Showing papers in "Ecohydrology in 2011"

Inter-disciplinary perspectives on processes in the hyporheic zone

Abstract: The interface between groundwater and surface water within riverine/riparian ecosystems--the hyporheic zone (HZ)--is experiencing a rapid growth of research interest from a range of scientific disciplines, often with different perspectives. The majority of the multi-disciplinary research aims to elucidate HZ process dynamics and their importance for surface water and groundwater ecohydrology and biogeochemical cycling. This paper presents a critical inter-disciplinary review of recent advances of research centred on the HZ and highlights the current state of knowledge regarding hydrological, biogeochemical and ecohydrological process understanding. The spatial and temporal variability of surface water and groundwater exchange (hyporheic exchange flows), biogeochemical cycling and heat exchange (thermal regime) are considered in relation to both experimental measurements and modelling of these phenomena. We explore how this knowledge has helped to increase our understanding of HZ ecohydrology, and particularly its invertebrate community, the processing of organic matter, trophic cascading and ecosystem engineering by macrophytes and other organisms across a range of spatial and temporal scales. In addition to providing a detailed review of HZ functions, we present an inter-disciplinary perspective on how to advance and integrate HZ process understanding across traditional discipline boundaries. We therefore attempt to highlight knowledge gaps and research needs within the individual disciplines and demonstrate how innovations and advances in research, made within traditional subject-specific boundaries (e.g. hydrology, biochemistry and ecology), can be used to enhance inter-disciplinary scientific progress by cross-system comparisons and fostering of greater dialogue between scientific disciplines.

A general predictive model for estimating monthly ecosystem evapotranspiration

Abstract: Accurately quantifying evapotranspiration (ET) is essential for modelling regional-scale ecosystem water balances. This study assembled an ET data set estimated from eddy flux and sapflow measurements for 13 ecosystems across a large climatic and management gradient from the United States, China, and Australia. Our objectives were to determine the relationships among monthly measured actual ET (ET), calculated FAO-56 grass reference ET (ETo), measured precipitation (P), and leaf area index (LAI)—one associated key parameter of ecosystem structure. Results showed that the growing season ET from wet forests was generally higher than ETo while those from grasslands or woodlands in the arid and semi-arid regions were lower than ETo. Second, growing season ET was found to be converged to within ± 10% of P for most of the ecosystems examined. Therefore, our study suggested that soil water storage in the nongrowing season was important in influencing ET and water yield during the growing season. Lastly, monthly LAI, P, and ETo together explained about 85% of the variability of monthly ET. We concluded that the three variables LAI, P, and ETo, which were increasingly available from remote sensing products and weather station networks, could be used for estimating monthly regional ET dynamics with a reasonable accuracy. Such an empirical model has the potential to project the effects of climate and land management on water resources and carbon sequestration when integrated with ecosystem models. Copyright © 2010 John Wiley & Sons, Ltd.

Evapotranspiration partitioning in semiarid shrubland ecosystems: A two-site evaluation of soil moisture control on transpiration

Abstract: Vegetation of dryland ecosystems is sensitive to precipitation pulses. Future climate scenarios suggest that the frequency and magnitude of precipitation events will change. How much and to what extent will these changes impact the hydrological cycle in creosotebush (Larrea tridentata) shrublands that dominate the three North American hot deserts? In this study, we examine the partitioning of precipitation inputs into bare soil evaporation (E) and transpiration (T) within creosotebush ecosystems at sites characterized by bimodal precipitation regimes: the Santa Rita Experimental Range (SRER) and the Walnut Gulch Experimental Watershed (WGEW). At both sites, during summer 2008, we measured evapotranspiration (ET) using eddy covariance, whole plant T using the heat-balance sap flow, and soil moisture at several depths. During the dry period preceding the summer monsoon, both ET and soil moisture were very low. With the onset of summer rains, E dominated ET; shrub transpiration did not respond to increases in soil moisture for approximately 3 more weeks. A series of large precipitation events increased moisture at deeper soil layers, and triggered T. Overall, ET was largely correlated to moisture levels in shallow soil layers typical of dryland ecosystems dominated by dry conditions, high evaporative demand, and poor soil infiltration. Under the current precipitation regime, characterized by many small storms and few large storms, soil moisture is low with most precipitation inputs lost as E. However, if climatic changes lead to less frequent but larger precipitation events, dryland communities could experience shifts in the partitioning of ET affecting the hydrologic budget of the ecosystem. Copyright © 2010 John Wiley & Sons, Ltd.

Thermopeaking in Alpine streams: event characterization and time scales

Abstract: The present study provides a detailed quantification of the "thermopeaking" phenomenon, which consists of sharp intermittent alterations of stream thermal regime associated with hydropeaking releases from hydroelectricity plants. The study refers to the Noce River (Northern Italy), a typical hydropower-regulated Alpine stream, where water stored in highaltitude reservoirs often has a different temperature compared to the receiving bodies. The analysis is based on a river water temperature dataset that has been continuously collected for one year at 30’ intervals in four different sections along the Noce River. A suitable threshold-based procedure is developed to quantify the main characteristics of thermopeaking, which is responsible for thermal alterations at different scales. The application of Wavelet Transform allows to separately investigate thermal regime alterations at sub-daily, daily and weekly scales. Moreover, at a seasonal scale, patterns of "warm" and "cold" thermopeaking can be clearly detected and quantified. The study highlights the relevance of investigating a variety of short-term alterations at multiple time scales for a better quantitative understanding of the complexity that characterises the river thermal regime. The outcomes of the analysis raise important interdisciplinary research questions concerning the effects of thermopeaking and of the related short- and medium-term effects on biological communities, which have been rather poorly investigated in ecological studies.

Quantifying structural and physiological controls on variation in canopy transpiration among planted pine and hardwood species in the southern Appalachians

Abstract: Recent studies have shown that planted pine stands exhibit higher evapotranspiration (ET) and are more sensitive to climatic conditions compared with hardwood stands. Whether this is due to management and stand effects, biological effects or their interaction is poorly understood. We estimated growing season canopy- and sap flux-scaled leaf-level transpiration (Ec and EL) in five major overstory species over 3 years. Four hardwood species, Liriodendron tulipifera, Carya spp., Quercus rubra and Quercus prinus, were measured in an unmanaged watershed. Pinus strobus was measured in an adjacent planted pine watershed. We hypothesized that (1) species would differ in EL and stomatal conductance (GS), and their relationship with vapour pressure deficit (D); and (2) differences in growing season ET between the stands would result primarily from the differences in interception (Ei). Growing season ET in the planted pine stand exceeded hardwood ET by twofold during all 3 years. Transpiration and Ei contributed similarly to the ET difference, suggesting that physiological differences were equally as important as structural factors to the overall difference in ET. Among species, mean EL and GS differed significantly, as did their relationship with D. EL and GS of oaks and hickories were least responsive to changing D, while L. tulipifera and P. strobus were most responsive. This species-level understanding of variation in EL and GS and their interactions with climatic driving variables has important implications for predicting watershed-level responses to stand management, species invasion and loss, and climate variability. Published in 2010. This article is a US Government work and is in the public domain in the USA.

Forest ecohydrological research in the 21st century: what are the critical needs?

Abstract: Modern ecohydrologic science will be critical for providing the best information to policy makers and society to address water resource challenges in the 21st century. Implicitly, ecohydrology involves understanding both the functional interactions among vegetation, soils, and hydrologic processes at multiple scales and the linkages among upland, riparian, and aquatic components. In this paper, we review historical and contemporary ecohydrologic science, focusing on watershed structure and function and the threats to watershed structure and function. Climate change, land use change, and invasive species are among the most critical contemporary issues that affect water quantity and quality, and a mechanistic understanding of watershed ecosystem structure and function is required to understand their impacts on water quantity and quality. Economic and social values of ecosystem services such as water supply from forested watersheds must be quantified in future research, as land use decisions that impact ecohydrologic function are driven by the interplay among economic, social, political, and biological constraints. Future forest ecohydrological research should focus on: (1) understanding watershed responses to climate change and variability, (2) understanding watershed responses to losses of native species or additions of non-native species, (3) developing integrated models that capitalize on long-term data, (4) linking ecohydrologic processes across scales, and (5) managing forested watersheds to adapt to climate change. We stress that this new ecohydrology research must also be integrated with socio-economic disciplines. Published in 2011. This article is a US Government work and is in the public domain in the USA.

Extreme flow variability and the ‘boom and bust’ ecology of fish in arid-zone floodplain rivers: a case history with implications for environmental flows, conservation and management

Abstract: Floodplain rivers in arid and semi-arid regions may be the most threatened of all river systems because water resource developments typically dampen their most distinctive characteristics-extreme flow variability and 'boom and bust' ecological dynamics This article shows how one of the world's most variable arid-zone river systems-Cooper Creek in Australia's Lake Eyre Basin-functions and how it supports its unique fish assemblage and productive fisheries The ecological roles of drought refugia, channel flows and flooding are reviewed in relation to fish persistence and losses, life history strategies, movement potential, food web processes and production levels Comparisons are drawn with other floodplain rivers and fisheries to draw out common understandings and universal principles for conservation and management of arid-zone rivers and their fish resources Ecological implications of hydrologic alterations and land-based activities are presented to highlight the importance of maintaining the hydrologic, geomorphic, sedimentary and biogeochemical processes of arid-zone river systems Preservation or restoration of natural flow intermittency, sequential flood pulses, complex habitat mosaics, connectivity and identification of the environmental flow requirements for highly valued species and processes are key scientific principles for the management of arid-zone floodplain rivers

Ecohydrologic impact of reduced stomatal conductance in forests exposed to elevated CO2

Abstract: Plants influence ecosystem water balance through their physiological, phenological, and biophysical responses to environmental conditions, and their sensitivity to climate change could alter the ecohydrology of future forests. Here we use a combination of measurements, synthesis of existing literature, and modelling to address the consequences of climate change on ecohydrologic processes in forests, especially response to elevated CO2 (eCO2). Data assessed from five free-air CO2 enrichment (FACE) sites reveal that eCO2-reduced stomatal conductance led to declines in canopy transpiration and stand water use in three closed-canopy forest sites. The other two sites were in the early stages of stand development, where a strong eCO2-stimulation of canopy leaf area led to enhanced stand water use. In the sweetgum FACE experiment in Oak Ridge, Tennessee (USA), eCO2 reduced seasonal transpiration by 10–16%. Intra-annual peak measured fluxes in transpiration ranged from 4·0–5·5 mm day−1, depending on year. The Biome-BGC model simulated similar rates of transpiration at this site, including the relative reductions in response to eCO2. As a result, simulations predict ∼75 mm average annual increase in potential water yield in response to eCO2. The direct effect of eCO2 on forest water balance through reductions in transpiration could be considerable, especially following canopy closure and development of maximal leaf area index. Complementary, indirect effects of eCO2 include potential increases in root or leaf litter and soil organic matter, shifts in root distribution, and altered patterns of water extraction. Copyright © 2010 John Wiley & Sons, Ltd.

Annual runoff and evapotranspiration of forestlands and non‐forestlands in selected basins of the Loess Plateau of China

Abstract: Large-scale forestation has been undertaken over decades principally to control the serious soil erosion in the Loess Plateau of China. A quantitative assessment of the hydrological effects of forestation, especially on basin water yield, is critical for the sustainable forestry development within this dry region. In this study, we constructed the multi-annual water balances to estimate the respective grand average of annual evapotranspiration (ET) and runoff for forestlands and non-forestlands of 57 basins. The overall annual runoff and corresponding runoff/precipitation ratio were low, with a mean of 33 mm (7%) ranging from 10 (2%) to 56 mm (15%). Taking the grand average of annual precipitation of 463 mm for all basins, the corresponding grand averages of annual ET and runoff were 447 and 16 mm for forestlands, 424 and 39 mm for non-forestlands, respectively. Thus, the corresponding ratios of annual ET and runoff to precipitation were 91Ð7 and 8Ð3% for non-forestlands, 96Ð6 and 3Ð4% for forestlands, respectively. Although the absolute difference in grand average of annual runoff was only 23 mm, it represents a large difference in relative terms, as it equates up to 58% of annual runoff from non-forestlands. We argue that the large-scale forestation may have serious consequences for water management and sustainable development in the dry region of NW China because of a runoff reduction. This study highlights the importance of quantifying the ET of forests and other land uses and to examine how land cover change may affect the water balances in an arid environment. Copyright  2011 John Wiley & Sons, Ltd.

Socio‐ecohydrology and the urban water challenge

Abstract: Urban water systems are highly engineered. However, hydrology and ecology are still closely linked in semi-arid urban ecosystems in which surface characteristics, vegetation, and water flows are all highly transformed. Although these systems are human-dominated, there are many uncertainties in the water budgets of semi-arid cities, because evapotranspiration, runoff, groundwater recharge, and leakage are poorly constrained. Decision-making, governance, and socioeconomic factors play important roles in determining urban hydrologic budgets. We offer a framework to integrate these factors in studies that combine biophysical and social dimensions of the urban water system using the example of western US cities, which are facing critical issues in water supply and demand, and which can benefit from a more comprehensive understanding of the factors that determine water consumption, distribution and availability. Because of the severity of the water crisis in the western US, and the biophysical, institutional, and cultural barriers to developing and implementing new water management practices, this region provides useful lessons for addressing water challenges in other regions. Copyright © 2011 John Wiley & Sons, Ltd.

Effects of Spring Drought on Carbon Sequestration, Evapotranspiration and Water Use Efficiency in the Songnen Meadow Steppe in Northeast China.

Abstract: Global climate change projections suggest an increasing frequency of droughts and extreme rain events in the steppes of the Eurasian region. Using the eddy covariance method, we measured carbon and water balances of a meadow steppe ecosystem in Northeast China during 2 years which had contrasting precipitation patterns in spring seasons in 2007 and 2008. The meadow steppe sequestrated only 64Ð2 gC m 2 year 1 in 2007 compared to 160Ð5 gC m 2 year 1 in 2008, due to a severe spring drought in 2007. The 2007 spring drought resulted in a dramatic reduction of leaf area index (LAI) and aboveground net primary productivity (ANPP). However, the meadow steppe still acted as a carbon sink in 2007. The strength of the sink was much greater than that in the typical steppes in Central Mongolia and Inner Mongolia. Spring drought also caused a reduction of plant transpiration (Tr) and total ecosystem evapotranspiration (ET). However, the suppression of ET in 2007 was relatively small in comparison to gross ecosystem productivity (GEP) reduction. Thus, ecosystem water use efficiency (WEU) (GEP/ET) in 2007 was reduced to 5Ð0 gCO2 kg 1 H2O or 75% of that of 2008. We concluded that spring drought detrimentally impacted meadow steppe ecosystem by reducing leaf areas, biomass, GEP, WUE and associated increases in soil evaporation (Es) that might aggravate soil salinization of the Songnen Plain. Copyright  2011 John Wiley & Sons, Ltd.

The role of groundwater pumping and drought in shaping ecological futures for stream fishes in a dryland river basin of the western Great Plains, USA

Abstract: Across the western Great Plains of North America, groundwater pumping for irrigated agriculture is depleting regional aquifers that sustain streamflow for native fishes. We investigated linkages between groundwater pumping from the High Plains Aquifer and stream fish habitat loss at multiple spatial scales during spring and summer 2005–2007 in the Arikaree River, eastern Colorado, USA. Monthly low-altitude flights showed that flowing reaches were reduced from about 65 to ⩽15 km by late summer, and long permanently dry segments in the lower basin prevent recolonization. Drying occurred rapidly during summer within three 6·4-km river segments, and patterns in habitat connectivity varied among segments owing to hydraulic conductivity. Most refuge pool habitats dried completely or lost more than half their volume, disconnecting from other pools by late summer. On the basis of these empirical habitat data, and historical groundwater and streamflow data, we constructed a MODFLOW model to predict how groundwater pumping will affect water table levels and fish habitat under three future scenarios. Under the most conservative scenario, we predicted that only 57% of refuge pools will remain in 35 years (2045), nearly all isolated in a 1·7-km fragment of river. A water balance model indicated that maintaining current water table levels and refuge pools for fishes would require a 75% reduction in groundwater pumping, which is not economically or politically feasible. Given widespread streamflow declines, ecological futures are bleak for stream fishes in the western Great Plains, and managers will be challenged to conserve native fishes under current groundwater pumping regimes. Copyright © 2010 John Wiley & Sons, Ltd.

Aeolian and fluvial processes in dryland regions: the need for integrated studies

Abstract: Aeolian and fluvial processes play a fundamental role in dryland regions of the world and have important environmental and ecological consequences from local to global scales. Although both processes operate over similar spatial and temporal scales and are likely strongly coupled in many dryland systems, aeolian and fluvial processes have traditionally been studied separately, making it difficult to assess their relative importance in drylands, as well as their potential for synergistic interaction. Land degradation by accelerated wind and water erosion is a major problem throughout the world's drylands, and although recent studies suggest that these processes likely interact across broad spatial and temporal scales to amplify the transport of soil resources from and within drylands, many researchers and land managers continue to view them as separate and unrelated processes. Here, we illustrate how aeolian and fluvial sediment transport is coupled at multiple spatial and temporal scales and highlight the need for these interrelated processes to be studied from a more integrated perspective that crosses traditional disciplinary boundaries. Special attention is given to how the growing threat of climate change and land-use disturbance will influence linkages between aeolian and fluvial processes in the future. We also present emerging directions for interdisciplinary needs within the aeolian and fluvial research communities that call for better integration across a broad range of traditional disciplines such as ecology, biogeochemistry, agronomy, and soil conservation. This article is a US Government work and is in the public domain in the USA. Published in 2011 by John Wiley & Sons, Ltd.

Climate and land use controls over terrestrial water use efficiency in monsoon Asia

Abstract: Much concern has been raised regarding how and to what extent climate change and intensive human activities have altered water use efficiency (WUE, amount of carbon uptake per unit of water use) in monsoon Asia. By using a process-based ecosystem model [dynamic land ecosystem model (DLEM)], we examined effects of climate change, land use/cover change, and land management practices (i.e. irrigation and nitrogen fertilization) on WUE in terrestrial ecosystems of monsoon Asia during 1948-2000. Our simulations indicated that due to climate variability/change, WUE in the entire area decreased by 3.6% during the study period, with the largest decrease of 6.8% in the 1990s. Grassland was the most sensitive biome to a drying climate, with a decrease of 16.2% in WUE in the 1990s. Land conversion from natural vegetation to croplands, accounting for 79% of the total converted land areas, led to a decrease in WUE, with the largest decrease of 42% while forest was converted to cropland. In contrast, WUE increased by more than 50% while cropland was converted to natural vegetation. Simulated results also showed that intensive land management practices could alleviate the decrease in WUE induced by climate change and land conversion. Changes in WUE showed substantial spatial variation, varying from the largest decrease of over 50% in northwestern China and some areas of Mongolia to the largest increase of over 30% in western, southern China, and large areas of India. To adapt to climate change and sustain terrestrial ecosystem production, more attention ought to be paid to enhance water use efficiency through land use and management practices, especially in the drying areas. Copyright (C) 2011 John Wiley & Sons, Ltd.

Conceptual frameworks in peatland ecohydrology: looking beyond the two‐layered (acrotelm–catotelm) model

Abstract: Northern peatlands are important shallow freshwater aquifers and globally significant terrestrial carbon stores. Peatlands are complex, ecohydrological systems, commonly conceptualized as consisting of two layers, the acrotelm (upper layer) and the catotelm (lower layer). This diplotelmic model, originally posited as a hypothesis, is yet to be tested in a comprehensive manner. Despite this, the diplotelmic model is highly prevalent in the peatland literature, suggesting a general acceptance of the concept. We examine the diplotelmic model with respect to what we believe are three important research criteria: complexity, generality and flexibility. The diplotelmic model assumes that all ecological, hydrological and biogeochemical processes and structures can be explained by a single discrete boundary—depth in relation to a drought water table. This assumption makes the diplotelmic scheme inherently inflexible, in turn hindering its representation of a range of ecohydrological phenomena. We explore various alternative conceptual approaches that might offer greater flexibility, including the representation of horizontal spatial heterogeneity and transfers. We propose that the concept of hot spots, prevalent in terrestrial biogeochemistry literature, might be extended to peatland ecohydrology, providing a more flexible conceptual framework. Hot spots are areas of a peatland which exhibit fast processing rates in a number of mechanistically linked hydrological, ecological and biogeochemical processes. The complementary concept of cold spots may also be useful in peatland ecohydrology, particularly with regards to understanding the vulnerability of peatlands to disturbance. The flexibility of our suggested scheme may allow the future incorporation of ecohydrological phenomena yet to be identified as important in peatlands. Copyright  2011 John Wiley & Sons, Ltd.

Longitudinal river ecohydrology: flow variation down the lengths of alluvial rivers

Abstract: Longitudinal flow variation is an emerging field of study in river ecohydrology. Longitudinal changes in the frequencies, magnitudes, durations and timing of floods, low-flows and intermittence create a dynamic environment for flow-dependent species and ecological processes. Analyses of flow variation and flow–ecosystem relationships in the longitudinal dimension require synoptic flow time-series at multiple sites along a river. Complex channel geomorphology and a scarcity of rivers equipped with multiple flow gauges have slowed progress in longitudinal ecohydrology. The empirical longitudinal flow model (ELFMOD) is a new statistical tool for estimating flows at multiple points along rivers; which circumvents the requirement for multiple gauges. In this study, we used ELFMOD to explore longitudinal flow variation in four alluvial rivers from different geological terrains and climate zones: the Albarine (France), Methow (USA) and Selwyn and Orari (New Zealand). Differences among rivers in longitudinal and temporal flow variation were evident on date × location flow matrices and longitudinal profiles. There were notable differences among longitudinal gradients in flow magnitude and flow percentiles, and in the recurrence, extent, and rate of expansion and contraction of dry river reaches. There were also large differences in longitudinal flow-permanence patterns. Temporal variation in the lengths of dry channel and numbers of dry reaches was predominately seasonal in the Albarine and Methow, and interannual in the Orari and Selwyn. Broad differences among the rivers in longitudinal flow patterns correspond to differences in the configuration of hydrogeomorphic discontinuities such as tributary confluences, channel divergences and convergences, and lithological contacts. Copyright © 2010 John Wiley & Sons, Ltd.

Factors controlling the spatial patterns of soil moisture in a grazed semi-arid steppe investigated by multivariate geostatistics

Abstract: Land use has a significant impact on spatial patterns of soil moisture, particularly in sensitive and poorly managed regions. This study evaluated the relative importance of soil, vegetation and topography in controlling the spatial moisture patterns in a grazed semi-arid steppe of Inner Mongolia. Five fields were investigated during 2004-2006: two ungrazed plots since 1979 (UG 79) and 1999 (UG 99); three grazed plots in winter grazed (WG), continuously grazed (CG) and heavily grazed (HG) with 0.5, 1.2 and 2.0 sheep units ha(-1) year(-1), respectively. The data were analysed using correlation and geostatistical analysis. Results showed that (1) grazing reduced the volumetric moisture contents (0-6 cm) and their spatial heterogeneity; (2) soil moisture patterns had weak to moderate spatial structures and (3) soil and plant properties, especially soil physical properties, were the main factors controlling spatial moisture patterns. Multivariate geostatistics further showed scale-dependent correlation for these controlling parameters depending on treatments. With increasing grazing intensity, heterogeneity of soil and plant properties decreased from a patchy to a homogeneous distribution. Specifically, the soil and plant properties strongly controlled the variation of soil moisture for UG 99 at short scale (45 m), and for CG and HG at long scale (90 m), however, weakly controlled the variation of soil moisture for UG 79 and WG. Our results have implications for the understanding ecohydrological processes of semi-arid steppe as well as model parameterization. We suggest that pasture management strongly modified soil moisture patterns, which should be considered in the hydrological models at multiple spatial scales. Copyright (C) 2010 John Wiley & Sons, Ltd.

Urbanization alters watershed hydrology in the Piedmont of North Carolina

Abstract: The ecohydrologic effects of urbanization that is dominated by forests clearing are not well understood in the southeastern United States. We utilized long-term monitoring data to quantify the annual water balance, stormflow characteristics, and seasonal flow patterns of an urbanized watershed (UR) (0Ð70 km 2 ) and compared it to a fully forested watershed (FOR) (2Ð95 km 2 ) in central North Carolina. The goal of this study was to assess how past urbanization altered watershed hydrology and to offer reference data for urban watershed planning. The mean annual discharge coefficient (discharge/precipitation) in the UR and FOR from 2000 to 2007 was 0Ð42 and 0Ð24, respectively. The UR generated about 75% more stormflow than the FOR. The UR had a lower mean evapotranspiration (ET) rate (58%) than the FOR (77%). Peakflow rates and stormflow volume of the UR were higher (e.g. 76Ð6 mm/day versus 5Ð8 mm/day for peakflow rate and 77Ð9 mm/day versus 7Ð1 mm/day for stormflow volume) than the FOR, especially during the growing season. Growing season precipitation minus discharge

Ecosystem level assessment of environmentally based flow restrictions for maintaining ecosystem integrity: a comparison of a modified peaking versus unaltered river

Abstract: Although dams have impounded the majority of the world's altered watercourses, there is a growing awareness of the importance of mitigating or reversing some of the negative effects on aquatic ecosystems and the related services they provide We used an ecosystem approach, including detailed studies on hydrology, geomorphology, invertebrates, fish, and food web dynamics on a river altered by waterpower production and a natural flowing river to assess system responses to a change in the altered flow regime (specifically the ramping rate or rate of change of flow) Although there was significant alteration in the flow and sediment regimes under the original restricted ramping rate regime, differences in many biotic variables in the two rivers were not significant including total invertebrate abundance and diversity, fish biomass, fish condition, and food web length However, significant differences in the abundance and distribution of some sensitive invertebrate taxa and fish diversity were observed between the altered and natural flowing rivers as was the energy base of the food web, measured with stable isotopes The altered river had lower overall abundance of Odonata, Ephemeroptera and Plecoptera, and Diptera, Trichoptera, Ephemeroptera, and Coleoptera increase in abundance towards the deeper and higher velocity thalweg On average, δ13C values were lighter in altered sites compared to unaltered sites, likely due to carbon export from the upstream reservoir Results will inform Canadian federal and provincial policy concerning the efficacy of ramping rate restrictions as a tool to mitigate the environmental impacts associated with peaking waterpower dam operations Copyright © 2010 John Wiley & Sons, Ltd and Crown in the right of Canada

Rainfall, topography and primary production relationships in a semiarid ecosystem

Abstract: A series of 15 Satellite Pour l'Observation de la Terra XS images, which were acquired during a single growing season, were used to study the spatial and temporal relationships between topography, rainfall and aboveground net primary production (ANPP) of annuals in a semiarid environment. A digital elevation model was used to locate five physiographic units: interfluve, shoulder, backslope, foot slope, and channel, along the slope catena. ANPP values were then surrogated by the normalized difference vegetation index (NDVI). Four phenological phases were interpreted from the seasonal NDVI profiles: germination, green-up, drying, and senescence. A significant difference between NDVI values of all physiographic units was found, mainly during the green-up phase. NDVI values at peak season were characterized as typical of semiarid ecosystems, except those of the footslope and the channel, which were found to have meaningfully high NDVI values, due to run-off distribution and a thick soil profile. The seasonal NDVI integral was related positively and linearly to model-derived water availability values for all physiographic units and the NDVI was correlated to multiple-timescale rainfall data and the length of dry spells. The 1-month rainfall data were found to have the highest correlation with the NDVI, indicating lag and cumulative effects of rainfall on production. This implies that the time required for the plants to use the water for production is around a month. It is concluded that studies of ecosystem functioning and capabilities in semiarid environments should consider not only mean annual rainfall amounts, but also the temporal rainfall distribution, mainly on a monthly scale, and the effect of physiographic units. Copyright © 2010 John Wiley & Sons, Ltd.

Modelling effects of land use/cover changes under limited data

Abstract: Watershed models are valuable tools used in the study of impacts of land use/cover (LULC) changes on hydrology. We use the Soil and Water Assessment Tool (SWAT) to study the impacts of LULC changes in a coastal Alabama watershed, where flow data did not exist at the onset of the study. We set up and calibrated the model in the neighbouring Magnolia River watershed. Relevant model parameters were then transferred to the Wolf Bay watershed. Impacts of LULC changes on hydrology are studied in the Wolf Bay watershed by running the model with the default parameters, transferred model parameters (from the Magnolia River watershed), and calibrated parameters at the Wolf Bay watershed with limited data that became available later during the study. The relative changes in flow duration curves (FDCs) due to differing LULC showed a similar pattern with each parameter set: There is a clear threshold of around 1% probability of exceedance where the relative change is at its maximum. The relative change in flow due to LULC change drops drastically with increasing probability of exceedance of beyond 2% until it reaches a plateau at p = 20%. Hence, small to medium range flows are less sensitive to the parameter set. Further, the impact of LULC change on flow gradually decreases with the size of the storm for very large events (probability of exceedance < 1%). Copyright © 2010 John Wiley & Sons, Ltd.

Water use patterns of three species in subalpine forest, Southwest China: the deuterium isotope approach

Abstract: Determination of water sources of plant species in a community is critical for understanding the hydrological processes and their importance in ecosystem functions. Such partitioning of plant xylem water into specific sources (i.e. precipitation, groundwater) can be achieved by analysing deuterium isotopic composition (δD) values for source waters. A subalpine dark coniferous forest in southwestern China was selected to examine water use strategies of three key species. Our objectives are to: (1) determine contributions of rainfall and groundwater to soil and xylem water and (2) examine effects of rain, days after rain, soil depth, and species on such contributions. We found that the three species tend to have different, but complementary water use patterns. The dominant canopy tree of Abies faxoniana relies primarily on groundwater (i.e. 66–96% of its water sources) and does not change its dependency on groundwater between seasons. In contrast, the midstory Betula utilis and the understory Bashania fangiana depend predominantly on rainwater (i.e. 13–94% and 32–93%, respectively), and tend to use water opportunistically, switching to groundwater as the main source under stressful conditions during the dry season. The complementary and, for some species, shifting water use strategies and the lack of dependency on rainwater by the foundation species of the subalpine coniferous forest ecosystem should act together to promote species co-existence and maintain community resiliency under potentially increasing water stress caused by climate change. Copyright © 2010 John Wiley & Sons, Ltd.

Changes to southern Appalachian water yield and stormflow after loss of a foundation species

Abstract: Few studies have examined how insect outbreaks affect landscape-level hydrologic processes. Wereport the hydrologic effects of the invasive, exotic hemlock woolly adelgid (HWA) in a headwater catchment in the southern Appalachian Mountains. The study watershed experienced complete mortality of an evergreen tree species, Tsuga canadensis (L.) Carr. (eastern hemlock), after infestation was first detected in 2003. Hemlock mortality resulted in a ~6% reduction in basal area in the watershed, and this loss was primarily concentrated inriparianzones.Weuseda paired-watershedapproachtoquantifychanges inwateryield andpeakstormflow using streamflow data from the infested watershed and a nearby watershed with significantly lower hemlock basal area. We hypothesizedthatyieldwouldincreaseshortlyafterhemlockinfestationbutdecreaseoverthelonger-term.Wefoundthatannualyield did not increase significantly in any year after infestation but decreased significantly by 12·0cm (~8%) in 2010. Monthly yield also decreased after infestation, but changes were limited to the dormant season. The decline in yield is likely to persist as hemlock is replacedbyspecieswithhighertranspirationrates.Peakflowincreasedsignificantlyafterinfestationduringthetwolargest flowevents in the post-infestation period. Changes in stormflow during extreme events may have been temporary as another evergreen, Rhododendron maximum, may have mitigated some of the changes after hemlock loss. Thus, streams draining watersheds where eastern hemlock has been lost due to HWA infestation demonstrate permanent reductions in yield and transient increases in peakflow during large-flow events. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.

Light as a first‐order control on ecosystem structure in a temperate stream

Abstract: An emerging issue in ecohydrology is the role of light in fluvial ecosystem dynamics. Here, we investigate how photosynthetically active radiation (PAR) influences the hydrogeomorphology and biogeochemistry of a second-order temperate stream with varying riparian communities from heavily shaded forest sections to unshaded grass sections. First, in-stream PAR was compared to submerged aquatic macrophyte distributions along a 1·2-km reach. The effects of macrophytes on water depth, sediment size, sediment volume, organic matter (OM) accumulation and nutrient uptake were then analysed. Compared with forested sites, non-forested sites had three times more benthic PAR, which resulted in a quadrupling of macrophyte biomass. This greater biomass at non-forested sites increased water depth, sediment accumulation and the uptake of soluble reactive phosphorous (SRP). Bed sediment size and OM were not significantly different between forested and non-forested sites. Finally, we used the above relations to estimate biogeochemical differences between a completely forested reach and a non-forested reach. Compared with a forested reach, the non-forested reach accumulated almost twice as much bed sediment and retained more than four times as much SRP. Thus, changes in riparian conditions may create a cascade through which shading drives changes in stream habitat, which in turn drives changes in hydrogeomorphology and biogeochemical cycles. Copyright © 2010 John Wiley & Sons, Ltd.

Benthic and hyporheic invertebrate community responses to seasonal flow recession in a groundwater‐dominated stream

Abstract: Natural hydrological variability in lotic ecosystems can include prolonged periods of flow recession. A reduction in discharge is accompanied by abiotic changes in benthic and hyporheic habitats, often including reductions in habitat availability. Whilst the benthic invertebrate community response to low flows is well documented, little research has considered how the composition of the community within the hyporheic zone is affected. We examined benthic and hyporheic invertebrate community composition during flow recession in a temperate karst stream, at sites with contrasting historic flow permanence regimes. Changes in benthic invertebrate community composition primarily reflected changes in habitat availability associated with discharge variability; in particular, the population density of the dominant amphipod, Gammarus pulex, increased as the area of submerged benthic sediments declined. Concurrent significant increases in the hyporheic abundance of G. pulex, and moderate increase in the proportion of the total G. pulex population inhabiting the hyporheic zone were recorded. It is postulated that G. pulex migrated into the hyporheic zone to reduce exposure to intensifying biological interactions in the benthic sediments. An increase in the hyporheic abundance of G. pulex was particularly pronounced at sites with historic intermittent flow, which could be attributed to downwelling stream water dominating vertical hydrologic exchange. The increase in G. pulex abundance reduced community diversity in the benthic sediments, but had no apparent detrimental effects on hyporheic invertebrate assemblages. Copyright © 2010 John Wiley & Sons, Ltd.

Surface and groundwater dynamics in the sedimentary plains of the Western Pampas (Argentina)

Abstract: Fil: Aragon, Myriam Roxana. Universidad Nacional de Tucuman. Facultad de Ciencias Naturales e Instituto Miguel Lillo. Laboratorio de Investigaciones Ecologicas de las Yungas; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Tucuman; Argentina

Resilience of Phreatophytic Vegetation to Groundwater Drawdown: Is Recovery Possible Under a Drying Climate?

Abstract: Banksia (Proteaceae) woodlands are one of a number of groundwater dependent ecosystems in southwestern Western Australia that are threatened by groundwater abstraction. In addition to this threat is an ongoing decline in regional water tables due to a drying climate. We used ecological resilience theory to analyse and interpret a long-term vegetation monitoring dataset from a site that has experienced an abstraction-induced acute groundwater drawdown in the late 1980s and early 1990’s. Despite reduced plant abundance, all dominant overand understorey species were still found on all transect plots in which they were recorded predrawdown. This suggests a notional resilience and a strong likelihood of recovery, in the event that pre-drawdown ecohydrological habitat conditions were to return. However, since the drawdown event, the regional water table continued to decline, with the vegetation responding through progressive and uni-directional change in abundance and composition. The change in composition was primarily manifested as a shift towards non-woody, shallowrooted species not dependent on specific hydrological conditions. This slow, progressive change in hydrology associated with reduced rainfall and land use changes has continued to force a transition in the floristics towards an alternative ecohydrological state. Despite the absence of an acute drawdown event, the same progressive floristic response was also observed at two reference sites that were not under the immediate influence of production bores. The challenge for adaptive water resource management will be to enhance the capacity for resilience in these groundwater-dependent ecosystems in a drying environment through appropriate regulation of groundwater abstraction.

Interstitial pore‐water temperature dynamics across a pool‐riffle‐pool sequence

Abstract: Hyporheic habitat conditions are controlled strongly by spatial and temporal dynamics of physicochemical processes at the aquifer–river interface. In particular, heat transport between groundwater and surface water has a great impact on streambed habitats. This study uses high resolution observations of vertical hydraulic gradients (VHGs) and interstitial pore-water temperatures to investigate space-time patterns of groundwater–surface water (GW–SW) exchange fluxes and streambed thermal conditions of a pool-riffle-pool sequence of a UK lowland river. The results indicate that, although groundwater is dominantly upwelling in the research area, exchange flow patterns are strongly influenced by the streambed geomorphology. Advective heat flux caused by groundwater upwelling is shown to have a moderating impact on interstitial temperature patterns and partly compensates the impact of conduction of diurnal surface water temperature fluctuations into the streambed. Consequently, diurnal temperature oscillations, which are clearly pronounced in the top 10 cm of the streambed (up to 2 °C) are reduced by > 90% at depths below 20 cm. This study provides evidence that even in groundwater upwelling conditions, the spatially variable impact of heat conduction from the streambed surface may cause a spatially heterogeneous interstitial habitat structure with thermal conditions differing significantly in a vertical (3 °C temperature gradient at a length scale of 0·4 m) as well as longitudinal (0·75 °C at 16 m) domain. These results not only enhance the understanding of thermal patterns in lowland rivers but also have implications for interstitial habitat ecohydrology, community structures and stability. Copyright © 2011 John Wiley & Sons, Ltd.

Potential plant species distribution in the Yellow River Delta under the influence of groundwater level and soil salinity

Abstract: This article describes a multidisciplinary approach to assessing potential vegetation types. The relation between vegetation distribution as derived from field survey and habitat characteristics in the Yellow River Delta (YRD) was analyzed using detrended canonical correspondence analysis (DCCA). The three-dimensional groundwater numerical simulation model MODFLOW yielded an accurate distribution of the shallow groundwater table within the study area. Groundwater table and soil salinity appeared to have the largest influence on the distribution patterns of specific indicator species. The quantitative relationships between species presence and environmental factors were further explored using logistic regression, allowing for the prediction of potential species distribution in relation to fluctuations in groundwater depth and soil salinity. Based on this, potential distribution maps for specific plant species and their communities were generated using ArcGIS. The potential vegetation map was compared to the actual vegetation map (interpreted from SPOT imagery), which leads to a discussion of the main factors responsible for fragmentation and degradation of the local vegetation system

Proposed principles governing how vegetation changes affect transpiration

Abstract: Understanding global variation in evapotranspiration (ET) is critical for accuracy of climate models, predictions used in water resources management, and assessment of land use change impacts on the water balance of ecosystems—yet we lack unifying principles to predict when transpiration (T) varies with land use. Plant T is a dynamic and often dominant component of ET, and is affected by a variety of processes controlled by land use changes superimposed onto edaphic conditions. We propose the following three principles that determine whether T will vary with changes in vegetation: variation will result if energy balance partitioning has been altered, if deeper or shallower active rooting depth has changed the amount of soil moisture accessible to plants, or if temporary changes in water use add up over longer time scales. Clearly these concepts are not new; however, they are often overlooked in favor of blanket assumptions that large changes in vegetation inevitably alter T. Not so. Our suggested framework incorporates both edaphic and plant traits that determine whether T will vary or not in response to altered land cover conditions. We suggest that this simple set of principles unifies results of wide-ranging studies of T following land use change and can explain underlying causes of T variation. These principles are illustrated through case studies from four different environments: Pacific Northwest forest, Texas mesquite brushland, Texas savanna and woodland, and Middle Rio Grande riparian forest. The proposed principles seem broadly applicable, should be further evaluated, and are directly relevant for land management. Copyright © 2011 John Wiley & Sons, Ltd.