4th Order Streams Research Articles

Comparative study of the drainage basin morphometry extracted from topographic maps and SRTM DEMs: an example from Ghadir watershed, Eastern Desert, Egypt

The drainage network of Wadi Ghadir watershed, southeastern Desert, Egyptwas extracted from topographic maps (1:50. 000), and from the 30 m digitalelevation data (DEM) of the Shuttle Radar Topography Mapping Mission(SRTM). Four topographic sheets were digitized and used for extraction.Archydro function in ArcGIS 10x was utilized for network extraction and formorphometric analysis. Networks derived from topographic sheets and DEMwere considerably coincident. Different morphometric parameters from bothsources were evaluated to examine the accuracy of DEM for hydrologicapplications. Results clarified 6th order streams for both drainage networks withmoderate to high drainage density (D) of 2.51 km.km2 (topographic) and 2.54km.km2 (DEM) reflecting that W. Ghadir drainage basin is impermeable withconsiderable surface runoff. DEM showed higher stream frequency (F) of 4.49than those derived from topographic maps (4.38). Calculated bifurcation ratio(Rb) of streams derived from topographic sheets reached about 3.47 and about4.60 for those derived from DEM. DEM-derived morphometric parametersprovided good and satisfactory information about the catchment characteristicsand revealed accurate watershed delineation confirming high potential ofsurface runoff of the W. Ghadir drainage basin. Finally, SRTM DEM provedadvantageous over the topographic sheets for drainage delineation and basinmorphometry for hydrologic analysis underpinned with the finer spatialresolution and the vertical accuracy.

Hydrological Spatial Analysis of Wadi Alkuf Catchment Area, Cyrenaica, Northeastern Libya

Morphometric analysis reveals that the Wadi Alkuf drainage, on the northern flank of Al Jabal Al Akhdar, Cyrenaica, northeastern Libya, is characterized by dendritic to sub-dendritic drainage pattern. The development of stream segments in the basin area is apparently affected by intermittent rainfall and geological structure control such as joints set, fractures and faults, as the general area is of limestone karstic character. The analysis reveals that the total number and total length of stream segments reach maximum of 6233 segments in first order streams but decrease to 620 segments in 6th order streams. The bifurcation ratio (Rb) between different successive orders varies between 0.7 in 6th order and 3.5 for third order passing through 2.43 in second order. A mean bifurcation ratio of 1.42 indicates a partial structural control. The stream frequency (Fs) value of 8.87 exhibits positive correlation with the drainage density value of 1.97, whereas the drainage density (Dd) indicates clearly that the region has permeable subsoil and relatively moderate vegetation cover. Calculated Circularity Ratio (Rc) of 0.215 and Elongation Ratio (Re) of 0.15 suggest that the drainage basin is typically elongated in shape, has a low discharge of runoff and relatively permeable subsoil condition. Form Factor (Rf) of 0.22, represents a flatter peak of flow for a longer duration. Flood flows of such elongated basins are easier to manage than of circular basins. It becomes evident that morphometric analysis would contribute to understanding of the dominant geo-hydrological characteristics and processing of watershed planning and management utilizing geospatial techniques based on GIS application and Digital Terrain Model (DTM) analysis.

Measurement of gas-exchange rate in streams by the oxygen–carbon method

The gas-exchange rate between streams and the atmosphere is needed to measure in-stream ecological processes and C processing in rivers and streams. Current methods include empirical relationships to hydraulics, direct injection of a tracer gas, and modeling based on O2 or C diel curves. All existing methods have strengths and drawbacks and most are limited to point measurements or are unable to measure diel variation in exchange rate. Researchers continue to search for better techniques, particularly for steep streams with high rates of gas exchange and low primary productivity. We present the O2−C (OC) method for calculating gas-exchange rates via simultaneous measurement of O2 and dissolved inorganic C (DIC). Gas-exchange rates are calculated by solving the combined stream transport equation for O2 and DIC. The output is a time-series of aeration rates at the same sampling frequency as the input O2 and C data. Field tests in a 4th-order montane stream in Oregon, USA, indicate that the method is suitable for stream reaches with high downstream gas-concentration gradients and saturation deficits. The mean modeled aeration rate adjusted to 17°C (3.25/h) agreed well with the value of 3.22/h from direct gas injection. Net ecosystem production calculated with the modeled aeration rate (−1.69 g O2 m−2 d−1) was consistent with the result obtained with direct gas injection (−1.60 g O2 m−2 d−1). An assumption of the model is a constant respiration quotient, but results indicated that the respiration quotient may be time variable. Sensitivity analysis indicated that application of the OC method is limited to reaches with a suitable change in combined O2 and CO2 concentration ≥ ∼4 μmol/L and combined O2 and CO2 saturation deficits ≈ 4 μmol/L, characteristic of smaller gaining streams. Preliminary application of the OC method indicates it could be useful to practitioners interested in continuous measurement of gas-exchange rates.

Using maximum entropy modeling to predict suitable habitat locations for the Cutshin Crayfish (Cambarus taylori)

The Cutshin Crayfish (Cambarus taylori) is a recently described species which is endemic to the Middle Fork of the Kentucky River basin. The Middle Fork of the Kentucky River lies within the anthracite coal fields of Eastern Kentucky, and thus a conservation assessment of C. taylori is warranted. The goal of this study was to predict suitable habitat locations for C. taylori through use of maximum entropy modeling (MaxEnt). The Middle Fork of the Kentucky River’s crayfish fauna was surveyed during the summer of 2014. The occurrence data from this study coupled with landscape scale environmental variables—such as stream order and land use data—was used to create the model. The mean area under the receiver operating characteristic curve (AUC) value was 0.898, showing the model had high predictive accuracy. The model indicated high probability of occurrence in streams at the southern end of the basin, and a low probability of occurrence at the northern end of the basin. Stream order and stream sinuosity had the highest contribution to the model showing that C. taylori prefers 3rd and 4th order streams with low sinuosity. Although the AUC value showed high predictive accuracy for the model, predicted sites will need to be ground validated to confirm the model’s predictive accuracy.

Trophic dynamics of macroinvertebrate communities of a subtropical river in China

This study was the first attempt to resolve both spatial and temporal patterns of macroinvertebrate trophic dynamics in a Chinese subtropical river continuum, the Shengli River, from 1st to 4th order. Gut content analysis was adopted to assess the trophic basis and consumption rates of communities. Furthermore, annual energy flow food webs were constructed. Trophic basis analyses showed that 34–79% of the diet of macrozoobenthos in the Shengli River and its tributaries was amorphous detritus. Leaf litter was the second most important food source, followed by animal material. Filamentous algae, diatoms, and fungi served only as subsidies, contributing no more than 5% to total consumption. The macroinvertebrates in 1st and 3rd order streams appeared to show seasonal consumption patterns of different food types, while the communities in 2nd and 4th order streams had the same diet composition throughout the year. Total consumption rates of the communities increased from 1st to 3rd order streams, and declined in 4th order streams. The energy flow food web of 1st order streams was simpler than those of higher‐order streams. With increasing stream order, the food webs increased in complexity until 3rd order, and became simpler again in 4th order streams.

Gravel bars are sites of increased CO2 outgassing in stream corridors

Streams are significant sources of CO2 to the atmosphere. Estimates of CO2 evasion fluxes (fCO2) from streams typically relate to the free flowing water but exclude geomorphological structures within the stream corridor. We found that gravel bars (GBs) are important sources of CO2 to the atmosphere, with on average more than twice as high fCO2 as those from the streamwater, affecting fCO2 at the level of entire headwater networks. Vertical temperature gradients resulting from the interplay between advective heat transfer and mixing with groundwater within GBs explained the observed variation in fCO2 from the GBs reasonably well. We propose that increased temperatures and their gradients within GBs exposed to solar radiation stimulate heterotrophic metabolism therein and facilitate the venting of CO2 from external sources (e.g. downwelling streamwater, groundwater) within GBs. Our study shows that GB fCO2 increased fCO2 from stream corridors by [median, (95% confidence interval)] 16.69%, (15.85–18.49%); 30.44%, (30.40–34.68%) and 2.92%, (2.90–3.0%), for 3rd, 4th and 5th order streams, respectively. These findings shed new light on regional estimates of fCO2 from streams, and are relevant given that streamwater thermal regimes change owing to global warming and human alteration of stream corridors.

Landscape context and the biophysical response of rivers to dam removal in the United States.

Dams have been a fundamental part of the U.S. national agenda over the past two hundred years. Recently, however, dam removal has emerged as a strategy for addressing aging, obsolete infrastructure and more than 1,100 dams have been removed since the 1970s. However, only 130 of these removals had any ecological or geomorphic assessments, and fewer than half of those included before- and after-removal (BAR) studies. In addition, this growing, but limited collection of dam-removal studies is limited to distinct landscape settings. We conducted a meta-analysis to compare the landscape context of existing and removed dams and assessed the biophysical responses to dam removal for 63 BAR studies. The highest concentration of removed dams was in the Northeast and Upper Midwest, and most have been removed from 3rd and 4th order streams, in low-elevation (< 500 m) and low-slope (< 5%) watersheds that have small to moderate upstream watershed areas (10–1000 km2) with a low risk of habitat degradation. Many of the BAR-studied removals also have these characteristics, suggesting that our understanding of responses to dam removals is based on a limited range of landscape settings, which limits predictive capacity in other environmental settings. Biophysical responses to dam removal varied by landscape cluster, indicating that landscape features are likely to affect biophysical responses to dam removal. However, biophysical data were not equally distributed across variables or clusters, making it difficult to determine which landscape features have the strongest effect on dam-removal response. To address the inconsistencies across dam-removal studies, we provide suggestions for prioritizing and standardizing data collection associated with dam removal activities.

Hydro-geomorphic controls of greenhouse gas fluxes in riparian buffers of the White River watershed, IN (USA)

Riparian ecosystems are defined by the nature and regularity of the interactions between a given river system and its floodplains, and past studies have often presented vegetation cover as the exclusive expression of these interactions. There has been to our knowledge, no systematic attempt at linking greenhouse gases (GHG) fluxes and types of riparian buffers. The present study was conducted to investigate the intensity and seasonality of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) fluxes in riparian buffers in three common hydro-geomorphic settings (HGM) across the White River watershed (Indiana, USA). These classes included riparian sites located: (i) in till plain depressions near 1st order streams (HGM-1), (ii) in incised narrow valleys with thin alluvium layers above glacial till (HGM-2), and (iii) along 3rd–4th order streams in broad floodplains with thick alluvial and glacial outwash deposits (HGM-3). For each class, 3 sites were selected and GHG fluxes were measured during the wet (May) and dry seasons (August). Strong relationships were found between GHG fluxes, soil properties and environmental factors, but these relationships varied with season and gas species, making it challenging to rely on these relationships for GHG fluxes upscaling. Analysis of variance and discriminant analysis showed that the HGM-defined riparian buffers were distinct in terms of GHG flux intensity. Regardless of season, the HGM-1 sites emitted CO2 at rates 1.6 times higher than at the other sites, likely due to difference in soil C quality. During the wet season, N2O emission was significantly higher at the HGM-3 than at the other sites (0.88 vs 0.27mgNm−2d−1), and was negatively related with the gradient of the adjacent channel (r2: 0.69). The riparian buffers acted as CH4 sinks, with the HGM-2 sites exhibiting CH4 uptake rates significantly greater than the other riparian types (−0.80 vs −0.34mgCH4-Cm−2d−1). The consistency of these results underscores the potential of an HGM-based monitoring approach to derive watershed-scale GHG budgets for riparian buffers.

Basin form characteristics, causes and implications of the ten kongduis in the upper reaches of the Yellow River

The ten kongduis (the transliteration of ephemeral flood gullies in Mongolian) are one of the main sediment sources of the upper reaches of the sediment-laden Yellow River in China. The basin form characteristics and their causal factors and environmental effects of the kongduis are important knowledge for understanding the geomorphic processes and for managing the kongduis. In this study, we extracted the drainage networks and watersheds of the kongduis from the DEM, calculated the geometric and structural indices of the watersheds and networks, investigated relations of the gully density with surface material composition, vegetation coverage and topography, and the relations of the sediment yield with gully density and other geometric indices of watersheds, and associated the gully density with the evolution stage of landforms of the basins. The results reveal that the ten kongduis are 5th - 6th order streams and their watersheds are long and narrow with a circularity ratio of 0.16–0.26, an elongation ratio of 0.29–0.43 and a power of drainage area of 0.89–4.52 in the power function between mainstream length and drainage area. Yet, the available data do not support the impacts of the geometric indices of watersheds on the sediment yield in the ten kongduis, and the insignificant relation between the specific sediment yield and drainage area denies the existence of scale effect in sediment yield in the kongduis. In contrast, the gully density is found to be closely and positively related with the sediment yield. The hypsometric integrals of the upstream reaches of the ten kongduis and the relation between gully density and hypsometric integral suggest that the kongduis are in the mature stage of landform evolution and the west five kongduis are in the early mature stage with a potential increase trend of gully density and a concomitant escalation of sediment yield in future.

Long-term effects of riparian forest harvest on light in Pacific Northwest (USA) streams

AbstractRiparian forests exert strong influence on abiotic and biotic processes in adjacent streams by regulating light. Harvesting of riparian forests was once common practice, and consequently, many streamside forests across North America are in varying stages of development as they regenerate, thereby affecting stream light regimes. We used 2 approaches to evaluate the influence of riparian forest harvest and stand recovery on light availability in small mountain streams. We estimated light and canopy cover every 25 m along 11.5 km of a 4th-order stream network dominated by late-successional riparian forests that included 7 streamside harvest units 50 to 60 y old. Estimates of stream light fluxes were lower in harvest units than in up- and downstream sections bordered by old-growth forests even though only 1 stream bank was harvested in 5 of 7 units. Differences in stream light between harvested reaches and adjacent old-growth sections were greater when both banks had been logged. We also conducted a s...

CO2 evasion from a steep, high gradient stream network: importance of seasonal and diurnal variation in aquatic pCO2 and gas transfer

Surface waters contribute substantially to carbon dioxide (CO2) emissions to the atmosphere. However, global estimates remain uncertain due to methodological difficulties, such as in precisely estimating gas transfer in steep upland streams. Here, we addressed the question of what drives CO2 evasion from steep mountainous stream network of the European Alps by assessing the spatial and temporal variation of partial pressure of CO2 (pCO2) for 148 streams and the gas transfer coefficient for CO2 (kCO2) for 88 locations within this 254 km2 watershed. Results show that log kCO2 can be predicted reasonably well (r2 = 0.71, p<0.001, n = 88) using a statistical model based on slope, average width, flow velocity and stream discharge. Also, most sites were supersaturated in CO2 with significant variation in pCO2 due to season (September vs. December) and time of day (day vs. night), but not stream order. Resulting median CO2 evasion rates were 145, 119, 46, 43, and 50 mg C m−2 h−1 at 1st to 5th order streams, respectively. CO2 evasion was dependent on season and time of day, with the highest evasion (184.0 kg C h−1) during growing season at nighttime, followed by 124.6 kg C h−1 during daytime. Dormant season nighttime evasion was 30.9 kg C h−1 and daytime evasion only 17.1 kg C h−1. Overall we conclude that CO2 evasion of steep mountainous streams depends on seasonal and diurnal variation in pCO2 and reach-specific variability in kCO2. These controls strongly alter landscape-scale CO2 evasion estimates, with implications for regional to global carbon budgets.

Morphometric analysis in basaltic Terrain of Central India using GIS techniques: a case study

Morphometric analysis is significant for investigation and management of the watershed. This study depicts the morphometric analysis of Miniwada Watershed in Nagpur district, Maharashtra, Central India using Geographic Information System (GIS) techniques, which has been carried out through measurement of various aspects like linear, aerial and relief aspects of watershed. The drainage network of the watershed was generated from Cartosat-I DEM (10 m) using ESRI Software ArcGIS (ver.10.2). The analysis reveals that drainage pattern is dendritic and the stream order in the watershed varies from 1 to 4. The total number of stream segments of all orders counted as 37, out of which the majority of orders (70.27 %) was covered by 1st order streams and 4th order stream segments covers only 2.70 %. The bifurcation ratio reflects the geological and tectonic characteristics of the watershed and estimated as 3.08. The drainage density of the watershed is 3.63 km/sq km and it indicates the closeness of spacing of channels. The systematic analysis of various parameters in GIS helps in better understanding the soil resources distribution, watersheds prioritization, planning and management.

The effects of catastrophic wildfire on water quality along a river continuum

AbstractTo further our understanding of the linkages among wildfire, streamflow pathways, and water chemistry, we used a network of water-quality sensors and streamflow gages to assess initial and long-term effects of wildfire along a river continuum. We assessed water quality of a 2nd- and a 4th-order stream in a single watershed for 5 monsoon seasons before, during, and after a catastrophic wildfire. Fire had significant and sustained long-term effects on both streams. In the 2nd-order stream, variability in dissolved O2 (DO) increased after the fire. Daily total precipitation was unchanged, but episodic storm events resulted in significant increases in stream discharge that led to elevated turbidity and specific conductance (SC). In the 4th-order stream, fire led to minimal measurable effects on turbidity, elevated SC, and greater variability of the DO signal. We also assessed water-quality data from 4 sites along the river continuum for a 4-mo period before, during, and after the wildfire. Large overl...

The varying role of water column nutrient uptake along river continua in contrasting landscapes

Nutrient transformation processes such as assimilation, dissimilatory transformation, and sorption to sediments are prevalent in benthic zones of headwater streams, but may also occur in the water column. The river continuum concept (RCC) predicts that water column processes become increasingly important with increasing stream size. We predicted that water column nutrient uptake increases with stream size, mirroring carbon/energy dynamics predicted by the RCC. We measured water column uptake of ammonium ( $${\text{NH}}_{4}^{ + }$$ ), nitrate ( $${\text{NO}}_{3}^{ - }$$ ), and soluble reactive phosphorus (SRP) in 1st through 5th order stream and river reaches (discharge: 50–68,000 L s−1) in three watersheds ranging from 70 % developed lands. We found that water column volumetric uptake (U vol ) of $${\text{NH}}_{4}^{ + }$$ , $${\text{NO}}_{3}^{ - }$$ , and SRP did not significantly differ among watersheds and we did not find any longitudinal patterns for U vol . Uptake velocity (v f ) of $${\text{NH}}_{4}^{ + }$$ increased with stream size, whereas $${\text{NO}}_{3}^{ - }$$ and SRP v f did not differ with stream size or among watersheds. Both U vol and v f were related to water column metabolism and material suspended in the water column, but specific relationships differed among solutes and uptake metrics. Median water column v f across 15 sites was 4, 9, and 19 % of median whole-stream $${\text{NH}}_{4}^{ + }$$ , $${\text{NO}}_{3}^{ - }$$ , and SRP v f based upon a previous meta-analysis. Thus, although we could not demonstrate a generalized longitudinal pattern in water column nutrient uptake, water column processes can be important. An improved mechanistic understanding of the controls on uptake and the ultimate fate of nutrients will facilitate effective management and restoration for mitigating downstream nutrient export.

The influence of geology and season on macroinvertebrates in Belizean streams: implications for tropical bioassessment

Considerable attention has been paid to the potentially confounding effects of geological and seasonal variation on outputs from bioassessments in temperate streams, but our understanding about these influences is limited for many tropical systems. We explored variation in macroinvertebrate assemblage composition and the environmental characteristics of 3rd- to 5th-order streams in a geologically heterogeneous tropical landscape in the wet and dry seasons. Study streams drained catchments with land cover ranging from predominantly forested to agricultural land, but data indicated that distinct water-chemistry and substratum conditions associated with predominantly calcareous and silicate geologies were key determinants of macroinvertebrate assemblage composition. Most notably, calcareous streams were characterized by a relatively abundant noninsect fauna, particularly a pachychilid gastropod snail. The association between geological variation and assemblage composition was apparent during both seasons, but significant temporal variation in compositional characteristics was detected only in calcareous streams, possibly because of limited statistical power to detect change at silicate sites, or the limited extent of our temporal data. We discuss the implications of our findings for tropical bioassessment programs. Our key findings suggest that geology can be an important determinant of macroinvertebrate assemblages in tropical streams and that geological heterogeneity may influence the scale of temporal response in characteristic macroinvertebrate assemblages.

Community assembly of adult odonates in tropical streams: an ecophysiological hypothesis.

Community assembly theory is founded on the premise that the relative importance of local environmental processes and dispersal shapes the compositional structure of metacommunities. The species sorting model predicts that assemblages are dominated by the environmental filtering of species that are readily able to disperse to suitable sites. We propose an ecophysiological hypothesis (EH) for the mechanism underlying the organization of species-sorting odonate metacommunities based on the interplay of thermoregulation, body size and the degree of sunlight availability in small-to-medium tropical streams. Due to thermoregulatory restrictions, the EH predicts (i) that larger species are disfavored in small streams and (ii) that streams exhibit a nested compositional pattern characterized by species’ size distribution. To test the EH, we evaluate the longitudinal distribution of adult Odonata at 19 sites in 1st- to 6th-order streams in the Tropical Cerrado of Brazil. With increasing channel width, the total abundance and species richness of Anisoptera increased, while the abundance of Zygoptera decreased. The first axis of an ordination analysis of the species abundance data was directly related to channel width. Mean and maximum thorax size are positively correlated to channel width, but no relationship was found for the minimum thorax size, suggesting that there is no lower size constraint on the occurrence of these species. Additionally, a nested compositional pattern related to body size was observed. Our results support the EH and its use as an ecological assembly rule based on abiotic factors. Forest cover functions as a filter to determine which species successfully colonize a given site within a metacommunity. As a consequence, the EH also indicates higher treats for small-bodied zygopterans in relation to the loss of riparian forests in tropical streams.

English

The study focused mainly on the geometry, more emphasis on the morphometric characteristics of the drainage basin. An attempt has been made to study drainage morphometry and its influence on hydrology of Sonar Sub-basin, M.P. India. For detailed study we used Shuttle Radar Topographic Mission (SRTM) data for preparing Digital Elevation Model (DEM), and slope maps, Geographical Information System (GIS) was used in evaluation of linear, areal and relief aspects of morphometric parameters. A total number of 196 streams were identified of which 146 are 1st order streams, 38 are 2nd order, 9 are 3rd order, 2 in 4th order and 1 is indicating 5th order stream. Drainage patterns of stream network from the basin have been observed as mainly dendritic type which indicates the homogeneity in texture and lack of structural control. The mean bifurcation ratio value is 3.65 for the study area falls within the standard range and shows that the basin conforms to the characteristics of a natural stream which indicates that the geological structures are less disturbing to the drainage pattern. The drainage density of the study area is 0.62 km/sq. km. This value indicates that for every square kilometer of the basin. This makes the study area fall into the group of low density basins which suggest that the low drainage density indicates that the basin is highly permeable subsoil and thick vegetative cover. These studies are very useful for planning rainwater harvesting and watershed management. Key words: Morphometric analysis, shuttle radar topographic mission (SRTM) data, geographical information system (GIS), Sonar sub-basin.

Assessing the significance of wetland restoration scenarios on sediment mitigation plan

Wetlands have many environmental, social, and economic values. However, due to accelerated land use change and lack of understanding of the functions of wetland ecosystems, they have deteriorated, if not been lost in many areas worldwide. Meanwhile, current functional wetland assessment techniques only provide rough estimations, and are in most cases site specific and qualitative. The overall goal of this project is to examine the sediment reduction benefit of wetland implementation scenarios both at subbasin and watershed scales. Two sets of models were used to accomplish this goal. First, a watershed model – the Soil and Water Assessment Tool (SWAT), was employed to estimate sediment load at the subbasin scale. However, due to limitations of wetland functions of SWAT, a second model – the System for Urban Stormwater Treatment and Analysis Integration (SUSTAIN) was used. The sediment load generated for each subbasin was incorporated in the SUSTAIN model. This allows for evaluating sediment reduction capability of wetlands at subbasin level. Next, a portion of sediment not treated by a wetland was fed back to the SWAT model and routed to the watershed outlet. The impacts of four different wetland surface areas (0.40, 0.81, 2, and 4ha) on sediment load mitigation were examined one-at-a-time for all subbasins within the River Raisin watershed located in southeastern Michigan and northeastern Ohio. Comparison of the sediment reductions due to different wetland restoration scenarios reveals the importance of wetland placement in a watershed. In general, the rate of streamflow reduction resulting from wetland implementation is higher than sediment reduction at the subbasin level but more comparable at the watershed level. In addition, clusters of wetlands installed at the distance of 150–200 stream km from the outlet outperformed other clustered wetlands at closer and farther distances. Wetlands associated with 1st order streams performed better at the subbasin level, while wetlands located at 4th order streams performed better at the watershed level. Considering environmental and economic issues of wetland restoration scenarios revealed that the 0.4ha wetlands were the most suitable for subbasin and watershed level implementation due to its sediment reduction efficiency and significantly lower cost of installation and maintenance.

Steady-state sulfur critical loads and exceedances for protection of aquatic ecosystems in the U.S. southern Appalachian Mountains

Atmospherically deposited sulfur (S) causes stream water acidification throughout the eastern U.S. Southern Appalachian Mountain (SAM) region. Acidification has been linked with reduced fitness and richness of aquatic species and changes to benthic communities. Maintaining acid-base chemistry that supports native biota depends largely on balancing acidic deposition with the natural resupply of base cations. Stream water acid neutralizing capacity (ANC) is maintained by base cations that mostly originate from weathering of surrounding lithologies. When ambient atmospheric S deposition exceeds the critical load (CL) an ecosystem can tolerate, stream water chemistry may become lethal to biota. This work links statistical predictions of ANC and base cation weathering for streams and watersheds of the SAM region with a steady-state model to estimate CLs and exceedances. Results showed that 20.1% of the total length of study region streams displayed ANC <100 μeq∙L−1, a level at which effects to biota may be anticipated; most were 4th or lower order streams. Nearly one-third of the stream length within the study region exhibited CLs of S deposition <50 meq∙m−2∙yr−1, which is less than the regional average S deposition of 60 meq∙m−2∙yr−1. Owing to their geologic substrates, relatively high elevation, and cool and moist forested conditions, the percentage of stream length in exceedance was highest for mountain wilderness areas and in national parks, and lowest for privately owned valley bottom land. Exceedance results were summarized by 12-digit hydrologic unit code (subwatershed) for use in developing management goals and policy objectives, and for long-term monitoring.

Late Quaternary landscape evolution, soil stratigraphy, and geoarchaeology of the Caprock Canyonlands, Northwest Texas, USA

In northwest Texas, USA, between the Southern High Plains to the west and the Central Lowlands to the east, lies a geographic boundary known as the “Escarpment Breaks” or “Caprock Canyonlands.” The canyonlands contain abundant springs, lithic resources, shelter, and plant and animal food sources that attracted hunter-gatherer groups. A geoarchaeological study was conducted in the canyonlands to determine the effects of late-Quaternary landscape evolution, especially intensive erosion, on the region's archaeological record. Geomorphic and stratigraphic field research and a total of 95 new radiocarbon age determinations, 94 of which were determined on paired samples, aid in reconstructing an understudied dynamic and erosive landscape, and explain how the landscape has changed. The pattern is similar to reported data from the Central Plains and western Rolling Plains but dissimilar to the Southern High Plains. High rates of erosion and geological controls on the South Fork of the Double Mountain Fork of the Brazos River, a 4th order stream, have hindered the discovery of deeply buried soils and in situ Paleoindian artifacts and features, but a late-Holocene pedocomplex is relatively intact in valley fills beneath remnants of the T-2 terrace of the South Fork. The eroding slopes near the edge of the caprock escarpment exposed a record of in situ Archaic to Protohistoric-aged materials. The eroding slopes should be targeted for future quantification of erosion and archaeological preservation bias for the canyonlands.