Nutrient budgets and biogeochemical dynamics in the coastal regions of northern Beibu Gulf, South China Sea: Implication for the severe impact of human disturbance.

This study examined the nutrient budgets and biogeochemical dynamics in the coastal regions of northern Beibu Gulf (CNBG). Nutrient concentrations varied spatially and seasonally among the different bays. High nutrient levels were found in the regions with high riverine inputs and intensive mariculture. Using a three end-member mixing model, nutrient biogeochemistry within the ecosystem was estimated separately from complex physical mixing effects. Nutrient consumption dominated in most bays in summer, whereas nutrient regeneration dominated in winter, likely due to phytoplankton decomposition, vertical mixing and desorption. Through the Land-Ocean Interaction Coastal Zone (LOICZ) model, the robust nutrient budgets were constructed, indicating that the CNBG behaved as a sink of dissolved inorganic nitrogen, phosphorus and silicon. River-borne nutrient inputs were the dominant nutrient source, while residual flows and water exchange flows transported nutrient off the estuaries. This study could help us better understand nutrient cycles and nutrient sources/sinks in the CNBG.

Potentially toxic elements and rare earth elements in sandy soils from the Brazilian Cerrado.

This study aims to determine the concentration of potentially toxic elements (PTEs) and rare earth elements (REEs) in Brazilian sandy soils under the Cerrado at the Parnaíba-São Francisco Basin transition. We also explored the geochemical correlation between these elements and pH, cation exchange capacity (CEC), total organic carbon (TOC), sand, clay, oxides from secondary minerals, and chemical index of alteration for each basin. Mineralogical, physical, and chemical analyses were used to examine PTE and REE geochemistry in six sand soil profiles from the Brazilian Cerrado. The background concentrations of these elements are low, but soils from the Parnaíba Basin have higher concentrations of PTEs than soils from the São Francisco Basin. In soils from the Parnaíba Basin, mainly Al2O3 has relevance in the V and Cr geochemistry, as these elements increase with increasing Al2O3 content. On the other hand, the REEs have CEC as a soil attribute of higher relevance in the geochemistry of those elements is soils from the Parnaíba Basin, and this relevance divides the TOC, Fe2O3, and TiO2 minerals from the clay fraction. In soils from the São Francisco Basin, the geochemistry of PTEs is possibly associated with kaolinite, especially Cu, V, and Zn. In contrast, the Ba concentration was associated with the presence of feldspar. Unlike soils from the Parnaíba Basin, the REEs do not correlate with the studied soil attributes, except for Ho and Lu. Ho had a positive association with Al2O3. Ho and Lu are negatively related to the presence of iron oxides.

C and P pool restoration by a no-tillage system on Brazilian Cerrado Oxisol in Piauí State.

The Cerrado soil is under constant modification, especially because of the use of agricultural systems, which affect soil carbon (C) and phosphorus (P) functioning. Thus, the objective of this study was to determine the C and P dynamics in Brazilian Cerrado Oxisol in Piauí State under natural and anthropic conditions, considering that conservational agricultural management and no-tillage systems can restore the C and P pools in that soil. Four soil samples with distinct characteristics (native Cerrado, NC; burned native Cerrado, BNC; conventional tillage agricultural system, CTS; and no-tillage agricultural system, NTS) were collected in the study area for chemical and physical laboratory analysis. The total organic carbon (TOC) concentrations found were 33 g kg-1, 27 g kg-1, 26 g kg-1, and 20 g kg-1 for CTS, NTS, NC, and BNC, respectively. The NTS had a total nitrogen (TN) concentration of 2.0 g kg-1. The CTS had 33.4 g kg-1 of soil-oxidizable C, followed by the NTS with 27.2 g kg-1. In both studied layers, the NTS had an organic P concentration > 200 mg kg-1. The higher TOC concentration in the CTS was because of the higher content of clay in comparison with that in the NTS. The organic P in the NTS was associated with a less labile fraction of C. Thus, despite the disturbance caused by agricultural systems, the adoption of the NTS could be an influential strategy in agricultural systems to restore soil organic functioning in the Brazilian Cerrado Oxisol in Piauí State.

Accumulation rates and chronologies from depth profiles of 210Pbex and 137Cs in sediments of northern Beibu Gulf, South China sea.

Beibu Gulf is a highly dynamic and complex coastal environment that is currently experiencing one of the largest rates of development and urbanization in west China. Little is known about the effects of this increased human activity on coastal sedimentation processes and on the rates of sediment accumulation and the variation of organic materials to the coast. In this study, four sediment cores were collected and applied the 210Pb dating method to reconstruct sedimentation rates and historical changes of materials to the northern Beibu Gulf over the past century. Depth profiles of excess 210Pb (210Pbex) showed highest activity values at the surface (28.4-104.0 Bq kg-1) followed by a linear or exponential decay with depth for all but one study site. 137Cs activity ranged between 0.236 and 2.034 Bq kg-1, and a distinct peak activity - representing the 1963 fallout maximum - was observed at all but one site. Sediment chronologies were determined using the Constant Rate of Supply (CRS) model. Calculated accumulation rates in the studied sites were the lowest in the late 1920s and early 1930s (mass accumulation rate (MAR): 0.06 ± 0.01 g cm-2 y-1; sediment accumulation rate (SAR): 0.08 ± 0.01 cm y-1) and increased gradually until reaching maximum values in the 2010s (MAR: 0.22 ± 0.09 g cm-2 y-1; SAR: 0.46 ± 0.32 cm y-1). Current accumulation rates are up to 800% higher than rates observed in the 1920s, with most of the increase happening after 1970, coinciding with the increasing rate of urbanization and development in the region. The highest increase in SAR over the last century (+877%) was observed in Sanniang Bay, with the lowest rate of increase (+283%) observed in Lianzhou Bay. TOC content in these sediments has also increased over the last 100 years. Current values (0.98-1.28%) are about 170% higher than historical concentrations (before 1970). The positive correlations between TOC and population density and GDP growth in major cities surrounding the gulf, provide further indication that human activities have significantly altered the sedimentary environment in recent decades along the northern Beibu Gulf coast.

Impact of temperature and storage time on the migration of antimony from polyethylene terephthalate (PET) containers into bottled water in Qatar.

Prosperity in Qatar and the consequent stresses on water resources resulted in a sustainable increase in the bottled drinking water market. Reports on health concerns and possible migration of chemicals from the plastic material into the water have driven the current investigation. This study aims to address the extent of antimony (Sb) leaching from polyethylene terephthalate (PET) water bottles subject to temperature variations (24-50 °C) due to Qatar's hot climate and improper storage conditions. A representative basket including 66 different imported and locally produced water bottles was considered. The concentrations of Sb in bottled water ranged from 0.168 to 2.263 µg/L at 24 °C and from 0.240 to 6.110 µg/L at 50 °C. Antimony concentrations in PET bottles at 24 °C was significantly lower than those at 50 °C (p = 0.0142), indicating that the temperature was a principal factor affecting the release of Sb from the plastic into the water. Although the detected Sb amounts were below the guidelines endorsed by WHO and Qatar (standard 5 µg/L) at 24 °C, the concentration measured at 50 °C was higher than the recommended WHO values (6.11 µg/L).