Adjacent Watersheds Research Articles

Effect of Check Dams on Sediment Concentration in a Watershed in the Loess Hilly Area During a Heavy Rain Event

ABSTRACTUnderstanding the changes of sediment concentration in rivers, especially under heavy rains, is of great significance to accurately evaluate the effectiveness of soil and water conservation measures in the Loess Hilly Area. On July 26, 2017, an extremely heavy rain (maximum rain intensity of 66.6 mm/h, the highest rainfall of 256.8 mm in 10 h, and a return period of 100 years) occurred over the 821 km2 Xiaoli River watershed in the Wuding River watershed. In order to understand the sediment concentration during the heavy rain event, 10 dam‐controlled catchments in the center of the rainstorm (3 in the Xiaoli River watershed and 7 in its adjacent watersheds) without drainage and damage were selected. All the retained runoff and sediment in the check dams were measured by the cross‐sectional survey according to the flood marks left by the heavy rain. Combined with the observed runoff and sediment transport data by the hydrological station at the outlet of the Xiaoli River watershed as well as the deposited sediment investigated in the watershed during the heavy rain event, the change of sediment concentration and the role of check dam were analyzed. Results showed that under heavy rain, all the sediment concentrations of runoff in the dam‐controlled catchments ranged from 344 to 552 kg/m3, suggesting that the sediment retaining effect of slope measures (woodland, grassland, and terrace) is limited and cannot prevent the occurrence of hyperconcentrated flows. The gully measures (check dams) in the Xiaoli River watershed can hold a large amount of sediment under heavy rain and make the runoff no longer a hyperconcentrated flow at the watershed outlet. In order to control the transport of hyperconcentrated flows to the downstream, more attention should be paid to the construction of check dams while carrying out vegetation ecological construction in the Loess Hilly Area.

Distribution, provenance, contamination, and probabilistic ecological risk of rare earth elements in surface sediments of Jiulong River estuary and adjacent watershed

Rare earth elements (REE) are increasingly recognized as emerging micropollutants in the environment, and concerns surrounding their presence are steadily growing. However, the understanding of possible pollution and ecological risks of REE in river sediments is relatively scarce. To address this, an investigation into the distribution, origins, pollution levels, and potential ecological risks of REE in sediments along the Jiulong River Estuary and adjacent watersheds was conducted. The results revealed that ΣREE in sediments ranged from 54.98 to 156.05 mg/kg along the Jiulong River and its estuary. The REE concentrations generally decreased from the Jiulong River to the estuary. Cluster analysis and geochemical parameter ratios suggested the high REE concentrations in Jiulong River may be derived from fertilizer and coal combustion. The sediments REE was normalized using the chondrites and exhibited apparent fractionation between LREE and HREE. Additionally, the REE in sediments was characterized by LREE enrichment and negative Ce and Eu anomalies. The evaluation of geo-accumulation and enrichment factors indicated that Gd, Yb, Lu, Tb and Dy were the elements most highly enriched in the sediments. Sites labeled S1–S3 and S5 were classified as moderately polluted, with Lu posing a moderate potential ecological risk, while other elements presented only mild ecological risks. Our findings suggest that anthropogenic activities significantly influence the pollution and potential ecological risks of REE in river sediments. Therefore, attention should be paid to the management of emerging contaminants in rivers and estuaries to protect ecosystems and local populations from potential risks associated with the accumulation of REE in sediments.

New report and range extension of invasive suckermouth armored catfishes of the genus Pterygoplichthys (Actinopterygii: Siluriformes: Loricariidae) in the Yucatan Peninsula

Commonly known as suckermouth armored catfishes or pleco, Pterygoplichthys spp. are a group of invasive fishes that are widely distributed in several countries, including Mexico. This paper reports the first records of suckermouth armored catfishes in the Candelaria River, thereby expanding its distribution within the Yucatan Peninsula. Fifteen individuals were collected from three sites in the upper and middle parts of the basin. They represented two phenotypically distinct species of catfishes: (vermiculate) Pterygoplichthys disjunctivus (Weber, 1991) and (spotted) Pterygoplichthys pardalis (Castelnau, 1855). Adults and juveniles were caught in lotic ecosystems in 2023 during the dry and rainy seasons. Results suggest that the invasive process of the Candelaria River is linked to the San Pedro River upper basin, in El Petén, Guatemala, through floodings enhanced by hurricanes, allowing these species to disperse. These records highlight the importance of connectivity between adjacent watersheds for the dispersal and expansion of these invasive fishes, mainly from rivers neighboring Guatemala. However, further research is necessary to explore the dynamics and connectivity between aquatic ecosystems and the possible mechanisms that promote the invasion of these fishes in this region.

Hydrological Variability in the El Cielo Biosphere Reserve, Mexico: A Watershed-Scale Analysis Using Tree-Ring Records

The El Cielo Biosphere Reserve (CBR) stands as a vital forested region in eastern Mexico due to its high biodiversity in flora and fauna and provision of environmental services. This study established a network of 10 ring-width chronologies of different species within the CBR and adjacent watersheds. The objective was to analyze their climatic response and reconstruct the seasonal streamflow contribution of each sub-basin to the main stream, utilizing data from a gauge network of eight hydrological stations located at strategic locations of the CBR. With chronologies ranging from 116 to 564 years, most exhibited association with the accumulated streamflow between January and June. Based on the adjusted R2, Akaike Information Criteria, and Variance Inflation Factor, the stepwise regression procedure was selected among different statistical methods for developing the reconstruction model. In spite of differences in the seasonal reconstructed periods, all the species showed potential to develop hydrological reconstructions as indicated by their common response to streamflow variability, as occurred in the wet years of 1976, 1993, 2000, and 2008, and dry years of 1980, 1982, 1996, and 2011. It was found that the response of the chronologies to gauge records increased as a function of the chronologies’ interseries correlation, average mean sensitivity, and distance of the tree-ring series to the gauge station. Streamflow reconstructions at the sub-basin level allowed a better understanding of the hydroclimatic variability characterizing the CBR, but also suggested the need to increase the network of chronologies for some particular sub-basins lacking tree-ring series to improve the reconstructed models.

Toward a Predictive Understanding of Cyanobacterial Harmful Algal Blooms through AI Integration of Physical, Chemical, and Biological Data.

Freshwater cyanobacterial harmful algal blooms (cyanoHABs) are a worldwide problem resulting in substantial economic losses, due to harm to drinking water supplies, commercial fishing, wildlife, property values, recreation, and tourism. Moreover, toxins produced from some cyanoHABs threaten human and animal health. Climate warming can affect the distribution of cyanoHABs, where rising temperatures facilitate more intense blooms and a greater distribution of cyanoHABs in inland freshwater. Nutrient runoff from adjacent watersheds is also a major driver of cyanoHAB formation. While some of the physicochemical factors behind cyanoHAB dynamics are known, there are still major gaps in our understanding of the conditions that trigger and sustain cyanoHABs over time. In this perspective, we suggest that sufficient data sets, as well as machine learning (ML) and artificial intelligence (AI) tools, are available to build a comprehensive model of cyanoHAB dynamics based on integrated environmental/climate, nutrient/water chemistry, and cyanoHAB microbiome and 'omics data to identify key factors contributing to HAB formation, intensity, and toxicity. By taking a holistic approach to the analysis of all available data, including the rapidly growing number of biological data sets, we can provide the foundational knowledge needed to address the increasing threat of cyanoHABs to the security of our water resources.

Globally coordinated acoustic aquatic animal tracking reveals unexpected, ecologically important movements across oceans, lakes and rivers

Acoustic telemetry is a popular approach used to track many different aquatic animal taxa in marine and freshwater systems. However, information derived from focal studies is typically resource‐ and geography‐limited by the extent and placement of acoustic receivers. Even so, animals tagged and tracked in one region or study may be detected unexpectedly at distant locations by other researchers using compatible equipment, who ideally share that information. Synergies through national and global acoustic tracking networks are facilitating significant discoveries and unexpected observations that yield novel insight into the movement ecology and habitat use of wild animals. Here, we present a selection of case studies that highlight unexpected tracking observations or absence of observations where we expected to find animals in aquatic systems around the globe. These examples span freshwater and marine systems across spatiotemporal scales ranging from adjacent watersheds to distant ocean regions. These unexpected movements showcase the power of collaborative telemetry networks and serendipitous observations. Unique and unexpected observations such as those presented here can capture the imagination of both researchers and members of the public, and improve understanding of movement and connectivity within aquatic ecosystems.

Numerical analysis of surface hydrogeological water budget to estimate unconfined aquifers recharge

Under changing climate, groundwater resources are the main drivers of socioeconomic development and ecosystem sustainability. This study assessed the contribution of two adjacent watersheds, Muse Street (MS) and West Wood (WW), with low and high urban development, to the Memphis aquifer recharge process in central Jackson, Tennessee, USA. The numerical MODFLOW model was created using data from 2017 to 2019 and calibrated using reported water budget components derived from in-situ data. The calibrated MODFLOW model was then used to investigate the impact of high and low urban developments on the recharge rate. The hydraulic parameters and recharge rates were optimized by adjusting the groundwater level based on the observed water level using PEST. The stochastic modeling was also carried out using the Latin Hypercube approach to reduce the uncertainty. The calibration results were satisfactory, with RMSE of 0.124 and 0.63 obtained in the WW and MS watersheds, respectively, indicating accurate estimation of the input parameters, precisely the hydrodynamic coefficients. The study results indicate that, per unit area, the MS watershed contributes 119% more to recharge and 186% more to riverbed leakage compared to the WW watershed. However, regarding total recharge and riverbed leakage, the WW watershed contributed more than the MS watershed. The results of this study have enhanced the knowledge of the impact of urbanization on hydrology and the recharge process in watersheds with diverse land uses.

Water chemistry and physical gradients across the coastal band of eastern Georgian Bay: A coherent habitat template

The 125 km long archipelago of islands, reefs and embayments composing the coastline of eastern Georgian Bay connects the adjacent watersheds of the Canadian Shield with the calcareous basin of Lake Huron resulting in gradients of nutrients, major ions, alkalinity-pH, DOC and water transparency. An investigation of the broad distribution of these gradients, extending over four regions of coastline and the 60 km of shoreline from 2014 to 2016 indicated that this onshore-offshore transition in water quality is a predictable feature of the nearshore stemming from the underlying geological transition from land to lake. Consolidating the onshore to offshore gradient is the quasi-channelized nature of mixing across the highly dissected coastal band that adds to the persistence of mixing areas. In addition to water quality, the coastal gradient also encompasses a broad range of physical attributes of the aquatic environment including the thermal, optical, exposure regimes and the physical character of lakebed substrate. Consequently, we hypothesize that diverse forms of aquatic life can be anticipated to select and preferentially distribute across the habitat template embodied by the gradients that span the coastal band of eastern Georgian Bay.

Geomorphic-based mine rehabilitation coupled with AMD chemical stabilisation in sulphide-rich ore deposits and soils: insights from a pioneering intervention at the Lousal mine, Iberian pyrite Belt

ABSTRACT The Lousal mine rehabilitation project proactively planned strategic milestones around key local geomorphic landforms and geochemical characteristics. GeoFluv™ method was used to design a rehabilitation topography mimicking natural landforms, on which a built-up soil cover with chemical buffering capabilities and open limestone channels were implemented across the intervention areas. Once these landform restoration works were completed, positive effects are observed in March 2022, with the native vegetation cover (the third main component of the restoration plan) established in most of the recovered area and a visible water quality improvement to the AMD treatment system water. Potentially Toxic Elements (PTEs) concentrations have reduced significantly after the reclamation actions, especially Fe (404 to 34 mg L−1), Zn (65.7 to 15.8 mg L−1) and Cd (122 to 0.8 µg L−1) concentrations. Minor problems detected have been processes of rill erosion associated with the inflow of adjacent watersheds, and the creation of ephemeral reducing conditions resulting from the leaching of the organic amendment of the topsoil. The Lousal mine reclamation project is the first built example in Europe where the concept of geomorphic reclamation has been combined with geochemical remediation in an area with intense acid mine drainage formation. Detailed monitoring of this project’s restorative progression throughout 2024 and beyond, should offer learning opportunities and innovations which will benefit future rehabilitation projects, with comparable underlying features.

Distribution and straying of minijack Chinook Salmon released from a captive broodstock hatchery program

AbstractObjectiveProduction of Chinook Salmon Oncorhynchus tshawytscha in hatcheries can unintentionally produce large numbers of age‐1 males, termed "minijacks," which pose ecological and genetic risks to target and nontarget populations. We evaluated the postrelease distribution of minijacks produced in a hatchery captive broodstock program targeting the White River in the Columbia River basin between 2010 and 2015.MethodsFish were passive integrated transponder (PIT)‐tagged in the hatchery (n = 218,555), and databases were searched to determine movement behavior and final detections on fixed PIT tag antenna arrays during the year in which they were released.ResultTwo main movement behaviors were detected: (1) residuals, which moved solely within the subbasin of release; and (2) migrants, which moved downstream into the Columbia River and then reascended the Columbia River in the year of release. Minijacks that reascended fish ladders in the Columbia River were most often detected at Rock Island and Bonneville dams, the nearest and furthest detection locations downstream of the Wenatchee River. Minijacks were last detected in all locations where spring Chinook Salmon spawn in the Wenatchee River subbasin (seven tributaries and one main‐stem area) and also in the Entiat River (an adjacent watershed); minijacks in eight of the nine locations were considered strays. Estimates of minijacks that strayed outside of the White River were between 61% and 100% annually and were influenced by release location. Minijacks were also more abundant than males of all older ages in some of the tributaries during some years. In addition, they were detected in these tributaries during periods when anadromous adults migrate into spawning areas and when spring Chinook Salmon spawn.ConclusionThe large amount of minijack production and the spatial and temporal overlap could pose genetic and ecological risks to both target and nontarget populations and particularly high straying poses risks to the maintenance of between‐population genetic variability.

Determining flood source areas in watersheds using data-driven models and a geographic information system

ABSTRACT This study explores the use of gene expression programming (GEP) and artificial neural networks (ANNs) to estimate flood index values based on the unit flood response (UFR) method in two adjacent watersheds (Ardak and Kardeh) located in northeast Iran. The performances of the studied data-driven models were compared according to certain statistical measures such as Root Mean Square Error (RMSE). The findings indicate that GEP models were more accurate than ANNs (RMSE = 0.0986 vs. 0.1512 for Ardak and RMSE = 0.1024 vs. 0.1112 for Kardeh, respectively). Another advantage of the GEP models was providing an explicit relationship between flood index values and physical attributes. As flood index values derived via the UFR method were close to each other, flood contribution area maps were developed using a geographic information system (GIS) to consider uncertainty. Then, fusion algorithms including ordinary averaging, linear regression, and GEP were applied to develop a flexible regional model.

Land-sea linkages on the Algerian Margin over the last 14 kyrs BP: Climate variability at orbital to centennial timescales

Past and present environmental conditions over the Holocene along the Algerian coast involve complex atmosphere-hydrosphere-biosphere interactions and anthropogenic activities on adjacent watersheds. Atlantic Ocean surface waters entering the western Mediterranean Sea at the Gibraltar Strait create the Algerian Current, which flows along the North African coast in a succession of strong and large-scale eddies. Deep-water upwelling plumes are other recurrent hydrological features of the Algerian margin affecting regional environmental features. However, vegetation and paleohydrological changes that have occurred over the Holocene have not yet been described. To bridge this gap, a suite of paleoclimate proxies was analysed in marine core MD04–2801 (2067 m water depth) at a secular-scale resolution over the last 14 kyrs BP. Terrestrial (pollen grains) and marine (dinoflagellate cysts or dinocysts) palynological assemblages, as well as sedimentological (grain-size analysis and XRD-based quantitative analysis of clay minerals) and biomarkers (alkenones and n-alkanes), were determined to explore the links between past sea surface hydrological conditions and regional environmental changes on nearby watersheds.The over-representation of heterotrophic dinocyst taxa (Brigantedinium spp.) indicates strong planktonic productivity in the study area. Results shows that the links between dryness on land and surface hydrological conditions are expressed by: (i) recurrent upwelling cells during the relatively dry climate conditions of the Younger Dryas (12.7 to 11.7 ka BP), the Early Holocene (11.7 to 8.2 ka BP) and from 6 ka BP onwards, (ii) enhanced fluvial discharges between 8.2 and 6 ka BP during the African Humid Period concomitant with the colonization of coastal lands by Mediterranean forest. Middle to Late Holocene transition around 4.2 ka BP characterizes by the intense event reffered to here as the Algerian Mega Drought (4.3 to 3.9 ka BP).

Optical Insight Into Riverine Influences on Dissolved and Particulate Organic Carbon in a Coastal Arctic Lagoon System

AbstractArctic coastal margins receive organic material input from rivers, melted sea ice, and coastal erosion, phenomena that are all undergoing changes related to global climate. The optical properties of coastal Arctic waters contain information on this organic material, and we examined three optical properties of seawater (absorption, backscatter, and fluorescence) for their relationships to variability in dissolved and particulate organic carbon (DOC and POC) in Stefansson Sound, Alaska, a coastal Arctic embayment. During open water periods in 2018 and 2019, DOC was inversely correlated with salinity (r2 = 0.97) and positively correlated with dissolved organic matter fluorescence (fDOM; r2 = 0.67). DOC showed strong correlation with the nonparticulate absorption coefficient at 440 nm (ag(440)) only in 2018 (r2 = 0.95). The vertical structure of fDOM in Stefansson Sound aligned with density profiles more strongly in 2018 than in 2019, and higher levels of fDOM, ag(440), and backscatter seen near the bottom in 2019 suggest wind‐driven mixing and/or bottom resuspension events. In both years, DOC correlated strongly with the spectral slope of the absorption coefficient between 412 and 550 nm (r2 = 0.70), and POC was well correlated with spectral backscattering at 470, 532, and 660 nm (r2 = 0.90, 0.71, and 0.59). These interannual differences in the spatial and vertical distributions of DOC and POC, and their respective correlations with optical proxies, likely reflect regional climatological factors such as precipitation over the adjacent watersheds, wind patterns, and residual sea ice in late summer.

Assessment of the effects of land use/cover changes on soil loss and sediment export in the Tul Watershed, Northwest Ethiopia using the RUSLE and InVEST models

ABSTRACT Numerous studies found that the main factor contributing to the export of sediment from the Ethiopian highlands is soil erosion, which is related to the expansion of cultivated land at the expense of steep slopes of natural vegetation covers. Plantation practices on steep slopes of bare surfaces and utilizing effective water and soil conservation measures on cultivated lands, may, however, have an impact on the rate of soil loss and the sediment yield ratio. Thus, the main objective of the research was to determine how changes in land use and land cover introduced by soil conservation affected the spatiotemporal variability in soil loss and sediment delivery ratio. RUSLE, InVEST, and integrated GIS technology were used to quantify the study's results. The expansion of farmed land at the expense of natural forests, woodlands, shrubs, and grasslands between 1990 and 2000 resulted in a significant increase in soil loss and sediment yield. This was mostly seen where natural vegetation cover areas on steep slopes were turned into cultivable land. Watershed development interventions significantly decreased both the mean annual soil loss and sediment yields between 2003 and 2021. For instance, from 2010 to 2021, the mean annual soil loss in the watershed dropped by 23.5 t ha−1 and the sediment export declined by 6.13 t ha−1yr−1. To prevent soil loss and sediment export at the extensive level, it is therefore concluded that sustainable soil management on cultivated land and plantation techniques on community land should be expanded up to the adjacent watersheds.

Beyond Inca roads: archaeological mobilities from the high Andes to the Pacific in southern Peru

The Andes offers a particularly effective focus for an archaeology of mobility because their extreme topography compresses enormous vertical resource diversity across short horizontal distances. In this article, the authors combine findings from two large-scale archaeological studies of adjacent watersheds—the Nasca-Palpa Project and One River Project—to provide the necessary context in which to explore changing mobilities from the Archaic Period to the Inca Empire, and from the Pacific coast to the high Andes. Analyses of obsidian lithics and stable isotopes in human hair are used to argue that changing patterns of mobility offer a new way of defining the ‘Horizons’ that have long dominated concepts of periodisation here.

Estimation of life history parameters for river catfish Eutropiichthys vacha: insights from multi-models for sustainable management

The river catfish, Eutropiichthys vacha is a vital protein source for rural communities and has high commercial value, but understanding its life history and management strategies reveals major inadequacies and ambiguities in the riverine ecosystems. Consequently, this study employs multi-models to analyze the life history parameters of E. vacha in the Ganges River (northwestern Bangladesh) from January to December, 2020. The total length (TL) and body weight (BW) of 362 individuals (male = 170, female = 192) were measured by a measuring board and a digital weighing balance, respectively. The overall sex ratio (male: female) was 1.0: 1.13 and did not oscillate statistically from the standard 1:1 ratio (p > 0.05). The TL varied from 6.7–19.2 cm for males and 6.3–19.0 cm for females. The length-frequency distributions (LFDs) revealed females outnumbered in 8.0–9.99 cm TL whereas males in 7.0–7.99 cm TL. The slope (b) of the length-weight relationship (TL vs. BW) for both sexes (b = 2.87) was substantially lower than isometry, specifying negative allometric growth pattern for E. vacha. Sex-specific relative (KR) and Fulton’s (KF) condition analysis revealed better state of well-being of males than females. Only KF exhibited significant correlation with both BW and TL, hence making it ideal condition for predicting the fitness of E. vacha in this river. Moreover, the relative weight (WR) suggests an imbalanced habitat for females with higher abundance of predators but suitable for males. The form factor (a3.0) was 0.0062 and 0.0065, whereas the size at first maturity (Lm) and mean natural mortality (MW) were 11.38 and 11.27 cm TL and 1.29 and 1.28 year−1 for the respective sexes. Besides, the calculated mean optimum catchable length (Lopt) was 13.58 and 13.09 cm TL for each sex. These findings will be crucial for further studies and to recommend appropriate strategy for the sustainable management of E. vacha in the Ganges River and adjacent watersheds.

Septic system-groundwater-surface water couplings in waterfront communities contribute to harmful algal blooms in Southwest Florida.

As human population growth has expanded in Southwest Florida, water quality has become degraded with an increased occurrence of harmful algal blooms (HABs). Red tide (Karenia brevis) originating offshore, intensifies in nearshore waters along Florida's Gulf Coast, and blue-green algae (Microcystis spp.) originating in Lake Okeechobee is discharged into the Caloosahatchee River. These HABs could be enhanced by anthropogenic nitrogen (N) and phosphorus (P) from adjacent watersheds. North Fort Myers is a heavily developed, low-lying city on the Caloosahatchee River Estuary serviced by septic systems with documented nutrient and bacterial pollution. To identify sources of pollution within North Fort Myers and determine connections with downstream HABs, this multiyear (2017-2020) study examined septic system- groundwater- surface water couplings through the analysis of water table depth, nutrients (N, P), fecal indicator bacteria (FIB), molecular markers (HF183, GFD, Gull2), chemical tracers (sucralose, pharmaceuticals, herbicides, pesticides), stable isotopes of groundwater (δ15N-NH4, δ15N-NO3) and particulate organic matter (POM; δ15N, δ13C), and POM elemental composition (C:N:P). POM samples were also collected during K. brevis and Microcystis spp. HAB events. Most (>80%) water table depth measurements were too shallow to support septic system functioning (<1.07 m). High concentrations of NH4+ and NOx, up to 1094 μM and 482 μM respectively, were found in groundwater and surface water. δ15N values of groundwater (+4.7‰) were similar to septic effluent (+4.9‰), POM (+4.7‰), and downstream HABs (+4.8 to 6.9‰), indicating a human waste N source. In surface water, FIB were elevated and HF183 was detected, while in groundwater and surface water sucralose, carbamazepine, primidone, and acetaminophen were detected. These data suggest that groundwater and surface water in North Fort Myers are coupled and contaminated by septic system effluent, which is negatively affecting water quality and contributing to the maintenance and intensification of downstream HABs.

Regional-Scale Distribution of Helium Isotopes in Aquifers: How Informative Are They as Groundwater Tracers and Chronometers?

This study presents an almost entirely unpublished dataset of 121 samples of groundwater analyzed for helium concentration and its isotopic ratio (3He/4He) in two adjacent watersheds of the St. Lawrence Lowlands, in a region with intensive agricultural activities in the southern Québec Province, Eastern Canada. Most of the samples were collected in the regional bedrock fractured aquifer hosted in mid-Ordovician siliciclastic shales, on a total surface of 7500 km2. Even with this low-density sampling, and in a heterogeneous and fractured aquifer, the helium isotopes bring precious information on the recharge conditions and on chemical evolution of water. The helium spatial interpolation does not show a clear isotopic gradient through the basin. However, it shows progressive enrichment of radiogenic 4He in the confined part of the aquifer. The atmospheric and/or tritiogenic-rich helium occurs at the recharge in the Appalachians and in the middle of the plain, where impermeable cover is limited, and local infiltration of meteoric freshwater reaches the bedrock aquifer. The relation between the total dissolved solids (TDS) and 3He/4He ratios remains elusive. However, on discriminating the samples with the dominant chemistry of water, a clear trend is observed with 3He/4He ratio, suggesting that radiogenic 4He accumulates together with dissolved solids and with increasing time (indicated by progressively older 14C ages). Finally, the noble gas temperatures (NGTs) obtained from concentrations of the other noble gases (Ne, Ar, Kr and Xe) brings constraints on the earlier recharge conditions during the Holocene. Particularly, the NGTs showed that the studied aquifers were continuously replenished, even under ice-sheet cover in the last 10,000 years.

Soil C:N:P Stoichiometric Characteristics and Soil Quality Evaluation under Different Restoration Modes in the Loess Region of Northern Shaanxi Province

Vegetation restoration is essential for the stability of the ecological system structure and function in the loess region of North Shaanxi Province. Natural and artificial restoration are the primary modes for vegetation recovery and soil quality improvement in this region. In this study, two adjacent watersheds with similar ecological environment conditions but different restoration modes were selected for research; one watershed is restored naturally (He Gou watershed), and the other is restored artificially (Chai Gou watershed). According to the study of soil stoichiometric characteristics and soil quality after the vegetation restoration in these two watersheds, the results showed: (1) Compared with the natural restoration, artificial restoration was more effective in increasing the content of soil organic carbon and total nitrogen, however, the total phosphorus content of the soil in the natural restoration mode was higher than that in the artificial restoration mode. (2) The ratios of soil C:N, C:P, and N:P showed a decreasing trend with the increase of soil depth at these two restoration modes. (3) In the 0–60 cm soil layer, the soil quality under the artificial restoration mode was better than that of the natural restoration, especially for the soil layer beneath 20 cm. (4) The minimal data set on the soil quality evaluation in the study area included soil organic carbon, capillary water holding quantity, available potassium, soil water content and available phosphorus. It showed a linear relation with the total index data set (y = 0.829x + 0.058, R2 = 0.76) and can reflect the soil quality more sensitively than the total indicator data set.

Macroinvertebrate responses to differing riparian treatments following forest harvest in the headwaters of Trask River watershed

Although it is well-established that macroinvertebrates are an integral part of a healthy stream ecosystem, studies designed to inform forest harvest best management practices for sustainability of macroinvertebrate communities in small streams have been limited. Current riparian management practices for headwater streams generally focus on providing adequate wood supply, reducing debris flows and transport of sediment, and maintaining water quality in larger streams that contain fish. Here we studied the effects of contemporary forest harvest practices on benthic macroinvertebrate density and community composition in 12 small headwater streams as part of the Trask River Watershed Study. To account for seasonal and year-to-year variability in macroinvertebrate densities, we sampled each site at the same time of year for six years before and four years after harvest. Three watersheds were clearcut with variable riparian buffers, three were clearcut with 12 m riparian buffers, and one was thinned with 15 m buffers. Five adjacent watersheds were not treated and were studied as reference sites. All sites had approximately 50 yr old conifer and alder forests, which had revegetated following fires and harvest in prior decades.In these steep mountain streams, benthic macroinvertebrate density and community composition were generally similar across watersheds prior to harvest. Collectors were the most abundant functional feeding group, followed by shredders; scrapers were the least abundant. After harvest, in two of the three clearcut watersheds with variable buffers, the total benthic density and percentage of collectors increased, primarily due to greater numbers of Chironomidae. We also observed more abundant emergence post-harvest at these two watersheds. In the third clearcut watershed with a variable buffer and in the three clearcut watersheds with uniform 12 m riparian buffers, we did not see changes in density or functional feeding groups after harvest. We explored the spatial and temporal aspects of the data using both non-parametric and parametric statistical methods. High variability swamped the treatment effect when watersheds were grouped by riparian treatment for the repeated measure analyses, while NMDS showed a significant shift post-harvest for the watersheds with variable buffers. In the clearcut watersheds with uniform buffers, macroinvertebrates densities and community composition did not shift. At two of the clearcut watersheds with variable buffers, we observed increased density for the first two years after harvest, and chironomids comprised up to 80% of the abundance in samples. In the subsequent years, we documented mixed responses for two watersheds. It was invaluable to have multiple pre- and post-harvest sampling periods in both harvested and reference watersheds in order to better identify site specific responses to treatment and to separate background variability from responses to harvest. We show that retention of riparian vegetation on headwater streams during clearcut harvesting minimized changes in total macroinvertebrate densities and community composition. Small buffers may be key to maintenance of diverse stream invertebrate communities in headwaters.