Geochemical characterisation and erosion stability of fine‐grained groyne field sediments of the Middle Elbe River

Because of the significant reduction of flow velocity relative to the main current there is an accumulation of sediment material in the centre of the groyne fields over time (years to decades) up to a maximum of 1.5 m. Based on the element‐ and compound‐specific depth functions of this fine‐grained material with high organic matter content the sedimentation history of the Elbe River sediments concerning the environmentally relevant nutrients and pollutants can be reconstructed. It could be shown that the fresh sediments are less polluted than the deeper older ones. During the extreme flood of the river Elbe in August 2002 the critical erosion shear stress in the groyne fields was high enough to remobilise a considerable portion of the sediment depot. The hazard to the environment is high due to the fact that a significant part of the remobilised polluted sediments was distributed over the recent floodplain which is normally used as pasture. Thus these groyne field sediments represent a temporary danger for the water quality of the river Elbe. But the hazard of the solids sedimented in the recent floodplain of the river can be viewed as long‐lasting.     

On the correspondence between morphological and hydrodynamical patterns of groyne fields

This paper examines a variety of recirculation flow patterns that develop in the groyne fields on rivers. A comprehensive data set was obtained from flume experiments at Delft University of Technology and field measurements performed on the Elbe River in Germany. The analysis focuses on patterns of velocity, scour and deposition, and corresponding change of riverbed morphology. The results show that velocity patterns in the groyne fields depend mainly on the aspect ratio between groyne length and length of groyne field. When the aspect ratio is greater than 0·5, a one‐gyre pattern of recirculation develops, while at groyne fields with aspect ratios less than 0·5 a two‐gyre recirculation pattern emerges. The spatial distribution of fine‐sediment deposition between the groynes coincides with the locations of gyres. Moreover, the thickness of the fine‐sediment layer decreases toward the gyre margins where recirculation velocities are greatest. Although the total concentration of suspended sediment in the river does not change considerably as the flow moves through the groyne field, the biological and gravimetrical composition of the suspended material changes substantially within the groyne field. These changes are due to preferential deposition of coarse mineral particles and the replacement of those minerals with finer organic material. Copyright © 2002 John Wiley & Sons, Ltd.     

Tracer measurements in groyne fields for the quantification of mean hydraulic residence times and of the exchange with the stream

Tracer experiments were carried out in groyne fields (GF) of the river Elbe near Havelberg (Germany) in order to estimate the hydraulic connectivity with the river channel. The characteristic times of the five groyne fields, which were estimated from the exponentially declining tracer curves in 43 runs, ranged between 15 min and 69 min and did not correlate with the water level. Methodological investigations show that single point injection and two measurements (in the outflowing water and in the dominant region) are sufficient to provide robust in‐situ tracer curves. Using simplified mathematical simulations with connected stirred tanks, the conditions are investigated for the development of breaks in tracer curves and for the occurrence of significant errors in the estimation of intrinsic residence times. It was shown that an initial uniform dye distribution is not mandatory for the estimation during steady states. In special cases, point injections are more advisable. Moreover, the mean hydraulic residence time was found to be not equivalent to the estimated characteristic time. In fact, it is mostly overestimated by tracer experiments. The degree of overestimation depends on mixing and the volumetric proportions between the different parts of the GF and can be calculated from measured dye concentration differences. For example, an overestimation of 32% was calculated for a groyne field with a commonly found circulation flow pattern.     

Continuous Multi‐probe Measurements in Fastflowing Waters Using a Hydrographic Slot

Taking continuous spatiotemporal in situ measurements with multi‐probes in fast‐flowing waters/rivers can be problematic because the sensors may be damaged by high shear forces and flotsam. To protect the multi‐probe and to enable easy access for the maintenance and calibration of the sensors, a special multi‐probe holder fixed in a hydrographic slot was developed. The validation of the probe system revealed a “memory effect” at short time scales (< 10 s) within sharp gradients caused by the overflow container of the multi‐probe rack keeping the sensors submerged in the sample water. Continuously recorded data (conductivity, temperature, pH, oxygen concentration and saturation, as well as in vivo fluorescence of chlorophyll‐a) from a research cruise on board the RV ALBIS along the river Elbe (river km 309) and entering the river Saale are presented. This river stretch upstream of the city of Magdeburg to the mouth of the Saale tributary was found to have a complex physicochemical character, which is attributable to the long mixing process of water from the river Saale and the river Elbe.     

Temporal and spatial variability in the Guadalquivir estuary: a challenge for real-time telemetry

Meteorological, hydrological, and hydrodynamic data for 3 years (2008–2010) have been used to document and explain the temporal and spatial variability of the physical–biogeochemical interactions in the Guadalquivir River Estuary. A real-time, remote monitoring network has been deployed along the course of the river between its mouth and Seville to study a broad range of temporal scales (semidiurnal, diurnal, fortnightly, and seasonal). This network consists of eight hydrological monitoring stations capable of measuring temperature, conductivity, dissolved oxygen, turbidity, and chlorophyll fluorescence at four depths. In addition, six stations have been deployed to study hydrodynamics, obtaining 20-cell water column current profiles, and there is a meteorological station at the river mouth providing data for understanding atmospheric interactions. Completing this data-gathering network, there are several moorings (tide gauges, current/wave sensors, and a thermistor chain) deployed in the estuary and river mouth. Various sources of physical forcing, such as wind, tide-associated currents, and river discharge, are responsible for the particular temporal and spatial patterns of turbidity and salinity found in the estuary. These variables force the distribution of biogeochemical variables, such as dissolved oxygen and chlorophyll fluorescence. In particular, episodes of elevated turbidity (when suspended particle matter concentration >3,000 mg/l) have been detected by the network, together with episodes of declining values of salinity and dissolved oxygen. All these patterns are related to river discharge and tidal dynamics (spring/neap and high/low tide).     

Shifts in the Processes of Oxygen and Nutrient Balances in the River Elbe since the Transformation of the Economic Structure

The reduction of pollution in the river Elbe since 1990 has resulted in changes in the processes taking place in the river. The heterotrophic degradation which dominated until 1990 was accompanied by a lack of oxygen, floating masses of sewage fungi, and sludge formation in the areas of still water. Since the early 1990s, autotrophic processes have come to dominate, with an increase in pH fluctuations and the oxygen production potential, but evidently not the chlorophyll level during the growing season. The degradable organic pollution of the Elbe is determined by algae production. The high levels of ammonium previously encountered in the Elbe were attributable to not only dischargers but also in particular the lack of oxygen in the water. Via heterotrophic nitrate assimilation, nitrate served as an oxygen reserve, resulting in high levels of nitrite. At present, when the oxygen contents are sufficient, the concentration reductions of nitrate and nitrite along the reach of the Elbe are approximately parallel, which in view of the lack of ammonium indicates the denitrification of microzones low in oxygen. The relative proportion of structurally bound substance turnover will become increasingly important for the Elbeπs material budget.     

The effect of Razdol’naya River on the environmental state of Amur Bay (the Sea of Japan)

Seasonal variations in biogenic substances (nitrates, nitrites, ammonium, phosphates, and silicates), dissolved oxygen, dissolved organic matter, chlorophyll, humus, and suspended matter at seven stations on the Razdol’naya River are examined. Based on seasonal variations, the local sources of river water pollution by biogenic substances were identified. The annual and daily fluxes of biogenic substances through the Razdol’naya River into Amur Bay are calculated. A diffuse pollution source—agricultural fields in river valley—are shown to be the main source of biogenic substance fluxes. The vast hypoxia in the bottom water of Amur Bay, detected by the authors in 2007 and 2008, is supposed to be mostly caused by floods on the Razdol’naya R., which create favorable conditions of water blooming in Amur Bay in summer. The biomass of dead phytoplankton, experiencing microbiological decomposition and oxidation, causes hypoxia of bottom waters in the bay.     

The dynamics of phytoplankton, bacteria and heterotrophic flagellates at two Banks near Magdeburg in the River Elbe (Germany)

The main objectives of this study were to describe the seasonal standing stock dynamics of phytoplankton, bacterioplankton and heterotrophic flagellates in the highly eutrophic River Elbe (Germany), and to compare the seasonal patterns observed with other streams. Emphasis was placed on examining and assessing abiotic and biotic controlling factors influencing the structure and dynamics of the riverine plankton. All the physico-chemical and biological parameters determined were within the range or somewhat higher (in the case of phytoplankton abundance and biomass) than reported for other large streams. The underwater light conditions resulting from atypically short phytoplankton growth periods of about 6 months per year and the low phytoplankton carbon to chl a ratio of 23 were identified as a major limiting factor for phytoplankton development in the River Elbe. The seasonal distribution pattern of bacterioplankton indicated probable tight trophodynamical coupling both with phytoplankton and with heterotrophic flagellates, whereas heterotrophic flagellates showed a more trophic link with bacterial densities. Although approximately constant DOC and DON levels throughout the year sustained bacterial growth rates, during the phytoplankton growing season an increase of bacterial standing stocks was observed. Although the left-bank sampling site of the Elbe is strongly influenced by the tributaries Mulde and Saale containing higher concentrations of chloride, nitrogen nutrients, heavy metals and organic pollutants, no clear differences were observed between the two sides of the river concerning the biological parameters measured. Possible reasons and the slightly higher phytoplankton abundance and diversity at the right bank are discussed.     

Zusammenhänge zwischen Chlorophyll a,Phytoplanktonvolumen, Seston,Sichttiefe und Trübung als Methoden zur Einschätzung der Wasserbeschaffenheit in Talsperren

The statistical relations between the different parameters of water quality are represented from investigations of an oligotrophic to mesotrophic storage reservoir carried out for several years. The significant linear regressions between chlorophyll a and the phytoplankton volume show seasonal differences depending on the aspect change of phytoplankton. Equally, there may occur differences of this relation for the euphotic layer and the intermixed layer. Chlorophyll, phytoplankton volume and dry matter of seston as well as turbidity show also close correlations with the depth of visibility. The scattering occuring for the individual regressions, the distribution of measured values and the relations of chlorophyll a to the phytoplankton volume of dominant algal groups are discussed.     

Analysis of patterns of vertical and temporal distribution of phytoplankton using multifactorial analysis: Acidic Lake Caviahue, Patagonia, Argentina

Most existing studies on the algal communities of acid lakes are based on environments that have been caused by anthropogenic disturbances. Such lakes have a different origin compared to the natural acidic lakes and could be expected to differ also in the mechanisms controlling phytoplankton and trophic status. Planktonic community in Lake Caviahue is somewhat diverse in spite of the low pH of the water. Algae have a distinctive vertical distribution: the values of phytoplankton biomass remain constant throughout the water column and at times were highest in the upper end of the hypolimnion, forming a maximum or a layer of chlorophyll a at depth. The goal of this work was to investigate the factors influencing the seasonal and vertical distribution of phytoplankton. The lake was sampled between the years 2004 and 2006. Physical, chemical and biological parameters at different depths throughout the water column were determined. The interrelationships between environmental variables at different sampling dates were analyzed using an integration of multivariate matrices, multiple factor analysis, to analyze any joint partnerships in the samples. We found that phytoplankton biomass is dominated by Keratococcus rhaphidioides. With regard to zooplankton, we found a single species of rotifers (Philodina sp.). The two arms of the lake and the depths have different behaviours showing differences in the arms' conductivity, dissolved oxygen and pH. The more superficial layers were characterized by high values of phytoplankton and zooplankton biomass, organic and inorganic carbon, dissolved oxygen and pH. The deeper layers showed high values of chlorophyll a, ammonium and phosphorus (dissolved and particulate). From the multivariate analysis the relationships of the each algal species with pH, as a possible indicator of the degree of “acidophilia”, could be extracted.     

Human‐induced sedimentation patterns of a channelized lowland river

Channelization of the severely polluted Odra and Vistula Rivers in Poland induced intensive accumulation of fine‐grained deposits rich in organic matter and heavy metals. These sediments have been identified in vertical profiles in a narrow zone along river banks both in groyne‐created basins and on the floodplain. Grain size, organic matter, zinc (Zn), lead (Pb), copper (Cu) content and cesium‐137 (¹³⁷Cs) was used for sediment dating and, stratigraphy and chemistry have been diagnostic features for these deposits, named industrial alluvium. In the most polluted river reaches stabilized by bank reinforcements and groynes, 2‐m‐thick slack water groyne deposits are composed of uniform strata of polluted silts with organic matter content over 10%, Zn content over 1000 mg/kg and average Cu and Pb over 100 mg/kg. The average rate of sediment accretion in groynes is higher than on the floodplain and reaches 5 cm/yr. Stratification which appears at higher levels in the groyne fields and on the levees reflects a change from in‐channel to overbank deposition and is typified by dark layers separated by bright, sandy, and less polluted strata. Stratified, 4‐m‐thick, sediment sequences have been found in groyne fields of incised river reaches. The average rate of sediment accretion in these reaches is of the order of 5 cm/yr. In stable and relatively less polluted river reaches, vertical‐accretion organic deposits are finely laminated and the average rate of deposition amounts to a few millimeters per year. Investigations indicate that groyne construction favors conditions for long‐term storage of sediments at channel banks. For this reason, groynes should be considered as structures that efficiently limit sudden release of sediment‐associated heavy metals stored in channels and in floodplains of the historically polluted rivers. Copyright © 2014 John Wiley & Sons, Ltd.     

Summer phytoplankton composition and nitrogen limitation of the deep, naturally-acidic (pH∼2.2) Lake Caviahue, Patagonia, Argentina

During the warm seasons of 1998-2004, the naturally-acidic (pH∼2.2) Lake Caviahue was sampled for conductivity, temperature, oxygen, light, nutrients, and phytoplankton (density, biomass and chlorophyll a) with a view to studying the summer phytoplankton population changes with relation to environmental factors, as well as the significance of nitrogen limitation on the phytoplankton yield. Lake Caviahue is characterized by its low transparency, CO₂, and N concentration; significant P values; a distinctive vertical distribution of phytoplankton biomass with high values along the water column; and sometimes maximum meta-hypolimnion values. Biodiversity is very low as a result of extreme environmental conditions, Chlorophyceae being the prevailing algae group. Two types of bioassays were carried out to assess nitrogen limitation. For the first bioassay, a solution of ammonium-nitrogen chloride and/or wastewater (rich in ammonium and phosphorus) was used, while one of the lake's sediments was the source of nutrients for the second bioassay. Contrary to the case of acidic mining lakes, N-ammonium proved to be a significant supportive capacity limiting factor as to phytoplankton yield. The present paper provides for the first time information on phytoplankton nitrogen limitation in a naturally-acidic lake.     

Nutrient Dynamics and Productivity in Three European Estuaries

The Scheldt, Gironde and Sado estuaries exhibit quite different characteristics regarding the annual river discharges, nutrient loads and oxygen conditions. Distribution patterns of nutrients, dissolved oxygen, suspended matter and chlorophyll a as well as the nutrient ratios and half saturation constants, allow the identification and comparison of specific processes. The Scheldt emerges as the most eutrophic estuary being, in general, not nutrient limited and functions as a source of phosphorus and nitrogen. Intense biogeochemical processes take place in this system. The Sado is shown to be a moderately productive system, the upper part being enriched in nutrients and chlorophyll a and showing a tendency for oxygen depletion in summer. Different factors seem to control phytoplankton production along the salinity gradient: light regime landwards and nitrogen seawards. By contrast, the Gironde does not show clearly the presence of sinks or sources regarding nutrients and exhibits a reduced productivity essentially controlled by turbidity. The high amounts of particles seem also to be responsible for localized processes such as phosphate sorption/desorption and silicate regeneration.     

Size-fractionated phytoplankton biomass,primary production and respiration in the Nervión–Ibaizabal estuary: A comparison with other nearshore coastal and estuarine ecosystems from the Bay of Biscay

The seasonal pattern of size-fractionated phytoplankton biomass, primary production and respiration was investigated along the longitudinal axis of the Nervión–Ibaizabal estuary (Bay of Biscay) from April 2003 to September 2004. Environmental factors influencing phytoplankton dynamics were also studied. Chlorophyll a biomass showed a longitudinal pattern of increase from the outer Abra bay to the inner estuary. On a seasonal scale, in the intermediate and inner estuary phytoplankton biomass maxima were registered in summer, the warmest and driest season, whereas in the outer bay chlorophyll a peaks occurred in May 2004, but were delayed to August 2003, likely due to a very rainy spring. Data suggest that river flow exerts a marked influence on the timing of phytoplankton biomass maxima in this estuary, decreased river flows providing a lowering of turbidity and an increase in water residence time needed for chlorophyll a to build up. Nutrient concentrations were high enough not to limit phytoplankton growth throughout the annual cycle, except silicate and occasionally phosphate in the outer bay during summer. Silicate concentration correlated positively with river flow, whereas ammonium and phosphate maximum values were generally measured in the mid-estuary, suggesting the importance of allochthonous anthropogenic sources. In the intermediate and inner estuary phytoplankton biomass was generally dominated by >8 μm size-fraction (ca. 60%), but in August 2003 <8 μm size-fraction increased its contribution in the intermediate estuary. It is argued that the lower nutrient concentrations measured in August 2003 than in August 2004 could have played a role. This is the first study in which phytoplankton primary production rates have been measured along the longitudinal axis of the Nervión–Ibaizabal estuary. Throughout the annual cycle these rates ranged from 0.001 to 3.163 g C m^?3 d^?1 and were comparable to those measured in nearby small estuaries of the Basque coast and other larger estuaries on the Bay of Biscay. Surface plankton community respiration rate maxima were measured during the spring 2004 chlorophyll a peak in the Abra bay and in summer months at the mid and inner estuary, coinciding with chlorophyll a biomass and primary production maxima. In general, respiration rates showed a positive correlation with temperature. In order to compare results from the Nervión–Ibaizabal estuary with other nearshore coastal and estuarine ecosystems within the Bay of Biscay a review of existing information on phytoplankton biomass and primary production dynamics was performed.     

Particle size characteristics of suspended and bed sediments in the rhône river

Ten large volume water samples were taken from the Rhône River (Switzerland-France) in November, 1989 for recovery of total suspended sediment by continuous flow centrifugation. the samples were freeze-dried and analysed for particle size, organic carbon, total nitrogen, and carbonate. for comparative purposes, four bed sediments collected in July, 1989 are also described. the Rhône can be subdivided into three sections on the basis of the origins of the water. the first section is the Upper Rhône River draining into Lake Geneva. Waters are derived from glaciers, with low temperature and conductivity and high turbidity. Suspended sediment is coarse, has a bimodal distribution, and is low in both organic matter and carbonate. the second reach is from Lake Geneva to the confluence with the Saône at Lyon and has warmer water with higher conductivity and very low turbidity. Suspended sediment is higher in organic matter, with high carbonate originating from the lake. the final section is from Lyon to Arles, with warmer water and higher conductivity and turbidity due to modification by the Saône. Sediment is rich in organic matter, which May, account for an observed decline in oxygen in the river waters downstream from Lyon. Carbonate in these sediments also decreases due to increased turbidity from the Saône. Suspended sediments other than from the Upper Rhône show a remarkable consistency in grain size, predominantly in the fine silts (mode 9-11 μm). This consistency indicates a high degree of suitability for geochemical analysis. Bed sediments were bimodal throughout, with a dominant coarse population in two out of the four samples. Grain size statistical parameters could be easily explained by application of the theory of mixing of two major populations in the sand size (bed traction load) and the fine silt/clay size (suspended sediment load).     

Zur Wirkung eingetragener Phytoplanktonbiomasse auf die Wasserbeschaffenheit eines schnell fließenden Tieflandgewässers

The effects of imported phytoplankton on a quick running lowland river in the district of the river Havel were investigated. The biomass of the phytoplankton (at the begin in the middle 25,6 mg/l, 184 μg/l chlorophyll) will become inactivated after a short time, a smaller part of about 15 % will be eliminated. On the balance of oxygen we could'nt find out effects because the rates of respiration and production are decreased. The oxygen content will be determined above all by the oxygen production in the upper region of the river with a high density of makrophytes and in the hypertrophic shallow lakes there are. Also the microbiological situation will not be determined by phytoplankton but the wastewater-pollution on the other hand brings for an increase of numbers of Coliformes and Enterococces.     

Spatial distribution and bonding forms of heavy metals in sediments along the middle course of the River Elbe (km 287ċ390)

Sediments of eight groyne fields along the middle course of the River Elbe (river km 287?390) were geochemically studied. The 78 sediment samples were analysed for pH and grain size distribution. The grain size fraction < 2 μm was used for mineralogical and chemical analysis: semiquantitative clay mineral analysis; total element content (Al, Ca, Fe, K, Mn, Cd, Cr, Cu, Ni, Pb, Zn), total inorganic and organic C, and bonding form fractionation with a six‐step sequential chemical extraction. The latter was performed on selected samples (n = 32). The sediments along the Elbe's course are still contaminated with heavy metals far above the local geogenic background level. An enrichment factor of more than 15 was calculated for zinc. Cr and Ni are the elements with the lowest enrichment. The bonding form analysis of selected heavy metals shows a dominance of relatively immobile bonding forms, e. g. the moderately reducible and the residual fraction, which implies a relative low mobility potential. Only Zn poses a higher potential threat to the environment, since it has a higher percentage of the first three extracted phases: adsorbed, carbonate, and easily reducible fraction.     

Initial growth of phytoplankton in turbid estuaries: A simple model

An idealised model is presented and analysed to gain more fundamental understanding about the dynamics of phytoplankton blooms in well-mixed, suspended sediment dominated estuaries. The model describes the behaviour of subtidal currents, suspended sediments, nutrients and phytoplankton in a channel geometry. The initial growth of phytoplankton and its spatial distribution is calculated by solving an eigenvalue problem. The growth rates depend on the position in the estuary due to along-estuary variations in nutrient concentration and suspended sediment concentration. The model yields an insight into how the onset of blooms in the model depends on physical and biological processes (turbulent mixing, fresh water discharge, light attenuation, imposed nutrient concentrations at the river and sea side). In particular, the model demonstrates that the joint action of spatial variations in turbidity and in nutrients causes the maximum phytoplankton concentrations to occur seaward of the estuarine turbidity maximum.     

Determination of suspended particulate matter concentration from turbidity measurements: particle size effects and calibration procedures

Measurements of suspended particulate matter concentration and turbidity point towards the possibility of a site‐specific algorithm (SPM), relating SPM to nephelometric turbidity units (NTU). In this paper regression models are presented that account for changes in the relationship of SPM and NTU as a result of changes in particle properties. The models have been developed by the use of daily measurements of SPM concentration and a continuous record of turbidity for the period from June 1996 to February 2001 in the River Elbe, a major river in the eastern part of Germany. The effect of changes in the particle properties with increasing water discharge was taken into account by varying the slope of a linear regression equation according to a logistic function. Water discharge, Q, was defined to be the only variable of this function—as an adequate substitute of the parameter bottom shear stress, which cannot be measured directly. Measurements of flow velocity in the River Elbe show that bottom shear stress is related almost linearly to water discharge up to bankful discharges. Regression models with slopes varying continuously with hydraulic parameters may account for the effects resulting from changes of particle characteristics and thus may have some advantages compared with models with a constant slope or models calibrated for different seasons. Copyright © 2003 John Wiley & Sons, Ltd.     

Optimum configuration of groynes for stabilization of alluvial rivers with fine sediments

Severe bank erosion at lowland rivers in Bangladesh devours vast tract of lands and renders thousands of people homeless at high flood; also,rapid deposition changes bed topographies and seriously redu...