Second-order Stream Research Articles

Ecological importance of low-order streams to macroinvertebrate community composition in Afromontane headwater streams

Low-order streams contribute to the abiotic and biotic character of large rivers and are renowned for harboring unique forms of aquatic flora and fauna. However, most studies on headwater streams mainly focus on the mainstems and overlook the contribution of the tributary systems. Moreover, low-order streams are generally overlooked in legislation and bioassessment programs, and consequently not protected in many countries. To contribute to the recognition of the ecological importance of low-orders streams, this study focused on determining whether river network characteristics and associated physico-chemical parameters can be used to effectively predict the variabilities in macroinvertebrate assemblage characteristics between first-order and second-order streams in the headwaters of the Nzoia River Basin, Kenya. The study quantified the structural and functional community composition, diversity, similarity, and richness of macroinvertebrate communities between the two river systems. Dissolved oxygen, coarse particulate organic matter, conductivity, stream width, depth, discharge and flow velocity were the main predictors of the diversity and distribution of macroinvertebrates in the first order and second-order streams. The first order streams recorded higher abundance of macroinvertebrates than the second-order streams. Taxa from families Ephydridae, Elmidae, Gomphidae, and genera Euthraulus, Neoperla, Orthothrichia and Prosopistoma were limited to the second-order stream sites while families Ceratopogonidae, Pisuliidae, Dytiscidae and genus Trichosetodes occurred exclusively in the first-order stream sites. Collector-filterers and collector-gatherers were the most abundant functional feeding groups (FFGs) in the two river systems. Scrapers were abundant in the second-order stream while shredders were abundant in the first order streams. The distinctness in the structural and functional composition of macroinvertebrates between the two river systems suggests that linkages among streams in a network as exemplified in the Nzoia River Basin, support and foster biodiversity.

Nitrogen retention in stream biofilms – A potential contribution to the self-cleaning capacity

Surface waters are under increasing pressure due to human activities, such as nutrient emissions from wastewater treatment plants (WWTPs). Using the retention of nitrogen (N) released from WWTPs as a proxy, we assessed the contribution of biofilms grown on inorganic and organic substrates to the self-cleaning capacity of second-order streams within the biosphere reserve Vosges du Nord/Palatinate forest (France/Germany). The uptake of N from anthropogenic sources, which is enriched with the heavy isotope 15N, into biofilms was assessed up- and downstream of WWTPs after five weeks of substrate deployment. Biofilms at downstream sites showed a significant positive linear relationship between δ15N and the relative contribution of wastewater to the streams' discharge. Furthermore, δ15N substantially increased in areas affected by WWTP effluent (∼8.5‰ and ∼7‰ for inorganic and organic substrate-associated biofilms, respectively) and afterwards declined with increasing distance to the WWTP effluent, approaching levels of upstream sections. The present study highlights that biofilms contribute to nutrient retention and likely the self-cleaning capacity of streams. This function seems, however, to be limited by the fact that biofilms are restricted in their capacity to process excessive N loads with large differences between individual reaches (e.g., δ15N: −3.25 to 12.81‰), influenced by surrounding conditions (e.g., land use) and modulated through climatic factors and thus impacted by climate change. Consequently, the impact of WWTPs located close to the source of a stream are dampened by the biofilms’ capacity to retain N only to a minor share and suggest substantial N loads being transported downstream.

Ecological aspects of Rhinoclemmys punctularia punctularia (Testudines: Geoemydidae) in two localities in northern Brazil

ABSTRACT Rhinoclemmys punctularia punctularia is the only turtle of the family Geoemydidae with part of its range in Brazil. The species is semi-aquatic and widely distributed across the Amazon basin but is still poorly studied. We evaluated aspects of the population structure, habitat use, seasonal activity, and diet of the species during one year, from the beginning of the rainy season to the end of the dry season, in two headwater localities in the Tocantins and Tapajós river basins, in the state of Pará, Brazil. We captured 45 individuals, 14 in the Tocantins basin and 31 in the Tapajós basin. The size-class frequency distributions of captured individuals did not differ between the two samples. The turtles were most frequently captured in first-order streams, followed by lentic (third-order dammed streams) and second-order streams. The capture rate did not vary significantly between sampling periods (start and peak of the rainy season; start and end of the dry season). The trapping effort to capture a single individual was much higher in the Tapajós basin (1,215 trap-hours) than in the Tocantins basin (136 trap-hours). Overall, the low capture rates confirm the secretive nature of the species in Amazonia and its apparent rarity. The individuals analyzed in this study consumed mainly plants.

Bioremediation of copper in sediments from a constructed wetland ex situ with the novel bacterium Cupriavidus basilensis SRS

The H-02 constructed wetland was designed to remove metals (primarily copper and zinc) to treat building process water and storm water runoff from multiple sources associated with the Tritium Facility at the DOE-Savannah River Site, Aiken, SC. The concentration of Cu and Zn in the sediments has increased over the lifetime of the wetland and is a concern. A bioremediation option was investigated at the laboratory scale utilizing a newly isolated bacterium of the copper metabolizing genus Cupriavidus isolated from Tim’s Branch Creek, a second-order stream that eventually serves as a tributary to the Savannah River, contaminated with uranium and other metals including copper, nickel, and mercury. Cupriavidus basilensis SRS is a rod-shaped, gram-negative bacterium which has been shown to have predatory tendencies. The isolate displayed resistance to the antibiotics ofloxacin, tetracycline, ciprofloxacin, select fungi, as well as Cu2+ and Zn2+. Subsequent ribosomal sequencing demonstrated a 100% confidence for placement in the genus Cupriavidus and a 99.014% match to the C. basilensis type strain. When H-02 wetland samples were inoculated with Cupriavidus basilensis SRS samples showed significant (p < 0.05) decrease in Cu2+ concentrations and variability in Zn2+ concentrations. Over the 72-h incubation there were no significant changes in the inoculate densities (106–108 cells/ML) indicating Cupriavidus basilensis SRS resiliency in this environment. This research expands our understanding of the Cupriavidus genus and demonstrates the potential for Cupriavidus basilensis SRS to bioremediate sites impacted with heavy metals, most notably copper.

Nitrous oxide concentration and flux in Min River Basin of southeast China: Effects of land use, stream order and water variables

Estimates of riverine nitrous oxide (N2O) emissions have great uncertainty partly due to the fact that the data is still sparse for stream sizes and land uses. Here we determined water dissolved N2O concentration and water–air interface N2O flux across the land uses and stream orders in Min River Basin of southeast China. N2O concentrations ranged from 11.1 to 27.4 nmol/L, increasing from first- to eighth-order rivers. The first- and second-order streams showed negative N2O flux (−0.33 and −0.05 µg m−2h−1, respectively) compared to third- to eighth-order rivers (from 0.29 to 2.85 µg m−2h−1). Average N2O flux was significantly higher in urban (1.60 µg m−2h−1) and cropland rivers (0.89 µg m−2h−1) than in forest rivers (−0.47 µg m−2h−1), which could be due to the main effect of land use was on the nitrogen load. Indirect N2O emission factor varied between 0.035 and 0.14 % across the rivers, which decreased from the urban to forest rivers and were lower than the IPCC default value (0.26 %). N2O concentration and flux were positively correlated with NO3−, NH4+, depth, velocity and temperature, suggesting the importance of stream surface hydromoprhology to N2O emissions. Land use indirectly affected N2O flux by affecting water NO3−, NH4+, DO, DOC, pH and temperature, which could further explain the land use dependence of N2O emissions on water variables. High DOC:NO3− ratio (>6) was the main factor of N2O sink in the small streams, which may be due to the enhanced N2O consumption and low N2O production. Therefore, riverine N2O emissions are highly variable across stream sizes and land uses, which are not only increased by inorganic nitrogen load and are also dependent on stream hydraulics and morphology.

Golden mussel geographic distribution paradox: how can stream theories explain?

Aquatic ecosystems have biological, social, and economic importance. Between the 1980s and 2000s, a few theoretical concepts emerged that attempt to provide a better understanding of the function and dynamics of freshwater ecosystems, including biotic and abiotic variables. The rationale for our research was based on observations of the distribution and abundance of an exotic bivalve mollusc, the golden mussel Limnoperna fortunei (Dunker, 1857). The species has been recorded from several river basins, but only occurs in large water bodies and fails to reach first-order streams. This study provides an overview of the main stream ecology concepts developed to explain the dynamics of lotic ecosystems in an attempt to solve this paradox. The river continuum concept was the first of many in river ecology. These theoretical concepts are not mutually exclusive, but interdependent. It is expected the main reasons for the non-occurrence of L. fortunei in small streams are twofold: fluctuations in physical and hydrologic conditions in small streams, generating instability, and reduced availability of plankton in first- and second-order streams.

Combining passive and active distributed temperature sensing measurements to locate and quantify groundwater discharge variability into a headwater stream

Abstract. Exchanges between groundwater and surface water play a key role for ecosystem preservation, especially in headwater catchments where groundwater discharge into streams highly contributes to streamflow generation and maintenance. Despite several decades of research, investigating the spatial variability in groundwater discharge into streams still remains challenging mainly because groundwater/surface water interactions are controlled by multi-scale processes. In this context, we evaluated the potential of using FO-DTS (fibre optic distributed temperature sensing) technology to locate and quantify groundwater discharge at a high resolution. To do so, we propose to combine, for the first time, long-term passive DTS measurements and active DTS measurements by deploying FO cables in the streambed sediments of a first- and second-order stream in gaining conditions. The passive DTS experiment provided 8 months of monitoring of streambed temperature fluctuations along more than 530 m of cable, while the active DTS experiment, performed during a few days, allowed a detailed and accurate investigation of groundwater discharge variability over a 60 m length heated section. Long-term passive DTS measurements turn out to be an efficient method to detect and locate groundwater discharge along several hundreds of metres. The continuous 8 months of monitoring allowed the highlighting of changes in the groundwater discharge dynamic in response to the hydrological dynamic of the headwater catchment. However, the quantification of fluxes with this approach remains limited given the high uncertainties on estimates, due to uncertainties on thermal properties and boundary conditions. On the contrary, active DTS measurements, which have seldom been performed in streambed sediments and never applied to quantify water fluxes, allow for the estimation of the spatial distribution of both thermal conductivities and the groundwater fluxes at high resolution all along the 60 m heated section of the FO cable. The method allows for the description of the variability in streambed properties at an unprecedented scale and reveals the variability in groundwater inflows at small scales. In the end, this study shows the potential and the interest of the complementary use of passive and active DTS experiments to quantify groundwater discharge at different spatial and temporal scales. Thus, results show that groundwater discharges are mainly concentrated in the upstream part of the watershed, where steepest slopes are observed, confirming the importance of the topography in the stream generation in headwater catchments. However, through the high spatial resolution of measurements, it was also possible to highlight the presence of local and highly contributive groundwater inflows, probably driven by local heterogeneities. The possibility to quantify groundwater discharge at a high spatial resolution through active DTS offers promising perspectives for the characterization of distributed responses times but also for studying biogeochemical hotspots and hot moments.

Establishment of geochemical thresholds for vanadium throughout Korea and at potential development sites using geochemical map data.

Geochemical maps can be used for a variety of purposes, one of which is to establish regional or local geochemical thresholds for the analyzed elements. In the case of vanadium, as industrial demand and use increase, it is necessary to expand the development of vanadium in Korea. However, the environmental management standards are insufficient. Therefore, in this study, using geochemical data, we derived geochemical threshold values for the entire country and areas with potential for the development of vanadium deposits. The regional (country-wide) threshold value was derived using logarithmic transformation of raw data (N = 23,548) of the first- and second-order stream sediments collected across the country in the late 1990s and the early 2000s. The median + 2 median absolute deviation (MAD) and Tukey inner fence (TIF) values were 116mg/kg and 200mg/kg, respectively. Of these, the TIF standard, which showed 0.6% of data exceeding the threshold, was judged to be appropriate for distinguishing clear enrichment or contamination of vanadium. In the case of the Geumsan and Pocheon, areas with potential for vanadium development, the TIF and median + 2 MAD values of 259mg/kg and 218mg/kg, respectively, can be used as the criteria for evaluating the impact of environmental pollution before and after deposit development. Likewise, by deriving threshold values of the target elements using geochemical map data, it is possible to provide basic environmental information for geochemical evaluation and follow-up management in advance during large-scale site development.

Environmental Fragility in a Permanent Preservation Area

Permanent preservation areas reduce the exposure of sediments and nutrients in aquatic medium and improve the quality of water. The analysis of natural features and anthropic use in rivers’ surroundings makes it possible detecting potential ecological unbalance. This study analyzed the potential and emerging environmental fragility in Permanent Preservation Areas (PPA). Environmental fragilities around drainage areas composing the sub-basin were assessed based on soil, relief, rainfall, land use/land cover (LULC) features. The degrees of emerging environmental fragility observed in the second-order stream were lower than those in first-order ones: 3.07 and 2.68, on average, respectively; and standard deviation of approximately 0.7 was recorded in each group. First-order streams are more closely associated with high slopes, and it increases their fragility. Then reduction of fragility levels around water springs due to conservationist practices will decrease material and energy transfer throughout network connections and rebalance the assessed aquatic ecosystem.

A new minute riffle beetle (Coleoptera: Elmidae: Pagelmis) from the Brazilian Amazon.

The monotypic genus Pagelmis Spangler, 1981 was described from six thousand specimens of Pagelmis amazonica Spangler, 1981 collected with blacklight traps in Ecuador. For many years the known distribution of this genus was restricted to its type-locality, and recently it was recorded in Venezuela, Suriname and Brazil (Roraima State). Now, 40 years after the description of the genus, we describe the second Pagelmis species, based on male and female collected in the Amazon forest (Amazonas State, Brazil). With the description of the second species in the genus we provide an emended diagnosis of Pagelmis. Since adults of this genus were previously collected only in light traps, no habitat information was known. We collected adults of the new species in the first- and second-order streams with black, acidic water and sandy streambeds. The main substrates available in these streams were leaves and roots of riparian vegetation.

The geochemistry of Irish rivers

Study regionIreland Study focusMultiple studies have established that catchment geology and weathering regime strongly influence surface water chemistry, and that geochemical cycling can vary due to seasonal climatic conditions. However, fewer studies have focused on the influence these controls in a holistic manner. We relate the water chemistry of a country-wide Irish river survey to atmospheric input, underlying geology, and the influence of bogs. Climatic conditions were defined by an atypically wet winter and an unusually dry summer, providing the opportunity to investigate river chemistry variation across hydrologic conditions. Sampling included 21 of Ireland’s 22 largest rivers ranked by discharge, first-order and second-order streams draining bog lands, a second-order stream draining a limestone catchment, and downstream transects along the River Shannon. All samples were analyzed for major elements, selected trace elements, and nutrients, and a subset was analyzed for δ34SSO4. New hydrological insightsMost catchments were dominated by carbonate weathering with little contribution from the weathering of aluminosilicates. River water composition also varied geographically along the prevailing wind direction due to inputs from marine aerosols, with additional weathering components important in some systems. Seasonal influences could be seen in the chemistry of the headwaters of the River Shannon, while the lower reaches of the river exhibited less variable behavior throughout seasonal changes, likely due to the influence of lakes in the River Shannon system.

Changes in the hydro-sedimentary balance: Impacts of the use of a borrow pit in a low-order stream.

Construction of dams for hydroelectric power requires significant quantities of soil and rock, which are often extracted in borrow pits from adjacent regions. Although the effects of dams on stream processes has received significant attention, the effects of borrow pits has not. The main objective of this study was to analyze the geomorphological and sedimentological aspects of two second-order streams, one of which was directly affected by the borrow pit located upstream of its source (Pedra Branca stream). Flow rates were measured and cross-sections of 600m stretches in both streams were monitored over a hydrological year. At the same time, sediments from the bed of the channels and soils on their banks had their physical and chemical characteristics evaluated. Streams sediments differed in their chemical and organic matter composition. The mean particle size of the sediment particles was different between the reference and degraded streams. The water flow was very similar to both streams, only varying along the seasonal seasons. However, the fluvial channels presented great geomorphological differentiation, mainly downstream, due to the location of the Pedra Branca stream and its proximity to the borrow pit. Despite the great importance for the production of clean electric energy, the construction of hydroelectric plants promotes persistent impacts that affect structural and functional aspects of the adjacent aquatic habitats. Borrow pits used for the construction of projects become large sources of sediment for aquatic environments, affecting the drainage network of the hydrographic basin and the balance of river erosion, transport and deposition processes. The results show the need to review the intervention protocols in borrow pits and the environmental legislation that regulates their rehabilitation.

Thaw-driven mass wasting couples slopes with downstream systems, and effects propagate through Arctic drainage networks

Abstract. The intensification of thaw-driven mass wasting is transforming glacially conditioned permafrost terrain, coupling slopes with aquatic systems, and triggering a cascade of downstream effects. Within the context of recent, rapidly evolving climate controls on the geomorphology of permafrost terrain, we (A) quantify three-dimensional retrogressive thaw slump enlargement and describe the processes and thresholds coupling slopes to downstream systems, (B) investigate catchment-scale patterns of slope thermokarst impacts and the geomorphic implications, and (C) map the propagation of effects through hydrological networks draining permafrost terrain of northwestern Canada. Power-law relationships between retrogressive thaw slump area and volume (R2=0.90), as well as the thickness of permafrost thawed (R2=0.63), combined with the multi-decadal (1986–2018) increase in the areal extent of thaw slump disturbance, show a 2 order of magnitude increase in catchment-scale geomorphic activity and the coupling of slope and hydrological systems. Predominant effects are to first- and second-order streams where sediment delivery, often indicated by formation of recent debris tongue deposits, commonly exceeds the transport capacity of headwater streams by orders of magnitude, signaling centennial- to millennial-scale perturbation of downstream systems. Assessment of hydrological networks indicates that thaw-driven mass wasting directly affects over 5538 km of stream segments, 889 km of coastline, and 1379 lakes in the 994 860 km2 study area. Downstream propagation of slope thermokarst indicates a potential increase in the number of affected lakes by at least a factor of 4 (n&gt;5692) and impacted stream length by a factor of 8 (&gt;44 343 km), and it defines several major impact zones on lakes, deltas, and coastal areas. Prince of Wales Strait is the receiving marine environment for greatly increased sediment and geochemical fluxes from numerous slump-impacted hydrological networks draining Banks Island and Victoria Island. The Peel and Mackenzie rivers are globally significant conveyors of the slope thermokarst cascade, delivering effects to North America's largest Arctic delta and the Beaufort Sea. Climate-driven erosion of ice-rich slopes in permafrost-preserved glaciated terrain has triggered a time-transient cascade of downstream effects that signal the rejuvenation of post-glacial landscape evolution. Glacial legacy, ground-ice conditions, and continental drainage patterns dictate that terrestrial, freshwater, coastal, and marine environments of western Arctic Canada will be an interconnected hotspot of thaw-driven change through the coming millennia.

Carbon dioxide hydrodynamics along a wetland-lake-stream-waterfall continuum (Blue Mountains, Australia).

The small-scale spatial variability in dissolved carbon dioxide (CO2) and water-air CO2 flux dynamics were investigated within first-order catchments of the upper Blue Mountains Plateau (New South Wales, Australia). Water samples were collected at 81 locations during winter and summer over two consecutive years across seven aquatic ecosystem types: wetland, impoundment, lake, tributary stream, mainstem, escarpment complex, and urban-aquatic interface. Dissolved [CO2] ranged from 15 to 880μM (94 to 4760%Sat), and dissolved [O2] from 0 to 350μM (0 to 101%Sat). CO2 supersaturation was typically highest in wetlands and vegetated impoundments of the upper plateau, and decreased downstream approaching atmospheric equilibrium at the escarpment waterfalls. Gas transfer velocities ranged from 0.18m d-1 in lentic waters to 292m d-1 at the bottom of waterfalls due to bubble-mediated transfer. The first- and second-order streams represented only 4.8% of the total open water area yet contributed to 61% of the total water-air CO2 outgassing. The lake, escarpment and mainstem group systems had narrow diel and seasonal CO2 concentration variability, while wetlands and vegetated impoundments had the widest ranges. Our high resolution spatio-temporal sampling was essential to identifying CO2 outgassing hotspots in these geomorphically diverse catchments. Overall, >95% of excess dissolved CO2 traversing the upper Blue Mountains Plateau was outgassed to the atmosphere.

Novel approaches to investigating spatial variability in channel bank total phosphorus at the catchment scale

Phosphorus (P) is often a limiting nutrient that leads to the eutrophication of aquatic systems. While dissolved P forms are the most bioavailable, the form, mobility, transport and fate of P are directly related to its association with fine-grained riverine sediment. Therefore, to implement successful P catchment management strategies it is important to understand the relative contribution of different sediment sources to P loads across the river continuum. While agricultural topsoil and, to a lesser extent, riverbed sediment are important sources of sediment-associated P, channel banks have been shown to be an important sediment source in some catchments. However, comparatively little is known about the P concentration and corresponding spatial variability in channel bank sediment and the associated implications for catchment management. The present study examines the spatial variability of P associated with channel bank profiles within a series of three nested catchments using both non-spatial and spatial statistical methods, where for the latter, a novel spatial approach was used to estimate the spatial averages and variances of P in channel bank sediment along the stream network. Channel bank P concentrations were compared to factors such as catchment scale, stream order, land use, bank exposure and location along the stream network. Concentrations of TP ranged between 129.6 and 1206.9 mg P kg−1 of which the water extractable P (WEP) content ranged from 0.01 to 0.12%. Stream order was found to influence TP concentrations, while land use and catchment scale provided only a moderate influence. This suggested that focussing channel bank sampling strategies at the largest catchment scale would capture key drivers of TP variability provided stream order is sufficiently represented. Whether the bank was had limited vegetation and was exposed and potentially eroding had a slight influence on TP variability in second-order stream banks in the larger of the two nested catchments. However, the slightly lower TP concentrations measured at these sites indicated that banks that are actually eroding may be contributing less TP than the total channel bank TP values measured across the catchments as a whole. The results of an explicitly spatial analysis demonstrated that local channel bank TP averages and TP variances vary along the stream network. Specifically, the most accurate spatial predictor of TP was local TP means with the use of ‘crow flies’ rather than stream network distances. Local TP variances were used to provide optimal designs for future channel bank TP sampling campaigns, given available resources. Throughout, both standard and outlier-resistant statistical analyses were applied to improve interpretation of the study findings.

Distribution Pattern of Ichthyofaunal Diversity in Different Habitats in the First-, Second- and Third-Order Streams of Randi Gad from Garhwal Himalaya, India

The present study was undertaken to report the ichthyofaunal diversity on spring-fed hill stream Randi Gad from Pauri Garhwal District, Uttarakhand, India. In this work, the author proposed one novel approach, viz. stream order-wise study of distribution and diversity of fish fauna from Garhwal Himalaya, India. A total of 121 fish species including 4, 12 and 22 fish species were collected from first-, second- and third-order streams of Randi Gad. The ichthyofaunal biodiversity observed belonged to 4 families, 10 genera and 22 species. The first-order stream had shown minimum diversity (4 species) and fish productivity of 07CPPs. The second-order stream showed productivity of 24CPPs (12 species). The third-order stream was the most diverse (22 species) and showed fish productivity of 38 CPPs (calculated productivity points system). Thus, the spring-fed hill stream Randi Gad has good potential for fish fauna.

Long-term monitoring of the recruitment and dynamics of large wood in Kamienica Stream, Polish Carpathians

Studies presenting long-term observations of the recruitment and mobility of large wood in mountain watercourses are scarce, but they can considerably contribute to the knowledge of river/riparian forest interactions and the assessment of flood hazard resulting from wood mobility during floods. Widespread dieback of riparian forest along the headwater course of Kamienica Stream in the Polish Carpathians, caused by bark beetle infestation of spruce trees, has raised concerns about potential increases of large wood recruitment to the stream and of the flood hazard to downstream valley reaches. In October 2009, 429 trees growing along three sections of the stream were tagged with numbered metal plates and monitored over 10 years to determine the timing and causes of their delivery to the channel and the lengths of their displacement during individual flood events. Moreover, in 2012 the mode of location of wood deposits and a degree of wood decay were determined in the second- to fourth-order stream reaches. The monitoring of tagged trees indicated that trees were recruited to the channel during highintensity meteorological and hydrological events, mostly as a result of bank erosion during floods or windthrow. With 22% of tagged trees recruited to the channel during 10 years, the rate of turnover of the riparian trees was estimated at 45 years. As the riparian area is overgrown with trees with ages up to ~160 years, the rate evidences substantial intensification of large wood recruitment to the channel in the recent period. Results of large wood inventory and the 10-year-long monitoring of tagged trees indicated variable mobility of large wood along the upper course of the stream. Wood mobility was negligible in the second-order stream reach, very small in the third-order reach, and greater, but still limited in the fourth-order reach. Wood is transported longer distances only during major floods. However, the advanced state of decay of most pieces leads to their disintegration during floods, precluding distant transport. Thus, large wood retained in the upper stream course does not constitute an important flood hazard to downstream, inhabited valley reaches.

The influence of environmental and spatial factors on benthic invertebrate metacommunities differing in size and dispersal mode

Understanding the drivers of species distribution is an important topic in conservation biology and ecology, pertaining to species traits like dispersal strategies and species–environment interactions. Here we examined the drivers of benthic species distribution at 20 sections of a second-order stream network. Environmental and spatial factors and the dispersal modes of the organisms were considered. We expected that species with aerial dispersal capabilities like insects would be less restrained by distance between sites and thus mostly affected by environmental factors. In contrast, we hypothesized that completely benthic species would mainly be affected by spatial factors due to limited dispersal. However, microscopic species like nematodes characterized by a high passive dispersal potential may be less limited by spatial factors. When using redundancy analyses and subsequent variance partitioning, the included variables explained 24% (insects), 24% (non-flying macrobenthos), and 32% (nematodes) of the variance in the respective community composition. Spatial factors mainly explained the species composition of all tested groups. In contrast with other larger species, nematodes were characterized by fine-scale patterns that might have been induced by random processes (e.g., random distribution and priority effects). Our study showed that dispersal processes are crucial in shaping benthic communities along streams albeit the relatively small sampling area (max. distance between sampling sites: 2 km). The demonstration of spatial factors as important drivers of the species distribution of passively dispersing benthic organismal groups highlights the role played by connectivity in determining species distribution patterns in river systems.

Hydrologic and cost benefit analysis at local scale of streambed recharge structures in Rajasthan (India) and their value for securing irrigation water supplies

A hydrological study of four streambed recharge structures, locally called check dams, in a monsoonal area of hard-rock terrain in Rajasthan, India, was conducted over 3 years to evaluate their contribution to agricultural production. Their catchment area totalled 3,003 ha, and mean annual recharge from the 4 impoundments was 779,000 m3 or 26 mm. The calculated components of the annual water balance of these check dams are presented, together with a sensitivity analysis on unmeasured parameters and documentation of capital and maintenance costs of check dams. The maximum recharge was found to occur in the wettest year for the two structures on first-order streams; however, for the two structures on second-order streams, the maximum recharge occurred in the average rainfall year because, at these sites, groundwater levels rose so that the stream became hydraulically connected to the aquifer for a period in the wettest year causing mean dry weather infiltration rates to diminish. The study also evaluated the effect of manual desilting and mechanical desilting on mean dry-weather-infiltration rate. For the check dam that was manually desilted, the recharge increased by 84% over that of the preceding year, whereas for the mechanically desilted check dam it reduced by 18%, and the two control check dams increased by 13%. A present value analysis for net benefits of additional crop production attributable to recharge from check dams indicated that, after accounting for average annual maintenance costs 2.9% of capital costs, the benefit:cost ratio of the four check dams averaged 4.1. Hence this study shows that these check dams are economically attractive at the local level for securing irrigation water supplies.

Reconstruction and characterization of the surface drainage system functioning during extreme rainfall: the analysis with use of the ALS-LIDAR data\u2014the case study in two small flysch catchments (Outer Carpathian, Poland)

A surface drainage system (SDS) controls catchment hydrology and acts as an indicator of geomorphologic processes. In this study, a field-based and GIS-integrated approach enabling reconstruction of a surface drainage system, which operates during heavy rainfall in small flysch catchments, has been proposed. The reconstruction is based on the ALS-LIDAR data. The reconstruction of the SDS gave the opportunity for analysis of the changes between the river system and the SDS operating during heavy rainfalls. Results have revealed that the SDS operating during heavy rainfalls is several times better developed than the river system. The density has increased from c.a. 1.5 to 13.7 km·km− 2. Moreover, the structure of the SDS has changed, what was confirmed by the parameters of the Hortonian type of the analyses. The most significant changes were related to the first- and second-order streams. These streams were, the most frequently, the man-origin incisions and natural-origin incisions/concavities on the hillslopes conditioned by micro-relief. The man-origin sub-system reached up to 35% of the SDS functioning during heavy rainfalls, whereas the sub-system composed of incisions/concavities conditioned by micro-relief reached up to 24% of this SDS. Smaller lateral valleys included to the SDS during heavy rainfalls constitute up to 37% of the SDS. The permanent streams constitute the remaining part of the SDS. Changes in the SDS have the influence on the drainage pattern, hydrological response of a catchment, and intensity of geomorphological processes; therefore, the changes in the SDS and their consequences have been discussed.