Under the dual influences of high-intensity anthropogenic activity and climate change, wetland hydrologic connectivity (HC) has decreased significantly, resulting in the severe fragmentation of wetlands, a decrease in wetland area, and a degradation of hydrological functions, resulting in a worsening disaster response to floods and droughts. Dynamic changes in wetland HC are affected by a variety of factors. Many degraded wetlands have undergone measures to restore HC. Recovery can improve the HC pattern of degraded wetlands. Based on the knowledge of practitioners and a review of the literature, it was found that recovery measures can be divided into structural recovery and functional recovery according to the specific recovery objectives. However, the current recovery method lacks a holistic analysis of the HC pattern. To this end, we propose a hydrologic network-water balance-based HC recovery and management framework that overcomes the limitations of single-drive-factor repair and local repair effects. Integr Environ Assess Manag 2020;16:438-451. © 2020 SETAC.

The application of graph theory and percolation analysis for assessing change in the spatial configuration of pond networks

Pond networks support high levels of biodiversity when compared to other freshwater ecosystems such as rivers, lakes and streams. The persistence of species in these small, sometimes ephemeral, aquatic habitats depends on the dispersal of individuals among ponds in the landscape. However, the number of ponds across the landscape is at a historical low as urbanisation and intensified agricultural practices have led to a substantial loss of ponds (nodes in the pond network) over more than a century. Here, we examine the extent and drivers of pond loss in a heavily urbanised landscape (Birmingham, UK) over 105 years and determine how pond loss influences key structural properties of the pond network using graph theoretic approaches. Specifically, we calculated minimum spanning trees (MST) and performed percolation analyses to determine changes in both the spatial configuration and resilience of the pond network through time. Pond numbers declined by 82% between ca1904 and 2009, such that pond density decreased from 7.1 km-2 to 1.3 km-2. The MST analyses revealed increased distance between ponds in the network (i.e. edge length increased) by up to 49% over the 105-year period, indicating that ponds in the modern landscape (2009) were considerably more isolated, with fewer neighbours. This study demonstrates that graph theory has an excellent potential to inform the management of pond networks in order to support ecological communities that are less vulnerable to environmental change.