Main Channel Sites Research Articles

Seasonal patterns in macroinvertebrate drift and seston transport in streams of an alpine glacial flood plain

1. We measured drift of macroinvertebrates and organic matter in five different channel types (upper and lower main channel, intermittent side‐channel, side‐slope tributary, and a groundwater channel) draining a glacial flood plain in the Swiss Alps. Samples were collected seasonally over 3 years (May 1997 to November 1999) to encompass major periods of floodplain expansion and contraction.2. Total wetted channel length ranged from ≤ 5 km during maximum floodplain contraction to ≥ 24 km under system expansion. Principal components analysis (PCA) of key physical and chemical measures collected over an annual cycle showed that the main and side channel sites differed spatially and seasonally from the tributary and groundwater sites, reflecting the glacial influence on the former.3. Two‐way ANOVA indicated a significant Site × Date interaction for all measured variables. Transported organic matter, caused by blooms of Hydrurus foetidus, was typically five to 10 times higher in the lower main channel and side‐channel than the other channel types, and was least variable among dates in the groundwater and tributary channels.4. The number of drifting macroinvertebrates was usually highest in the groundwater channel, although highly variable among years. Other channel types had highest drift rates in November and lowest rates in May, reflecting seasonal changes in the life cycles of particular taxa, such as Baetis alpinus and the Simuliidae. The lower main channel exhibited the greatest, and the groundwater the lowest, seasonality in drift compared with the other channels.5. The Chironomidae displayed the highest drift rates in most seasons, especially in summer when other taxa were relatively low in the drift. The number of taxa in the drift also varied among channel types and season, ranging from less than two in early spring to four to six in other seasons.6. The observed differences in drift rate and transported organic matter among channel types and seasons have important implications for ecosystem dynamics, through its effect, for instance, on dispersal among channel types or on organic matter exchange.

Localization of Water Molecules and Sodium Ions in Na-Mordenite, by Thermally Stimulated Current Measurement

Dielectric relaxation properties of dehydrated and hydrated Na-mordenite are measured by means of thermally stimulated depolarization current (TSDC) spectroscopy. TSDC spectroscopy allows us to determine two characteristic terms which depend on the hydration state: on one hand, the site selectivity of sodium ions and water molecules and on the other hand, the sodium/network interaction energy. Upon hydration, half of the Na+ ions remain embedded in site A, whereas the other Na+ ions are extracted from the main channel sites (sites D and E). Besides, according to the water content, we show that water molecules are adsorbed in different sites, first in sites H or F, then in sites B, C, or G, and finally in sites G. Furthermore, it is pointed out that the interaction energy (Na+/zeolite) value depends on the sodium localization following the sequence: Esite A > Esite D > Esite E. Finally, it is shown that the interaction energy decreases as the water content increases (typically from 0.79 eV to 0.44 eV). Thi...

Stable isotope analysis of macroinvertebrates and their food sources in a glacier stream

1. Food sources and trophic structure of the macroinvertebrate community along a longitudinal gradient were examined in a glacier stream of the Swiss Alps (Val Roseg). Analysis of multiple stable isotopes (δ13C and δ15N) and measurement of C : N ratios were used to differentiate between allochthonous and autochthonous organic matter.2. Although isotopic signatures of algae varied widely among sites and dates, it was possible to discriminate between allochthonous and autochthonous food sources using a site‐specific approach.3. Dominant food sources of herbivorous invertebrates in all main channel sites were epilithic diatoms and the filamentous gold alga Hydrurus foetidus. Allochthonous organic matter was of some importance only in a groundwater‐fed stream close to the floodplain margin.4. Seasonal changes in the δ13C signature of the macroinvertebrates corresponded with seasonal changes in δ13C of the gold alga H. foetidus. This indicated that the energy base remains autochthonous throughout the year.5. Because of limited food sources, feeding plasticity of the invertebrate community was high. Both grazers and shredders fed predominantly on algae, whereas gatherer‐collectors seemed to be omnivorous.6. The overall enrichment of δ15N was 2.25‰ (r2=0.99) per trophic level. On a gradient from the glacier site to a downstream forested site trophic enrichment was constant but variation in δ15N within trophic levels decreased.

Relationship between catchment characteristics and nutrient concentrations in an agricultural river system

We examined the effects of catchment characteristics and riverine processes on the concentrations of nutrients and total suspended solids (TSS) using data from the outlets of 12 tributaries (9–139 km 2) and 22 main channel sites of a river draining an intensely cropped area of 1088 km 2 in SW Finland. For the tributaries, the flow-weighted mean concentrations of TSS and total phosphorus (TP), which both reflect erosion, were best explained by field percentage and the mean slope of the fields of the catchment. The best model describing the concentration of dissolved reactive P (DRP) included field percentage and catchment area. Total nitrogen (TN) and nitrate+nitrite-nitrogen (NO x -N) correlated only with field percentage. Except for DRP, the regression models derived from the tributary data rather accurately predicted the concentrations in the main river channel. Our results suggest that, with regard to lakeless catchments of 10–1000 km 2, the export of TP, TSS and N per unit area remains constant. Furthermore, although some P in eroded soil particles may be released into dissolved, algal-available form during the river transport, erosion control appears not to efficiently reduce dissolved P.

Quantification of Brønsted Acidity in Mordenites

FTIR and NMR spectroscopy have been applied to quantification of Brønsted acid sites in various mordenite samples. A standardised deconvolution procedure has been developed for reliable decomposition of the complex hydroxyl region in the infrared spectra of mordenites into high frequency and low frequency peaks, and the peak extinction coefficients have been determined. As a result, the overall number of Brønsted acid sites, their distribution between main channels and side pockets, and the amount of extraframework aluminium can be determined. Results obtained by both FTIR and NMR are in good agreement and support each other. For instance, it is shown that for fully exchanged H-MOR, the distribution of Brønsted hydroxyls between main channels and side pockets is approximately 2:1. On partial ion exchange Na-MOR→HNa-MOR, protons are first introduced into main channel sites, with Na remaining in the side pockets.

Radiological assessment of the Ribble Estuary—III. Redistribution of radionuclides

The Ribble Estuary in the UK is contaminated by radionuclides derived from BNFL Sellafield and Springfield. Following the temporary shutdown of the Springfields plant, beta dose and gamma air kerma rates were measured at a range of sites in the estuary. Sediment surface samples were analysed for 137Cs, 234mPa, 234Th and 241Am activity concentrations by gamma spectrometry, 230Th and Pu isotopes by alpha spectrometry and sediment grain size (percentage < 63 μm) by wet sieving. Temporal variations in Springfieldsderived radionuclides are explained by variations in discharges by radionuclides and the distribution of fine grained sediments in the estuary which is controlled mainly by the spring-neap tidal cycle and river runoff. Radionuclide dynamics, modelling variations in the 234Th 137Cs activity concentration ratio and calculating environmental beta dose rate and 234Th half-lives allow the estuary to be split into three areas: (a) upper estuary where fine grained sediments tend to be deposited during periods of low and average river flow; (b) middle reaches of the estuary which encompass most of the main channel sites where fine grained sediments are probably deposited and removed on most tides; (c) outer estuary including large areas of salt marshes which tend to accumulate fine grained sediment. This is confirmed by similar results derived from the 234Th 239,240Pu ratio.

Influence of side‐arms on aquatic macroinvertebrate drift in the main channel of a large river

1. Drift from lotic and lentic side‐arms to the main channel was studied over 2 years in different sections of the Upper Rhône River (France). The hypothesis of an influence of drift on the main channel was tested by measuring drift in the main river at sites downstream and upstream from the confluences with two side‐arms, as well as in the two side‐arms themselves.2. Side‐arms were differentiated from the main channel by having a typical composition of macrofauna with a high propensity to drift, particularly in spring–summer and during spates. Drift densities in side‐arms averaged more than twice those measured in main channel sites, but these inputs did not significantly affect taxon richness and total drift density in the main channel.3. Nevertheless, some taxa found in the more lotic of the two side‐arms were more abundant downstream of the confluence than upstream, indicating that they had drifted into the main channel; no such direct effect was found throughout the sampling period for the more lentic side‐arm. The densities of two competitive filter feeders (Hydropsyche and Simuliidae) were significantly higher below the confluences than above, suggesting that side‐arms were also contributing substantial amounts of seston to the main channel.4. Therefore, side‐arms influence the community structure of drifting macroinvertebrates in the Upper Rhône River, both directly through immigration—depending on the degree of connectivity to the river—and indirectly via food supply.

Calorimetric study of NH 3 and CO 2 adsorption on erionites and zeolites L

The heats of adsorption of CO 2 and NH 3 on sodium-potassium, calcium-potassium and hydrogen erionites and on zeolites L containing Na +, K +, Ca 2+, Mg 2+ and La 3+ ions were calorimetrically measured. At low coverages a considerably smaller number of Ca 2+ ions in erionites is involved in the interaction with CO 2 molecules compared with NH 3 molecules. The substitution of Na + ions by Ca 2+, Mg 2+ or La 3+ in zeolites L leads to a decrease in heats of adsorption of CO 2. The number of Mg 2+ ions forming adsorption complexes with NH 3 in zeolites L significantly exceeds the corresponding numbers of Ca 2+ and La 3+ ions. The ion exchange data suggest that a greater number of Mg 2+ ions in contrast to Ca 2+ and La 3+ ions occupy the main channel sites.

Fluctuations in the community composition of water-column protozoa in two southeastern blackwater rivers (Georgia, USA)

This study addresses protozoan population dynamics of two southeastern blackwater rivers in Georgia: the sixth order Ogeechee River and fourth order Black Creek. The density and composition of the protozoan community was assessed by counting the protozoans into size classes. Particularly abundant flagellate types (bloom forms) and ciliates were enumerated separately. Protozoan density in these blackwater rivers is high. Observations during a two week and a ten month census showed that the rate of community change is rapid and that the range in diversity is great. A backwater site showed the highest percentage of bloom forms, while the main channel sites of Black Creek and the Ogeechee River had fewer bloom forms. Rapid increases in density during a two week microcosm study were attributed to isolation of the water-column from filter-feeders, the benthos, and different source areas. An analogous situation may exist in the low order swamp streams and backwater habitats where many dense blooms occur. The high protozoan population densities observed were partially due to rapid changes in the physical characteristics of the environment, reactions of the protozoa to such changes, growth in the swamp tributaries and backwater areas, subsequent washing into the river, and further growth as the water moves toward the sea.

Backwater areas as nursery habitats for fishes in pool 13 of the Upper Mississippi River

Samples of larval and juvenile fishes were collected at two depths weekly during spring and summer 1983 near the mouths of backwater areas in Pool 13 of the Upper Mississippi River. The study was conducted to determine the relative value of these habitats as nursery areas for fishes present and to note any interactions that might occur between the backwaters which are being rapidly lost to siltation, and the main channel. The larvae and juveniles collected represented 13 families divided into 27 lower taxa. Cyprinidae, Clupeidae, and Sciaenidae made up 90% of the total catch. Both larvae and juveniles were more abundant near the surface than near the bottom. Densities differed greatly among the three backwater areas studied. Larval fishes were grouped on the basis of their relative abundance in the backwaters or main channel. Overall, more larvae were captured in the backwaters than in main-channel habitats, indicating that backwaters were more productive. In the main channel, densities were greater downstream from the mouths of the backwaters than upstream-possibly indicating that (1) larval fish drifted out of the backwater areas, (2) water rich in nutrients or zooplankton that flowed into the main channel created productive downstream sites that were used as nursery areas, or (3) adult fishes selected downstream sites as spawning areas. Juvenile forms were more abundant in the backwater areas then in the main-channel habitats, some bottom-dwelling fishes excepted. The backwater areas were judged to be important nursery areas for larval and juvenile fishes, and seemed to benefit downstream main-channel sites. Any loss of these habitats would be detrimental to the Mississippi River as a whole.

Water in homoionic and heteroionic mordenites: a calorimetric study. Part 2.—Divalent and trivalent transition metal forms

Heats of immersion in liquid water are reported for a range of di- and tri-valent transition metal ion exchanged forms of Na-Zeolon and also for some H-Zeolons. In each case the approximately two exchanged divalent metal cations remain in main channel sites bonded to framework oxygens during dehydration but on immersion in liquid water they rehydrate fully in the main channels; a similar situation is envisaged for the M3+ exchanged forms. Using a correlation between heats of immersion for homoionic monovalent exchanged forms and heats of solvation of gaseous ions a method is proposed for obtaining heats of immersion of fully exchanged transition metal forms from experimental data for the partially exchanged zeolites. The correlation is further used to calculate dielectric constants and refractive indices for the exchanged zeolites.