Freshwater Runoff Research Articles

Distinct structure, assembly, and gene expression of microplankton in two Arctic estuaries with varied terrestrial inputs

The Laptev Sea is a major Marginal Sea in the Western Arctic Ocean. The Arctic amplification brought by global warming influences the hydrological properties of rivers passing through the permafrost zone, which would alter the biological community structure at continental margin. In this study, the structure, assembly, and gene expression of planktonic microbial communities in two estuaries (Protoka Ularovskaya River Estuary, PURE; Lena River Estuary, LRE) of Laptev Sea were examined to investigate the environmental effects of polar rivers. PURE and LRE exhibited distinct environmental characteristics: low temperature and high salinity for PURE, and high temperature and low salinity for LRE, influenced by runoff size. Salinity more closely influenced microbial communities in LRE, with freshwater species playing a significant role in community composition. The findings revealed differences between two estuaries in community composition and diversity. Prokaryotes and microeukaryotes had shown different assembly patterns in response to habitat changes caused by terrestrial freshwater input. Furthermore, compared with the PURE, the co-occurrence and inter-domain network of the LRE, which was more affected by terrestrial input, was more complex and stable. Functional gene prediction revealed a higher gene expression of methane metabolism in LRE than in PURE, particularly those related to methane oxidation, and this conclusion could help better explore the impact of global warming on the methane cycle in the Arctic Marginal Seas. This study explored the increased freshwater runoffs under the background of global warming dramatically affect Arctic microplankton communities from community structure, assembly and gene expression aspects.

Evolution of Freshwater Runoff in the Western Adriatic Sea over the Last Century

The evaluation of the hydrography and biogeochemistry of the Adriatic Sea over the last century was summarized in this review to point out any changes in river runoff and provide an overview of the cause and effect of these trends on marine ecosystems. Although several rivers flow into the Adriatic, the most affected area is the northern Adriatic, where the Po River loads into the basin half of the total freshwater input, carrying river runoff and causing algal blooms and hypoxia phenomena. These fresh waters of the northern Adriatic flow predominantly along the entire western side, reaching the southernmost part of the basin up to the Mediterranean Sea. Here, and in the whole basin, variations in river runoff and nutrient concentration have been observed through the years. Starting from 1960 until the end of the century, an increase in nutrient discharge and phytoplankton activity was reported, with negative repercussions on local fisheries, species richness, and recreational activities within the basin. However, a recent decrease in river inflow has been observed along the coastal belt, which can trigger negative consequences for the food web of the marine ecosystem. These trends, more broadly, corroborate the vulnerability of the Adriatic Sea and stress the importance of implementing strategies for the defense of the relevant ecosystems within its confines.

Is Chelidonichthys lucerna (Linnaeus, 1758) a Marine Estuarine-Dependent Fish? Insights from Saccular Otolith Microchemistry

Tub gurnard, Chelidonichthys lucerna (Linnaeus, 1758), is a Mediterranean-Atlantic benthic species usually captured as by-catch by Portuguese traditional fisheries and considered the most important commercial fish species of the family Triglidae. However, to date, little is known about its habitat residency and whether the species can be considered a marine estuarine-dependent fish. Otolith microchemistry has proven effective in providing information about fish movement patterns throughout different water salinities. In this study, core-to-edge transects of Sr:Ca in the fish saccular otoliths of 35 juveniles of C. lucerna captured in March 2007 by a scientific survey along the Portuguese coast were used to assess the species movement between brackish and marine waters. Data suggest that most individuals (97%) have an estuarine-dependent profile, with 63% showing a clear presence in marine waters during the early life history periods. Evidence of an estuarine residence throughout the fish life cycle was found in only 3% of individuals. Ba:Ca profiles did not reflect an inverse relationship with Sr:Ca salinity results but corroborated findings from other authors about the influence of upwelling processes and freshwater runoffs on Ba incorporation into the otoliths of coastal fish. Furthermore, the data also showed that C. lucerna can occupy and migrate among habitats with diverse salinity degrees, showing high environmental plasticity and adaptation.

Impact of Extreme Wind and Freshwater Runoff on the Salinity Patterns of a Mesotidal Coastal Lagoon

The interaction between tide, river runoff, and wind in coastal lagoons induces complex salinity gradients, which are remarkable when the meteorological forcing is exacerbated. This work aims to characterize the salinity structure under extreme freshwater and wind events in the Ria de Aveiro coastal lagoon (Portugal). The Delft3D model was implemented and validated in 3D mode and used to perform simulations forced with extreme freshwater and wind scenarios. Results show that forcing conditions determine salinity stratification intensity and location. Generally, stratification increases as the freshwater increases, while the salinity intrusion moves downstream. Extreme wind tends to destroy stratification but fails to promote full-depth mixing, which is also dependent on the wind direction, as shown for the Espinheiro channel. The salinity intrusion is also impacted by wind events, being NW storms responsible for an upstream salt transport along the Mira channel and a downstream transport along the Espinheiro channel, and SW storms for an upstream displacement of the salinity intrusion along the São Jacinto channel. Finally, it is observed that the advection of a freshwater plume from the Vouga River into the middle of the São Jacinto channel under high freshwater scenarios causes an unusual local salinity pattern. This plume can either be pushed upstream or prevented from entering the channel, depending on the wind direction.

A Turbulence Survey in the Gulf of Naples, Mediterranean Sea, during the Seasonal Destratification

The seasonality of the vertical mixing at coastal sites is not well characterized yet. Here, a time series of the dissipation rate of turbulent kinetic energy (ε) was obtained from weekly morning microstructure observations covering the destratification period (July 2015, February 2016) at a coastal site in the western Mediterranean Sea, influenced by freshwater runoffs. Estimated with bulk parameters from the public re-analyzed dataset ERA5, the Ekman layer, and the convective penetration depth scale with the mixed layer depth (MLD) with a good agreement. Below the MLD, peaks of ε are observed in the baroclinic layers that progressively overlap with the bottom layer, where repeated near-bottom turbidity peaks provide evidence of sediment resuspension, suggesting energetic processes within the bottom boundary layer. In the subsurface, moderate values (10−9 to 10−8 W kg−1) are observed, following a Burr type XII distribution. Significant correlation with ε at MLD is obtained with a model combining the effects of wind, wind–wave, and convection, highlighting a calm sea bias in our data, plus a sunrise bias when morning buoyancy fluxes are stabilizing. Another correlation, obtained from a pure-wind estimation 18 h before, suggests the role of wind in generating internal waves in the stratified layers, thus, impacting mixing intensity.

Summer Distributional Characteristics of Surface Phytoplankton Related with Multiple Environmental Variables in the Korean Coastal Waters

Multiple environmental variables related to ocean currents, freshwater runoff, and upwelling in a coastal area have complex effects on the phytoplankton community. To assess the influence of environmental variables on the phytoplankton community structure during the summer of 2019, we investigated the various abiotic and biotic factors in Korean coastal waters (KCWs), separated into five different zones. Summer environmental factors in KCWs were strongly influenced by Changjiang Diluted Water (CDW) in St. SO (Southern Offshore) 1 and 2, upwelling in St. SI (Southern Inshore) 2–4, and Nakdong River discharge in St. SI 12. In particular, low–salinity water masses (p < 0.05 for nearby locations) of CDW gradually expanded from the East China Sea to southwestern KCWs from June to July. In addition, there were high levels of nutrients following freshwater runoff from the Nakdong River in southeastern KCW, which led to the dominance of Cryptomonas spp. (81%), a freshwater and brackish water algae. On the other hand, upwelling areas in southwestern KCW were dominated by diatoms Skeletonema spp., and are characterized by high phosphate concentrations (p < 0.05) and low temperatures (p < 0.05) compared to nearby locations. Leptocylindrus danicus (20%) was dominant due to the effect of water temperature in the SE (Southeastern area) zone. Low nutrient concentrations were maintained in the East Sea (dissolved inorganic nitrogen (DIN) = 0.39 ± 0.40 μM; dissolved inorganic phosphate (DIP) = 0.09 ± 0.03 μM) and the Yellow Sea (DIN = 0.40 ± 0.07 μM; DIP = 0.04 ± 0.02 μM), which were characterized by low levels of chlorophyll a and dominated by unidentified small flagellates (35, 40%). Therefore, our results indicated that hydro–oceanographic events such as upwelling and freshwater run–off, but not ocean currents, provide nutrients to the euphotic layers of the coastal environment and play important roles in determining the phytoplankton community structure during summer in the KCWs.

COVID-19 pandemic and antimicrobial resistance in developing countries

A wide range of antimicrobial agents were touted as potential remedies during the COVID-19 pandemic. While both developed and developing countries have recorded an increase in the use of antimicrobial drugs, use and misuse have occurred to a far greater degree in developing countries. This can have deleterious consequences on antimicrobial resistance, especially when various developing countries have already reported the emergence of various drug-resistant organisms even before the pandemic. Telemedicine services, societal and cultural pressures, and bacterial co-infections can predispose to overwhelming antimicrobial prescriptions. The emergence of new multidrug resistance species is a major concern for the developing world especially since health services are already overburdened and lack the diagnostic capabilities and basic amenities for infection prevention and control. This can lead to outbreaks and the rampant spread of such microorganisms. Improper waste management and disposal from hospitals and communities establish freshwater runoffs as hubs of various microorganisms that can predispose to the rise of multidrug-resistant species. Microplastics' ability to act as vectors for antibiotic-resistant organisms is also particularly concerning for lower-middle-income countries. In this review, we aim to study the impact of antimicrobial use during the COVID-19 pandemic and antimicrobial resistance in lower middle-income countries, by understanding various determinants of resistance unique to the developing world and exploring solutions to combat the problem.

Will low primary production rates in the Amundsen Basin (Arctic Ocean) remain low in a future ice-free setting, and what governs this production?

Abstract The study is based on a very extensive data-set of physical, biological, and optical parameters from below the sea ice in the western Amundsen Basin, central Arctic Ocean, in August–September 2012 during the record low sea ice extent. The water column was strongly stratified at all stations related to salinity differences between a surface layer of reduced salinities ( 34). A nitrate utilization-based budget in the surface layer gave a primary production of 67.5 mg C m−2 d−1, which reduced to 3.9 mg C m−2 d−1 in August 2012. Amundsen Basin primary production rates are lower than rates determined for other Arctic Ocean deep-water basins, and also lower compared to rates on the shelf. Below ice phytoplankton was well adapted to low light conditions in the Amundsen Basin and the photosynthetic potential was high, but limited by the low nutrient fluxes induced by the strong stratification. Amundsen Basin is foreseen to be ice-free in summer in 3–4 decades, and the question whether primary production will increase when ice-free was resolved with a coupled physical-biogeochemical model. Results showed that production will increase 10 to 14 times from the present 3.9 mg C m−2 d−1 to 37.4 and 55.2 mg C m−2 d−1 for an ice-free August and July–August, respectively. The study substantiates that both present and future ice-free low production rates were related to the strong stratification, reduced nutrient fluxes, and deep lying nutrient rich waters. Low production rates and strong stratification are discussed in the view of parameters that increase this stratification as higher freshwater run off or reduce stratification as wind.

Toxoplasma gondii in edible fishes captured in the Mediterranean basin.

The issue of whether market fish can be involved in the transmission of Toxoplasma gondii in the marine environment is highly debated since toxoplasmosis has been diagnosed frequently in cetaceans stranded along the Mediterranean coastlines in recent times. To support the hypothesis that fishes can harbour and effectively transmit the parasite to top‐of‐the‐food‐chain marine organisms and to human consumers of fishery products, a total of 1,293 fishes from 17 species obtained from wholesale and local fish markets were examined for T. gondii DNA. Real‐time PCR was performed in samples obtained by separately pooling intestines, gills and skin/muscles collected from each fish species. Thirty‐two out of 147 pooled samples from 12 different fish species were found contaminated with T. gondii DNA that was detected in 16 samples of skin/muscle and in 11 samples of both intestine and gills. Quantitative analysis of amplified DNA performed by both real‐time PCR and digital PCR (dPCR) confirmed that positive fish samples were contaminated with Toxoplasma genomic DNA to an extent of 6.10 × 10−2 to 2.77 × 104 copies/ml (quantitative PCR) and of 1 to 5.7 × 104 copies/ml (dPCR). Fishes are not considered competent biological hosts for T. gondii; nonetheless, they can be contaminated with T. gondii oocysts flowing via freshwater run‐offs (untreated sewage discharges, soil flooding) into the marine environment, thus acting as mechanical carriers. Although the detection of viable and infective T. gondii oocysts was not the objective of this investigation, the results here reported suggest that fish species sold for human consumption can be accidentally involved in the transmission route of the parasite in the marine environment and that the risk of foodborne transmission of toxoplasmosis to fish consumers should be further investigated.

Notes on the distribution and habitat of Ochthebius lobicollis Rey, 1885, a poorly known north-western Mediterranean coastal species (Coleoptera: Hydraenidae)

Ochthebius (Ochthebius) lobiccoastal habitatsollis Rey, 1885 is recorded for the first time from the Iberian Peninsula (Girona) and the island of Corsica; new records are also given for the islands of Menorca and Sardinia. The species is known only from coastal habitats through the Gulf of Lion and the Ligurian and Balearic seas, typically living in rockpools of different salinity or small trickles or freshwater runoffs. Genetic data of the cytochrome oxidase 1 gene from Iberian, Menorcan and Sardinian specimens shows less than 1% divergence, suggesting lack of isolation between populations.

Impact of Continental Freshwater Runoff on Coastal Sea Level

Freshwater discharge to the coastal ocean is a fundamental component of the global water cycle. It can impact coastal sea level over a broad range of spatial and temporal scales. Here we review the status of the current knowledge based on observational and modeling approaches. The main limitation in studies of the influence of rivers on coastal sea level has been the lack of consolidated discharge databases. We first provide an inventory of the main data sources currently available. We then review the existing knowledge about the runoff forcing of coastal sea level, differentiating between the mass and steric height contributions. Both mechanisms are important for coastal sea level budget, although they act on different scales. The mass contribution is related to a global ocean response that is established on relatively short timescales through barotropic processes while the steric contribution is associated with more of a regional adjustment that takes place on longer timescales by means of baroclinic dynamics. While numerical models required to simulate the runoff impact on coastal sea level variability have been improving over the past decades, a similar evolution is awaited for observational techniques, both for in situ observation and for remote sensing.

Bacterioplankton abundance and biomass stimulated by water masses intrusions over the Southern Brazilian Shelf (between 25°57'S and 29°24'S)

In order to understand the distribution of bacterioplankton along the continental shelf off the Santa Catarina coast (25°57'S and 29°24'S) and whether water masses were affecting this distribution, we measured abundance, biovolume, and biomass of bacterioplankton, and the physico-chemical characteristics of the water masses in three transects in two distinct seasons: summer and winter of 2010. During the austral summer, high continental runoffs from the Itajaí River and Babitonga Bay mix over the shelf with Tropical Water (TW) and originate the summer Subtropical Shelf Water (STSW). Bacterial biomass reached an average of 2.5–5.0 μgC L−1 in summer, with values observed in the southernmost transect (Araranguá) being one order of magnitude higher when compared to the others, where nutrient-rich South Atlantic Central Water (SACW) intrusions are often near the coast. On the contrary, in the austral winter, the Plata Plume Water (PPW) spread on the first 40 m of water positively influenced bacterial abundance and biomass, which were on average ten times higher than those observed in the summer (abundance of up to 2.5 × 109 cells L−1, and biomass up to 60 μgC L−1). As a conclusion, PPW, indicated by the colder waters, high silicate and Kd values, and high concentrations of particulate organic carbon have a positive effect on the abundance and biomass of bacterioplankton, whereas the intrusions of SACW, and local freshwater runoffs have secondary effects on bacterial parameters. This is the first description of the influence of PPW intrusions over the dynamics of bacterioplankton, considering two contrasting environmental periods, and, consequently, to carbon budget studies in the Southern Brazilian Shelf (SBS). Taking into account both abundance and biomass of bacterioplankton and their association with water masses in the SBS, our results provide fundamental information for further biogeochemical studies.

Dissolved Methane Distribution in the Reloncav\xed Fjord and Adjacent Marine System During Austral Winter (41\xb0\u201343\xb0 S)

Within the earth’s atmosphere, methane (CH4) is one of the most important absorbers of infrared energy. It is recognized that coastal areas contribute higher amounts of CH4 emission; however, there is a lack of accurate estimates for these areas. This is particularly evident within the extensive northern fjord region of Chilean Patagonia, which has one of the highest freshwater runoffs in the world. Oceanographic and biogeochemical variables were analyzed between the Reloncaví fjord (41° S) and the Interior Sea of Chiloé (ISC) (43° S), during the 2013 austral winter. Freshwater runoff into the fjord influences salinity distribution, which clearly delimits the surface (<5 m depth) and subsurface layers (>5 m depth), and also separates the estuarine area from the marine area. In the estuary, the highest CH4 levels are generally observed in the cold and brackish nutrient-depleted surface waters (N- and P-depleted), ranging from 16.97 to 151.4 nM (mean ± SD 52.20 ± 46.49), equivalent to 640–4537% saturation except for the case of Si(OH)4. Conversely, subsurface waters have lower CH4 levels, fluctuating from 14.3 to 29.6 nM (mean ± SD 22.75 ± 4.36 nM) or 552–1087% saturation. A significant negative correlation was observed between salinity and CH4, and a positive correlation between Si(OH)4 and CH4, suggesting that some of the CH4 in estuarine water is due to continental runoff. Furthermore, the accumulation of seston and/or plankton at the pycnocline may potentially generate the accumulation of CH4 via microbial processes, as observed in estuarine waters. By contrast, the marine area (the ISC), which is predominantly made up of modified subantarctic water, has a relatively homogenous CH4 distribution (mean ± SD 9.84 ± 6.20 nM). In comparison with other estuaries, the Reloncaví fjord is a moderate source of CH4 to the atmosphere, with effluxes ranging from 23.9 to 136 μmol m−2 day−1. This is almost double the levels observed in the ISC, which ranges from 22.2 to 46.6 μmol m−2 day−1. Considering that Chilean Patagonia has numerous other fjord systems that are geomorphologically alike, and in some cases have much greater freshwater discharge, this study highlights their potential to be a significant natural source of this greenhouse gas.

Greenland Freshwater Runoff. Part II: Distribution and Trends, 1960–2010

Abstract Runoff magnitudes, the spatial patterns from individual Greenland catchments, and their changes through time (1960–2010) were simulated in an effort to understand runoff variations to adjacent seas and to illustrate the capability of SnowModel (a snow and ice evolution model) and HydroFlow (a runoff routing model) to link variations in terrestrial runoff with ocean processes and other components of Earth’s climate system. Significant increases in air temperature, net precipitation, and local surface runoff lead to enhanced and statistically significant Greenland ice sheet (GrIS) surface mass balance (SMB) loss. Total Greenland runoff to the surrounding oceans increased 30%, averaging 481 ± 85 km3 yr−1. Averaged over the period, 69% of the runoff to the surrounding seas originated from the GrIS and 31% came from outside the GrIS from rain and melting glaciers and ice caps. The runoff increase from the GrIS was due to an 87% increase in melt extent, 18% from increases in melt duration, and a 5% decrease in melt rates (87% + 18% − 5% = 100%). In contrast, the runoff increase from the land area surrounding the GrIS was due to a 0% change in melt extent, a 108% increase in melt duration, and an 8% decrease in melt rate. In general, years with positive Atlantic multidecadal oscillation (AMO) index equaled years with relatively high Greenland runoff volume and vice versa. Regionally, runoff was greater from western than eastern Greenland. Since 1960, the data showed pronounced runoff increases in west Greenland, with the greatest increase occurring in the southwest and the lowest increase in the northwest.

Greenland Freshwater Runoff. Part I: A Runoff Routing Model for Glaciated and Nonglaciated Landscapes (HydroFlow)

Abstract A gridded linear-reservoir runoff routing model (HydroFlow) was developed to simulate the linkages between runoff production from land-based snowmelt and icemelt processes and the associated freshwater fluxes to downstream areas and surrounding oceans. HydroFlow was specifically designed to account for glacier, ice sheet, and snow-free and snow-covered land applications. Its performance was verified for a test area in southeast Greenland that contains the Mittivakkat Glacier, the local glacier in Greenland with the longest observed time series of mass-balance and ice-front fluctuations. The time evolution of spatially distributed gridcell runoffs required by HydroFlow were provided by the SnowModel snow-evolution modeling system, driven with observed atmospheric data, for the years 2003 through 2010. The spatial and seasonal variations in HydroFlow hydrographs show substantial correlations when compared with observed discharge coming from the Mittivakkat Glacier area and draining into the adjacent ocean. As part of its discharge simulations, HydroFlow creates a flow network that links the individual grid cells that make up the simulation domain. The collection of networks that drain to the ocean produced a range of runoff values that varied most strongly according to catchment size and percentage and elevational distribution of glacier cover within each individual catchment. For 2003–10, the average annual Mittivakkat Glacier region runoff period was 200 ± 20 days, with a significant increase in annual runoff over the 8-yr study period, both in terms of the number of days (30 days) and in volume (54.9 × 106 m3).

Lobomycosis-like disease and other skin conditions in Indo-Pacific bottlenose dolphins Tursiops aduncus from the Indian Ocean

Lobomycosis is a chronic mycotic disease of the skin and subdermal tissues caused by the yeast-like organism Lacazia loboi, which affects humans and Delphinidae. Cases of lobomycosis and lobomycosis-like disease (LLD), a disease very similar to lobomycosis but for which a histological diagnostic is missing, have been reported in small cetaceans from the Americas and Europe. Here we report on LLD in Indo-Pacific bottlenose dolphins Tursiops aduncus from the tropical lagoon of Mayotte, between Mozambique and Madagascar. From July 2004 to June 2008, boat surveys were conducted in Mayotte waters. At least 71 adult dolphins were photo-identified. Six (5 males, 1 female) had multiple raised, greyish nodules on the dorsal fin, head, flanks, belly, back and tailstock that suggested LLD. The lesions were extensive in some cases. The calf of the positive female was also affected. LLD has been present in this community since at least 1999. As sampling was not possible, the aetiology of the disease could not be explored. The emergence of LLD in Mayotte may be related to degradation of the coastal environment associated with rapid urbanization, expanding agriculture and increased release of untreated freshwater runoffs. Other skin lesions included scars, healing wounds, whitish lesions and lumps.

Influence of the very polluted inputs of the Tinto–Odiel system on the adjacent littoral sediments of southwestern spain: A statistical approach

A spatial and temporal analysis (period 1990–2003) of 15 sampling points distributed along the southwestern Spanish coast permits to delimitate the influence area of the extremely polluted discharges coming from the Tinto–Odiel system in the bottom sediments of the adjacent littoral area. As, Cu, Pb and Zn are the main heavy metals transported by the freshwater runoffs toward the shallow shelf and present very high negative ( r < −0.7) and significant ( p < 0.001) correlations with the distance to the estuarine mouth. The statistical analysis (index of geoaccumulation, Pearson correlation matrix, cluster analysis) of their concentrations in the littoral sediments located between the Guadiana and Guadalquivir mouths delimitates three zones: (a) Zone 1 (from the estuarine mouth to 6 km to the east), characterized by moderate to strongly polluted bottom sediments and main responsible of the mean annual variations of the former heavy metals in the area studied; (b) Zone 2 (from 21.2 km to the west to 29 km to the east), characterized by moderate pollution levels; and (c) Zone 3, located near the Guadiana and Guadalquivir mouths, with very low As–Cu–Pb contents and unpolluted to moderately levels of Zn due to urban sewages or the presence of local low mobility areas for this element.

Transitions in Ancient Inland Freshwater Resource Management in Sri Lanka Affect Biota and Human Populations in and around Coastal Lagoons

The increasing anthropogenic pressure on natural environments results in impacts that affect tropical forest areas and their biodiversity. Adverse impacts on terrestrial and oceanic environments often compound in the intertidal area, where mangrove forest ecosystems thrive. In tropical coastal areas of many developing countries where people depend on wood and other mangrove forest products and services, forest degradation leads to socioeconomic problems. At the same time, increasing freshwater needs in these areas are expected to cause additional problems. On the basis of remote sensing and ground truthing complemented by colonial archival material from the Dutch East India Company (1602-1800), we report that changes to the historic system of inland freshwater management have increased dramatically in recent times. Hydrological changes, such as interbasin transfers, have resulted in a qualitative ecological and socioeconomic degradation in three coastal lagoons in southern Sri Lanka. Variations in river hydrology have caused changes in the areas suitable as mangrove habitat and, thus, have resulted in an altered distribution. However, increases in mangrove area can mask the degradation of the site in terms of floristic composition, significance of the species, and biodiversity (this effect is termed "cryptic ecological degradation"). It is important that such changes be carefully monitored to ensure biological and socioeconomic sustainability.

CDOM distribution and CO 2 production on the Southwest Florida Shelf

Partial pressures of carbon dioxide ( pCO 2) were measured in river and coastal waters on two cruises in November 1999 and June 2000 on the Southwest Florida Shelf. Supersaturation with respect to the atmosphere was observed for most river and near-shore waters in November 1999. pCO 2 ranged from 403 μatm in the Gulf of Mexico to 1280 μatm in the Shark River. The coastal waters of the Southwest Florida Shelf had unusually low salinities at this time due to high inputs of freshwater runoffs after Hurricane Irene. In general, pCO 2 levels decreased with increasing salinity, but at different gradients for the different river systems. In June 2000, salinity gradients were considerably reduced during this drought year, with hypersalinity indicating reduced freshwater inputs. However, high pCO 2 levels were still observed in and near the mouth of the Shark River ( pCO 2=383–1280 μatm). A positive correlation of pCO 2 levels with colored dissolved organic matter (CDOM) and chlorophyll was observed in all systems examined. CO 2 in natural waters may be produced from the photochemical degradation of CDOM, microbial respiration or via shifts in the carbonate equilibrium. Some evidence for a small contribution from photochemical production was observed in the Shark River mouth in a dry season diel study, but not in the wet season. Differences between the rivers are primarily attributed to the significantly higher total alkalinity and lower pH values in the Shark River, and associated higher pCO 2 levels. In general, spatial variability in pCO 2 is dominated by the chemical characteristics of the river inputs, with temporal variability modulated by changes in pH, photochemical production in low flow seasons and draw down by primary production.

Flow Field in the Inner Shelf Along the Central East Coast of India During the Southwest Monsoon Season

Current measurements collected along the inner shelf off the central East Coast of India at seven stations during August–September 1988 are discussed. Data indicate a southerly flowing alongshore current, which occupies the whole of the water column over the inner continental shelf. The southerly flow was found to be continuous over the period of measurement except at the northern most station, where southerly flow was interrupted by short period reversals. The velocity of the southerly flowing alongshore current increases from north to south and reaching maximum off Madras (37 cm s−1). Residual water circulation patterns show that there is an outflow of water to the south/south west from the entire water column except at the surface of the Stations 1 and 6. The mean kinetic energy and the eddy kinetic energy show direct relationship with the turning of the flow direction with depth. The energy associated is high if the turning of the flow with depth is more to the right and vice versa. The flow is normally opposed to the mean northeastward directed wind stress and it is thought to be associated with an alongshore pressure gradient. The source of this pressure gradient may be the large scale general circulation of the Bay of Bengal due to the influence of freshwater run off or it may be the result of some upstream or downstream forcing mechanism of a Munk layer driven Sverdrup flow due to wind stress curl.