Hydrological–morphological processes in the mouth area of the Congo R. and the effect of submarine canyon on these processes

The general geographic, hydrographic, climatic, and hydrological characteristics of the Congo R. basin are considered. The major features of the riverine and marine factors that have their effect on the hydrological regime and morphology of the delta and estuary of the Congo R. are identified; the effect of a submarine canyon on the morphological features of the estuary is analyzed in detail; and changes in river delta structure in the XX century and currently are considered. The hydrological—morphological characteristics of the largest mouths of African rivers, the formation conditions of water and sediment runoff, and variations of their deltas are compared.     

Deltas as Indicators of Natural and Human-Induced Changes in the Regimes of Rivers and Seas

The way in which the joint action of fluvial and marine factors control delta formation is illustrated by examples of the mouths of rivers discharging into the Black and Mediterranean seas. The processes of active delta out-building under the effect of cold, wet climatic conditions and human-induced erosion in river basins and the processes of sea-wave erosion of deltas under the effect of a significant decrease in the sediment discharge of rivers that was caused by impact of human activities in the second half of the 20th century are discussed.     

Many-year variations in river delta structures

Data on several river deltas are used to analyze the regularities in their dynamics in the context of variations of water and sediment runoff, sea level, and hydroengineering activities in delta areas. The basis for this analysis includes the results of many-year studies of river deltas in Russia and the world. The specific features of the evolution of the structure and morphometry of bayhead deltas, forming in bays, lagoons, and estuaries are shown in the case of the Alikazgan delta in the Terek mouth area and the deltas of two watercourses in the Mississippi mouth area. Data on many-year variations of the morphometric characteristics of modern protruding deltas in open coastal zones are systematized, and the factors that have an effect on these changes are analyzed. The types of delta formation processes and the types of deltas are considered with regard to the factors involved. The majority of modern river deltas are found to slow down their progradation into seas under the effect of anthropogenic runoff decline; moreover, some deltas have started retreating and degrading.     

Hydrological and morphological features of the Upper Angara mouth area

The hydrological and morphological processes in the mouth area of the Upper Angara (which ranks second in terms of water abundance among Baikal Lake tributaries) are considered. The major external factors that determine those processes have been revealed. The main features of the delta??s water regime, including the effect of anthropogenic level rise in the lake, are described. Specific attention is paid to morphological processes in the delta and on the barrier bar, separating a large mouth lagoon from the lake.     

Water chemistry in Onega Lake and its tributaries

The results of studies of water chemistry carried out in the water body in 1965–2009 are presented. This period features a considerable industrial and agricultural rise in the lake drainage basin, followed by a decline since the 1990s, manifesting themselves in the dynamics of some hydrochemical characteristics of water bodies. The multipurpose use of Onega Lake is shown to cause its pollution and eutrophication. The results of studies are used to evaluate the major components of the external load onto the lake and trends in variations of chemical characteristics under the effect of natural and anthropogenic factors.     

Eutrophication in the Polish coastal zone: the past, present status and future scenarios

In the Baltic Sea eutrophication processes have accelerated in the past 50 years of the 20th century and presently there exists a major ecological problem for this sea. The Polish coastal zone of the southern Baltic Sea is the recipient of riverine inputs from two major sources, namely the Odra and Vistula, as well as a number of smaller rivers along the central coast. Hence, the entire coastal zone remains under severe anthropogenic pressure. The variability of nutrient concentrations, especially the winter nutrient pool in the euphotic zone, summer level of total nitrogen and total phosphorus, together with such eutrophication indicators as water oversaturation with oxygen and the summer oxygen minimum, were analysed in the data time series 1959-2001. The temporal trends were investigated using linear regression and the non-parametric Whirsch test. The future characteristics of the Baltic Sea are discussed taking into account the development of driving forces.     

Quantifying threats to groundwater resources in the Republic of Maldives Part I: Future rainfall patterns and sea‐level rise

Reserves of fresh groundwater on atoll islands are extremely fragile due to climatic and anthropogenic stresses. Of major concern is the quantity of water to be available in the coming decades under the influence of variable rainfall patterns, rising sea level, environmental conditions, and expected population growth that depends on groundwater resources. In this study, a 3‐dimensional numerical modelling approach using the SEAWAT modelling code is used to estimate freshwater lens volume fluctuation for 4 representative islands in the Republic of Maldives in response to long‐term changes in rainfall, sea‐level rise (SLR), and anthropogenic stresses such as groundwater pumping and short‐term impacts from tsunami‐induced marine overwash events. This work is divided into 2 papers. This first paper presents numerical model set‐up and calibration, and the effect of future rainfall patterns and SLR on fresh groundwater reserves. The second paper focuses on marine overwash events. The results of simulated future freshwater lens volume presented in the first study contribute to efficient groundwater resources planning and management for the Maldives in the upcoming decades. Freshwater lenses in small atoll islands (area < 0.6 km²) are shown to have a strong variability trends in the upcoming decades with expected reduction in lens volume between 11% and 36% due to SLR. In contrast, freshwater lenses in larger atoll islands (area > 1.0 km²) are shown to have less variability to changing patterns with expected reduction in lens volume between 8% and 26% due to SLR. Study results can provide water resource managers with valuable findings for consideration in water security measures.     

The hydrological regime and the morphological structure of the Godavari River delta (India)

The major hydrological and geographic characteristics of the Godavari River and the coastal zone of the Bay of Bengal that have their effect on the hydrological regime and the morphological structure of the river delta are considered. The hydrographic, climatic, and environmental conditions in the Godavari delta are described. The specific features of hydrological processes in the delta are considered, including river and bay water mixing and the impact of tropic storms and hurricanes on the delta. The main features of morphological processes in the delta are revealed, including cyclic changes in the delta in Holocene and the dynamics of the channel network and delta coastline in the past 150 years. It is shown that the processes of erosion and retreat of the delta coastline became more active in the late XX century.     

Seasonal to decadal forcing of high water level percentiles in the German Bight throughout the last century

For the purpose of coastal planning and management, especially under changing climatic conditions, enhanced knowledge about the evolution of extreme sea levels in the past, present, and future is required. This paper presents statistical analyses of high seasonal water level percentiles of 13 tide gauges in the German Bight, spanning over a period of up to 109 years throughout the twentieth and twenty-first centuries. Seasonal and annual high percentile time series of water levels were investigated in comparison to the mean sea level (MSL) for changes on seasonal, inter-annual, and decadal timescales. While throughout the first half of the twentieth century extreme water levels generally followed changes in MSL, during the second half of the century, linear extreme sea level trends exceeded those in MSL in the order of 9–64 cm per century. The largest, although insignificant, contribution to the magnitude of these trends occurs in the winter season (January to March), while smaller but, due to the generally lower atmospheric variability, significant changes are observed during spring (April to June). The observed multi-decadal trends are generally in good agreement with multi-decadal trends in the corresponding percentiles of local zonal surface winds. Only small parts of the trends remain unexplained. It is suggested that these remaining trends result from modifications in the local tidal regime. For the aspects of coastal planning, the findings clarify that in the German Bight, in addition to changes in MSL, potential changes in storminess and in the tidal regime significantly contribute to the development of extreme water levels. Since these factors have influenced the characteristic of extremes throughout the recent past, they also have to be taken into account when estimating design water levels for, e.g., dikes (in a warming climate) under changing greenhouse gas emissions.     

Sulfate reduction in natural water bodies. 1. The effect of environmental factors and the measured rates of the process

Sulfate reduction is an important oxidation process involving transformation of organic matter and its components and taking place in the aquatic environment and bottom sediments of water bodies (both fresh and marine) under anaerobic conditions. The intensification of sulfate reduction in water bodies is a sign of a stronger anthropogenic impact on the environment and natural water bodies. The development of sulfate reduction under natural conditions reflects the influence of many environmental factors. The effect of the most important factors (the concentration of organic matter and its components and sulfates, the temperature of aquatic environment, and the abundance and activity of sulfate-reducing bacteria) on the process of sulfate reduction in the aquatic environment and bottom sediments in water bodies is considered.     

Changes in Moskva R. runoff under anthropogenic impacts

An algorithm has been proposed for assessing the hydrological role of the main anthropogenic factors governing the formation of Moskva R. runoff both separately and in total. The effect of landscape transformations, hydroengineering structures, and water use on the runoff in the Moskva R. basin has been analyzed for characteristic periods in the recent 150 years (the middle XIX century, the early XX century, 1960–1980, and the first decade of the XXI century, the period of calculation of the average long-term runoff). The main hydrological effect of urbanization in the Moskva R. basin on river runoff formation in recent decades has been demonstrated. The shares of the anthropogenic and climatic factors in the overall changes in Moskva R. runoff in the early XXI century have been evaluated.     

The effect of water abundance in a territory on the population health

The paper presents the results of analysis of present-day scientific data on the dynamics of global hydroclimatic processes (with the establishment of long-term variations in the global water exchange processes) and the features of water abundance in territories under the effect of various natural and anthropogenic factors. Possible transformations of the hydrogeological situation under global climate changes are considered. The basic principles of the concept regarding the assessment of the effect of global hydroclimatic changes on the population health are presented. Medical-environmental data on the consequences of water-triggered environmental crises, taken as analogous natural models, are analyzed. The processes and regularities in the development of human pathology under the conditions of higher and lower water abundance in a territory are identified. The succession, time stages, and phases of the development of infection, parasitic, noninfectious pathologies are determined. Cause-and-effect relationships were established between the observed pathology and the effect of a complex of changing natural, anthropogenic, and social-environmental factors. Methodological approaches to the assessment of medical-environmental consequences of distinct changes in the water abundance in the territories are described. The possible use of subsurface water sources as a reserve of domestic water supply under emergencies are considered.     

Variations in sediment runoff in the lower reaches and the delta of the Kuban River in the XX–XXI centuries

Data of network and expedition measurements and information about water management arrangements were used to study in detail the peculiarities of along-channel and long-term variations in the major characteristics of suspended sediment runoff in the lower reach and the delta of the Kuban River. For characteristics periods, the annual volumes of actual and estimated sediment runoff and the contribution of economic activity in its variations are evaluated and possible changes in sediment runoff characteristics in the XXI century are forecasted. The specific features, values, and causes of sediment runoff transformation in Kuban delta in the past and the present are analyzed; sediment balance in the delta is calculated.     

Evolution of the Yellow River delta,China: Impacts of channel avulsion and progradation

The evolution of the Yellow River delta is characterized by heavy sediment load,rapid seaward migration,frequent avulsions,and intense anthropogenic disturbances.Evolution of the delta channel following avulsions is very complex and has not yet been thoroughly understood.In the research presented by this paper,we conducted comprehensive analyses of the changes in the water stages,slopes,longitudinal profiles,and the erosion and deposition in the Yellow River delta channels during a time period of over five decades.Results showed that,following each avulsion,channels migrated seaward at decaying rates and the slopes at the downstream of the avulsion point decreased exponentially with time and completed its major adjustment within about four to five years.A generalized geometric model was proposed to describe the changes in the longitudinal profiles of the delta channels.A calculation method to determine the characteristic water stages at the delta was proposed based on the geometric model and the delayed response model for the morphological responses of fluvial rivers to perturbations.Water stages corresponding to a discharge of 3000 m3/s at Lijin and Xihekou during 1954 through 2012 were calculated by using the proposed method.The proposed method may be used to predict the evolution of the delta channels in response to artificial avulsions at the Yellow River delta in the future.     

Assessment of the impact of nitrogen mineral compounds on bottom-dwelling fish in Black Sea bays

Data on the effect of physiological, ecological, and anthropogenic factors on the concentration of nitrosamines in the tissues of bottom-dwelling fish—Scorpaena porcus L. and Mesogobius batrachocephalus Pallas—inhabiting two Black Sea bays with different anthropogenic load are presented. Seasonal dynamics in the concentration of nitrosamines in fish tissues, manifesting itself in its decrease in summer and increase in autumn is revealed. Problems of the environmental risk resulting from the excessive concentration of nitrogen compounds in the marine environment are discussed.     

Internal Variability Versus Anthropogenic Forcing on Sea Level and Its Components

In this paper we review and update detection and attribution studies in sea level and its major contributors during the past decades. Tide gauge records reveal that the observed twentieth-century global and regional sea level rise is out of the bounds of its natural variability, evidencing thus a human fingerprint in the reported trends. The signal varies regionally, and it partly depends on the magnitude of the background variability. The human fingerprint is also manifested in the contributors of sea level for which observations are available, namely ocean thermal expansion and glaciers’ mass loss, which dominated the global sea level rise over the twentieth century. Attribution studies provide evidence that the trends in both components are clearly dominated by anthropogenic forcing over the second half of the twentieth century. In the earlier decades, there is a lack of observations hampering an improved attribution of causes to the observed sea level rise. At certain locations along the coast, the human influence is exacerbated by local coastal activities that induce land subsidence and increase the risk of sea level-related hazards.     

Spatial and temporal patterns of dissolved organic matter quantity and quality in the Mississippi River Basin, 1997–2013

Recent studies have found insignificant or decreasing trends in time‐series dissolved organic carbon (DOC) datasets, questioning the assumption that long‐term DOC concentrations in surface waters are increasing in response to anthropogenic forcing, including climate change, land use, and atmospheric acid deposition. We used the weighted regressions on time, discharge, and season (WRTDS) model to estimate annual flow‐normalized concentrations and fluxes to determine if changes in DOC quantity and quality signal anthropogenic forcing at 10 locations in the Mississippi River Basin. Despite increases in agriculture and urban development throughout the basin, net increases in DOC concentration and flux were significant at only 3 of 10 sites from 1997 to 2013 and ranged between ?3.5% to +18% and ?0.1 to 19%, respectively. Positive shifts in DOC quality, characterized by increasing specific ultraviolet absorbance at 254 nm, ranged between +8% and +45%, but only occurred at one of the sites with significant DOC quantity increases. Basinwide reductions in atmospheric sulfate deposition did not result in large increases in DOC either, likely because of the high buffering capacity of the soil. Hydroclimatic factors including annual discharge, precipitation, and temperature did not significantly change during the 17‐year timespan of this study, which contrasts with results from previous studies showing significant increases in precipitation and discharge over a century time scale. Our study also contrasts with those from smaller catchments, which have shown stronger DOC responses to climate, land use, and acidic deposition. This temporal and spatial analysis indicated that there was a potential change in DOC sources in the Mississippi River Basin between 1997 and 2013. However, the overall magnitude of DOC trends was not large, and the pattern in quantity and quality increases for the 10 study sites was not consistent throughout the basin.     

The enrichment characteristics of mercury in the sediments of Dongjiu and Xijiu, Taihu lake catchment, in the past century

The concentration and the enrichment factors of mercury (Hg) in the sediment cores of Dongjiu and Xijiu, Taihu Lake catchment, were studied. The accumulation fluxes, anthropogenic input concentration and anthropogenic accumulation fluxes of Hg in recent 100 years were also analyzed based on the 210Pb dating. The results indicate that the increasing concentrations of Hg in the sediments are influ-enced by natural factors and anthropogenic input simultaneously. Generally, about 2/3 of the Hg in the sediment was from anthropogenic sources. In the early 20th century, the anthropogenic input was owing to the urban development and fossil fuel consumptions surrounding the Taihu Lake and the worldwide atmospheric deposition of Hg since the industrial revolution. The concentration and an-thropogenic fluxes of Hg increased with the industrial development in the catchment since the 1930s. It reached the maximum during the middle 1970s and middle 1990s, and decreased since the middle 1990s with constraints on high pollution industries.     

Natural and anthropogenic long-term variations of water runoff and suspended sediment load in the Huanghe river

The hydrographic, climate, hydrological, and landscape features of the Huanghe R. Basin are considered. Water runoff and suspended sediment load in the Huanghe R. are shown to have dropped significantly in 1950–2009 under the effect of regional climate changes and economic activity in the basin. Water balance method and the concept of flow transport competency were used to assess the contribution of natural and anthropogenic factors (decline in precipitation, water withdrawal for economic needs, and the effect of reservoirs) to the decrease in river water runoff and suspended sediment load.     

Nitrogen isotope ratios in estuarine biota collected along a nutrient gradient in Narragansett Bay, Rhode Island, USA

Stable nitrogen isotope ratios were used to study the incorporation of anthropogenically-derived nitrogen into the food webs of salt marsh systems along a contamination gradient in Narragansett Bay. Nitrogen isotope ratios (delta(15)N) were measured in six estuarine species collected from three marshes along this gradient, monthly from June to October between 1997 and 1999. A significant decrease in delta(15)N was found with distance along the estuary for four of the six species. Significant differences were found among monthly isotope ratios for some species. Nitrogen isotope ratios in sea lettuce (Ulva lactuca) increased during the summer season with highest delta(15)N values measured during September and October. This trend was most pronounced at the station receiving the highest nutrient inputs. Elevated delta(15)N values at this station appeared to correlate with seawater ammonia/nitrate concentration ratios. The temporal variations in delta(15)N suggest that care should be taken in species selection and the design of sampling schemes of studies using delta(15)N for monitoring anthropogenic nutrients in aquatic systems. Sampling programs designed to determine long-term trends should consider species that do not show rapid fluctuations in isotope ratios. The mud snail, Nassarius obsoletus, responded this way in the present study. Studies designed to measure short-term changes should include species such as U. lactuca, which rapidly respond to isotope changes. The results from this study also help to establish a baseline for nitrogen isotope values in Narragansett Bay. This information can be used to monitor future trends in nitrogen inputs to this estuary.