Effects Of Hydrological Changes Research Articles

Analysis of the suitable ecological flow of benthic animals in the lower reaches of Xiangjiaba Reservoir in the upper reaches of the Yangtze River based on the physical habitat model

Abundant water resources have facilitated the completion and operation of numerous large-scale water conservation projects. However, the operation of cascade hydropower stations has changed the natural hydrological regime of rivers, thereby affecting the integrity and stability of downstream benthic animal habitats. To quantitatively evaluate the impact of infrastructure development, we proposed a coupling of hydrodynamic and habitat models, with benthic animals as indicator species (because they are highly sensitive to hydrological changes). This study established a physical habitat model of benthic animals in the upper reaches of the Yangtze River, from the Xiangjiaba to Zhutuo sections by coupling the MIKE21 hydrodynamic model with a habitat model. This model coupled the changes in hydrological conditions and ecological processes to quantitatively reflect the effects of flow changes on river habitat quality, which can be used to predict the effects of hydrological changes on water ecosystems and provide fundamental information for ecological flow and scheduling decisions. Our results showed that by jointly regulating the suitable outflow of the Xiangjiaba Reservoir and the inflow of the Tuojiang, Minjiang, and Hengjiang rivers (three tributaries with water conservancy projects), the minimum flow in the non-flood season and the maximum flow in the flood season could be controlled more precisely. This increases the suitable habitat area for benthic animals as well as improves the stability of their habitat. This study fills the gap in the physical habitat model of benthic animals in the upper reaches of the Yangtze River as well as enriches the research ideas of ecological flow regulation. Moreover, this indicates the first application of the physical habitat model to the joint ecological flow regulation of the main tributaries, thus opening new directions for the application of the physical habitat model.

Effect of drying dynamics on the functional structure of a fish assemblage from an intermittent river network

We are living in a fast-changing world promoted by anthropogenic actions and ecosystems’ functioning has been constantly changed. One example is the globally reduction of river flow that can lead to more than 50% of the rivers and streams around the world becoming intermittent. However, the relationship between environmental changes and biological communities has been limited to taxonomic approach, rather than the functional approach. Functional structure determines how individuals interact with the environment and evaluating the effects of hydrological changes in functional variation can elucidate the responses of aquatic biota under climate changes. Thus, we hypothesized that hydrological phases (dry, re-wetting and wet) would influence both environmental conditions and fish composition (i.e., taxonomic richness and functional structure) in one intermittent river. In addition, we expected that: 1) fish assemblages will have higher values of species richness and Functional Diversity indexes—Richness (FRic), Dispersion (FDis), Specialization (FSpe), and Originality (FOri) in drier phases (dry and re-wetting); and 2) higher values of Functional Diversity indexes related to evenness (FEve) and divergence (FDiv) in the wet phase, due to the predominance of species with high dispersal capacity when sites are connected. Sampling was conducted in the Cruxati river during the three hydrological phases along four sites (250 m each). Functional diversity analysis, involving traits of dispersion, life history and trophic ecology were used to apply Functional Diversity indexes. Indexes were compared from null models and all species were ordered in a multidimensional functional space using principal coordinate analysis (PCoA). In the dry phase, taxonomic richness and FRic between communities is higher, as well as FSpe and FOri, showing that each assemblage has unique characteristics with different strategies allowing the establishment in this hydrological phase. However, communities are less functionally dispersed. In the wet phase, when the river is connected, FDis between communities is higher and species abundances are more equitable with regular distribution in the functional space. Therefore, we conclude that local ecological processes (i.e., dynamics of hydrology) may promote the establishment of species according to their functional traits and thereby the functional structure of local assemblages.

The effects of hydrological variations on chemical weathering: Evidences from temporal water chemistry, stable carbon and sulfur isotopes

The negative feedbacks between chemical weathering and climate change were hypothesized to regulate the atmospheric CO2 over short-term and geologic timescales. In this study, we collected temporal water samples from the Jialing River, and analyzed water chemistry, stable isotopic compositions of dissolved inorganic carbon (δ13CDIC) and sulfur isotope of sulfate (δ34SSO4) to investigate the effects of hydrological changes on chemical weathering. The results of the inverse model based on the Monte Carlo method showed that major cations were mainly derived from carbonate (63.9%) and silicate (12.0%) weathering, and sulfuric acid plays an important role in carbon biogeochemical processes. Based on water chemistry, δ34SSO4 and δ13CDIC, the carbon biogeochemical processes were investigated, showing the influence of secondary processes. We estimated the weathering rates of carbonate (19.7 t/km2yr) and silicate (3.9 t/km2yr) in the Jialing River, and then estimated CO2 consumption flux by carbonate weathering (24.5 t/km2yr), silicate weathering (8.1 t/km2yr), and total CO2 consumption flux (27.5 t/km2yr) deducting the influence of pyrite oxidation. Our research showed the significant role of pyrite oxidation in carbon cycling. This study highlighted the impacts of hydrological variabilities on the generation and transport of solutes, which have significant implications for understanding carbon cycling under ongoing climate change.

Effects of hydrological environment on litter carbon input into the surface soil organic carbon pool in the Dongting Lake floodplain

Litter carbon is the main source of the surface soil organic carbon pool (S-SOCP). However, the impact of changes in the hydrological environment of natural wetlands on litter input to S-SOCP remains unclear. In the present study, the effects of hydrological changes (soil water content [SWC] and days of flooding [DF]) on the litter decomposition process and S-SOCP were investigated from January 2018 to November 2019 in the Dongting Lake floodplain of China. Furthermore, the contribution of litter to the S-SOCP in Carex meadow and Reed wetland were calculated. The results showed that a large part of litter (approximately 50%–70%) decomposed annually, especially during the flooding season. Litter contributed 283.68 g C m−2 a–1 to the S-SOCP in the Carex meadow and 275.24 g C m−2 a–1 to the Reed wetland. In the Carex meadow and Reed wetland, the belowground litter contribution was higher than the aboveground litter during the non-flooding season. In contrast, during the flooding season, the aboveground litter contribution in the Carex meadow is higher, whereas the belowground litter dominates in the Reed wetland. The SWC indicated a positive correlation with soil organic carbon (SOC) and a negative correlation with the microbial biomass carbon (MBC) and dissolved organic carbon (DOC) in the Carex meadow. However, SWC shows a negative correlation with SOC and a positive correlation with MBC in the Reed wetland during the non-flooding season. During the flooding season, the variation of DOC during the flooding season (ΔDOC) is positively correlated with DF in the Carex meadow and Reed wetland. SWC and DF are the main drivers of litter decomposition into the S-SOCP in non-flooding and flooding seasons, respectively. Therefore, the construction of microhabitat with prolonged flooding and relatively higher soil water content are essential ways to improve the carbon sequestration potential in floodplains.

Projected changes of regional lake hydrologic characteristics in response to 21st century climate change

ABSTRACT Inland lakes are socially and ecologically important components of many regional landscapes. Exploring lake responses to plausible future climate scenarios can provide important information needed to inform stakeholders of likely effects of hydrologic changes on these waterbodies in coming decades. To assess potential climate effects on lake hydrology, we combined a previously published spatially explicit, processed-based hydrologic modeling framework implemented over the lake-rich landscape of the Northern Highlands Lake District within the United States with an ensemble of climate change scenarios for the 2050s (2041–2070) and 2080s (2071–2100). Model results quantify the effects of climate change on water budgets and lake stage elevations for 3692 lakes and highlight the importance of landscape and hydrologic setting for the response of specific lake types to climate change. All future climate projections resulted in loss of ice cover and snowpack as well as increased evaporation, but variability in climate projections (warmer conditions, wet winters combined with wet or dry summers) interacted with lake characteristics and landscape position to produce variable lake hydrologic changes. Water levels for drainage lakes (lakes with substantial surface water inflows and outflows) showed nearly no change, whereas minimum water levels for seepage lakes (minimal surface water fluxes) decreased by an average of up to 2.64 m by the end of the 21st century. Our physically based modeling approach is parsimonious and computationally efficient and can be applied to other lake-rich regions to investigate interregional variability in lake hydrologic response to future climate scenarios.

Effects of hydrological change on the risk of riverine algal blooms: case study in the mid-downstream of the Han River in China.

Algal blooms usually occur in semi-closed water bodies such as lakes or estuaries; however, it has occurred frequently in the mid-downstream of the Han River (MSHR) in China since the 1990s. We made a comparative analysis of the hydrological conditions and identified the hydrological condition thresholds that induce algal blooms. From the hydrodynamic point of view, the changes and characteristics of the hydrological conditions in the MSHR were analyzed. Furthermore, the influence on the risk of algal blooms under different design water transfer schemes for the middle route of the South-to-North Water Diversion Project (SNWDP) was studied. The results indicated that (1) the flow in the MSHR less than 900 m3/s and water level in the Yangtze River higher than 14 m provided a suitable hydrological environment for diatoms multiply. (2) The flow of the MSHR showed a downtrend, while the water level of the Yangtze River showed an uptrend. There were variations in hydrological processes. Through specific IHA index analysis, the fact of flow reduction in the MSHR was demonstrated, and further indicated that algal bloom outbreak was in low flow period. (3) The water transfer in the middle route of SNWDP affected the risk probability of algal blooms. The more the amount of water transfer, the greater the risk probability of algal blooms. It was the Water Diversion Project from Yangtze River to Han River (WDPYHR) that replenished flow of the MSHR and was conducive to the prevention and control of algal bloom risk.

Hydrological effects of change in vegetation components across global catchments

As an important component of the terrestrial system, vegetation plays a pivotal role in hydrological processes and water yield. Many studies have examined hydrological effects of changes in total vegetation coverage and density, whereas the impact of change in vegetation components (i.e., proportion of different vegetation types) is rarely considered and little known. Actually, even though the changes in total vegetation coverage and density are similar, the differences in vegetation components alteration among catchments can be pronounced, and thus result in distinct hydrological consequence. Here, using a state-of-the-art dataset of vegetation composition including tree canopy (TC) cover, short vegetation (SV) cover and bare ground (BG) cover, we quantitatively assess the hydrological consequences of vegetation components change in 76 large catchments globally under the water balance framework. We find SV is apparently the most sensitive vegetation component for runoff change, which is reinforced in regions with a drier climate. Attributing water yield change shows that runoff variations caused by TC change are usually offset by those caused by SV change. In typical afforested catchments across the world, the loss of SV can alleviate 39.3–108.7% runoff decrease due to the expansion of TC and the contraction of BG. Our results imply that hydrological sensitivity is much diverse among vegetation types, and trade-offs exist among the hydrological effects of different vegetation components. These previously unrevealed findings suggest that more vegetation properties (including vegetation composition) should be accounted when evaluating the impact of vegetation change on regional water resources.

A Simplified Hydro-Economic Model of Guadalquivir River Basin for Analysis of Water-Pricing Scenarios

This study describes an economic model in the Guadalquivir river basin (Southern Spain) that considers inter-sectoral and hydrological effects of changes in water use as a response to various water-pricing policy scenarios. The main economic variables include water use, gross regional product, return flows in the river basin, and employment at sectoral and basin levels. The response of the different sectors to water pricing and of the sectoral productivity is derived from official data. The background of the model is based on previous research for the implementation of the UN System of Environmental-Economic Accounts and on the application of this framework to the Guadalquivir basin. Results based on the elicited curves illustrate that the structure of the demand function for irrigated agriculture passes from inelastic to elastic sections, while the function corresponding to the remaining economic sectors shows a continuous decreasing function with minor change in the elasticity structure of the curve. Results show that the impact of extreme measures of water pricing reduces water abstraction by up to 42% vs. the baseline scenario, with an economic reduction in regional Gross Domestic Product (GDP) of 1%.

An investigation of the hydrological influence on the distribution and transition of wetland cover in a complex lake–floodplain system using time-series remote sensing and hydrodynamic simulation

Hydrology is a critical environmental condition for the evolution of wetland ecosystems. The effects of hydrological changes on wetland cover are of great importance for preserving its ecological functions. In this study, the hydrological influences on wetland cover distribution and transition in a large complex lake–floodplain system, Poyang Lake (China), were investigated. Utilizing time-series satellite remote sensing observations, wetland cover types in Poyang Lake during 2000–2009, including water, mudflat, and the major vegetation communities, were extracted and related to the wetland hydrological characteristics calculated by the hydrodynamic simulations. The statistical results of annual inundation conditions for different wetland cover types indicated that vegetation communities were preferential to hydrological environments with shorter annual inundation than water and mudflats, and different vegetation communities were distributed in areas with considerable variations in annual inundation, which suggested a substantial hydrological influence on the distribution of wetland cover in Poyang Lake. Furthermore, this study investigated the impact of hydrological changes on the wetland cover transitions between typical dry and wet years. The results showed that hydrological fluctuations had various degrees of influences on different types of wetland cover transformation. The spatial analysis indicated that hydrological changes were probably the dominant factor for the wetland cover evolution in the floodplain areas of the northern and central parts of Poyang Lake, but not the unique determined factor for wetland cover transitions in the shallow floodplains near the sink of the inflows in the eastern and southwestern parts of Poyang Lake. This study provides a practical reference for the effects of hydrological regulation in the protection and restoration of Poyang Lake wetland.

Disentangling effects of forest harvest on long-term hydrologic and sediment dynamics, western Cascades, Oregon

The magnitude of sediment yield following forest timber harvest is controlled by increases in both sediment supply and streamflow. Since the relation between sediment transport and streamflow typically follows a power law, small increases in streamflow may translate into large increases in sediment transport. Interpreting the geomorphic effects of streamflow increases is confounded by the fact that timber harvest influences both the hydrologic regime and sediment supply of a watershed simultaneously, making it difficult to isolate the streamflow effect alone. Here we report on a novel approach to this problem using long-term data from two paired catchments located in the H.J. Andrews Experimental Forest, Oregon, USA. We use observed streamflow from the treated (clearcut) and control watersheds to reconstruct a natural streamflow time series for the treated watershed, one that represents streamflow response in conditions prior to harvest. We combine this reconstructed natural streamflow time series with observed relations between streamflow and sediment transport to quantify the background sediment yield and disentangle the relative effects of changes in hydrology and sediment supply. Results indicate that while increases in streamflow can account for modest increases in sediment transport, this is dwarfed by the increased supply of sediment that accompanies most timber harvest. These results have broad relevance to forest timber harvest and fuel management practices worldwide and can be used to constrain or set bounds on likely effects of more modest (i.e., thinning) techniques.

Can water level management, stock enhancement, and fishery restriction offset negative effects of hydrological changes on the four major Chinese carps in China’s largest freshwater lake?

Habitat degradation and fragmentation have been the leading cause of reduced fishery yields in many freshwater ecosystems around the world. In Poyang Lake, the largest freshwater lake in China, recent hydrological changes driven by the operation of Three Gorges Dam (TGD) and drought have caused a drastic loss of fishery resources. In response, managers have planned to build a sluice at Poyang Lake's outlet to manage the lake's water level and, as the sluice will unavoidably limit the river–lake migration of many fishery species, managers have also proposed implementing stock enhancement programs and restricting fisheries to sustain fisheries in the lake. In this study, we built and implemented a Poyang Lake Ecopath with Ecosim model to evaluate effects of water level management, stock enhancement, and fishery restriction on biomass of the four major Chinese carps: grass carp (Ctenopharyngodon idella), silver carp (Hypophthalmichthys molitrix), bighead carp (H. nobilis), and black carp (Mylopharyngodon piceus), of which all are river–lake migratory and important to fisheries. Results showed that the total biomass of the four major Chinese carps could increase with increases in water level, increases in stocking biomass, and decreases in fishing pressure. However, even in the best management effort scenario (i.e., highest water level, highest stocking biomass, and no fishing), simulated total biomass of the four major Chinese carps was still 16% lower than the biomass estimate in 2000, three years before the operation of TGD. These results suggest that a combination of managing water level, stocking, and restricting fisheries can substantially offset negative effects of hydrological changes on the four major Chinese carps, but may not be enough to restore the biomass of the four major Chinese carps to high levels that had occurred before the operation of TGD, because of the blockage of river–lake connectivity by the Poyang Lake sluice.

Hydrological response of loess slopes with reference to widespread landslide events in the Heifangtai terrace, NW China

In the Heifangtai terrace, NW China, flooding irrigation is common for the cropland production and has increased the groundwater table by 20–30 m over the past five decades. It is believed that excessive irrigation has induced a large number of loess landslides in this area. However, these loess landslides responses to hydrological changes have still not been well understood. Therefore, 43 boreholes and 51 2D Electrical resistivity tomography (ERT) profiles with a total length of 40 km have been investigated to analyze the hydrological characteristics for the whole terrace and characterize the effects of hydrological changes on the occurrence of different types of loess landslides. Our main findings are as follows: (1) Three groundwater domes are found in the center and eastern part of the Heitai terrace and the groundwater table is gradually rising in the whole terrace based on the ERT results. (2) The rising rate of groundwater table at the center of the terrace is twice greater than that at the margin of the terrace and it takes approximately 4 months for irrigation water to penetrate from the top surface to the saturated layer. (3) Landslide deposits could block drainage channels of groundwater, increase the localized hydraulic gradient and result in rising of local groundwater table at the edge of the terrace. (4) The resultant hydraulic gradient impels the groundwater from the center to seep out on the eastern and southern margins and new landslides are prone to occur in the main scarp of landslides with rising groundwater table. The type and magnitude of landslides are affected by groundwater seepage and movement. In order to fundamentally control the occurrence of landslides, effective drainage system and the restrained amount of irrigation water are needed.

Quantifying the effects of hydrological changes on long-term water quality trends in temperate reservoirs: insights from a multi-scale, paleolimnological study

Declining water quality in reservoirs is of growing concern in many regions, yet there is still little understanding of long-term water quality trends in these systems. Across the landscape, reservoirs have diverse origins, functions, and operational strategies. In temperate environments, winter water-level drawdown is a common operational practice in reservoirs but the long-term impacts of this hydrological modification has not been extensively studied. We paired a comparative, pre-dam-to-contemporary study (i.e. a top–bottom design) of 12 reservoirs with a detailed paleolimnological study of a focal lake to generate quantitative insights into the relative effect of hydrological changes vs. landscape and climatic drivers on water quality. The focal reservoir, Grand Lac Saint-Francois, is of relatively similar morphometry, geography, and limnology to our other sites, and has experienced annual winter water-level drawdown of ~ 5 m since it was dammed approximately 100 years ago. Based on our top–bottom analysis, we did not find strong correlations between long-term changes in water quality (i.e. diatom-inferred TP estimates) and winter water-level drawdown amplitudes. Instead, reservoir morphometry and watershed characteristics (i.e. geography, maximum depth, and cropland areas) appeared to be stronger drivers of trends across the region. From the detailed paleolimnological analysis, we found that sedimentary pigments and DI-TP concentrations significantly increased over the last century based on Mann–Kendall trend analyses. Breakpoint analyses showed that changes in biological-proxy trends, as well as the sedimentology (i.e. lithology and accumulations rates), coincided with dam construction and the onset of water level regulation. However, given the high variability in metrics and the extent of water level monitoring records, we were unable to quantitatively associate the impacts of drawdown with water quality trends at Grand Lac Saint-Francois. Conversely, we did find that watershed nutrient surpluses from livestock farming, and warming temperatures were significant explanatory variables of water quality metrics.

Beaver and state transition in Yellowstone

Extirpation of wolves from the Greater Yellowstone Ecosystem (GYE) in the 1920shypothetically triggered a behaviorally-mediated trophic cascade in which elk (Cervus elaphus), released from the fear of wolf (Canis lupus) predation, over-browsed riparian zones. Eventually, vast areas of meadow-wetland complexes transitioned to grass-lodgepole systems. The importance of beaver (Castor canadensis) in wetland losses has received less attention. Beaver abandoned most of the GYE by the 1950s, possibly due to resource limitations. Researchers from Colorado State University established an experimental system for Long Term Environmental Research in Biology (LTREB) along several streams in the Lamar Valley of Yellowstone sixteen years ago. To evaluate effects of hydrologic changes and elk browsing on productivity of willows (Salix spp.) and state transition, they built small experimental dams with browsing exclosures. In 2015, beaver began recolonizing the region. I am investigating how their biologic as well as hydrologic impacts affect the underlying mechanisms of state transition: nutrient cycling, productivity, and stream respiration. I posit that beaver are keystone species, meaning that the sustained recovery of wetland-meadow complexes is unlikely without the higher levels of riparian productivity triggered by the biological influence of beaver.
 
 Featured photo by Ben Amaral on Unsplash. https://unsplash.com/photos/rohY54N6auU

Effects of hydrological changes on cooperation in transnational catchments: the case of the Syr Darya

ABSTRACTWater allocation along the Syr Darya River may be affected by climate change. Here we statistically model cooperation strategies, country profits, and sensitivity of cooperation, showing that the hydrological regime affects transboundary cooperation. Climate change in the twenty-first century may reduce glacial cover, and reducing stream flows, decreasing chances of cooperation and potentially raising conflicts. Comparison with other transboundary catchments in Central Asia indicates moderate-to-high risk of conflicts for the Syr Darya. A template is provided for assessment of the stability of cooperation in the Syr Darya basin, and in catchments similarly dependent on water availability.

Restoration of Eutrophic Lakes with Fluctuating Water Levels: A 20-Year Monitoring Study of Two Inter-Connected Lakes

Eutrophication continues to be the most important problem preventing a favorable environmental state and detrimentally impacting the ecosystem services of lakes. The current study describes the results of analyses of 20 year monitoring data from two interconnected Anatolian lakes, Lakes Mogan and Eymir, receiving sewage effluents and undergoing restoration. The first step of restoration in both lakes was sewage effluent diversion. Additionally, in hypertrophic Lake Eymir, biomanipulation was conducted, involving removal of benthi-planktivorous fish and prohibition of pike fishing. The monitoring period included high (H) and low (L) water levels (WL) enabling elucidation of the effects of hydrological changes on lake restoration. In shallower Lake Mogan, macrophyte abundance increased after the sewage effluent diversion in periods with low water levels even at turbid water. In comparatively deeper Lake Eymir, the first biomanipulation led to a clear water state with abundant macrophyte coverage. However, shortly after biomanipulation, the water clarity declined, coinciding with low water level (LWL) periods during which nutrient concentrations increased. A second biomanipulation was conducted, mostly during high water level (HWL) period, resulting in a major decrease in nutrient concentrations and clearer water, but without an expansion of macrophytes. We conclude that repetitive fish removal may induce recovery but its success may be confounded by high availability of nutrients and adverse hydrological conditions.

New model to assessing nutrient assimilative capacity in plant-dominated lakes: Considering ecological effects of hydrological changes

Assessing nutrient assimilative capacity of water body is an essential component of the Total Maximum Daily Load program. Nutrient assimilative capacity of lakes is affected by hydrological changes through physical effects on the dilution capacity of water body and ecological effects on nutrient removal processes. Previous research has focused on the effects of hydrological changes on dilution capacity, but rarely considered the ecological effects on nutrient assimilative capacity. In this study, a process-based model considering both ecological effects and dilution effects of hydrological changes is proposed for assessing nitrogen and phosphorus assimilative capacities of plant-dominated lakes. Plant uptake and biological denitrification are two crucial nutrient removal processes. Water depths in a lake affect plant growing area. Lake submerged condition affects nutrient accumulation capacity of plants and the intensity of biological denitrification. The model considered dynamic variations of lake water depths and submerged condition, and the associated effects on nutrient removal by plant nutrient uptake and biological denitrification in lake systems. It is a discrete 0D model depending on a small amount of data and has satisfactory simulation accuracy. We chose the largest freshwater lake in northern China (Baiyangdian Lake) as a case. The annual total assimilative capacity in the lake was 1536t for nitrogen and 157t for phosphorus. Assimilative capacity during plant-growing season accounted for over 90% of the annual total capacity. The results determined by the new model were less than half of that from previous model, demonstrating the significance of considering ecological effects of hydrological changes. The new assessment model offers a useful tool for directing pollutant emission control and eutrophication prevention in global plant-dominated lakes.

Detecting runoff variation in Weihe River basin, China

Abstract. Dramatic changes in hydrological factors in the Weihe River basin are analysed. These changes have exacerbated ecological problems and caused severe water shortages for agriculture, industries and the human population in the region, but their drivers are uncertain. The Mann-Kendall test, accumulated departure analysis, sequential clustering and the sliding t-test methods were used to identify the causes of changes in precipitation and runoff in the Weihe basin. Change-points were identified in the precipitation and runoff records for all sub-catchments. For runoff, the change in trend was most pronounced during the 1990s, whereas changes in precipitation were more prominent earlier. The results indicate that human activities have had a greater impact than climate change on the hydrology of the Weihe basin. These findings have significant implications for the establishment of effective strategies to counter adverse effects of hydrological changes in the catchment.

Response of Sphagnum Peatland Testate Amoebae to a 1-Year Transplantation Experiment Along an Artificial Hydrological Gradient

Peatland testate amoebae (TA) are well-established bioindicators for depth to water table (DWT), but effects of hydrological changes on TA communities have never been tested experimentally. We tested this in a field experiment by placing Sphagnum carpets (15 cm diameter) collected in hummock, lawn and pool microsites (origin) at three local conditions (dry, moist and wet) using trenches dug in a peatland. One series of samples was seeded with microorganism extract from all microsites. TA community were analysed at T0: 8–2008, T1: 5–2009 and T2: 8–2009. We analysed the data using conditional inference trees, principal response curves (PRC) and DWT inferred from TA communities using a transfer function used for paleoecological reconstruction. Density declined from T0 to T1 and then increased sharply by T2. Species richness, Simpson diversity and Simpson evenness were lower at T2 than at T0 and T1. Seeded communities had higher species richness in pool samples at T0. Pool samples tended to have higher density, lower species richness, Simpson diversity and Simpson Evenness than hummock and/or lawn samples until T1. In the PRC, the effect of origin was significant at T0 and T1, but the effect faded away by T2. Seeding effect was strongest at T1 and lowest vanished by T2. Local condition effect was strong but not in line with the wetness gradient at T1 but started to reflect it by T2. Likewise, TA-inferred DWT started to match the experimental conditions by T2, but more so in hummock and lawn samples than in pool samples. This study confirmed that TA responds to hydrological changes over a 1-year period. However, sensitivity of TA to hydrological fluctuations, and thus the accuracy of inferred DWT changes, was habitat specific, pool TA communities being least responsive to environmental changes. Lawns and hummocks may be thus better suited than pools for paleoecological reconstructions. This, however, contrasts with the higher prediction error and species’ tolerance for DWT with increasing dryness observed in transfer function models.Electronic supplementary materialThe online version of this article (doi:10.1007/s00248-014-0367-8) contains supplementary material, which is available to authorized users.

Climate change impacts on high-elevation hydroelectricity in California

While only about 30% of California's usable water storage capacity lies at higher elevations, high-elevation (above 300 m) hydropower units generate, on average, 74% of California's in-state hydroelectricity. In general, high-elevation plants have small man-made reservoirs and rely mainly on snowpack. Their low built-in storage capacity is a concern with regard to climate warming. Snowmelt is expected to shift to earlier in the year, and the system may not be able to store sufficient water for release in high-demand periods. Previous studies have explored the climate warming effects on California's high-elevation hydropower by focusing on the supply side (exploring the effects of hydrological changes on generation and revenues) ignoring the warming effects on hydroelectricity demand and pricing. This study extends the previous work by simultaneous consideration of climate change effects on high-elevation hydropower supply and pricing in California. The California's Energy-Based Hydropower Optimization Model (EBHOM 2.0) is applied to evaluate the adaptability of California's high-elevation hydropower system to climate warming, considering the warming effects on hydroelectricity supply and pricing. The model's results relative to energy generation, energy spills, reservoir energy storage, and average shadow prices of energy generation and storage capacity expansion are examined and discussed. These results are compared with previous studies to emphasize the need to consider climate change effects on hydroelectricity demand and pricing when exploring the effects of climate change on hydropower operations. (C) 2013 Elsevier B.V. All rights reserved. (Less)