Basin Surface Area Research Articles

Sources and main controls of dissolved organic and inorganic carbon in river basins: A worldwide meta-analysis

Despite dissolved carbon (C) exports from continents being crucial in the connection between terrestrial, atmospheric and oceanic C pools, the relative contribution and process controls on dissolved organic (DOC) and inorganic (DIC) fluxes within river basins are not fully understood. This paper presents an analysis of data from 843 sites worldwide from 45 Web of Science SCI-Expanded (ex ISI) indexed papers that report both the DOC and DIC contents and fluxes in conjunction with chemical elements, such as Si, Na and 13C abundance, to investigate the likely origin, pathways and fate of the dissolved C. The reviewed papers also report on selected environmental factors (e.g., MAP and MAT: mean annual precipitation and temperature respectively; Climate, LU: land use, A: basin surface area). Regarding dissolved C fluxes rivers transported on average, 8.4 GT C yr−1 of dissolved C with 7.7 GT C yr−1 (92%) being DIC and remaining (8%) DOC. Asia has the highest within-river dissolved C transport (5.8 GT C yr−1) followed by Europe (2.0 GT C yr−1), America (0.4 GT C yr−1), and Africa (0.1 GT C yr−1). The dissolved C fluxes tend to increase with river water fluxes and contribution of interflow as seen in the tropical climate, which results in the export of relatively fresh DOC with low aromaticity. In contrast, the lower river water fluxes in sub-tropical and temperate climates corresponds to high concentration of comparatively more decomposed DOC, which pointed to a high proportion of groundwater contribution to the water fluxes. The results also imply that surface area and morphology of the river basins, as well as land use, has insignificant impact on dissolved C dynamics. Such quantitative results, including on the important role of climate on the dynamics of dissolved C in river basins, are helpful in improving predictions on the impact of climate change on the global C cycle. New and innovative multidisciplinary research on the subject is called for.

Evolutionary time best explains the latitudinal diversity gradient of living freshwater fish diversity

AbstractAimThe evolutionary causes of the latitudinal diversity gradient are debated. Hypotheses have ultimately invoked either faster rates of diversification in the tropics or more time for diversification owing to the tropical origins of higher taxa. Here, we perform the first test of the diversification rate and time hypotheses in freshwater ray‐finned fishes, a group comprising nearly a quarter of all living vertebrates.LocationGlobal.Time period368–0 Ma.Major taxa studiedExtant freshwater ray‐finned fishes.MethodsUsing a mega‐phylogeny of actinopterygian fishes and a global database of occurrence records, we estimated net diversification rates, the number of colonizations and regional colonization times of co‐occurring species in freshwater drainage basins. We used generalized additive models to test whether these factors were related to latitude. We then compared the influence of diversification rates, numbers of colonizations, colonization times and surface area on species richness, and how these factors are related to each other.ResultsAlthough both diversification rates and time were related to richness, time had greater explanatory power and was more strongly related to latitude than diversification rates. Other factors (basin surface area and number of colonizations) also helped to explain richness but were unrelated to latitude. The most diverse freshwater basins of the world (Amazon and Congo rivers) were dominated by lineages having Mesozoic origins. The temperate groups dominant today arrived near the Cretaceous–Palaeogene boundary, leaving comparatively less time to build richness. Diversification rates and colonization times were inversely related: recently colonized basins had the fastest rates, whereas ancient species‐rich faunas had slower rates.Main conclusionsWe concluded that time is the leading driver of latitudinal disparities in richness in freshwater fish faunas. We suggest that the most likely path to building very high species richness is through diversification over long periods of time, rather than through rapid diversification.

Passive and active performance of a multi-side-stepped square pyramid solar still; experimental and modeling

Abstract New design of a multi-side-stepped square pyramid solar still (MSSPSS) covered with four-side glass was investigated experimentally and theoretically in passive and active moods. In comparison with single slope solar still with the same basin surface area, total area of the cover glass and the absorber area of the basin collector per square meter of solar still surface increased by 65% and 79.4%, respectively. This new design decreases the heat loss from the bottom and provides the ability of natural heat recovery of the basin's waste energy. Purification yield per square meter solar still surface (PY) for passive mood was found 2.035 for sunny day and 1.8 liters in a semi-cloudy in autumn, and 11.93, 12.39 liters for two sunny days in summer. Under active circumstances the inlet brine preheated with a salt-gradient solar pond, indicated PY of 13.99 a summer day, and 1.13 in the night, up to 13% and 9% increase in the diurnal and nocturnal production. Correlation between inlet water's rate and production has a crucial effect on PY. A thermal model was proposed to seek the effect of important parameters on the performance of MSSPSS and annual yield estimation. During the autumn, the radiative heat loss plays an important role while during the summer, the evaporation mechanism is more important. Error of the proposed model is 13.5% on average for estimation of PY and maximum error of 8.2% for thermal behavior. The estimated annual yield is around 2538 liters. Water-glass temperature difference has important effect on the MSSPSS performance. The correlation between inlet water's rate and production has crucial effect on PY.

Wintertime Coastal Upwelling in Lake Geneva: An Efficient Transport Process for Deepwater Renewal in a Large, Deep Lake

AbstractCombining field measurements, 3‐D numerical modeling, and Lagrangian particle tracking, we investigated wind‐driven, Ekman‐type coastal upwelling during the weakly stratified winter period 2017/2018 in Lake Geneva, Western Europe's largest lake (max. depth 309 m). Strong alongshore wind stress, persistent for more than 7 days, led to tilting and surfacing of the thermocline (initial depth 75–100 m). Observed nearshore temperatures dropped by 1°C and remained low for 10 days, with the lowest temperatures corresponding to those of hypolimnetic waters originating from 200 m depth. Nearshore current measurements at 30 m depth revealed dominant alongshore currents in the entire water column (maximum current speed 25 cm s−1) with episodic upslope transport of cold hypolimnetic waters in the lowest 10 m mainly during the first 3 days. The observed upwelling dynamics were well reproduced by a 3‐D hydrodynamic model (RMSE 0.2°C), whose results indicated that upwelled waters spread over approximately 10% of the lake's main basin surface area. Model‐based Lagrangian particle tracking confirmed that upwelled waters originated from far below the thermocline, that is, >150 m depth, and descended back to around 150–200 m depth over a wide area after wind stress ceased. Observational and particle tracking results suggest that wintertime coastal upwelling, which can occur several times during winter, is an overlooked transport process that is less sensitive to the effects of global warming than convective cooling. It can provide an effective but complex 3‐D pathway for deepwater renewal in Lake Geneva, and other large, deep lakes with a sufficiently long wind fetch.

Long-term impact of Central Basin hypoxia and internal phosphorus loading on north shore water quality in Lake Erie

ABSTRACTWe hypothesized that north shore water quality of Lake Erie’s Central Basin is impacted by Central Basin hypoxia and, by extension, related to redox-dependant internal phosphorus (P) loading from the profundal sediments. To evaluate this hypothesis, we first quantified Central Basin hypoxia as hypoxic factor (HF, days in Aug–Sep that a sediment area equal to the Central Basin surface area was hypoxic) from published annual hypoxic (<2.0 mg/L dissolved oxygen) areal extent and duration. From 1985 to 2012, mean HF values were 15.2 (SE 1.45) d/Aug–Sep and ranged between 0 (1996) and 34.3 (2012) d/Aug–Sep. Second, we estimated internal load from an areal P release rate of 8 mg/m2/d, multiplied by HF. The estimate of 122 (SE 11.6) mg/m2/Aug–Sep (1985–2012, n = 28) is supported by an independent estimate of 136 (SE 20.3) mg/m2/summer (1970–1986, n = 15) computed from total P concentration increases at fall turnover and by an estimate for 1970. Third, 2013 temperature and oxygen profiles demonstrated periodic upwelling on the north shore of the Central Basin, in agreement with other studies. Fourth, we analysed P, chlorophyll a (Chl-a) and phytoplankton species data at 2 north shore drinking water intake stations. HF and internal loading were significantly correlated with summer soluble reactive P, August–October Chl-a concentrations, and cyanobacteria abundance at the Central Basin site but not at the control site in the Western Basin. While these correlations are weak, suggesting other effects including benthic productivity, they may be partially caused by hypolimnetic water circulated toward the shoreline.

Upstream Remotely-Sensed Hydrological Variables and Their Standardization for Surface Runoff Reconstruction and Estimation of the Entire Mekong River Basin

River water discharge (WD) is an essential component when monitoring a regional hydrological cycle. It is expressed in terms of surface runoff (R) when a unit of river basin surface area is considered. To compensate for the decreasing number of hydrological stations, remotely-sensed WD estimation has been widely promoted over the past two decades, due to its global coverage. Previously, remotely-sensed WD was reconstructed either by correlating nearby remotely-sensed surface responses (e.g., indices and hydraulic variables) with ground-based WD observations or by applying water balance formulations, in terms of R, over an entire river basin, assisted by hydrological modeling data. In contrast, the feasibility of using remotely-sensed hydrological variables (RSHVs) and their standardized forms together with water balance representations (WBR) obtained from the river upstream to reconstruct estuarine R for an entire basin, has been rarely investigated. Therefore, our study aimed to construct a correlative relationship between the estuarine observed R and the upstream, spatially averaged RSHVs, together with their standardized forms and WBR, for the Mekong River basin, using estuarine R reconstructions, at a monthly temporal scale. We found that the reconstructed R derived from the upstream, spatially averaged RSHVs agreed well with the observed R, which was also comparable to that calculated using traditional remote sensing data (RSD). Better performance was achieved using spatially averaged, standardized RSHVs, which should be potentially attributable to spatially integrated information and the ability to partly bypass systematic biases by both human (e.g., dam operation) and environmental effects in a standardized form. Comparison of the R reconstructed using the upstream, spatially averaged, standardized RSHVs with that reconstructed from the traditional RSD, against the observed R, revealed a Pearson correlation coefficient (PCC) above 0.91 and below 0.81, a root-mean-squares error (RMSE) below 6.1 mm and above 8.5 mm, and a Nash–Sutcliffe model efficiency coefficient (NSE) above 0.823 and below 0.657, respectively. In terms of the standardized water balance representation (SWBR), the reconstructed R yielded the best performance, with a PCC above 0.92, an RMSE below 5.9 mm, and an NSE above 0.838. External assessment demonstrated similar results. This finding indicated that the standardized RSHVs, in particular its water balance representations, could lead to further improvement in estuarine R reconstructions for river basins affected by various systematic influences. Comparison between hydrological stations at the Mekong River Delta entrance and near the estuary mouth revealed tidally-induced backwater effects on the estimated R, with an RMSE difference of 4–5 mm (equivalent to 9–11% relative error).

Rapid and punctuated Late Holocene recession of Siling Co, central Tibet

Variations in the strength of the Asian monsoon during Holocene time are thought to have been associated with widespread changes in precipitation across much of Tibet. Local records of monsoon strength from cave deposits, ice cores, and lake sediments typically rely on proxy data that relate isotopic variations to changes in precipitation. Lake expansion and contraction in response to changing water balance are likewise inferred from sedimentologic, isotopic and paleobiologic proxies, but relatively few direct records of changes in lake volume from preserved shorelines exist. Here we utilize relict shoreline deposits and associated alluvial fan features around Siling Co, the largest lake in central Tibet, to reconstruct centennial-to-millennial-scale variations in lake area and volume over the Holocene. Mapping and surveying of lacustrine shorelines coupled with optically stimulated luminescence dating of associated deposits indicate protracted occupation of a highstand elevation from >8 ka to 4 ka, followed by rapid recession that was likely punctuated by several stillstands of centennial-scale duration. Calculation of the changes in lake surface area and past hydrologic indices of the Siling Co basin suggests the effective moisture during the early Holocene highstand was approximately three times greater than today. In contrast to other lakes in central and western Tibet, our results suggest that Siling Co did not begin to recede synchronously with decreasing solar insolation at ca. 9–8 ka. Rather, initial recession of Siling Co appears to correspond to a time period of enhanced aridity and weakened monsoon in both Africa and Asia at ca. 4.2 ka. Our results add to a growing body of literature that suggest a period of relatively severe aridity on the Tibetan Plateau at this time. We suggest that subsequent punctuated recession of Siling Co was punctuated by similar periods of abrupt climate change during the Late Holocene.

Simulation of energy balance and carbon dioxide emission for microalgae introduction in wastewater treatment plants

A case study is described in which the activated sludge process is replaced with a microalgae-activated sludge process. The effects on the heat and electricity consumption and carbon dioxide emissions were evaluated in a system model, based on mass and energy balances of biological treatment and sludge handling process steps. Data for use in the model was gathered from three wastewater treatment plants in Sweden. The evaluation showed that the introduction of microalgae could reduce electricity and heat consumption as well as CO2 emissions but would require large land areas. The study concludes that a 12-fold increase in the basin surface area would result in reductions of 26–35% in electricity consumption, 7–32% in heat consumption and 22–54% in carbon dioxide emissions. This process may be suitable for wastewater treatment plants in Nordic countries, where there is a higher organic load in summer than at other times of the year. During the summer period (May to August) electricity consumption was reduced by 50–68%, heat consumption was reduced by 13–63% and carbon dioxide emissions were reduced by 43–103%.

Behavioral studies on the use of open water basins by American mink (Neovison vison)

The aims of this study were to investigate whether farmed mink use swimming basins as an environmental enrichment factor and to identify layouts suitable to allow mink to perform their characteristic behavior to a large extent. Furthermore, an assessment of the water quality was intended. In 2006, the German “Order on the Protection of Animals and the Keeping of Production Animals” (German designation: Tierschutz-Nutztierhaltungsverordnung) stated mandatory husbandry requirements for fur animals for the first time in Germany. For mink, these include a water basin which is suitable for swimming. Forty American mink (Neovison vison) from a commercial mink farm were housed in 2 identically constructed free-range enclosures at the age of 13 weeks. In each of the 2 enclosures, the mink were offered 3 different water basins, which differed in shape, depth, and surface area and included a rectangular “swimming pool” (surface area approximately 20.5 m2, depth approximately 30 cm), a round “pond” (surface area 4.9 m2, depth approximately 80 cm), and a flowing “creek” (surface area 4.0 m2, length approximately 10.0 m, width 40 cm, depth 3-4 cm). Twenty nest boxes were placed in each enclosure (animal-to-nest box ratio: 1:1). The animal behavior in both groups was assessed by direct and video observations. Results showed that the mink generally accepted all 3 water basins and used them extensively from the beginning to the end of the study. Descriptive and negative binomial model analysis of water contact counts obtained from direct observations showed that mink preferred the swimming pool. However, in relation to the basin surface area, the preference effect is more pronounced for the pond. Overall, the animals spent a considerable amount of time at and in the water during their main activity time. On average, each mink could be observed 7 minutes per hour (12.0%) at and in the pool or 3 minutes per hour (5.5%) in the pond. The water quality was very good throughout the study. Although the mink used the water frequently, the total bacteria count and the level of Enterobacteriaceae were always very low. There were no traces of salmonella in any water sample.

Contemporary suspended sediment dynamics within two partly glacierized mountain drainage basins in western Norway (Erdalen and Bødalen, inner Nordfjord)

This paper focuses on environmental controls, spatiotemporal variability and rates of contemporary fluvial suspended sediment transport in the neighboring, partly glacierized and steep Erdalen (79.5km2) and Bødalen (60.1km2) drainage basins in the fjord landscape of the inner Nordfjord in western Norway. Field work, including extended samplings and measurements, was conducted since 2004 in Erdalen and since 2008 in Bødalen. The distinct intra- and inter-annual temporal variability of suspended sediment transport found is mostly controlled by meteorological events, with most suspended sediment transport occurring during pluvial events in autumn (September–November), followed by mostly thermally determined glacier melt in summer (July–August), and by mostly thermally determined snowmelt in spring (April–June). Extreme rainfall events (>70mmd−1) in autumn can trigger significant debris-flow activity that can cause significant transfers of suspended sediments from ice-free surface areas with sedimentary covers into main stream channels and is particularly important for fluvial suspended sediment transport. In years with occurring relevant debris-flow activity the total annual drainage-basin wide suspended sediment yields are strongly determined by these single extreme events. The proportion of glacier coverage, followed by steepness of slopes, and degree of vegetation cover in ice-free surface areas with sedimentary covers are the main controls for the detected spatial variability of suspended sediment yields. The contemporary sediment supply from glacierized surface areas and the Jostedalsbreen ice cap through different defined outlet glaciers shows a high spatial variability. The fact that the mean annual suspended sediment yield of Bødalen is with 31.3tkm−2yr−1 almost twice as high as the mean annual suspended sediment yield of Erdalen (16.4tkm−2yr−1) is to a large extent explained by the higher proportion of glacier coverage in Bødalen (38% of the drainage basin surface area) as compared to Erdalen (18% of the drainage basin surface area) and by a significantly higher sediment yield from the glacierized area of the Bødalen drainage basin compared to the glacierized surface area in Erdalen. When looking at the total annual mass of suspended sediments being fluvially exported from both entire drainage basin systems, the total amount of suspended sediments coming from the ice-free drainage basin surface areas altogether dominates over the total amount of suspended sediments coming from the glacierized surface area of both drainage basins. Drainage-basin wide annual suspended sediment yields are rather low when compared with yields of other partly glacierized drainage basin systems in Norway and in other cold climate environments worldwide, which is mainly due to the high resistance of the predominant gneisses towards glacial erosion and weathering, the altogether only small amounts of sediments being available within the entire drainage basin systems, the stable and nearly closed vegetation cover in the ice-free surface areas with sedimentary covers, and the efficiency of proglacial lakes in trapping sediments supplied by defined outlet glaciers. Both contemporary and long-term suspended sediment yields are altogether supply-limited. Contemporary suspended sediment transport accounts for nearly two-thirds of the total fluvial transport and, accordingly, plays an important role within the sedimentary budgets of the entire Erdalen and Bødalen drainage basins.

Environmental correlates of body size distribution in Cyprinidae (Actinopterygians) depend on phylogenetic scale

AbstractThe pattern of increasing species body size with increasing latitude has been noticed in different groups of animals. Here, we used seven key environmental factors and independent contrasts to assess body size latitudinal clines in Cyprinidae at two phylogenetic levels (inter‐ and intragenera), which were defined using a genus‐level supertree. Model selection procedures revealed that environmental factors shaping body size variation in Cyprinidae differed according to the phylogenetic scale considered. At the higher phylogenetic level, we found that both temperature (negative effect) and habitat availability (positive effect of drainage basin surface area) constituted mechanistic explanations of large‐scale body size distribution. No temperature‐related body size cline was observed at the intragenus level. Instead, competitive interaction (negative effect of species richness), habitat availability (positive effect of drainage basin surface area), migration ability and available energy (positive effects of glacial coverage and actual evapotranspiration) constitute alternative explanations at this lower phylogenetic scale. We conclude that (i) at the intergenus level, cyprinids do show a tendency to be smaller at high temperatures and larger at low temperatures, (ii) this tendency no longer exists at the intragenus level, (iii) latitude per se is a weak predictor of body size clines whatever the taxonomic level analysed, (iv) generalising geographical body size patterns may be rendered difficult by the superimposition of a series of mechanisms across different taxonomic scales, and (v) habitat size, here acting positively at both taxonomic scales, may play a major role in shaping riverine species body size clines.

Impacts of Flocculation on Sediment Basin Performance and Design

<abstract> <bold><sc>Abstract.</sc></bold> There is increasing interest in controlling turbidity in construction site runoff using chemical flocculant treatments. Since flocculated sediment is likely to behave much differently from untreated sediment, changes to current sediment basin designs may be appropriate. This study evaluated a system consisting of three fiber check dams in a lined ditch discharging to sediment basins that differed in their configuration. Three different basin configurations were tested with and without granular polyacrylamide (PAM) applied to the weir of each check dam: (1) standard basin with a 2:1 length to width (L/W) ratio, (2) horizontal basin with a 1:2 L/W ratio, and (3) standard basin with a rising floor toward the exit (spillway). All configurations included two porous baffles of jute/coir netting across the full width of the basin. For each treatment of PAM and basin configuration, sediment-laden stormwater flows (0.014 to 0.056 m³ s^-1) were introduced to the ditch for 29 min, and water samples were collected at the ditch entrance (influent), ditch exit, and basin exit. Regardless of PAM treatment, total suspended solids (TSS) concentrations were reduced by more than 55% at the ditch exit and by up to 90% at the basin exit relative to the influent (3,700 mg L^-1). The 1:2 L/W basin reduced TSS more than either of the 2:1 L/W basins without flocculation, but there was no significant difference in TSS when sediment was treated with PAM. Turbidity at the ditch exit was similar to the influent (less than 10% difference) without flocculation but was greatly reduced (>66%) with flocculation. The PAM treatment lowered turbidity further (>88%) at the basin exit and was similar among all basin configurations. The particle size distribution of flocculated sediment was shifted into coarser fractions, enhancing settling in the basin. The estimation of basin surface area requirement based on the measured particle size suggested that basins receiving flocculated sediment could be reduced in surface area and altered in configuration while improving water quality for construction site discharges.

Regional vs local drivers of phylogenetic and species diversity in stream fish communities

Summary Regional and local processes are thought to influence community phylogenetic and species diversity, but have proved challenging to distinguish. We disentangled the effects of local (limiting similarity and habitat filtering) and regional processes (biogeography, history and geographical constraints) on the species and phylogenetic diversity of native riverine fish communities across France. Fish species richness (SR), phylogenetic diversity (estimated as the phylogenetic species variability metric, PSV) and trait evenness (estimated from 17 ecological and life‐history traits) were estimated for fish at 932 sampling sites across 42 river basins in France. A phylogenetic signal in traits and species responses to environment variation were estimated using linear models. Null models were developed to test whether river basins constrain the PSV of the communities. Hierarchical linear models were fitted to PSV and SR to partition the variance explained by local and regional processes. Fish species richness and phylogenetic diversity were negatively correlated across sites (r = −0.589, P &lt; 0 001). There was a phylogenetic signal in species traits, but only a weak signal in species responses to environmental variation across sites. The null models suggested that river basins constrain community PSV. Local‐scale predictors (temperature, landscape position and trait evenness) explained the variation in both PSV and SR, while regional‐scale predictors (latitude, longitude and basin surface area) explained the variation only in SR. Significant interaction terms between local‐ and regional‐scale predictors were also detected for both metrics. Local‐scale processes, habitat filtering and limiting similarity, probably determine the species composition of fish communities across France, while broad‐scale, regional processes constrain community composition both directly and indirectly by affecting the strength of these local‐scale processes. By analysing phylogenetic diversity and species richness simultaneously, a full picture of the drivers of local‐scale diversity can be determined.

Integrated Methodology of Design for Construction Site Sedimentation Basins

The performance of four sedimentation basins (SBs) at a Pennsylvania Department of Transportation I-99 highway construction site was evaluated based on their particle removal ability. Suspended solids data from the basins indicated poor particle removal, peaks in suspended solid concentration that correlated with rainfall peaks and possibility of sediment resuspension. The current Pennsylvania Department of Environmental Protection basis for basin design is the allocation of 28 m³ (1,000 ft³) of sediment storage zone and 140 m³ (5,000 ft³) of drainage zone per disturbed acre of the drainage basin. Overflow rate, which is a scientific basis for particle removal, is currently not considered in the design of basins. This paper presents a methodology for developing an integrated design for SBs, applying rainfall probability plots to determine an appropriate basin settling volume. The revised universal soil loss equation is used to identify sediment zone volume, and an overflow rate is determined to design basin surface area. The method presented is a comprehensive procedure for designing SBs with flexibility to choose the extent of particle removal and runoff capture, and to vary construction costs.

Controls on the sedimentology of an ice-contact jökulhlaup-dominated delta, Kangerlussuaq, west Greenland

This paper characterises the sedimentary impact of a glacial outburst flood or ‘jökulhlaup’ on an ice-contact delta topset at Russell Glacier, Kangerlussuaq, west Greenland. Rapid drainage of an ice-dammed lake in July 1987 generated a jökulhlaup with a peak discharge of ∼ 1300 m 3 s − 1 , which drained across a 500-m-wide, 200-m-long, delta top into a proglacial lake. The delta topset comprises boulder clusters, ice block obstacle marks with relief of up to 4 m, and is graded to lake levels up to 6 m higher than those during typical non-jökulhlaup conditions. The delta top was dissected by the 1987 jökulhlaup causing a fan-shaped extension of the delta front by 30 m. Surface grain size on the delta decreases rapidly away from the main flood flow direction, reflecting rapid downstream reduction in sediment transport capacity. The 1987 jökulhlaup was predominantly fluidal and turbulent and had peak stream powers of 2846 W m − 2 proximally and < 400 W m − 2 distally. Delta topset sedimentation can be characterised by four lithofacies associations in order of decreasing flow energy: (A) coarse-grained deposits related to a flow expansion; (B) finer-grained peripheral deposits located at the margins of the main flow; (C) lobate bars and delta fronts deposited within distal locations and (D) fine-grained deposits at distance from the delta front associated with slackwater conditions. Jökulhlaup-dominated delta topsets are controlled by the geometry of the channel expansion into the proglacial lake, jökulhlaup hydrograph form, the sediment availability and character, proglacial lake basin depth and surface area, lake outflow spillway erodibility and cross-sectional area, and history of previous jökulhlaups.

Stream fish assemblages and basin land cover in a river network

This study focused on characterizing fish assemblages in the Adour–Garonne basin and identifying the relative influences of landscape-scale features on observed patterns in stream fish assemblages. Two different artificial neural network algorithms were used: a self-organizing map (SOM) and a multilayer perceptron (MLP). A SOM was applied to determine fish assemblage types, and a MLP was used to predict the fish assemblage types defined by the SOM. Thirty four species were collected at 191 sampling sites in a major river-system, the Adour–Garonne basin, and topographical factors, namely altitude, distance from source and surface area of drainage basin were measured. Using GIS, land cover types (agricultural land, forests and urbanized artificial surface) were calculated for each site and expressed as percentage of the surface area of basin. These variables were introduced to the MLP and factorial discriminant analysis for the prediction of assemblage types. As a result, the SOM distinguished three fish assemblage types according to the differences of species composition, and the assemblage types were better predicted with landscape-scale features by MLP than discriminant analysis. The percentages of agricultural land and the surface area of a basin showed the greatest influence on assemblage types 1 and 2, and distance from source was the most important factor to determine assemblage type 3.

Modelling of base flow of the basin of Kolubara river in Serbia

Summary This study presents a physically founded hydrologic–hydraulical model for determining the base flow of the catchment by analysing the water balance of the basin and vertical exchange of water between the atmosphere, unsaturated media and ground water, basing on the known physical characteristics of the basin (climatic, paedological, geological and vegetation ones) on the example of the 340 km 2 Kolubara River basin up to “Valjevo” water level monitoring station in Serbia in three characteristic years: an extremely rainy year (1970), an average year (1985) and an extremely dry year (1990). Taking into consideration that the amount of base flow of a basin is impossible to measure at the catchment outlet, the hydrograph of the base flow values obtained by separating from the streamflow hydrograph registered at the outlet of a drainage basin by application of the graphical local minimum method was used for checking the model’s functioning. It was finally determined that the total base flow values at the outlet point of the catchment, obtained by application of the graphical local minimum method, equal approximately the total groundwater recharge from the whole surface area of the basin, representing the summary of groundwater recharge originating from different soil types covered with different types of vegetation, under the influence of atmospheric conditions of the soil surface. Thus it was confirmed that when characteristics of a basin are known, it is possible to obtain information on the base flow values.

Three‐dimensional modeling of lacustrine diatom habitat areas: Improving paleolimnological interpretation of planktic : benthic ratios

Three‐dimensional modeling of lake morphometry enables the calculation of lake volume, planar surface area, and basin surface area, which are critical components of a conceptual model of how planktic and benthic habitat areas change with changing lake level. We have applied three‐dimensional modeling to Foy Lake, Montana, and compared model results of changing ratios of planktic and benthic habitat areas at all possible lake levels to sediment cores recovered from the lake. The model allows us to produce semiquantitative depth reconstructions and greatly improves lake‐level reconstruction of this morphometrically complex basin. The conceptual model also was modified to examine the influence of resuspension versus gravity redistribution of diatomaceous material on the sedimentary record. Comparison of the model results with both long and short sedimentary records from Foy Lake, Montana, suggests that planktic : benthic ratios may be a better predictor of mean lake depth than maximum lake depth. The model developed here is simple enough to be easily implemented, has few requirements, can be adapted to suit any lake basin, and can be augmented to examine a variety of different lake processes that affect habitat availability.

Equilibrium and cross-sectional stability of tidal inlets: application to the Frisian Inlet before and after basin reduction

The focus of this paper is on the adaptation of the inlet cross-sectional area after basin reduction. To calculate the new equilibrium and degree of stability, use is made of a method first proposed by Escoffier. As part of this study his largely empirical approach is expanded and given a physical basis. The inlet channel is divided in an entrance and interior section. Sand enters the entrance section on the flood and is removed by the ebb tidal current. On annually average basis, the volume of sand entering the inlet is assumed to be a constant fraction of the littoral drift. A theoretical expression for the ebb tidal sand transport as a function of the tidal velocity amplitude and a length dimension of the cross-section is derived. An important ingredient in the stability analysis is the empirical cross-sectional area versus tidal prism relationship for inlets in equilibrium and the related equilibrium velocity. A physical justification for this relationship is presented. As a measure for cross-sectional stability, a stability index, S, is introduced. For S≥1, the inlet is very stable. Stability increases with increasing values of S. For inlets that are very stable, the value of S can be related to P/ V, i.e. the ratio of tidal prism and volume of littoral drift. A method to determine the time scale for the entrance section to return to a new equilibrium after a change in basin surface area is presented. To illustrate its practical use, the Escoffier method is applied to the Frisian Inlet before and after basin reduction. In 1969, the basin area and tidal prism were reduced by approximately 30%. Based on the Escoffier method, the original equilibrium cross-sectional area of 22,000 m 2 is expected to reduce to 15,500 m 2. The adaptation time scale is estimated to be 30 years. Even after basin reduction, the inlet remains very stable with S=31 and P/ V=585.

Vegetation and environmental conditions in recently restored wetlands in the prairie pothole region of the USA

How closely the vegetation of restored wetlands resembles that of comparable natural wetlands is a function of the probability of propagules of wetland species reaching reflooded wetlands and how similar environmental conditions in the restored wetland are those in the natural wetlands. Three years after reflooding, we examined the vegetation composition, water level fluctuations, soil organic carbon content, and soil bulk density as well as surface water pH, alkalinity, conductivity, and calcium and magnesium concentrations of 10 restored and 10 natural wetlands. In the restored wetlands, more species of submersed aquatics colonized than were found in natural wetlands, and they rapidly spread to form extensive beds that were larger than those found in natural wetlands. Emergent and wet meadow species in restored wetlands, however, were found in only sparse stands as were a variety of annuals. The vegetation of natural wetlands was predominantly large stands of emergent species. Fluctuations in water storage volume and basin surface area were similar for both restored and natural wetlands. The surface water in restored wetlands had higher pH and lower alkalinity, conductivity, and calcium and magnesium concentrations than that in natural wetlands. Soils of restored wetlands have a lower organic carbon content and higher bulk density than do those of natural wetlands. Our results suggest that for submersed aquatics, dispersal of propagules to restored wetlands is rapid and environmental conditions in restored wetlands are very suitable for their establishment. For other guilds of wetland species, e.g., sedges and other wet meadow species, dispersal to restored wetlands is likely much slower and may pose a serious problem for the re-establishment of these species in restored wetlands. Even if dispersal is not limiting, low surface organic carbon and high bulk density may prevent the establishment of these species in restored wetlands.