In-channel Habitat Research Articles

An evaluation of tradeoffs in restoring ephemeral vs. perennial habitats to conserve animal populations

IntroductionHabitat loss and degradation pose significant threats to global fish and wildlife populations, prompting substantial investments in habitat creation and restoration efforts. Not all habitats provide equal benefits, leading to challenges in prioritizing restoration actions. For example, juvenile anadromous salmonids require high quality rearing aquatic habitats to achieve the physiological requirements needed to successfully migrate to the ocean. However, there are profound disagreements among anadromous salmon restoration managers whether it is best to focus efforts on restoring in-channel habitats that are available for the entire rearing period or floodplain habitats that, while facilitating greater growth and survival than in-channel habitats, are only available for a few weeks at a time and are typically only activated every two-to-three years.MethodsWe used an existing fall-run Chinook salmon decision-support model to evaluate under what conditions floodplain restoration would provide greater benefits than in-channel habitat restoration. The simulations included a wide range of floodplain inundation frequencies and durations and floodplain benefits in the form of increased survival and growth relative to in-channel habitats.ResultsThe simulations results indicated that in-channel habitat restoration was always the best habitat restoration action when there was no existing in-channel habitat despite simulating a wide range of flood frequency, duration, and growth and survival benefits. Floodplain restoration was generally best when there was sufficient in-channel habitat available to successfully rear most of the juveniles produced by the returning adult salmon.DiscussionWe hypothesize that in-channel and floodplain habitats have different roles in salmon population maintenance with in-channel habitats regulating the overall population size and floodplains acting as recurrent resource pulses. Our study provides a quantitative framework to evaluate the benefit of these two habitat types and provides generalizable rulesets that can be used by managers when implementing habitat restoration strategies for species that inhabit both in-channel and floodplain habitats.

Removal of Riprap within Channelized Rivers: A Solution for the Restoration of Lateral Channel Dynamics and Bedload Replenishment?

Riverbank erosion is an essential morphodynamic process for the improvement of river health and the ecohydrogeomorphological functioning of alluvial rivers. Lateral channel dynamics and sediment supply caused by bank erosion largely create and maintain heterogeneous in-channel habitats for fauna and aquatic or riparian plant species. However, humans very early started to stabilize riverbanks in order to favour navigation or to prevent valuable land and infrastructures close to the channel from eroding. During the 20th century, bank protection works such as riprap considerably increased and blocked lateral channel erosion, causing a loss of local sediment supply, which in turn resulted in a decrease in local bedload transport and channel incision. The aim of the article is to evaluate to what extent riprap removal may be an efficient restoration measure in terms of the reactivation of bank erosion and the replenishment of the local bedload in gravel-bed floodplain rivers with a sufficient amount of freedom space. An experimental in situ restoration approach was chosen. First, riprap was removed at two geomorphologically contrasting sites on the Allier River, France. Second, bank retreat was monitored, and the volumes eroded were quantified using photogrammetric and LiDAR surveys. Third, in the case of post-restoration bank erosion, grain size and morphological channel evolution analyses were carried out. Our results suggested that the removal of riprap is an effective measure for certain but not all channelized floodplain reaches. The geomorphological and sedimentary contexts are two criteria that should be considered when selecting sites for restoration. Thus, this study helps river managers to better target the criteria to be taken into account for the selection of sites with high potential for the restoration of lateral channel dynamics.

Towards improving an Area of Concern: Main-channel habitat rehabilitation priorities for the Maumee River

The Maumee River watershed in the Laurentian Great Lakes Basin has been impacted by decades of pollution and habitat modification due to human settlement and development. As such, the lower 35 km of the Maumee River and several smaller adjacent watersheds comprising over 2000 km2 were designated the Maumee Area of Concern (AOC) under the revised Great Lakes Water Quality Agreement in 1987. As part of pre-rehabilitation assessments in the Maumee AOC, we assessed fish and invertebrate communities in river km 24–11 of the Maumee River to identify: 1) areas that exhibit the highest biodiversity, 2) habitat characteristics associated with high biodiversity areas, 3) areas in need of protection from further degradation, and 4) areas that could feasibly be rehabilitated to increase biodiversity. Based on benthic trawl data, shallow water habitats surrounding large island complexes had the highest fish diversity and catch per unit effort (CPUE). Electrofishing displayed similar fish diversity and CPUE patterns across habitat types early in the study but yielded no discernable fish diversity or CPUE patterns towards the end of our study. Although highly variable among study sites, macroinvertebrate density was greatest in shallow water habitats <2.5 m and around large island complexes. Our results provide valuable baseline data that could act as a foundation for developing rehabilitation strategies in the lower Maumee River and for assessing the effectiveness of future aquatic habitat rehabilitation projects. In addition to increasing in-channel habitat, watershed-scale improvements of water quality might be necessary to ensure rehabilitation strategies are successful.

Scale-depended effects of hydromorphology and riparian land-use on benthic invertebrates and fish: implications for large river management

Large river management is in increasing demand to establish the ecological quality set by sustainability-oriented legislation. However, there is still a lack of research regarding most relevant scales at which pressures should be addressed. In this study, we compared the relative effects of riparian land-cover at 16 different buffer sizes and hydromorphology at four different river lengths on benthic invertebrate (BI) and fish assemblages in large rivers. Environmental data were obtained digitally (applying GIS) on a broad range of abiotic conditions and were related to biological data using direct gradient analyses. Compared to land-cover, hydromorphology showed greater effect on BI and fish, with in-channel habitat quality characteristics explaining most biotic variability. Both assemblages were best explained by hydromorphology inventoried at the largest 5,000 m scale. We found, however, consideration of longer river segments to be more important for explaining fish variability. Riparian land-cover explained similar percentages of biotic variability across most analysed riparian buffers. Nevertheless, a significant effect of riparian length rather than width was identified. Our findings indicate that, in large rivers, hydromorphological and riparian land-cover conditions affect BI and especially fish at generally longer river segments, implying potential ecological benefits of management measures implemented at larger spatial scales.

Riparian and in-channel habitat properties linked to dragonfly emergence

In freshwater ecosystems, habitat alteration contributes directly to biodiversity loss. Dragonflies are sentinel species that are key invertebrate predators in both aquatic (as larvae) and terrestrial ecosystems (as adults). Understanding the habitat factors affecting dragonfly emergence can inform management practices to conserve habitats supporting these species and the functions they perform. Transitioning from larvae to adults, dragonflies leave behind larval exoskeletons (exuviae), which reveal information about the emergent population without the need for sacrificing living organisms. Capitalizing on Atlantic Canada’s largest freshwater wetland, the Grand Lake Meadows (GLM) and the associated Saint John/Wolastoq River (SJWR), we studied the spatial (i.e., across the mainstem, tributary, and wetland sites) and temporal (across 3 years) variation in assemblages of emergent dragonflies (Anisoptera) and assessed the relative contribution of aquatic and terrestrial factors structuring these assemblages. The GLM complex, including the lotic SJWR and its tributaries and associated lentic wetlands, provided a range of riparian and aquatic habitat variability ideal for studying dragonfly emergence patterns across a relatively homogenous climatic region. Emergent dragonfly responses were associated with spatial, but not temporal, variation. Additionally, dragonfly communities were associated with both aquatic and terrestrial factors, while diversity was primarily associated with terrestrial factors. Specific terrestrial factors associated with the emergence of the dragonfly community included canopy cover and slope, while aquatic factors included water temperature, dissolved oxygen, and baseflow. Our results indicate that management of river habitats for dragonfly conservation should incorporate riparian habitat protection while maintaining aquatic habitat and habitat quality.

Are we overlooking the eco-geomorphic importance of wood in braided rivers?: A case study in Grand Teton National Park

A decades-long body of research has hypothesized a fundamental incompatibility between braided rivers, which form due to a lack of bank cohesion and a highly-mobile channel bed, with vegetation, which stabilizes channel surfaces and hinders sediment mobilization. At the same time, many researchers have observed high densities of wood, occurring either as large jams or dense stands of mature trees, along the braid plain of multi-thread rivers worldwide. Here we seek to reconcile the perceived incompatibility of wood and braided rivers with the high densities of vegetation found along these streams using two multi-thread, gravel-bed rivers in Grand Teton National Park. In August of 2017, we completed topographic surveys along ~500 m reaches of Pacific and Pilgrim Creeks, tributaries to the Snake River in Jackson Hole. We seek to compare digital elevation models generated from these surveys with 2014 elevation data collected via airborne lidar to determine whether in-channel wood drives increases in bar density, depth variability, and in-channel habitat suitability for native salmonids. While the majority of our efforts following the August 2017 field campaign have been focused on lidar data processing and cleaning, our initial results indicate that wood is a dominant driver of bar formation in both Pilgrim and Pacific Creek, and may be the dominant driver of depth variability (e.g., pool scour) in gravel-bed braided streams in Grand Teton National Park.&#x0D; &#x0D; Featured photo by Grand Teton on Flickr. https://flic.kr/p/MyszYZ

Catchments in the future North: interdisciplinary science for sustainable management in the 21st Century

Catchments in the future North: interdisciplinary science for sustainable management in the 21^st Century

Understanding Riverine Habitat Inundation Patterns: Remote Sensing Tools and Techniques

Regulated flow releases are key components in the ecological restoration of river ecosystems. Understanding relationships among hydrology, habitat inundation, and ecological processes at appropriate spatial scales is required to optimise ecological outcomes. This study used high-resolution remotely sensed data to develop a three-dimensional (3D) channel and floodplain riverine habitat inundation model. High-resolution LiDAR and digital imagery data were used to develop 3D digital-elevation models. Data segmentation techniques were used to map channel and non-channel areas, while in-channel habitats were identified through topographic characteristics. Object-oriented analysis was used to separate overbank vegetated and non-vegetated areas. Field surveys were undertaken to record the location and diameter of large woody debris (LWD), and canopy foliar density in addition to general landscape description. A qualitative evaluation of the accuracy of the habitat map showed that LiDAR-based discrimination of topographic features and the derivation of a canopy foliar density layer was successful. Mapping of LWD was unsuccessful due to size relative to the LiDAR point cloud density and vertical resolution. The high-resolution remotely sensed data used in this study provide a useful tool for understanding river processes at reach scales by linking inundation patterns to geomorphic features, providing a framework for predicting ecological outcomes from river flow regimes.

Logjam controls on channel:floodplain interactions in wooded catchments and their role in the formation of multi-channel patterns

The role of wood in the formation and maintenance of complex dynamic floodplain surfaces is important and to date has received relatively limited attention compared to in-channel habitat processes. This paper explores the role of logjams as important agents of channel:floodplain interaction. We draw on a specific case study as well as examples from the literature to show that although the processes of interaction differ, the resulting dynamic floodplain patchwork is a common feature of rivers with logjams. In addition, we contend that the presence of logjams is an important factor in the evolution and maintenance of multiple channel patterns in both montane and lowland river environments. These observations have important implications for the definition of reference targets for river restoration. The specific results of this research show: 1) The presence of a range of types of multiple channel network dissecting the floodplains of low order channels that are strongly associated with the presence of logjams. 2) The relatively rapid formation of floodplain channels following logjam formation. 3) The dynamic nature of logjams within headwater channels on both seasonal and annual timescales that lead to a highly dynamic habitat mosaic on the floodplain surface. 4) An increased frequency of overbank flooding and high rates of floodplain sediment accumulation upstream of logjams and along floodplain channel networks that create the complex topography observed in the case study forested floodplains.

Grazed Riparian Management and Stream Channel Response in Southeastern Minnesota (USA) Streams

The U.S. Department of Agriculture-Natural Resources Conservation Service has recommended domestic cattle grazing exclusion from riparian corridors for decades. This recommendation was based on a belief that domestic cattle grazing would typically destroy stream bank vegetation and in-channel habitat. Continuous grazing (CG) has caused adverse environmental damage, but along cohesive-sediment stream banks of disturbed catchments in southeastern Minnesota, short-duration grazing (SDG), a rotational grazing system, may offer a better riparian management practice than CG. Over 30 physical and biological metrics were gathered at 26 sites to evaluate differences between SDG, CG, and nongrazed sites (NG). Ordinations produced with nonmetric multidimensional scaling (NMS) indicated a gradient with a benthic macroinvertebrate index of biotic integrity (IBI) and riparian site management; low IBI scores associated with CG sites and higher IBI scores associated with NG sites. Nongrazed sites were associated with reduced soil compaction and higher bank stability, as measured by the Pfankuch stability index; whereas CG sites were associated with increased soil compaction and lower bank stability, SDG sites were intermediate. Bedrock geology influenced NMS results: sites with carbonate derived cobble were associated with more stable channels and higher IBI scores. Though current riparian grazing practices in southeastern Minnesota present pollution problems, short duration grazing could reduce sediment pollution if managed in an environmentally sustainable fashion that considers stream channel response.

A Comparison of the Areal Extent of Fish Habitat Gains and Losses Associated with Selected Compensation Projects in Canada

We conducted a review of studies that evaluated the effectiveness of fish habitat compensation projects in achieving the conservation goal of no net loss of productive capacity of fish habitat in Canada. Combined, the 103 compensation projects assessed in the 10 studies created and/or restored 493,205 m2 of fish habitat to offset habitat impacts totalling 1,142,648 m2. Most of the compensation projects assessed were a result of impacts to estuarine and riverine in-channel habitats. Forestry and urban development activities resulted in the greatest percentage of compensation projects. Overall, 64% of the projects were deemed to have achieved no net loss. Fifty percent of the projects had a compensation ratio (compensation area:impacted area) of less than 1:1. The small number of studies found in the literature suggests that performance evaluations are rarely conducted, limiting our ability to practice adaptive management. We advocate that a national monitoring program be developed through which the achievement of no net loss can be assessed on an ongoing basis.

Fish, Flows and Flood Plains: Links between Freshwater Fishes and their Environment in the Murray-Darling River System, Australia

Knowledge of the biology of native fishes of the Murray-Darling Basin is based largely on studies conducted under hatchery conditions and on a limited number of recreationally important species. From observations that increases in water level in aquaculture ponds initiate spawning in some species, and from limited studies of wild fishes and studies in overseas floodplain river systems, a perception has emerged of the importance of flooding and the flood plain in the life cycles of Murray-Darling fishes in general. However, there is little confirmatory evidence of the use of temporary floodplain habitats by larvae, juveniles or adults. The significance of in-channel habitats, especially for rearing, has received little attention. Murray-Darling fish species can be placed into three life history modes, based mainly on spawning style and time and developmental intervals of larvae at first feeding. Fish in each group may be able to take advantage of floods if the timing is right and prey are plentiful, however, the larvae of some species are able to recruit under non-flood conditions within the main river channel. This forms the basis of the ‘low flow recruitment hypothesis’, which attempts to explain why some species spawn during the warmest months and lowest flows and how they are able to recruit under these conditions. This hypothesis is then placed in the context of the current state of knowledge of the relationships between flow and the biology of Murray-Darling fishes, specifically cues for spawning, movement and recruitment. The lack of widespread evidence for floodplain use by any life history interval of fish may be due to a paucity of study, however, there are some fundamental factors, such as the predictability of timing and duration of high flow events as well as the lack of coincidence of high flows and high temperatures in some regions of the Basin, which may be important in determining the use of floodplain habitats by fish.