Inorganic phosphate in exposed sediments of the River Garonne

Fractionation of inorganic phosphates in sediments of the River Garonne was carried out during a period of low water discharge. Sediments were collected under 5 cm of water (LS), in the dried river bank (MS) and in the riparian forest (RS). Sediments were sampled at two dates, during a period in which the water level fell gradually, causing sediment LS to be air exposed.Sediments were analysed for total phosphate, iron bound phosphate (Fe(OOH)P) using Ca-NTA and Ca bound phosphate (CaCO₃P) using Na-EDTA.Total-P varies from 552 (RS at date 1) to 2072 µg g^–1 (LS at date 2). There are significant differences between sediments and a significant increase from date 1 to date 2 in sediment LS only (1825 to 2072 µg g^–1). Fe(OOH)P varies from 186 (RS at date 1) to 874 µg g^–1 (LS at date 2). The highest values correspond to sediment LS. Moreover, Fe(OOH)P increased significantly between date 1 and 2 in LS (560 to 874 µg g^–1) as well as in sediment MS (248 to 432 µg g^–1). Ca bound P concentrations differed significantly between sediments (75, 112, 235 µg g^–1 for sediments RS, MS and LS respectively) but not between sampling dates.These differences are attributed to the conditions of deposition of the sediments (such as morphology and hydrology of the river) and to the changes in chemical composition during the drying out of the sediments.     

Estimation of the available phosphate for phytoplankton stored in the soft sediments of the river Lot

Bioassays have been carried out with the green algae Scenedesmus crassus on samples of soft sediments collected along the river Lot (about fifty samples distributed over a 300 km length) in order to evaluate the phosphate bioavailability. From an other study, it was possible to know the percent of bottom surface covered by soft sediments. The link between the distribution of soft sediment and phosphate bioavailability leads to a longitudinal representation of the storage in the whole river. The results point out the parts of the river where bioavailable phosphate is stored and have implications for possible role of the stored phosphate in the eutrophication process in some areas of the river Lot.     

Trace metal fractionation in water and sediments of an urban river stretch

Abstract

In this study, the fractionation and ecotoxic potential of Cr, Ni, Cu and Pb in water and sediments of the river Yamuna (Delhi stretch) is presented. The river water is used for various purposes such as irrigation, industrial, domestic and drinking. The investigations suggest that the availability of metals in water follows the sequence Ni>Cr>Pb>Cu whereas a different pattern (Pb>Cu>Ni>Cr) is observed in sediments. Statistically significant spatial variations are indicated by two-way ANOVA in different geochemical forms of the metals and physicochemical parameters of water and sediments of the river Yamuna. Principal component analysis (PCA) suggests a similar source for all four metals probably from the sewage from municipal drains. PCA also indicates some independent sources of Cu and Pb. The hot spots were identified using hierarchical cluster analysis considering bioavailable forms of the metals in water and sediments as objects and the sampling sites as variables. Risk assessment code analysis indicates that metals generally pose medium to high risk at different sites. However, at a few locations either Ni or Pb cross the level of very high ecological risk.     

Relation between algal available phosphate in the sediments of the River Garonne and chemically-determined phosphate fractions

Concentrations of total and inorganic phosphate were measured in forty-seven sediments of the River Garonne (France) using an anion resin, NaOH 0.1 M, Ca-NTA and Na-EDTA. Algal available P was measured using Scenedesmus crassus. The sediments presented a wide range of Tot-P concentrations (226 to 923 μg g⁻¹). Resin P varied between 1.1 to 55.5 μg g⁻¹ and NaOH-P between 3.5 to 262 μg g⁻¹. NTA-P and EDTA-P varied between 13.9 and 178 μg g⁻¹ and between 14.4 to 261 μg g⁻¹ respectively. Algal available P varied between 8.8 to 262 μg g⁻¹/ All forms of P are highly correlated and specially with algal available P (r = 0.70, 0.77, 0.88 and 0.77 for resin-P, NaOH-P, NTA-P and EDTA-P respectively). Nevertheless the partial correlation between EDTA-P and algal available P dropped to 0.05 when the concentration of NTA-P was considered as constant, indicating a spurious correlation with apatitic phosphate (extracted by Na-EDTA). Because of the strongest R ² and the lowest standard error of estimate, phosphate extracted by Ca-NTA can be considered as the best predictor of algal available phosphate.     

Presence of and phosphate release from polyphosphates or phytate phosphate in lake sediments

NaOH is often used as an extractant for thefractionation of sediment-bound phosphates. Besidesorthophosphate, a certain quantity of phosphate whichis called ‘non-reactive NaOH-extractable phosphate’is also extracted. In recent literature it has beensuggested that this fraction consists of bacterialpolyphosphates and might be responsible for the phosphate release from aquatic sediments under anoxicconditions. In a previous publication we have already shown thatNaOH is not an accurate extractant as both theconcentration of NaOH and the duration of theextraction have an influence on the quantity ofphosphate extracted, due to the hydrolysis of organicphosphates. In this article we show that cold NaOH does not onlyextract iron-bound phosphate but phytate phosphate aswell. Non-reactive phosphate in this extract was notrelated to the presence of polyphosphate, but mainlyto phytate and humic phosphates. As it has been shownthat phytate may disappear from sediments when theybecome anoxic, we suggest that phytate mineralizationmay be an important mechanism for anoxic phosphaterelease from sediments. This revised version was published online in July 2006 with corrections to the Cover Date.     

Particulate organic carbon and nitrogen in the Orinoco river (Venezuela)

Total suspended solids (TSS), particulate organic carbon (POC) and particulate nitrogen (PN) were measured over a two year period, 1983–1985, in the Orinoco River at Ciudad Bolívar, 450 km from its mouth. Additionally, samples of the main stem at other localities and main tributaries were included in the present study.The suspended sediment concentrations showed a peculiar pattern of temporal variations: two maxima (May–June and November) and two minima (March–April and August–September).The POC and PN concentrations fluctuated with the water discharge, and higher values were observed during the rising limb than during the falling limb of the hydrograph. As dry weight percent of solids, the values ranged between 0.84 and 9.06% for organic carbon and between 0.08 and 1.45% for total nitrogen. The carbon-nitrogen ratio in the sediment averaged 9.1. The major contribution of organic carbon and nitrogen in particulate form to the Orinoco main stem comes from the left margin tributaries, which have their headwater in the mountainous regions of the Andes.     

Structure and composition of benthic macroinvertebrates of a tropical forest stream, River Nyamweru, western Uganda

Benthic invertebrates from River Nyamweru, a tropical forest stream in western Uganda were sampled bimonthly between April and December 1997 using a modified Hess Sampler. A total of 3708 benthic fauna from thirteen taxonomic orders were collected. Benthic samples were dominated by Diptera (mainly Chironomidae) representing over 60% of all the organisms, followed by Ephemeroptera. Benthic invertebrate densities ranged from 63 ± 9.03 organisms/m² to 300 ± 33.36 organisms/m², with higher densities occurring during the dry season and lower densities during the wet season. The benthic community structure in River Nyamweru reflected mainly collectors and scrapers as the most important groups (83%), while predators were very rare (3.1%). River discharge influenced benthic abundance, with more invertebrates at lower discharge and fewer invertebrates at higher discharge. The applicability of the River Continuum Concept to tropical forest stream situation is discussed.     

Fractionation of phosphate in sediments of four representative mangrove stages (French Guiana)

Phosphate was fractionated in Guianese mangrove sediments. Fe(OOH)P was extracted using a Ca-EDTA + Na-dithionite solution buffered at pH 8. CaCO₃P was extracted using Na₂-EDTA solution at pH 4.5. Next, Acid Soluble Organic Phosphate (ASOP) was extracted by H₂SO₄ 0.5 N. Finally, Residual Organic Phosphate (ROP) was digested with H₂SO₄ + H₂O₂. Four representative mangrove stages have been studied: sea edge pioneer mangroves, mature coastal mangroves, mixed riverine mangroves, and declining to dead mangroves. The sum of the P-fractions varied between 638 to 804 g g^-1 in pioneer and mixed mangroves respectively. In all the stages, the percentage of inorganic phosphate was larger than 50% of the total P. Fe(OOH)P varied between 221 (pioneer mangrove) to 426 g g^-1 (dead mangrove). CaCO₃P varied between 75 to 102 g g^-1 in mixed, dead or mature mangroves and attained 125 g g^-1 in pioneer mangrove. The sum of the concentrations of organic phosphate (ASOP + ROP) increased markedly from the dead mangrove (189 g g^-1) to the mixed mangrove (380 g g^-1). Guianese mangroves, are relatively rich in total phosphate, possibly because they are narrowly related to the 'Amazon dispersal system. Each mangrove stage can be characterised by a prevailing form of phosphate. The concentrations of these different forms were ascribed to the marked relations with the seawater which controls import or export of suspended matters and to the wave action which controls the resuspension of the sediments and subsequently exchange of phosphate between the suspended matter and the water column.     

Ecotoxicological Risk Assessment of Polychlorinated Biphenyls (PCBs) in Bank Sediments from along the Yamuna River in Delhi,India

The River Yamuna originates from the Yamunotri glacier of the Himalayas and travels 22 km in the Delhi region. The river is used for various purposes in Delhi including drinking water supply. Twenty-eight polychlorinated biphenyls (PCBs) congeners were measured in bank sediments along the river, and their ecotoxicological risk was evaluated. Concentrations of ∑28PCBs varied from 0.20–21.16 ng g^?1 (dry wt.) with mean and median values of 6.63 ng g^?1 and 5.84 ng g^?1 (±0.69 ng g^?1), respectively. The concentration of 12 dl-PCBs concentrations varied from 0.04–2.86 ng g^?1 with a mean of 1.04 ± 0.11 ng g^?1, and their toxic equivalency ranged between <0.01–28.67 pg WHO-TEQ g^?1 with a mean of 10.77 ± 1.06 pg WHO-TEQ g^?1. CB-37, CB-44, CB-114, and CB-118 congeners were dominant among all PCBs congeners. The tri-PCBs (49%) were the main contributors to the PCB homolog followed by tetra-PCBs (35%), and penta-PCB (14%). Because there are no environmental guidelines in India for PCBs in river and marine sediments, concentrations of PCBs and their toxic equivalents were compared in a screening-level assessment with established freshwater sediment quality guidelines and found lower than those guideline values, which suggests no adverse ecotoxicological effect.     

Transport of mercury by the Katun river,West Siberia

Some results of a 2-year study of mercury pollution of the Katun river (Siberia) are summarised. Measurements of water flow, sediment transport and mercury concentrations were made and used to calculate the amount of mercury transported by the river. The distribution of transport between water phase and suspended material is calculated. It is concluded that suspended sediments play the main role in this process. The significance of different fractions of suspended sediment is also discussed.     

Development and ecological importance of phytoplankton in a large lowland river (River Meuse,Belgium)

The ecological importance of the River Meuse phytoplankton with regard to carbon and nutrient transport has been examined in two reaches of the Belgian course of the river.Field measurements of total particulate organic carbon (POC), particulate organic nitrogen (PON) and particulate phosphorus (PP) show that the large autochtonous production of organic matter strongly affects the carbon and nutrient budget of the aquatic system. During the growing season, phytoplankton accounts for nearly 60% of the POC and dominates the PON. Calculations of the carbon and oxygen budget in the upper reach of the Belgian Meuse demonstrates that the ecosystem is autotrophic, i.e. that autochtonous FPOM (fine particulate organic matter) production is the major carbon input. This suggests that in large lowland rivers, primary production (P) may exceed community respiration (R), i.e. P:R>1, whereas they are assumed to be heterotrophic (P:R<1) in the River Continuum concept.The question of maintenance of phytoplankton in turbid mixed water columns is also addressed, and the case of the River Meuse is treated on the basis of studies of photosynthesis and respiration (ETS measurements). The results suggest that the potamoplankton may show some low-light acclimation, through an increase of chlorophyll a relative to biomass, when it comes to deep downstream reaches, and that algal respiration rate may be reduced. A simulation of the longitudinal development of the algal biomass shows the different phases of algal growth and decline along the river and brings support to the importation hypothesis for explaining maintenance of potamoplankton in the downstream reaches.     

Factors affecting the distribution and abundance of Cloeon and Caenis (Ephemeroptera) larvae in a tropical impounded river, Nigeria

Impoundment of rivers affects the mayfly (Ephemeroptera) fauna inhabiting such water bodies, especially with respect to their distribution and abundance. A two‐year study of the mayfly fauna and some of the physicochemical parameters of the Opa stream–reservoir revealed that there are two mayfly genera inhabiting it, Cloeon and Caenis. The number of Cloeon larvae collected was 10,930 while the number of Caenis larvae was 450. It was observed that although both genera occurred at all the sampling stations, their numbers were reduced in the stream below the dam due to increased water current velocity. There were significant differences in the abundance of Cloeon among the stations, but none for Caenis. Submerged aquatic plants and water current velocity were found to be the major factors responsible for the significant differences. There were significant correlations between the number of Cloeon larvae and pH as well as between dissolved oxygen concentration and Caenis. These findings are discussed with reference to inter‐specific differences in patterns of response to environmental parameters. A species‐specific approach is suggested for studies on the strategies that enable mayfly species maintain their populations in stressed and unstable aquatic ecosystems.     

The determination of heavy metals in water,suspended materials and sediments from Langat River,Malaysia

The distributions of heavy metals in the Langat River were studied for a period of six months between September 1984 and February 1985. Heavy metals such as arsenic, cadmium, cerium, cobalt, chromium, caesium, lanthanum, rubidium, antimony, scandium, thorium and zinc were determined in water, suspended materials and sediment samples from the Langat River by neutron activation and atomic absorption spectrometry. The concentrations of arsenic, cadmium, cerium, cobalt, scandium, antimony, and zinc were generally highest in the suspended materials, whereas the concentrations of chromium, rubidium and thorium were always highest in the sediments: Arsenic concentrations in the river were slightly higher than the natural concentration, while other elements were generally at their natural concentration levels. The use of arsenical herbicides in plantations along the river could be a source of arsenic pollution.     

Transport of phosphorus,nitrogen, and carbon by the Apure River,Venezuela

The concentrations and transport of carbon, nitrogen, and phosphorus were studied in the Apure River, Venezuela, over a period of 21 months. The drainage basin, which is in western Venezuela, encompasses 167,000 kM², most of which has low relief and supports tropical savanna vegetation. Average runoff for the period of study was 361 mm/year. Discharge-weighted mean concentrations were 188 ug/l for total P, 957 ug/l for total N, and 9.8 mg/l for organic C. Annual transport was 0.68 kg· ha^-1· year^-1 for total P, 3.45 kg · ha^-1· year^-1 for total N, and 35.4 kg · ha^-1 · year^-1 for organic C. Particulate matter accounted for 68% of P, 54% of N, and 37% of C transport. The yield of carbon from the Apure watershed agrees well with empirical predictions, based mostly on the temperate zone, for watersheds of similar size and water yield.Seasonal patterns in chemistry are tied strongly to the hydrologic cycle. When the wet season begins, rising water flushes organic matter from side channels and produces a sharp increase in particulate C and N. Particulate P, which is associated more with mineral material, also increases during rising water. All dissolved constituents except inorganic C also increase over the rising-water phase. As the river inundates the floodplain, the concentration of nitrate declines, whereas the concentrations of dissolved organic C and N continue to rise. At high water the floodplain appears to store sediments that are later remobilized. During low water, all fractions except dissolved inorganic C tend to be at minimum concentration.Soluble reactive P, total dissolved P, dissolved inorganic C, and dissolved organic C were successfully modelled as hyperbolic functions of discharge. No significant relationships were found between concentration and discharge for any particulate fraction because the flushing and storage mechanisms affecting these fractions occurred within specific hydrologic phases, rather than as a smooth function of discharge. No significant relationships were found for any nitrogen fraction. For nitrate, and thus for total dissolved N, of which nitrate is a major component, poor conformance to standard models is explained by association of key mechanisms (e.g. uptake) with specific hydrologic phases. Particulate components and nitrate in this sense violate the continuity assumptions implicit in the standard models.     

Rotifers from Saladillo river basin (Santa Fe province,Argentina)

Seventy two taxa of rotifers, belonging to 24 genera, are recorded from Saladillo river basin for the first time. Among them twelve are new for Argentina. These especies are described and illustrated. Ecological and biogeographical information is also given.     

The importance of qualitative inventory sampling using electric fishing and nets in a large,tropical river (Brazil)

Qualitative fish sampling (single catch) using three methods (electric fishing, gillnets, seine nets) was assessed at three sites in the Ivai River (Paraná State, Brazil) to check their usefulness for quick inventory investigations. Electric fishing at a constant effort (15 min per each) was considered to be the best sampling technique. Taxon richness was calculated as the expected number of species using a rarefraction technique. Samples of 300–325 individuals, and 6–10 repetitions in neighbouring segments were sufficient. Even though electric fishing was conducted with the same effort in similar segments at each site there were many differences in species abundance. This suggests that the estimated fish specimen number obtained with constant effort is of limited validity on one sampling occasion and may be best considered as an ‘index of density’ only. The differences may partially be caused by the segments being located along the right and left bank of the large river (problem of different habitats). Qualitative and quantitative differences between electric fishing, gill-netting and seine-netting samples were very high at a high significance level. Nevertheless, as 22.4% taxa were caught only by gill or seine nets, these gears were important for complementing the species list. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effects of the water discharge on periphyton abundance and diversity in a large river (River Danube,Hungary)

This paper examines the relevance of intermediate disturbance theory in the context of in a large river the algal flora attaching to artificial substrata. It was observed that the theory is in good agreement with most of the communities analysed, however, with different frequency intervals compared to phytoplankton. Floods provided the most significant disturbances. As a rough generalization, we can say that in case of floods following each other in 8–14 days, respectively, the disturbance is of medium frequency. In case of 8 days, high frequency is more typical while in case of 14 days, low frequency is more characteristic. Owing to the fact that riverine periphytic algal organisms are attached in different ways and with differing efficiencies, the changes in the total mass occurring as a result of changes in water discharge lead to changes in diversity. The analysis of individual numbers can help in investigating the intensity of the disturbing effect on the algal communities. Negative correlation was found between water discharge and numbers of individuals, that is, the numbers of algae increase with low water discharge and decrease with high water level in the river. This second observation is valid only within a certain range of discharges (in this case up to 100 m³ s^–1), which will be specific to particular rivers and individual reaches. Below the upper limit of the range, the increased water flows carry more nutrients to the organisms but with no severe wash-off effect. Beyond the upper limit (in this case in range 100–400 m³ s^–1) the numbers of individuals is roughly in inverse proportion to the wash-off effect of the current, and the community is in equilibrium. In cases when discharge surpasses 400 m³ s^–1 decrease in individual numbers is general. We suggest that in the environments similar to the study area, the periphyton of the artificial substrata (e.g., pontoons) undergo similar processes. In respect of the periphyton formed on the surface of the riverbeds in large rivers with considerable changes in water level, a more complex system can be supposed where part of the periphyton is periodically dried and flooded alternately.     

Comparison of bacterial production in sediments, epiphyton and the pelagic zone of a lowland river

1. The microbial metabolism of organic matter in rivers has received little study compared with that of small streams. Therefore, we investigated the rate and location of bacterial production in a sixth‐order lowland river (Spree, Germany). To estimate the contribution of various habitats (sediments, epiphyton, and the pelagic zone) to total bacterial production, we quantified the contribution of these habitats to areal production by bacteria. 2. Large areas of the river bottom were characterized by loose and shifting sands of relatively homogenous particle size distribution. Aquatic macrophytes grew on 40% of the river bottom. Leaf areas of 2.8 m² m^?2 river bottom were found in a 6.6 km river stretch. 3. The epiphyton supported a bacterial production of 5–58 ng C cm^?2 h^?1. Bacterial production in the pelagic zone was 0.9–3.9 μg C L^?1 h^?1, and abundance was 4.0–7.8 × 10⁹ cells L^?1. Bacterial production in the uppermost 2 cm of sediments ranged from 1 to 8 μg C cm^?3 h^?1, and abundance from 0.84 to 6.7 × 10⁹ cells cm^?3. Bacteria were larger and more active in sediments than in the pelagic zone. 4. In spite of relatively low macrophyte abundance, areal production by bacteria in the pelagic zone was only slightly higher than in the epiphyton. Bacterial biomass in the uppermost 2 cm of sediments exceeded pelagic biomass by factors of 6–22, and sedimentary bacterial production was 17–35 times higher than in the overlying water column. 5. On a square meter basis, total bacterial production in the Spree was clearly higher than primary productivity. Thus, the lowland river Spree is a heterotrophic system with benthic processes dominating. Therefore, sedimentary and epiphytic bacterial productivity form important components of ecosystem carbon metabolism in rivers and shallow lakes. 6. The sediments are focal sites of microbial degradation of organic carbon in a sand‐bottomed lowland river. The presence of a lowland river section within a river continuum probably greatly changes the geochemical fluxes within the river network. This implies that current concepts of longitudinal biogeochemical relationships within river systems have to be revised.     

Seasonal alternation of lentic/lotic conditions in the Mapire system,a tropical floodplain lake in Venezuela

We studied the changing hydrological conditions of a transient system at the Mapire River mouth (Orinoco) and their effect on hydrochemistry of the system at six locations. Subjected to strong annual waterlevel fluctuations, the Orinoco River acts as a dam to the Mapire River discharge, resulting in the formation of a standing lake-like waterbody that covers the gallery forest to the canopy for five to six months. The Mapire floodplain fills primarily with Mapire waters and only secondarily with Orinoco water. The latter enters into the Mapire basin, but mixing of both waters is poor, resulting in chemically and physically different waterlayers. A significant thermal stratification is observed. This transient lake revverts to flowing conditions during the dry season. The Mapire River moutth, therefore, behaves as a cyclic system in which lotic/lentic and terrestrial/ aquatic conditions alternate seasonally. Some ecological implications are suggested and comparisons with similar systems are made.     

Seston sedimentation in a lowland river (River Spree,Germany): their spatial and temporal variations and controlling factors

Sedimentation of organic particles plays a decisive role in streams in relation to pelagic loss as well as retention of nutrients and other substances. The plate sediment trap allows for the direct measurement of these net fluxes. Biweekly measurements were undertaken in the eutrophic lowland River Spree (MQ 14 m³ s^–1) 10 km upstream of Berlin in 1999 and 2000. Trapping rates between 0.5 and 25 g DW m^–2 day^–1 were found near the bank. The variance of seston sedimentation is controlled by the seston concentration, the settling velocity of the particles and the flow velocity. The sinking velocity exhibits significant seasonal fluctuations with highest values in summer. It is shown that the critical flow velocity for sedimentation is another important parameter. This controls the distribution of sedimentation over the width of the river and thus the effective average sedimentation rate for the entire river segment. This average rate ranged between 0.9 and 6.6 g DW m^–2 day^–1.