River Habitat Research Articles

Characteristics and Impacts of Pollution and Remediation on Riverine Greenhouse Gas Emissions: A Review

Rivers are not only a vital part of the Earth’s water cycle but also sources and sinks for greenhouse gases (GHGs), exerting a significant influence on the global carbon budget. Rapid urbanization and intense human activities lead to water pollution and river habitat degradation, thereby affecting riverine greenhouse gas (GHG) emissions indirectly. Artificial management and restoration measures taken for rivers further increase the uncertainty of GHG emissions from rivers. In the context of carbon neutrality goals, research on GHG emissions from rivers has gradually become a hot topic. However, there is a scarcity of collective and comparative studies on the spatiotemporal patterns and mechanisms of riverine GHG emissions, especially a lack of summaries exploring the impacts of pollution and restoration on GHG emissions from rivers. This work systematically reviews recent studies concerning the emissions of CO2, CH4, and N2O from rivers, with a particular focus on the characteristics and driving factors. Results have shown that riverine GHG emissions exhibit significant spatiotemporal heterogeneity. Besides hydrological factors such as wind speed, flow velocity, rainfall, and water level, large amounts of pollutants entering rivers strongly affect the production and emission of GHGs, since nutrients, organic matter, heavy metals, microplastics, and antibiotics can alter the biogeochemical processes in river ecosystems. Remediation measures can reduce water pollution levels, but some measures may further increase the emission of GHGs from rivers. This work emphasizes the need for conducting in-depth research on the synergies between treating river pollution and reducing riverine GHG emissions. It also proposes to reinforce the monitoring of GHGs and construct emission databases of rivers for sustainable watershed management.

Microhabitat conditions and habitat configuration influence juvenile salmonid use of off‐channel features in the Cedar River, Washington

AbstractObjectiveOff‐channel habitats are crucial for freshwater rearing of juvenile Pacific salmon Oncorhynchus spp., but many of these river floodplain habitats have been lost to human development. While there is a clear need to restore and reconnect off‐channel habitats to help recover imperiled salmonid populations, uncertainty exists regarding which characteristics to prioritize when constructing off‐channel habitats to maximize the salmonid rearing capacity of these features. To address this uncertainty, we quantified the relative influence of microhabitat conditions and habitat configuration on juvenile salmonid densities within off‐channel features of the Cedar River (Washington State).MethodsWe measured microhabitat conditions (water velocity, water depth, cover, and large wood density), habitat configuration (habitat type, distance from the main‐stem river, and feature width), and salmonid densities at randomly selected sample units within side channels and backwaters.ResultWater velocity and depth were strongly associated with subyearling Chinook Salmon O. tshawytscha, subyearling Coho Salmon O. kisutch, and yearling Coho Salmon densities, although the relationships varied among the species–age cohorts and some relationships changed during the spring sampling season. Cover and wood density were also associated with salmonid densities, but the relationships were weaker than for velocity and depth. Habitat configuration was associated with salmonid densities as well, although the relationships varied among the species–age cohorts and between habitat types. For example, within backwaters, subyearling Chinook Salmon densities were highest close to the main‐stem river but yearling Coho Salmon densities were highest far from the main stem. Additionally, subyearling Chinook Salmon and Coho Salmon densities were highest within intermediate‐width side channels, while yearling Coho Salmon densities exhibited a more complex response to side channel width.ConclusionOur results indicate that both microhabitat conditions and spatial configuration influence juvenile salmonid densities within off‐channel habitats. These results also suggest that restoration practitioners should carefully weigh trade‐offs among design alternatives because different habitat configurations will differentially benefit certain species or life stages.

Application of the River Habitat Survey Method in the Assessment of the Human Pressure Within the Lowland River Catchment: The Mollusc Biodiversity Versus Habitat Features

The objectives of our study were to analyse the degree of human pressure within the lowland river catchment in relation to the mollusc communities and to assess the usefulness of the River Habitat Survey as a field method in determining the human pressure in the mollusc biodiversity context. The River Habitat Survey (RHS), an essential method for hydromorphological studies of rivers under the requirements of the European Union Water Framework Directive, was applied. This study showed that the diversity of molluscs was impacted by several environmental factors acting simultaneously, including pH, concentration of ammonium nitrogen in water, and the habitat features depending on the degree of human pressure on the river. The result of the RHS method confirmed that the occurrence of molluscs including Unio crassus and Pseudanodonta complanata, the endangered species on a global scale, was associated with the extensive presence of several natural habitat features in the river channel. The RHS method proved to be an indispensable tool for assessing the relationships between the diversity of aquatic organisms and the degree of habitat anthropogenic modification of river environments. It seems innovative and necessary, especially in restoring the natural character of rivers.

Disturbance by jet boating increases corticosterone concentrations in the black-backed gull (Larus dominicanus)

ABSTRACT Recreational activities such as jet boating have the potential to disturb native birds that rely on braided river habitats. To examine whether jet boating affects levels of glucocorticoid hormones, which can increase in animals under stress, we compared concentrations of corticosterone in the faeces of nesting black-backed gulls (Larus dominicanus) between days with differing levels of jet boat activity and to a nearby braided river site with no jet boating. The corticosterone titers of gull faeces sampled on the weekends (when jet boating activity was high) were almost twice that collected in the same area during the week (when jet boating activity was low). Corticosterone titers were also lower in the site without jet boating. Corticosterone levels were not significantly related to whether faeces were sampled in the centre or margin of the colony, nor did they vary significantly with number of birds in the colony. It is not known if increased concentrations of corticosterone have any negative effects on the survival or reproductive success of black-backed gulls, but our results suggest that the disturbance created by jet boating has the potential to alter hormone levels in this and perhaps other species that occur in braided river habitats.

Numerical Simulations of Impact River Morphology Evolution Mechanism Under the Influence of Floodplain Vegetation

Shallow floodplains play a crucial role in river basins by providing essential ecological, hydrological, and geomorphic functions. During floods, intricate hydrodynamic conditions arise as flow exits and re-enters the river channel, interacting with the shallow vegetation. The influence and mechanism of shoal vegetation on channel hydrodynamics, bed topography, and sediment transport remain poorly understood. This study employs numerical simulations to address this gap, focusing on the Xiaolangdi–Taochengpu river section downstream of the Yellow River. Sinusoidal-derived curves are applied to represent the meandering river channel to simulate the river’s evolutionary process at a true scale. The study simulated the conditions of bare and vegetated shallow areas using rigid water-supported vegetation with the same diameter but varying spacing. The riverbed substrate was composed of non-cohesive sand and gravel. The analysis examined alterations in in-channel sediments, bed morphology, and bed heterogeneity in relation to variations in vegetation density. Findings indicated a positive correlation between vegetation density and bed heterogeneity, implying that the ecological complexity of river habitats can be enhanced under natural hydrological conditions in shallow plain vegetation and riparian diffuse flow. Therefore, for biological river restoration, vegetation planting in shallow plain regions can provide greater effectiveness.

Asymmetric competition for habitats between the temperate Japanese eel Anguilla japonica and the tropical Indo-Pacific eel A. marmorata

Habitat segregation is a common phenomenon among anguillids in rivers where multiple species coexist. However, despite the growing need to conserve their river habitats, the mechanisms underlying such segregation remain unknown. Here, we conducted tank experiments to investigate the competitive superiority for habitats between the temperate Japanese eel Anguilla japonica and the tropical Indo-Pacific eel Anguilla marmorata, which co-occur in East Asian subtropical rivers. Using eight interspecific pairs of these two species of comparable total length, we compared the use of a single pipe shelter, recorded over a 24-h experimental period, between solitary and paired conditions. The changes in shelter use patterns between conditions indicated that in the paired condition, the shelter was occupied by A. marmorata in five pairs (62.5%) by the end of the experiment while A. japonica appeared to occupy the shelter in only one pair (12.5%). Furthermore, agonistic behaviors, which occurred mainly at night, such as biting and head-butting, were observed much more frequently for A. marmorata toward A. japonica (mean ± standard deviation: 23.2 ± 36.6 times per individual) than for A. japonica toward A. marmorata (0.4 ± 0.5 times per individual), indicating an asymmetry in aggressiveness. These results suggest that A. marmorata can negatively affect the diurnal habitat use and nocturnal activities of sympatric A. japonica. These findings, combined with those from previous field studies, suggest that A. marmorata may competitively exclude A. japonica from stream habitats with large substrate sizes. This asymmetric competition can contribute to shaping their riverine distribution and composition within rivers where they co-occur.

Using two- and three-dimensional landmark data to examine the shape variation of Elliptio complanata from two heavily impounded rivers in northern New York (USA)

ABSTRACT Despite vast improvements in the quantification of shape variation with geometric morphometric methods, evaluating morphological variation in unionids has remained difficult due to the lack of measurable landmarks on shells and their overall morphological plasticity. In this study, we supplement traditional two-dimensional landmark data with three-dimensional landmark data. Using photogrammetry, we generate three-dimensional models that are landmarked. This approach adds a new, third dimension to capture shape changes, providing a more detailed understanding of the shell topography. With this method, we explore the differences in shell shape along river stretches of two heavily impounded rivers in northern New York (USA). We ask whether isolation by distance, presence of dams and/or difference in land use around sampling localities impact the shell morphologies of Elliptio complanata populations. Our data suggest that, although separated for almost a century, these unionid populations do not show a pattern of increased morphological difference with distance. But we find that broad, rounded morphs that are posteriorly extended occur more frequently in reservoir environments while unaltered river habitats have a higher number of slim and more elongated variants.

Spatiotemporal distribution of cyanobacteria in relation to water chemistry of Sutlej River, Punjab (India).

In this investigation, the spatiotemporal distribution of cyanobacteria and their relationships with variations in water chemistry (physico-chemical parameters and heavy metal) of Sutlej River, Punjab (India) has been analyzed by employing multivariate statistical methods. Sutlej River exhibits a rich array of cyanobacterial diversity, comprising 28 species across 15 genera, distributed among 11 families and spanning 5 orders within the class Cyanophyceae. In terms of relative abundance, Microcystis aeruginosa (17.47%) was documented as the most abundant taxa followed by Microcystis robusta (16.55%), Merismopedia punctata (11.03%), Arthrospira fusiformis (6.67%) and Pseudanabaena galeata (3.68%). Significant variations were observed among sampling sites in most of the physico-chemical parameters. Principal Component Analysis delineated sampling sites into two discernible groups according to variations in water chemistry. River Pollution Index (RPI) showed that river water is under the unpolluted (RPI 1.5) to negligibly polluted category in the upstream sites, while moderately polluted (RPI 5.5) in the downstream sites. Heavy metal Pollution Index (HPI) revealed consistent heavy metal contamination at sites RWS7 and RWS8 across all seasons. Conversely, site RWS1 consistently exhibited lower HPI values throughout the three studied seasons. Further, Canonical Correspondence Analysis identified that pH, TDS, TA, NO3, Na, and NH4 are the key physicochemical parameters which affect the spatiotemporal distribution of cyanobacteria in the studied river system. Overall, this study will offer significant information for hydrologists, ecologists, and taxonomists to develop future holistic strategies for further monitoring of the Sutlej River and other similar habitats.

Landscape changes of alpine grasslands in the Zhari Namco basin of the central‐southern Qiangtang plateau, 2001–2021

AbstractThe alpine grasslands of the Qiangtang Plateau face significant ecological risks due to extensive human activities, particularly in areas along lakeshores and riverbanks, where overgrazing has caused severe degradation and salinization of the grasslands. Conducting fieldwork in such environments presents significant challenges for long‐term community‐scale landscape ecological research. In this study, the habitat characteristics of dominant plant communities in the alpine basin of Zhari Namco were quantified from three perspectives: topography, hydrology, and fractional vegetation cover. Using Aster GDEM and Landsat imagery, five grassland types were mapped for 2001–2021. Based on the spatial variables of area, shape, and distance, 13 landscape indices were selected to observe spatiotemporal changes. The results revealed several key findings: (1) The patch structure of the zonal vegetation Stipa purpurea steppe has undergone a pattern of dispersion‐aggregation‐dispersion in the past 20 years, yet the core habitat area remains unchanged by more than 52%, indicating fundamental stability in the southern Qiangtang alpine grassland; (2) Using the minimally grazed Kobresia pygmaea meadow as a reference, other communities exhibit stability similar to or approaching it, but with significant differences in aggregation level. The gradual expansion of grazing and economic activities has been a driving factor; and (3) Water conservation projects have diversified the use of water resources in river and lakeside habitats. Stipa purpurea + Carex moorcroftii steppe and Carex swamp meadow exhibit optimal carrying capacity, making them the only areas with relatively high sustainability. The study underscores that the current ecological benefits are a result of effective management. However, without proper management, the region could trend towards landscape fragmentation, becoming the most vulnerable zone in the watershed. Therefore, it is essential to strengthen retrospective analysis of grazing intensity and trend analysis of habitat changes to provide a scientific basis for local economic development and grazing management.

Biodiversity Assessment of a Mississippi River Backwater Complex Using eDNA Metabarcoding

The backwater lowland habitats of large rivers, like the Mississippi River in North America, present complex and often inaccessible environments for traditional capture-based fish biodiversity sampling. Our knowledge of the assemblages of the fishes that occupy such habitats is often incomplete, and this can compromise management efforts. We employed environmental DNA (eDNA) metabarcoding methods to sample a Mississippi River bottom wetland system to assess the ichthyofaunal diversity and the assemblage structure across habitat types, and we compared our results with capture-based survey records for the same habitats. We collected water samples in the spring and fall of 2022 from slough, ditch, shallow lake, and bayou habitats that varied in depth, vegetation, seasonal variability, and connectivity to the Mississippi River channel. We detected a diverse array of fish species that included 51 taxa. Nearly all the species previously documented in the habitats were detected using eDNA metabarcoding, and we increased the number of documented species by more than a third. Most of the species were ubiquitous across the range of habitats, but there was also a substantial assemblage structure, with some species exhibiting clear habitat specificity. Fall sampling was limited to the deeper bayou habitats where seasonal variation between the spring and fall was minimal. eDNA metabarcode sampling was demonstrated to be effective at detecting invasive species as well as uncommon species, which included several species of conservation concern.

Neglecting biodiversity baselines in longitudinal river connectivity restoration impacts priority setting

River habitats are fragmented by barriers which impede the movement and dispersal of aquatic organisms. Restoring habitat connectivity is a primary objective of nature conservation plans with multiple efforts to strategically restore connectivity at local, regional, and global scales. However, current approaches to prioritize connectivity restoration do not typically consider how barriers spatially fragment species' populations. Additionally, we lack knowledge on biodiversity baselines to predict which species would find suitable habitat after restoring connectivity. In this paper, we asked how neglecting these biodiversity baselines in river barrier removals impacts priority setting for conservation planning. We applied a novel modelling approach combining predictions of species distributions with network connectivity models to prioritize conservation actions in rivers of the Rhine-Aare system in Switzerland. Our results show that the high number and density of barriers has reduced structural and functional connectivity across representative catchments within the system. We show that fragmentation decreases habitat suitability for species and that using expected distributions as biodiversity baselines significantly affects priority settings for connectivity restorations compared to species-agnostic metrics based on river length. This indicates that priorities for barrier removals are ranked higher within the expected distributions of species to maximize functional connectivity while barriers in unsuitable regions are given lower importance scores. Our work highlights that the joint consideration of existing barriers and species past and current distributions are critical for restoration plans to ensure the recovery and persistence of riverine fish diversity.

Minimum environmental flow assessment: a fuzzy TOPSIS decision-making system for selecting the best approach

The literature has explored various methods for assessing minimum environmental flow. Implementing holistic approaches proves to be prohibitively expensive and impractical for many small and medium projects. Hence, desktop and cost-effective methods are commonly employed without an integrated decision-making system to justify the assessed values. This study introduces a systematic decision-making framework aimed at selecting the most suitable method for assessing the actual needs of river habitats. Employing a fuzzy technique known as the Order Preference Similarity to the Ideal Solution (FTOPSIS), the study considers factors such as physical, thermal, and dissolved oxygen habitat suitability, maximum habitat area, and water demand loss function to determine the most appropriate method among established ones, including the Tennant method, flow duration curve analysis method, wetted perimeter method, and physical habitat simulation method. The results prioritize physical habitat simulation, wetted perimeter by slope method, and flow indices of 70%, 75%, and 80% by flow duration curve analysis method as the optimal approaches for assessing minimum environmental flow. This proposed decision-making system offers a viable platform to explore the applicability of existing cost-effective methods for assessing minimum environmental flow. It also serves as an effective mechanism for reducing negotiations among stakeholders by comprehensively considering all relevant aspects in the environmental management of river ecosystem requirements.

Modelling the distribution of fish habitat type and habitat diversity in natural rivers

Analyzing the spatial distribution and habitat diversity of river habitats not only helps us understand river ecology and guides effective management, but also informs efforts to create suitable habitats for fish and restore environmental diversity. Henceforth, we developed a Two-Dimensional Habitat Diversity Construction Model to predict and analyze the variation and spatial distribution of fish habitat types under the normal (for both dry and wet seasons) and flood flows (for different return periods). Shannon and Simpson Index, and Habitat Diversity Index (HDI) were used to assess the habitat diversity under normal and flood flow conditions. The simulation results showed that under normal flow, fish habitat distribution is along the channel while under flood flow it is more on the banks. Under average annual flow and high flow during the rainy season, 4.4 % and 20.51 % of water-covered areas, respectively, lack suitable habitats. For flood flows with return periods of 2 years and 100 years, 55.6 % and 73.36 % of water-covered areas do not support any habitat types. Regardless of the flow type, the model can reasonably evaluate the spatial distribution and habitat diversity of various habitat types in the river. Findings from this study will assist in conserving existing fish habitats, and in introducing missing/lacking habitats. In addition, it could provide a reference for creating ecological habitats for fish in rivers and restoring habitat diversity.

Effects of log booms on physical habitat, water quality, and benthic invertebrates in the lower Fraser River and estuary

To facilitate the movement and processing of timber in some regions of the Pacific Northwest, logs are tied together to form large rectangular rafts (often called “booms”) which are transported and stored in aquatic environments. In the lower Fraser River, British Columbia, some reaches have >50% of shoreline with adjacent log booms, yet our understanding of the effects of log booms on habitats and biota is very limited. We compared sites that have never had log booms to nearby ones with active boom storage occurring to examine differences in environmental characteristics. In contrast to reference sites, nearly all active sites had compacted sediments and little vegetation coverage, likely caused by logs “grounding” onto benthic environments due to tidally influenced water level changes. Total benthic invertebrate abundance was higher at reference sites which had relatively more Amphipoda and Trichoperta, but fewer Haplotaxida, compared to active sites whose compacted and more detrital-laden sediments should favour haplotaxids. Water quality variables generally did not differ between reference and active sites. Grounding of log booms and contact with the below substrate is in contradiction of best management practices and has clear effects on the physical habitat and biota of the area underneath booming sites.

Comparing Sediment Bacterial Communities of Volcanic Lakes and Surrounding Rivers in Inner Mongolia Autonomous Region, Northeastern China.

Volcanic lakes originate from a volcanic crater or caldera, and were a crucial component of aquatic ecosystems. Sediment bacteria play an important role in the nutrient cycling of aquatic ecosystems; however, their patterns distribution in volcanic lakes and the surrounding river habitats are unknown. In this study, we compare the sediment bacterial communities and their co-occurrence networks between these two habitats in the Inner Mongolia Autonomous Region, Northeastern China (the Arxan UNESCO Global Geopark), using 16S rRNA gene amplicon sequencing. The results revealed that there were significant variations in the physicochemical parameters of the sediment between these two habitats. The bacterial α-diversity, β-diversity, and community composition of the sediment also significantly differed between these two habitats. Network analysis showed that the co-occurrence patterns and keystone taxa in the sediment differed between these two habitats. The sediment bacterial communities in the river habitats were more stable than those in the lake habitats in the face of environmental change. Canonical correspondence analysis demonstrated that both physical (pH and MC) and nutrition-related factors (TN, TP, LOI, and TOC) were the most important environmental factors shaping the variations of bacterial community composition (BCC) in the sediment between these two habitats. This work could greatly improve our understanding of the sediment BCC of the sediment from aquatic ecosystems in the UNESCO Global Geopark.

Natural soundscapes of lowland river habitats and the potential threat of urban noise pollution to migratory fish

Migratory fish populations have experienced great declines, and considerable effort have been put into reducing stressors, such as chemical pollution and physical barriers. However, the importance of natural sounds as an information source and potential problems caused by noise pollution remain largely unexplored. The spatial distribution of sound sources and variation in propagation characteristics could provide migratory fish with acoustic cues about habitat suitability, predator presence, food availability and conspecific presence. We here investigated the relationship between natural soundscapes and local river conditions and we explored the presence of human-related sounds in these natural soundscapes. We found that 1a) natural river sound profiles vary with river scale and cross-sectional position, and that 1b) depth, width, water velocity, and distance from shore were all significant factors in explaining local soundscape variation. We also found 2a) audible human activities in almost all our underwater recordings and urban and suburban river parts had elevated sound levels relative to rural river parts. Furthermore, 2b) daytime levels were louder than night time sound levels, and bridges and nearby road traffic were much more prominent with diurnal and weekly patterns of anthropogenic noise in the river systems. We believe our data show high potential for natural soundscapes of low-land river habitat to serve as important environmental cues to migratory fish. However, anthropogenic noise may be particularly problematic due to the omnipresence, and relatively loud levels relative to the modest dynamic range of the natural sound sources, in these slow-flowing freshwater systems.

Wood you believe it? Experimental addition of nonnative wood enhances instream habitat for native dryland fishes

AbstractFlow alteration and riparian vegetation encroachment are causing habitat simplification with severe consequences for native fishes. To assess the effectiveness of enhancing simplified habitat in a large dryland river, we experimentally added invasive wood at 19 paired treatment and reference (no wood added) subreaches (50–100 m) within the main channel of the San Juan River. Using a before‐after‐control‐impact design, we sampled fishes and macroinvertebrates, and quantified habitat complexity. After wood addition, total native fish densities were 2.2× higher in treatments compared with references, whereas total nonnative fish densities exhibited no response. Macroinvertebrate densities were 6.8× higher, and habitat complexity increased in treatments. Counts of geomorphic features in treatments increased from 1 to a maximum of 11 following wood addition, while the number of features in references remained unchanged. Wood addition has potential to instigate natural riverine processes, ultimately enhancing native fish habitat by increasing macroinvertebrate densities and habitat complexity in dryland rivers. Water overallocation and increasing aridity will continue to challenge efforts to improve habitat conditions with environmental flows alone, and managers might consider integrating non‐flow alternatives like addition of abundant, invasive wood to reduce habitat simplification.

Influence of dams on sauger population structure and hybridization with introduced walleye.

Dams have negatively affected freshwater biodiversity throughout the world. These negative effects tend to be exacerbated for aquatic taxa with migratory life histories, and for taxa whose habitat is fundamentally altered by the formation of large reservoirs. Sauger (Sander candadensis; Percidae), large-bodied migratory fishes native to North America, have seen population declines over much of the species' range, and dams are often implicated for their role in blocking access to spawning habitat and otherwise negatively affecting river habitat. Furthermore, hybridization appears to be more frequent between sauger and walleye in the reservoirs formed by large dams. In this study, we examine the role of dams in altering sauger population connectivity and facilitating hybridization with introduced walleye in Wyoming's Wind River and Bighorn River systems. We collected genomic data from individuals sampled over a large spatial scale and replicated sampling throughout the spawning season, with the intent to capture potential variation in hybridization prevalence or genomic divergence between sauger with different life histories. The timing of sampling was not related to hybridization prevalence or population divergence, suggesting limited genetic differences between sauger spawning in different time and places. Overall, there was limited hybridization detected, however, hybridization was most prevalent in Boysen Reservoir (a large impounded section of the Wind River). Dams in the lower Wind River and upper Bighorn River were associated with population divergence between sauger upstream and downstream of the dams, and demographic models suggest that this divergence has occurred in concordance with the construction of the dam. Sauger upstream of the dams exhibited substantially lower estimates of genetic diversity, which implies that disrupted connectivity between Wind River and Bighorn River sauger populations may already be causing negative demographic effects. This research points towards the importance of considering the evolutionary consequences of dams on fish populations in addition to the threats they pose to population persistence.

Expanding the habitat quality assessment of rivers in Greece using an updated River Habitat Survey toolbox

Although most of the EU members have adopted methods for assessing the hydromorphological quality of lotic ecosystems in line with the Water Framework Directive, until now, Greece lacked an integrated approach. In this article, we present the results of the first nationwide assessment of habitat quality for rivers in Greece, using the River Habitat Survey (RHS) alongside a typology of Greek rivers. The RHS toolbox software has been updated with data from the Greek monitoring program which allowed for type-specific assessments using the Habitat Quality Assessment (HQA) score. The HQA scores from 366 monitoring sites were analyzed to identify spatial patterns and significant variations. Sites were classified in five HQA classes based on the position of their HQA score relative to sites of similar types. We also investigated whether Ecological Quality Ratios (EQRs) for three biological quality elements (benthic diatoms, benthic macroinvertebrates and fish) differed significantly among HQA classes. Correlations showed that sites at mid and high altitude catchments with natural land cover had better HQA scores than lowland sites with agricultural land cover. In addition, large urbanized districts (e.g. Attica), and central Greece displayed lower habitat quality than Epirus and Western Macedonia. Our findings revealed that EQR values varied significantly among the HQA classes, with these differences being more prominent for small and medium lowland streams. This study shows that this approach can identify sites that are prone to habitat degradation and require further management, whilst providing a consistent framework for exploring the relationships between biota and hydromorphological conditions.

Population Responses of Blueback Herring to Dam Passage Standards and Additive Mortality Sources

Abstract The management of anadromous fishes is inherently complicated because this suite of species exhibits complex life histories in multiple habitats and is subject to varying natural and anthropogenic influences during discrete ontogenetic periods. Fishery scientists and managers often adopt life history–based simulation models to help understand potential effects of management decisions on fish populations while incorporating uncertainty in life history, climate, and other components of resource management systems. We applied one such model to Blueback Herring Alosa aestivalis in the Hudson River watershed, New York, USA. Our goal was to better understand influences of historical habitat loss on anadromous fishes and determine to what extent and under what conditions novel habitat created by canal infrastructure might confer increased population abundance. We found that access to historical habitat in the upper Hudson River increased population abundance at all upstream dam passage rates with sufficient downstream survival of adult and juvenile Blueback Herring but that abundance decreased with increasing upstream passage relative to the “no passage” scenario when downstream survival through dams was not sufficiently high. Access to novel spawning habitat in the Mohawk River canal system resulted in increased abundance of Blueback Herring when downstream survival of adults and juveniles was at least 0.80/dam, and both upstream passage and probability of using the Mohawk River were greater than approximately 0.25. Both mortality during upstream passage of locks in the Mohawk River and marine fishery mortality had the potential to reduce Blueback Herring abundance below historical population abundance, despite access to novel spawning habitat. These results highlight the complexity associated with effects of upstream and downstream fish passage standards on population responses while emphasizing similarities observed in other diadromous species and watersheds.