Changes In Hydrological Conditions Research Articles

Introduction to the special issue on the impact of climate change on water in the UK

There is widespread, if sometimes tacit, agreement that action is needed to anticipate and adapt to future changes in hydrological conditions that have consequences for water supply (e.g. Charlton and Arnell, 2011; Dessai and Hulme, 2007), floods (e.g. Prudhomme et al., 2010; Thorne et al., 2007) and management and protection of the water environment (e.g. Ormerod, 2009; Wilby et al., 2010). However, practical adaptation actions seem scarce: Charlton and Arnell (2011: 247) observe, in an assessment of UK water supply plans, that ‘there is an air of ambivalence towards the impacts [of climate change]’ and that in many cases ‘climate change simply seems to disappear from the important discussions in the options appraisals’. The UK Adaptation SubCommittee, part of the statutory Climate Change Committee, finds that ‘current levels of investment . . . will not keep pace with the increasing risks of flooding’ (ASC, 2012: 80) and that ‘suggested measures to increase [water] supply and reduce demand . . . only meet a low and midrange level of climate risk’ (p. 81). So what prevents or slows progress on climate change adaptation in the water sector? Fankhauser et al. (1999) argue that anticipatory adaptation requires foresight and planning, which is improved by reliable information on climate change and its impacts. Communities may be best placed to understand their own exposure and vulnerability to climate change, but need the support of researchers and scientists to help them understand the changing risk (Smit and Wandel, 2006). Moser and Ekstrom (2010) view a lack of resources, including information and technical resources, as one of the common barriers to adaptation, although they caution that providing more science resources will not necessarily lead to more action unless resources are also found for the necessary adaptation actions themselves. While good information about the possible impact of climate change will not, on its own, make adaptation happen, it seems that a lack of appropriate information may act as a significant barrier to effective adaptation. This special issue addresses this possible barrier to climate change adaptation: the availability of reliable, clear information about the possible impacts of climate change on hydrology and the

Forest Reproductive Material and Conservation of Forest Genetic Resources in Croatia

Conservation of genetic diversity of forest tree species represents the foundation for sustainable forest management and preservation of natural structure of forest stands in Croatia. Diversity of geographical regions in Croatia has generated various ecological conditions and thus diverse forest communities which are directly affected by habitat degradation, various anthropogenic effects like pollution of air and water, excessive use of certain more valuable species of forest trees and by the increasing impact of global climatic changes. The need for conservation of genetic diversity is related to the species pertaining to social broadleaves—the prevailing species in terms of economic utilization as Pedunculate Oak (Quercus robur), Sessile Oak (Quercus petraea) and Common Beech (Fagus sylvatica). Among the conifers Silver Fir (Abies alba) is the most endangered species, with more than 70% of its population being seriously damaged. Other native coniferous species must be preserved from a decrease in genetic diversity as well. Conservation of the noble broadleaves should encompass a larger number of species from various genera (Fraxinus, Alnus, Ulmus, Prunus, Juglans, Castanea, Sorbus, Acer, Malus, Pyrus, Tilia). These are partially endangered because of their exposure to different pests and diseases, as well as by permanent exploitation due to their technical value. Changes in hydrological conditions of rivers have led difficulties in regeneration of the riparian forests and decreased the genetic variability of European Black and White Poplar in their habitats (Populus nigra, P. alba). In Croatia’s Adriatic coastal areas, there is a need for conservation of genetic resources of Dalmatian Black Pine (P. nigra ssp. dalmatica) and Mediterranean Oaks (Quercus ilex, Quercus pubescens). Conservation of genetic diversity of various forest tree species is conducted within the programmes that include in situ and ex situ methods with ensuring quality forest reproductive materials. In Croatia, a total of 125 seed stands have been selected, covering a total area of 3885.53 ha. The ex situ method is implemented by establishment of a total of 50 plots (clonal seed orchards, provenances and progeny trials, clonal archives), covering 114.85 ha.

Impacts of land use changes on hydrological components and macroinvertebrate distributions in the Poyang lake area

AbstractLand use and land cover changes are important issues globally resulting in changing hydrological and ecological conditions. In addition to field sampling and measurements, we applied a model cascade comprising an ecohydrological model and a species distribution model. We developed five land use scenarios (three deforestation and two afforestation scenarios) for our Chinese study basin in the Poyang lake area. In detail, we assessed the impact of land use changes on the hydrologic regime and stream macroinvertebrate distributions for the most likely deforestation scenario.Simulated deforestation scenarios result in higher streamflow and surface runoff compared with the base model. The spatial distribution of stream macroinvertebrates, a group of organisms well known as water quality indicators, was modelled to describe the effect of the changing environmental conditions on the freshwater ecosystem. For the deforestation scenario, species richness was reduced, and the occurrence of the stonefly Togoperla sp. decreased considerably. Copyright © 2014 John Wiley & Sons, Ltd.

Navigating financial and supply reliability tradeoffs in regional drought management portfolios

AbstractRising development costs and growing concerns over environmental impacts have led many communities to explore more diversified water management strategies. These “portfolio”‐style approaches integrate existing supply infrastructure with other options such as conservation measures or water transfers. Diversified water supply portfolios have been shown to reduce the capacity and costs required to meet demand, while also providing greater adaptability to changing hydrologic conditions. However, this additional flexibility can also cause unexpected reductions in revenue (from conservation) or increased costs (from transfers). The resulting financial instability can act as a substantial disincentive to utilities seeking to implement more innovative water management techniques. This study seeks to design portfolios that employ financial tools (e.g., contingency funds and index insurance) to reduce fluctuations in revenues and costs, allowing these strategies to achieve improved performance without sacrificing financial stability. This analysis is applied to the development of coordinated regional supply portfolios in the “Research Triangle” region of North Carolina, an area comprising four rapidly growing municipalities. The actions of each independent utility become interconnected when shared infrastructure is utilized to enable interutility transfers, requiring the evaluation of regional tradeoffs in up to five performance and financial objectives. Diversified strategies introduce significant tradeoffs between achieving reliability goals and introducing burdensome variability in annual revenues and/or costs. Financial mitigation tools can mitigate the impacts of this variability, allowing for an alternative suite of improved solutions. This analysis provides a general template for utilities seeking to navigate the tradeoffs associated with more flexible, portfolio‐style management approaches.

Influence of river channel morphology and bank characteristics on water surface boundary delineation using high‐resolution passive remote sensing and template matching

ABSTRACTAccurate mapping of water surface boundaries in rivers is an important step for monitoring water stages, estimating discharge, flood extent, and geomorphic response to changing hydrologic conditions, and assessing riverine habitat. Nonetheless, it is a challenging task in spatially and spectrally heterogeneous river environments, commonly characterized by high spatiotemporal variations in morphology, bed material, and bank cover. In this study, we investigate the influence of channel morphology and bank characteristics on the delineation of water surface boundaries in rivers using high spatial resolution passive remote sensing and a template‐matching (object‐based) algorithm, and compare its efficacy with that of Support Vector Machine (SVM) (pixel‐based) algorithm. We perform a detailed quantitative evaluation of boundary‐delineation accuracy using spatially explicit error maps in tandem with the spatial maps of geomorphic and bank classes. Results show that template matching is more successful than SVM in delineating water surface boundaries in river sections with spatially challenging geomorphic landforms (e.g. sediment bar structures, partially submerged sediment deposits) and shallow water conditions. However, overall delineation accuracy by SVM is higher than that of template matching (without iterative hierarchical learning). Vegetation and water indices, especially when combined with texture information, improve the accuracy of template matching, for example, in river sections with overhanging trees and shadows – the two most problematic conditions in water surface boundary delineation. By identifying the influence of channel morphology and bank characteristics on water surface boundary mapping, this study helps determine river sections with higher uncertainty in delineation. In turn, the most suitable methods and data sets can be selectively utilized to improve geomorphic/hydraulic characterization. The methodology developed here can also be applied to similar studies on other geomorphic landforms including floodplains, wetlands, lakes, and coastlines. Copyright © 2014 John Wiley & Sons, Ltd.

Littoral landforms and pedosedimentary sequences indicating late Holocene lake-level changes in northern central Europe — A case study from northeastern Germany

A multidisciplinary study was carried out at Lake Großer Fürstenseer See (LFS) in order to explore the potential of littoral sediments, palaeosols and landforms as indicators of historical lake-level changes. This research was initiated to investigate the extent to which lakes in northern central Europe responded hydrologically to climatic and land-use changes in the last millennium. Specific landforms investigated comprise lake terraces, beach ridges, local basins/peatlands and dunes, revealing a wealth of sedimentary sub-environments at the lakeshore. Eleven sections were recorded with subsequent sedimentological–pedological, geochronological (OSL, 14C) and palaeobotanical (pollen, macro remains) analyses. Most of the pedosedimentary littoral sequences show a succession of basal glacial sand, intermediate palaeosols and lacustrine sand on top. A broader number of (semi-)terrestrial buried palaeosols along the lakeshore were systematically identified and analysed, providing evidence for changing hydrological conditions during the late Holocene. Additional historical data from the last centuries (e.g. maps, aerial photos, public records) allow the lake-levels reconstructed from geoarchives to be connected with modern gauging data. All local data sources available enable a tracing of lake level changes of the LFS during the last millennium, comprising periods of relatively low (c. 1200AD, 2000s AD) and relatively high water levels (c. 1250–1450AD, c. 1780AD, 1980s AD). The amplitude of lake-level changes during the last c. 1000years amounts to c. 3m, so that the fluctuations of the last 30years recorded by lake-level monitoring only reflect a small amount of the potential variability. Regional climate and local land-use history suggest that the Medieval lake-level dynamics of LFS were primarily governed by climate and secondarily influenced by human impact on the drainage system. At present the lake level is additionally influenced by the impact of highly water-consuming pine plantations in the catchment area. The regional significance of the local development at LFS can be demonstrated by comparison with other regional and supra-regional lake-level data. The present study underlines the potential of a closer examination of the littoral zone for lake-level reconstructions with high altitudinal precision.

Characterization of groundwater and surface water mixing in a semiconfined karst aquifer using time‐lapse electrical resistivity tomography

AbstractGroundwater flow in karst includes exchange of water between large fractures, conduits, and the surrounding porous matrix, which impacts both water quality and quantity. Electrical resistivity tomography combined with end‐member mixing analysis (EMMA) and numerical flow and transport modeling was used to study mixing of karst conduit and matrix waters to understand spatial and temporal patterns of mixing during high flow and base flow conditions. To our knowledge, this is the first time EMMA and synthetic geophysical simulations have been combined. Here we interpret an 8 week time‐lapse electrical resistivity data set to assess groundwater‐surface mixing. We simulate flow between the karst conduits and the porous matrix to determine fractions of water recharged to conduits that has mixed with groundwater stored in the pore space of the matrix using a flow and transport model in a synthetic time‐lapse resistivity inversion. Comparing the field and synthetic inversions, our results enable us to estimate exchange dynamics, spatial mixing, and flow conditions. Results showed that mixing occurred at a volumetric flux of 56 m3/d with a dispersivity around 1.69 m during the geophysical experiment. For these conditions, it was determined that conduit water composition ranged from 75% groundwater during base flow conditions to less than 50% groundwater in high flow conditions. Though subject to some uncertainties, the time‐lapse inversion process provides a means to predict changing hydrologic conditions, leading to mixing of surface water and ground water and thus changes to water quantity and quality, as well as potential for water‐rock reactions, in a semiconfined, sink‐rise system.

Population resources of an endangered species Salix lapponum L. in Polesie Lubelskie Region (eastern Poland)

This research, carried out in the years 2011–2013, aimed to evaluate <em>Salix lapponum</em> stands in the peat bogs of Polesie Lubelskie Region as well as to determine the condition of the population and the changes that have taken place since the 1950’s. An inventory carried out in 25 stands of <em>S. lapponum </em>known from the literature shows that the number of its stands has decreased by 80% in Polesie Lubelskie Region. In all the confirmed locations, a decrease in population numbers was also found in relation to the data known from the literature since the 1950’s. In the majority of the population locations that were considered to be extinct, there were no significant changes in habitat conditions, and ecological succession and changes in hydrological conditions could have been the cause of habitat changes only at a few sites. In the light of the study, the preservation of the <em>S. lapponum </em>population in Polesie Lubelskie seems to be impossible if appropriate active conservation measures are not taken immediately. Because area-based conservation, which covers most of the habitats of the studied species, does not bring the expected results, the possibility of <em>ex situ</em> conservation and enlargement of the populations existing in the natural environment in peat bog ecosystems in Polesie should be explored.

Ecological Responses of a Large Shallow Lake (Okeechobee, Florida) to Climate Change and Potential Future Hydrologic Regimes

We considered how Lake Okeechobee, a large shallow lake in Florida, USA, might respond to altered hydrology associated with climate change scenarios in 2060. Water budgets and stage hydrographs were provided from the South Florida Water Management Model, a regional hydrologic model used to develop plans for Everglades restoration. Future scenarios include a 10% increase or decrease in rainfall (RF) and a calculated increase in evapotranspiration (ET), which is based on a 1.5 °C rise in temperature. Increasing RF and ET had counter-balancing effects on the water budget and when changing concurrently did not affect hydrology. In contrast, when RF decreased while ET increased, this resulted in a large change in hydrology. The surface elevation of the lake dropped by more than 2 m under this scenario compared to a future base condition, and extreme low elevation persisted for multiple years. In this declining RF/increasing ET scenario, the littoral and near-shore zones, areas that support emergent and submerged plants, were dry 55% of the time compared to less than 4% of the time in the future base run. There also were times when elevation increased as much as 3 m after intense RF events. Overall, these changes in hydrologic conditions would dramatically alter ecosystem services. Uncertainty about responses is highest at the pelagic-littoral interface, in regard to whether an extremely shallow lake could support submerged vascular plants, which are critical to the recreational fishery and for migratory birds. Along with improved regional climate modeling, research in that interface zone is needed to guide the adaptive process of Everglades restoration.

The diversity and longitudinal changes of zooplankton in the lower course of a large, regulated European river (the lower Vistula River, Poland)

AbstractThe diversity and longitudinal variation of zooplankton in the lower Vistula River were analyzed. Samples were taken from 40 stations located along a 272-km long section of the lower river course. During the study the unique technique of taking samples from “the same water” was used. The zooplankton community was dominated by rotifers and nauplii — larval stages of copepods. The most abundant species were: Brachionus angularis, Brachionus calyciflorus and Brachionus budapestiensis. The zooplankton species diversity in the main channel of the lower Vistula River was similar to other large European rivers; however, its abundance was lower. The diversity, abundance and biomass of potamoplankton steadily decreased downstream. This could be related both to scarcity of storage zones for potamoplankton development in the river due to the extensive regulation processes, and changes in hydrological conditions of the main channel (by the straightening of riverbed) where the samples were collected.

Ein besseres Verständnis des Lurbach-Karstsystems durch ein konzeptionelles Niederschlags-Abfluss-Modell

A parsimonious lumped-parameter rainfall-runoff model was tested to determine if it could be used to appro- priately represent a karst hydrological system, the Lurbach system in Austria. Simulated and observed hydrographs of spring discharge were favorably simulated for a time pe- riod of seven years in spite of the small number of free parameters. Following this period the four year discharge records were only reproducible using strongly different pa- rameter values. Results suggest during this period overflow to neighboring catchments and the capacity of production or routing store have strongly increased. This relationship is also observed in tracer test and baseflow recession data sets and is attributed to the likely redistributions of sedi- ments. Such dynamic processes are rarely accounted for in rainfall-runoff models, and may cause severe prediction un- certainties. However, in the Lurbach system a parsimonious hydrological model was used successfully to characterize changes in hydrological conditions.

The effects of sediment supply and concentrations on the formation timescale of martian deltas

We used a comprehensive 2-D and 3-D basin-filling morphodynamical model to explore the effects of changing hydrologic and sedimentary conditions on delta formation under martian conditions. Spatial and temporal deposition of sediment into a body of standing water was simulated using event-based time stepping (e.g. seasons). River and sediment discharge were calculated using the Darcy–Weisbach equation for width- and depth-averaged flow velocity and well-known and tested terrestrial sediment transport predictors modified for application to martian flows. A range in sediment grain sizes was determined from both landers and orbiting spacecraft data in order to include grain sizes typical of Mars and yet representative of the martian deltas. Several different scenarios of seasonal river discharge and sediment supply were explored to encompass a range of possible formation conditions.With the ability to track sediment as it is transported throughout the basin, it is apparent that non-negligible amounts of material are moved beyond the delta-forming region. This loss of sediment increased with river discharge, increasing the gap between the calculated and modeled formation timescales. These results have important implications for the formation timescales of the deltas and the small number of identifiable deltas on Mars today. Formation timescales that consider only the supply of sediment to the system and do not take into account factors affecting deposition and delta formation are underestimates of the actual amount of time needed to form the deposits. The lack of identifiable deltas in many paleolakes is likely a result of significant sediment transport beyond the channel mouth, causing the expected delta deposit to be draped throughout the basin.

Depositional history and archaeology of the central Lake Mungo lunette, Willandra Lakes, southeast Australia

Lake Mungo, presently a dry lake in the semi-arid zone of southeastern Australia, preserves a unique record of human settlement and past environmental change within the transverse lunette that built up on its downwind margin. The lunette is >30 km long and the variable morphology along its length suggests spatial variability in deposition over time. Consequently this presents differential potential for the preservation of past activity traces of different ages along the lunette. Earlier work at Lake Mungo focused primarily on the southern section of the lunette, where two ritual burials of considerable antiquity were found. Here we describe the depositional history of the central section of the Lake Mungo lunette, together with the first single grain optically stimulated luminescence (OSL) chronology of the full stratigraphic sequence and of three hearths. We thereby lay the foundation for systematic investigation of the distribution of archaeological traces through the sedimentary record.The older depositional units (Lower and Upper Mungo) were deposited ca. 50–40 ka and ∼34 ka respectively, and are substantially thinner in the central section of the lunette compared with the south. By contrast, the overlying unit of interbedded sands and clayey sands (Arumpo–Zanci units), deposited ca. 25–14 ka, is markedly thicker and dominates the stratigraphic sequence in the central portion of the lunette. Although the sequence broadly reflects previous models of the lunette's depositional history and changing hydrological conditions, our results indicate spatially variable deposition of sediments, possibly as a result of changes in prevailing wind regimes. Archaeological traces are exposed in all stratigraphic units deposited after ca. 50 ka, including sediments deposited after the final lake drying ca. 15 ka, indicating human occupation of the area under a range of palaeoenvironmental conditions. Dating and stratigraphical examination of individual hearth features demonstrates that even within individual stratigraphic units, human occupation persisted under variable conditions. Mid-Holocene occupation of the area following the final lake retreat took place during a period of relatively humid climate.

Changes in phytoplankton biomass due to diversion of an inflow into the Urayama Reservoir

The three-dimensional hydrodynamic Estuary, Lake and Coastal Ocean Model (ELCOM) coupled with the ecological Computational Aquatic Ecosystem DYnamics Model (CAEDYM) was applied to Urayama Reservoir in order to examine the effect of an inflow bypass on the water quality in the reservoir. The bypass system functions by intaking water from upstream of the reservoir and transferring it to the reservoir selective withdrawal tower in order to avoid turbid-water withdrawal. The model was calibrated using data measured in 2009. Simulated results of water temperature, dissolved oxygen, turbidity, nutrients and four groups of phytoplankton (cyanobacteria, diatoms, chlorophytes and cryptophytes) were in good agreement with field measurements. Some bypass operational scenarios and model parameter test scenarios were performed. The results showed that the bypass operation altered the nutrient load and in-reservoir concentrations as well as the heat budget, which changed the water temperature, dissolved oxygen and other water quality parameters, including chlorophyll a (Chla) concentration in the reservoir. Detailed examination of the growth of phytoplankton revealed that cyanobacteria were most affected by the bypass operation because of the interaction between the change of hydrological conditions and the buoyancy control of cells. The results suggested that the operation of the bypass system was useful in decreasing inflow nutrient loads as well as decreasing the transport of the algal biomass from upstream to the dam wall, which generally helped to decrease the magnitude of algal biomass near the offtake region of the reservoir.

System Dynamics Modeling of Nitrogen Removal in a Stormwater Infiltration Basin with Biosorption‐Activated Media

Stormwater infiltration basins, one of the typical stormwater best management practices, are commonly constructed for surface water pollution control, flood mitigation, and groundwater restoration in rural or residential areas. These basins have soils with better infiltration capacity than the native soil; however, the ever-increasing contribution of nutrients to groundwater from stormwater due to urban expansion makes existing infiltration basins unable to meet groundwater quality criteria related to environmental sustainability and public health. This issue requires retrofitting current infiltration basins for flood control as well as nutrient control before the stormwater enters the groundwater. An existing stormwater infiltration basin in north-central Florida was selected, retrofitted, and monitored to identify subsurface physiochemical and biological processes during 2007-2010 to investigate nutrient control processes. This implementation in the nexus of contaminant hydrology and ecological engineering adopted amended soil layers packed with biosorption activated media (BAM; tire crumb, silt, clay, and sand) to perform nutrient removal in a partitioned forebay using a berm. This study presents an infiltration basin-nitrogen removal (IBNR) model, a system dynamics model that simulates nitrogen cycling in this BAM-based stormwater infiltration basin with respect to changing hydrologic conditions and varying dissolved nitrogen concentrations. Modeling outputs of IBNR indicate that denitrification is the biogeochemical indicator in the BAM layer that accounted for a loss of about one third of the total dissolved nitrogen mass input.

Hydrologic profiling for greenhouse gas effluxes from natural grasslands in the prairie pothole region of Canada

AbstractThe prairie pothole physiographic region of North America is likely to be affected by climate change, and it is important to establish its baseline global warming potential as a basis for assessing global change effects. This study estimated the hydrologic effects on soil greenhouse gas efflux during the growing season along hydrologic profiles within natural prairie potholes ranging from the southern to northern limits of the prairie pothole region within central Canada. Soil moisture was found to be an important driver of differences in soil efflux along the hydrologic profiles and along the south‐to‐north gradient. The position of peak cumulative soil efflux varied along the hydrologic profile, with the N2O peak occurring at the backslope, the CO2 peaks at footslope and toeslope, and the CH4 peaks at toeslope and surface waters. When cumulative soil efflux was converted to global warming potential (Mg CO2 eq), the largest values were restricted to the narrow land‐water interface in the south but expanded to a broader area of the hillslope in the north. CO2 was the major (> 95%) contributor to global warming potential. Omitting hydrologic controls on greenhouse gas fluxes from estimates of global warming potential led to substantial underestimates of the contributions of N2O and CH4. Arid regions in the south had smaller global warming potential than wetter regions in the north. If future climate projections for a warmer, drier climate in this region are realized, global warming potential from soil greenhouse gas fluxes will be smaller in this landscape, because the changing hydrologic conditions should result in a reduction of global warming potential from land surfaces, even as global warming potential from surface waters increases.

Fish (Spinibarbus hollandi) dynamics in relation to changing hydrological conditions: physical modelling, individual‐based numerical modelling, and case study

ABSTRACTThe paper reports the development of an individual‐based fish dynamics model, of which the key components are the rules for the movement of individual fish and the definition of the habitat suitability. The distribution of the fish mainly depends on the flow conditions (velocity, depth, substrate) and life cycle of the fish. A major contribution is the refinement of the rules for fish movement, based on laboratory experiments under volitional swimming conditions, which also provided the ranges of preferential velocities and substrate size for the target fish, Spinibarbus hollandi. Moreover, they provided data on the fish trajectories and distribution patterns that allowed for validation of the movement rules. The validated fish dynamics model was applied to investigate the effect of discharge increase during the dry season by means of reservoir operation in the Lijiang River, which was the subject of field investigations in 2007 and 2008. The model results indicated that reservoir operation leads to an increase of fish biomass. According to the fish movement rules, fish cannot always escape from riverbed regions that dry during decreasing discharge events, which causes them to be trapped and die. Reservoir operation decreases the area of dry riverbed and reduces the travel distance for fish to escape from dry regions. Critical advantages of the individual fish model over global models defined on the population level are that they can account for the time that the fish needs to reach a region of suitable habitat and for the spatial pattern of suitable zones and their connectivity. Copyright © 2013 John Wiley & Sons, Ltd.

Hydrological processes behind annual and decadal-scale variations in the water quality of runoff in Finnish catchments with acid sulfate soils

Summary In this study we assess long- and short term temporal variations in the impact of acid sulfate (a.s.) soils on river water quality. We demonstrate how such variations depend on changes in hydrological conditions driven by land use, meteorological variations and potential changes in climate with important implications on mitigation strategies, water ecology and utilization of water resources. Quality of river water discharging into the Larsmo-Oja Lake in Midwestern Finland was studied by using long term water data collected during 1963–2009. Acid sulfate soils are extremely acidic soils (pH

Trajectories of Vegetation Response to Water Management in Taylor Slough, Everglades National Park, Florida

Ecosystem management practices that modify the major drivers and stressors of an ecosystem often lead to changes in plant community composition. This paper exam- ines how closely the trajectory of vegetation change in seasonally-flooded wetlands tracks management-induced al- terations in hydrology and soil characteristics. We used trajectory analysis, a multivariate method designed to test hypotheses about rates and directions of community change, to examine vegetation shifts in response to changes in water management practices within the Taylor Slough basin of Everglades National Park. We summarized vegetation data by non-metric multidimensional scaling ordination, and ex- amined the time trajectory of each site along environmental vectors representing hydrology and soil phosphorus gradi- ents. In the Taylor Slough basin, vegetation change trajec- tories closely followed the hydrologic changes caused by the operation of water pumps and detention ponds adjacent to the canals. We also observed a shift in vegetation com- position along a vector of increasing soil phosphorus, which suggests the need for implementing measures to avoid P- enrichment in southern Everglades marl prairies. This study indicates that shifts in vegetation composition in response to changes in hydrologic conditions and associated parameters may be detected through trajectory analysis, thereby provid- ing feedback for adaptive management of wetland ecosystems.

Why does the Late Pleistocene archaeology of Sahul look so different from that of the Americas?

Lake Mungo, presently a dry lake in the semi-arid zone of southeastern Australia, preserves a unique record of human settlement and past environmental change within the transverse lunette that built up on its downwind margin. The lunette is >30 km long and the variable morphology along its length suggests spatial variability in deposition over time. Consequently this presents differential potential for the preservation of past activity traces of different ages along the lunette. Earlier work at Lake Mungo focused primarily on the southern section of the lunette, where two ritual burials of considerable antiquity were found. Here we describe the depositional history of the central section of the Lake Mungo lunette, together with the first single grain optically stimulated luminescence (OSL) chronology of the full stratigraphic sequence and of three hearths. We thereby lay the foundation for systematic investigation of the distribution of archaeological traces through the sedimentary record.The older depositional units (Lower and Upper Mungo) were deposited ca. 50–40 ka and ∼34 ka respectively, and are substantially thinner in the central section of the lunette compared with the south. By contrast, the overlying unit of interbedded sands and clayey sands (Arumpo–Zanci units), deposited ca. 25–14 ka, is markedly thicker and dominates the stratigraphic sequence in the central portion of the lunette. Although the sequence broadly reflects previous models of the lunette's depositional history and changing hydrological conditions, our results indicate spatially variable deposition of sediments, possibly as a result of changes in prevailing wind regimes. Archaeological traces are exposed in all stratigraphic units deposited after ca. 50 ka, including sediments deposited after the final lake drying ca. 15 ka, indicating human occupation of the area under a range of palaeoenvironmental conditions. Dating and stratigraphical examination of individual hearth features demonstrates that even within individual stratigraphic units, human occupation persisted under variable conditions. Mid-Holocene occupation of the area following the final lake retreat took place during a period of relatively humid climate.