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Hydrological Change (hydrological + change)
Selected AbstractsMultiple stressors and regime shifts in shallow aquatic ecosystems in antipodean landscapesFRESHWATER BIOLOGY, Issue 2010JENNY DAVIS Summary 1. Changes in land management (land use and land cover) and water management (including extraction of ground water and diversion of surface waters for irrigation) driven by increases in agricultural production and urban expansion (and fundamentally by population growth) have created multiple stressors on global freshwater ecosystems that we can no longer ignore. 2. The development and testing of conceptual ecological models that examine the impact of stressors on aquatic ecosystems, and recognise that responses may be nonlinear, is now essential for identifying critical processes and predicting changes, particularly the possibility of catastrophic regime shifts or ,ecological surprises'. 3. Models depicting gradual ecological change and three types of regime shift (simple thresholds, hysteresis and irreversible changes) were examined in the context of shallow inland aquatic ecosystems (wetlands, shallow lakes and temporary river pools) in southwestern Australia subject to multiple anthropogenic impacts (hydrological change, eutrophication, salinisation and acidification). 4. Changes in hydrological processes, particularly the balance between groundwater-dominated versus surface water-dominated inputs and a change from seasonal to permanent water regimes appeared to be the major drivers influencing ecological regime change and the impacts of eutrophication and acidification (in urban systems) and salinisation and acidification (in agricultural systems). 5. In the absence of hydrological change, urban wetlands undergoing eutrophication and agricultural wetlands experiencing salinisation appeared to fit threshold models. Models encompassing alternative regimes and hysteresis appeared to be applicable where a change from a seasonal to permanent hydrological regime had occurred. 6. Irreversible ecological change has potentially occurred in agricultural landscapes because the external economic driver, agricultural productivity, persists independently of the impact on aquatic ecosystems. 7. Thematic implications: multiple stressors can create multiple thresholds that may act in a hierarchical fashion in shallow, lentic systems. The resulting regime shifts may follow different models and trajectories of recovery. Challenges for ecosystem managers and researchers include determining how close a system may be to critical thresholds and which processes are essential to maintaining or restoring the system. This requires an understanding of both external drivers and internal ecosystem dynamics, and the interactions between them, at appropriate spatial and temporal scales. [source] Decadal change in wetland,woodland boundaries during the late 20th century reflects climatic trendsGLOBAL CHANGE BIOLOGY, Issue 8 2010DAVID A. KEITH Abstract Wetlands are important and restricted habitats for dependent biota and play vital roles in landscape function, hydrology and carbon sequestration. They are also likely to be one of the most sensitive components of the terrestrial biosphere to global climate change. An understanding of relationships between wetland persistence and climate is imperative for predicting, mitigating and adapting to the impacts of future climate change on wetland extent and function. We investigated whether mire wetlands had contracted, expanded or remained stable during 1960,2000. We chose a study area encompassing a regional climatic gradient in southeastern Australia, specifically to avoid confounding effects of water extraction on wetland hydrology and extent. We first characterized trends in climate by examining data from local weather stations, which showed a slight increase in precipitation and marked decline in pan evaporation over the relevant period. Remote sensing of vegetation boundaries showed a marked lateral expansion of mires during 1961,1998, and a corresponding contraction of woodland. The spatial patterns in vegetation change were consistent with the regional climatic gradient and showed a weaker co-relationship to fire history. Resource exploitation, wildland fires and autogenic mire development failed to explain the observed expansion of mire vegetation in the absence of climate change. We therefore conclude that the extent of mire wetlands is likely to be sensitive to variation in climatic moisture over decadal time scales. Late 20th-century trends in climatic moisture may be related primarily to reduced irradiance and/or reduced wind speeds. In the 21st century, however, net climatic moisture in this region is projected to decline. As mires are apparently sensitive to hydrological change, we anticipate lateral contraction of mire boundaries in coming decades as projected climatic drying eventuates. This raises concerns about the future hydrological functions, carbon storage capacity and unique biodiversity of these important ecosystems. [source] Mountain Hydroclimatology and Snow Seasonality,Perspectives on climate impacts, snow seasonality and hydrological change in mountain environmentsHYDROLOGICAL PROCESSES, Issue 7 2009Carmen de Jong First page of article [source] Instream Flow Science For Sustainable River Management,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 5 2009Geoffrey E Petts Abstract:, Concerns for water resources have inspired research developments to determine the ecological effects of water withdrawals from rivers and flow regulation below dams, and to advance tools for determining the flows required to sustain healthy riverine ecosystems. This paper reviews the advances of this environmental flows science over the past 30 years since the introduction of the Instream Flow Incremental Methodology. Its central component, Physical HABitat SIMulation, has had a global impact, internationalizing the e-flows agenda and promoting new science. A global imperative to set e-flows, including an emerging trend to set standards at the regional scale, has led to developments of hydrological and hydraulic approaches but expert judgment remains a critical element of the complex decision-making process around water allocations. It is widely accepted that river ecosystems are dependent upon the natural variability of flow (the flow regime) that is typical of each hydro-climatic region and upon the range of habitats found within each channel type within each region. But as the sophistication of physical (hydrological and hydraulic) models has advanced emerging biological evidence to support those assumptions has been limited. Empirical studies have been important to validate instream flow recommendations but they have not generated transferable relationships because of the complex nature of biological responses to hydrological change that must be evaluated over decadal time-scales. New models are needed to incorporate our evolving knowledge of climate cycles and morphological sequences of channel development but most importantly we need long-term research involving both physical scientists and biologists to develop new models of population dynamics that will advance the biological basis for 21st Century e-flow science. [source] Short-term variation in the ecological status of a Mediterranean coastal lagoon (NE Iberian Peninsula) after a man-made change of hydrological regimeAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 7 2008Anna Badosa Abstract 1.The Ter Vell (NE Iberian Peninsula) is a eutrophic coastal lagoon that has been mostly flooded by excessive irrigation water during recent decades. During 2001 and 2002 the lagoon was subject to several water management actions, the main consequence of which was a change in the hydrological regime due to drastically reduced irrigation water inputs to the lagoon. 2.In order to comply with the Water Framework Directive, all the management actions in an ecosystem should be focused on protecting and, where necessary, improving its ecological status. 3.The aims of this study were (1) to analyse whether the hydrological change caused by management actions have affected the ecological status of the lagoon, and (2) to discuss the suitability of several physicochemical and biological indicators for the assessment of the ecological status in this kind of coastal ecosystem. 4.After the change in the hydrological regime, a general improvement of the ecological status was observed mainly as a result of the significant decrease in the nitrogen Trophic State Index and in the abundance of rotifer indicative of eutrophy, and in turn by the significant increase in the water quality index QAELS, based on crustaceans and insect assemblages. 5.Contradictory results emerged with regard to some of the indicators used. After the hydrological change, the increase in the phosphorus Trophic State Index was related with the fact that Mediterranean confined coastal ecosystems are typically P-enriched. In contrast with general assumptions, low diversity and richness of the zooplankton and the dominance of a few species have been related with an improvement of the ecological status after the hydrological change, when freshwater inputs were reduced and the lagoon became more confined. Copyright © 2008 John Wiley & Sons, Ltd. [source] Climate and human induced hydrological change since AD 800 in an ombrotrophic mire in Pomerania (N Poland) tracked by testate amoebae, macro-fossils, pollen and tree rings of pineBOREAS, Issue 2 2009MARIUSZ LAMENTOWICZ This high-resolution, multiproxy, palaeoenvironmental study of the S,owi,skie B,ota raised bog in N Poland, 10 km from the Baltic Sea, covering the last 1200 years reveals different aspects of environmental change in a range of spatial scales from local to regional. Testate amoebae allowed quantitative reconstruction of the local water table using a transfer function based on a training set from N and W Poland. Special attention is paid to the testate amoeba Arcella discoides, which responds to rapid water-table fluctuations more than to average surface wetness. Macrofossils supported by local pollen tracked the local vegetation dynamics caused by local human impact and disturbance, including nutrients. Regional pollen showed human-induced landscape change outside the bog. Tree rings of Pinus sylvestris reflected the history of tree establishment and desiccation of the bog. Strong correlations between DCA axes 1 of regional pollen, of macrofossils and of testate amoebae, and a testate-amoebae-based water-table reconstruction that excludes A. discoides, indicate that changes on all spatial scales are linked, which is explained by a strong hydrologic connection between bog and surroundings. The combination of proxies shows that groundwater levels were modified by both human impact and climate change. [source] Modelling rising groundwater and the impacts of salinization on terrestrial remnant vegetation in the Blackwood River BasinECOLOGICAL MANAGEMENT & RESTORATION, Issue 1 2004Geoff Hodgson Summary Southwest Western Australia has a particularly rich biodiversity. Clearing for agriculture has greatly reduced the extent of native vegetation in wheatbelt catchments; it also set into train hydrogeological and hydrological changes that are still evolving toward a new equilibrium. With those changes come widespread land salinization that presents a further risk to remnant vegetation, particularly in low portions of the landscape. The equilibrium position of shallow groundwater was modelled for the Blackwood Catchment, and used to assess the extent of risk to a set of remnant vegetation classes. A total of 37 368 ha of remnant vegetation was identified to be at risk of salinization when hydrological equilibrium is reached. Further hydrological modelling assessed the rate of development of these watertables (and hence the rate of impact on remnants), as well as the potential to protect remnants by controlling groundwater recharge with revegetation. The results demonstrate that only high levels of revegetation are effective at protecting high value remnants in the longer term. The timing of events is dependant on the accuracy of estimating recharge. [source] Evaluating local hydrological modelling by temporal gravity observations and a gravimetric three-dimensional modelGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2010M. Naujoks SUMMARY An approach for the evaluation of local hydrological modelling is presented: the deployment of temporal terrestrial gravity measurements and gravimetric 3-D modelling in addition to hydrological point observations. Of particular interest is to what extent such information can be used to improve the understanding of hydrological process dynamics and to evaluate hydrological models. Because temporal gravity data contain integral information about hydrological mass changes they can be considered as a valuable augmentation to traditional hydrological observations. On the other hand, hydrological effects need to be eliminated from high-quality gravity time-series because they interfere with small geodynamic signals. In areas with hilly topography and/or inhomogeneous subsoil, a simple reduction based on hydrological point measurements is usually not sufficient. For such situations, the underlying hydrological processes in the soil and the disaggregated bedrock need to be considered in their spatial and temporal dynamics to allow the development of a more sophisticated reduction. Regarding these issues interdisciplinary research has been carried out in the surroundings of the Geodynamic Observatory Moxa, Germany. At Moxa, hydrologically induced gravity variations of several 10 nm s,2 are observed by the stationarily operating superconducting gravimeter and by spatially distributed and repeated high-precision measurements with transportable relative instruments. In addition, hydrological parameters are monitored which serve as input for a local hydrological catchment model for the area of about 2 km2 around the observatory. From this model, spatial hydrological variations are gained in hourly time steps and included as density changes of the subsoil in a well-constrained gravimetric 3-D model to derive temporal modelled gravity variations. The gravity variations obtained from this combined modelling correspond very well to the observed hydrological gravity changes for both, short period and seasonal signals. From the modelling the amplitude of the impact on gravity of hydrological changes occurring in different distances to the gravimeter location can be inferred. Possible modifications on the local hydrological model are discussed to further improve the quality of the model. Furthermore, a successful reduction of local hydrological effects in the superconducting gravimeter data is developed. After this reduction global seasonal fluctuations are unmasked which are in correspondence to GRACE observations and to global hydrological models. [source] A record of Lateglacial and early Holocene environmental and ecological change from southwestern Connecticut, USA,JOURNAL OF QUATERNARY SCIENCE, Issue 6 2009W. Wyatt Oswald Abstract Analyses of a sediment core from Highstead Swamp in southwestern Connecticut, USA, reveal Lateglacial and early Holocene ecological and hydrological changes. Lateglacial pollen assemblages are dominated by Picea and Pinus subg. Pinus, and the onset of the Younger Dryas (YD) cold interval is evidenced by higher abundance of Abies and Alnus viridis subsp. crispa. As climate warmed at the end of the YD, Picea and Abies declined and Pinus strobus became the dominant upland tree species. A shift from lacustrine sediment to organic peat at the YD,Holocene boundary suggests that the lake that existed in the basin during the Lateglacial interval developed into a swamp in response to reduced effective moisture. A change in wetland vegetation from Myrica gale to Alnus incana subsp. rugosa and Sphagnum is consistent with this interpretation of environmental changes at the beginning of the Holocene. Copyright © 2009 John Wiley & Sons, Ltd. [source] A new European testate amoebae transfer function for palaeohydrological reconstruction on ombrotrophic peatlands,JOURNAL OF QUATERNARY SCIENCE, Issue 3 2007Dan J. Charman Abstract Proxy climate data can be obtained from reconstructions of hydrological changes on ombrotrophic (rain-fed) peatlands using biological indicators, such as testate amoebae. Reconstructions are based on transfer functions, relating modern assemblage composition to water table and moisture content, applied to fossil sequences. Existing transfer functions in Europe and elsewhere are limited geographically and there are often problems with missing or poor analogues. This paper presents a new palaeohydrological transfer function based on sampling raised mires from across Europe. Relationships between assemblages and hydrological variables are described using ordination analyses. Transfer functions are developed for depth to water table (n,=,119) and moisture content (n,=,132) with root mean squared errors (RMSEP) of 5.6,cm and 2.7% respectively. Both transfer functions have an r2 of 0.71, based on ,leave one out' cross-validation. Comparisons with an existing transfer function for Britain show that the European transfer function performs well in inferring measured water tables in Britain but that the British data cannot be used to infer water tables for other European sites with confidence. Several of the key missing and poor analogue taxa problems encountered in previous transfer functions are solved. The new transfer function will be an important tool in developing peat-based palaeoclimatic reconstructions for European sites. Copyright © 2006 John Wiley & Sons, Ltd. [source] Climatic oscillations in central Italy during the Last Glacial,Holocene transition: the record from Lake Accesa,JOURNAL OF QUATERNARY SCIENCE, Issue 4 2006Michel Magny Abstract This paper presents an event stratigraphy based on data documenting the history of vegetation cover, lake-level changes and fire frequency, as well as volcanic eruptions, over the Last Glacial,early Holocene transition from a terrestrial sediment sequence recovered at Lake Accesa in Tuscany (north-central Italy). On the basis of an age,depth model inferred from 13 radiocarbon dates and six tephra horizons, the Oldest Dryas,Bølling warming event was dated to ca. 14,560,cal.,yr,BP and the Younger Dryas event to ca. 12,700,11,650,cal.,yr,BP. Four sub-millennial scale cooling phases were recognised from pollen data at ca. 14,300,14,200, 13,900,13,700, 13,400,13,100 and 11,350,11,150,cal.,yr,BP. The last three may be Mediterranean equivalents to the Older Dryas (GI-1d), Intra-Allerød (GI-1b) and Preboreal Oscillation (PBO) cooling events defined from the GRIP ice-core and indicate strong climatic linkages between the North Atlantic and Mediterranean areas during the last Termination. The first may correspond to Intra-Bølling cold oscillations registered by various palaeoclimatic records in the North Atlantic region. The lake-level record shows that the sub-millennial scale climatic oscillations which punctuated the last deglaciation were associated in central Italy with different successive patterns of hydrological changes from the Bølling warming to the 8.2,ka cold reversal. Copyright © 2006 John Wiley & Sons, Ltd. [source] The hydrological impacts and sustainability of wetland drainage cultivation in Illubabor, EthiopiaLAND DEGRADATION AND DEVELOPMENT, Issue 1 2002A. B. Dixon Abstract Wetlands are critical resources in the highlands of southwest Ethiopia, where they perform numerous environmental functions and provide a range of benefits for local communities. In recent years, however, an increase in the drainage and cultivation of these areas and reports of wetland degradation have raised concerns over the sustainability of wetland agriculture. This paper presents the results of a study in which groundwater levels were monitored in a series of wetlands undergoing different stages of drainage and cultivation, to establish the hydrological changes taking place as a consequence. The results suggest that drainage and cultivation induce extreme spatial and temporal variations in the wetland watertable. This is linked in part to structural and chemical changes in the wetland soil which affect hydraulic conductivity. Statistical analysis of this variability revealed the existence of wetland subunits, exhibiting specific hydrological behaviour, which may reflect the influence of current and past land use. Although degradation of these wetlands does occur, many wetland users are aware of their impacts and have developed practices which, in most cases, prevent overdrainage to the extent that the wetlands cannot support agriculture. In this respect, it is argued that wetland use remains hydrologically sustainable, although this ultimately rests upon the ability of communities to continue to develop and apply their indigenous wetland management practices under rapidly changing environmental, socio-economic and political conditions. Copyright © 2002 John Wiley & Sons, Ltd. [source] | ||||||||||||||||