Increase Of Chlorophyll-a Concentration Research Articles

Effects of climate change on aquaculture site selection at a temperate estuarine system

Aquaculture is one of the food industries that most evolved in recent years in response to increased human demand for seafood products, which has led to a progressive stock threat in nature. With a high seafood consumption per capita, Portugal has been exploring its coastal systems to improve the cultivation of fish and bivalve species with high commercial value. In this context, this study aims to propose the use of a numerical model as a tool to assess the impact of climate change on aquaculture site selection in a temperate estuarine system (Sado estuary). Therefore, the Delft3D model was calibrated and validated, showing good accuracy in predicting the local hydrodynamics, transport, and water quality. Furthermore, two simulations for the historical and future conditions were performed to establish a Suitability Index capable of identifying the most appropriate sites to exploit two bivalve species (one clam and one oyster), considering both winter and summer seasons. Results suggest that the estuary's northernmost region presents the best conditions for bivalves' exploitation, with more suitable conditions during summer than winter due to the higher water temperature and chlorophyll-a concentrations. Regarding future projections, the model results suggest that environmental conditions will likely benefit the production of both species due to the increase in chlorophyll-a concentration along the estuary.

Global ocean colour trends in biogeochemical provinces

Satellite-derived ocean colour data provide continuous, daily measurements of global waters and are an essential tool for monitoring these waters in a changing climate. Merging observations from different satellite sensors is necessary for long-term and continuous climate research because the lifetime of these sensors is limited. A key issue in deriving long-term trends from merged ocean colour data is the inconsistency between the spatiotemporal coverage of the different sensor datasets that can lead to spurious multi-year fluctuations or trends in the time series. This study used the merged ocean colour satellite dataset produced by the Ocean Colour Climate Change Initiative (OC-CCI version 6.0) to infer global and local trends in optically active constituents. We applied a novel correction method to the OC-CCI dataset that results in a spatiotemporally consistent dataset, allowing the examination of long-term trends of optically active constituents with greater accuracy. We included sea surface temperature, salinity, and several climate oscillations in our analysis to gain insight into the underlying processes of derived trends. Our results indicate a significant increase in chlorophyll-a concentration in the polar waters, a decrease in chlorophyll-a concentration in some equatorial waters, and point to ocean darkening, predominantly in the polar waters, due to an increase in non-phytoplankton absorption. This study contributes to broader knowledge of global trends of optically active constituents and their relation to a changing environment.

Differential response of chlorophyll-a concentrations to explosive volcanism in the western South Pacific

When it is deposited in the ocean, volcanic ash has the potential to release iron and other nutrients into surface water to stimulate ocean productivity. In the western South Pacific Ocean (SPO), one of the most important volcanic ash deposition regions, occasional widespread transport of volcanic ash may supply the nutrients not only locally around source islands but also within the wider the western SPO, accompanied by phytoplankton response. Through a comparative analysis of satellite and reanalysis data for the past 19 years (2004–2022), this study reveals that four explosive volcanic eruptions, Rabaul volcano, Papua New Guinea (October, 2006), Ambae volcano, Vanuatu (July, 2018), Ulawun volcano, Papua New Guinea (June, 2019), and Hunga volcano, Tonga (January, 2022), had the most strong stratospheric injection (>15 km) and mass loading of volcanic materials over the wider the western SPO (covering an area of >765,000 km2). The transport of 2006, 2018, 2019 volcanic emissions, was not likely associated with significant ash deposition over the western SPO. However, the Hunga eruption led to the deposition of ash-laden volcanic plumes over a wide area (~2,000 km from source), and was followed by the increase in chlorophyll-a concentrations (Chl-a) in the region (~70% increase). Minor changes related to other nutrient sources (e.g., hydrothermal input) suggest a link between the increase in Chl-a and 2022 Hunga ash falls over the western SPO. Our results indicate that volcanic ash deposition has implications for phytoplankton productivity in the western SPO, and highlights the need for further research into understanding how nutrient supply alleviated limitations of phytoplankton at the community level.

Increase in chlorophyll-a concentration in Lake Taihu from 1984 to 2021 based on Landsat observations

Lake Taihu, located in a densely populated and highly industrialized area in eastern China, has experienced dramatic changes in water quality since the reform and opening-up in the 1980s. Landsat data can be used to trace water quality changes over approximately 40 years. However, chlorophyll-a (Chla) estimation, which characterizes the trophic status, has not been thoroughly explored (especially in turbid water using wide bandwidth Landsat) due to the interference of suspended particulate matter (SPM) to Chla. In this study, we used Landsat TM/OLI for turbid water Chla inversion and to analyze the spatiotemporal variation of Chla in Lake Taihu for 38 years and its influencing factors. An optical classification algorithm based on Rrs(green)/Rrs(red) was used to exclude highly turbid waters dominated by SPM; Chla was estimated only in waters with low SPM. We constructed an exponential estimation model based on Rrs(NIR)/Rrs(red), and verified the accuracy of the model using the measured Chla synchronized with satellite data. The model was applied to Landsat images to calculate the Chla concentration in Lake Taihu during 1984–2021, and its spatiotemporal distribution patterns were further analyzed. Spatially, the Chla concentrations in the western and northern regions of Lake Taihu were higher than those in other regions, probably because these areas are estuaries with large exogenous pollutant discharge and more nutrients are imported from exogenous sources. Chla showed an overall significant upward trend from 1984 to 2021 probably because of temperature rise, wind speed reduction, and nutrient increase. The results of the spatial and temporal variation of Chla and the influencing factors in this study provide supporting data for eutrophication monitoring and management in Lake Taihu. The proposed Chla estimation method can be extended to assess the spatial and temporal distribution of eutrophication in other inland waters with similar optical properties.

Increased oceanic dimethyl sulfide emissions in areas of sea ice retreat inferred from a Greenland ice core

Ocean phytoplankton are an important source of dimethyl sulfide, which influences marine cloud formation. Model studies suggest that declines in Arctic sea ice may lead to increased dimethyl sulfide emissions, however observational support is lacking. Here, we present a 55-year high-resolution ice core record of methane sulfonic acid flux, an oxidation product of dimethyl sulfide, from the southeast Greenland Ice Sheet. We infer temporal variations in ocean dimethyl sulfide emissions and find that springtime (April–June) fluxes of methane sulfonic acid correlate well with satellite-derived chlorophyll-a concentration in the Irminger Sea. Summertime (July–September) methane sulfonic acid fluxes were 3 to 6 times higher between 2002–2014 than 1972–2001. We attribute this to sea ice retreat day becoming earlier and a coincident increase in chlorophyll-a concentration in the adjacent open coastal waters.

Environmental impacts of three Asian dust events in the northern China and the northwestern Pacific in spring 2021

In March 2021, China experienced three dust events (Dust-1, 2, 3), especially the first of which was reported as the strongest one in recent ten years. Their environmental impacts have received great attention, demanding comprehensive study to assess such impacts quantitatively. Multiple advanced measurement methods, including satellite, ground-based lidar, online aerosol speciation instrument, and biogeochemical Argo float, were applied to examine and compare the transport paths, optical and chemical properties, and impacts of these three dust events on urban air quality and marine ecosystem. The results showed that Dust-1 exhibited the largest impacts on urban area, increasing PM10 concentration in Beijing, Shuozhou, and Shijiazhuang up to 7525, 3819, and 2992 μg m−3, respectively. However, due to fast movement of the Mongolian low-pressure cyclone, the duration of northwest wind over the land was quite short (e.g., only 10 h in Beijing), which prevented the transport of dust plume to the northwestern Pacific, resulting in limited impact on the ocean. Dust-2 and Dust-3, though weaker in intensity, were transported directly to the sea, and led to a substantial increase in chlorophyll-a concentration (up to near 3 times) in the northwestern Pacific, comparing to climatological value. This indicates that the impacts of dust events on ocean was not necessarily and positively correlated to their impacts on land. Based on the analyses of land-ocean-space integrated observational data and synoptic systems, this study examined how marine ecosystem responded to three significant Asian dust events in spring 2021 and quantitatively assessed the overall impacts of mega dust storms both on land and ocean, which could also provide an interdisciplinary research methodology for future research on strong aerosol emission events such as wildfire and volcanic eruption.

Application of remote sensing data for monitoring eutrophication of floodplain water bodies

The aim of this article was to investigate the influence of structural features of the floodplain water network on the spatial and temporal dynamics of chlorophyll-a concentration as an indicator of eutrophication. The research was conducted in the waters of the “Dnipro-Orilskiy” Nature Reserve. The geographic information base with polygonal objects which represented water bodies of the reserve was created on the basis of detailed geographical maps and the high resolution space images. The water bodies were characterized using such parameters as the distance of the water body centroid from the nearest shore of the Dnipro River, the area of the water body, the order of the water body and the connectivity of the water body. Chlorophyll-а concentration was estimated based on the surface algal bloom index. The information was obtained about 148 water bodies, 141 of which are water bodies in the floodplain of the Dnipro River. The area of floodplain water bodies within the reserve was 3.28 million m2. The area of floodplain water bodies ranged from 300–232,500 m2. Trophic State Index allows us to estimate the trophic level of Dnipro River waters as mesotrophic, water bodies of first and second order as eutrophic, and water bodies of third and fourth order as hypereutrophic. The dynamics of chlorophyll-a content in water followed the seasonal course of temperatures. The concentration was lowest in the cold period of the year and reached its maximum in the second half of summer. The autumn decrease occurred at the end of September. The seasonal course of air temperature was superimposed on the peculiarities of the temperature regime of a particular water body, which depended on its depth and flow rate. The time, water body area, distance from the Dnipro River channel, connectivity and order of water bodies were the statistically significant predictors of chlorophyll concentration in water and were able to explain 85% of the variation of this indicator. The increase in chlorophyll-a concentration with increasing order of a water body is due to a decrease in the intensity of water exchange and a decrease in the depth of water bodies of higher order. An increase in the order of a water body is accompanied by a branching network of water bodies, the ability of water bodies to clear sediments decreases. Sediment accumulation leads to a decrease in their depth. Warming of shallow ponds and accumulation of organic matter in them are factors of intensive growth of blue-green algae. The evacuation of surplus organic matter, which results from mass vegetation development with excessive nutrient inputs, is a key driver of the eutrophic regime of water bodies. The increasing importance of regulatory processes develops in agreement with an increase in chlorophyll-a concentration in a water body. The importance of the considered factors reaches the highest level in summer time, when simultaneous maximum warming of water bodies and minimum water level in them take place. Accordingly, the differences between deep and relatively cool water bodies and shallow water bodies that warm up quickly, which significantly stimulates the growth of organic mass, reach the greatest contrast. The spatial patterns of variation in chlorophyll-a concentration have a complex multiscale structure, indicating the multiple nature of the acting factors. The spatial variability was represented as a composition of broad-scale and medium-scale spatial processes. The broad-scale process is most dependent on connectivity, whereas for the medium-scale process the leading one is the effect of water body order.

On Investigating the Dynamical Factors Modulating Surface Chlorophyll-a Variability along the South Java Coast

Twelve years of remotely sensed all-sat merged chlorophyll-a concentration unveils strong signatures of chlorophyll-a blooms along the south Java coast. An unprecedented three-times increase in chlorophyll-a concentration is significantly observed along the south Java coast during the southeast monsoon (June–October) than the northwest monsoon (December–April). The multiple regression analysis of dynamic factors evidently indicates that seasonal upwelling is predominantly controlled by the seasonally evolving coastal eddies associated with the seasonally reversing south Java coastal currents (SJCC) and Ekman mass transport (EMT), followed by the relative roles of sea surface temperature (SST) and wind stress curl. The eddy-induced upwelling and EMT-induced coastal upwelling lead to chlorophyll-a blooms during southeast monsoon, well-supported by the entrainment of cold and saline waters (thermocline doming) with low spiciness. On the other hand, the coastal eddies associated with SJCC and SST anomalies play a significant role in modulating the interannual surface chlorophyll-a variability in the domain. Intense chlorophyll-a blooms are observed during the positive IOD years, whereas the least chlorophyll-a concentration is observed during the negative IOD years. The unprecedentedly least chlorophyll-a concentrations during 2010 and 2016 are attributed to the intense and prolonged surface marine heatwaves.

Monthly anomalies of sea surface chlorophyll-a concentration in the Khanh Hoa waters of Vietnam related to ENSO phenomenon

Based on the monthly averaged sea surface chlorophyll-a concentration data continuously for more than 17 years (Jul. 2002–Dec. 2019), the analyzed results show that the averaged chlorophyll-a concentration in Khanh Hoa waters was 0.58 mg/m3, and the monthly average variation was ± 0.14 mg/m3 (that is equivalent to about ± 24%). Under the impact of ENSO phenomena, in the years when the double La Niña events occurred (two consecutive years in the La Nina event occurs), the chlorophyll-a anomaly index fluctuated from -0.99 mg/m3 to 1.62 mg/m3. These are very strong fluctuation levels, corresponding to the decrease or increase in chlorophyll-a concentration from 86% to 279%. In the El Niño years, the fluctuations of chlorophyll-a concentration were little affected unless the two previous years in which the double La Niña event occurred. These fluctuations have significantly impact nutritional resources and water quality because chlorophyll-a concentration is one of the key indices in studying the health status of any natural marine ecosystem. In addition, chlorophyll-a concentration in Khanh Hoa waters often varies between seasons. The averaged chlorophyll-a concentration reaches its maximum value in the winter, then decreases gradually in the spring and usually reaches the minimum value in the summer, then rises gradually again in the autumn.

Bio-Physical Changes in the Gulf of Mexico During the 2018 Hurricane Michael

We investigate the impacts of one of the strongest recorded hurricanes to have hit the Florida Panhandle, Hurricane Michael (2018), on the upper ocean using a suite of satellite data, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> profiles, and outputs from the HYbrid Coordinate Ocean Model (HYCOM). Strong, low-level cyclonic winds associated with the hurricane generated strong Ekman suction that propagated ahead of the hurricane and caused changes in the surface and subsurface ocean. Following the passage of Hurricane Michael, a 3 °C drop in sea surface temperature (SST) was accompanied with a 4–5 mg <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{m}^{-3}$ </tex-math></inline-formula> increase in chlorophyll-a concentration. In the subsurface, a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 15$ </tex-math></inline-formula> m mixed layer deepening preceded upward displacements of the isotherms and cooling of the mixed layer. The impact of hurricane conditions on sea surface salinity (SSS) was localized and influenced by competing processes, with upwelling of salty subsurface water increasing SSS and enhanced precipitation decreasing SSS. During the peak of the hurricane, the impact of upwelling was greater than that of enhanced precipitation and, thus, SSS increased. Further away from the upwelling centers, hurricane-influenced precipitation, and river runoff freshened SSS.

CHLOROPHYLL ESTIMATION OF LAKE WATER AND COASTAL WATER USING LANDSAT-8 AND SENTINEL-2A SATELLITE

Abstract. Chlorophyll-a is an optically active compound (OAC) commonly used as a proxy for phytoplankton biomass in an aquatic environment. Retrieving the concentration of chlorophyll-a remains a challenge due to the presence of several OAC particularly in water bodies which are in proximity to the land-based activities. In this study, an effort has been made to estimate the chlorophyll-a concentration of both the freshwater Lake Biwa and the coastal water of Wakasa Bay in Japan. A spectral decomposition algorithm was used to determine the chlorophyll-a using the satellite images. The algorithm was applied to the satellite images from two different sensors namely Landsat-8/OLI and Sentinel-2A/MSI. The satellite-derived chlorophyll-a concentration for the lake and coastal water from two different sensors were compared to assess the performance of both the sensors. The accuracy of the chlorophyll-a results derived from the images was evaluated with the in-situ measurement data of the chlorophyll-a for the Lake Biwa and the coastal water of Wakasa Bay. Both satellite sensors appear to give the best results for the coastal water (R2 &gt; 0.80) with an RMSE &lt; 0.3 μg/L. However, slight underestimation of chlorophyll-a noted for the Landsat-8 image with an increase in chlorophyll-a concentration. For the lake water, Sentinel-2A results were relatively better (R2 &gt; 0.70) than Landsat-8, with an RMSE of &lt; 1.0 μg/L. The obtained results will be useful to evaluate the primary productivity of both freshwater and coastal water body.

Carbon chemistry variability around a tropical archipelago

Oceanic islands affect the surrounding oceanic circulation by producing upwelling or vortices, resulting in the rising of a richer and colder subsurface water mass. This process increases primary production and can change some biogeochemical processes, such as carbon chemistry and the biological pump. The aim of this study was to describe the vertical variability of carbon chemistry around Fernando de Noronha Archipelago (FNA) and to verify how the island mass effect (IME) can affect carbon distribution. Two transects on opposite sides of the FNA were established according to the direction of the central South Equatorial Current, and samples were collected in July 2010, September 2012 and July 2014 from the surface down to a depth of 500m. The results showed strong stratification, with an uplift of the thermohaline structure, which resulted in an increase of chlorophyll-a concentration downstream of the island during the 2010 and 2014 cruises. Carbon chemistry parameters were strongly correlated with temperature, salinity and dissolved oxygen along the water column and did not change between sides of the island in the periods studied. We conclude that the IME did not significantly affect carbon chemistry, which was more correlated with thermohaline gradient.

The impact of ENSO on regional chlorophyll-a anomaly in the Arafura Sea

The El Niño-Southern Oscillation (ENSO) is a naturally occurring phenomenon that involves fluctuating ocean temperature in the equatorial Pacific. ENSO influences ocean climate variability in Indonesia including the Arafura Sea. The relationship between oceanic chlorophyll-a and ENSO has been the focus of study over the past decade. Here we examine the impact of ENSO on regional chlorophyll-a anomaly in the Papua waters using 14 years of chlorophyll-a and sea surface temperature (SST) data from AQUA MODIS and sea level anomaly data from AVISO. It is found that when El Niño events occur the negative SST anomaly in the Papua waters as well as the enhanced upwelling cause the increase of chlorophyll-a concentration. The highest chlorophyll-a concentration (> 1 mg–cm-3) occured during El Niño and observed around the Aru archipelago. In contrast during La Niña event, the positive SST anomaly in Papua waters and the suppressed upwelling cause the decrease of chlorophyll-a concentration. Our results suggest that during El Niño (La Niña), the enhanced (suppressed) upwelling related to the significant decreasing (increasing) of sea level anomaly.

Island Activities Detected by VIIRS and Validation with AIS

A possibility to monitor the reclamation activities by remote sensing was discussed. The lights observed in the night time by Day Night Band (DNB) of Visible Infrared Imaging Radiometer Suite (VIIRS), ocean color observed in the day time by visible bands of VIIRS were the tools to monitor the surface activities, and the Automated Information System (AIS) was used to verify the types and number of vessels associated with the reclamation activities. The lights as the radiance from the surface were monitored by the object based analysis, where the object was defined as a radius of 5 km from the center of the Mischief Reef in the South China Sea (SCS). The time history of surface lights exhibited the increase of the radiance from January to May 2015 and the radiance was kept in the certain level to December 2016 with some variations. The ocean color, chlorophyll-a concentration as a proxy of sediments, showed an increase from February to June 2015 and returned to a low concentration in August 2015. According to the historical data of AIS, the number of dredgers has increased from February to August 2015 and the maximum number of dredgers was recorded in June 2015. The timing of increase of lights from surface, increase of chlorophyll-a concentration, and increase of number of vessels are consistent.

Modeling metabolism in an integrated subtropical watershed-reservoir system

ABSTRACT Reservoirs are considered transition systems between rivers and lakes with particular features due to its morphology and watershed inflows. Studies about aquatic metabolism in subtropical aquatic ecosystems, particularly in reservoirs, have been based on direct measurements and statistical relationships in specific gauge stations of the system rather than on analytical models, which are capable of representing the metabolic processes at different temporal and spatial scales. This paper aimed to evaluate the temporal variability of metabolism in a subtropical reservoir, named Faxinal reservoir, located in Caxias do Sul, Rio Grande do Sul state, Brazil, by using an ecological model (IPH-ECO) which was coupled with a hydrological model (IPH-II) to estimate inflows and nutrient loadings from the watershed. After model calibration, metabolic daily rates of gross primary production (GPP) and respiration (R) were estimated over a 1-year period (from November 2011 to December 2012), considering a process-based algorithm based on dissolved-oxygen budget implemented in the IPH-ECO model. Faxinal reservoir were net heterotrophic 97% of the simulation period. The temporal variability of GPP and R followed the general pattern of phytoplankton biomass in reservoir, which was more related to autochthonous factors such as water residence time, light availability, nutrient concentration and zooplankton grazing. Only during heavy rainfall period, increasing the terrestrial exports, the concentration of phosphorus was higher leading to an increase of chlorophyll-a concentration and hence metabolic rates of GPP and R. Therefore, considering the long dry period during the simulation, the aquatic metabolism of Faxinal reservoir is more influenced by the internal dynamic of the aquatic ecosystem than the watershed inputs.

Atmospheric cyclones and seasonal cycles of biological productivity of the ocean

Remotely sensed wind speed, translation speed, atmospheric pressure, atmospheric precipitation rate and chlorophyll-a concentration were used to verify the hypothesis that the response of the phytoplankton community to propagating atmospheric cyclones should be associated with the phase of the seasonal cycle of this community and the translation speed of a cyclone. For the 12 cyclones investigated from the Indian Ocean, Pacific Ocean and the Mediterranean Sea the maximal sustained wind speed varied twofold, whereas the translation speed of cyclones and the chlorophyll ratio (characterizing chlorophyll concentration before and after cyclone passage) varied by 10-fold. It was shown that cyclones affecting the phytoplankton community approaching its seasonal maximum either could not stimulate or stimulated a weak response of further increase of chlorophyll-a concentration (due to explicitly available nutrients). Controversially, cyclones affecting the community approaching its seasonal minimum could induce gradual increase of chlorophyll-a concentration. An exponential type of relationship between chlorophyll ratio and translation speed of cyclones was evaluated. In the range of translation speeds from 1 to 10 ms−1, the increase of chlorophyll-a concentration due to cyclone passage was most pronounced with regard to slow moving cyclones.

Meteorological aspects of mud bank formation along south west coast of India

The study mainly intends to investigate the meteorological aspects associated with the formation of mud banks along southwest coast of India. During the formation of mud bank, the prominent monsoon organized convection is located in the equatorial region and relatively low clouding over Indian mainland. The wind core of the low level jet stream passes through the monsoon organized convection. When the monsoon organized convection is in the equatorial region, the low level wind over the southwest coast of India is parallel to the coastline and toward south. This wind along the coast gives rise to Ekman mass transport away from the coastline and subsequently formation of mud bank, if the high wind stress persists continuously for three or more days. As a result of the increased alongshore wind stress, the coastal upwelling increases. An increase in chlorophyll-a concentration and total chlorophyll can also be seen associated with mudbank formation.

Ciclo anual de la clorofila a satelital en el archipielago de Juan Fernandez (33 S), Chile

The spatial and temporal variability of the annual cycle of chlorophyll-a in the Juan Fernandez archipelago is analyzed through eight years of satellite data of chlorophyll-a, wind, currents and sea level. This archipelago consists of three islands: Robinson Crusoe-Santa Clara (RC-SC) and Alexander Selkirk (AS). The RC-SC islands are in a region of high eddy kinetic energy and higher concentrations of chlorophyll-a, defined as Coastal Transition Zone, whereas the AS is in a region with low eddy kinetic energy and lower concentrations of chlorophyll-a called Oceanic Zone. RC-SC has an increase in chlorophyll-a concentrations on the southwest side, while AS has its highest concentrations on the west side, indicating the presence of different forcing. On both islands the annual cycle of chlorophyll is significant and begins to increase in April, reaching relatively high values between June and November, decreasing to its lowest values in December, reaching a minimum in late March. This annual cycle does not appear related with the wind, but it appears related with the eddy kinetic energy. The increase of chlorophyll-a in winter is associated with mesoscale eddies coming from continental region, while spring increases could be associated with local processes linked to the island mass effect. On both islands, it appears a significant increase in chlorophyll-a in the annual and bi-annual bands, but only in AS was found a significant inter-annual fluctuation linked with the El Nino and the Southern Oscillation.

Prediction of Chlorophyll-a Changes due to Weir Constructions in the Nakdong River Using EFDC-WASP Modelling

To evaluate the effect of the 4 major rivers restoration project in the Nakdong River to water quality of the river, the Environmental Fluid Dynamics Code (EFDC) and Water Quality Analysis Simulation Program (WASP), are applied in series. Results showed overall decrease in biochemical oxygen demand (BOD5) concentrations and increase in chlorophyll-a concentrations, while total nitrogen and total phosphorous concentrations did not show significant changes, relatively. Decrease in BOD 5 concentrations seems to be influenced by an increased hydraulic residence time, which may allow more time for the degradation of organic material. Changes in Chlorophyll-a (Chl-a) concentration, due to the project were more significant for the upper stream areas that show relatively low Chl-a concentration ranges (less than 20 g/L). After the introduction of the Geumho River in the middle part of the Nakdong River, rapid growth of phytoplankton was observed. However, in this middle part of the Nakdong River, the ratio of Chl-a concentration change are less significant, compared to the upper stream areas, due to the project. In the lower stream area, Chl-a concentration decreased after the project. This seems to be resulted from the decreased light availability, due to increased depth, while the nutrient concentrations have been high enough to support phytoplankton growth.

Assessing the impact of chloroacetanilide herbicides and their metabolites on periphyton in the Leyre River (SW France) via short term growth inhibition tests on autochthonous diatoms

The Leyre River is the main tributary to the Bassin d'Arcachon lagoon. Herbicides belonging to the chloroacetanilide class have been found in the river (S-metolachlor and acetochlor) as well as some of their metabolites at higher concentrations. As the environmental toxicity of these molecules is not well known, ecotoxicological tests have been carried out on river periphyton at different levels of biological diversity: from the clone of one diatom species (Nitzschia nana) to the population of the same species (several clones) up to the multi-specific species community dominated by diatoms. Moreover, tests were performed on diatoms coming from an unpolluted upstream site and from a contaminated downstream site, in order to investigate possible tolerance acquisition to pollutants. The method consisted in measuring diatom growth inhibition at different doses of each substance from the increase of chlorophyll-a concentration after 4 days. It resulted that acetochlor was clearly more toxic than S-metolachlor at all levels of biological diversity. EC(50) values estimated from the tests suggest no effect of contaminants on diatom growth or biomass in the river. The toxicity of the metabolites appeared very low compared to that of their parent compounds. No difference in tolerance to the herbicides was demonstrated between summer diatom communities from the two sites in spite of different specific compositions. However, concerning the populations of N. nana isolated in winter following the highest herbicide concentrations in the river (about 0.5 μg L(-1)), the downstream population showed a higher tolerance to acetochlor but there was no co-tolerance to S-metolachlor. Thus, it appeared that acetochlor represents the highest toxic pressure on periphyton among the other contaminants in the Leyre River.