Disentangling the impact of anthropogenic and natural processes on the environment in a subtropical subalpine lake catchment in northeastern Taiwan over the past 150 years.

Human activities impose significant changes on sedimentation processes and vegetation cover within lake catchments. However, the needed time for an anthropogenically disturbed natural state to be reversed back to its natural state by environmental protection programs is still ambiguous. Here we employ a multi-proxy approach to delineate major environmental disturbances such as logging and forest fires on the catchment in Cueifong Lake, a subtropical subalpine lake in northeastern Taiwan. X-ray Fluorescence (XRF) core scanning, bulk total organic carbon (TOC), bulk total nitrogen (TN), stable carbon isotope (δ13Corg) analysis, and macro-charcoal counting were utilized to reconstruct changes in the catchment environment based on a sediment core from Cueifong Lake. The results show that the element content changed distinctly around 1975 CE, which coincided with the onset of profound deforestation in the lake vicinity recorded in historical documents and aerial photos. After the cessation of the logging event, the detrital input increased, accompanied by decreasing C/N ratios and increasing δ13Corg values. This suggests that increased terrestrial nutrient input promoted algae growth. After the deforestation phase, our results imply a gradual recovery of elemental composition in the catchment environment. By extrapolating the XRF element records, we suggest that it might take >50 years for the sedimentary regime to reach its pre-logging baseline. In contrast to the depositional system, the C/N and δ13Corg shifted significantly - potentially irreversibly - towards an algae-dominant environment instead of recovering to the pre-logging condition. This could be due to both 1) the changes in the different vegetation species used for reforestation and/or 2) anthropogenically introduced fishes in the 1980s. This study proposes the first assessment of the needed recovery time for subtropical Asian subalpine forests after large-scale logging activity and thus provides an apparent reference for policy decisions on natural resource development and environmental protection.

Application of the paleolimnological method to assess metal contaminant distribution (As, Cu, Pb, Zn) in pulp mill stabilization basin sediments, Nova Scotia, Canada.

The paleolimnological method was used to decouple geogenic and anthropogenic metal (loids) contributions in a sediment stabilization basin (Boat Harbour) located in Nova Scotia, Canada. Boat Harbour has been impacted by industrial effluents discharged by a bleached kraft pulp mill (1967 to 2019) and a chlor-alkali plant (1971 to 1992). The former estuary now contains >577,000 m3 of unconsolidated sediment, impacted by inorganic and organic contaminants, including metal[loid]s, polycyclic aromatic hydrocarbons and polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans. Previous studies indicated significant knowledge gaps in our understanding of the spatial, stratigraphic, and temporal variation of sediment contamination. Twenty-five lakebed sediment gravity cores were obtained between 2016 and 2019 to determine spatiotemporal distribution of sediment As, Cu, Pb, and Zn concentrations which consistently exceeded guidelines for aquatic sediments. Results demonstrate there is no distinct spatial trend in metal concentrations despite point source effluent inputs. High and variable concentrations of Cu and Zn in contaminated sediment likely represent a combination of cation capture by highly organic sediment and influence of pulp mill on lakebed sediment chemistry. Elevated Pb in contaminated sediment is the result of atmospheric deposition from combustion of fossil fuels and bioaccumulation in effluent feedstock. Average sedimentation rate (1 cm every 3 years) is high compared to a nearby freshwater lake and is enhanced by increased nutrient loading and more productive water column conditions associated with effluent introduction. Temporal trends indicate significantly higher concentrations of Zn and Cu in top sediment samples consistent with changes in effluent treatment procedures as well as composition of effluent solids. Comparison of geochemistry of effluent influenced sediment and pre-effluent substate sediment at Boat Harbour to freshwater and marine reference was required to understand the degree to which geogenic and anthropogenic sources of metal(loids) have influenced effluent chemistry. This study demonstrates that undisturbed, time transgressive samples from both impacted sites and reference sites combined with non-destructive, rapid, small sample analytical techniques such as X-ray fluorescence, provide an accurate assessment of sediment metal contaminant distribution, data required to guide remediation and environmental effects monitoring and compliance.

Macrofaunal control of microbial community structure in continental margin sediments.

Through a process called "bioturbation," burrowing macrofauna have altered the seafloor habitat and modified global carbon cycling since the Cambrian. However, the impact of macrofauna on the community structure of microorganisms is poorly understood. Here, we show that microbial communities across bioturbated, but geochemically and sedimentologically divergent, continental margin sites are highly similar but differ clearly from those in nonbioturbated surface and underlying subsurface sediments. Solid- and solute-phase geochemical analyses combined with modeled bioturbation activities reveal that dissolved O2 introduction by burrow ventilation is the major driver of archaeal community structure. By contrast, solid-phase reworking, which regulates the distribution of fresh, algal organic matter, is the main control of bacterial community structure. In nonbioturbated surface sediments and in subsurface sediments, bacterial and archaeal communities are more divergent between locations and appear mainly driven by site-specific differences in organic carbon sources.

Discharge of deeply rooted fluids from submarine mud volcanism in the Taiwan accretionary prism.

Qualitative and quantitative assessments of fluid cycling are essential to address the role and transport of deeply sourced fluids in subduction systems. In this study, sediment cores distributed across a submarine mud volcano (SMV) offshore southwestern Taiwan were investigated to determine the characteristics of fluids generated through the convergence between the Eurasian and Phillippine Sea Plates. The low dissolved chloride concentration combined with the enrichment of 18O, and depletion of 2H of pore fluids suggest the discharge of deep freshwater formed by smectite dehydration at an equilibrium temperature of 100 to 150 °C. The upward fluid velocities, decreasing from 2.0 to 5.0 cm yr-1 at the center to a negligible value at margin sites, varied with the rate and efficiency of anaerobic methanotrophy, demonstrating the impact of fluid migration on biogeochemical processes and carbon cycling. By extrapolating the velocity pattern, the flux of fluids exported from 13 SMVs into seawater amounted up to 1.3-2.5 × 107 kg yr-1, a quantity accounting for 1.1-28.6% of the smectite-bound water originally stored in the incoming sediments. Our results imply that SMVs could act as a conduit to channel the fluids produced from great depth/temperature into seafloor environments in a subduction system of the western Pacific Ocean.

A comprehensive sediment dynamics study of a major mud belt system on the inner shelf along an energetic coast.

Globally mud areas on continental shelves are conduits for the dispersal of fluvial-sourced sediment. We address fundamental issues in sediment dynamics focusing on how mud is retained on the seabed on shallow inner shelves and what are the sources of mud. Through a process-based comprehensive study that integrates dynamics, provenance, and sedimentology, here we show that the key mechanism to keep mud on the seabed is the water-column stratification that forms a dynamic barrier in the vertical that restricts the upward mixing of suspended sediment. We studied the 1000 km-long mud belt that extends from the mouth of the Changjiang (Yangtze) River along the coast of Zhejiang and Fujian Provinces of China and ends on the west coast of Taiwan. This mud belt system is dynamically attached to the fluvial sources, of which the Changjiang River is the primary source. Winter is the constructive phase when active deposition takes place of fine-grained sediment carried mainly by the Changjiang plume driven by Zhe-Min Coastal Currents southwestward along the coast.

Effects of environmental regulations on heavy metal pollution decline in core sediments from Manila Bay.

We investigated the high-resolution heavy metal pollution history of Manila Bay using heavy metal concentrations and Pb isotope ratios together with (210)Pb dating to find out the effects of environmental regulations after the 1990 s. Our results suggested that the rate of decline in heavy metal pollution increased dramatically from the end of the 1990 s due to stricter environmental regulations, Administrative Order No. 42, being enforced by the Philippines government. The presented data and methodology should form the basis for future monitoring, leading to pollution control, and to the generation of preventive measures at the pollution source for the maintenance of environmental quality in the coastal metropolitan city of Manila. Although this is the first report of a reduction in pollution in Asian developing country, our results suggest that we can expect to find similar signs of pollution decline in other parts of the world as well.

Occurrence of azaarenes in sediments of the Danshuei River, Taiwan: the use of azaarenes as indicator of anthropogenic source to the estuarine system.

Azaarenes belong to the newly identified classes of anthropogenic pollutants. To our knowledge, this study presents the first result of pollution history of azaarenes and their controlling factors in estuary. To understand the transport mechanisms, surface sediment samples were collected from 18 sites of the Danshuei River during the summer and the winter of 2005. The highest concentrations of azaarene, 21.9 ng g(-1) for 2-ring, 9.89 ng g(-1) for 3-ring, and 9.17 ng g(-1) for 4-ring, were observed in midstream surface sediments near the Shi-Zi-Tou waste water pumping station. Therefore, this waste water pumping station not only provides a good sediment accumulation environment but also discharges small particle size sediments, which contain mass amounts of azaarenes into the Danshuei River. This research also finds highly significant covariations among 3-ring and 4-ring azaarenes, which suggests similar source strengths and transport mechanisms for these compounds. Additionally, core samples were collected from two sites of the Danshuei River and analyzed to determine the pollution history. Values found in the core sediments correspond to pollution events in recent history. Contaminant inputs via in situ burning of dumping field and wastewater discharge for the periods of 1975-1985 and 2004-2005, respectively, were two major sources of azaarenes to the Danshuei River.

Authentication labels based on guided-mode resonant filters.

A guided-mode resonance (GMR) filter with wide angular tolerances is experimentally demonstrated as an authentication label illuminated with unpolarized white light. The proposed filter, based on a free-standing silicon nitride membrane suspended on a silicon substrate, is fabricated by using anisotropic wet etching to remove the substrate beneath the silicon nitride layer. Both grating and waveguide structures without a lower cladding layer, i.e., a substrate, are fabricated simultaneously on a silicon nitride membrane. Since the silicon nitride is transparent within the spectra of visible and infrared light, such suspended-membrane-type GMR filters are well suited for applications within the visible spectrum. Moreover, the high refractive index of silicon nitride allows the proposed filters to have strongly modulated gratings and an immunity to high angular deviation. The measured reflection resonance has an angular tolerance up to +/-5 degrees under normal incidence for the wavelength of 629.5 nm.