Using heavy metals to detect the human disturbances spatial scale on Chinese Yellow Sea coasts with an integrated analysis

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.

The scale identification associated with priority zone management of the Yangtze River Estuary

Watershed and catchment area-based water quality management are important methods for comprehensive management of rivers and lakes. The impacts of land use/land cover (LULC) on river water quality vary with spatial scales, such as watersheds, catchments, and riparian zones. Achieving an effective spatial scale relationship between LULC and water quality, determining priority management areas, and reaching sustainable development of large estuarine deltas remain problematic. In this study, buffering analysis on the water quality data of the Yangtze River Estuary from 2009 to 2018 was conducted based on LULC, and the priority management areas of the basin were identified. Also, we infer that future river restoration or management efforts should focus on priority management area construction of a 1500 m riparian zone and a 150 km reach zone. Conclusively, establishing a priority management area within the effective buffer zone is key to watershed water quality management.

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.

Lead isotopes in the Central Yellow Sea Mud: Evidence of atmospheric deposition and its implication for regional energy consumption shift

Anthropogenic activities have increased lead (Pb) emissions and impacted their spatiotemporal distributions in coastal seas. To quantify the increasing variability of Pb and identify the specific origins and their corresponding magnitudes, Pb and Pb isotopes are investigated in a well-placed sediment core covering the period of 1928-2008 in the Central Yellow Sea Mud (CYSM). The concentration of Pb varied from 27.17 μg/g to 37.30 μg/g upwardly along the core, with pronounced anthropogenic disturbance since the late 1960s. The Pb input history of the CYSM experienced five stages according to industrialization levels and Pb contamination, with relative pristine stages from 1928 to 1969 and human activity-impacted stages from 1969 to 2008. The ²⁰⁶Pb/²⁰⁷Pb ratio demonstrated an overall decreasing profile while the ²⁰⁸Pb/²⁰⁶Pb ratio displayed the reverse trend upwardly along the core, possibly due to the atmospheric delivery of anthropogenic Pb emissions from northern China. Furthermore, ²⁰⁸Pb/²⁰⁶Pb vs. ²⁰⁶Pb/²⁰⁷Pb shows certain linearity between natural sediment sources and anthropogenic emissions of Pb (atmospheric deposition); thus, atmospheric inputs account for 34-43% of the Pb in the sediment since Pb enrichment using the two-endmember mixing model. Moreover, the steep decrease in ²⁰⁶Pb/²⁰⁷Pb and rapid increase in ²⁰⁸Pb/²⁰⁶Pb since the 1970s suggest the introduction of leaded gasoline and the increasing proportionate consumption of gasoline relative to total energy consumption. The continuously decreasing ²⁰⁶Pb/²⁰⁷Pb ratio and increasing ²⁰⁸Pb/²⁰⁶Pb ratio since 2000 are the combined results of coal consumption, nonferrous smelting, and residual Pb contamination from leaded gasoline, which is quite distinctive from cases in North America and Europe. The relatively high ²⁰⁶Pb/²⁰⁷Pb and low ²⁰⁸Pb/²⁰⁶Pb ratios before 1969 represent the natural Pb isotopic signatures. Hence, Pb input is significantly affected by regional energy consumption and restructuring, and the Pb isotopic ratios may be a potential proxy for the shift in energy consumption.

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.

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

The question of where and how to carry out reclamation work in coastal areas is still not well addressed in coastal research. To answer the question, it is essential to quantify the impact of reclamation and the associated ecological and/or environmental responses. In this study, ordinary least square (OLS) analysis and geographical weighted regression (GWR) analysis were performed to identify the reclamation variables that affect soil and vegetation characteristics. Reclamation related variables, including residential population (RP), years of reclamation (YR), income per capita (IP), and land use-based human impact index (HII), were used to explain nitrate, ammonium, total phosphorous, and heavy metals in soil, and the height, density, and above-ground biomass of native hydrophytic vegetation. It was found that variables IP, RP, and HII could be used to explain the height of Scirpus and Phragmites australis as well as above-ground biomass with a R² value of no >0.55, and almost all the variables could explain the hydrophytic vegetation characteristics with a higher R² value. In comparison to OLS, GWR more reliably reflected the reclamation effects on soil and vegetation characteristics. By GWR analysis, total soil phosphorous, and nitrate and ammonium nitrogen could be explained by RP, YR, and HII, with the highest Ad-R² value of 0.496, 0.631 and 0.632, respectively. Both of the GWR and OLS analysis revealed that HII and RP were the better variables for explaining the soil and vegetation characteristics. This work demonstrated that coastal reclamation was highly spatial dependent, which sheds a light on the future development of spatial explicit and process-based models to guide coastal reclamation around the world.

Characterizing the physical and demographic variables associated with heavy metal distribution along urban-rural gradient

This paper describes a study of how the demographic and physical variables affected the heavy metal (HM) contamination along the urban-rural gradient in PuDong New District, Shanghai. The road density (RDi) and the percentage of built-up areas (BAi) were calculated for various widths of buffers around the soil sampling sites. Through distance allocation, the demographic values of the population change index (PCI) were assigned, with the value being associated with the nearest town. We initiated the use of the population migration rate from 2000 to 2010, i.e., PCI, to represent the urbanization rate. Regression analysis between the soil HM concentrations and the PCI, the RD, and the BA was estimated. The results indicated that the PCI significantly affected the Cd and Cu distribution (p < 0.05), while the RD of the 3-km buffer affected the Pb concentrations. The BA of 2-km buffers affected the spatial distribution of Cd, Cu, and Zn. Zn was also affected by the RD within the 4-km buffer. Using the median values of the PCI and the BA of the 2-km buffer, and the RD of the 3-km buffer, logistic analysis was performed to identify the priority areas for managing HM hazards. The two identified priority areas were the towns of Kangqiao and Zhuqiao, both of which were rapidly urbanized areas with higher PCI values. Our research demonstrated that understanding the rate of urbanization may be as important as the degree of urbanization when examining associated HM contamination patterns.

Anthropogenic Black Carbon Emission Increase during the Last 150 Years at Coastal Jiangsu, China

Black carbon (BC) is one of the major drivers of climate change and a useful indicator of environmental pollution from industrialization, and thus it is essential to reconstruct the historical trend in BC flux to better understand its impact. The Yancheng coastal wetland reserve in Jiangsu province is an area sensitive to global sea level change and is also located in the most developed as well as most polluted region of China. We investigated the concentration and historical flux of BC over the past 150 years through geochemical analysis of two 210Pb-dated sediment cores from Yancheng coastal wetland. Measured BC contents ranged from 0.24 mg g-1 to 1.41 mg g-1 with average values of 0.51mg g-1-0.69 mg g-1, and BC fluxes ranged from 0.69 g m-2 yr-1 to 11.80 g m-2 yr-1 with averages of 2.94g m-2 yr-1-3.79 g m-2 yr-1. These values are consistent with other records worldwide. Both BC content and flux show a gradual and continuous increase over time and clearly reflect increased emissions from anthropogenic activities. The BC records have a significant peak in recent years (from 2000 to 2007), which is accompanied by the sharp increase of energy consumption and total carbon emission in the region. It is reasonable to conclude that changes in BC from increasing human activities have controlled BC fluxes during the last 150 years. Industrial contamination, especially BC emission, in the coastal region of eastern China should be taken into account when developing management strategies for protecting the natural environment.

Trace element concentration and speciation in selected urban soils in New York City

A long history of urbanization and industrialization has affected trace elements in New York City (NYC) soils. Selected NYC pedons were analyzed by aqua regia microwave digestion and sequential chemical extraction as follows: water soluble (WS); exchangeable (EX); specifically sorbed/carbonate bound (SS/CAR); oxide-bound (OX); organic/sulfide bound (OM/S). Soils showed a range in properties (e.g., pH 3.9 to 7.4). Sum of total extractable (SUMTE) trace elements was higher in NYC parks compared to Bronx River watershed sites. NYC surface horizons showed higher total extractable (TE) levels compared to US non-anthropogenic soils. TE levels increased over 10 year in some of the relatively undisturbed and mostly wooded park sites. Surface horizons of park sites with long-term anthropogenic inputs showed elevated TE levels vs. subsurface horizons. Conversely, some Bronx River watershed soils showed increased concentrations with depth, reflective of their formation in a thick mantle of construction debris increasing with depth and intermingled with anthrotransported soil materials. Short-range variability was evident in primary pedons and satellite samples (e.g., Pb 253 ± 143 mg/kg). Long-range variability was indicated by PbTE (348 versus 156 mg/kg) and HgTE (1 versus 0.3 mg/kg) concentrations varying several-fold in the same soil but in different geographic locations. Relative predominance of fractions: RES (37 %) > SS/CAR (22 %) > OX (20 %) > OM/S (10 %) > EX (7 %) > WS (4 %). WS and EX fractions were greatest for Hg (7 %) and Cd (14 %), respectively. RES was predominant fraction for Co, Cr, Ni, and Zn (41 to 51 %); SS/CAR for Cd and Pb (40 and 63 %); OM/S for Cu and Hg (36 and 37 %); and OX for As (59 %).

Evaluation of the anthropogenic influx of metal and metalloid contaminants into the Moulay Bousselham lagoon, Morocco, using chemometric methods coupled to geographical information systems

Superficial and cored sediment samples from the Moulay Bousselham lagoon and sub-watershed were analyzed for Al, Fe, Cu, Zn, Pb, Mn, Ni, Cr, As, Hg, and Cd. The temporal and spatial distributions of the main contamination sources of heavy metals were identified and described using chemometric and geographic information system (GIS) methods. Sediments from coastal lagoons near urban and agricultural areas are commonly contaminated with heavy metals, and the concentrations found in surface sediments are significantly higher than those from 50-100 years ago. The concentrations of these elements decrease sharply with depth in the sediment column, and the elements are preferentially enriched in the <2-μm-sized fraction of the sediment. The zones of enhanced risk of heavy metals were detected by means of GIS-based geostatistical modeling. According to sediment pollution indices and statistical analysis, heavy metals (Pb, Cu, Ni, Zn, Cr, and Hg) that pose a risk have become largely enriched in the lagoon sediments during the recent period of agricultural intensification.

A method of identifying priority spatial patterns for the management of potential ecological risks posed by heavy metals

An approach of identifying priority spatial patterns in response to different ecological risk levels associated with heavy metals (HM) is proposed. First, ecological hotspots (EH) are delineated by integrating NDVI-based assessment with the impact assessment of anthropogenic impact sources. Second, the HM potential ecological risks index (PERI) is calculated and spatially interpolated. Finally, the EH with different PERI values are identified through logic calculation. Study results show that 45.2% of the study region has low HM risks, 53.2% with moderate HM risks, and only 1.6% with high HM risks. In addition, the percentage of EH with low HM risks is 6.5%; the percentage with moderate HM risks is 5.4%; and the percentage with high HM risks is 0.4%. The EH with low and moderate HM ecological risks are proposed to be the regions in priority for management. This approach is potentially useful to HM ecological risk assessment and HM contamination management around the world.