Food-web dynamics in a large river discontinuum

Cross, W.F., C.V. Baxter, E.J. Rosi-Marshall, R.O. Hall, Jr., T.A. Kennedy, K.C. Donner, H.A. Wellard Kelly, S.E.Z. Seegert, K.E. Behn, and M.D. Yard, 2013: “Food-web dynamics in a large river discontinuum.” Ecological Monographs, v. 83, pp. 311-337, doi: 10.1890/12-1727.1.

Nearly all ecosystems have been altered by human activities, and most communities are now composed of interacting species that have not co-evolved. These changes may modify species interactions, energy and material flows, and food-web stability. Although structural changes to ecosystems have been widely reported, few studies have linked such changes to dynamic food-web attributes and patterns of energy flow. Moreover, there have been few tests of food-web stability theory in highly disturbed and intensely managed freshwater ecosystems. Such synthetic approaches are needed for predicting the future trajectory of ecosystems, including how they may respond to natural or anthropogenic perturbations.

We constructed flow food webs at six locations along a 386-km segment of the Colorado River in Grand Canyon (Arizona, USA) for three years. We characterized food-web structure and production, trophic basis of production, energy efficiencies, and interaction-strength distributions across a spatial gradient of perturbation (i.e., distance from Glen Canyon Dam), as well as before and after an experimental flood. We found strong longitudinal patterns in food-web characteristics that strongly correlated with the spatial position of large tributaries. Above tributaries, food webs were dominated by nonnative New Zealand mudsnails (62% of production) and nonnative rainbow trout (100% of fish production). The simple structure of these food webs led to few dominant energy pathways (diatoms to few invertebrate taxa to rainbow trout), large energy inefficiencies (i.e., <20% of invertebrate production consumed by fishes), and right-skewed interaction-strength distributions, consistent with theoretical instability.

Below large tributaries, invertebrate production declined 18-fold, while fish production remained similar to upstream sites and comprised predominately native taxa (80–100% of production). Sites below large tributaries had increasingly reticulate and detritus-based food webs with a higher prevalence of omnivory, as well as interaction strength distributions more typical of theoretically stable food webs (i.e., nearly twofold higher proportion of weak interactions). Consistent with theory, downstream food webs were less responsive to the experimental flood than sites closest to the dam. We show how human-induced shifts to food-web structure can affect energy flow and interaction strengths, and we show that these changes have consequences for food-web function and response to perturbations.

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Water consumption from hydropower plants – review of published estimates and an assessment of the concept

Bakken, T.H., Å. Killingtveit, K. Engeland, K. Alfredsen, and A. Harby, 2013: “Water consumption from hydropower plants – review of published estimates and an assessment of the concept.” Hydrology and Earth System Sciences, v. 17, pp. 3983-4000, doi: 10.5194/hess-17-3983-2013.

Since the report from IPCC on renewable energy (IPCC, 2012) was published; more studies on water consumption from hydropower have become available. The newly published studies do not, however, contribute to a more consistent picture on what the “true” water consumption from hydropower plants is. The dominant calculation method is the gross evaporation from the reservoirs divided by the annual power production, which appears to be an over-simplistic calculation method that possibly produces a biased picture of the water consumption of hydropower plants. This review paper shows that the water footprint of hydropower is used synonymously with water consumption, based on gross evaporation rates.

This paper also documents and discusses several methodological problems when applying this simplified approach (gross evaporation divided by annual power production) for the estimation of water consumption from hydropower projects. A number of short-comings are identified, including the lack of clarity regarding the setting of proper system boundaries in space and time. The methodology of attributing the water losses to the various uses in multi-purpose reservoirs is not developed. Furthermore, a correct and fair methodology for handling water consumption in reservoirs based on natural lakes is needed, as it appears meaningless that all the evaporation losses from a close-to-natural lake should be attributed to the hydropower production. It also appears problematic that the concept is not related to the impact the water consumption will have on the local water resources, as high water consumption values might not be problematic per se. Finally, it appears to be a paradox that a reservoir might be accorded a very high water consumption/footprint and still be the most feasible measure to improve the availability of water in a region. We argue that reservoirs are not always the problem; rather they may contribute to the solution of the problems of water scarcity. The authors consider that an improved conceptual framework is needed in order to calculate the water footprint from hydropower projects in a more reasonable way.

Open Access

Evaluation of uneven water resource and relation between anthropogenic water withdrawal and ecosystem degradation in Changjiang and Yellow River basins

Nakayama, T., and D. Shankman, 2013: “Evaluation of uneven water resource and relation between anthropogenic water withdrawal and ecosystem degradation in Changjiang and Yellow River basins.” Hydrological Processes, v. 27, pp. 3350–3362, doi: 10.1002/hyp.9835.

The diverse hydro-climate between northern and southern China causes serious complications related to increasing food demand, declining water availability, and increasing flood risk in Changjiang and Yellow River basins. The huge projects of Three Gorges Dam (TGD) for diminishing flood and South-to-North Water Transfer Project (SNWTP) for driving water from Changjiang to Yellow and Hai Rivers to compensate for an imbalance of environmental resources will not necessarily solve all of the problems that they were originally intended to address. A sophisticated eco-hydrological model is required to evaluate the optimum amount of transferred water associated with these projects, together with socio-economic and environmental consequences. For this purpose, the process-based National Integrated Catchment-based Eco-hydrology (NICE) model was modified to couple with complex sub-systems in irrigation, stream junction, reservoir operation, and water transfer, to develop coupled human and natural systems and evaluate cause and effect of uneven water resources. The model clarified the impact of irrigation on eco-hydrological processes and predicted hydrologic change after TGD and SNWTP to estimate whether dilemmas between water stress, crop productivity, and ecosystem degradation would diminish. The result also showed the missing role of surface water – groundwater interactions and lateral subsurface flow, usually not considered important by assuming stationarity in previous researches of continental scales. A heterogeneous pattern of Time-Integrated Normalized Difference Vegetation Index gradient in agricultural fields helped to estimate uneven crop yield and its relation to water availability. This integrated approach will have some roles not only to re-consider this complex process from the view point of hydrologic and biogeochemical cycles, but also to clarify how the substantial pressures of complicated problems can be overcome by effective trans-boundary solutions.

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Influence of four run-of-river dams on channel morphology and sediment characteristics in Illinois, U.S.A.

Csiki, S.J.C., and B.L. Rhoads, 2013: “Influence of four run-of-river dams on channel morphology and sediment characteristics in Illinois, U.S.A.” Geomorphology, doi: 10.1016/j.geomorph.2013.10.009.

Dams are known to create discontinuities in river flow and sediment transport, with ensuing effects on the fluvial geomorphology of dammed systems. While the effects created by large impoundment dams are well documented, less is known about the influence of small run-of-river dams (common across the eastern United States) on river geomorphology. Recent emphasis on dam removal has focused on run-of-river structures, highlighting the need for improved understanding of the geomorphological effects of these types of dams. This research examines spatial variation in channel morphology and bed sediment character upstream and downstream of four run-of-river dams in Illinois. Results show that the four dams do not create major discontinuities in channel morphology or sediment character. Silt/clay content of bed material at the four sites is higher upstream of the dams than downstream, but this size fraction generally is a minor component by weight of the sediment samples collected. Although percentages of sand are generally higher upstream of the dams and gravel percentages are generally higher downstream, not all of these differences are statistically significant. Longitudinal profiles through the dams and changes in channel depth upstream and downstream of the dams indicate that no major accumulations of sediment have occurred behind the dams. Analysis of 137Cs in sediment cores at two sites shows no evidence of long-term fine sediment storage. Apparently, these dams are not acting as major sediment traps, nor do these structures produce substantial downstream channel erosion. Variability in spatial patterns of channel morphology and sediment characteristics among the sites suggests that local site-specific factors have an important influence on geomorphological responses. Because of this variability, the findings of this study indicate that information on site-specific conditions should be an important consideration in the removal planning process for run-of-river dams.

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River flow changes related to land and water management practices across the conterminous United States

Eng, K., D.M. Wolock, and D.M. Carlisle, 2013: “River flow changes related to land and water management practices across the conterminous United States.” Science of The Total Environment, vv. 463-464, pp. 414-422, doi: 10.1016/j.scitotenv.2013.06.001.

The effects of land and water management practices (LWMP)—such as the construction of dams and roads—on river flows typically have been studied at the scale of single river watersheds or for a single type of LWMP. For the most part, assessments of the relative effects of multiple LWMP within many river watersheds across regional and national scales have been lacking. This study assesses flow alteration—quantified as deviation of several flow metrics from natural conditions—at 4196 gauged rivers affected by a variety of LWMP across the conterminous United States. The most widespread causes of flow changes among the LWMP considered were road density and dams. Agricultural development and wastewater discharges also were associated with flow changes in some regions. Dams generally reduced most attributes of flow, whereas road density, agriculture and wastewater discharges tended to be associated with increased flows compared to their natural condition.

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A decade of geomorphic and hydraulic response to the La Valle Dam Project, Baraboo River, Wisconsin

Greene, S.L., A.J. Krause, and J.C. Knox, 2013: “A decade of geomorphic and hydraulic response to the La Valle Dam Project, Baraboo River, Wisconsin.” Journal of the American Water Resources Association, doi: 10.1111/jawr.12100.

We investigate stream response to the La Valle Dam removal and channel reconstruction by estimating channel hydraulic parameter values and changes in sedimentation within the reservoir. The designed channel reconstruction after the dam removal included placement of a riffle structure at the former dam site. Stream surveys undertaken in 1984 by Federal Emergency Management Agency and in 2001 by Doyle et al. were supplemented with surveys in 2009 and 2011 to study the effects of the instream structure. We created a model in HEC-RAS IV and surface maps in Surfer© using the 1984, 2009, and 2011 surveys. The HEC-RAS IV model for 2009 channel conditions indicates that the riffle structure decreases upstream channel shear stress and velocity, causing renewed deposition of sediment within the former reservoir. We estimate by 2009, 61% of former reservoir sediments were removed during dam removal and channel reconstruction. Between 2009 and 2011 renewed sedimentation within the former reservoir represented approximately 7.85% of the original reservoir volume. The HEC-RAS IV models show the largest impacts of the dam and riffle structure occur at flood magnitudes at or below bankfull. Thus, the riffle and the dam similarly alter channel hydraulics and sediment transport. As such, our models indicate that the La Valle Dam project was a dam replacement rather than a removal. Our results confirm that channel reconstruction method can alter channel hydraulics, geomorphology, and sediment mobility.

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Assessment of consequences of sediment deficit on a gravel river bed downstream of dams in restoration perspectives: Application of a multicriteria, hierarchical and spatially explicit diagnosis

Rollet, A.J., H. Piégay, S. Dufour, G. Bornette, and H. Persat, 2013: “Assessment of consequences of sediment deficit on a gravel river bed downstream of dams in restoration perspectives: Application of a multicriteria, hierarchical and spatially explicit diagnosis.” River Research and Applications, doi: 10.1002/rra.2689.

As regards river restoration, it is fundamental to better link human pressures and environmental responses and to take into consideration not only target species or habitat but diverse ecological elements. This permits to assess sustainable restoration plan, especially concerning sediment augmentation below dams. The use of a hierarchical multicriteria approach on the Ain River permits us to assess a diagnosis of sediment deficit impact integrating several morphological (channel shifting, river bed degradation and river bed coarsening) and ecological components (Riparian and floodplain lake and fish communities). Our diagnosis also integrates a temporal and spatial approach better to link human pressures and environmental responses and to identify the dam effects amongst other drivers (e.g. grazing decline and channel regulation). The results confirm causality links between sediment deficit and slight channel bed degradation (0.01 m.year−1) or channel bed paving and thus highlight the impact of the dam on the drying of the riparian forest and on former channel community. However, the relationship between incision and reduction in active channel lateral mobility is more difficult to establish. The role of sediment deficit in the current variability of the riparian regeneration capacity and, thereby, landscape diversity along the lower valley remains unclear. This study also confirms the relevance of using different ecological indicators, notably because all components present different adjustment time scales, whereas some of them are more sensitive to other impacts.

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A method to consider whether dams mitigate climate change effects on stream temperatures

Null, S.E., S.T. Ligare, and J.H. Viers, 2013: “A method to consider whether dams mitigate climate change effects on stream temperatures.” Journal of the American Water Resources Association, doi: 10.1111/jawr.12102.

This article provides a method for examining mesoscale water quality objectives downstream of dams with anticipated climate change using a multimodel approach. Coldwater habitat for species such as trout and salmon has been reduced by water regulation, dam building, and land use change that alter stream temperatures. Climate change is an additional threat. Changing hydroclimatic conditions will likely impact water temperatures below dams and affect downstream ecology. We model reservoir thermal dynamics and release operations (assuming that operations remain unchanged through time) of hypothetical reservoirs of different sizes, elevations, and latitudes with climate-forced inflow hydrologies to examine the potential to manage water temperatures for coldwater habitat. All models are one dimensional and operate on a weekly timestep. Results are presented as water temperature change from the historical time period and indicate that reservoirs release water that is cooler than upstream conditions, although the absolute temperatures of reaches below dams warm with climate change. Stream temperatures are sensitive to changes in reservoir volume, elevation, and latitude. Our approach is presented as a proof of concept study to evaluate reservoir regulation effects on stream temperatures and coldwater habitat with climate change.

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The possible negative consequences of underground dam and reservoir construction and operation in coastal karst areas: An example of the hydro-electric power plant (HEPP) Ombla near Dubrovnik (Croatia)

Roje-Bonacci, T., and O. Bonacci, 2013: “The possible negative consequences of underground dam and reservoir construction and operation in coastal karst areas: An example of the hydro-electric power plant (HEPP) Ombla near Dubrovnik (Croatia).” Natural Hazards and Earth System Sciences, v. 13, pp. 2041-2052, doi: 10.5194/nhess-13-2041-2013.

The Ombla Spring represents a typical abundant coastal karst spring located in the vicinity of the town of Dubrovnik (Croatia). Its outlet is at an altitude of 2.5 m above sea level (m a.s.l.) and the water from it immediately flows into the Adriatic Sea. The minimum and maximum measured discharges are 3.96 m3 s−1 and 117 m3 s−1, respectively. The Trebišnjica River traverses through its catchment. The mean annual discharge, after the canalization of over 60 km of its watercourse with spray concrete (in the time span 1981–2011), is 24.05 m3 s−1. Before massive civil engineering work which took place during 1968–1980, the mean annual discharge was 28.35 m3 s−1. There is a project for construction of the hydro-electric power plant (HEPP) Ombla, which will exclusively use groundwater from the Ombla Spring karst aquifer. The underground dam will be constructed about 200 m behind the existing karst spring outflow in the karst massif, by injecting a grout curtain. The top of the grout curtain is planned to be at an altitude of 130 m a.s.l. This karst system is complex, sensitive, vulnerable and ecologically extremely valuable. The grout curtain, as well as the HEPP Ombla development, could lead to extremely dangerous technical and environmental consequences. In this paper some probable, negative consequences of the HEPP Ombla construction and development are explained. The HEPP Ombla could result in many large and hard-to-predict negative consequences which are specific for this particular HEPP, for example (1) severe spring discharge change; (2) unpredictable regional groundwater redistribution; (3) threatening of endemic fauna; (4) induced seismicity; (5) induced sinkholes; (6) occurrence of landslides; (7) conflict regarding internationally shared karst aquifers; (8) intensification of karst flash floods; (9) sea water intrusion in coastal karst aquifer; etc.

Open Access

Sediment trapping by dams creates methane emission hot spots

Maeck, A., T. DelSontro, D.F. McGinnis, H. Fischer, S. Flury, M. Schmidt, P. Fietzek, and A. Lorke, 2013: “Sediment trapping by dams creates methane emission hot spots.” Environmental Science and Technology, v. 47, pp. 8130-8137, doi: 10.1021/es4003907.

Inland waters transport and transform substantial amounts of carbon and account for 18% of global methane emissions. Large reservoirs with higher areal methane release rates than natural waters contribute significantly to freshwater emissions. However, there are millions of small dams worldwide that receive and trap high loads of organic carbon and can therefore potentially emit significant amounts of methane to the atmosphere. We evaluated the effect of damming on methane emissions in a central European impounded river. Direct comparison of riverine and reservoir reaches, where sedimentation in the latter is increased due to trapping by dams, revealed that the reservoir reaches are the major source of methane emissions (0.23 mmol CH4 m–2 d–1 vs 19.7 mmol CH4 m–2 d–1, respectively) and that areal emission rates far exceed previous estimates for temperate reservoirs or rivers. We show that sediment accumulation correlates with methane production and subsequent ebullitive release rates and may therefore be an excellent proxy for estimating methane emissions from small reservoirs. Our results suggest that sedimentation-driven methane emissions from dammed river hot spot sites can potentially increase global freshwater emissions by up to 7%.

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