Pei Sun Loh

Evaluating relationships between sediment chemistry and anoxic phosphorus and iron release across three different water bodies

Abstract This study evaluated phosphorus (P) and iron (Fe) release from anoxic sediment cores in 3 different water bodies, Lake Winnipeg in Manitoba and Lake Simcoe and Hamilton Harbour in Ontario, and developed empirical models to predict P and Fe release rates as functions of sediment and water chemistry. Maximum P and Fe sediment release rates, which occurred shortly after sulfate (SO4) was depleted in most cores, showed unique positive linear relationships for each lake. High P release rates only occurred from Lake Simcoe and Lake Winnipeg sediments with molar ratios =8.1 of NaOH-extractable aluminum (Al) to reducible Fe (Fe extractable with bicarbonate-dithionite [BD]). High Fe release rates only occurred in Lake Winnipeg sediments, perhaps due to low SO4 reduction rates (<115 mg m-2 d-1). Three approaches were used to develop linear regression models for maximum P and Fe release rates using data from all lakes: only Lake Winnipeg, only Lake Simcoe, and low (=8.1) and high molar ratios (>20) of NaOH-extractable Al to BD-extractable Fe. Regression models differed depending on the study sites used, and only 3 of the 5 significant regression models for P release had high predictive value (R2 > 0.7). Four of the 5 significant Fe release models had R2 > 0.7, but we were unable to find a significant Fe model for Lake Simcoe. These results are important because they delineate the limitations of this approach to modeling release using operationally defined fractions.

Optimised recovery of lignin-derived phenols in a Scottish fjord by the CuO oxidation method

Lignin is found only in vascular plant tissues, hence monitoring of lignin in aquatic environments is important in the determination of the sources and fate of terrestrial organic matter (OM). Concentrations of lignin-derived phenols provide an estimate of the amount of terrestrial OM in a system. Other lignin parameters such as the ratios of syringyl to vanillyl (S/V) and cinnamyl to vanillyl (C/V) phenols provide information on vegetation sources; and the ratios of vanillic acid to vanillin, (Ad/Al)v, and syringic acid to syringaldehyde, (Ad/Al)s, indicate the degradation stage of lignin materials. Concentrations of lignin-derived phenols were determined for the surface and subsurface sediments of a Scottish sea loch, Loch Creran, using a CuO oxidation method. In order to achieve the highest methodological efficiency, a series of validation experiments for each procedural step were carried out. As a result, several procedural steps were optimized. It was found that a lower oxidation temperature resulted in higher product yield and the duration and temperature of the silylation step have no effect on the outcome of the process. Studies of seasonal variations of lignin parameters showed that the occasional increase in lignin content in sediment trap samples was attributable to materials discharged from River Creran and the incoming water from the direction of Creagan bridge. The flow regime caused resuspension of surface sediments and entrainment of lignin materials into the water column. Lignin parameters exhibited more significant trends across an axial transect of the loch (from the head to mouth). Total lignin content decreased and the C/V ratios increased from upper to lower Loch Creran as these lignin materials were transported further down the loch and were subjected to hydrodynamic sorting processes.

Sedimentary Organic Matter and Phosphate along the Kapuas River (West Kalimantan, Indonesia)

This study assessed the sedimentary organic matter (OM) and phosphate along the world’s longest river on an island: the Kapuas River in West Kalimantan, Indonesia. The surface sediment was tested using the loss-on-ignition experiment to determine the % labile OM, % refractory OM, and % total OM and the Rp values (the ratio of refractory to total OM). The C/N ratios and the inorganic phosphate (IP), organic phosphate (OP), and total phosphate (TP) levels were also determined. The combination of high Rp values and low C/N ratios along the upper river indicated the possible presence of relatively degraded material; the low Rp values and high C/N ratios downstream were indicative of a fresher terrestrial signal. Sedimentary P levels were the highest along the densely populated areas downstream from the Kapuas River; the second highest along the midstream river, which is surrounded by oil palm plantations; and the lowest along the upper river, which is surrounded by forest. Higher levels of OM, IP, OP, and TP downstream along the Kapuas River indicated the presence of anthropogenic sources of OM and P.

Ecological risk and contamination history of heavy metals in the Andong tidal flat, Hangzhou Bay, China

ABSTRACT In this study, we collected two sediment cores (C1 and C2) from the Andong tidal flat, Hangzhou Bay, and studied the temporal variations of heavy metals in the cores. Vertical distributions of heavy metals were almost unchanged in both the cores before 2000. After 2000, however, the heavy metal concentrations increased dramatically, suggesting that the sediments have been affected by enhanced human pollution in the recent decade. In the core C1, the sediments were severely polluted by Pb, moderately to considerably polluted by Cr and Zn, and low to moderately polluted by other heavy metals. The core C2 was relatively unpolluted before 2000 and low to moderately polluted after 2000. Multi-statistical analyses indicated that the core C1 was additionally contaminated by local human activities such as wastewater discharge and the Hangzhou Bay Bridge. The heavy metals in the core C2, however, were largely contributed by the Yangtze River and controlled by sedimentation process. The calculated sedimentary flux (4–8 g m−2 a−1) of heavy metals generally increased with time. It was closely related to the wastewater discharge in adjacent areas. This study reconstructed the local heavy metal pollution history and provides important information for environmental protection and policy making.

Sediment fluxes and carbon budgets in Loch Creran, Western Scotland

Abstract Sea lochs are regions where riverine and marine organic carbon (OC) undergoes decomposition, deposition or transportation to shelf slopes and the deep sea. According to the OC budget presented here, discharge from River Creran (1.44×106 kg a−1) and phytoplankton material (0.89×106 kg a−1) make up a significant input of OC to Loch Creran while 0.67×106 kg a−1 OC is from other sources. A total of 1.28×106 kg a−1 OC is deposited in the loch and 1.14×106 kg a−1 OC is oxidized in the water column. Discharge to the Lynn of Lorn consists of 0.58×106 kg a−1 OC. Hence Loch Creran is a sink for OC where 42.7% of the total OC input is buried and 38% and 1.7% decomposed in the water column and subsurface sediments, respectively. River Creran contributes 63% labile and 37% refractory organic matter to the loch. More than 95% of each of the total OC, lignin and organic matter deposited onto the surface sediments is buried in the subsurface sediments. Seventy-five percent of the total organic matter decomposed in the water column is labile. Output to Lynn of Lorn consists of 54.6% refractory organic matter.

Sources and distribution of sedimentary organic matter along the northern Bering and Chukchi Seas

In this study, lignin-derived phenols were used to determine the sources and distribution of sedimentary organic matter along the northern Bering Sea and Chukchi Sea of the Arctic Ocean. The lignin parameter syringyl/vanillyl (S/V) and cinnamyl/vanillyl (C/V) ratios are used to indicate vegetation sources; and the ratios of vanillic acid/vanillin, (Ad/Al)v and syringic acid/syringaldehyde, (Ad/Al)s are used as indicators of lignin diagenesis. Results showed the predominance of woody gymnosperm signal at the easternmost location in the northern Bering Sea, a mixture of refractory non-woody angiosperm and fresher gymnosperm tissues in the Chukchi Sea, and signal of fresher woody gymnosperm tissues in the northernmost locations in the Chukchi Sea. The lignin materials showed gradual increase in decomposition stage during transport along the northern Bering Sea. Hydrodynamic sorting process, which is the retention of coarser materials nearshore and transportation of finer particles farther offshore, most probably occurred along the east coast of the northern Bering Sea. In Chukchi Sea, the non-woody angiosperm tissues could have originated from the Canadian Arctic and gymnosperm tissues could be from the Russian Arctic side. The fresher materials in the northernmost Chukchi Sea could have been transported here via the ice-rafting process. Detection of fresh lignin materials and the occurrence of lignin decomposition mean that this region could be sensitive to the impact of climate change.

Sources, distribution, and decomposition stages of sedimentary organic matter in estuaries and its adjacent areas

ABSTRACT Lignin-derived phenols, C/N ratios and ratios of refractory to total organic matter were used to study the sources, distribution, and diagenesis of sedimentary organic matter along estuary, river bank, and salt marsh systems. The Changjiang Estuary showed a higher signal of terrestrial organic matter at the river mouth which decreased farther offshore. The locations along the Qiantang River were affected by their adjacent surroundings, and the Andong salt marsh showed higher terrestrial organic matter signal at the upper marsh compared to the lower marsh. All studied areas showed slight increases in organic matter decomposition farther downstream and towards the sea. Study of these three different systems will improve our understanding on their ecotoxicological impact. The Changjiang Estuary had higher pollutant levels near the river mouth, which decreased farther offshore due to dilution. The midstream Qiantang River was most likely affected by pollution from their adjacent surroundings. Pollutants were likely to be accumulated in the Andong salt marsh due to the presence of marsh plants and small-sized particles. Organic pollutants were likely to be decomposed during transport along the systems. The ability of the sediments to release inorganic pollutants was determined by whether these systems were oxic or anoxic.

Heavy metal distribution and accumulation in the Spartina alterniflora from the Andong tidal flat, Hangzhou Bay, China

In order to study the heavy metal accumulation and distribution in the roots, stems, and leaves of Spartina alterniflora, we collected S. alterniflora samples and the associated sediments along three transects at the Andong tidal flat, Hangzhou Bay. Co, Ni, Cd, Pb, Cu, and Zn were mainly accumulated in the aerial parts (stems and leaves) of the plants, and their distributions depended on their mobility and their roles during the metabolism processes of S. alterniflora. The concentrations of Cu, Zn, Cd, Hg, and Pb were significantly enhanced with the increasing of heavy metal concentrations in the sediments, while those of Co and Ni remained relatively constant. Bioaccumulation factors results showed that the serious heavy metal contamination in the sediments from the transect A may overwhelm the accumulation capability of the plants. In addition, the physicochemical properties of the sediments and the pore water therein also play a role in the heavy metal concentrations and accumulations in the plants, because they can influence the behaviors and bioavailabilities of heavy metals during nutrition and bioaccumulation processes of the plants. The sediments with vegetation did not show significantly decreased heavy metal concentration with respect to the unvegetated sediments, although the plants did absorb heavy metals from the sediments. Principal component analysis and correlation analyses indicated that Co–Ni, Cu–Cd–Hg behaved coherently during accumulation, which may be ascribed to their similar accumulation mechanisms. This work provided essential information on the heavy metal accumulation by plants in a tidal flat, which will be useful for the environmental control through phytoremediation at estuaries.