River Discharge Regime Research Articles

Impacts of river flow and thermal regimes on fish growth dynamics during early life history

Growth during early life stages is critical to fish population persistence. Few studies explore how river discharge and thermal regimes impact growth dynamics of young-of-the-year (YOY) fishes. We used otolith biochronologies and generalised additive mixed models to partition the effects of age, individual, river, temperature, discharge, and variance in discharge on daily growth rates of YOY fishes with an opportunistic life-history strategy: Galaxias vulgaris and Gobiomorphus breviceps. Growth of both species increased with temperature. Galaxias growth decreased with discharge, while Gobiomorphus growth increased with lowered discharge but only to a point (ca. 1/3 of median discharge), after which growth plateaued. Floods had a strong negative effect on YOY growth. Our study systems and species had different characteristics to those that formed the basis of the Riverscape Recruitment Synthesis Model (RRSM) and may explain why our results were only partially consistent with flow predictions for opportunistic species of the RRSM. Further, Galaxias growth was a negative function of high-frequency, daily variation in flow, and we present testable hypotheses to explain this result.

Discharge regimes of Slovenian rivers: 1991–2020

Discharge regimes of Slovenian rivers: 1991–2020

Variability of hydrographic and biogeochemical properties in the North-western Adriatic coastal waters in relation to river discharge and climate changes

The dynamics of hydrographic and biogeochemical properties in a Northwestern coastal area of the Adriatic Sea were investigated. The time series data from continuous observation (2007–2022) allowed the investigation of annual trends and seasonal cycles along a coastal transect influenced by local river discharge. Various statistical models were used to investigate water temperature, salinity, chlorophyll a, dissolved organic, inorganic and particulate nutrients, precipitation and river discharge. It was found that the local river discharge regime played an essential role in interannual, and seasonal biogeochemical dynamics associated with global climate change in the Mediterranean region. A significant trend towards oligotrophic conditions was detected, as evidenced by the downward trend in the river mouth and on the sea of chlorophyll a (−0.2 μg L−1 in the sea), dissolved organic and inorganic nitrogen and phosphorus (i.e., −0.43 μM yr−1 of DON in the sea and −6.67 of DIN μM yr−1 in the river mouth or −0.07 μM yr−1 of DOP and −0.02 μM yr−1 of DIP in the river mouth) and silicate (−2.47 μM yr−1 in the river mouth) concentrations. Salinity showed a long-term increase in the sea (0.08 yr−1), corresponding to a significant decrease in water discharge from the local river (−0.27 m3 s−1 yr−1) and precipitation (−0.06 mm yr−1). The dissolved organic and inorganic nutrients highlighted a different seasonal accumulation under the river runoff regime. The nutrient enrichment was predominantly driven by river contribution. Data analysis showed that the coastal biogeochemical properties dynamics were mostly influenced by river discharge and precipitation regimes, which in turn are driven by climate change variability in the North-western Adriatic Sea.

A moderately chocked estuary: Influence of a constriction on the water level variations of the Wouri estuary (Cameroon)

We study the water-level (WL) evolution in the Douala basin (DB), a sub-basin of the Wouri estuary, separated from the ocean by a natural constriction and influenced by tides and river inflow. Our objective is to assess whether floods in Douala city could result from water overflow from the Douala basin due to Wouri river floods. We first evaluate the constriction’s damping effect by analyzing tide amplitude variations from the ocean to the basin. A simplified model for basin WL variation is developed, incorporating a dissipation parameter (Г) that is evaluated using weak tidal amplitude modulation from the ocean to the basin over the dry season of 2023. Results in the DB reveal nondimensional choking-parameter (P) values of 12–19, indicating moderate dissipation. The basin's relatively small area results in a nondimensional river discharge parameter (S) of 0–12, indicating high river discharge regimes. Subsequently, the model is used to evaluate the mean and maximum WL, as well as tide amplitude variations of the DB, as functions of river flow and ocean tides. The mean WL increases, but the maximum tide amplitude decreases as river input increases. The maximum WL in the basin always exceeds the maximum amplitude of ocean tides but is only significantly higher when river input is above 1000 m3/s. In current conditions, where maximum observed river input is around 1800 m3/s, it is unlikely that flooding will extend beyond the basin borders into the city of Douala. For a moderate increase (20%) in future maximum river fluxes, it is also unlikely that the DB will overflow into Douala city. Only a drastic increase in mean ocean level and river fluxes (which are possible scenarios associated with climate change) could potentially lead to a significant rise in basin WL, resulting in severe flooding.

Origin and partitioning of mercury in the polluted Scheldt Estuary and adjacent coastal zone

Estuaries and coastal zones are areas with complex biogeochemical and hydrological cycles and are generally facing intense pollution due to anthropogenic activities. An emblematic example is the Scheldt Estuary which ends up in the North Sea and has been historically heavily contaminated by multiple pollutants, including mercury (Hg). We report here Hg species and their levels in surface waters of the Scheldt Estuary and the Belgian Part of North Sea (BPNS) from different sampling campaigns in February–April 2020 and 2021. Along the estuary, Hg concentration on suspended particles ([HgSPM]) progressively decreased with increasing salinity and was strongly correlated with organic matter content (%Corg) and origin (identified with δ13Corg). While [HgSPM] drives total Hg concentration in the estuary (total dissolved Hg, HgTD is only 7 ± 6 %), annual and daily variations of total Hg levels were mostly attributed to changes in SPM loads depending on river discharge and tidal regime. In the BPNS, a significant fraction of total Hg occurs as HgTD (40 ± 21 %) and the majority of this HgTD was reducible (i.e. labile Hg), meaning potentially available for microorganisms. Compared to the ‘90s, a significant decrease of [HgSPM] was observed in the estuary, but this was not the case for [HgTD], which can be due to (1) still significant discrete discharges from Antwerp industrial area, and (2) higher Hg partitioning towards the dissolved phase in the water column relative to the ‘90s. Our results highlight the important contribution of the Scheldt estuary for the Hg budget in North Sea coastal waters, as well as the need for seasonal monitoring of all Hg species.

Efeitos de diferentes configurações de embocadura na qualidade da água de um complexo estuarino-lagunar no nordeste do Brasil

ABSTRACT The Mundaú-Manguaba Estuary Lagoon Complex (CELMM), located on the coast of Alagoas state in Northeastern Brazil, consists of two choked coastal lagoons connected to the Atlantic Ocean by a series of narrow channels, establishing a single tidal inlet, which dynamically alters their position. This study uses the modeling system SisBaHiA® (in Portuguese, Sistema Hidrodinâmico Ambiental) and Trophic Index (TRIX) to evaluate how morphological changes in the CELMM can influence the water quality of the lagoons. The results showed that water quality is mainly influenced by river discharge regimes, with no major changes in the region of the tidal inlet for the three simulated years (2006, 2014 and 2017). Trophic index showed greater changes in the rainy season, with a decline in values as river discharge increases, mainly in the northwest and central portions of the Mundaú Lagoon. In the Manguaba Lagoon an opposite pattern was found, namely a rise in the Trophic index with increased river discharges.

Freshwater discharge from the large and coastal peninsular rivers of India: Areassessment for sustainable water management.

This study offers an updated mean annual water discharge of 10 large and 11 coastal basins of the Indian Peninsula and looks into environmental parameters influencing the water flux and discharge trends. The mean annual discharge of large and coastal rivers is estimated to be 221 and 294 km3. Thus, despite draining 25% of the Indian Peninsula, coastal rivers deliver more than half of the annual flux, and west-flowing coastal rivers contribute 85% of it. This study demonstrates temporal changes in the water discharge of various river basins. The presence of dams regulates discharge regimes of large rivers. The construction of large dams resulted in a significant decline in the water discharge of the Krishna, Cauvery, and Narmada. Through this study, we demonstrate the role of rainfall, catchment size, water loss through evapotranspiration and infiltration, and societal use of water in determining the runoff of each basin. We recommend tapping the water resources of the west-flowing rivers for proper planning, development, and management to reduce the water stress in the peninsular region and promoting sustainable management.

Climate change may impair electricity generation and economic viability of future Amazon hydropower

Numerous hydropower facilities are under construction or planned in tropical and subtropical rivers worldwide. While dams are typically designed considering historic river discharge regimes, climate change is likely to induce large-scale alterations in river hydrology. Here we analyze how future climate change will affect river hydrology, electricity generation, and economic viability of > 350 potential hydropower dams across the Amazon, Earth’s largest river basin and a global hotspot for future hydropower development. Midcentury projections for the RCP 4.5 and 8.5 climate change scenarios show basin-wide reductions of river discharge (means, 13 and 16%, respectively) and hydropower generation (19 and 27%). Declines are sharper for dams in Brazil, which harbors 60% of the proposed projects. Climate change will cause more frequent low-discharge interruption of hydropower generation and less frequent full-capacity operation. Consequently, the minimum electricity sale price for projects to break even more than doubles at many proposed dams, rendering much of future Amazon hydropower less competitive than increasingly lower cost renewable sources such as wind and solar. Climate-smart power systems will be fundamental to support environmentally and financially sustainable energy development in hydropower-dependent regions.

Attribution of Amazon floods to modes of climate variability: A review

AbstractAnomalous conditions in the oceans and atmosphere have the potential to be used to enhance the predictability of flood events, enabling earlier warnings to reduce risk. In the Amazon basin, extreme flooding is consistently attributed to warmer or cooler conditions in the tropical Pacific and Atlantic oceans, with some evidence linking floods to other hydroclimatic drivers such as the Madden–Julian Oscillation (MJO). This review evaluates the impact of several hydroclimatic drivers on rainfall and river discharge regimes independently, aggregating all the information of previous studies to provide an up‐to‐date depiction of what we currently know and do not know about how variations in climate impact flooding in the Amazon. Additionally, 34 major flood events that have occurred since 1950 in the Amazon and their attribution to climate anomalies are documented and evaluated. This review finds that despite common agreement within the literature describing the relationship between phases of climate indices and hydrometeorological variables, results linking climate anomalies and flood hazard are often limited to correlation rather than to causation, while the understanding of their usefulness for flood forecasting is weak. There is a need to understand better the ocean–atmosphere response mechanisms that led to previous flood events. In particular, examining the oceanic and atmospheric conditions preceding individual hydrological extremes, as opposed to composite analysis, could provide insightful information into the magnitude and spatial distribution of anomalous sea surface temperatures required to produce extreme floods. Importantly, such an analysis could provide meaningful thresholds on which to base seasonal flood forecasts.

Standard normal homogeneity test as a tool to detect change points in climate-related river discharge variation: case study of the Kupa River Basin

ABSTRACTThe study addresses homogeneity testing of annual discharge time series for eight hydrological stations and five annual climate time series for one weather station in the Kupa River Basin, between Slovenia and Croatia, and global annual average surface temperature time series for the period 1961–2010. The standard normal homogeneity test (SNHT) was used to detect both abrupt and gradual linear trend homogeneity breaks. The results reveal natural change points at the beginning of the 1980s. Absolute homogeneity testing of average annual weather station-level air pressure, annual precipitation, differences between precipitation totals and potential evapotranspiration and surface runoff from the independent observation time series confirmed an abrupt shift, also at the beginning of the 1980s. The trend of local air temperature for 1985–2000, which partly coincides with global surface temperature trend for 1974–2005, strengthened the river discharge regime shift since the beginning of the 1980s. These results could improve climate variation monitoring and estimation of the impact of climate variation on the environment in the area. Generally, an indication of climate regime change points and an assessment of their duration could provide significant benefits for the society.

Modelling Behaviour of the Salt Wedge in the Fraser River and Its Relationship with Climate and Man-Made Changes

Agriculture is an important industry in the Province of British Columbia, especially in the Lower Mainland where fertile land in the Fraser River Delta combined with the enormous water resources of the Fraser River Estuary support extensive commercial agriculture, notably berry farming. However, where freshwater from inland meets saltwater from the Strait of Georgia, natural and man-made changes in conditions such as mean sea level, river discharge, and river geometry in the Fraser River Estuary could disrupt the existing balance and pose potential challenges to maintenance of the health of the farming industry. One of these challenges is the anticipated decrease in availability of sufficient freshwater from the river for irrigation purposes. The main driver for this challenge is climate change, which leads to sea level rise and to reductions in river flow at key times of the year. Dredging the navigational channel to allow bigger and deeper vessels in the river may also affect the availability of fresh water for irrigation. In this study, the salinity in the river was simulated using H3D, a proprietary three-dimensional hydrodynamic numerical model which computes the three components of velocity (u,v,w) in three dimensions (x,y,z) on a curvilinear grid developed specially for Fraser River, as well as scalar fields such as salinity and temperature. The results indicate various levels of impact to the salinity in the river and adaptive measures must be established to maintain the long-term viability of the industry. This study found that sea level rise and changes in river discharge would have a larger impact on the availability of fresh water than would channel deepening at the present sea water level. In a low river discharge regime, the impact from sea level change is more significant than in the high river discharge regime. On the other hand, the influence from changes in river discharge on withdrawal appears to increase when water level is lowered. Dredging the channel to accommodate larger vessels with deeper draft would further affect the salinity and shorten the withdrawal window; the effect of channel deepening becomes more pronounced in the lower flow period.

Saltwater intrusion in a subtropical estuary

River discharge, precipitation, wind, water level and salinity measurements were used to investigate saltwater intrusion in a subtropical estuary. The upstream limit of saltwater intrusion was defined by the position of the 2 g/kg isohaline (X2) as it changed each tidal cycle. Observations were obtained from November 2014 to November 2015 along the Suwannee River, at Florida's Big Bend. Observations provided information to construct a first-order autoregressive Markov-chain model and predict X2. The model predicts X2 from its position in the previous tidal cycle, from river discharge, from water level, from precipitation and from wind velocity. In order to capture the seasonality of the Suwannee River discharge, the analysis was done separately for high and low river discharge regimes. The high discharge regime for the particular year of observations coincided with the cold season and had a mean value of 360 m3/s. The low discharge regime overlapped with the warm season and had a mean of 198 m3/s. As expected, saltwater intrusion was inversely related to river discharge. Values of X2 were 0.4 km for a discharge of 377 m3/s, and 6 km for a discharge of 195 m3/s. The autoregressive model was able to reproduce the observed seasonality of saltwater intrusion in the Suwannee River. The model was then used to project values of X2 for different scenarios of climate change as represented by possible combinations of river discharge and water levels.

Modelling climate change effects on Atlantic salmon: Implications for mitigation in regulated rivers

Climate change is expected to alter future temperature and discharge regimes of rivers. These regimes have a strong influence on the life history of most aquatic river species, and are key variables controlling the growth and survival of Atlantic salmon. This study explores how the future abundance of Atlantic salmon may be influenced by climate-induced changes in water temperature and discharge in a regulated river, and investigates how negative impacts in the future can be mitigated by applying different regulated discharge regimes during critical periods for salmon survival. A spatially explicit individual-based model was used to predict juvenile Atlantic salmon population abundance in a regulated river under a range of future water temperature and discharge scenarios (derived from climate data predicted by the Hadley Centre's Global Climate Model (GCM) HadAm3H and the Max Plank Institute's GCM ECHAM4), which were then compared with populations predicted under control scenarios representing past conditions. Parr abundance decreased in all future scenarios compared to the control scenarios due to reduced wetted areas (with the effect depending on climate scenario, GCM, and GCM spatial domain). To examine the potential for mitigation of climate change-induced reductions in wetted area, simulations were run with specific minimum discharge regimes. An increase in abundance of both parr and smolt occurred with an increase in the limit of minimum permitted discharge for three of the four GCM/GCM spatial domains examined. This study shows that, in regulated rivers with upstream storage capacity, negative effects of climate change on Atlantic salmon populations can potentially be mitigated by release of water from reservoirs during critical periods for juvenile salmon.

Tributaries affect the thermal response of lakes to climate change

Abstract. Thermal responses of inland waters to climate change varies on global and regional scales. The extent of warming is determined by system-specific characteristics such as fluvial input. Here we examine the impact of ongoing climate change on two alpine tributaries, the Aare River and the Rhône River, and their respective downstream peri-alpine lakes: Lake Biel and Lake Geneva. We propagate regional atmospheric temperature effects into river discharge projections. These, together with anthropogenic heat sources, are in turn incorporated into simple and efficient deterministic models that predict future water temperatures, river-borne suspended sediment concentration (SSC), lake stratification and river intrusion depth/volume in the lakes. Climate-induced shifts in river discharge regimes, including seasonal flow variations, act as positive and negative feedbacks in influencing river water temperature and SSC. Differences in temperature and heating regimes between rivers and lakes in turn result in large seasonal shifts in warming of downstream lakes. The extent of this repressive effect on warming is controlled by the lakes hydraulic residence time. Previous studies suggest that climate change will diminish deep-water oxygen renewal in lakes. We find that climate-related seasonal variations in river temperatures and SSC shift deep penetrating river intrusions from summer towards winter. Thus potentially counteracting the otherwise negative effects associated with climate change on deep-water oxygen content. Our findings provide a template for evaluating the response of similar hydrologic systems to on-going climate change.

Changes in discharge regimes of rivers in Croatia

This paper presents the results of the first comprehensive national analysis of changes in discharge regimes of rivers in Croatia. Seven types of discharge regimes have been defined for rivers in Croatia. We analyzed the changes in discharge regimes of all types, comparing the standard period from 1961 to 1990 with the most recent period from 1990 to 2009. We found evidence of a redistribution of discharge throughout the year, an increase in autumn and winter discharges (especially for rivers dominantly fed by snowmelt), and a decrease in summer discharge values. Furthermore, we detected a change in the month of the appearance of mean discharge maxima and minima. In most cases, the changes can be explained by changes in the regime of climate elements (temperature, precipitation, and evapotranspiration). The results are consistent with those from upstream countries; that is, Slovenia, Austria, and Bosnia and Herzegovina.

Analysis of multi-dimensional hydrological alterations under climate change for four major river basins in different climate zones

Changes in river discharge regimes are regarded as the primary drivers of change of many in-stream ecological processes. While a lot of assessments addressing the hydrological alteration caused by human activities have been conducted for many river basins worldwide, a comprehensive analysis of hydrological alteration over major river basins worldwide under climate change is still limited to date. This study aims to address multi-dimensional hydrological alterations (alterations of multiple river flow characteristics) under climate change for four major rivers on three continents, by means of a consolidated framework consisting of two hydrological models, bias-corrected scenarios from five general circulation models (GCMs), and three Representative Concentration Pathways (RCPs) scenarios. The multi-dimensional hydrological alterations are quantified via the general Indicators of Hydrological Alteration approach (IHA) and two modified IHA methods based on dimensionality reduction. The reliability and advantages for the modified IHA methods are also analyzed. The results show that: (1) A modified IHA method (“NR-IHA method”) where the selected non-redundant IHA indices are basin specific is a valid alternative to the conventional IHA method for evaluating flow regime alteration, in consideration that high agreements in the simulated overall flow regimes alteration degree between it and the conventional IHA method are found during historical and future scenario periods, over four basins (the Upper Yellow River, the Lena River, the Tagus River and the Upper Amazon River). (2) Climate change is expected to remarkably alter overall flow regimes in the Tagus River and Upper Yellow River, especially at the end of the 21st century and under high RCP scenarios, whereas the dominant alteration extent tends to be low in the Lena River and Upper Amazon River in the two future periods. (3) The modified IHA method, preventing double-counting some aspects of the flow regime when assessing alteration degree of overall flow regimes, can save 65 % computation time and is more efficient than the conventional IHA method. It could be beneficial to figure out adaptive countermeasures for water resource management and restoration of eco-environmental systems under climate change.

Species composition of macrozoobenthos in lagoons of Sakhalin Island

Species composition of macrozoobenthos in lagoons of Sakhalin Island (in total, 637 species) is described on the base of cited data and results of author’s surveys. Its species composition is formed under influence of wide spectrum of environmental factors, as size of lagoon, water salinity, periodicity of connection with the sea and type of the water exchange, river discharge regime, climatic and geographical isolation, etc. Generally, 6 types of lagoons are determined on the coast of Sakhalin differed by composition of benthic fauna: 1) large semiclosed salty lagoon (Lake Busse in southern Sakhalin); 2) small semiclosed salty lagoons with water stratification and periodic connection with the sea (Lake Izmenchivoe and Lake Ptichye in southern Sakhalin); 3) large shallow semiclosed lagoons (in northern Sakhalin); 4) small isolated brackish lagoon (Kuegda Bay in northern Sakhalin); 5) closed oligosaline lagoons (Lake Tunaicha and Lake Aynskoe in southern Sakhalin); 5) isolated freshwater lagoons (Vavaysko-Chibisanskaya lake system in southern Sakhalin). Salty and freshwater lagoons are distinguished by the highest species diversity.

The impact of commercially treated oil and gas produced water discharges on bromide concentrations and modeled brominated trihalomethane disinfection byproducts at two downstream municipal drinking water plants in the upper Allegheny River, Pennsylvania, USA

In 2010, a dramatic increase in the levels of total trihalomethane (THM) and the relative proportion of brominated species was observed in finished water at several Pennsylvania water utilities (PDW) using the Allegheny River as their raw water supply. An increase in bromide (Br−) concentrations in the Allegheny River was implicated to be the cause of the elevated water disinfection byproducts. This study focused on quantifying the contribution of Br− from a commercial wastewater treatment facility (CWTF) that solely treats wastes from oil and gas producers and discharges into the upper reaches of the Allegheny River, and impacts on two downstream PDWs. In 2012, automated daily integrated samples were collected on the Allegheny River at six sites during three seasonal two-week sampling campaigns to characterize Br− concentrations and river dispersion characteristics during periods of high and low river discharges. The CWTF discharges resulted in significant increases in Br− compared to upstream baseline values in PDW raw drinking water intakes during periods of low river discharge. During high river discharge, the assimilative dilution capacity of the river resulted in lower absolute halide concentrations, but significant elevations Br− concentrations were still observed at the nearest downstream PDW intake over baseline river levels. On days with active CWTF effluent discharge the magnitude of bromide impact increased by 39ppb (53%) and 7ppb (22%) for low and high river discharge campaigns, respectively. Despite a declining trend in Allegheny River Br− (2009–2014), significant impacts from CWTF and coal-fired power plant discharges to Br− concentrations during the low river discharge regime at downstream PDW intakes was observed, resulting in small modeled increases in total THM (3%), and estimated positive shifts (41–47%) to more toxic brominated THM analogs. The lack of available coincident measurements of THM, precursors, and physical parameters limited the interpretation of historical trends.

Speciation, Size Fractionation and Transport of Trace Elements in the Continuum Soil Water–Mire–Humic Lake–River–Large Oligotrophic Lake of a Subarctic Watershed

The concentration and size fractionation of major and trace elements (TEs) linked to organo-mineral colloids along the landscape gradient soil water–peat mire–humic lakes–river–large oligotrophic lake have been investigated within two watersheds located in the subarctic region (Karelia, Russia) in the summer base-flow period. A large volume of natural waters was filtered in the field using cascade filtration and ultrafiltration (UF) with a progressively decreasing pore size [100, 20, 10, 5, 0.8, 0.4, 0.22, 0.1, 0.046, 0.0066 (100 kDa), 0.0031 (10 kDa) and 0.0014 µm (1 kDa)] followed by multi-elemental ICP-MS and dissolved organic carbon (DOC) analysis. In situ dialysis with 10 and 1 kDa molecular weight cutoff membranes was also conducted. According to the TE distribution among different size fractions in the continuum soil (mire)–humic lake–river–large lake, the following groups of elements could be distinguished: (1) elements significantly bound to the colloidal (1 kDa—0.22 µm) fraction and decreasing the proportion of this fraction from the feeding lake and stream to the terminal oligotrophic lake (Fe, Ti and U); (2) colloidally dominated (>80 %) elements exhibiting similar size fractionation in all studied settings (Y, REEs, Zr, Hf and Th); (3) elements appreciably bound to colloids (20–40 %) in organic-rich soil and bog waters and decreasing their colloidal fraction to approximately 10 % in the oligotrophic lake (Mg, Ca, Sr, Rb and Mo); and (4) elements linked to the colloidal fraction (40–80 %) and not demonstrating any systematic variation between different landscape units (Ni, Co, Cu, Cd, Cr, Mn, Zn and Pb). The in situ dialysis technique produced a similar picture of the colloidal size fractionation with generally lower proportions of elements in the colloidal fraction compared to the UF. Thermodynamic modeling of trace element speciation using available codes demonstrated that complexation with dissolved organic matter and adsorption at the surface of ferric colloids can adequately model the observed colloidal speciation of divalent metals. However, the modeling could not describe the distribution of trivalent and tetravalent hydrolysates (TE3+,4+) among different size fractions and cannot reproduce the experimentally observed proportion of their colloidal forms. Therefore, coprecipitation with organo-ferric colloids should be considered to account for the partitioning of TE3+,4+ between truly dissolved (<1 kDa) and various colloidal fractions. It follows from the results of this study that autochthonous processes of organic matter fractionation, such as (1) transformation of initially allochthonous soil-derived colloids via photo- and biodegradation or (2) new organic ligand production by plankton and periphyton, cannot appreciably affect the distribution of TEs among various size fractions of colloids and particles along the landscape gradient from soil water to terminal lake. Thus, even crucial changes in the environmental conditions, such as the river discharge regime and relative lake versus bog coverage, surface water pH, pCO2 and DOC changes that are likely to occur according to the “extreme” scenario of the climate warming in the Arctic, should not affect the size fractionation and, therefore, the potential aquatic lability and biodisponibility of TEs present as organic (divalent transition metals, alkaline earth metals) and organo-mineral (Fe, Al, insoluble trivalent and tetravalent elements and U) colloids.

Observation of a turbid plume using MODIS imagery: The case of Douro estuary (Portugal)

The Douro is one of the longest rivers in the Iberian Peninsula and represents the most important freshwater input into the Atlantic Ocean in the northwestern Portuguese coast. In order to fill the gaps on the comprehension of the spatial variability of the Douro estuarine plume, an innovative methodology was applied to observe and characterize this plume and its spatial and temporal variability. Using images of normalized water-leaving radiance at 555nm from MODIS (Moderate Resolution Imaging Spectroradiometer) in combination with long-term concurrent wind, tidal and river discharge data (2003–2011), this work evaluates the effect of the main drivers (river discharge, wind and tide) on the plume features. Expected strong relationships between river discharge and turbid levels were detected. A circular pattern is well distinct off Douro estuary when the flow exceeds 500m3s−1. Under upwelling favorable winds and high river discharge regime, an offshore expansion is observed. During southerly winds, there is a plume confinement to the coast. Easterly winds produce a bulge formation with an offshore detachment from the coast while westerly winds tend to confine freshwater close to the shoreline and decrease the cross-shore advection. Under high river discharges, a remarkable tidal influence in the near-field regions is observed close to the coast and near the river mouth.