Distribution of Coomassie Blue Stainable Particles in the Pearl River Estuary, China, Insight Into the Nitrogen Cycling in Estuarine System

Distributions of Coomassie Blue stainable particles (CSP), the sources and transports, as well as their implications for nitrogen biogeochemical cycles in the Pearl River estuary (PRE) were investigated during two cruises in August 2016 and January 2017. CSPcolor concentrations (CSP concentration determined spectrophotometrically) were 73.7–685.3 μg BSA eq L–1 [μg Bovine serum albumin (BSA) equivalent liter–1] in August 2016 and 100.6–396.4 μg BSA eq L–1 in January 2017, respectively. CSP concentrations were high in low-salinity waters (<5), and declined from the river to the middle estuary by 80% in the wet season and 55.6% in the dry season, respectively, then increased again in the lower estuary due to high primary production. CSP concentrations were mainly associated with chlorophyll a (Chl a) concentration except for the turbid mixing zone, suggesting that autochthonous phytoplankton production served as the primary source of CSP in the PRE. The concentrations of nitrogen (N) as CSP in the PRE were comparable to the nitrogen content of particulate hydrolysable amino acids (PHAA). Pictures of CSP taken by microscopy and the correlation between composition of PHAA and the ratio of Chl a/CSPcolor showed that CSP were relatively degraded due to delivery of old terrestrial protein to river section and extensive microbial degradation during mixing at the upper and middle parts of the estuary, whereas CSP in lower estuary appeared to be more labile due to higher fresh algal production. The contribution of CSP nitrogen (CSP-N) to the particulate nitrogen (PN) pool was 34.98% in summer and 30.8% in winter. The conservative estimate of CSP-N input flux in the Pearl River Delta was about 6 × 106 mol N d–1. These results suggested that CSP was a significant pool of organic nitrogen in the PRE. The study of CSP composition in terms of nitrogen provides new insight into the roles of CSP on nitrogen biogeochemical processes in the turbid and productive estuarine system.

The Rance tidal power station: a preliminary study of its impact on tidal patterns and sediments dynamics in the Rance estuary (France) from 1957 to 2018

<p>The Rance tidal power station (located on the Brittany coast of Northern France), was opened in 1966 as the world’s first and largest tidal power station, with peak output capacity of 240 Megawatts. It is currently the second world’s largest tidal power installation after the Sihwa Lake Tidal power station (South Korea). The power plant is located at the mouth of a small steep-sided ria, with a maximum perigean spring tidal range of 13.5 m and an average fluvial discharge of 7 m<sup>3</sup>/s. The dam is 750 m long and the tidal basin measures 22.5 km<sup>2</sup>. Despite a well-known effect of the plant on the damping of estuarine water levels, little attention has been given to the consequences of the dam in the estuarine environment in terms of hydrodynamics, for instance, the propagation of the tidal wave and tidal currents along the estuary are still little understood. Moreover, net siltation has been reported by several observations, but there is no specific knowledge on the role of the plant on sedimentation. In this study, we analyze the impact of the tidal power station on tidal wave patterns and sediment dynamics in this particular man-engineered system. To this goal, a numerical model based on a two-dimensional depth-averaged approach is implemented to predict the tide propagation and tidal currents along the estuary accounting for the presence of the tidal power station. Three modelling scenarios were performed: the first considering the bathymetry of 1957 (before the plant’s construction), a second scenario considering the bathymetry of 2018 without the presence of the power station and a third scenario considering the bathymetry of 2018 with the power station. Preliminary results showed that, with and without the tidal power station, the upper estuary exhibits a flood dominant behavior, with longer duration of falling water than rising water, and conversely the lower estuary is ebb dominant with shorter duration of falling water than rising water. This analysis also revealed that the tidal power station might switch the flood dominance in the central estuary to ebb dominance. These findings imply a net seaward transport of both coarse and fine sediments in the lower estuary. Therefore, the tidal power station might have a considerable role in modulating the estuarine turbidity maximum and channels’ morphology. Finally, these results are compared with preliminary numerical simulations of suspended sediment transport to further quantify the impact of the tidal power plant on the dynamics of the estuarine turbidity maximum.</p>

Biotic vs. abiotic forcing on plankton assemblages varies with season and size class in a large temperate estuary

Large river estuaries experience multiple anthropogenic stressors. Understanding plankton community dynamics in these estuaries provides insights into the patterns of natural variability and effects of human activity. We undertook a 2-year study in the Columbia River Estuary to assess the potential impacts of abiotic and biotic factors on planktonic community structure over multiple time scales. We measured microplankton and zooplankton abundance, biomass and composition monthly, concurrent with measurements of chlorophyll a, nutrient concentrations, temperature and salinity, from a dock in the lower estuary. We then statistically assessed the associations among the abundances of planktonic groups and environmental and biological factors. During the late spring high flow period of both years, the lower estuary was dominated by freshwater and low salinity-adapted planktonic taxa, and zooplankton grazers were more strongly associated with the autotroph-dominated microplankton assemblage than abiotic factors. During the early winter period of higher salinity and lower flow, nutrient (P) availability exerted a strong influence on microplankton taxa, while only temperature and upwelling strength were associated with the zooplankton assemblage. Our results indicate that the relative influence of biotic (grazers) and abiotic (salinity, flow, nutrients and upwelling) factors varies seasonally and inter-annually, and among different size classes in the estuarine food web.

Detection of Squalius cephalus (Linnaeus, 1758), Carassius carassius (Linnaeus, 1758) and the khromist of Rutilus rutilus (Linnaeus, 1758) in the lower reaches of the Dnipro river in recent years

The article presents the materials on the detection of two very rare species of fish: the European chub Squalius cephalus (Linnaeus, 1758) and the crucian carp (the golden carp) Carassius carassius (Linnaeus, 1758) in the waters of the lower estuary of the Dnipro river in recent years. C. carassius is listed in the Red Book of Ukraine (2009). The article also describes the first encounter in these waters with the khromist of the common roach Rutilus rutilus (Linnaeus, 1758), which has a yellow-golden colour of the whole body. The basin of the Lower Dnipro includes the Kakhovske reservoir, the Ingulets river, several small tributaries and the lower unregulated part of the Dnipro riverbed along with the straits. Over the entire period of observation, up to 72 species of the round-mouthed fish and the fish from 59 genera and 19 families have been spotted in the fish fauna of the Lower Dnipro basin. According to some data, it is stated that within the migratory and freshwater species of the round-mouthed fish and the fish of the Lower Dnipro's ichthyocenosis only 21 out of 47 species of the native fish fauna have survived here. In general, the current fish fauna of the unregulated part of the Lower Dnipro amounts to 51 species of fish. The habitat of 28 species of fish in the lower estuary of the Dnipro river was confirmed in 2019.

Extent of predation bias present in migration survival and timing of Atlantic salmon smolt (Salmo salar) as suggested by a novel acoustic tag

Background Acoustic telemetry is increasingly being used as a tool to measure survival, migration timing and behaviour of fish. Tagged fish may fall prey to other animals with the tag continuing to be detected whilst it remains in the gastrointestinal tract of the predator. Failure to identify post-predation detections introduces “predation bias” into the data. We employed a new predator tag technology in the first known field trial to understand the extent these tags could reduce predation bias in Atlantic salmon (Salmo salar L.) smolt migration through a 65-km zone beginning in freshwater and extending through an estuary. These tags signal predation by detecting a pH change in the predators’ gut during digestion of a tagged prey. We quantified survival and timing bias by comparing measurements from non- and post-predated detections of tagged individuals’ to only those detections where predation was not signalled. Results Of the 50 fish tagged, 41 were detected with 24 of these signalling as predated. Predation bias was greatest in the upper estuary and decreased towards the bay. Survival bias peaked at 11.6% at river km 54. Minimum and maximum migration time were both biased long and were 16% and 4% greater than bias corrected timing at river km 66 and 54, respectively. After correcting for bias, the apparent survival from release through freshwater and estuary was 19% and minimum and maximum migration timing was 6.6 and 7.0 days, respectively. Conclusions Using this tag, we identified a high proportion of predation events that may have otherwise gone unnoticed using conventional acoustic tags. Estimated survival presented the greatest predation bias in the upper estuary which gradually declined to nearly no apparent bias in the lower estuary as predated tags failed through time to be detected. This is most likely due to tag expulsion from the predator between or upstream of receiver arrays. Whilst we have demonstrated that predation can bias telemetry results, it appears to be rather short-lived given the apparent retention times of these tags within the predators introducing the bias.

Characteristics of Absorption Spectra of Chromophoric Dissolved Organic Matter in the Pearl River Estuary in Spring

In this study, absorption variation of chromophoric dissolved organic matter (CDOM) was investigated based on spectroscopic measurements of the water surface and bottom during a cruise survey on 2–12 May 2014 in the Pearl River Estuary (PRE). Multiple spectral signatures were utilized, including the absorption ratios E2/E3 (a(250)/a(365)) and E2/E4 (a(254)/a(436))) as well as the spectral slopes over multiple wavelength ranges. The horizontal variations of a(300), E2/E3, spectral slope (S) of Ultraviolet C (SUVC, 250–280 nm), Ultraviolet B (SUVB, 280–315 nm), and S275–295 (275–295 nm) were highly correlated, revealing that CDOM of terrigenous origin in the upper estuary contained chromophores of larger molecular size and weight, while the marine CDOM in the lower estuary comprised organic compounds of smaller molecular size and weight; the molecular size of surface CDOM was generally larger than that at the bottom. Results of Gaussian decomposition methods showed that CDOM in the middle estuary of terrigenous origin produced more Gaussian components per spectrum than those of marine origin in the lower estuary and the adjacent Hong Kong waters. The surface CDOM composition was more diverse than at the bottom, inferred by the finding that the average number of Gaussian components yielded per surface sample (5.44) was more than that of the bottom sample (4.8). A majority of components was centered below 350 nm, indicating that organic compounds with relatively simple structures are ubiquitous in the estuary. Components centered above 350 nm only showed high peaks at the head of the estuary, suggesting that terrigenous CDOM with chromophores in complex structures rapidly lose visible light absorptivity during its transport in the PRE. The relatively low and homogenous peak heights of the components in Hong Kong waters imply higher light stability and composition consistency of the marine CDOM compared with the terrigenous CDOM.

Use of a species-rich and highly eutrophic tropical estuary in the South Atlantic by Pleuronectiformes (Teleostei: Acanthopterygii)

A total of 1,471 specimens of 16 species of flatfishes (Pleuronectiformes) were caught during 48 sampling campaigns between July 2005 and June 2007 at ten stations in Guanabara Bay, Rio de Janeiro, Brazil. Paralichthyidae was the dominant family, with Etropus crossotus as the dominant species. The outer stations, especially those on the western side of the lower estuary, were distinguished as a result of their higher abundance of flatfishes and number of species. The spatial distribution of E. crossotus and its population structure indicate that this species is an estuarine resident despite the apparent reduction in its area of occupation within the estuarine complex. Among the other species, nine were classified as marine stragglers (Achirus declivis, Bothus ocellatus, Cyclopsetta chittendeni, Etropus longimanus, Paralichthys orbignyanus, P. patagonicus, Syacium micrurum, Symphurus diomedeanus and Trinectes paulistanus) and three as estuarine opportunists (Bothus robinsi, Citharichthys macrops and Syacium papillosum); another three could not be classified due to the small number of captures or lack of previous data (S. tessellatus, A. lineatus and C. spilopterus).

Resource depletion and mechanisms for food web robustness in a Neotropical estuary

Human activities severely threaten biological communities in Neotropical estuaries. Nevertheless, these communities have been poorly studied in comparison to low biodiversity regions, despite the fact that conservation efforts in these habitats are expected to require longer time-scales and greater efforts. In the present study we simulated resource depletion in a consumer–resource food web in a high-diversity Neotropical estuary. We first describe the feeding patters of local assemblages, split across distinct upper and lower estuary habitats. Further, because fish are opportunistic consumers of locally abundant prey, we modelled community robustness using resource availability, number of resources consumed, consumption diversity and environmental constraints. We found different feeding patterns between the upper and lower estuary habitats. Although crustaceans and detritus were preferably consumed in both habitats, thorough identification demonstrated higher dissimilarity between sites of different habitats relative to sites within the same habitat. We found that community robustness has a positive relationship with consumption diversity and that habitat type (upper or lower estuary) was a poor predictor of robustness. However, the modelling results also indicated an interaction between consumption diversity and habitat type. This suggests that promoting spatial gradients across resources, abiotic conditions and local feeding patterns within habitats can help protect against human-mediated disturbances.

Optical properties of size fractions of suspended particulate matter in littoral waters of Québec

Mass-specific absorption (ai∗(λ)) and scattering (bi∗(λ)) coefficients were derived for four size fractions (i = 0.2–0.4, 0.4–0.7, 0.7–10, and > 10 µm, λ = wavelength in nm) of suspended particulate matter (SPM) and with samples obtained from surface waters (i.e., 0–2 m depth) of the Saint Lawrence Estuary and Saguenay Fjord (SLE-SF) during June of 2013. For the visible–near-infrared spectral range (i.e., λ = 400–710 nm), mass-specific absorption coefficients of total SPM (i.e., particulates > 0.2 µm) (hereafter aSPM∗) had low values (e.g., < 0.01 m2 g−1 at λ = 440 nm) in areas of the lower estuary dominated by particle assemblages with relatively large mean grain size and high particulate organic carbon and chlorophyll a per unit of mass of SPM. Conversely, largest aSPM∗ values (i.e., > 0.05 m2 g−1 at λ = 440 nm) corresponded with locations of the upper estuary and SF where particulates were mineral-rich and/or their mean diameter was relatively small. The variability of two optical proxies (the spectral slope of particulate beam attenuation coefficient and the mass-specific particulate absorption coefficient, hereafter γ and Svis, respectively) with respect to changes in particle size distribution (PSD) and chemical composition was also examined. The slope of the PSD was correlated with bi∗(550) (Spearman rank correlation coefficient ρs up to 0.37) and ai∗(440) estimates (ρs up to 0.32) in a comparable way. Conversely, the contribution of particulate inorganic matter to total mass of SPM (FSPMPIM) had a stronger correlation with ai∗ coefficients at a wavelength of 440 nm (ρs up to 0.50). The magnitude of γ was positively related to FSPMi or the contribution of size fraction i to the total mass of SPM (ρs up to 0.53 for i = 0.2–0.4 µm). Also, the relation between γ and FSPMPIM variability was secondary (ρs = −0.34, P > 0.05). Lastly, the magnitude of Svis was inversely correlated with aSPM∗(440) (ρs = −0.55, P = 0.04) and FSPMPIM (ρs = −0.62, P = 0.018) in sampling locations with a larger marine influence (i.e., lower estuary).

Spatial variability in surface-water <i>p</i>CO₂ and gas exchange in the world's largest semi-enclosed estuarine system: St. Lawrence Estuary (Canada)

The incomplete spatial coverage of CO2 partial pressure (pCO2) measurements across estuary types represents a significant knowledge gap in current regional- and global-scale estimates of estuarine CO2 emissions. Given the limited research on CO2 dynamics in large estuaries and bay systems, as well as the sources of error in the calculation of pCO2 (carbonic acid dissociation constants, organic alkalinity), estimates of air–sea CO2 fluxes in estuaries are subject to large uncertainties. The Estuary and Gulf of St. Lawrence (EGSL) at the lower limit of the subarctic region in eastern Canada is the world's largest estuarine system, and is characterized by an exceptional richness in environmental diversity. It is among the world's most intensively studied estuaries, yet there are no published data on its surface-water pCO2 distribution. To fill this data gap, a comprehensive dataset was compiled from direct and indirect measurements of carbonate system parameters in the surface waters of the EGSL during the spring or summer of 2003–2016. The calculated surface-water pCO2 ranged from 435 to 765 µatm in the shallow partially mixed upper estuary, 139–578 µatm in the deep stratified lower estuary, and 207–478 µatm along the Laurentian Channel in the Gulf of St. Lawrence. Overall, at the time of sampling, the St. Lawrence Estuary served as a very weak source of CO2 to the atmosphere, with an area-averaged CO2 degassing flux of 0.98 to 2.02 mmol C m−2 d−1 (0.36 to 0.74 mol C m−2 yr−1). A preliminary analysis revealed that respiration (upper estuary), photosynthesis (lower estuary), and temperature (Gulf of St. Lawrence) controlled the spatial variability in surface-water pCO2. Whereas we used the dissociation constants of Cai and Wang (1998) to calculate estuarine pCO2, formulations recommended for best practices in open ocean environments may underestimate pCO2 at low salinities, while those of Millero (2010) may result in overestimates.