Reclamation history and development intensity determine soil and vegetation characteristics on developed coasts

Identifying critical source areas of non-point source pollution to enhance water quality: Integrated SWAT modeling and multi-variable statistical analysis to reveal key variables and thresholds

By integrating soil and water assessment tool (SWAT) modeling and land use and land cover (LULC) based multi-variable statistical analysis, this study aimed to identify driving factors, potential thresholds, and critical source areas (CSAs) to enhance water quality in southern Alabama and northwest Florida's Choctawhatchee Watershed. The results revealed the significance of forest cover and of the lumped developed areas and cultivated crops ("Source Areas") in influencing water quality. The stepwise linear regression analysis based on self-organizing maps (SOMs) showed that a negative correlation between forest percent cover and total nitrogen (TN), organic nitrogen (ORGN), and organic phosphorus (ORGP), highlighting the importance of forests in reducing nutrient loads. Conversely, Source Area percentage was positively correlated with total phosphorus (TP) loads, indicating the influence of human activities on TP levels. The receiver operating characteristic (ROC) curve analysis determined thresholds for forest percentage and Source Area percentage as 37.47 % and 20.26 %, respectively. These thresholds serve as important reference points for identifying CSAs. The CSAs identified based on these thresholds covered a relatively small portion (28 %) but contributed 47 % of TN and 50 % of TP of the whole watershed. The study underscores the importance of considering both physical process-based modeling and multi-variable statistical analysis for a comprehensive understanding of watershed management, i.e., the identification of CSAs and the associated variables and their tipping points to maintain water quality.

Optical properties of sedimentary dissolved organic matter in intertidal zones along the coast of China: Influence of anthropogenic activities

The intertidal zone, due to its location in the transition zone of terrestrial and marine ecosystems, is seriously disturbed by anthropogenic activities such as fuel combustion and industrial production, causing significant increase in dissolved organic matter (DOM). However, the distribution and properties of DOM in intertidal sediments at the large scale and their correlations with local socio-economic indicators remain unclear. In this study, we collected sediment samples from 13 intertidal zones across 11 coastal provinces in China and analyzed optical properties and compositions of sedimentary DOM. The results showed that the physico-chemical properties of sediment, such as pH and texture, affected the content of organic matter, thereby influencing the concentration of sedimentary DOM indirectly. The contents of fulvic acid- and protein-like components were relatively higher than humic acid-like component at all sampling sites. Moreover, urbanization could lead to the release of aromatic and humified organic matters into intertidal zones. Unlike coal, oil consumption exhibited positive correlation with SUVA₂₅₄, indicating that the combustion of oil released more aromatic compounds. These findings revealed the impact of anthropogenic activities on sedimentary DOM and provided theoretical basis for predicting and regulating intertidal carbon sink.

Ecological evolution during the three-year restoration using rhizosphere soil cover method at a Lead-Zinc tailing pond in Karst areas

A major challenge for the restoration of the Lead-Zinc tailing pond in Karst areas lies in how to establish vegetation with less soil and restore the ecological functions of the substrate. In this study, a novel method, rhizosphere soil cover method (RSC), was applied to recover the vegetation at a Pb-Zn tailing pond in Karst areas. Two local tolerate plants, Miscanthus sinensis and Pueraria phaseoloides, were planted as pioneer species. Although 68 % of the tailing pond was not covered with soil, the vegetation coverage has reached over 90 % after restoration for three years. Compared with the natural revegetation process (vegetation coverage was <5 % after 20 years of natural succession), the revegetation in the tailing pond was accelerated by RSC and planting pioneer species. Both the plant's diversity and richness have significantly increased in the tailings pond during the restoration (p < 0.05). The important value indicators of M. sinensis and P. phaseoloides were the highest in the plant community, indicating the dominant role of these two plants in revegetation. Moreover, the total organic carbon, total nitrogen, total phosphorus, and total potassium in the tailings increased annually (p < 0.05), which demonstrated that the revegetation has improved the chemical properties in the substrate. In addition, the Shannon diversity index of bacteria in the tailings increased significantly from 4.11 to 5.51. The relative abundance of microbial genes related to carbon fixation and nitrogen fixation in the tailings increased by 17 % and 43 %, respectively. Meanwhile, the physicochemical properties, microbial community structure, and nutrient cycling function in the tailings without topsoil were improved more obviously than those in soils. It is thereby concluded that RSC is an efficient means for ecological restoration of the tailing ponds in Karst areas to improve the ecosystem structure and function of Pb-Zn tailings.

Distribution Characteristics and Restoration Application of Vegetation in Chengcun Bay Surrounding Areas of Yangjiang City

In recent years, global warming and sea level rise have further aggravated the risk of coastal erosion. Coastal vegetation plays an important role in resisting storm surges and alleviating coastal erosion. Therefore, screening plant species for the purpose of constructing ecological seawalls to protect or repair damaged coastal zones has become a hot issue. In this paper, a field survey was conducted to investigate the vegetation in Chengcun Bay surrounding areas of Yangjiang City by combining a line survey and sample plot survey. By understanding the vegetation types, distribution and community structure in the bay's surrounding areas and analyzing the restricting environmental factors of those plants, we put forward some countermeasures for coastal vegetation restoration in difficult site conditions from the aspects of plant species selection, vegetation configuration and restoration technology, so as to provide reference for ecological vegetation restoration in similar locations.

Assessing Coastal Reclamation Success in the East China Coast by Using Plant Species Composition

Quantitative analysis of the species composition and succession law of a plant community in a coastal reclamation area is of great significance for revealing the community construction and species coexistence mechanisms, and provides a basis for the rational use and conservation in coastal reclamation areas. Through the investigation of natural plant communities in Dongtai reclamation area and the adjacent national nature reserves in Jiangsu Province, eastern China, the composition and succession of plant communities were studied. A quantitative method was explored to analyze the process of plant succession and its representative species. The results showed that (1) A total of 65 species were found in the vegetation survey. These belonged to 26 families and 61 genera, and Poaceae is the most common plant species. The plant communities in the unreclaimed areas were mainly composed of Poaceae and Cyperaceae. The plant species increased after reclamation, which were mainly composed of Poaceae and Asteraceae; (2) The plant coverage greatly reduced after three years of reclamation, from 80% of the tidal flat to 37.34%, then gradually increased, and remained generally between 50% and 70%; (3) The above-ground biomass of the plant community was sharply reduced after reclamation, from 1.823 kg/m2 in the tidal flat to 0.321 kg/m2 in three years of reclamation, and then maintained at 0.11~0.27 kg/m2; (4)The species succession process of the plant community in the coastal wetland ecosystem that was affected by the reclamation activities transformed from a halophyte community that was dominated by a salt marsh plant community (Suaeda salsa, Spartina alterniflora, Scirpus mariqueter, and Phragmites australis) to a mesophyte plant community that was constructed with pioneer species such as Setaria viridis, Eleusine indica, etc., and eventually succeeded to a xerophyte plant community that was dominated by Humulus scandens and Cyperus difformis, etc. Reclamation activities have a profound impact on the characteristics and succession rules of natural vegetation communities along coastal wetland ecosystems. The period of seven years is presumed to be the tipping point in the succession of the plant community in coastal reclamation areas. The results of this study can provide a basis and reference for ecological protection and restoration in coastal reclamation areas.

A multiscale approach to identifying spatiotemporal pattern of habitat selection for red-crowned cranes

Effective conservation measures largely depend on knowledge of habitat selection of target species. Little is known about the scale characteristics and temporal rhythm of habitat selection of the endangered red-crowned crane, limiting the habitat conservation. Here, two red-crowned cranes were tracked with Global position system (GPS) for two years in Yancheng National Nature Reserve (YNNR). A multiscale approach was developed to identify the spatiotemporal pattern of habitat selection of red-crowned cranes. The results revealed that Red-crowned cranes preferred to select Scirpus mariqueter, ponds, Suaeda salsa, and Phragmites australis, and avoid Spartina alterniflora. In each season, habitat selection ratio for Scirpus mariqueter and ponds was the highest during the day and night, respectively. Further multiscale analysis showed that the percent coverage of Scirpus mariqueter at the 200-m to 500-m scale was the most important predictor for all habitat selection modeling, emphasizing the importance of restoring a large area of Scirpus mariqueter habitat for red-crowned crane population restoration. Additionally, other variables affect habitat selection at different scales, and their contributions vary with seasonal and circadian rhythm. Furthermore, habitat suitability was mapped to provide a direct basis for habitat management. The suitable area of daytime and nighttime habitat accounted for 5.4%-19.0% and 4.6%-10.2% of the study area, respectively, implying the urgency of restoration. The study highlighted the scale and temporal rhythms of habitat selection for various endangered species that depend on small habitats. The proposed multiscale approach applies to the restoration and management of habitats of various endangered species.

Soil nitrogen and phosphorous dynamics by in situ soil experiments along an urban-rural gradient in Shanghai, China

An in situ soil experimental system was designed to determine how urbanization impacts soil nitrogen and phosphorus dynamics. Variables including the road density, normalized difference vegetation index, distance to the nearest highway and industrial area from the soil experimental site, land use impact index, population density, population change index, total population, and percentage of water area were used to quantitatively explain the soil nitrogen and phosphorous contents. The results showed that the total phosphorous in the soil increased slowly after September 2013, indicating a phosphorous accumulation phenomenon in the soil in urban areas. The nitrate nitrogen in the soil had a higher value in September 2013, while the soil ammonium nitrogen content was higher during the winter. Moreover, the soil ammonium nitrogen content was higher than the nitrate nitrogen content during most of the experimental period. The distance from the urban centre, road density, proportion of built-up land, and population density can explain the soil nutrient dynamics quantitatively, showing that 45.4% of the soil nitrate nitrogen content, 84.1% of the soil ammonium nitrogen content, 44.6% of the ratio of NO₃/NH₄, 58.1% of the ratio of total inorganic nitrogen (TIN)/total phosphorous (TP), and 81.6% of the TIN could be explained by one of these variables at most. The potential factors affecting the changes in soil N contents include changes in human dietary habits as more people migrate to cities and industrial wastewater discharge. This study is helpful in quantitatively understanding the urbanization process and associated environmental impacts.

Shift of bacterial community structure along different coastal reclamation histories in Jiangsu, Eastern China

Tideland reclamation has drastic effects on coastal ecosystem involved in soil microorganisms. However, the knowledge regarding temporal variations of microbial community along reclamation chronosequence and their environmental variable predictor is still poorly known. Using Illumina sequencing, we qualified bacterial community composition in soils collected from one tideland and four reclamation stages, i.e. 2-year, 7-year, 19-year and 39-year in Jiangsu, Eastern China. Across all samples, the dominant groups were Proteobacteria, Bacteroidete, Acidobacteria, Planctomycetes and Chloroflexi. Reclamation activity and its histories greatly altered bacterial community structure, and only 0.28% of phylotypes were shared by five soils. Specially, some typical marine bacteria (Gaetulibacter, Alcanivorax …) disappeared in reclamation soils, while other groups (Niabella, Flavisolibacter…) were gradually eminent. Generally, bacterial diversity and richness increased with reclamation histories. Bacterial community was correlated with most of soil physico-chemical properties. Amongst, mean weight diameter of soil aggregates (MWD) was detected as a primary factor predicting bacterial community composition. Together, our results indicated that effects of reclamation on bacterial community varied with diked histories, and MWD was a major factor predicting bacterial community during progressive reclamation. These findings offer predicting case study for understanding the impact of reclamation and its histories on microbial community in a coastal ecosystem.