			Home About us Contact

Hydrological Connectivity (hydrological + connectivity)

Distribution by Scientific Domains

Life Sciences	75%

Selected Abstracts

Hydrological connectivity of soil pipes determined by ground-penetrating radar tracer detection

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 4 2004
Joseph Holden
Abstract Soil pipes are common and important features of many catchments, particularly in semi-arid and humid areas, and can contribute a large proportion of runoff to river systems. They may also signi,cantly in,uence catchment sediment and solute yield. However, there are often problems in ,nding and de,ning soil pipe networks which are located deep below the surface. Ground-penetrating radar (GPR) has been used for non-destructive identi,cation and mapping of soil pipes in blanket peat catchments. While GPR can identify subsurface cavities, it cannot alone determine hydrological connectivity between one cavity and another. This paper presents results from an experiment to test the ability of GPR to establish hydrological connectivity between pipes through use of a tracer solution. Sodium chloride was injected into pipe cavities previously detected by the radar. The GPR was placed downslope of the injection points and positioned on the ground directly above detected soil pipes. The resultant radargrams showed signi,cant changes in re,ectance from some cavities and no change from others. Pipe waters were sampled in order to check the radar results. Changes in electrical conductivity of the pipe water could be detected by the GPR, without data post-processing, when background levels were increased by more than approximately twofold. It was thus possible to rapidly determine hydrological connectivity of soil pipes within dense pipe networks across hillslopes without ground disturbance. It was also possible to remotely measure travel times through pipe systems; the passing of the salt wave below the GPR produced an easily detectable signal on the radargram which required no post-processing. The technique should allow remote sensing of water sources and sinks for soil pipes below the surface. The improved understanding of ,owpath connectivity will be important for understanding water delivery, solutional and particulate denudation, and hydrological and geomorphological model development. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Hydrological connectivity in coastal inland systems: lessons from a Neotropical fish metacommunity

ECOLOGY OF FRESHWATER FISH, Issue 1 2010
P. H. M. De Macedo-Soares
de Macedo-Soares PHM, Petry AC, Farjalla VF, Caramaschi EP. Hydrological connectivity in coastal inland systems: lessons from a Neotropical fish metacommunity. Ecology of Freshwater Fish 2010: 19: 7,18. © 2009 John Wiley & Sons A/S Abstract,,, We assessed the influence of hydrological connectivity in structuring fish communities through seasonal samplings of environmental variables and fishes in a coastal lagoon and associated pools in the Restinga de Jurubatiba National Park, Brazil. Community structure attributes such as species richness, numerical density and biomass, Shannon,Wiener diversity index and evenness were compared between periods of the lowest and highest hydrological connectivity, while the environmental gradient and fish zonation were explored through ordination techniques. The greater hydrological connectivity established in the rainy season promoted the homogenisation of most environmental variables and fish species, which differed markedly from the arrangement observed in the dry season. Despite variation in fish species composition, community attributes showed non-significant differences between the dry and rainy seasons. The patterns of composition and numerical density in pools were strongly influenced by local factors, especially salinity, dissolved oxygen, total phosphorous concentration and water colour in the dry season, in addition to total nitrogen concentration and depth in the rainy season. Comparable to the role played by flood pulses in river-floodplain systems, the hydrological connectivity in these tropical coastal waterbodies seems to strongly influence fish community structure, and, therefore to determine regional biodiversity. [source]

Hydrological connectivity and microbiological fluxes in montane catchments: the role of seasonality and climatic variability

HYDROLOGICAL PROCESSES, Issue 9 2010
D. Tetzlaff
First page of article [source]

Understanding ,hot-spot' problems in catchments: the need for scale-sensitive measures and mechanisms to secure effective solutions for river management and conservation

AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue S1 2010
Malcolm Newson
Abstract 1.Regulatory progress in controlling point sources of chemical river pollution has progressively thrown the attention of public policy towards anthropogenic physical impacts, many of which are scaled to the catchment via the runoff/sediment system. At the same time, concern over diffuse chemical pollution has reinforced ,catchment consciousness': land-use and land-management planning and control must be considered to conserve or restore river ecosystem integrity. 2.The scientific, political and legal elements of this scale change are, however, complex and uncertain: ,myths' abound. Landscape-scale consideration of ,pressures' suggests an unequal distribution of regulatory costs and benefits and large uncertainties in the evidence from a ,land-use hydrology' and fluvial geomorphology perspective. 3.,Hydrological connectivity' brings together a number of knowledge themes about catchment spatial organization which facilitate applying mitigation measures to much smaller areas, helping to offset uncertainty and reduce costs. 4.Instead of blanket ,remedies', more practical use is needed of process evidence from hydrology and fluvial geomorphology; this tends to suggest that ,hot-spots' dominate risks and impacts of factors such as leaching, surface flow generation and silt entrainment. 5.Set in a realistic policy framework, from strategic spatial planning to grant-aided best practice, a ,catchment acupuncture' approach to measures provides a cost-effective contribution to improving ecological status and may also increase resilience to the impacts of climate change. 6.The European Union's Water Framework Directive (WFD) encourages ,joined-up thinking' on this issue but it remains to be seen whether spatial scales, structures and concepts already enshrined in the WFD and the relevant UK national policies for land use and nature conservation can be exploited to permit the much-needed practical uptake of this new riparianism. Copyright © 2010 John Wiley & Sons, Ltd. [source]

Morphodynamics of the exit of a cutoff meander: experimental findings from field and laboratory studies,

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 3 2010
J. Le Coz
Abstract The morphological evolution of the entrances and exits of abandoned river channels governs their hydrological connectivity. The study focusses on flow and sediment dynamics in the exit of a cutoff meander where the downstream entrance is still connected to the main channel, but the upstream entrance is closed. Two similar field and laboratory cases were investigated using innovative velocimetry techniques (acoustic Doppler profiling, image analysis). Laboratory experiments were conducted with a mobile-bed physical model of the Morava River (Slovakia). Field measurements were performed in the exit of the Port-Galland cutoff meander, Ain River (France). Both cases yielded consistent and complementary results from which a generic scheme for flow patterns and morphological evolution was derived. A simple analogy with flows in rectangular side cavities was used to explain the recirculating flow patterns which developed in the exit. A decelerating inflow deposits bedload in the downstream part of the cavity, while the upstream part is eroded by an accelerating outflow, leading to the retreat of the upstream bank. In the field, strong secondary currents were observed, especially in the inflow, which may enhance the scouring of the downstream corner of the cavity. Also, fine sediment deposits constituted a silt layer in a transitional zone, located between the mouth of the abandoned channel and the oxbow-lake within the cutoff meander. Attempts at morphological prediction should consider not only the flow and sediment conditions in the cavity, but also the dynamics of the main channel. Copyright © 2010 John Wiley & Sons, Ltd [source]

Hydrological connectivity of soil pipes determined by ground-penetrating radar tracer detection

Hydrological connectivity in coastal inland systems: lessons from a Neotropical fish metacommunity

Genetic diversity and migration patterns of the aquatic macrophyte Potamogeton malaianus in a potamo-lacustrine system

FRESHWATER BIOLOGY, Issue 6 2009
YUANYUAN CHEN
Summary 1.,Previously, the Yangtze River connected thousands of shallow lakes which together formed a potamo-lacustrine system capable of sustaining a rich variety of submerged macrophytes. 2.,Potamogeton malaianus is one of the dominant submerged macrophytes in many lakes of this area. Genetic variation and population structure of P. malaianus populations from ten lakes in the potamo-lacustrine system were assessed using inter-simple sequence repeat markers. 3.,Twelve primer combinations produced a total of 166 unambiguous bands of which 117 (70.5%) were polymorphic. Potamogeton malaianus exhibited a moderate level of population genetic diversity (PP = 70.5%, HE = 0.163 and I = 0.255), as compared with that of plants in the same habitat and range. The main factors responsible for this moderate value were the plant's mixed breeding system (both sexual and asexual) and the hydrological connectivity among habitats. 4.,F statistics, calculated using different approaches, consistently revealed a moderate genetic differentiation among populations, contributing about 20% of total genetic diversity. An estimate of gene flow (using FST) suggested that gene flow played a more important role than genetic drift in the current population genetic structure of P. malaianus (Nm = 1.131). 5.,The genetic diversity of P. malaianus did not increase downstream. A high level of linkage,disequilibrium at the whole population level suggested that metapopulation processes may affect genetic structure. The migration pattern of P. malaianus was best explained by a two-dimensional stepping stone model, indicating that bird-mediated dispersal could greatly influence gene movements among lakes. [source]

Influence of lateral gradients of hydrologic connectivity on trophic positions of fishes in the Upper Mississippi River

FRESHWATER BIOLOGY, Issue 3 2009
KATHERINE A. ROACH
Summary 1. Riverscapes consist of the main channel and lateral slackwater habitats along a gradient of hydrological connectivity from maximum connection in main channel habitats to minimum connection in backwaters. Spatiotemporal differences in water currents along this gradient produce dynamic habitat conditions that influence species diversity, population densities and trophic interactions of fishes. 2. We examined the importance of lateral connectivity gradients for food web dynamics in the Upper Mississippi River during spring (high flow, moderately low temperatures) and summer (low flow, higher temperatures). We used literature information and gut contents analyses to determine feeding guilds and stable isotope analysis to estimate mean trophic position of local fish assemblages. During June and August 2006, we collected over 1000 tissue samples from four habitats (main channel, secondary channels, tertiary channels and backwaters) distributed within four hydrologic connectivity gradients. 3. Mean trophic position differed among feeding guilds and seasons, with highest values in spring. Mean trophic position of fish assemblages, variability in trophic position and food chain length (maximum trophic position) of the two dominant piscivore species (Micropterus salmoides and M. dolomieu) in both seasons were significantly associated with habitat along the lateral connectivity gradient. Food chain length peaked in tertiary channels in both seasons, probably due to higher species diversity of prey at these habitats. We infer that food chain length and trophic position of fish assemblages were lower in backwater habitats in the summer mainly because of the use of alternative food sources in these habitats. 4. A greater number of conspecifics exhibited significant among-habitat variation in trophic position during the summer, indicating that low river stages can constrain fish movements in the Upper Mississippi River. 5. Results of this study should provide a better understanding of the fundamental structure of large river ecosystems and an improved basis for river rehabilitation and management through knowledge of the importance of lateral complexity in rivers. [source]

Abundance and microhabitats of freshwater sponges (Spongillidae) in a Danubean floodplain in Austria

FRESHWATER BIOLOGY, Issue 6 2007
IRIS DRÖSCHER
Summary 1. This study examined the abundance and distribution of freshwater sponges (Spongillidae) at 32 sites in a floodplain on the Danube within the ,Donau-Auen' National Park east of Vienna, Austria. Ranked from abundant to rare, the species inventory comprised Ephydatia fluviatilis, Spongilla lacustris, Ephydatia mülleri, Eunapius fragilis and Trochospongilla horrida. 2. The presence of hard substratum was essential for the growth of sponges. Timber stands near the water and drifting dead wood increased the abundance of E. fragilis, E. fluviatilis and E. mülleri, whereas stony substrata were important for S. lacustris. A small fraction of E. fluviatilis was collected from macrophytes (Phragmites). 3. Based on the area colonised, the abundance of S. lacustris, E. fragilis and E. fluviatilis was highest (94.2,100% of the total) in floodplain waters where hydrological connectivity with the Danube was low (0,6 days year,1), whereas E. mülleri and T. horrida made up 20.3,35.9% of the total at sites connected for up to 179 days year,1. Moreover, the area colonised by T. horrida at a current velocity >0.20 m s,1 was larger than in the remaining species. Sites with E. mülleri and T. horrida had a higher silicon concentration (0.9 mg L,1) than sites where the remaining three species were collected (0.4,0.6 mg L,1). 4. In most species, the length of macroscleres (the larger spicules) was positively correlated with conductivity and negatively with pH. With respect to aberrant macroscleres, hooks were observed most frequently, whereas the proportion of centrotylotes (ie with the one on more globular swellings along the spicule) was lowest. 5. Freshwater sponges have a great deal of potential as bioindicators and restoration measures that improve floodplain connectivity will favour rare species, such as E. mülleri and T. horrida, while impairing others (e.g. E. fragilis, S. lacustris and E. fluviatilis). [source]

Ecological effects of perturbation by drought in flowing waters

FRESHWATER BIOLOGY, Issue 7 2003
P. S. Lake
SUMMARY 1Knowledge of the ecology of droughts in flowing waters is scattered and fragmentary, with much of the available information being gathered opportunistically. Studies on intermittent and arid-zone streams have provided most of the information. 2Drought in streams may be viewed as a disturbance in which water inflow, river flow and water availability fall to extremely low levels for extended periods of time. As an ecological perturbation, there is the disturbance of drought and the responses of the biota to the drought. 3Droughts can either be periodic, seasonal or supra-seasonal events. The types of disturbance for seasonal droughts are presses and for supra-seasonal droughts, ramps. 4In droughts, hydrological connectivity is disrupted. Such disruption range from flow reduction to complete loss of surface water and connectivity. The longitudinal patterns along streams as to where flow ceases and drying up occurs differs between streams. Three patterns are outlined: ,downstream drying', ,headwater drying' and ,mid-reach drying'. 5There are both direct and indirect effects of drought on stream ecosystems. Marked direct effects include loss of water, loss of habitat for aquatic organisms and loss of stream connectivity. Indirect effects include the deterioration of water quality, alteration of food resources, and changes in the strength and structure of interspecific interactions. 6Droughts have marked effects on the densities and size- or age-structure of populations, on community composition and diversity, and on ecosystem processes. 7Organisms can resist the effects of drought by the use of refugia. Survival in refugia may strongly influence the capacity of the biota to recover from droughts once they break. 8Recovery by biota varies markedly between seasonal and supra-seasonal droughts. Faunal recovery from seasonal droughts follows predictable sequences, whilst recovery from supra-seasonal droughts varies from one case to another and may be marked by dense populations of transient species and the depletion of biota that normally occur in the streams. 9The restoration of streams must include the provision of drought refugia and the inclusion of drought in the long-term flow regime. [source]

Allochthonous and autochthonous particulate organic matter in floodplains of the River Danube: the importance of hydrological connectivity

FRESHWATER BIOLOGY, Issue 2 2003
Thomas Hein
SUMMARY 1.,The elemental composition, the proportion of living organic carbon and the carbon stable isotope signatures of particulate organic matter (POM) were determined in a large river floodplain system in order to elucidate the major carbon sources in relation to the hydrological conditions over a 13-month period. 2.,Two floodplain segments and the main channel of the River Danube downstream of Vienna (Austria), were compared on the basis of discharge and water age estimations. The more dynamic floodplain was connected to the main channel for 46% of the study period and drained up to 12% of total discharge at high water. 3.,The mean C : N ratio and ,13C signature of the POM increased from the floodplain site that was more isolated from the river (6.6; ,33,) to the main channel (8.4; ,25,). At the dynamic floodplain site, the C : N ratio and the ,13C signature of the POM increased with hydrological connectivity (expressed as water age). 4.,Only during flood events (4% frequency of occurrence), a considerable input of riverine POM was observed. This input was indicated by a C : N ratio of the POM pool of more than 10, the amount of detrital carbon (>80% of the total POM pool) and a ,13C signature of POM of more than ,25, in the dynamic floodplain. 5.,Plankton derived carbon, indicated by C : N ratios less than eight and ,13C values lower than ,25,, dominated the particulate organic carbon (POC) pool at both floodplain sites, emphasising the importance of local (autochthonous) production. Phytoplankton was the major plankton compartment at the dynamic site, with highest biomasses at medium water ages. 6.,At the dynamic floodplain site, the Danube Restoration Project has enhanced the duration of upstream surface connection with the main channel from 4 to 46% frequency of occurrence. Therefore, the export of living POC to the main channel is now established during phases of maximum phytoplankton production and doubled the estimated total export of non-refractory POM compared with prerestoration conditions. [source]

Floodplains of a regulated southern alpine river (Brenno, Switzerland): ecological assessment and conservation options

AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 6 2002
M. Brunke
Abstract 1.The fifth-order southern alpine Brenno River and its floodplains are severely impaired by embankments, water abstractions and the construction of dams for hydropower generation. The river's annual mean discharge is reduced to 27% of the natural flow and the number of small (50,100 m3 s,1) and medium-sized (101,150 m3 s,1) floods is reduced significantly. 2.Lateral hydrological connectivity has decreased strongly as a result of the flow regulation, whereas the significance of vertical connectivity has increased. The remnants of the middle and lower floodplains still contain springbrooks, ponds, and intermittently connected channels, which are all sustained by emerging groundwater. 3.Aquatic floodplain habitats can be classified partially by faunal composition. The lotic/lentic gradient appears to be a dominant compound factor structuring invertebrate assemblages when considering all aquatic habitats. The exfiltration of groundwater in conjunction with a reduced lateral connectivity enables the occurrence of many stenotopic species. 4.A comparison of present floodplains with those shown on historical maps shows that the fluvial landscape has changed markedly. The proportions of functional floodplain units characterized by autogenic succession and trends to late successional stages (i.e. senescence) have increased. 5.Floodplains of the Brenno river are still considered to represent important ecological areas and they are protected by law. Whilst the legislative protection of floodplains is the basis for conservation, this does not include the restoration of driving hydrological processes. An annual release of small- and medium-sized floods could generate a diversity of disturbances, thereby promoting rejuvenation and counteracting senescence. 6.Alternative conservation options that circumvent ongoing contracts of water use, though generally promising, are limited because of the operation of hydropower schemes. At present the exfiltrations of groundwater mitigate the impacts of flow regulation on the ecological integrity of the floodplains. Copyright © 2002 John Wiley & Sons, Ltd. [source]