Phytoplankton Distribution in the Coastal Area Subject to the Impact with the Tiber River Outfall

The taxonomic composition and geographical distribution of phytoplankton in the coastal zone surrounding the River Tiber mouth were investigated in twelve surveys from April 1978 to September 1979. Ninety phytoplankton species were identified from 168 samples. Diatoms were clearly the dominating species, accounting for more than 95 per cent of total phytoplankton.— Principal Component Analysis was utilized to analyse the total information obtained.—The direct impact on the coastal environment of River Tiber water and its considerable nutrient load were seen as providing a permanent potential for the development of less structured phytoplankton communities. Heterogeneity of local hydrological conditions and fluctuations in the river's impact, lead to a virtually constant instability in the neritic environment near the Tiber River outfall.     

Dynamics of main nutrient input to Xiangxi Bay of the Three-Gorges Reservoir

Based on routine monitoring data in Xiangxi River and its main tributary Gaolan River from September 2000 to June 2005, this paper estimates the contribution of riverine nutrients, and analyzes the monthly dynamics of concentrations and fluxes of nutrients. The results show that Xiangxi Bay annually receives 1623.49 tons of total nitrogen (TN) and 331.85 tons of total phosphorus; Xiangxi River alone accounts for 68.50% of the total nitrogen fluxes and 91.74% of the total phosphorus fluxes. In these two rivers, dissolved inorganic nitrogen (DIN) is the dominating form of nitrogen; fluxes of DIN and TN are high during summer (July), mid-spring and autumn, and relatively low in winter; non-point source pollutants that flow into rivers are the most important pathway of nitrogen. Orthophosphate is the dominating form of phosphorus in Xiangxi River, relatively low in Gaolan River; fluxes of phosphorus are high during summer and late spring, relatively low during winter and late autumn in Gaolan River, but fluctuate irregularly in Xiangxi River; phosphorus in Gaolan River is mainly caused by non-point source pollutants, while point source pollutants of phosphorus play an important role in Xiangxi River. Soil erosion probably represents the major way of non-point source pollutants, while the drainages of phosphorus diggings and factory discharges play the most important role in the point source pollutants of phosphorus. This research suggests that measures must be taken to control the point source pollutants of phosphorus in Xiangxi River in order to protect Xiangxi Bay of the Three-Gorges Reservoir.     

Dynamics of main nutrient input to Xiangxi Bay of the Three-Gorges Reservoir

Based on routine monitoring data in Xiangxi River and its main tributary Gaolan River from September 2000 to June 2005, this paper estimates the contribution of riverine nutrients, and analyzes the monthly dynamics of concentrations and fluxes of nutrients. The results show that Xiangxi Bay annually receives 1623.49 tons of total nitrogen (TN) and 331.85 tons of total phosphorus; Xiangxi River alone accounts for 68.50% of the total nitrogen fluxes and 91.74% of the total phosphorus fluxes. In these two rivers, dissolved inorganic nitrogen (DIN) is the dominating form of nitrogen; fluxes of DIN and TN are high during summer (July), mid-spring and autumn, and relatively low in winter; non-point source pollutants that flow into rivers are the most important pathway of nitrogen. Orthophosphate is the dominating form of phosphorus in Xiangxi River, relatively low in Gaolan River; fluxes of phosphorus are high during summer and late spring, relatively low during winter and late autumn in Gaolan River, but fluctuate irregularly in Xiangxi River; phosphorus in Gaolan River is mainly caused by non-point source pollutants, while point source pollutants of phosphorus play an important role in Xiangxi River. Soil erosion probably represents the major way of non-point source pollutants, while the drainages of phosphorus diggings and factory discharges play the most important role in the point source pollutants of phosphorus. This research suggests that measures must be taken to control the point source pollutants of phosphorus in Xiangxi River in order to protect Xiangxi Bay of the Three-Gorges Reservoir.     

The Effect of Weather Conditions on Eutrophication in the Neva River Estuary

Analysis of long-term data on chlorophyll a and total phosphorus concentrations, plankton primary production, organic matter mineralization, and weather conditions in the middle of summer in 2003–2017 revealed eutrophication processes in the Neva River estuary. Weather conditions in the region exerted a strong effect on organic matter prodaction and mineralization processes in the estuary. Rainy and cold summers of the recent years promoted massive development of algae due to increased washout of nutrients from the catchment area, but the rate of organic matter mineralization in the water column was reduced because of low water temperature.     

Seasonal and spatial variability of dissolved organic matter composition in the lower Amazon River

We analyzed the molecular composition of dissolved organic matter (DOM) in the lower Amazon River (ca. 850 km from Óbidos to the mouth) using ultrahigh-resolution mass spectrometry and geochemical tracers. Changes in DOM composition along this lower reach suggest a transition from higher plant-derived DOM to more algal/microbial-derived DOM. This result was likely due to a combination of autochthonous production, alteration of terrigenous DOM as it transits down the river, and increased algal inputs from floodplain lakes and clearwater tributaries during high discharge conditions. Spatial gradients in dissolved organic carbon (DOC) concentrations varied with discharge. Maximal DOC concentrations were observed near the mouth during high water, highlighting the importance of lateral inputs of DOM along the lower river. The majority of DOM molecular formulae did not change within the time it takes the water in the mainstem to be transported through the lower reach. This is indicative of molecules representing a mixture of compounds that are resistant to rapid alteration and reactive compounds that are continuously replenished by the lateral input of terrestrial organic matter from the landscape, tributaries, and floodplains. River water incubations revealed that photo- and bio-transformation alter at most 30% of the DOM molecular formulae. River discharge at the mouth differed from the sum of discharge measurements made at Óbidos and the main gauged tributaries in the lower Amazon. This indicates that changes in hydrology and associated variations in the source waters along the lower reach affected the molecular composition of the DOM that is being transported from the Amazon River to the coastal ocean.     

Nutrient biogeochemistry in the water column (N,P, Si) and porewater (N) of sandy sediment of the Scheldt estuary (SW-Netherlands)

The Scheldt river drains a densely populated and industrialized area in northern France, western Belgium and the south-west Netherlands. Mineralization of the high organic load carried by the river leads to oxygen depletion in the water column and high concentrations of dissolved nitrogen and phosphorus compounds. Upon estuarine mixing, dissolved oxygen concentrations are gradually restored due to reaeration and dilution with sea water. The longitudinal redox gradient present in the Scheldt estuary strongly affects the geochemistry of nutrients. Dissolved nutrients in the water column and dissolved nitrogen species in sediment porewaters were determined for a typical summer and winter situation. Water column concentration-salinity plots showed conservative behaviour of dissolved Si during winter. During summer (and spring) dissolved Si may be completely removed from solution due to uptake by diatoms. The geochemistry of phosphorus was governed by inorganic and biological processes. The behaviour of nitrogen was controlled by denitrification in the anoxic fluvial estuary, followed by nitrification in the upper estuary (prior to oxygen regeneration). In addition, nitrogen was taken up during phytoplankton blooms in the lower estuary. Dissolved inorganic nitrogen species in porewaters from the upper 20 cm of sediments were obtained from a subtidal site in the middle of the lower estuary. Dissolved nutrient concentrations were low in the upper 10–15 cm of the sandy and organic poor (<1% POC) sediments mainly as a result of strong sediment mixing. The porewater profiles of ammonium and nitrate were evaluated quantitatively, using a one-dimensional steady-state diagenetic model. This coupled ammonium-nitrate model showed ammonification of organic matter to be restricted to the upper 4 to 7 cm of the sediments. Total nitrification ranged from 3.7–18.1 mmol m^?2 d^?1, converting all ammonium produced by ammonification. The net balance between nitrification and denitrification depended on the season. Nitrate was released from the sediments during winter but is taken up from the water column during summer. These results are in good agreement with data obtained from the independently calibrated water column model for the Scheldt Estuary (VAN GILSet al., 1993).     

Glass eel (Anguilla anguilla) acclimation to freshwater and seawater: morphological changes of the digestive tract

Glass eels ( Anguilla anguilla , L. 1758) caught during ascent at the mouth of the River Tiber were kept in aquaria with freshwater and full strength salinity (35 %) for four months.
Morphological features of glass eels at capture and after four months of experimental rearin are described. The structure of the gut, an important osmoregulatory organ, observed in glass eels in seawater experimental rearing suggests that they undergo an irreversible process of adaptation to freshwater, despite the fact of survival in seawater.     

Nutrient limitation and algal blooms in urbanizing tidal creeks

Tidal creeks are commonly found in low energy systems on the East and Gulf Coasts of the United States, and are often subject to intense watershed human development. Many of these creeks are receiving urban and suburban runoff containing nutrients, among other pollutants. During the period 1993-2001, we studied three tidal creeks located in southeastern North Carolina, a rapidly urbanizing area. All three creeks received anthropogenic nutrient loading. Oligohaline to mesohaline stations in upper tidal creek regions had much higher nutrient (especially nitrate-N) concentrations than lower creek areas, and hosted spring and summer phytoplankton blooms that at times exceeded 200 μg chlorophyll a l⁻¹. Phytoplankton biomass during winter was low at all stations in all three creeks. Spring and summer nutrient addition bioassay experiments were conducted to characterize the nutrients limiting phytoplankton growth. Water from high salinity stations in all three creeks always showed significant positive responses to nitrate-N inputs, even at concentrations as low as 50 μg N l⁻¹. Low salinity stations in upper creek areas often showed significant responses to nitrate-N inputs, but on occasion showed sensitivity to phosphorus inputs as well, indicating the influence of anthropogenic nitrate loading. During several experiments, one of the upper stations showed no positive response to nutrient inputs, indicating that these stretches were nutrient replete, and further phytoplankton growth appeared to be light-limited either by phytoplankton self-shading or turbidity. Water from upper creek areas yielded much higher chlorophyll a concentrations in bioassay experiments than did lower creek water. In general, these urbanizing tidal creeks were shown to be very sensitive to nitrogen loading, and provide a physical environment conducive to phytoplankton bloom formation in nutrient-enriched areas. Tidal creeks are important ecological resources in that they are considered to be nursery areas for many species of fish and shellfish. To protect the ecological function of these small, but very abundant estuarine systems, management efforts should recognize their susceptibility to algal blooms and focus on control of nonpoint source nutrient inputs, especially nitrogen.     

Seasonal and Spatial Variation in Hydrochemical Characteristics of a Semi-Arid River Basin,China

The analysis of river pollution and assessment of spatial and temporal variation in hydrochemistry is essential for control of river water pollution in China. Here, we investigated water quality issues based on an analysis of monitoring data from 32 sites in the Luanhe River Basin in northern China. During 2000–2010, flow and 12 hydrochemical parameters were monitored monthly in the main channel and breach streams. Hydrochemical characteristics of river water were assessed using the water quality identification index. Our results showed that concentrations were not necessarily related to flow. Flow was greatest in summer, but concentrations of nutrients and some heavy metal indicators were smallest in autumn; flow was smallest and concentrations of nutrients were greatest in winter, and concentrations of metals were greatest in spring. Hydrochemical parameters showed significant spatial variation as well; the most seriously polluted sites are located in urban areas, mainly due to discharge of wastewater from domestic and industrial sources. Sites with large and intermediate levels of pollution were located primarily in the main river channel and the larger tributaries, whereas sites of low-level pollution were in the smaller tributaries. Our findings provide valuable information for water pollution control in the Luanhe River Basin.     

基于氮磷比解析太湖苕溪水体营养现状及应对策略

生态化学计量学是评价水体营养状态的重要手段,利用其氮磷比指标探讨了我国太湖主要入湖河流苕溪的营养状态。野外监测结果显示,苕溪水体氮素超标严重,磷素污染轻度,硝酸盐、颗粒态磷为氮磷的主要赋存形态,且氮磷浓度呈现相似的季节变化规律,表明苕溪主要受农业面源污染影响。氮磷比分析表明,苕溪水体春、秋季处于磷素限制状态,夏季适合藻类生长,冬季低温条件下不利于藻类的大量繁殖;苕溪生物量增长受磷素限制,线性拟合亦显示其氮磷比主要受磷素波动的调控;苕溪干流大面积暴发蓝藻水华的风险较部分支流及死水区低,苕溪水入湖后,特别是夏季其暴发风险将显著提高。针对苕溪水体的富营养化现状,提出若干条水质改善应对策略。     

Variations in environmental factors and their effects on biological characteristics of meromictic Lake Abashiri

 To clarify the variations in environmental factors and biological characteristics of eutrophic, brackish, meromictic Lake Abashiri, Japan, we studied long-term variations in concentrations of chloride and nutrients in lake water and characteristics of their supply. This lake has an anoxic layer containing much chloride, nutrients, and sulfide. Although a dense Anabaena bloom appeared in the lake every summer before 1986, the bloom did not appear after upwelling from the bottom layer (a blue tide) occurred in spring 1987. A dense layer of photosynthetic bacteria (Chlorobium sp.) formed at the top of the anoxic layer from 1989 to May 1992. The concentrations of nutrients and chloride in the oxygenic layer were determined by the balance between nutrients from influent rivers, including dissolved inorganic nitrogen, and matter supplied from the anoxic layer, including chloride and dissolved inorganic phosphorus. These influences controlled the dominant phytoplankton species and their biomass. The appearance of an Anabaena bloom in Lake Abashiri is promoted by nitrogen limitation caused by decreased loading from influent rivers and/or by a stable supply of phosphorus from the anoxic layer (no formation of photosynthetic bacterial layer and small upwelling), but the appearance is inhibited by a high chloride ion concentration with large upwelling. The main reason for the formation of a photosynthetic bacterial layer from 1989 to May 1992 was that sunlight reached the top of the anoxic layer because of the increase in transparency due to inhibition of the Anabaena bloom with upwelling. The dense layer of photosynthetic bacteria blocked nutrient diffusion from the anoxic layer to the oxygenic layer by uptake, and decreased the biomass of phytoplankton in the oxygenic layer. Received: January 11, 2002 / Accepted: April 9, 2002     

Plankton composition and water chemistry in the mixing zone of the Selenga River with Lake Baikal

Chemical and biological components of the Selenga River waters, the largest tributary of Lake Baikal, differ significantly from the lake waters. Active transformation processes of river waters into the lake ones occur in the vast barrier-like zone in the river-sea boundary areas. This study presents results on the spatial distribution and dynamics of water chemistry as well as the quantity and diversity of phyto- and bacterioplankton at a distance of 14 km off the Selenga River mouth. The most representative tracers of river and lake waters are total amount of ions and sulphates. Principal changes of chemical and biological parameters were fixed at 1–3 km off the Selenga River mouth that was determined as a mixing zone. Intense development of phytoplankton and eukaryotic picoplankton causing the decrease of nitrate and phosphate concentrations and organic matter rise were registered in this area. Gradual replacement of river phytoplankton by the lake one, abundance reduction of microorganisms and organotrophic bacteria and percentage increase of oligotrophic and psychrotolerant bacteria occurred in the mixing zone. Replacement of PC-rich picocyanobacteria by PE-rich ones was also recorded here. At a distance of 5–7 km off the shore, nutrient concentration and plankton composition were similar to those of Lake Baikal.     

鸭绿江口及邻近海域生物群落的胁迫响应

利用ABC曲线法结合粒径谱理论对鸭绿江口近岸海域的生物群落特征、优势种演替、多样性水平、稳定性状况等进行了分析,并尝试构建了鸭绿江口近岸海域生物群落稳定性的评估模型.研究结果表明,鸭绿江口滨海湿地生物群落结构相对简单,优势种演替明显,受外界干扰较大.春、夏季浮游植物以r-对策者为主,群落数量偏离平衡点;秋季以r-对策者为主的微小型浮游植物逐渐被中大型k-对策者演替,群落完成反馈调节,恢复到平衡点.浮游动物由于较高的能量供应其幼体全年一直处于较高优势水平,但生态效率转换相对较慢.潮间带底栖生物群落结构相对简单,优势种演替明显,系统具有低多样性低密度的特点,群落在夏季受外界扰动较大.游泳生物群落主要以小型个体为主,已处于极不稳定状态.构建的群落稳定性评估模型测算结果与上述结论基本一致,这也验证了该评估模型具有一定的有效性与实用性.综合以上分析结果,说明鸭绿江口近岸海域生物群落稳定性较差,受外界干扰比较严重.     

Physico-chemical environment,phytoplankton biomass and production in oligotrophic,softwater lake kalgaard,Denmark

Water chemistry of Lake Kalgaard in 1976–77 was characterized by low concentrations of total-CO₂ and inorganic nutrients. The ionic composition resembled that of precipitation (Na>Ca>Mg >K and Cl>SO₄>HCO₃). The seasonal pattern of total-CO₂ and PO₄ was regulated by internal processes and maximum concentrations as a result of decomposition processes occurred during summer stagnation. NO₃ concentrations showed the opposite pattern and were relatively high from late autumn through spring and were extremely low during summer. Total-P and PO₄ increased during summer due to release from the sediment. The phytoplankton biomass of surface water was low. The water chemistry suggested a shift from N-limitation of phytoplankton during summer to P-limitation at other seasons. Maximum algal concentrations occurred at 6 m during summer, probably due to a supply of nutrients (especially NH₄) from deeper layers. Phytoplankton productivity was often bimodal, with an upper maximum at depths of 0 or 2 m and a second maximum at 6 m.     

Modeling impacts of Yangtze River water transfer on water ages in Lake Taihu, China

To improve water quality and alleviate eutrophication in Lake Taihu, the third largest freshwater lake in China, a Yangtze River water transfer project was initiated in 2002 to bring water from the Yangtze River to Lake Taihu to dilute and divert pollutants out of the lake. We used a three-dimensional numerical model, Environmental Fluid Dynamics Code, to study the impacts of water transfer on the transport of dissolved substances in the lake by using the concept of water age. In particular, the influences of inflow tributaries and wind forcing on water age were investigated. Model results showed that the effect of water transfer on transport processes in the lake is strongly influenced by hydrodynamic conditions induced by wind and inflow/outflow tributaries. During the simulation year (2005), the water ages in Lake Taihu were highly variable both spatially and temporally, with a mean of approximately 130 days in summer and 230 days in the other seasons. Southeasterly winds—dominant in the summer—could improve the quality of water by reducing the water age in the eastern areas of the lake, which are used as a drinking water source, and in Meiliang Bay, the most polluted bay. In terms of dilution, the most efficient flow rate for transferred water was predicted to be approximately 100 m³/s. The spatial distribution of water ages showed that water transfer may preferentially enhance exchanges in some areas of the lake unless nutrient concentrations in the transferred water are reduced to a reasonable level. This study provides useful information for a better understanding of the complex hydrodynamic and mass transport processes in the lake, which is important for developing and implementing effective ecological restoration strategies in the region.     

Accumulation and Retranslocation of Mineral Nutrients in Developing Needles in Relation to Seasonal Growth of Young Radiata Pine Trees

The growth, accumulation and movement of mineral nutrients (nitrogen,phosphorus, potassium (calcium) and chlorophyll in needles ofyoung radiata pine trees (Pinus radiata D. Don) were examined,from bud break in spring through the following year. Retranslocationof nutrients from needles was measured and is discussed in relationto nutrient requirements for seasonal growth. During the first 4–5 months after bud break when mostneedle growth occurred, all nutrients and chlorophyll accumulatedprogressively, although the concentrations of nitrogen, phosphorusand potassium decreased. During summer, substantial amounts of phosphorus were withdrawnfrom needles less than 6 months old, regardless of positionon the tree and silvicultural practice. In young needles andunder certain environmental conditions, this led to a markedtemporary decline in concentrations, even in fertilized treeson a fertile site. However, the phosphorus content of needleswas quickly restored following autumn rains. Similar fluctuations,including nutrient withdrawal in summer, occurred for nitrogenand potassium, but these were smaller than those observed forphosphorus. Phosphorus was also withdrawn from relatively olderneedles during summer. It was estimated that on a tree basis 86, 48 and 39 per centof the phosphorus, nitrogen and potassium, respectively, insummer shoots could have come from the retranslocation of nutrientsfrom young needles formed during the preceding spring. These results highlight the importance of nutrients stored inneedles to meet the nutrient requirements for growth when environmentalfactors may not be conducive to nutrient uptake from the soil. Pinus radiata D. Don, mineral nutrition, retranslocation, phosphorus, nitrogen, seasonal effects, pine needle growth     

Palaeolimnological evidence for the independent evolution of neighbouring terminal lakes,the Murray Darling Basin,Australia

Phytoplankton composition and production are highly unpredictable within an estuary, due to the high variability of forcing factors, such as freshwater flow, salinity, nutrients and light. The Guadiana estuary has shown sharp inter-annual differences in freshwater flow, related to variable precipitation, which is expected to affect nutrient loadings, light availability and phytoplankton succession. Water retention due to dam construction will further enhance changes in river flow and ecosystem dynamics. The main goal of the present study was to describe and relate phytoplankton succession and environmental conditions, namely nutrients and light, in the Guadiana upper estuary (south-western Iberian Peninsula), a dam regulated temperate estuary. From March 2004 to October 2005, water samples were collected in three stations along a longitudinal transect covering the upper estuary. Several water variables were determined and phytoplankton composition was studied through inverted and epifluorescence microscopy. A typical freshwater phytoplankton succession was observed, from a diatom spring bloom to cyanobacteria dominance in the summer, and a second diatom bloom in the autumn. Neither nutrients nor light availability seemed to be related to the observed succession, especially the seasonal variation of diatom abundance. During summer, nutrient concentrations (especially Si) were high and non-limiting, whilst light was available in the mixing layer. However, diatoms were present in low numbers. Grazing pressure was probably responsible for the regulation of diatom seasonal succession in the Guadiana upper estuary, which should be addressed in future studies. Handling editor: K. Martens     

Modelling population dynamics of the pelagic larval shrimp Metapenaeus ensis in the Osaka Bay estuary

Aiming at providing numerical tools useful to assess the impacts of coastal development pressures on marine life, a Lagrangian model for population dynamics of pelagic eggs and larvae of the greasyback shrimp, Metapenaeus ensis, in Osaka Bay was developed and improved based on laboratory experiments. The model was combined with a 3-D Eulerian numerical model that predicts physical and biological conditions of the habitat. A series of numerical experiments was done to investigate their transport processes from the spawning grounds, and the concentration process of full-grown larvae towards the mouth of Yodo River that flows into the innermost basin. Model results revealed, as a general tendency, that the early larval developmental stages through nauplius to zoea continue to drift like a passive tracer, and begin to concentrate at the river mouth area after the mysis stage, mainly avoiding low saline environment in the surface layer. This suggests that the full-grown larvae may be favored with chance to take advantage of the river-induced gravitational circulation that dominates the innermost estuarine basin. In addition, it was found that tidal condition around the spawning period also exerts a considerable influence upon the fate of pelagic larvae.     

The Mechanism Controlling Plant Nutrient Concentrations in the Northern Adriatic Sea

A 20 year data set for the northern Adriatic was analyzed and the factors establishing the nutrient environment identified. Concentrations ranged widely (TIN 0.0–78, PO₂ 0.01–1.1, and SiO₄ 0.0–59 mmol m⁻³). In early winter remineralization increased concentrations. Characteristic winter, late spring and fall phytoplankton blooms alternately decreased and increased concentrations, as modified by river input. In summer nutrients were minimal under a semi-closed circulation pattern and high vertical stability, due to closely coupled nitrogen and phosphorus assimilation-regeneration processes and biogenic silica sedimentation. “New” primary production supported mainly by river input of “new” nutrients approximated “regenerated” primary production supported by regenerated nutrients, making the ecosystem especially sensitive to eutrophication pressure from anthropogenic increases in the Po River nutrient load.     

Formation,Transport and Retention of Aggregates in a River‐Lake System (Spree,Germany)

The formation, particle size distribution, structure and retention of aggregates were studied in a river‐lake system of the lowland River Spree and factors influencing these processes were evaluated. Samples were taken from the inflow and outflow of a flushed lake, as well as along the adjacent flowing reach of the River Spree, between April 2001 and May 2002. The aim was to record the influence of the seasons and different turbulence intensities on the size, shape, composition, abundance and transport properties of the particles. As additional parameters, the phytoplankton biomass, the concentration of suspended particulate matter, the concentrations of nutrients and the discharge were measured. The abundance of the particles showed a strong seasonality in the investigated period, which closely correlated with the concentrations of suspended particulate matter and particulate organic matter in the water column. The organic carbon content of the suspended matter varied between 37% (dry weight) in summer and about 14% in winter. The concentration of particles ranged between 500 and 2500 particles/ml. The number of particles was significantly lower upstream from the lake than at the downstream transects. The majority of the aggregates in the River Spree were smaller than 500 µm, most of the particles even showing a diameter less than 50 µm. Many particles, above all algae, were washed out of the lake Neuendorfer See into the adjacent flowing reach of the River Spree. Algae influenced the abundance of the particles and contributed to the formation of aggregates with their stickiness. In the river flowing section large particles were formed by turbulence structures, whilst simultaneously the number of smaller particles decreased in the water column caused by aggregation processes. In general, an increasing flow velocity and discharge rate resulted in a larger amount of aggregates in the water column. On the other hand, particle abundance was reduced in the flow direction when the flow velocity was low. Under these conditions particles were retained by sedimentation and benthic filter‐feeding. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)