Habitat conditions in streams influence Odonata larval assemblages in the eastern Amazon

The growth of agricultural and mining activities in the Amazon has impacted land-use and caused significant changes in the local environmental conditions of streams. In the face of these changes, our study aimed at assessing how environmental changes affect Odonata larval assemblages in streams in the eastern Amazon. We hypothesized that habitat conditions in streams are strong predictors of Odonata larval assemblages. We sampled 30 headwater streams (1st through 3rd order) in the eastern Amazon. We corroborated our hypothesis that regional- and local-scale environmental changes are important predictors of the Odonata larval assemblage structure. These results indicate that environmental conditions within the stream channel are important to maintain Odonata larval assemblages, as they provide important resources for larval development. For new studies, we recommend the assessment of temporal dynamics to evaluate whether these patterns are stable across time. Finally, evaluating various environmental scales of the original impact is extremely relevant for preventing the deterioration of or recuperating aquatic assemblages in Amazonian streams, considering the ongoing rapid environmental changes and deforestation in the region. Here we demonstrate that in-stream environmental conditions are important to assemblage structure and this must be considered in environmental restoration plans.

Bedrock depth influences spatial patterns of summer baseflow, temperature, and flow disconnection for mountainous headwater streams

In mountain headwater streams the quality and resilience of cold-water habitat is regulated by surface stream channel connectivity and groundwater exchange. These critical hydrologic processes are thought to be influenced by the stream corridor bedrock contact depth (sediment thickness), which is often inferred from sparse hillslope borehole information, piezometer refusal, and remotely sensed data. To investigate how local bedrock depth might control summer stream temperature and channel disconnection (dewatering) patterns, we measured stream corridor bedrock depth by collecting and interpreting 191 passive seismic datasets along eight headwater streams in Shenandoah National Park (Virginia USA). In addition, we used multiyear stream temperature and streamflow records to calculate summer baseflow metrics along and among the study streams. Finally, comprehensive visual surveys of stream channel dewatering were conducted in 2016, 2019, and 2021 during summer baseflow conditions (124 total km of stream length). We found that measured bedrock depths were not well-characterized by soils maps or an existing global-scale geologic dataset, where the latter overpredicted measured depths by 12.2 m (mean), or approximately four times the average bedrock depth of 2.9 m. Half of the eight study stream corridors had an average bedrock depth of less than 2 m. Of the eight study streams, Staunton River had the deepest average bedrock depth (3.4 m), the coldest summer temperature profiles, and substantially higher summer baseflow indices compared to the other study steams. Staunton River also exhibited paired air and water annual temperature signals suggesting deeper groundwater influence, and the stream channel did not dewater in lower sections during any baseflow survey. In contrast, streams Paine Run and Piney River did show pronounced, patchy channel dewatering, with Paine Run having dozens of discrete dry channel sections ranging 1 to greater than 300 m in length. Stream dewatering patterns were apparently influenced by a combination of discrete deep bedrock (20 m+) features and more subtle sediment thickness variation (1–4 m), depending on local stream valley hydrogeology. In combination these unique datasets show the first large-scale empirical support for existing conceptual models of headwater stream disconnection based on underflow capacity and shallow groundwater supply.

Water Quality Assessment with Biotic Index Based on Abundance and Diversity of Aquatic Insects in a Hilly Stream, Bangladesh

Study of stream insect fauna provide valuable insights into aspects of the stream channel ecosystem. The present study was conducted to investigate the aquatic stream living insect community, abundance and diversity in a hilly stream, Balukhali chora of Chittagong University campus to determine the water quality. The insects were collected with bottom dredge net from the edge and benthic regions of the Riffle zone and the Pool zone of the stream from January 2018 to December 2018. Insects were sampled using standard entomological method and determined their tolerance value. A total of 2535 insects were recorded, belonging to six insect orders, 30 families and 45 genera. The abundance ratio was higher in all the months in the Pool zone excepting the months of April, May, June and October. The orders Ephemeroptera, Odonata and Diptera were abundant in the Pool zone, while Hemiptera, Coleoptera and Lepidoptera were abundant in the Riffle zone. On the basis of Biotic Index, the most dominating orders Odonata and Hemiptera indicated good water quality, though the dipteran genus Chironomus spp. indicated poor quality in some of the months. The stream insect community structure of the two zones indicated that the overall water quality of the stream water was very good. Both manmade and natural interruption occurred in the stream channel due to human settlement, agricultural runoff and natural disasters. The study was conducted to know the abundance and diversity of aquatic insect community which indicated the water quality of the stream.

Detention Reservoir: Proposal for Flood Control in the Ipiranga Stream Basin, Juiz de Fora, MG, Brazil

In order to provide parameters for sizing a damping reservoir, which was intended to control the floods that occur in the Ipiranga Stream basin, a routine developed in Visual Basic for Applications (VBA) is used. From the identification of the most critical point of the flood, hydrological flow data are presented, estimated by dividing the basin into sub-basins, using the Rational method, resulting in a value of flow higher than the admissible one for the stream channel. The method used in dimensioning the reservoir was flood routing. After making a pre-selection of the most interesting place to position the reservoir, insertions of the situation existent were made to the VBA application, in order to generate scenarios and enable the choice of an ideal situation, in view of the presented constraints. A very acceptable and feasible result is pointed out, indicating general parameters for sizing a reservoir to control floods in the Ipiranga Stream basin.

Location of Active Faults using Geomorphic Indices in Eroded Landscapes, South Taranaki, New Zealand

<p>South Taranaki region has a number of active faults that show surface expression in the younger and harder materials near the coast and central volcanoes of the North Island, but these traces finish abruptly inland when they cross into older, heavily eroded, mudstone and sandstone. Current methods to locate surface evidence of active faults (i.e. geomorphic interpretation of stereographic aerial photography) are not fully successful in this region. Erosion occurs here at a greater rate than surface rupture of faults which causes the removal of surface expression, and/or dense tree cover obscures surface expression. International studies of tectonic activity in eroded landscapes have identified geomorphic indices as useful reconnaissance tools to locate active faults. This research applies geomorphic indices to the Taranaki region for the first time. Four indices are tested; stream length-gradient index, stream channel sinuosity, hypsometry and drainage basin asymmetry. Results are obtained by applying the indices to four freely available national Digital Elevation Models (DEMs) of differing resolutions. This allowed comparison between DEMs, providing the ability to test DEM quality and at what scale geomorphic indices could be applied to these freely available data. Results show that the geomorphic indices used can identify changes to the equilibrium state at a catchment and stream channel scales. However, the myriad of physical processes occurring at a range of temporal scales within this area make identification of a tectonic signature a challenging task. Conclusive examples of tectonic processes are evident and analysis suggests that these examples are likely to be due to recent or large fault ruptures. There are many areas where a tectonic influence to the equilibrium state of a stream or catchment can be inferred. These areas could then be targeted for detailed geophysical or ground based geological studies. Furthermore, the comparison of results from the four DEMs highlights a range of issues with DEM collection methods and resolution. This study concludes that geomorphic indices can provide an effective method to locate evidence of recent and large faulting events. However, this type of analysis is hindered by the resolution of available digital elevation data.</p>

Location of Active Faults using Geomorphic Indices in Eroded Landscapes, South Taranaki, New Zealand

<p>South Taranaki region has a number of active faults that show surface expression in the younger and harder materials near the coast and central volcanoes of the North Island, but these traces finish abruptly inland when they cross into older, heavily eroded, mudstone and sandstone. Current methods to locate surface evidence of active faults (i.e. geomorphic interpretation of stereographic aerial photography) are not fully successful in this region. Erosion occurs here at a greater rate than surface rupture of faults which causes the removal of surface expression, and/or dense tree cover obscures surface expression. International studies of tectonic activity in eroded landscapes have identified geomorphic indices as useful reconnaissance tools to locate active faults. This research applies geomorphic indices to the Taranaki region for the first time. Four indices are tested; stream length-gradient index, stream channel sinuosity, hypsometry and drainage basin asymmetry. Results are obtained by applying the indices to four freely available national Digital Elevation Models (DEMs) of differing resolutions. This allowed comparison between DEMs, providing the ability to test DEM quality and at what scale geomorphic indices could be applied to these freely available data. Results show that the geomorphic indices used can identify changes to the equilibrium state at a catchment and stream channel scales. However, the myriad of physical processes occurring at a range of temporal scales within this area make identification of a tectonic signature a challenging task. Conclusive examples of tectonic processes are evident and analysis suggests that these examples are likely to be due to recent or large fault ruptures. There are many areas where a tectonic influence to the equilibrium state of a stream or catchment can be inferred. These areas could then be targeted for detailed geophysical or ground based geological studies. Furthermore, the comparison of results from the four DEMs highlights a range of issues with DEM collection methods and resolution. This study concludes that geomorphic indices can provide an effective method to locate evidence of recent and large faulting events. However, this type of analysis is hindered by the resolution of available digital elevation data.</p>

Engineered hyporheic zones: design and applications in stream health restoration- a review

Anthropogenic deterioration of streams and rivers have affected their surface-subsurface linkages. This has led to the degradation of hyporheic zones, a sensitive interface between stream channel and its surrounding sediments, responsible for transforming pollutants, natural solutes and supporting benthic communities. Several authors have reported the influence of stream restoration measures on hyporheic exchanges and have called for the inclusion of hyporheic zone restorations in stream management. Engineered Hyporheic Zones (EHZ) is the creation of artificial transition area due to induced hyporheic flows, brought about by some feature modifications done to the stream channel or its subsurface. These feature modifications and its implications have been investigated through lab experiments, outdoor flumes, modelling and field studies for several years. This paper attempts to summarize the endeavours made in the study of EHZ and its applications in water quality improvement and habitat restoration. A comprehensive review of upto date literature with specific focus on the influence of engineered structures on hyporheic exchanges is presented, followed by the comparison of preferences opted for different studies and their limitations. The paper ends with suggestive future scope in EHZ studies and its potential as a low cost alternative treatment technology for river restoration.