Lateral Hydrological Connectivity Research Articles

The seasonality of macroinvertebrate β diversity along the gradient of hydrological connectivity in a dynamic river-floodplain system

Anthropogenic disturbance to natural hydrological connectivity, both longitudinal, lateral, and vertical, is threatening the ecological integrity of the freshwater realm. River-floodplain system is particularly adversely affected by the reduction in lateral hydrological connectivity (LHC), representing one of major biodiversity hotspots under increasingly pressure. Many studies have demonstrated that LHC has great influence on the spatial variations of flora and fauna communities (i.e. spatial β diversity) through facilitating dispersal. However, to fully understand the impact of anthropogenic disturbances on biodiversity, we must also understand how ecological communities change over time (i.e. temporal β diversity, TBI) and the underlying processes. To evaluate the processes structuring ecological communities, we examined the macroinvertebrate TBI in habitats along the gradient of LHC for an entire hydrological cycle in West Dongting Lake, a Ramsar-listed floodplain wetland at the middle reach of Yangtze River. Our results showed that the total spatial β diversity fluctuated with water level and peaked at high-water phase, and LHC was the driving forcing affecting both species richness and abundance in all hydrological periods. In particular, species richness and abundance were highest in habitats with medium LHC levels for water-rising and high-water periods reflecting the intermediate disturbance hypothesis except for water-recessing, during which there was no clear pattern. While replacement determined β diversity in most sites at water-rising and high-water phases, the contribution of nestedness were high during water-withdrawing phase. From water-rising to high-water, macroinvertebrates from other habitats spread to the modified mudflats, which had the lowest LHC, along with the floods. During water-withdrawing period, β diversity and its turnover component of all habitats were low compared with other hydrological phases. Temporal β diversity analysis illustrated that the species dispersal was the main mechanism underlying the temporal and spatial variations in the observed community patterns. These findings demonstrated that hydrological connectivity was critical to maintaining the ecological integrity of river-floodplain ecosystems.

Decomposition and nutrient variations of Suaeda salsa litters under different hydrological connectivities and placement patterns in a typical Chinese estuary

A 200-day tethered litter experiment was performed to evaluate the effects of two dimensions of hydrological connectivity (lateral and longitudinal, two perpendicular dimensions) and three placement treatments (surface, semi-buried, and buried) on Suaeda salsa litter decomposition and nutrient release. We used the hydrodynamic condition to represent hydrological connectivity. Mass loss in semi-buried and buried treatments was higher than the surface treatment (p < 0.05), and the former two were basically the same except for the area farthest from the tidal creek. The enhancement of lateral hydrological connectivity significantly accelerated mass loss under the surface and semi-buried treatments (p < 0.05). Sulfur (S) and nitrogen (N) concentrations in the surface treatment were higher than another two treatments in most cases. N concentrations increased with enhancing lateral hydrological connectivity, while potassium (K) concentrations showed a decreasing trend under stronger hydrological connectivity. Phosphorus (P) and S concentrations were not affected by hydrological connectivity. The amount of nutrient release increased with the enhancement of the lateral hydrological connectivity in the surface and semi-buried treatments except for N, and the longitudinal hydrological connectivity only influenced K under the surface treatments. The amount of nutrient release under the surface treatments was lower than another two treatments (p < 0.05). Our findings suggest that the lateral hydrological connectivity has a greater impact on mass loss and nutrient release than the longitudinal hydrological connectivity. If Suaeda. salsa litters are excessively exposed to soil, decomposition processes would increase rapidly and the effects of hydrological connectivity might become minimal.

Lateral hydrological connectivity differentially affects the community characteristics of multiple groups of aquatic invertebrates in tropical wetland pans in South Africa

Abstract River–floodplain connectivity (i.e. lateral hydrological connectivity, LHC) can directly affect the community characteristics by promoting dispersal of organisms but can also have profound indirect effects by altering local habitat characteristics. A major challenge is to disentangle the relative importance of direct and indirect effects of LHC on organisms. Combining taxonomic data with trait information allows a more mechanistic understanding of how LHC affect biotic communities in floodplains. Here, we attempted to determine the relative importance of the direct and indirect effects of LHC on local environmental variables and community characteristics (taxonomic and trait composition) of three different taxonomic organism groups in a set of 33 temporary floodplain pans along a gradient of LHC. In addition, we specifically aimed to unravel the underlying mechanisms shaping patterns of taxonomic diversity by partitioning compositional dissimilarity between ponds into components of nestedness and spatial turnover. Variation partitioning revealed that most differences in macroinvertebrate and zooplankton community composition between pans resulted from variation in local environmental variables, particularly macrophyte cover and the presence of fish. For large branchiopod crustaceans, however, partitioning indicated that LHC did significantly affect both taxonomic and trait community composition, and reduced local taxon diversity. Partitioning taxonomic and trait β‐diversity showed that community dissimilarity between pans was largely determined by turnover, rather than by nestedness. Overall, our study revealed that the effects of LHC on aquatic invertebrate communities act mainly indirectly by altering local environmental conditions. Although the effects of LHC were significant, they were small compared to those of environmental variables. Our results from the partitioning of taxonomic and trait β‐diversity have important implications for biodiversity conservation efforts in the Ndumo region. We demonstrate the need to conserve multiple pans along the LHC gradient to sustain high regional diversity. A common practice in the study area mainly focuses on the conservation of river‐connected or larger pans.

Acoustic communities reflects lateral hydrological connectivity in riverine floodplain similarly to macroinvertebrate communities

Recent studies revealed that information on ecological patterns and processes can be investigated using sounds emanating from animal communities. In freshwater environments, animal communities are strongly shaped by key ecological factors such as lateral connectivity and temperature. We predict that those ecological factors are linked to acoustic communities formed by the collection of sounds emitted underwater. To test this prediction, we deployed a passive acoustic monitoring during 15 days in six floodplain channels of the European river Rhône. The six channels differed in their temperature and level of lateral connectivity to the main river. In parallel, we assessed the macroinvertebrate communities of these six channels using classical net sampling methods. A total of 128 sound types and 142 animal taxa were inventoried revealing an important underwater diversity. This diversity, instead of being randomly distributed among the six floodplain channels, was site-specific. Generalized mixed-effects models demonstrated a strong effect of both temperature and lateral connectivity on acoustic community composition. These results, congruent with macroinvertebrate community composition, suggest that acoustic communities reflect the interactions between animal communities and their environment. Overall our study strongly supports the perspectives offered by acoustic monitoring to describe and understand ecological patterns in freshwater environments.

Effects of loss of lateral hydrological connectivity on fish functional diversity

Loss of lateral hydrological connectivity (LHC) is a major cause of biodiversity decline in river floodplains, yet little is known about its effects on aquatic functional diversity in these ecosystems. We quantified functional alpha and beta diversity of fish assemblages in Yangtze River floodplain lakes and explored their responses to loss of LHC with generalized linear mixed models. Functional richness was much lower in lakes that were not connected to the Yangtze River (i.e., disconnected lakes), where functional evenness and divergence were higher. LHC was the most important factor shaping fish diversity patterns in this region. Predicted reductions in functional richness and taxonomic richness due to LHC loss were higher for functional richness (0.47-0.82) than taxonomic richness (0.32) for all species assemblages except nonmigratory species. The distribution of functional strategies of migratory and nonmigratory fishes was highly uneven throughout the floodplain. Taxonomic beta diversity was much higher than functional beta diversity. The former was due mainly to spatial turnover (73.6-83.8%), which suggested that dissimilarity of diversity among fish assemblages was largely induced by species replacement. The latter was induced by the nestedness-resultant component of overall beta diversity (70.7-86.0%), which indicated a high degree of function loss without replacement. Both taxonomic and functional beta diversity were higher in disconnected lakes, where they were significantly correlated with fishing activity and water quality, than in river-connected lakes. We showed for the first time the effects of loss of LHC on fish functional diversity in large river floodplains. We found a serious decline of fish functional richness in the Yangtze floodplain, and functional diversity remained highly vulnerable to loss of LHC even though this is a species-rich ecosystem.

Toward floodplain rejuvenation in the middle Ebro River (Spain): From history to action

The Mediterranean region is recognized as one of Earth's biodiversity hotspots, but disconnection of habitats and fluxes of energy and nutrients have made them particularly vulnerable to external perturbations in the current context of global warming. This paper presents a multitemporal approach to understand how past human impacts have led to present deficits in fluvial dynamics and to propose and assess possible future restoration scenarios. First, biogeomorphic regression and progression dynamics of the middle Ebro River (Spain) were studied at the reach scale over a period of 90 years (1927–2014). River bank fixations, flood defenses, and incision have caused a disconnection between the river and its floodplain leading to a remarkable tendency for stabilization and vegetation progression to forest. Restoration of processes is necessary for those rivers where rejuvenation is no longer occurring. Second, the selected restoration target for the studied middle Ebro River section focuses on the improvement of lateral hydrological connectivity and partial recovery of regression processes (bank erosion and riverbank vegetation succession disruption). Besides the base scenario (situation in 2014), three more restoration scenarios include levee opening, levee complete removal, and side channel reactivation. Finally, results from two-dimensional hydraulic simulations allow for sensitivity analysis, comparing the current situation with the proposed scenarios. The study of shear stress is used as a proxy for the initiation of side erosion and vegetation succession disruption. Outcomes indicate that scenarios would create conditions for mobilization of habitat patches in formerly stable floodplain areas, especially with the scenario of levee removal. The possibility of regaining channel mobility and floodplain connection would allow the fluvial system to increase its water retention capacity and, thus, to adapt to floods and droughts associated to climate change.

Targeting lateral connectivity and morphodynamics in a large river‐floodplain system: The upper Rhine River

AbstractAs a consequence of historical damming and channelization, most large rivers are disconnected from their floodplains, which therefore endure severe deficits in fluvial dynamics. Regaining some degree of lateral connectivity can lead to improved geomorphological and biological interactions. Yet, it is necessary to take into account limitations posed by current uses and legislation. This study presents a methodological approach to the selection of a realistic restoration target for a heavily modified large river segment, the free‐flowing Upper Rhine River downstream of Iffezheim dam (France–Germany border), based on the analysis of the existing biogeomorphic deficits, constraints set by human uses, and previous restoration experiences. To achieve the selected restoration target, proposed scenarios include embankment removal, bank lowerings, and side channel widenings with the aim of increasing lateral hydrological connectivity and promoting morphodynamics (bank erosion in lateral channels) that allow for the renewal of floodplain habitats. Results from 2‐D hydraulic simulations allow for a sensitivity analysis, comparing the current situation with the proposed scenarios, through parameters such as shore length of side channels actively connected at both ends to the main channel (eupotamon), and shear stress as a proxy for initiation of gravel erosion. Outcomes indicate that the two proposed restoration scenarios would succeed in reconnecting side channels and in increasing areas prone to substrate erosion, while maintaining flood protection and the heaviest navigation use among European rivers. The presented approach aids in the assessment of potential large river restoration scenarios and, thus, in the discussion of water management strategies.

Longitudinal variability in lateral hydrologic connectivity shapes fish occurrence in temporary floodplain ponds

Dynamic flow regimes maintain critical connections between main channel and adjacent floodplain habitats that provide fish access to shelter, foraging, and spawning opportunities. Our study advances the understanding of these processes by exploring the importance of coupled longitudinal–lateral connectivity for determining species occurrence in headwater streams of the Amazon. Using a multispecies occupancy model, we revealed a clear pattern of species addition in the downstream direction in temporary floodplain ponds, associated with changes in the pool of potential colonists present in the channel and with increasing lateral hydrologic connectivity. Species that are more tolerant of stagnant waters and those able to disperse in shallow habitats (e.g., Anablepsoides micropus) occurred frequently in ponds along the entire longitudinal extent, whereas those species preferring lotic habitats were present only in the most downstream sites. We also observed increasing similarity of pond and channel communities with distance downstream. This study provides insights on the spatial structuring of tropical fish communities in response to flood-induced hydrologic connectivity and further highlights the vulnerability of floodplain fishes to modification in flooding regimes.

Modeling hydrologic connectivity and virtual fish movement across a large Southeastern floodplain, USA

Lateral hydrologic connectivity between a river and its floodplain is important for exchanges of organisms and materials that support healthy, functioning riverine ecosystems. We use a GIS-based distance, cost-weighted spatial model to measure the possible pathways and travel durations for fish migrating from a mainstem river channel to ten different floodplain lakes during a range of discharge magnitudes. We modeled routes of movement and fish swim times for five discharges that ranged from 140 to 1585 m3 s−1 and represented a gradient of hydrologic connectivity. Hydrologic travel pathways included perennial floodplain channels (tributaries and permanent lakes) and intermittently active floodplain channels (channels re-occupying abandoned meander segments, meander-scrolls, batture channels, and crevasses). The different hydrologic pathways made available during the different discharge magnitudes were represented using spatially-variable, raster-based cost surfaces. Fish swim times and route of movement varied with discharge magnitude and lake location. Two distinct patterns emerged between the fish swim times and routes of movement. One group of five floodplain lakes experienced very little change in the route or rate of fish movement with increasing discharge, while another group of five lakes exhibited significant decreases in swim time with increasing discharge. These responses indicate the importance of managing for flood pulses of various magnitudes that hydrologically connect the river and floodplain through different pathways, enabling dynamic spatial and temporal exchanges of organisms and materials.

Beaver‐mediated lateral hydrologic connectivity, fluvial carbon and nutrient flux, and aquatic ecosystem metabolism

AbstractRiver networks that drain mountain landscapes alternate between narrow and wide valley segments. Within the wide segments, beaver activity can facilitate the development and maintenance of complex, multithread planform. Because the narrow segments have limited ability to retain water, carbon, and nutrients, the wide, multithread segments are likely important locations of retention. We evaluated hydrologic dynamics, nutrient flux, and aquatic ecosystem metabolism along two adjacent segments of a river network in the Rocky Mountains, Colorado: (1) a wide, multithread segment with beaver activity; and, (2) an adjacent (directly upstream) narrow, single‐thread segment without beaver activity. We used a mass balance approach to determine the water, carbon, and nutrient source‐sink behavior of each river segment across a range of flows. While the single‐thread segment was consistently a source of water, carbon, and nitrogen, the beaver impacted multithread segment exhibited variable source‐sink dynamics as a function of flow. Specifically, the multithread segment was a sink for water, carbon, and nutrients during high flows, and subsequently became a source as flows decreased. Shifts in river‐floodplain hydrologic connectivity across flows related to higher and more variable aquatic ecosystem metabolism rates along the multithread relative to the single‐thread segment. Our data suggest that beaver activity in wide valleys can create a physically complex hydrologic environment that can enhance hydrologic and biogeochemical buffering, and promote high rates of aquatic ecosystem metabolism. Given the widespread removal of beaver, determining the cumulative effects of these changes is a critical next step in restoring function in altered river networks.

Latitudinal variation of migratory life histories of riverine Galaxias maculatus in Chile (36°- 47°S)

Event Abstract Back to Event Latitudinal variation of migratory life histories of riverine Galaxias maculatus in Chile (36°- 47°S) Konrad Górski1, 2*, Evelyn M. Habit2 and Aliro J. Manosalva2 1 Universidad Católica de la Santísima Concepción, Departamento de Ecología, Chile 2 Universidad de Concepción, Facultad de Ciencias Ambientales, Chile A relationship between life histories and increasing latitude has been described for Northern Hemisphere riverine fish, whereby life cycles that complete most of the growth in the ocean are favoured at higher latitudes. In the riverine ecosystems of the Southern Hemisphere many species of galaxiids display highly flexible migratory life histories and the mechanisms driving employment of different strategies remain unclear. Our objective was to assess the mechanisms driving the selection of migratory strategies of Galaxias maculatus from rivers across a gradient of latitude. Fifteen fish from three size classes as well as water samples were collected from upper, middle and lower sections of 10 river systems in Chile across latitudes 36°- 47°S. Otoliths and water samples were analysed for a suite of trace elements using Laser Ablation Inductively Coupled Plasma Mass Spectrometry. Otolith elemental composition was analysed through depth profiling to assess the frequency of marine migrations in each section of each river. The propensity of marine migrations was strongly related to latitude as well as flow and temperature dynamics of each river system. Fish in river systems at higher latitudes more frequently displayed use of marine and brackish habitats, potentially enabling them to maximise foraging opportunities and increase recruitment success. River systems originating from large Andean lakes with more predictable flow pattern (large scale spring floodplain inundations and therefore more predictable food supplies) accommodated more resident individuals with no marine signatures even at higher latitudes. Therefore, climate as well as both longitudinal (headwaters-estuary) and lateral (main channel-floodplains) hydrologic connectivity seem to govern migratory strategies of riverine Galaxias maculatus. Consequently, management strategies that promote both lateral and longitudinal connectivity within riverine ecosystems are crucial to maximise habitat availability for this native fish species. Acknowledgements Financial support: Fondecyt 3130690, DIUC 213.310.063-1AP Keywords: Fish migration, Diadromy, LA-ICP-MS, Otolith microchemistry, Puye, īnanga Conference: XV European Congress of Ichthyology, Porto, Portugal, 7 Sep - 11 Sep, 2015. Presentation Type: Oral Presentation Topic: Otoliths as a tool to study fish life cycles Citation: Górski K, Habit EM and Manosalva AJ (2015). Latitudinal variation of migratory life histories of riverine Galaxias maculatus in Chile (36°- 47°S). Front. Mar. Sci. Conference Abstract: XV European Congress of Ichthyology. doi: 10.3389/conf.fmars.2015.03.00031 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 23 Oct 2015; Published Online: 04 Nov 2015. * Correspondence: Dr. Konrad Górski, Universidad Católica de la Santísima Concepción, Departamento de Ecología, Concepción, Chile, konrad.gorski@uach.cl Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Konrad Górski Evelyn M Habit Aliro J Manosalva Google Konrad Górski Evelyn M Habit Aliro J Manosalva Google Scholar Konrad Górski Evelyn M Habit Aliro J Manosalva PubMed Konrad Górski Evelyn M Habit Aliro J Manosalva Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Flooding and Surface Connectivity of Taxodium‐Nyssa Stands in a Southern Floodplain Forest Ecosystem

AbstractAn understanding of the factors controlling the permanent and episodic links between the main stem of a river and the ecosystems of its alluvial floodplain is necessary for evaluating the influence of modern river processes on floodplain ecology and habitat diversity and for the successful implementation of flow regimes that meet human needs for water in a manner that sustains the ecological integrity of affected systems. In this study, we examined relationships between river hydrology and lateral hydrological connectivity, which is crucial to directing fluxes of water, material, and organisms into and across a floodplain. We did so by translating measures of river discharge for the Congaree River into high resolution maps of flood conditions for the floodplain at Congaree National Park using a 2D flood inundation model. Utilizing a graph network approach, we then analyzed the connectivity of a key wetland ecosystem, Taxodium‐Nyssa forested swamps, to the main stem river and to each other under different flows. Our results underscore that floodplain connectivity is initiated at sub‐bankfull discharges and does not depend on levee overtopping, while also clarifying that various sources of connectivity are triggered at different flow levels in specific reaches. Further, our findings demonstrate the sensitive and non‐linear response of floodplain connectivity to river flows and provide useful information to facilitate the management of flood processes in the Congaree River watershed. Copyright © 2014 John Wiley &amp; Sons, Ltd.

BioEarth: Envisioning and developing a new regional earth system model to inform natural and agricultural resource management

As managers of agricultural and natural resources are confronted with uncertainties in global change impacts, the complexities associated with the interconnected cycling of nitrogen, carbon, and water present daunting management challenges. Existing models provide detailed information on specific sub-systems (e.g., land, air, water, and economics). An increasing awareness of the unintended consequences of management decisions resulting from interconnectedness of these sub-systems, however, necessitates coupled regional earth system models (EaSMs). Decision makers’ needs and priorities can be integrated into the model design and development processes to enhance decision-making relevance and “usability” of EaSMs. BioEarth is a research initiative currently under development with a focus on the U.S. Pacific Northwest region that explores the coupling of multiple stand-alone EaSMs to generate usable information for resource decision-making. Direct engagement between model developers and non-academic stakeholders involved in resource and environmental management decisions throughout the model development process is a critical component of this effort. BioEarth utilizes a bottom-up approach for its land surface model that preserves fine spatial-scale sensitivities and lateral hydrologic connectivity, which makes it unique among many regional EaSMs. This paper describes the BioEarth initiative and highlights opportunities and challenges associated with coupling multiple stand-alone models to generate usable information for agricultural and natural resource decision-making.

Floodplain connectivity facilitates significant export of zooplankton to the main River Murray channel during a flood event

This study assessed the role that floods play in providing lateral connectivity between riverine habitats and floodplains, stimulating productivity and contributing zooplankton from the floodplain to the river channel. The study took place on the Chowilla Floodplain of the River Murray, Australia, and the adjacent River Murray Channel throughout the 2010–2011 floods. We found that a considerable transfer of zooplankton from the floodplain into the river channel occurred. Average zooplankton abundance was higher on the floodplain than the main river channel and increased the zooplankton abundance in the river channel downstream. At the peak of the flood, flows reached ~93 000 megalitres per day (ML d−1), inundating ~67 km2 of floodplain. At the time of this study, up to 6.3 ± 1.6 (SD) tonnes per day of zooplankton (dryweight) was being exported from the Chowilla floodplain. Differences in species assemblages were also observed within the River Murray, which seemed to be caused by the influence of the Chowilla Floodplain. This study demonstrated that floodplains provide significant zooplankton biomass, which constitutes a resource input into the riverine food web. These results provide some evidence for the Flood Pulse Concept, which highlights the importance of lateral hydrological connectivity between riverine habitats and floodplains in stimulating productivity and providing a linkage between habitats for biota. Management of regulated lowland rivers should consider not only the provision of water to the floodplain, but also the return of the floodplain waters to the river to sustain riverine food webs .

Assessing fish assemblages similarity above and below a dam in a neotropical reservoir with partial blockage.

Damming rivers disrupts the water flow and changes the ichthyofauna organisation. We investigated an impoundment with permanent connection and homogeneous environmental conditions between the zones above and below the dam. Temperature was comparatively higher during wet season irrespective of zone, and both zones had higher dissolved oxygen, conductivity and transparency in the dry season. A total of 1687 individuals comprising 27 species were collected in the downriver zone, while the reservoir had 879 individuals and 23 species. Each zone had different fish assemblage composition and structure, but assemblages were not explained by the examined environmental variables (r2 = 0.08; p = 0.307). Migratory species such as Pimelodus maculatus, Pimelodus fur, Leporinus copelandii and Prochilodus lineatus were the most affected, and probably are prevented to perform upriver migrations. On the other hand, lentic adapted species such as G. brasiliensis, Hoplias malabaricus and Hoplosternum littorale successfully colonised the reservoir. Therefore we conclude that the presence of the lateral hydrological connectivity alone does not guarantee the ecological connectivity since fish assemblage similarity differed between the two zones. Fish passage facilities should be monitored and managed to evaluate and improve their functionality.

Cyanobacteria enhance methylmercury production: A hypothesis tested in the periphyton of two lakes in the Pantanal floodplain, Brazil

The toxic potential of mercury (Hg) in aquatic systems is due to the presence and production of methylmercury (MeHg). Recent studies in tropical floodplain environments showed that periphyton associated with the roots of aquatic macrophytes produce MeHg. Periphyton communities are the first link in the food chain and one of the main MeHg sources in aquatic environments. The aim of this work was to test the hypotheses that the algal community structure affects potential methylation, and ecologically distinct communities with different algal and bacterial densities directly affect the formation of MeHg in the roots of macrophytes. To evaluate these, net MeHg production in the roots of Eichhornia crassipes in relation to the taxonomic structure of associated periphytic algae was evaluated. Macrophyte root samples were collected in the dry and flood season from two floodplain lakes in the Pantanal (Brazil). These lakes have different ecological conditions as a function of their lateral hydrological connectivity with the Paraguay River that is different during times of drought. Results indicated that MeHg production was higher in the flood season than in the dry season. MeHg production rates were higher in the disconnected lake in comparison to the connected lake during the dry season. MeHg production exhibited a strong positive co-variation with cyanobacteria abundance (R2=0.78; p<0.0001 in dry; R2=0.40; p=0.029 in flood) and with total algal biomass (R2=0.86; p<0.0001), and a negative co-variation with Zygnemaphyceae (R2=0.50; p=0.0018) in the lake community in dry season. This indicates that ecological conditions that favour the establishment and development of cyanobacteria are associated with higher rates of methylation in aquatic systems. This suggests that cyanobacteria could be a proxy for sites of MeHg production in some natural aquatic environments.

Global river hydrography and network routing: baseline data and new approaches to study the world's large river systems

AbstractDespite significant recent advancements, global hydrological models and their input databases still show limited capabilities in supporting many spatially detailed research questions and integrated assessments, such as required in freshwater ecology or applied water resources management. In order to address these challenges, the scientific community needs to create improved large‐scale datasets and more flexible data structures that enable the integration of information across and within spatial scales; develop new and advanced models that support the assessment of longitudinal and lateral hydrological connectivity; and provide an accessible modeling environment for researchers, decision makers, and practitioners. As a contribution, we here present a new modeling framework that integrates hydrographic baseline data at a global scale (enhanced HydroSHEDS layers and coupled datasets) with new modeling tools, specifically a river network routing model (HydroROUT) that is currently under development. The resulting ‘hydro‐spatial fabric’ is designed to provide an avenue for advanced hydro‐ecological applications at large scales in a consistent and highly versatile way. Preliminary results from case studies to assess human impacts on water quality and the effects of dams on river fragmentation and downstream flow regulation illustrate the potential of this combined data‐and‐modeling framework to conduct novel research in the fields of aquatic ecology, biogeochemistry, geo‐statistical modeling, or pollution and health risk assessments. The global scale outcomes are at a previously unachieved spatial resolution of 500 m and can thus support local planning and decision making in many of the world's large river basins. Copyright © 2013 John Wiley &amp; Sons, Ltd.

Maintaining and restoring hydrologic habitat connectivity in mediterranean streams: an integrated modeling framework

Hydrologic alterations designed to provide a stable water supply and to prevent flooding are commonly used in mediterranean-climate river (med-rivers) basins, and these alterations have led to habitat loss and significant declines in aquatic biodiversity. Often the health of freshwater ecosystems depends on maintaining and recovering hydrologic habitat connectivity, which includes structural components related to the physical landscape, functionality of flow dynamics, and an understanding of species habitat requirements for movement, reproduction, and survival. To advance our understanding of hydrologic habitat connectivity and benefits of habitat restoration alternatives we provide: (1) a review of recent perspectives on hydrologic connectivity, including quantitative methods; and (2) a modeling framework to quantify the effects of restoration on hydrologic habitat connectivity. We then illustrate this approach through a case study on lateral hydrologic habitat connectivity that results from channel restoration scenarios using scenarios with different historic and climate-change flows to restore fish floodplain habitat in a med-river, the San Joaquin River, California. Case study results show that in addition to the channel alterations, higher flows are required to recover significant flooded habitat area, especially given reductions in flows expected under climate change. These types of studies will help the planning for restoration of hydrologic habitat connectivity in med-rivers, a critical step for mediterranean species recovery.

Effects of hydrologic connectivity on aquatic macroinvertebrate assemblages in different marsh types

AB Aquatic Biology Contact the journal Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AB 18:149-160 (2013) - DOI: https://doi.org/10.3354/ab00499 Effects of hydrologic connectivity on aquatic macroinvertebrate assemblages in different marsh types Sung-Ryong Kang1,*, Sammy L. King2 1School of Renewable Natural Resources, LSU AgCenter, Baton Rouge, Louisiana 70803-4301, USA 2US Geological Survey, Louisiana Fish and Wildlife Cooperative Research Unit, LSU AgCenter, Baton Rouge, Louisiana 70803-4301, USA *Email: skang1@tigers.lsu.edu ABSTRACT: Hydrologic connectivity can be an important driver of aquatic macroinvertebrate assemblages. Its effects on aquatic macroinvertebrate assemblages in coastal marshes, however, are relatively poorly studied. We evaluated the effects of lateral hydrologic connectivity (permanently connected ponds: PCPs; temporary connected ponds:TCPs), and other environmental variables on aquatic macroinvertebrate assemblages and functional feeding groups (FFGs) in freshwater, brackish, and saline marshes in Louisiana, USA. We hypothesized that (1) aquatic macroinvertebrate assemblages in PCPs would have higher assemblage metric values (density, biomass, Shannon-Wiener diversity) than TCPs and (2) the density and proportional abundance of certain FFGs (i.e. scrapers, shredders, and collectors) would be greater in freshwater marsh than brackish and saline marshes. The data in our study only partially supported our first hypothesis: while freshwater marsh PCPs had higher density and biomass than TCPs, assemblage metric values in saline TCPs were greater than saline PCPs. In freshwater TCPs, long duration of isolation limited access of macroinvertebrates from adjacent water bodies, which may have reduced assemblage metric values. However, the relatively short duration of isolation in saline TCPs provided more stable or similar habitat conditions, facilitating higher assemblage metric values. As predicted by our second hypothesis, freshwater PCPs and TCPs supported a greater density of scrapers, shredders, and collectors than brackish and saline ponds. Aquatic macroinvertebrate assemblages seem to be structured by individual taxa responses to salinity as well as pond habitat attributes. KEY WORDS: Coastal marsh · Aquatic macroinvertebrate assemblage · Hydrologic connectivity · Functional feeding groups Full text in pdf format PreviousNextCite this article as: Kang SR, King SL (2013) Effects of hydrologic connectivity on aquatic macroinvertebrate assemblages in different marsh types. Aquat Biol 18:149-160. https://doi.org/10.3354/ab00499 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AB Vol. 18, No. 2. Online publication date: April 03, 2013 Print ISSN: 1864-7782; Online ISSN: 1864-7790 Copyright © 2013 Inter-Research.

Functional diversity in a large river floodplain: anticipating the response of native and alien macroinvertebrates to the restoration of hydrological connectivity

Summary Rivers and floodplains are among the most threatened ecosystems. Hydroelectric power plants and embankments have reduced the hydrological connectivity between rivers and their floodplain channels, leading to loss of freshwater habitats and biological communities. To prevent and reverse such loss, numerous restoration programmes have aimed at rejuvenating the lateral hydrological connectivity between rivers and floodplain channels. Despite considerable global attention, we know remarkably little about the ecological benefits of floodplain restoration programmes. We analysed the functional diversity of different macroinvertebrate groups (natives and aliens) along a gradient of lateral hydrological connectivity on the Rhône river in France. We used 36 sampling sites to describe the functional diversity (Rao's quadratic entropy) before and after the enhancement of the lateral hydrological connectivity by restoration. The effects of restoration on functional diversity were tested for each macroinvertebrate group and at multiple spatial levels (alpha and beta). Before restoration, alpha functional diversity of the entire macroinvertebrate community peaked in sites with a high lateral connectivity. The contribution of the native groups to functional diversity was higher than that of the alien group. The latter was not constrained by high values of lateral hydrological connectivity and reached a maximum in highly connected sites. After restoration, within‐site functional diversity (alpha FD) declined linearly following the enhancement of lateral hydrological connectivity. The restoration operations increased the contribution of the aliens to functional diversity and reduced the contribution of a group of native taxa. In addition, among‐sites functional diversity (beta FD) was successfully enlarged by restoration. Synthesis and applications. The lateral hydrological connectivity (LHC) represents a key parameter for explaining the functional diversity (FD) of macroinvertebrates in a floodplain ecosystem. Our results demonstrate that restoration‐induced changes to functional diversity can be predicted. Controversially, restoration‐induced enhancement of lateral hydrological connectivity increased the functional diversity of the alien macroinvertebrates. However, these species contributed only to a small part of the total macroinvertebrate functional diversity. We recommend that restoration programmes diversify the levels of lateral hydrological connectivity among the channels to ensure an optimal functional diversity at the floodplain scale.