Stream Vegetation Research Articles

Quantifying wake dynamics subjected to stream vegetation patch elongation: The influence of patch-edge vortices

Vortices are generated across a wide range of scales due to the interaction between in-stream vegetation and surrounding flows, significantly influencing hydro-geomorphodynamics in earth surface water systems. Recent advance in vegetation patch hydrodynamics has revealed that the elongation of the middle channel patch can generate complex wake flow patterns by adjusting the bleed flow from the patch and triggering the patch-edge Kelvin–Helmholtz (KH) vortices. With a broader range of experimental configurations, this study reveals how the patch wake mixing is apparently strengthened by the presence of KH vortices, indicated by a larger steady wake velocity, a shorter steady wake length, and a damped energy of wake von Karman vortex. Furthermore, we quantify these characteristic metrics of patch wake behavior with and without the influence of KH vortices. Our findings provide insights into the role of vegetation-induced vortex interactions in regulating mixing processes, thereby promoting informed practices in environmental flows.

Riverine aquatic plants trap propagules and fine sediment: Implications for ecosystem engineering and management under contrasting land uses

AbstractPlants in streams act as physical ecosystem engineers, both influencing and responding to hydrogeomorphic processes such as fine sediment retention. Instream vegetation may also influence propagule dispersal and retention, shaping plant community dynamics. These plant‐sediment interactions may result in synergistic feedback promoting hydrogeomorphic complexity and biogeomorphic succession. However, the role of aquatic plants (submerged or mostly submerged) in trapping propagules, fine sediment and organic matter in degraded lowland streams is uncertain. In this study, we sampled sediment (≤5 cm depth) from eight streams ranging in land use from rural to urban, including within patches of aquatic vegetation and unvegetated locations. We conducted a propagule bank trial to identify the abundance and diversity of propagules and analysed the particle size and organic matter composition of the samples. A total of 8,365 seedlings from 113 plant species were recorded with a range of hydrological tolerances. Aquatic plants retained 56% more propagules and 32% more species, and marginal vegetation retained 250% more propagules and 48% more species, than open channel locations (the least retentive location). Similar patterns were found for fine sediment and organic matter retention. Propagule bank communities were different across land‐use types but not sampling locations. The trapping effect of aquatic vegetation diminished as catchments became more urbanised. This study provides evidence that aquatic plants retain more propagules and species, and fine sediment and organic matter than vegetation‐free channel locations. Improving aquatic vegetation in streams may be an important early step in restoring hydrogeomorphic complexity and propagule retention, and the facilitation of biogeomorphic succession in degraded streams. Unfortunately, heavily urbanised streams with flashy flow regimes are unlikely to benefit from this function unless catchment‐scale hydrology is addressed.

Catchment-scale hydrology limits the benefits of geomorphic complexity for instream vegetation communities

Improving instream habitat complexity is a common stream restoration approach despite often limited improvements to stream biota with catchment-scale stressors such as altered hydrology thought to be more important. Instream vegetation is a critical component of lowland stream ecosystems, providing multiple ecological benefits. Thus, we asked: How does instream vegetation respond to (1) geomorphic complexity; (2) different flow regime components; and (3) what is the relationship between geomorphic complexity and flow in driving instream vegetation?We surveyed instream vegetation and geomorphology along 23 lowland stream reaches. We investigated associations between six measures of geomorphic complexity, six flow metrics, and amphibious and aquatic vegetation richness, Shannon diversity and cover.Amphibious vegetation was negatively associated with simplified channels and increasing flood frequency. Increasing depth and width variation, and Julian day low flow variability, were positively associated with aquatic vegetation. Considering sites with complex (stable) or simplified (unstable) geomorphology separately, only vegetation at stable sites showed strong relationships to flow regime components, with variables related to flow flashiness negatively associated with both amphibious and aquatic vegetation, and Julian day low flow variability positively associated with aquatic vegetation.We identified channel complexity, variables related to flow flashiness and variation in low flow timing, as key geomorphic and flow drivers of instream vegetation, respectively. Importantly, our results suggest that instream vegetation benefits from improving geomorphic complexity are likely to be limited without also addressing altered flow regimes.

Experimental Study on Influence of Different Patterns of an Emergent Vegetation Patch on the Flow Field and Scour/Deposition Processes in the Wake Region

AbstractFlume experiments were conducted to comprehend the impact of different patterns of an emergent vegetation patch on the flow field and the scour process in natural rivers. Velocity measurements, flow visualization, and scour tests were undertaken around different vegetation patch patterns, which were simulated inspired by the expansion process of a typical instream vegetation. The patch expansion process was idealized with an initially circular patch of rigid emergent stems becoming elongated due to positive and negative feedbacks. The expansion of the vegetation patch was considered to occur in three stages, in which the density of the patch from the previous stage was increased while the patch was also elongated by connecting at its downstream side with another sparser vegetation patch. These stages were replicated succesively by increasing the density and elongating the patch. In this way, two processes (i.e., elongation and decrease in permeability), which usually have hydrodynamically opposite effects on flow fields, were simulated at the same obstruction. Despite generally elongated obstacles being streamlined bodies, the morphometric analysis obtained by laser scanner revealed that streamlined elongation of permeable patches amplifies global scour and enhances localization of the local scour hole. This situation implies that as the patch expands, in the wake region, the steady‐wake region becomes shorter, turbulence diminishes, lateral shear stress enhances, and deposition cannot occur far from the patch. Consequently, as the patch expands, the hydrodynamic consequences may restrict further patch expansion after a certain length/density.

Identifying the stability trajectory of a large braided Brahmaputra river using reach-scale process-based approach

The dynamic evolution of a large braided river system is characterized by sporadic operation, impacted by a diverse range of natural and anthropogenic factors. The hydro-geomorphological interaction within the river corridor and its surrounding ecosystem presents a complex process, posing challenges in comprehending its dynamics. This study investigated the spatiotemporal heterogeneity in the vegetation-flow regime of a large braided reach of mighty Brahmaputra river. A detailed statistical analysis for the last three decades (1990 to 2019) was performed to demonstrate the in-stream vegetation characteristics for the selected middle reach (240 km) of the river. Google earth engine platform and advanced geospatial techniques have been used in this study. A novel indicator called stability trajectory indicator was developed that utilized vegetation information to identify the stability state of braided reaches. The findings of this study indicate a substantial increase in moderate and dense vegetation cover compared to light vegetation cover over the past decade. These results highlight the pronounced influence of increased moderate and dense vegetation type on the stability criteria of the reach, surpassing the contribution of light vegetation. The approach outlined in this study holds potential for river engineers to develop an effective management strategy for monitoring and maintaining river health.

Looking back to move forward: Restoring vegetated canals to meet missing Water Framework Directive goals in agricultural basins

Nitrate pollution and eutrophication remain pressing issues in Europe regarding the quality of aquatic ecosystems and the safety of drinking water. Achieving water quality goals under the Water Framework Directive (WFD) has proven to be particularly challenging in agricultural catchments, where high nitrate concentrations are the main reason for the failure of many water bodies to meet a good ecological status. Canals and ditches are common man-made features of irrigated and drained landscapes and, when vegetated, have recently been identified as denitrification hotspots.By combining experimental data and GIS-based upscaling estimation, the potential capacity of the canal network to reduce nitrate loads was quantified in several scenarios differing in the level of nitrate pollution and in the extent of the canal network length where conservative management practices are implemented. The analysis was carried out in the irrigated lowlands of the Po River basin, which is the largest hydrographic system in Italy and a global hotspot for nitrogen inputs and eutrophication.Scenario simulations showed that maintaining aquatic vegetation in at least 25 % of the canal network length, selecting sites with high nitrate availability (>2.4 mg N L−1), would promote a greater potential for permanent N removal. The increased denitrification capacity would meet the load reduction target required to achieve a WFD good ecological status in waters draining into the Adriatic Sea during the spring-summer months, when the eutrophication risk is higher. Promoting denitrification in the canal network by postponing the mowing of in-stream vegetation to the end of the growing season could be an effective mitigation strategy to improve water quality in agricultural basins and contribute to achieving the WFD goals.

Effect of logged forests on diet of small characids from Neotropical streams

AbstractStudies relating to fish trophic ecology provide important insights regarding their life history. However, there is a lack of information linking fish diet composition with riparian cover in small streams. To investigate whether diet composition varied between streams with pristine and logged forests, I compared the food items consumed by four characid species: Bryconops melanurus, Moenkhausia collettii, Moenkhausia dichroura, and Moenkhausia oligolepis. I sampled 18 first‐order streams in the eastern Amazon: six with pristine forest, six with conventional logging, and six with selective logging. All fish species were classified as omnivorous, with diverse food categories recorded in their diets: mainly terrestrial insects for Moenkhausia species and aquatic insect nymphs for B. melanurus. However, the relative importance of each category varied only in streams with conventional logged forests. In these streams, all fish species consumed mainly autochthonous items, especially aquatic insect nymphs. In addition, terrestrial insects and seeds were absent in these streams with reduced riparian cover. In summary, this study highlighted that fish diet in conventional logged forests strongly differed from areas with pristine and selective logged forests. This finding states that managed forests may support a diverse diet for fish community, similar to that found in pristine forests. Therefore, management and conservation strategies of riparian vegetation in Amazonian streams are important to maintain habitat and food quality, which may be associated with a diverse diet for fish species.

Root development is faster in common species of Potamogeton compared to declining species of Potamogeton in Danish lowland streams

The decline in biodiversity in freshwater ecosystems occurs at an alarming rate throughout the world. In Denmark, we know from historical records that several species within the plant genus Potamogeton, that were previously widespread in Danish freshwater ecosystems, are now under severe decline. In this study, we explore root development in two common and three declining Potamogeton species applying an experimental approach. Specifically, we examined if root development characteristics can contribute to explain the contrasting success of these species in the contemporary stream vegetation in Denmark. In accordance with our hypothesis, our results showed that common species of Potamogeton produced roots faster, had longer roots and produced more roots per growth node than declining Potamogeton species. This was particularly clear for P. crispus. Overall, our results expose a mechanism that is likely to affect the ability of these species to maintain populations in highly disturbed lowland streams in Denmark and therefore contribute to explain the contrasting success of these species.

Comparison of Velocity and Reynolds Stress Distributions in a Straight Rectangular Channel with Submerged and Emergent Vegetation

Vegetation in rivers and streams plays an important role in preventing erosion and improving bank stability. Comparison between emergent vegetation (bank vegetation) and submerged vegetation, in terms of velocity and Reynolds stress distributions, for the same aspect ratio and flow discharge, has received limited attention in the literature. This study investigates the velocity and Reynolds stress, as well as the log law for submerged and emergent vegetation in a laboratory flume and compares the results for a different set up with different sediment size and aspect ratio but the same discharge. The results indicate that the influence of submerged vegetation on the secondary currents generation is less than emergent vegetation. In addition, the log law application is valid for both submerged and emergent vegetation cases, however, it is valid up to y/h = 0.75 for emergent vegetation (in which the vegetation cover in banks is partly out of the water) but up to y/h = 0.25 for vegetation bank. For both submerged and emergent vegetation, Reynolds stress distribution presents a convex form but with a different turning point. Comparison of the results with those in an artificial pool over submerged vegetation and low aspect ratio (<5) keeps almost the same form for velocity and Reynolds stress distributions but decreases the turning point in Reynolds stress distribution. For the submerged vegetation cover, the location of zero shear stress superposes that of maximum velocity, but for the emergent vegetation approaching the bank vegetation and shifting the maximum velocity towards the bed, the location of zero shear stress approaches the bed.

Experimental and Artificial Neural Network (ANN) Modeling of Instream Vegetation Hydrodynamic Resistance

This study examines the impact of upstream structures on the bulk drag coefficient of vegetation through experimental means, which has not been previously conducted. An embankment model was placed upstream of the vegetation, both with and without a moat/depression. The results showed that the presence of an upstream structure reduced the bulk drag coefficient of vegetation as the structure shared the drag. When only the embankment was placed upstream, a maximum decrease of 11% in the bulk drag coefficient was observed. However, when both the embankment and moat models were placed upstream, a 20% decrease in the bulk drag coefficient was observed. Regression models and artificial neural network (ANN) models were developed to predict the bulk drag coefficient based on the variables affecting it. Five ANN models with different training functions were compared to find the best possible training function, with performance indicators such as coefficient of determination (R2), root mean square error (RMSE), Nash–Sutcliffe efficiency (NSE), sum of square error (SSE), mean absolute error (MAE), and Taylor’s diagrams used to evaluate the model performance. The ANN model with nine neurons in each hidden layer performed the best, achieving the highest R2 and NSE values and the lowest RMSE, SSE, and MAE values. Finally, the comparison between the regression model and the ANN model showed that the best ANN model outperformed the regression models, achieving R2 values of 0.99 and 0.98 for the training and validation subsets, respectively.

HeadwaterstreamSNevada: Data on riparian vegetation and water parameters of headwater streams in Sierra Nevada, Spain.

Providing historical data on riparian plant biodiversity and physico-chemical parameters of stream water in Mediterranean mountains helps to assess the effects of climate change and other human stressors on these sensitive and critical ecosystems. This database collects data from the main natural headwater streams of the Sierra Nevada (southeastern Spain), a high mountain (up to 3479 m above sea level [m asl]) recognized as a biodiversity super hotspot in the Mediterranean basin. On this mountain, rivers and landscapes depend on snowmelt water, representing an excellent scenario for evaluating global change's impacts. This dataset covers first- to third-order headwater streams at 41 sites from 832 to 1997 m asl, collected from December 2006 to July 2007. Our goal is to supply information on the vegetation associated with streambanks, the essential physico-chemical parameters of stream water, and the physiographic features of the subwatersheds. Riparian vegetation data correspond to six plots sampled at each site, including total canopy, individual number, height and DBH (diameter at breast height) in woody species, and cover percentage for herbs. Physico-chemical parameters were measured in situ (electric conductivity, pH, dissolved O2 concentration, stream discharge) and determined in the laboratory (alkalinity, soluble reactive phosphate-phosphorus [SRP], total phosphorus [TP], nitrate-nitrogen [ -N], ammonium-nitrogen [ -N], total nitrogen [TN]). Watershed physiographic variables comprise drainage area, minimum altitude, maximum altitude, mean slope, orientation, stream order, stream length, and land cover surface percentage. We recorded 197 plant taxa (67 species, 28 subspecies, and 2 hybrids), representing 8.4% of the Sierra Nevada vascular flora. Due to the botanical nomenclature used, the database can be linked to FloraSNevada database, contributing to Sierra Nevada (Spain) as a laboratory of global processes. This data set can be freely used for non-commercial purposes. Users of these data should cite this data paper in any publications resulting from its use.

The Impact of Urban Land-Use Regimes on the Stream Vegetation and Quality of a Mediterranean City

Urban streams are ecosystems of great ecological and hydrological importance for human environments. However, they face pressure on biodiversity, hydromorphology, and water quality. In this study, an urban riparian system of a Mediterranean city (Thessaloniki, Greece) which interacts with several land-use classes, namely forests, pastures, cultivations, industrial-commercial infrastructure, and light and dense urban fabric, is assessed. The analyzed data were collected by implementing mainly QBR and ancillary RMP protocols on 37 plots of the Dendropotamos stream. The QBR protocol provided an assessment of total riparian vegetation cover, cover structure and quality, as well as channel alterations. The RMP protocol was used to enhance the quantitative assessment of dominant tree and shrub cover. Parts of Dendropotamos surrounded by agricultural (median QBR score: 27.5), industrial (50), and dense residential areas (27.5) suffer, in general, from low riparian vegetation cover, bad vegetation structure and quality, the continuous presence of alien/introduced species, and channel alterations. A variety of riparian habitat conditions characterize the sparse residential areas (60) where cover structure and quality of vegetation is improved. The reduction in grazing pressure has improved the riparian habitat in the greatest part of Dendropotamos that is surrounded by semi-natural pastures (65). Within forested areas (85), the stream conditions are considered quasi-natural. All previous land uses are differentiated in terms of the dominant trees found in the vegetation of Dendropotamos: Platanus orientalis in forested areas, alien Ailanthus altissima mainly in residential and industrial areas, and native shrubs, e.g., Quercus coccifera and Pyrus spinosa, in pastures. The QBR protocol could be a valuable tool in urban environment planning to help identify areas with potential for restoration, such as those with moderate residential pressure.

Towards i5 Ecohydraulics: Field Determination of Manning’s Roughness Coefficient, Drag Force, and Macroinvertebrate Habitat Suitability for Various Stream Vegetation Types

Ecohydraulic models have commonly used the flow velocity, water depth, and substrate type (i3 models) as the three fundamental determinants of the distribution of freshwater biota, but a fourth determinant has largely been neglected: stream vegetation. In this study, we provide the hydraulic and habitat information required to develop vegetation-adapted ecohydraulic models (i4 models) in streams. We calculated drag forces and Manning’s roughness coefficients (nV) for nine types of submerged, emergent, and overhanging stream vegetation. In addition, we developed habitat suitability curves (HSCs) for benthic macroinvertebrates for these stream vegetation types. Hydraulic modules can now be upgraded to simulate stream vegetation by including the vegetation-adapted nV values within an additive approach in which nV is added to the n value of the inorganic substrate to which the vegetation is rooted. Habitat modules can also be upgraded to include macroinvertebrate HSCs for stream vegetation, again by adding the vegetation-adapted habitat suitability to that of the inorganic substrate to which the vegetation is rooted. In combination, i4 ecohydraulic models (including vegetation) can now be designed and applied, and we suggest that ecohydraulic research should further focus on including a fifth variable (water temperature) to ultimately advance to i5 ecohydraulic models that will optimally simulate the hydroecological reality.

Modeling the relative morphodynamic influence of vegetation and large wood in a dryland ephemeral stream, Arizona, USA

Compared to perennial streams, studies investigating the impact of large wood on sediment transport and river corridor morphology in ephemeral streams are lacking. Due to the flashy nature of ephemeral flow regimes, opportunities to directly investigate the influence of wood in ephemeral channels are limited. Additionally, given prior studies showing a strong association between existing riparian vegetation and large wood deposition in ephemeral streams, the geomorphic impact of wood is entangled with that of vegetation. Here, we develop a hydro-morphodynamic model to investigate changes to channel and floodplain morphology due to wood and vegetation in an ephemeral stream in southeastern Arizona, USA. Three scenarios are modeled: the actual configuration of the river corridor; an experiment in which jams are removed; and an experiment in which vegetation is removed. Both large wood and vegetation effectively confined flow to the main, unvegetated channel, which became wider and deeper over the course of a single moderate flood. When isolating the impact of large wood, model results show that wood enhances channel change created by vegetation, resulting in ±0.1 to 0.3 m of additional scour or aggradation. The simulated removal of vegetation resulted in more channel change than the removal of wood alone, partially because vegetation occupies a much greater area within the stream corridor than large wood. We propose a conceptual framework where large wood could mediate sedimentation as well as the recruitment and growth of vegetation in ephemeral streams, contributing to the evolution of ephemeral stream morphology over time.

Assessing Riverbed Surface Destabilization Risk Downstream Isolated Vegetation Elements

A few decades ago, river erosion protective approaches were widely implemented, such as straightening the river course, enhancing riverbed/bank stability with layers of concrete or riprap, and increasing channel conveyance capacity (i.e., overwidening). However, recent research has established that such practices can be tremendously costly and adversely affect the rivers’ ecological health. To alleviate these effects, green river restoration has emerged as a sustainable and environmentally friendly approach that can reduce the negative impact of the riverbed and bank destabilization and flooding. One of the typical green restoration measures, especially for instream habitat improvement, is the establishment of instream vegetation, which leads to a more diversified flow regime, increasing habitat availability and serving as refugia for aquatic species. Within the perspective presented above, flow–vegetation interaction problems for several decades received significant attention. In these studies, rigid rods have commonly been used to simulate these vegetative roughness elements without directly assessing the riverbed destabilization potential. Here, an experimental study is carried out to investigate the effect of different instream vegetation porosity on the near-bed flow hydrodynamics and riverbed destabilization potential for a range of simulated vegetation species. Specifically, the flow field downstream, four distinct simulated vegetation elements is recorded using an acoustic Doppler velocimetry (ADV), assuming about the same solid volume fraction for the different vegetation elements. In addition, bed destabilization potential is assessed by recording with optical means (a He-Ne laser with a camera system) the entrainment rate of a 15 mm particle resting on the uniform bed surface and the number of impulses above a critical value. Results revealed that the number of impulses above a critical value at the normalized distance equal to two is a good indicator for cylinder and five for other vegetation to assess the riverbed destabilization potential. The experimental findings from this study have interesting geomorphological implications regarding the destabilization of the riverbed surface (removal of coarse particles induced by high magnitude turbulent impulses) and the successful establishment of seedlings downstream of instream vegetation.

A process-based recovery indicator for anthropogenically disturbed river system

The present paper utilizes entropy theory and Google earth engine cloud computing technique to investigate system state and river recovery potential in two large sub-basins of the Mahanadi River, India. The cross-sectional intensity entropy (CIE) is computed for the post-monsoon season (October–March) along the selected reaches. Further, a normalized river recovery indicator (NRRI) is formulated to assess the temporal changes in river health. Finally, NRRI is related to a process-based variable-LFE (low flow exceedance) to comprehend the dominating system dynamics and evolutionary adjustments. The results highlight the existence of both threshold-modulated and filter-dominated systems based on CIE and NRRI variabilities. In addition, the gradual decline in CIE and subsequent stabilization of vegetated landforms can develop an ‘event-driven’ state, where floods exceeding the low-flow channel possess a direct impact on the river recovery trajectory. Finally, this study emphasizes the presence of instream vegetation as an additional degree of freedom, which further controls the hierarchy of energy dissipation and morphological continuum in the macrochannel settings.

Factors Affecting Avifaunal Diversity in Selected Agro-Ecosystems of Himachal Pradesh Agricultural University, Palampur, Himachal Pradesh, India

Avifaunal diversity in eight different habitats of Himachal Pradesh Agricultural University, Palampur was studied in order to find factors affecting the occurrence of bird species. Bird populations were sampled in different agro-ecosystems such as farm fields (experimental and organic), wetland, abandoned tea plantation, administration area, playground, secondary forest and stream vegetation. A total of 125 species of birds belonging to 51 families, including 33 winter visitors and 27 summer visitors have been recorded. Among them, 78 insectivores followed by 18 carnivores were recorded. The abandoned tea field was a diverse habitat that maintained the highest species richness recording 50 species, followed by stream vegetation and organic farm. Seasonal variations and habitat heterogeneity play crucial role in shaping species richness. Plant diversity, vegetation structure and microhabitats support different feeding guilds, temporary refuge and migratory route which result in increased bird diversity. Based on different categories of birds, the cluster analysis revealed three distinct clusters of habitats, first cluster containing administration area and secondary forest habitats, experimental farm and wetland grouped in cluster II, whereas cluster III contained habitats viz. abandoned tea plantation, playground, organic farm and stream vegetation. Several conservation measures such as increasing plant diversity, conducting regular and long-term systematic studies, introducing bird friendly management plan are recommended to conserve and enhance avifaunal diversity in the university.

Reach-scale experiments on deposition process in vegetated channel: Suspended sediment capturing ability and backwater effect of instream plants

Instream plants, which act as biological processors, have emerged as potentially advantageous eco-morphologic tools to be used in river management and restoration. Most of the study on the geomorphic role of vegetation as it interacts with flow and sediment has focused on local patch-scale dynamics. In this study, we present flume experiments aimed at improving our understanding of how vegetation patches link together to impact reach-scale hydraulics and suspended sediment transport and disposition. On the hydraulics side, we investigate a) the relationship between the imposed instream vegetation configuration and water surface slopes, b) the secondary flow patterns which arise because of the imposed vegetative obstructions, and c) the role of vegetative resistance on residence time within reach. We also examine how different vegetation arrangements determine the patterns, quantity, and caliber of suspended sediment deposited in the flume. A key result of vegetation within the channel is the overall non-uniformity in flow conditions it imposes upstream, within, and downstream of the vegetated reach. At steady-state, vegetated patches locally increase the resistance, leading to a backwater condition upstream of the patch and high water-surface slopes within the patch. In general, this leads to enhanced deposition of suspended sediment upstream of the patch and reduced deposition within the patch relative to a case with no vegetation at all.

A New Species of Scinax Wagler (Amphibia, Anura, Hylidae) from the Atlantic Forest, Southeastern Brazil

The Scinax catharinae clade comprises the S. perpusillus and S. catharinae groups. The S. catharinae group has 38 species, mostly from Brazil's Atlantic Forest. We describe a new species of S. catharinae group based on external morphology, color pattern, and bioacoustics. The new species calls from herbaceous vegetation of slow-flowing streams from Santa Teresa, State of Espírito Santo, southeastern Brazil. The new species is distinguished from species of the S. catharinae group by the following combination of characters: male SVL 24.8–28.3 mm and female SVL 31.2–38.6 mm; males with hypertrophied forearms and inguinal glands; interocular region with a dark blotch not exceeding beyond the anterior margin of tympanic level; black blotches on a whitish-green background on the inguinal region and hidden surfaces of legs; call type A of 0.301–0.883 s, and 12–30 notes emitted at a rate of 31.4–42.0 notes/s. We also provide remarks on its natural history and conservation status.

The achievement of Water Framework Directive goals through the restoration of vegetation in agricultural canals

Decreasing nitrate concentrations is one of the most relevant Water Framework Directive (WFD) goals, which today is still unreached in several European countries. Vegetated canals have been recognized as effective filters to mitigate nitrate pollution, although rarely included in restoration programs aimed at improving water quality in agricultural watersheds.The Po di Volano basin (713 km2, Northern Italy) is a deltaic territory crossed by an extensive network of agricultural canals (~1300 km). The effectiveness in buffering nitrate loads via denitrification was assessed for different levels of in-stream emergent vegetation maintenance by employing an upscale model based on extensive datasets of field measurements. The scenarios differed for the canal network length (5%, 20%, 40%, and 60%) where conservative management practices were adopted by postponing the mowing operations from the middle of summer, as nowadays, to the early autumn, i.e., the vegetative season end.The scenario simulations demonstrated that the capacity to mitigate diffuse nitrate pollution would increase up to four times, compared to the current condition (5% scenario), by postponing the vegetation mowing to the end of the vegetative season in 60% of the canal network length. By preserving the in-stream vegetation in 20% of the canal network, its denitrification capacity would equal the nitrate load reduction target required for achieving, from May to September, the good ecological status according to the WFD in waters delivered to the coastal areas. Changing the timing of vegetation mowing may create a large potential for permanent nitrate removal via denitrification in agricultural landscapes, thus protecting the coastal areas when the eutrophication risk is higher. Conservative management practices of in-stream vegetation might be promoted as an effective low-cost tool to be included in the WFD implementation strategies.