ABSTRACT The larval chironomid community of the bed sediment surface and the hyporheic interstitial was examined in a gravel stream between September 1984 through August 1985 and between March and June 1993.

Spatial and temporal species turnover between horizontally adjacent sampling sites fluctuated distinctly in all sediment depth layers. The species composition showed a significantly lower spatial turnover in the upper 10 cm of the bed sediments than in deeper layers (P<0.05). Moreover, species abundance patterns of a five-species assemblage implied random assortment (sensu Tokeshi, 1990) and indicated a high probability for a species assembly to be dictated by environmental stochasticity. Neutral models were developed to evaluate the significance of observed overlap values in spatial distribution amongst abundant chironomid species (sensu Schmid, 1993). The spatial organization of a larval chironomid assemblage in the gravel stream Oberer Seebach seemed to be governed by coexistence due to random colonization processes, which reduce the probability of strong competitive interactions. Larval species colonization into open microhabitat patches of interstitial space (47.8 cm3) was rapid with representatives of a species assemblage arriving within less then 24 hours of the start of the colonization experiment. Moreover, possible random movement across and between sediment depth layers of larval chironomid species may promote a rapid colonization in this gravel stream.

ABSTRACT A small forest catchment in Sweden is drained via a peatland. The mature spruce stand (108 years) was clearcut after which a younger stand (60 years) on the peatland was accidentally stormfelled the next year. The clearcutting causes nitrification in the upland. To maintain the nitrogen reduction function of the peatland, planting on mounds was practiced instead of the conventional fishbone drainage pattern. During the fourth and fifth years after the clearcutting the nitrogen flux from the upland to the peatland was 17 kg ha−1.a while only 7 kg left the peatland. While about 85% of the nitrogen entering the peatland was in the form of nitrate, the fraction of nitrate in the runoff was only 40%. The establishment of new forest stands on peatland soils by planting on mounds gives considerable environmental advantages as compared to conventional drainage. Both fluxes of nutrients and suspended matter are decreased. Spontaneous regeneration of the wetland spruce stand results in loss of about ten years of growth and a younger stand on the wetland than on the upland with the risk of the stormfelling being repeated after the upland forest has been harvested.

ABSTRACT The 137 km long Szigetköz side-arm system extends on the right side of the river Danube in Hungary and shows the unique characteristics of river, shore, riparian forest, and groundwater ecotones. The investigated three side arms are in different alluvial stages, their surface sediment is variable: sand, sandy mud, mud, mud covered with detritus. The composition, life forms, and cover of aquatic macrophyte stands are good describers of the different side arms. On the surface of the sediment, the habitats are numerous and varied, and linked to the vegetation and open water region. Crustacean communities of these habitats are very diverse, mosaic-form, and are in dynamic connection with each other mainly through the developing stages, and even through certain stenoecious species.

ABSTRACT This paper considers the increased interest in groundwater/surface water ecotones. That clearly appeared within the framework of the UNESCO/MAB and IHP projects on the role of land/inland water ecotones in landscape management and restoration. Groundwater/Surface water ecotones are transition zones, the limits between very contrasted systems. At different space and time scales they provide, favour, filter or stop exchanges and they can also modify interactions between ecosystems. This paper outlines the content and the structure of the book.

ABSTRACT Ground penetrating RADAR was used in an attempt to map sediment accumulation in active and abandoned beaver {Castor canadensis) ponds in northern Minnesota and to map buried paleochannels of the Flathead River floodplain in Montana. We attempted to map ice thickness, water depth, sediment depth, depth to parent material (bedrock or clay), thickness of soil horizons, organic deposits (peat), frost penetration, and depth to the water table in the beaver ponds. Ground penetrating RADAR successfully located some of the subsurface interfaces between these layers but water saturation and the high clay content of the soils interfered with the ground penetrating RADAR signal while the physical complexity of the subsurface hampered data interpretation. In Montana, paleochannels and water tables were located, but the stony nature of the substrate prevented immediate excavation for verification. In both Montana and Minnesota, success depended strongly on physical characteristics of the sites and specific interfaces. Generally, our efforts were only successful where the physical subsurface interfaces had abrupt, well defined boundaries, and where clay content was low.

ABSTRACT The Amboseli ecosystem consists of the basement plains, the lacustrine saline plains with fresh water swamps and the volcanic slopes of the Kilimanjaro. The area is well known for its large and varied population of wild herbivores, supporting a large tourist industry. The two major fresh spring zones sustaining some 20 km2 of swamps and an additional 16 km2 of wet areas chiefly covered by grass, belong to the relatively shallow part of a regional groundwater flow system in the volcanic complex. A 7.5 m rise of the groundwater table since the 1960s and the recent expansion of one of the swamps has caused concern. The rise cannot be explained by the available rainfall data and may be related to more frequent runoff, because of overgrazing, in the catchment feeding episodically the seasonal Lake Amboseli. In addition, tectonic movements may have increased the outflow of the the deeper diffuse part of the flow system.

The dynamics of the swamps have been studied. Available data suggest that no major changes are likely to affect the swamps in the near future. A good proportion of the annual recharge of the springs, about 14 % of the estimated rainfall, takes place in the Tanzanian part.

ABSTRACT Vertical and temporal distribution of paniculate organic matter (POM) in river bed sediments was observed in two different stations in the Morava River. Samples of river sediments from 0–70 cm depths were taken by inserting a steel cylinder with a special grab. The main type of organic matter found in bed sediments was fine particulate organic matter (FPOM < 1 mm). The organic matter had a variable distribution in the hyporheic zone. Generally, the concentration of organic matter was higher in the top 0–40 cm of sediment. The annual mean storage of buried organic matter (0–70 cm depth) was 5352.13 g AFDW.rn−3. The exchange of organic matter between surface sediments and deep river bed sediments is influenced mainly by flooding activity. The maximum storage of organic matter in the hyporheic zone appears in the spring when floods are decreasing.

ABSTRACT Faunal sampling was carried out in 1990–91 on three springs of a karstic system located at 15 km north-east of the city of Dijon (France) to investigate the filter effect of these outlets on the drifting population of the hypogean amphipod Niphargus virei. Results showed that, in places where limestones outcropped, the karstic spring ecotone did not modify the structure of the drifting population. In that case, faunal sampling of the springs during the floods was an effective method to study the dynamics of the population living in the aquifer. However, this method could not be applied in places where deep karstic ground-water circulated through water-saturated superficial deposits prior to emerge at the land surface. Indeed, in that case, the size frequency histograms of the drifting population of N. virei were characterised by abnormally low percentages of small size individuals and/or to a lesser extent by low percentages of large size individuals. These changes in the population structure were probably caused by two types of filters exerted by the karstic spring ecotone: 1) a mechanical filter which corresponded to the change of matrix between the deep karstified limestone aquifer and the shallow aquifer; 2) a biological filter probably due to the predation exerted by benthic invertebrates which have colonised the shallow aquifer.

ABSTRACT

Groundwater/surface water interactions are often characterised by hydrological and hydrochemical processes which result in complex abiotic and biotic gradients. Therefore a study was made of the hydrochemistry and ecohydrology of a groundwater discharge area in a low coastal area, lying in front of a higher sandy recharge area in the southwest of the Netherlands.

A hydrochemical facies analysis was applied to identify and map the major factors accounting for variations in hydrochemical processes. Research was concentrated in a relatively small fresh water upwelling zone in the discharge area, to obtain insight into the actual interrelationship between groundwater, surface water, aquatic ecology and human influence. During 1992 surface water samples and groundwater samples were taken along four regional transects. In the upwelling zone, sampling of shallow groundwater and surface water was combined with detailed mapping of aquatic vegetation. In total, 43 species were found and over 275 water samples were analysed in the laboratory. The two main water systems, the Brabantse Wai hydrosome and the polder hydrosome, are described by seven chemical watertypes, redox potential index, eutrophication potential index and calcite saturation index. The regionally derived maps of ground and surface water quality correspond fairly accurately. In the fresh water upwelling zone four types of aquatic vegetation (noda) have been discerned. Each nodum has distinct ecological amplitudes for alkalinity, pH and salinity of the surface water. These do not match general indicative values for the Netherlands, as described in literature. The hydrochemical characteristics of the ground and surface water in the upwelling zone deviate to a large extent. This points to an increasing contribution of polluted groundwater from a shallow groundwater flow system.…

ABSTRACT Interstitial animals were collected during spring, summer, and autumn from eight sampling sites along a Rocky Mountain river to examine small scale patterns of diversity, abundance, and faunal composition across the groundwater/surface water ecotone. At each site samples were taken from benthic habitats (superficial bed sediments), hyporheic habitats (underflow 30 cm below the bed surface), and phreatic habitats (30 cm below the water table of adjacent alluvial bars). Total taxa decreased markedly along the epigeanhypogean gradient. Crustaceans and insects (the majority of animals in all three habitats) progressively increased (Crustacea) or progressively declined (Insecta) in relative abundance along the epigean-hypogean gradient. Most of the 142 common taxa exhibited one of four types of distribution patterns along the gradient (hypogean, epigean, transitional, eurytopic). This study demonstrated a marked faunal gradient on a scale of meters across the groundwater/surface water ecotone. Faunal similarity coefficients (e.g., Jaccard) and detrended correspondence analysis of faunal distributions may provide comparative measures of ecotone permeability between physically contiguous interstitial habitats.

ABSTRACT Groundwater-surface water ecotones control hydraulic exchange between groundwater and surface water and, together with land-water ecotones, serve as a temporary or permanent sink of catchment-derived inorganic and organic matter. These factors and the chemistry of water entering an ecotone, determine the ecotone's effect on water quality One of the problems when studying ecotones is their high heterogeneity in space and time. The heterogeneity is caused by several thousand years of human impact, which has been exacerbated during the last century, and by local geology, surface water effects and various ecotonerelated processes (capillary-fringe effect, evapotranspiration, anti-clogging, clogging). The heterogeneity is measurable and at least partly predictable, and should be considered when preparing sampling strategies and evaluating data. Ecotones often function as filters of nutrients and particulate matter, thus improving the quality of water passing through them. The adsorption or buffering capacity of the ecotone, however, may be exhausted which may result in the enrichment of water by organic matter, dissolved metals etc. This ‘malfunctioning’ occurs often naturally as a result of decomposition of accumulated organic matter, but may also be due to the excessive leaching of fertilizers or other substances from upstream areas. Losses from catchments may be diminished by increasing the area and improving the function of the ecotones. The ecotone-oriented measures, however, must be combined with modified land use of the whole catchments if we want to use the landscape in a sustainable way.

ABSTRACT In order to better understand the structure of the surface-groundwater organismal assemblages (SGOA), the concept of global aquifer/river system (GARS) of Castany is recalled. The pattern of SGOAs emerges within different space and time scales. Examples of SGOAs and of the processes which form them are presented using case studies from the alluvial sediment fauna of the rivers Rhone, the Danube at Vienna, and the Lachein brook, in southern France. The structure of these assemblages depends on the boundary conditions of the groundwater system, mainly the hydrologic dynamics, and on the initiating conditions offered by the ecological tolerances of each species which contributes in the assemblages. The possible role of the macroorganisms in the functioning of the groundwater ecosystem is discussed. Their role appears less important than was thought earlier. Finally we emphasize the necessity of protecting the diversity of ecotonal assemblages. Scientific, cultural and practical arguments are presented.