Recent advances in biological production of 1,3-propanediol：new routes and engineering strategies

1,3-Propanediol (1,3-PDO) is an important chemical which has been widely used in cosmetic, pharmaceutical, and especially polymer industries. Production of 1,3-PDO from renewable feedstocks by green processes is attracting broad...

Red Tide Events and Seasonal Variations in the Partial Pressure of CO2 and Related Parameters in Shellfish-Farming Bays, Southeastern Coast of Korea

Mixed results have been reported on the evaluation of the coastal carbon cycle and its contribution to the global carbon cycle, mainly due to the shortage of observational data and the considerable spatiotemporal variability arising from complex biogeochemical factors. In this study, the partial pressure of carbon dioxide (pCO2) and related environmental factors were measured in the Jinhae–Geoje–Tongyeong bay region of the southeastern Korean Peninsula in February 2014, August 2014, April 2015, and October 2015. The mean pCO2 of surface seawater ranged from 215 to 471 μatm and exhibited a high correlation with the surface seawater temperature when data for August were excluded (R2 = 0.69), indicating that the seasonal variation in CO2 could be largely attributed to the variation in seawater temperature. However, a severe red tide event occurred in August 2014, when the lowest pCO2 value was observed despite a relatively high seawater temperature. It is considered that the active biological production of phytoplankton related to red tides counteracted the summer increase in pCO2. Based on the correlation between pCO2 and temperature, the estimated decrease in pCO2 caused by non-thermal factors was approximately 200 μatm. During the entire study period, the air–sea CO2 flux ranged from −14.2 to 3.7 mmol m–2 d–1, indicating that the study area served as an overall sink for atmospheric CO2, and only functioned as a weak source during October. The mean annual CO2 flux estimated from the correlation with temperature was −5.1 mmol m–2 d–1. However, because this estimate did not include reductions caused by sporadic events of biological production, such as red tides and phytoplankton blooms, the actual uptake flux is considered to be higher. The mean saturation state (ΩAr) value of carbonate aragonite was 2.61 for surface water and 2.04 for bottom water. However, the mean ΩAr of bottom water was <2 in August and October, and the ΩAr values measured at some of the bottom water stations in August were <1. Considering that the period from August to October corresponds to the reproduction and growth stages of shellfish, such low ΩAr values could be very damaging to shellfish production and the aquaculture industry.

Biological CO2 Uptake and Upwelling Regulate the Air-Sea CO2 Flux in the Changjiang Plume Under South Winds in Summer

The partial pressure of CO2 (pCO2) in the sea and the air-sea CO2 flux in plume waters are subject to interactions among biological production, horizontal advection, and upwelling under wind events. In this study, time series of pCO2 and other biogeochemical parameters in the dynamic Changjiang plume were presented to illuminate the controlling factors of pCO2 and the air-sea CO2 flux after a strong south wind event (July 23–24, maximum of 11.2 ms–1). The surface pCO2 decreased by 310 μatm (to 184 μatm) from July 24 to 26. Low-pCO2 waters (<200 μatm) were observed in the following 2 days. Corresponding chlorophyll a and dissolved oxygen (DO) increase, and a significant relationship between DO and npCO2 indicated that biological uptake drove the pCO2 decrease. The salinity of undersaturated-CO2 waters decreased by 3.57 (from 25.03 to 21.46) within 2 days (July 27–28), suggesting the offshore advection of plume waters in which CO2 had been biologically reduced. Four days after the wind event, the upwelling of high-CO2 waters was observed, which increased the pCO2 by 428 μatm (up to 584 μatm) within 6 days. Eight days after the onset of upwelling, the surface pCO2 started to decrease (from 661 to 346 μatm within 3 days), which was probably associated with biological production. Regarding the air-sea CO2 flux, the carbon sink of the plume was enhanced as the low-pCO2 plume waters were pushed offshore under the south winds. In its initial stage, the subsequent upwelling made the surface waters act as a carbon source to the atmosphere. However, the surface waters became a carbon sink again after a week of upwelling. Such short-term air-sea carbon fluxes driven by wind have likely occurred in other dynamic coastal waters and have probably induced significant uncertainties in flux estimations.

Decreasing Biological Production and Carbon Export Due to the Barrier Layer: A Case Study in the Bay of Bengal

A freshwater-induced barrier layer (BL) is a common physical phenomenon both in coastal waters and the open ocean. To examine the effects of BL on the biological production and the associated carbon export, a physical-biogeochemical survey was conducted in the Bay of Bengal. Severe depletions of surface phosphorus and the deepening of the nutricline were observed at the BL-affected stations due to the vertical mixing prohibition. The lowered surface chlorophyll a (Chl a) and squeezed deep Chl a maximum (DCM) layer also resulted in the ~18% lowered vertically integrated Chl a at the said stations. The composition of the net-sampled zooplankton was altered, and the abundance decreased by half at the BL-affected station (29.68 ind. m−3) compared with the unaffected station (55.52 ind. m−3). Such reductions in major zooplankton groups were confirmed by a video plankton recorder (VPR). The VPR observation indicated that there was a lower (by one-half) abundance of detritus at the BL-affected station, while the much lower carbon export flux rates were estimated to be at the BL-affected station (0.31 mg C m−2 d−1) rather than the unaffected station (0.77 mg C m−2 d−1). An idealized one-dimensional nutrient-phytoplankton-detritus model identified that the existence of BL can lead to decreased surface nutrients and phytoplankton concentrations, squeezed DCM layers, and lower detritus abundances. Finally, this study indicated that BL layers inhibit biological production and reduce carbon export, thus playing an important role in the ocean biogeochemical cycles.

Anthropogenic Influences on Dissolved Organic Matter in Three Coastal Bays, North China

Coastal bays bear anthropogenic influence strongly, and thus dissolved organic matter (DOM) in coastal bays, which is an important component of global carbon cycling, could be heavily affected by anthropogenic inputs. Utilizing absorbance, fluorescence spectroscopy, and stable carbon isotope (δ13C), this study analyzed the characteristics and distribution of DOM in three coastal bays (Jiaozhou Bay, Sishili Bay, and Taozi Bay), located in North China. The results showed that there was always a high concentration of DOM near the river mouth in all three bays and the DOM concentration decreased along the salinity gradient in Jiaozhou Bay, indicating the riverine inputs are the main factor that causes the variation of DOM in these coastal bays. The effects of inflowing rivers on DOM in coastal bays differed with their watershed characteristics (i.e., agricultural/urban). In addition, humic-like DOM components were found to be positively correlated with the apparent oxygen utilization, suggesting microbial activities could contribute to the DOM in this region. There was generally a higher averaged concentration of fluorescent DOM in surface water than that in bottom water in Jiaozhou Bay. In contrast, higher humic-like DOM was found in bottom water than that in surface water in Sishili Bay and Taozi Bay, which could be attributed to aquaculture activities and biological production. Moreover, photodegradation/photobleaching, dumping, and sewage discharge had their effects on DOM in coastal bays. This study demonstrates that DOM in coastal bays is regulated by multiple sources (rivers, aquaculture, dumping, and sewage) and processes (biological production and photodegradation), and anthropogenic activities have their influences on optical and isotopic characteristics of DOM in coastal bays.