Manganese in Narragansett Bay1

Decadal ventilation and mixing of Indian Ocean waters

Endogenous phosphorus (P) release and its complex biogeochemical transformation pose ongoing challenges for effective P management in estuarine ecosystems. However, the understanding of how these processes respond to runoff regulations remains rarely constrained. This study investigated the spatiotemporal distribution of P forms in bottom water and sediment of the Liao River Estuary under anthropogenic runoff regulations characterized by low runoff in summer and normal runoff in winter. The sediment P adsorption capacity and release potential were studied through adsorption kinetics and thermodynamic experiments. Soluble reactive P (SRP) and total dissolved P (TDP) concentrations in bottom water were low in summer but increased markedly in winter (p<0.01). The average sediment total P (TP) concentrations were 495.26 mg/kg in summer and 399.62 mg/kg in winter, with higher TP levels mainly observed in the nearshore muddy areas, likely attributable to the high proportion of fine particles. Equilibrium P concentration generally exceeded the SRP concentration in bottom water under both conditions, indicating that the sediment served as a P source. The sediment P eutrophication risk index (ERI) further showed that release risk was predominantly moderate in summer, whereas it was low in winter. Both PLS-PM and correlation analysis showed that the concentrations of Fe, Al, organic matter, and the proportion of fine particles served as key determinants influencing the content of aluminum-bound P (NaOH-rP), organic P (NaOH-nrP), and calcium-bound P (HCl-P). Furthermore, elevated SRP levels combined with reduced salt in winter likely constrain P accumulation in the sediment. This study offers novel insight into the migration and transformation of P in the estuarine environment under anthropogenic runoff regulations.

Dissolved oxygen and suspended particles regulate the benthic flux of iron from continental margins

Unraveling antibiotic fate in a highly urbanized estuary: Spatiotemporal patterns, multi-media partitioning, and contaminant prioritization.

Characterization of marine microbial communities around an Arctic seabed hydrocarbon seep at Scott Inlet, Baffin Bay

In highly eutrophicated Tokyo Bay, anoxic, sulfide-containing bottom water is formed in warm stagnant seasons. It seems to develop especially in the northeast area where there are many large holes made by dredging to collect sand in addition to navigation channels. At such dredged sites, the seasonal variation in the rate of sulfate reduction in sediment was examined by a radiotracer method together with various environmental factors for two years and the results were compared with those obtained at a site on the natural sea floor. The rate of sulfate reduction was much higher at the dredged sites than on the natural sea floor. The dissolved oxygen concentration in bottom water and sulfate concentration in the sediment layer were lower, and the density of sulfate-reducing bacteria and acid-volatile sulfides were higher at the dredged sites than the natural floor site. However, there was no significant correlation between the sulfate reduction rate and any of the environmental factors examined (temperature, ignition loss, DO in bottom water and density of sulfate-reducing bacteria). The rate on an area basis seemed to fluctuate in a similar pattern to the change of chlorophyll a in the water column. The addition of seston mainly composed of diatoms to the sediment sample greatly stimulated sulfate reduction in contrast to the addition of lactate. Sulfate reduction at these sites might be controlled by the supply of organic substrates especially those of algal origin.

Abstract. Hydroelectric reservoirs bury significant amounts of organic carbon (OC) in their sediments. Many reservoirs are characterized by high sedimentation rates, low oxygen concentrations in bottom water and a high share of terrestrially derived OC, and all of these factors have been linked to a high efficiency of OC burial. However, investigations of OC burial efficiency (OCBE, i.e., the ratio between buried and deposited OC) in reservoirs are limited to a few studies, none of which include spatially resolved analyses. In this study we determined the spatial variation in OCBE in a large subtropical reservoir and related it to sediment characteristics. Our results show that the sediment accumulation rate explains up to 92 % of the spatial variability in OCBE, outweighing the effect of other variables, such as OC source and oxygen exposure time. OCBE at the pelagic sites varied from 48 to 86 % (mean 67 %) and decreased towards the dam. At the margins, OCBE was lower (9–17 %) due to the low sediment accumulation in shallow areas. Our data show that the variability in OCBE both along the rivers–dam and the margin–pelagic axes must be considered in whole-reservoir assessments. Combining these results with a spatially resolved assessment of sediment accumulation and OC burial in the studied reservoir, we estimated a spatially resolved mean OC burial efficiency of 57 %. Being the first assessment of OCBE with such a high spatial resolution in a reservoir, these results suggest that reservoirs may bury OC more efficiently than natural lakes.

Aluminum sulfate was applied to eutrophic Eau Galle Lake to control internal phosphorus recycling from anoxic sediments for a period of five years, and to provide increased user benefits at a reasonable cost. Treatment dose (11.3 g Al/m2) was based on mass balance estimates of summer Internal phosphorus loading rates; no attempt was made to curtail external loading rates. Phosphorus concentrations in bottom waters, internal phosphorus loading rate, and the abundance of blue-green algae were reduced relative to previous years; however, algal biomass remained relatively high. The proliferation of the dinoflagellate Ceratium hirundinella, a vertical migrator, suggested that these algae may have obtained phosphorus from interflowing river waters having a high nutrient content.

Decadal changes in nutrient fluxes and environmental effects in the Jiulong River Estuary

Terrigenous dissolved organic matter input and nutrient-light-limited conditions on the winter microbial food web of the Beagle Channel

We analyzed publicly available data of Fukushima 137Cs concentrations in coastal fish, in surface and bottom waters, and in surface marine sediments and found that within the first year of the accident pelagic fish lost 137Cs at much faster rates (mean of ∼1.3% d-1) than benthic fish (mean of ∼0.1% d-1), with benthopelagic fish having intermediate loss rates (mean of ∼0.2% d-1). The loss rates of 137Cs in benthic fish in the first year were more comparable to the decline of 137Cs concentrations in sediments (0.03% d-1), and the declines in pelagic fish were more comparable to the declines in seawater. Retention patterns of 137Cs in pelagic fish were comparable to that in laboratory studies of fish in which there were no sustained 137Cs sources, whereas the benthopelagic and benthic fish species retained 137Cs to a greater extent, consistent with the idea that there is a sustained additional 137Cs source for these fish. These field data, based on 13 511 data points in which 137Cs was above the detection limit, are consistent with conclusions from laboratory experiments that demonstrate that benthic fish can acquire 137Cs from sediments, primarily through benthic invertebrates that contribute to the diet of these fish.

The ratio of ionium to thorium varies exponentially with depths in deepsea sediments of the Pacific Ocean and gives rates of accumulation of the order of millimeters per thousand of years. Surface values of the ratio were not constant over the eastern Pacific Ocean. This observation may result from differences in thorium isotope concentrations in near bottom waters which furnish these isotopes to the sediments.

Results of three long cycles of 24-hour measurements of the carbon dioxide content in the surface and bottom water in the ice period of 2014-2016 in the Baikal coastal zone are analyzed. The diurnal dynamics of the СО₂ concentration in the subglacial water, in which photosynthesis plays the leading role, is described. It is found that, in comparison with the surface subglacial water (that is, directly adjacent to the ice bottom), the more pronounced diurnal rhythm of СО₂ is observed in the bottom layer in all realizations. This rhythm is well correlated with pyranometer readings. The data on the diurnal dynamics of СО₂ are used to estimate the gross primary production in the bottom water with the DIEL method based on the analysis of temporal variability of the carbon dioxide concentration in water <i>in situ</i>.

Mapping Soils under Water

Using investigation data on Cadmium (Cd) in waters in Jiaozhou Bay 1989, we analyzed the spatial and temporal distributions of Cd, and identified the homogenous process of Cd contents. Results showed that by means of vertical water’s effect Cd contents in both surface and bottom waters were showing seasonal variations of spring > summer. High Cd contents in surface waters could result in dilution effect in bottom waters, while low Cd contents in surface waters could result in accumulation effect in bottom waters. That was the homogenous process of Cd contents in marine bay. Ocean is a large container in where every substances discharged into would be homogeneous distributed finally no matter the contents are high or low.