Total River Length Research Articles

A new perspective on water quality: Exploring spatial and temporal patterns of impaired waters

Managing surface water quality is a global challenge, and understanding spatial and temporal patterns of water quality is a key component to effective management. However, analysis of spatiotemporal patterns of impaired waters over broad areas is sparse due to disparate water quality data and variable water quality standards. Thus, here we leverage the Alabama 303(d) List of impaired waters to present a new perspective for investigating spatiotemporal water quality patterns. Every two years, each state in the United States is required to assess its surface water quality and compile a list of impaired waterbodies, meaning waters that do not meet water quality standards for their designated usage – referred to as the 303(d) List. The purpose of the 303(d) List is to identify impaired waters so that corrective action can be taken to reduce pollutant loads and, ultimately, improve water quality. Using GIS, a space time cube was created to analyze and visualize spatiotemporal patterns of the impaired rivers added to the Alabama 303(d) Lists from 1996 to 2022. For this analysis, the percentage of river length impaired out of the total river length, and number of times each impairment cause was listed, were summarized within Alabama sub-basins (Hydrologic Unit Code 8) (n = 51). Trend and hot spot analyses were conducted on the river impairment and causes. There was an up trend in river impairment for eight sub-basins across the state and a downtrend in one sub-basin. Over half of the sub-basins with an up trend in impairment also had an up trend in the number of times pathogens was listed as a cause of impairment. Additionally, coastal sub-basins were found to be a hot spot for river impairment. Interestingly, there was a down trend in the number of times nutrients, ammonia, and siltation were listed as a cause of impairment at the state and sub-basin scales of analysis. Altogether, these findings show the use of spatiotemporal pattern analysis of impaired waters and can indicate where, both spatially and by pollutant, management should prioritize water quality improvement efforts.

A changing river: Long‐term changes of sinuosity and land cover in the Navasota River Watershed, Texas

AbstractThe Navasota River Basin, itself a tributary of the Brazos River in Texas, is a dynamic watershed undergoing many natural and anthropogenic changes. Local stakeholder involvement in this watershed is quite high, and many landowners in the southern portion of the watershed have concerns regarding the increasing frequency and duration of flooding on private property adjacent to the river, often attributing these impacts to the construction of the Lake Limestone dam. In this study, we examine historical flow data, channel morphology, land use/land cover, and precipitation. Our findings indicate that while there appears to be increasing flow in the northern portion of the watershed, temporal data gaps near the watershed outfall prevent the indication of such a trend in the southern portion of the watershed. Nevertheless, other natural and anthropogenic factors are evident in the watershed that may have a significant influence on downstream flooding. Overall river sinuosity (meandering) declined over the study period, with some river segments encountering significant straightening. Total river length declined by 4.3 km from 1972 to 2020. The number and length of offtake channels also decreased substantially during this period. Land use/land cover use shifted dramatically, with a 39.2% increase in impervious cover and a 12.5% decrease in herbaceous cover since 1972. Finally, yearly precipitation increased, with the change point occurring in 1972. Our findings suggest that the shortening and straightening of the river has reduced its volumetric capacity over time. Coupled with increasing impervious surface cover and precipitation, more water is being delivered downstream at a rate exceeding the watershed's ability to discharge it, thereby contributing to flooding issues expressed by stakeholders. We recommend that bathymetric data and supplemental flow monitoring and modeling within the watershed is needed to fully understand how anthropogenic and natural forces may further affect streamflow in the future.

A model of temporal and spatial river network evolution with climatic inputs

Predicting the temporal and spatial evolution of the river network is part of the Earth's critical zone investigations, which has become an important endeavor. However, modeling integration of the river network and critical zone over millions of years is rare. We address the problem of how to predict integrated river length development as a function of time within a framework of addressing the critical zone depth as a function of time. In case of groundwater-river interaction, we find a non-linear spatio-temporal scaling relationship between time, t, and total river length L, given by t≈Lp with power p being near 1.2. The basis of our model is the presumption that groundwater flow paths are relevant to river integration. As river integration may proceed over disconnected basins with irregular relief, the relevant optimal subsurface flow paths are proposed to be defined within a 3D network, with optimal path exponent 1.43. Because the 2D model of the river length has already been shown to relate to a power of the Euclidean distance across a drainage basin with the predicted universal optimal path exponent from percolation theory, Dopt = 1.21, the optimal groundwater paths should relate to the surface river length with an exponent equaling the ratio 1.43/1.21 = 1.18. To define a predictive relationship for the river length, we need to use specific length and time scales. We assume that the fundamental specific length scale is a characteristic particle size (which is commonly used to define the pore scale flow network), and the fundamental time scale is the ratio of the particle size to the regional groundwater flow rate. In this paper, we consider cases of predicting spatio-temporal scaling of drainage organization in the southwestern USA–the Amargosa, Mojave, Gila (and its tributaries) and the Rio Grande, and Pecos Rivers. For the Mojave and Gila Rivers, theoretical results for time scales of river integration since ca. 10 Ma are quite predictive, though the predicted time scales exceed observation for the Rio Grande and Pecos.

Warming overrides eutrophication effects on leaf litter decomposition in stream microcosms

Several human activities often result in increased nitrogen (N) and phosphorus (P) inputs to running waters through runoff. Although headwater streams are less frequently affected by these inputs than downstream reaches, the joint effects of moderate eutrophication and global warming can affect the functioning of these ecosystems, which represent two thirds of total river length and thus are of major global relevance. In a microcosm study representing streams from a temperate area (northern Spain), we assessed the combined effects of increased water temperature (10.0, 12.5, and 15.0 °C) and nutrient enrichment (control, high N, high P, and high N + P concentrations) on the key process of leaf litter decomposition (mediated by microorganisms and detritivores) and associated changes in different biological compartments (leaf litter, aquatic hyphomycetes and detritivores). While warming consistently enhanced decomposition rates and associated variables (leaf litter microbial conditioning, aquatic hyphomycete sporulation rate and taxon richness, and detritivore growth and nutrient contents), effects of eutrophication were weaker and more variable: P addition inhibited decomposition, addition of N + P promoted leaf litter conditioning, and detritivore stoichiometry was affected by the addition of both nutrients separately or together. In only a few cases (variables related to detritivore performance, but not microbial performance or leaf litter decomposition) we found interactions between warming and eutrophication, which contrasts with other experiments reporting synergistic effects. Our results suggest that both stressors can importantly alter the functioning of stream ecosystems even when occurring in isolation, although non-additive effects should not be neglected and might require exploring an array of ecosystem processes (not just leaf litter decomposition) in order to be detected.

Recording earthworm diversity on the tropical island of Martinique using DNA barcoding unveiled endemic species in bromeliad plants

In a context of accelerating biodiversity loss, some species may become extinct before taxonomists have time to collect and describe them. This is an even more critical problem for taxa with poor taxonomic knowledge, such as earthworms in the tropics. To overcome this taxonomic impediment, we investigated earthworm diversity on the tropical island of Martinique using DNA barcoding. Firstly, we sampled earthworms at 81 sites evenly distributed in two categories corresponding to natural and anthropized environments. We obtained a total of 684 sequences of a fragment of the COI gene. MOTU delimitation and morphological identification suggested that this dataset corresponded to 49 putative species, of which 16 were known exotic species. The rarefaction curve suggested that the sampling effort was not sufficient to capture total earthworm diversity in the natural environment and that many more species could be discovered. Secondly, we focused on a heterogeneous landscape around the town of Morne Rouge, where arboreal earthworms were sampled using a standardized protocol. We found 8 different species in epiphytic plants, three of which were found almost exclusively in bromeliad plants that were sampled above 1.4 m from the ground. The presence of these species, probably endemic to Martinique and new to science, was significantly correlated to the proportion of forest land cover. The most common earthworm in these habitats was Dichogaster andina, an exotic species found in bromeliads and Heliconia plants that were sampled at every height from the bottom of the tree up to 6.8 m. Its presence was correlated to the proportion of total river length in the landscape, suggesting that rivers may act as a dispersal vector. This study therefore highlights the great diversity of earthworms in Martinique, while emphasizing the main threats to this biodiversity, namely the alteration of habitats and the presence of invasive species.

Optimal operating method of gate and pump switching in water transfer project

Abstract The Yellow River diversion project consists of three gates, two pumping stations, and one plain reservoir, with a total river length of 17.46 km in the Panzhuang Yellow River irrigation area, which provides the primary water source for the Dezhou central city, Shandong Province, China. The project is subject to the constraints of the Yellow River diversion sluice diverting water time, reservoir diverting water time, and combinations of pumping stations with self-flowing gates. The opening and closing forms of the gates and pumps are complicated and irregular, and the switching of the gates and pumps mainly depends on the experience of the staff, which makes the water transfer cost high and the water transfer time long. Based on engineering compositions in the study area, an optimal mathematical model is constructed by the dynamic programming method. By combining the flow and water level, the objectives of the minimum operation cost, the shortest water transfer time and the combination of the two are established. A new optimization scheme of the switch between gates and pumps combined with water level and flow is proposed, which reduces the operation cost by 20% and the water transfer time by 8%, providing an efficient operation mode.

Factors controlling floodplain sediment storage in two tropical upland river catchments in the Lake Tana basin, Ethiopia

Floodplain sediment storage is an important component of a catchment’s sediment budget. Here, we present the first quantification of floodplain sediment storage for tropical river catchments draining to Lake Tana, NW Ethiopia. The catchments are characterized by relatively gently sloping to flat lowlands towards the lake (1788 m a.s.l.) and steeper river reaches in the uplands towards Mount Guna (4120 m a.s.l.). Sediment storage for 65 homogeneous floodplain segments was estimated by combining information on floodplain spatial extent obtained through the field- and remote sensing-based approaches, with information on sediment thickness obtained through sediment coring and the analysis of river cut-banks. Extrapolation to the entire catchment was done making use of floodplain typology and following the classification scheme of Nanson and Croke (1992) and other floodplain properties and catchment-wide variables. The results showed average sediment storage of 284 Mg m−1 river length or 21,760 Mg ha−1 floodplain area for the Gumara and approx. 227 Mg m−1 river length or 16,909 Mg ha−1 floodplain area for the Rib River catchments. Total floodplain sediment storage at the catchments scale, above the upper gauging stations, amounts to 92.9 Mt and 35.5 Mt for the Gumara and Rib River catchments, respectively. At the scale of homogeneous floodplain segments, sediment storage is related to floodplain width, floodplain slope, upstream catchment area, the average slope of the upstream catchment area, sinuosity, and floodplain type. Overall, floodplain geomorphology largely controls sediment storage. Approx. 70 % of the sediment is stored in low-energy cohesive floodplains which only take up 11 % of the total river length in both catchments. For most of the total river and valley extent, where rivers are incised and have more energy, storage is limited. Comparing our findings with similar studies in temperate catchments of Europe and N-America showed that sediment storage in the Gumara and Rib Rivers is lower by approx. 1 order of magnitude, for similar-sized catchments.

River lengths in Croatia determined from a topographic map at a scale of 1:25,000

This study presents methodologically consistent length measurements of rivers with a total length of 40 kilometres or more in the Republic of Croatia. These measurements were performed by vectorising river channels from a topographic map at a scale of 1:25,000. Contemporary orthophoto maps were used as additional cartographic sources for verification. The approaches used to determine the starting and ending points of rivers, i.e. sources and mouths or confluences, have been explained and their spatial coordinates were listed. The results showed that in terms of total river length, the 21 rivers in this study differed from the available official data by less than 5%. Considerable differences were found for rivers where significant river engineering works had been carried out to channelize and divert flow, as well as for rivers in the Adriatic Basin where there have been methodological differences in determining the river mouth, and for large lowland rivers where changes in channel planform are common due to natural dynamics and engineering interventions. Moreover, this research revealed that the longest Croatian river, with its source, confluence, and both river banks situated entirely within the territory of Croatia, is the Karašica River, with a total length of 148 km.

The legacy of over a century of introductions: Spread debt of rainbow trout (Oncorhynchus mykiss) in Mpumalanga Province, South Africa

AbstractFor over a century, rainbow trout (Oncorhynchus mykiss) has been widely introduced into lakes and rivers in South Africa to create and enhance sport‐fishing opportunities. Despite its long history of introduction, naturalized populations of rainbow trout are still localized to a few areas with suitable habitats and climate. This study assessed the spread debt (i.e., the increase in area invaded by invasive species over time) of rainbow trout in Mpumalanga Province, South Africa to highlight areas with known introductions, the extent of the invasion, and to identify areas that are suitable for establishment but are still invasion‐free. The total river length that was predicted as suitable for rainbow trout under current climate was about ca. 3,500 km in an extension of about ca. 15,000 km. Current occupancy (river length predicted as suitable with known rainbow trout occurrence records) was ca. 1,220 km (35%) and the invasion debt was therefore estimated as 65%. While these data infer a large invasion debt, they are confounded by a lack of knowledge on sampling effort and verified true absence and should therefore be recognized as an estimate. In addition, the extent of the suitable area varied under different climate change scenarios where it was projected to decrease under RCP 4.5 scenarios and increase under the RCP 8.5 scenarios. This study demonstrates some of the difficulties of quantifying the potential future extent and impacts of biological invasions and how the invasion debt concept can be applied to provide an important link between invasion biology, management, and policy.

The re-greening of east coast Australian rivers: An unprecedented riparian transformation

Eastern Australia has a climate characterised by extreme variability and the occurrence of multiple years of drought conditions. Arguably one of the severest droughts on record – the Big Dry ended in many areas with the La Niña of 2009/2010. A succession of subsequent dry years brought a return to drought conditions across much of eastern Australia in 2018 and 2019, ending with the catastrophic fires of 2019/2020. An analysis of river gauges in eastern Australia demonstrates that unregulated rivers have been subject to reduced monthly and total annual flow for far longer than the recent multi-year droughts. A breakpoint regression model on the annual streamflow data shows statistically significant declines in total annual flow (by up to a factor of three) since 1992/93 on the far South coast of New South Wales (NSW). In the monthly data, fifteen of the nineteen gauges analysed exhibit modelled breakpoints, but with statistically significant differences in monthly mean discharge between consecutive periods only occurring in three of these gauges (occurring between 1972 and 1993 in both the North and South coast). The trend toward reduced flow over the last few decades has, for many rivers, coincided with land use and river management changes resulting in increases in woody riparian vegetation. To show this we use a remote sensing technique and estimate the magnitude of vegetation change along all major rivers and their tributaries on the eastern seaboard of NSW (28 catchments with total river length assessed of 19,750 km) using a normalized difference vegetation index (NDVI) analysis of woody vs non-woody riparian vegetation extent. Predicted vegetation change between 1987 and 2020 is spatially variable across catchments but the mean increase in woody riparian vegetation across all catchments is 9–51% (0.2 and 0.1 NDVI increases). Such increases are perhaps the largest biogeomorphic change the SE Australian drainage network has experienced since the initial clearance of vegetation associated with European colonisation in the late 18th and early 19th centuries.

Global riverine theoretical hydrokinetic resource assessment

Hydrokinetic energy conversion refers to the conversion of kinetic energy in moving water to electricity. It offers an alternative to conventional hydropower, with benefits of modularity and scalability, in addition to being environmentally and socially less impactful. This study aims to determine the theoretical global riverine hydrokinetic resource. We use a 35 year modelled daily discharge data set and vectorised representation of rivers, with near-global coverage and suitable spatiotemporal resolution, to determine the mean annual energy yield of 2.94 million river reaches. The mean global resource (excluding Greenland) is estimated to be 58 400±109 TWh yr−1 (6.660±0.012 TW). Consideration of global spatial distribution, by river reach, illustrates regional variation and shows a tendency for potential to be concentrated along major rivers and in areas of significant elevation change. China, Russia and Brazil are found to be the countries with the greatest potential. After normalisation by total river length, Bhutan, Nepal and Tajikistan also show great potential. Hydrokinetic energy conversion can benefit isolated communities currently without access to electricity. We consider how the specific advantages of this particular technology have the potential to be combined with and complement other established forms of renewable energy technology, providing the means to support the reduction of energy poverty.

High-resolution satellite-derived river network map reveals small Arctic river hydrography

Small rivers (width <30 m) are crucial components of Arctic terrestrial river networks. Yet to date, spatial resolution limitations of commonly used satellite imagery have inhibited quantification of their hydrography. By merging newly available Sentinel-2 multispectral satellite imagery with 2-m ArcticDEM digital elevation data, we created a continuous actively-flowing river network map of the Colville (Kuukpik) River Basin (∼36 000 km2) in Alaska, which includes small rivers as narrow as 10 m. We quantified the river hydrography (stream order and river width, length,surface area, velocity, slope, sinuosity, and catchment area) of the Colville river network in detail, revealing the dominant role of small rivers. Our results show that: (1) small rivers occupy >80% of total river length and surface area of the Colville river network and drain >90% of the catchment area; (2) including numerous small rivers increases the peak of hillslope-channel travel time distribution (TTD) by ∼4 times and shortens the mean hillslope-channel travel time by at least an order of magnitude compared to coarser-resolution river hydrography products; and (3) 87% of the Colville River Basin’s carbon dioxide is emitted from small rivers. In sum, we show that small Arctic rivers greatly influence streamflow TTD and carbon cycle. These findings expand our understanding of Arctic river hydrography to a 10-m spatial resolution and raise prospects for tracking dynamic surface water processes with high-resolution satellite observations.

A simple method to assess the fragmentation of freshwater fish meta-populations: Implications for river management and conservation

Rivers are very vulnerable to fragmentation caused by the presence of man-made barriers. To restore river basin connectivity, numerous indices have been developed to calculate river fragmentation and optimise barrier mitigation actions. These methods usually calculate connectivity for whole river basins, but sometimes it is useful to analyse the connectivity for certain elements of interest. The main goal of this study was to develop a simple method to calculate the connectivity of specific riverine habitats or fish meta-populations.The framework of the Dendritic Connectivity Index (DCI) created by Cote et al. in 2009 was changed to develop the Population Connectivity Index (PCI). This index would depend on the number of populations, the total river length occupied by each population, the distance between populations, the dispersal capability of the fish species and the presence of barriers in the river. The outcome of the index is a percentage that measures the degree of connectivity in a meta-population. The PCI was tested in four Iberian fish species with different dispersal capabilities: Salmo trutta, Luciobarbus comizo, Anaecypris hispanica and Cobitis vettonica.The results show a natural connectivity between populations (without considering dams) of 7.95–47.48%. The most connected meta-population was L. comizo while the most naturally fragmented meta-population was A. hispanica. When large impassable dams were added to the index the results show a connectivity of 2.19–16.48%. Dams reduce connectivity between 5.37 and 30.99 points. Dams were ranked according to their impact in the fragmentation of each studied meta-population.This PCI allows to find out naturally isolated fish meta-populations and to assess the impact of dams in the fragmentation of fish meta-populations. It can also be used in dam prioritization decisions such as dam removals and new dam location selection. It also can aid in the creation of river ecological corridors between endangered or important fish populations.

Impact of large human constructions on a karst river hydrology: Case of the Cetina river (Dinaric karst)

The paper studies drastic hydrological changes caused by construction of five reservoirs and six hydro-electric power plants (HEPP), built mostly in the 1960s, along the watercourse of the karst river Cetina, located in deep and well-developed Dinaric karst. The total river length from its spring to mouth in the Adriatic Sea is about 105 km. Discharges are monitored at nine gauging stations and then compared using statistical methods. Discharges measured before construction of hydraulic structures were compared with discharges measured afterwards. Analysis of the results determined that the complex natural hydrologic regime has been completely destroyed. The hydrology of the upper river, from the spring to the Prančevići Dam (length of about 65 km), is changed by the development and operation of the Peruča Reservoir and the Peruča HEPP, as well as the Lipa and the Buško Blato Reservoirs and Buško Blato and Orlovac HEPPs. Water diversion from the Prančevići Reservoir through two tunnels and pipelines to power the Zakučac HEPP has dangerously altered hydrological regime of the Cetina River’s 40 km-long downstream section. In the 65 km-long upstream section, instantaneously after the Peruča Reservoir putting in operation. In the downstream section the majority of natural flow is lost. The mean annual discharges dropped from more than 100 m3 s-1 to less than 10 m3 s-1. Due to HEPPs operation, minimum annual discharges have drastically and dangerously decreased.

Morphological Response to Discharge Reduction in a Partially Abandoned Channel of the Catawba River, North Carolina, USA

Examples of partial avulsion and river bifurcation around large stable islands make up a small but locally important portion of the total length of rivers in the Piedmont physiographic province of North Carolina (U.S.). Despite remaining ecologically significant, the partially abandoned (or “abandoning”) branches along such reaches have received less attention than the often dominant newly created branches. The existence of perennial flow through abandoning channels may be contingent upon their ability to rapidly adjust their morphologies to declining flows. In this paper we study the response of a partially abandoned channel of the upper Catawba River in North Carolina to major loss of flow following flood-induced partial avulsion in 1977. Human activities have strongly modified the floodplain in this area, assisting the avulsion and possibly influencing the natural erosion and sedimentation processes responsible for subsequent adjustments of the abandoning channel. Using a combination of downstream gaging data, flow estimation functions, channel mapping, and hydraulic geometry analyses, we assess the degree to which channel capacity reduction matches the amount of post-avulsion diminished discharge. Construction of fluvial sediment benches inset within the old single-thread channel has occurred along 83% of the channel's length, and most of these have crest elevations in the 1–2 yr flood stage range. Hydraulic geometry reconstructions indicate that length-weighted mean channel width, depth, and capacity deviate from predicted values by 36%, 18%, and 61%. Thus, channel cross-section dimensions for the abandoning channel appear substantially larger than predicted, a condition that is potentially discordant with a hypothetical necessity of rapid width adjustment for maintaining an open channel, depending on what constitutes a rapid rate of adjustment. Variables such as the morphology of the bifurcation node and load properties also influence the longevity of abandoning channels, and rates of adjustment or infilling can vary widely. Stratigraphic, pedogenic, and vegetative evidence together suggest that channel narrowing via inset bench formation has occurred gradually over at least two or more decades following initial flow loss. Comparisons with channel dimensions predicted from existing Piedmont regional curves show greater agreement, supporting the contention that Piedmont valley characteristics exercise at least as strong an influence on channel morphology as does the higher relief watershed topography and associated flow regime. The presence of perennial flow and active geomorphological processes in the abandoning channel indicates that it remains part of a dynamic and ecologically significant river reach, despite being currently designated as land in county land parcel records.

Impact of Urbanisation on New Zealand Freshwater Quality

Urban waterways represent less than 1% of the total river length in New Zealand. However, they are the most visible of all rivers, as 86% of New Zealanders live in urban areas. Urban waterways are impaired due to elevated levels of pathogens, turbidity, nutrients and heavy metals originating from anthropogenic activities. In addition to being conduits of storm water run-off from urban areas, some urban waterways also receive discharges from wastewater treatment plants and combined sewage overflows, thus greatly reducing their capacity to provide ecosystem services such as recreation, tourism, biodiversity and mahinga kai. This article summarises the state of New Zealand’s urban freshwater quality, the major drivers of pollution, and mitigation measures needed to restore urban waterways.

Controls of Chloride Loading and Impairment at the River Network Scale in New England.

Chloride contamination of rivers due to nonpoint sources is increasing throughout developed temperate regions due to road salt application in winter. We developed a river-network model of chloride loading to watersheds to estimate road salt application rates and investigated the meteorological factors that control riverine impairment by chloride at concentrations above thresholds protective of aquatic organisms. Chloride loading from road salt was simulated in the Merrimack River watershed in New Hampshire, which has gradients in development density. After calibration to a regional network of stream chloride data, the model captured the distribution of regional discharge and chloride observations with efficiencies of 93 and 75%, respectively. The estimate of road salt application is within uncertainties of inventoried estimates of road salt loading and is 122 to 214% greater than recommended targets. Model predictions of chloride showed seasonal variation in chloride concentrations despite a large groundwater storage pool. Interannual variation of mean summer chloride concentration near the outlet varied up to 18%, and the total river length exceeding impairment thresholds varied 12%. Annual snowfall, which drives road salt loading, correlated with chloride impairment only in headwater streams, whereas concentration variability at the outlet was driven primarily by dilution from clean runoff-draining undeveloped forested areas of the watershed. The role of summer meteorology complicates the protection of freshwater systems from chloride contamination.

Linking otolith microchemistry and dendritic isoscapes to map heterogeneous production of fish across river basins.

Production patterns of highly mobile species, such as anadromous fish, often exhibit high spatial and temporal heterogeneity across landscapes. Such variability is often asynchronous in time among habitats, which stabilizes production at aggregate scales of complexity. Reconstructing production patterns explicitly in space and time across multiple scales, however, remains difficult but is important for prioritizing habitat conservation. This is especially true for fishes inhabiting river basins due to long-range dispersal, high mortality at early life stages, complex population structure and elusive life history variation. We develop a new approach for mapping production patterns of Pacific salmon across a large river basin by integrating otolith microchemistry and dendritic isoscape models. The geographically continuous Bayesian assignment framework presented here yielded high accuracies (>90%) and relatively high precisions (precisions <4%; i.e., assignment areas of <530 river km of the 13 100km total river length) when used to determine the natal source of known-origin juvenile Chinook salmon captured throughout the study region. Integrating these methods enabled us to base estimates of provenance and habitat use of individuals on a per location basis using strontium isotopic data throughout the continuous spatial domain of a river network. Such a framework provides substantial advantages over the more common nominal approach to employing otolith microchemistry to reconstruct movement patterns of fish. In doing so, we reconstructed the spatial production patterns of adult Chinook salmon returning to a large watershed in Bristol Bay, Alaska and illustrate the power of such an approach to conservation efforts.

Drastic hydrological changes caused by hydroelectrical development in karst: a case of the karst river Zrmanja (Croatia)

This paper has analysed changes in the hydrological regime along the karst river Zrmanja (the Dinaric karst of Croatia) caused by operation of the reversible or pumped-storage hydroelectric power plant Velebit (RHEPP Velebit), which started operations in 1985. The total river length from the spring to the mouth in the Adriatic Sea is 70 km. Discharges along the whole river course are monitored at nine hydrological gauging stations. For all nine analysed stations, the decrease of the mean annual discharges starting from 1985 has proven to be statistically significant. However, it should be stressed that the Zrmanja River natural regime is extremely complex due to a deep, well developed and generally undiscovered subsurface karst morphology and its influence on regional surface and groundwater circulation. The influence of RHEPP Velebit operation on the maximum annual discharges is not statistically significant. Statistically significant decrease on the minimum annual discharges is observed at only one gauging station located at the Zrmanja River downstream of the Razovac Reservoir. At the same time, climatological changes have been monitored in the analysed area. It has been established that there has been an annual increase in air temperature since 1988 and an annual decrease in rainfall since 1983. A general conclusion is that the decrease in the mean annual discharges along the Zrmanja River is mainly caused by the RHEPP Velebit operation and only in a smaller degree by climatological changes. On the basis of the available data it was not possible to separate precisely the influences of these two factors.

Identification and Characterization of Swarming Sites used by Bats in Nova Scotia, Canada

For bats that are year-round residents of temperate areas, underground openings such as caves and abandoned mines are critical resources in winter as hibernacula, and in autumn for swarming behaviours (mating, socialization, etc.). Like many parts of the world, Nova Scotia, Canada, has many underground openings that have not been surveyed for bats. The feature(s) that affect the suitability of these sites for hibernation or swarming is not known. As such, it is not possible to predict which ones are used by local bats (Myotis lucifugus, Myotis septentrionalis and Perimyotis subflavus). Because it was not safe to enter the sites to conduct hibernation counts, our goal was to relate bat activity at the entrance of underground openings during swarming to quantifiable external metrics and to pre-existing data on internal site characteristics. Specifically, our objectives were to 1) identify abandoned mines and caves that are used by bats for swarming and 2) quantitatively characterize factors which best differentiate between underground openings that are used for swarming, and those that are not. We assumed that sites used by bats for swarming were likely also used for hibernation. Acoustic and/or trapping surveys were conducted at 17 abandoned mines and eight caves in Nova Scotia, five of which were previously known to be hibernacula. Results suggest that at least 12 of the 25 sites were swarming sites (including seven newly identified sites). Logistic regression analysis of nine a priori selected models indicated that internal chamber length was the best predictor of swarming activity. Two external variables, degree of shelter at entrance and total length of rivers in landscape, were also important predictors. These variables have the potential to be used as indicators to identify swarming sites at other sites in eastern North America. The swarming sites identified in Nova Scotia should be targeted for monitoring in light of the devastating impacts that white-nose syndrome is having on North American bats.