The long,the short and the stalled: on the attributes of phytoplankton selected by physical mixing in lakes and rivers

Paradoxically, although turbulence characterises the open water environments of planktonic organisms in lakes, rivers and seas, most species of phytoplankton are smaller than the size of the smallest eddies dissipating the energy and, so, must function in an immediate medium which is inherently viscous. Intensively mixed systems, such as wind-stirred shallow lakes, rivers and estuaries, however, constantly readjust the vertical position of suspended algae and, often, other non-living, light-absorbing particles with the effect that the light field to which the algae are subject is erratic and the received day-time light dose is aggregately depressed: cells need to photoadapt accordingly. In fluvial environments the additional constraint of rapid, horizontal, supposedly unidirectional, transport is applied, requiring the attribute of rapid processing of primary products and cell replication. Significant downstream recruitment, however, is benefitted by the presence of so-called dead-zones which retain water (and suspended plankton) sufficiently to accommodate additional cell divisions.     

Erosion,phosphorus and phytoplankton response in rivers of South-Eastern Norway

The development of P fractions and phytoplankton was studied in three rivers with varying concentrations of seston.Less than 1% of the yearly TP transport may take place during periods with high algal biomass.The observation of a high growth rate of phytoplankton in the rivers coinciding with high concentrations of RP, low content of seston and high TP:Chl a ratio, indicate that the growth was often not P-limiting. During short periods with high phytoplankton biomass the ratio TP:Chl a may be low, indicating that a high fraction of TP was available.The content of P in soil samples and in samples with high seston content was about 0.1% of dry weight, and the algal availability of P often varied between 25 and 75% of TP for both types of samples.Decreasing biomass or low growth rates were observed at secchi depths less than 0.5 m and seston concentrations less than about 25 mg dry weight 1^–1. High flow rate also depressed the development of the total phytoplankton biomass. The assimilation of available P is incomplete under such conditions, i.e. under conditions of light limitation and high dilution rate.The availability of P for phytoplankton in rivers with different length, light conditions and stream velocity is discussed.     

Responses of phytoplankton diversity to physical disturbance under manual operation in a large reservoir, China

In aquatic ecosystems, physical disturbances have been suggested to be one of the main factors influencing phytoplankton structure and diversity. To elucidate whether large-scale artificial operation of a hydroelectric reservoir has potential impacts on phytoplankton diversity, the impact on phytoplankton biodiversity of physical disturbances under artificial operation from May 2007 to April 2008 in tributaries of the Three Gorges Reservoir (TGR), China, was analysed. Two disturbance parameters, i.e. the absolute incremental rates of discharge (R _d,i ) and precipitation (R _p,i ), were created in this study for evaluating physical disturbance intensities during low and high water level periods of the TGR. Results showed that river discharge seemed to be the main factor controlling the phytoplankton diversity in low water level periods (≤151 m), and that precipitation was a potential promoter of the physical disturbance. During the 156-m impoundment process, the species diversity clearly decreased due to the high dilution effect on the phytoplankton communities. At high water level periods (>151 m), the low levels of disturbance eventually allowed the phytoplankton community to approach competitive exclusion in late February 2008. Sharply declining diversity values appeared when the Dinophyta blooms occurred in late March and late April 2008 (Peridinium and Ceratium, respectively).     

Quantifying fluid and bed dynamics for characterizing benthic physical habitat in large rivers

Sturgeon use benthic habitats in and adjacent to main channels where environmental conditions can include bedload sediment transport and high near‐bed flow velocities. Bed velocity measurements obtained with acoustic Doppler instruments provide a means to assess the concentration and velocity of sediment moving near the streambed, and are thus indicative of the bedload sediment transport rate, the near‐bed flow velocity, and the stability of the substrate. Acoustic assessments of benthic conditions in the Missouri River were conducted at scales ranging from the stream reach to individual bedforms. Reach‐scale results show that spatially‐averaged bed velocities in excess of 0.5 m s⁻¹ frequently occur in the navigation channel. At the local scale, bed velocities are highest near bedform crests, and lowest in the troughs. Low‐velocity zones can persist in areas with extremely high mean bed velocities. Use of these low‐velocity zones may allow sturgeon to make use of portions of the channel where the average conditions near the bed are severe. To obtain bed velocity measurements of the highest possible quality, it is necessary to extract bottom‐track and GPS velocity information from the raw ADCP data files on a ping‐by‐ping basis. However, bed velocity measured from a point can also be estimated using a simplified method that is more easily implemented in the context of routine monitoring. The method requires only the transect distance and direction data displayed in standard ADCP data‐logging software. Bed velocity estimates obtained using this method are usually within 5–10% of estimates obtained from ping‐by‐ping processing.     

Importance of phytoplankton carbon to heterotrophic bacteria in the Ohio,Cumberland, and Tennessee rivers,USA

The flux of carbon and nutrients through aquatic systems is largely dependent upon interactions between autotrophic and heterotrophic processes. As a means of assessing the relative importance of autotrophy and heterotrophy in large rivers, we compared phytoplankton production, heterotrophic bacterial production and community respiration in three regulated rivers of the Midwestern USA. Samples were collected monthly (March to December 1999) from impoundments of the Ohio (McAlpine Pool), Cumberland (Lake Barkley), and Tennessee (Kentucky Lake) Rivers. Bacterial production was tightly coupled to phytoplankton production at each site (r ² = 0.63–0.85). Ratios of phytoplankton production to bacterial production ranged from <1 to 15 in the Tennessee and Cumberland Rivers and 2 to 90 in the Ohio River. The ratio of primary production to community respiration (P:R) ranged from 0.03 to 2.76 across all sites, with average P:R values lower in the Ohio River (0.14) than the Tennessee River (0.39) and the Cumberland River (1.10). P:R values above unity (P > R) were observed only in the Tennessee and Cumberland Rivers during seasonal (April–July) spikes in primary production. We estimate that 3, 6, and 20% of annual bacterial carbon requirements were met by exudates from in situ phytoplankton in the Ohio River, Tennessee River, and Cumberland River, respectively. Our findings indicate that heterotrophic bacteria were largely dependant upon allochthonous carbon. Autochthonous sources provided supplemental organic matter (up to 40% of bacterial carbon demand) during summer low flow. Handling editor: J. Padisak     

Stress gradients in the walls of large arteries

Elastic behavior of vascular wall, assuming the vessels to be ‘thick-walled’ and utilizing finite deformation theory, was investigated. It was found that canine carotid arterial wall is neither isotropic nor transversely isotropic. Previously, stress-strain relations were obtained for carotid arteries on the basis of membrane theory (Doyle and Dobrin, 1971). Since strain gradients across the wall are fairly steep, the applicability of such expressions, for pointwise evaluation of stress, required examination. The study indicated that these relationships between mean circumferential stress and mean extension ratio in the circumferential direction could be used to relate the specific circumferential stress value to the specific extension ratio at any designated point within the wall. From this analysis it was possible to evaluate circumferential and radial wall stresses. Both of these stresses are maximal at the inner surface of the intima. At this point the radial stress is equal to the transmural pressure and is compressive, while the circumferential stress is tensile and is 1·5 to 2 times the value of the mean stress, i.e. the product of transmural pressure and the ratio of internal radius-to-wall thickness. Both stresses are lowest at the outer edge of the adventitia. These stress distributions were considered with respect to the spacing of the elastic lamellae and the absence of discernible vasa vasora in the inner third of the wall.     

Stability and change of phytoplankton communities in a highly dynamic environment—the case of large,shallow Lake Balaton (Hungary)

Time series data of key environmental variables (water temperature, global radiation, vertical light attenuation, internal P load) and biomass of four colour classes of photosynthetically active algae were collected during 2003 and 2004 with daily resolution. Using these data, seasonal patterns of phytoplankton were analyzed as a function of the dynamic environment. Abstraction of the environmental state as a point in multi-dimensional space was used to identify habitat templates of bloom-forming groups and derive an indicator of environmental stability/physical disturbance. These templates were synthesized into a simple threshold model that sufficiently simulated development and collapse of various blooms. Blooms were, however, rare events related to specific environments with strong, unidirectional forcing. Tentative quantification of disturbance and compositional stability/community change allowed discriminating disturbance-driven changes and autogenic succession with reasonable success. The two processes were found to be equally important in shaping the composition and biomass of phytoplankton.     

Composition and structure of phytoplankton in lowland rivers of the upper Ob basin

Taxonomic composition and structure of the phytoplankton were studied in the lowland rivers of the upper Ob basin: Barnaulka, Bol’shaya Losikha, and lower Inya. It has been shown that the phytoplankton of a large river system in Eurasia, exemplified by the Ob basin, is characterized by spatial heterogeneity in its taxonomic composition.     

Island-dominated landscapes of large floodplain rivers, a European perspective

1. The landscapes of large floodplain rivers are characterised by heterogeneous environments related to the interplay of flood flows, sediment transport and vegetation dynamics.
2. The large rivers of Europe, and probably most rivers throughout the forest biomes, were characterised by islands but over the period of major human interference, many have become dominated by incision and narrowing so that they are now characterised by single-thread and relatively simple channel forms.
3. Vegetation plays an active role in developing heterogeneous channel forms through (a) biotic processes such as seed dispersal, vegetative regeneration and succession and (b) abiotic effects such as increasing flow resistance inducing sedimentation, and decreasing bank erodibility.
4. In particular, accumulations of living driftwood (cf. dead driftwood accumulations and dispersed seedlings) accelerate sedimentation and island development.
5. River reaches with vegetated islands have a high habitat diversity.
6. The natural influences of flood disturbance, wood accumulation, vegetation growth, island development and tree die-off, cause island-dominated reaches to undergo cycles of island growth and decay that are related to cycles of aquatic habitat diversification and simplification.     

Universal multifractals and ocean patchiness: phytoplankton, physical fields and coastal heterogeneity

We argue that a wide-range scaling approach is demanded by standardStommel diagrams and that it can unify the treatment of phytoplanktonvariability over wide ranges of scales. By investigating theeffects of coastal heterogeneity on the variability of in situsalinity (S), oxygen (     

Global patterns of dissolved N, P and Si in large rivers

The concentration of dissolved inorganic nitrogen (DIN), dissolved nitrate-N, Total-N (TN), dissolved inorganic phosphate (DIP), total phosphorus (TP), dissolved silicate-Si (DSi) and their ratios in the world's largest rivers are examined using a global data base that includes 37% of the earth's watershed area and half its population. These data were compared to water quality in 42 subbasins of the relatively well-monitored Mississippi River basin (MRB) and of 82 small watersheds of the United States. The average total nitrogen concentration varies over three orders of magnitude among both world river watersheds and the MRB, and is primarily dependent on variations in dissolved nitrate concentration, rather than particulate or dissolved organic matter or ammonium. There is also a direct relationship between the DIN:DIP ratio and nitrate concentration. When nitrate-N exceeds 100 g-at l^–1, the DIN:DIP ratio is generally above the Redfield ratio (16:1), which implies phosphorus limitation of phytoplankton growth. Compared to nitrate, the among river variation in the DSi concentration is relatively small so that the DSi loading (mass/area/time) is largely controlled by runoff volume. The well-documented influence of human activities on dissolved inorganic nitrogen loading thus exceeds the influences arising from the great variability in soil types, climate and geography among these watersheds. The DSi:nitrate-N ratio is controlled primarily by nitrogen loading and is shown to be inversely correlated with an index of landscape development – the City Lights nighttime imagery. Increased nitrogen loading is thus driving the world's largest rivers towards a higher DIN:DIP ratio and a lower DSi:DIN ratio. About 7.3 and 21 % of the world's population lives in watersheds with a DSi:nitrate-N ratio near a 1:1 and 2:1 ratio, respectively. The empirical evidence is that this percentage will increase with further economic development. When the DSi:nitrate-N atomic ratio is near 1:1, aquatic food webs leading from diatoms (which require silicate) to fish may be compromised and the frequency or size of harmful or noxious algal blooms may increase. Used together, the DSi:nitrate-N ratio and nitrate-N concentration are useful and robust comparative indicators of eutrophication in large rivers. Finally, we estimate the riverine loading to the ocean for nitrate-N, TN, DIP, TP and DSi to be 16.2, 21, 2.6, 3.7 to 5.6, and 194 Tg yr^–1, respectively.     

Optical gradients and phytoplankton production in the Mackenzie River and the coastal Beaufort Sea

We sampled a 300-km transect along the Mackenzie River and its associated coastal shelf system (western Canadian Arctic) in July–August of 2004 to evaluate the gradients in optical, phytoplankton and photosynthetic characteristics. The attenuation of photosynthetically available radiation (PAR) was best explained by coloured dissolved organic matter (CDOM) and turbidity (non-algal particles), while UV attenuation correlated most strongly with CDOM. Bacillariophyceae and Chlorophyceae dominated in the river, and shifted to Cryptophyceae and Prasinophyceae in the estuarine transition zone. In the coastal shelf waters, picoplanktonic cells dominated the surface autotrophic communities while both large and small cells occurred in the deep chlorophyll maximum. High PAR attenuation reduced the integral primary production rate in the river, while at an offshore marine site, 55% of integral production was at or below the pycnocline, under low PAR. Climate change is likely to increase the sediment and CDOM loading to these waters, which would exacerbate light limitation of photosynthesis throughout the system.     

Selective recruitment and resurgence of tropical river phytoplankton: evidence from the Nile system of lakes,rivers, reservoirs and ponds

The recruitment of major species-components of phytoplankton is considered with reference to diverse water-bodies—rivers, headwater lakes, reservoirs and lateral waters—of the Nile system. The importance of massive ‘inocula’, carried in flowing and inter-communicating waters, is emphasised; the most direct evidence is from quantitative population dynamics in longitudinally sampled river-reservoir systems. Other indications of extraneous derivation are taken from geographical distribution and apparent invasions of newly recorded species. For five reservoirs, there are records of initial colonisation (in two) and of the annual colonisation of seasonally impounded water (in three). There was a selective recruitment of reservoir/river major species over 1 year to newly created ponds, from a massive inoculum of added river water, studied in relation to the novel and changing physical and chemical environment. Periods of predominant decomposition were there linked with the abundance of other species not observed in the original river water. Reservoir species can be carried to extend abundance far downstream, as observed in the Blue Nile where normal succession was altered by a new reservoir upstream; also in Egypt below the former Aswan Reservoir and the later High Dam Lake. The different and distinctive compositions of the phytoplankton communities in headwater lakes reflect large environmental differences that, with high downstream turbulence, probably make them insignificant for recruitment of most species typical of the downstream waters. There is evidence from hydrology and floristic similarities for recruitment from lateral standing waters along the river, especially those of one major swamp area.     

Seasonal distribution of large phytoplankton in the Keban Dam Reservoir

The Keban Dam Reservoir (KDR), in eastern Anatolia, is one of the largest man-made reservoirs of the world with a storage capacity of <30 billion m³. In the KDR, long-term water quality surveys have been carried out in order to determine the trophic status of this rather unique reservoir. In this paper, the focus is on the large phytoplankton species that were identified during the field studies conducted between 1991 and 1993. According to the results of the surveys, the overall phytoplankton density is low during the fall and winter months. However, species belonging to various groups started to become abundant in the spring when the water level began to rise. In terms of species diversity, the most dominant group was the Bacillariophyta. Other dominant species belonged to the Cyanophyta, Chlorophyta, Pyrrophyta, Chrysophyta and Euglenophyta. The effects of various physicochemical quality parameters on the seasonal distribution and succession of the above taxa, as well as the interrelation with eutrophication, are also discussed.      

Evolution to the extreme: origins of the highly modified apical system in pourtalesiid echinoids

The apical system of the genus Pourtalesia displays a plate architecture that falls so far outside that typical of other echinoids that plate homologies remain problematic. A new approach using the Extraxial–Axial Theory (EAT) that develops homologies for the Echinodermata is proposed. The exploration of apical plate patterns throughout ontogenetic sequences shows that the typical holasteroid pattern found in the youngest specimens undergoes a series of disturbances that result in a multiple disjunction accompanied by isolation or disappearance of certain genital plates. We propose a new interpretation of the apical architecture of the genus that agrees with: (1) the plate addition processes as predicted by the EAT; (2) patterns observed in other genera of the Pourtalesiidae as well as in its sister‐group (plexechinids); and (3) the patterns known from Palaeocene holasteroids. In the context of the EAT, the genus Pourtalesia appears to represent the extreme in a reduction of the extraxial part of the body wall. © 2004 The Linnean Society of London, Zoological Journal of the Linnean Society, 2004, 140 , 137–155.     

Periphytic algal assemblages along environmental gradients in the rivers of the Lake Ladoga basin,Northwestern Russia: implication for the water quality assessment

The purpose of this study was to examine the role of geological, hydrological, and anthropogenic factors in structuring periphytic algal assemblages in the rivers of the Lake Ladoga basin (Northwestern Russia). Canonical correspondence analysis (CCA) conducted on spring dataset showed that water temperature, color, and river morphology were primary factors shaping the structure of algal assemblages during the spring post-flood period. CCA on summer and autumn dataset revealed that conductivity and total phosphorus were the most important variables during the base flow period. Cluster analysis carried out on algal assemblages separated all rivers into two main groups that corresponded to the two geomorphological regions of the Lake Ladoga basin: the northern and the southern sub-basins. The separation of the northern and the southern groups were best explained by the pattern of conductivity reflecting geological and land use differences in the watersheds. The values of the Specific Pollution sensitivity Index (IPS) and the Biological Diatom Index (IBD) were higher, indicating better water quality, for rivers of the northern sub-basin than for rivers of the southern sub-basin. Mean values of the IPS and IBD for rivers of the northern and the southern sub-basins varied within the boundaries of a good water quality.     

Morphofunctional traits reflect differences in phytoplankton community between rivers of contrasting flow regime

A morphofunctional traits approach has been adopted to identify how environmental factors shape the phytoplankton community. This approach has been applied in two rivers where hydrodynamical conditions are expected to be the main factor acting on the phytoplankton community. Hence, morphological traits (motility, shape, size, mucilage, and silica) related to sedimentation resistance have been chosen. We have shown that differences in flow regulation through differences in flow velocities induce shifts in phytoplankton community. These shifts depend mostly on shape, buoyancy regulation, and motility of phytoplankton cells. Elongated shapes are the characteristic of unregulated sites with high flow velocities, while cells able to regulate actively their position or to reduce their density (mucilaginous colonies) are found in regulated sites with low flow velocities. Flattened shapes are also the characteristic of sites with rather low flow velocities. These results highlight the key role of flow velocity as a driving factor controlling the structure of phytoplankton community. In this study, flow velocity also structures phytoplankton community according to location rather than seasonality.