Watershed Scale Research Articles

Principais preditores na ocorrência do fitoplâncton em sistemas lóticos

Abstract: Aim Our goal was to relate the phytoplankton metacommunity to its possible determinants in a micro watershed: (I) determinants related to landscape-scale filtering, (II) determinants referring to local microhabitat filtering, (III) determinants referring to previous colonization, and (IV) determinants representing three different dispersal routes. Methods Eight sampling stations were selected along the Cascavel River watershed, located in the state of Paraná, Brazil. Samples were collected quarterly for three years. All phytoplankton samples were quantitatively analyzed to determine the density of the metacommunity. In addition, it was characterized the landscape in terms of land use and occupation, and environmental characterization in terms of physical and chemical variables of the water. All data underwent relevant statistical analysis, where variance partitioning was carried out using partial RDA models, with prior selection of predictor variables, to estimate the relative role of each predictor in the community. We also compared three possible dispersal routes: “Asymmetric Eigenvector Map” (AEM), “Overland” and “Watercourse”. Results It was found that the metacommunity was best explained by “asymmetric eigenvector mapping” (AEM), indicating that because it is a small spatial scale the high connectivity between the sampling stations enables species to disperse overland as well. The different filters act together and depend on rainfall variation. Besides fluctuating temporally, the influence of these mechanisms is subject to which dispersal hypothesis is being considered. Conclusions At the watershed scale, we argue that small-scale processes should be considered, since they homogenize the landscape and consequently leave the environmental gradient similar between sampling stations. In addition, the connectivity of colonization patches is essential to understand the behavior of microalgae that have a high dispersal capacity and are not restricted only to the river course.

Water Quality Sampling Provides Insight into Nutrient Sources and Pathways in an Agricultural Watershed in the Midwestern USA

HighlightsHysteresis and flushing indices were calculated for 23 storm events.Wetter conditions led to a dilution effect for nitrate during storm events.Travel times were faster for all nutrients during the winter, likely due to lack of vegetative cover.Results can be used to choose practices that effectively target specific nutrient sources and pathways.Abstract. Understanding where agricultural nutrients originate in the landscape can help mitigate downstream transport by selecting and installing best management practices that target nutrient sources. We collected flow and water quality data from 2017–2021 at two similar HUC-12 watersheds in northeastern Indiana, which provided an opportunity to link nutrient sources with transport processes in intensively managed agricultural watersheds. We calculated metrics to represent changes in nutrients during a storm event, including hysteresis (the change in concentration on the rising limb of the hydrograph compared to the recession limb) and the flushing index (the difference between concentrations at peak discharge and baseflow). We compared storm-based and annualized concentration-discharge (C-Q) relationships for NO3-N, soluble reactive phosphorus (SRP), total P (TP), and dissolved organic carbon (DOC) to land use and climate variables. Together, these provide insight into nutrient storage zones and transport pathways at the small watershed scale. Our results suggest these landscapes have plentiful and widely distributed sources of nitrogen (N) that are activated in the spring, which we observed as chemostatic behavior (i.e., concentration remained relatively constant during different flows). While this has been shown at larger scales in agricultural watersheds, these patterns are challenging to parse at the small watershed scale. We saw concentrating effects (i.e., increased concentrations as flow increased) for DOC, TP, and SRP during storms, suggesting activation of flow-paths connecting land-based sources to receiving streams. We also noted faster travel times in the winter for all four constituents when subsurface tile drains are most active and plant uptake is negligible. Our results differentiate nutrient delivery mechanisms and can aid management decisions by identifying environmental factors that most influence transport and selecting conservation practices that target these nutrient pathways. Keywords: Agriculture, Carbon, Concentration-discharge, Hysteresis, Nitrogen, Phosphorus, Watershed management.

Modeling economic-environmental-ecological trade-offs for non-point source control strategies: A case study of Dianchi lake watershed, China

Non-point source (NPS) pollution has become a primary threat to the water environment. With the implementation of numerous control projects, striking a balance between economic costs and efficiency has become an urgent issue for decision-makers. To identify the optimization solutions for best management practices (BMPs) at the watershed scale, a genetic algorithm and the Soil and Water Assessment Tool (SWAT) model were combined to evaluate the trade-offs of NPS control strategies. The BMPs considered in this model included soil testing and fertilizer application technology, integrated pest management projects, conservation tillage, lakeside belt ecological construction, forest construction, and vegetation filter strips. The decision variables are the type and size of the BMPs, with the objective of minimizing costs while simultaneously maximizing both total phosphorus (TP) reduction and ecosystem service value. TP reduction was simulated usinga calibrated SWAT model that successfully assessed NPS pollution in the Dianchi lake watershed. Considering NPS generation and transfer, three NPS control scenarios were designed: source reduction, process retention, and integrated control. The upper limits of the costs for three scenarios were 157, 4921, and 5013 million yuan, respectively. It is suggested that the ecological benefits should be taken into account in the BMPs design. This finding is conducive to generating optimized control schemes that can effectively balance the trade-offs between socioeconomic costs and environmental sustainability.

Geospatial Interpolative Analytics of Gauged Rainfall in Network under Semi-arid Situation of Krishna Basin on a Watershed Scale

Kriging as a Geospatial interpolative delineation of optimal radial distance around existing rainfall stations with in the purview of flat land (1-3 %) watershed (Hti-2 4D7B3) situated in Krishna basin. The smaller (15 and 30 min) and medium (45 min to 1h 45 min) events of the were analyzed focusing on their distribution whereas events of longer duration (>2 h) analyzed with their depth across 14 gauging stations. Analysis of 14 gauged rainfall network stations and their corresponding rainfall data during 2014-2020 used to derive relationship between recurring events of classified duration (15 min to 2 h) vis-a-vis weighted influence of number and depth due to spatial morphology and limitations of watershed. The event vise rainfall network distribution of Huti-2 watershed found to be significantly uniform in number and depth within the radial distance upto 3 km around each station prevailed by strong coefficient of determinant (R2) more than 0.8.

Examining soil nutrient balances and stocks under different land use and management practices in contrasting agroecological environments

AbstractAgricultural sustainability and land degradation can be monitored through studying soil nutrient dynamics. This study was conducted to investigate the balance and stocks of nitrogen (N) and phosphorus (P) under major land use types and land management (LM) practices in three contrasting agroecological environments in Ethiopia. We employed a nutrient monitoring approach and assessed soil N and P inputs and outputs at watershed and plot scales. Field data were collected from 72 sites representative of the major land uses of the three watersheds for the watershed scale analysis. In addition to the watershed data, 16 experimental runoff plots were established and the response of nutrient balances to improved LM practices for the major land uses, including cropland with three treatments (control, farmyard manure [FYM] and soil bund), grazing land with three treatments (control, exclosure and FYM + exclosure) and bushland with two treatments (control and exclosure). Nutrient balances, flows and stocks varied significantly among agroecological settings, land‐use types and LM practices. Severe and negative N balances were found in all agroecological environments, with midland (−70.8) > highland (−61.7) > lowland (−50.3 kg ha−1 yr−1), whereas slightly positive P balances were found in all agro‐ecosystems. As a result, the midland (4.2% yr−1) and highland (2.1% yr−1) sites had greater N depletion rates than the lowland site (1.0% yr−1). Our results also demonstrated that applied LM practices improved N balances: by 32%–40% in cropland through FYM and mineral fertilizer, by 7%–18% in grazing land via FYM and exclosure, and by 6%–36% in degraded bushland via exclosure, implying that, implementing FYM and mineral fertilizer for cropland and implementing FYM with exclosure on non‐croplands can reverse nutrient depletion in the study sites and in other areas having similar agroecological conditions.

Spatial variation characteristics and influencing factors of CO2 partial pressure in the middle reaches of the Yellow River during summer

AbstractThe partial pressure of CO2 in rivers regulates the intensity and direction of carbon dioxide (CO2) exchange at the water–air interface. Environmental, nutrient factors, and their stoichiometric ratios within the watershed may affect the level of carbon dioxide partial pressure in rivers. However, the relationship between pCO2 responses to the environment, nutrient factors, and their stoichiometric ratios at a large watershed scale was not well understood. In this study, water samples from 20 locations in the mainstream and 16 tributaries of the middle reaches of the Yellow River were collected to study the spatial characteristics of pCO2 and its influencing factors. pCO2 vales showed spatial heterogeneity ranging from 45.57 to 3631.48 μatm, and an average of 1341.87 μatm. Relative to the atmospheric equilibrium value (415 μatm), 90% of the samples were supersaturated. During the study period, higher pCO2 appeared in the Wanjiazhai Reservoir at the northernmost part of the mainstream in the middle reaches, and in the tributaries of the Fen, Wei, and Beiluo Rivers. Overall, the transition from carbon sink to carbon source was experienced in the middle reaches of the Yellow River from north to south. River pCO2 exhibited a significant correlation with phosphorus concentrations and their associated stoichiometric ratio, suggesting that microbial metabolism drove CO2 saturation in rivers. In addition, different land use proportions contributed significantly to changes in river pCO2.

Identification and quantification of nutrients sources in the Aspio watershed (Italy). Insight from geogenic mineralization and anthropogenic pressure

An accurate evaluation of river water quality could be challenging due to the complex hydrological and anthropogenic processes which affect its nature. Reliable water quality data are mandatory to identify long-term trends and regional variability at the watershed scale. In this study, a combined approach using time series, regression, and multivariate statistical analysis along with SWAT modelling was applied to identify the relevant hydrogeochemical processes and the nutrients sources within the Aspio watershed (Ancona, Italy). The analysis detected different processes: i) the geogenic origin of Cl- and SO42-, ii) the heavy metals (Cu and Ni) and hydrocarbons pollution due to runoff from urban and industrial areas, and iii) the agricultural contribution of pesticides, nitrogen, and phosphorous. A SWAT model was implemented to quantify the nutrients load in the Aspio river. A calibration for streamflow, river sediment yield, and for nutrients load was obtained considering agricultural, urban, and wastewater treatment plant contributions. Agriculture and treated wastewater contributed to the overall nitrogen load only for 4% and 12% respectively, while the majority was due to leakage from urban sewage (84%). A scenario with only fertilizers’ load (excluding other sources) highlighted that nitrogen and phosphorous export from agricultural lands did not significatively impact the Aspio river. The spatial representation of runoff susceptibility also showed how the highest susceptibility for nitrogen and phosphorous loads is due to areas located close to urban settlements.

Seasonal dynamics and key drivers of pharmaceutical pollution in a peri-urban watershed

Peri-urban ecosystems are strongly influenced by their natural environmental conditions and surrounding landscape. However, landscape patterns and landscape-related variables driving pharmaceutical pollution in peri-urban watersheds with rapid urbanization remain poorly understood. Herein, we investigated the occurrence and spatiotemporal distribution of 28 pharmaceuticals and their potential influencing factors in a peri-urban watershed (Zhangxi River Watershed) in Zhejiang province, Eastern China. Paraxanthine (detection frequency 97 %, mean concentration 223.07 ng/L) and anhydro-erythromycin (95 %, 4.01 ng/L) were the most prevalent compounds. Total pharmaceutical concentrations (sum of all target compounds) were significantly higher in the wet season (summer and autumn) than in the dry season (spring and winter; P < 0.05). Information theoretic-based analysis revealed that landscape pattern and dissolve organic matter were the main drivers of watershed-scale pharmaceutical pollution rather than water quality parameters and topographic characteristics. Correlation analysis showed that total pharmaceutical concentrations were more highly correlated with landscape pattern during the dry season than the wet season. The importance analysis and indicator interaction analysis revealed that interspersion and juxtaposition index (IJI), mean patch size (AREA-MN), patch density (PD), terrestrial humic-like substances C2, dissolved organic carbon (DOC) and fluorescent dissolved organic matter (FDOM) played a vital role in the occurrence and distribution of pharmaceutical in the watershed. Maintaining natural landscape is conducive to reduce antibiotic concentration in Zhangxi River. These results suggest that landscape patterns and dissolved organic matter strongly influence pharmaceutical pollution in the peri-urban ecosystem at a watershed scale.

Environmental selection and gene flow jointly determine the population genetic diversity and structure of Diaphanosoma dubium along a watershed elevation

Biodiversity of local communities has been found to generally decrease with elevation. However, the elevational patterns of intraspecific genetic diversity remain unclear, especially in passive dispersers and species with short life histories. In this study, we investigated the populations of a tropical dominant Cladoceran, Diaphanosoma dubium, along elevation in the largest watershed of South China. The studied populations were grouped into four regional groups based on elevation and habitat connectivity. No significant elevation pattern was observed for mitochondrial genetic diversity, but nuclear diversity was influenced by habitat type. The haplotype network showed a radial pattern with a common haplotype at the centre, and many private haplotypes existed in each regional group. Four clusters of D. dubium populations were identified and exactly corresponding to the four investigated regions, indicating a strong spatial genetic structure. Weak but significant isolation by distance (IBD) supported the critical role of environmental selection with elevation. Precipitation significantly explained population genetic variation at the watershed scale. Bidirectional gene flow was a common pattern that occurred among the four regional groups. Our results highlight that habitat selection with gene flow plays an important role in shaping the genetic pattern of tropical freshwater Cladocera along an elevational gradient.

Using the SWAT model to characterise the water regime of soils in agrolandscapes

The classification of soils water regimes a basic scientific basis in the form of an interdependent relationship between the movement of water and the formation of a soil profile, i. e. it is soil-genetic classification. This kind of classification provides a scientific and methodological platform for studying both the water regimes of soils in the landscape and the distribution of soils in the soil cover of the landscape. Numerical methods for representing the hydrological regimes of soils in the agricultural landscape are based on physically validated mathematical models of the soil water movement and spatial GIS information, which together allow to calculate, analyze and predict soil water regime, runoff in the scale of watersheds, substance transport in the soil profile, leaching processes, as well as the content of available soil moisture reserves in the agrolandscape structure – which is important for practice. A spatial-dynamic SWAT (Soil-Water-Atmosphere-Tool) model is presented to describe the water regimes of soils in the agro-landscape of the finite moraine ridge of the Upper Volga postglacial region (East European Plain, Tver region), as an example of landscape numerical hydrological models. Some examples are given in the article, which demonstrate that modeled data correspond well with experimental data on soil moisture dynamics in several points of agrolandscape for 3 depth levels, reflecting surface, deep (at groundwater level) and middle layers of soil profile, i. e. 10–20, 50–60 and 90–100 cm. On the one hand, the data were obtained by calculations with the help of the considered landscape-dynamic model; and on the other hand, – by classical soil drilling, sampling and gravimetric method for soil moisture content determination. It has been shown that the landscape model, adapted for specific conditions, using a digital elevation model with a resolution of 1×1 m per pixel, to calculate the soil water regime at different points of the agrolandscape satisfactorily describes the spatial-dynamic profile data on soil moisture.

Spatiotemporal heterogeneity of soil available nitrogen during freeze–thaw cycles in a watershed: A 3‐year investigation

AbstractThe spatial pattern of soil available nitrogen (AN) is the key reference for farmland fertilization however, it is still unclear how freeze–thaw cycles (FTC) altered the spatiotemporal heterogeneity of AN at the watershed scale. In this study, the geostatistical, traditional analysis and structural equation models were used to detect how topography, land management, and soil properties influence the spatiotemporal heterogeneity of AN in both before‐ and after FTCs of Mollisols of a watershed in Northeast China for three consecutive years. The results showed that AN decreased in &gt;88% of areas of the watershed after FTCs, and the mean value significantly decreased by &gt;7.6% (&gt;10.4 mg kg−1) in 0–20 cm soil depth during 2016–2017 years and 2017–2018 years. The AN distribution, especially in the surface soil layer, tended to be aggregated after FTCs. The AN decreased in the areas near the areas of top slope position, while it tended to increase in areas of downslope position covered by forest although the total N decreased here after FTCs. The AN‐change (ANbefore FTCs minus ANafter FTCs) influenced by land use types was greater than slope steepness. The slope aspect as the key factor combined with slope steepness, slope position, and previous crops influenced the spatiotemporal heterogeneity of AN‐change after FTCs. The higher content of AN before FTCs accelerated more N loss during FTCs, and this process was mainly influenced by soil pH, nitrogen (N), and phosphorus. The N loss (5.7%) did not significantly alter the AN‐change after FTCs in the watershed. Generally, the spatial heterogeneity of AN‐change was mainly influenced by topography, land management, and soil properties (before FTCs) during FTCs in the watershed. In order to sustain a high level of AN, the mediation of N transformation and both vertical‐ and horizontal migration, caused by the dynamics of soil water potential and snowmelt erosion should be considered during FTCs.

A landscape source–sink model to understanding the seasonal dynamics of antibiotics in soils at watershed scale

Human and veterinary antibiotics occur widely in soil ecosystems and pose a serious threat to soil health. Landscape structure can be linked to Earth surface processes and anthropogenic footprints and may influence the variability of antibiotics in soil. In this study, an improved landscape source–sink model was used to characterize source–sink structures using the location-weighted landscape index (LWLI), which can be linked to antibiotic seasonality. The topographic wetness index was employed to identify source and sink landscapes, which represent antibiotic transport pathways via topography-driven hydrological processes. The results indicate that LWLI values and antibiotic seasonality are typically higher in farmland soils than in forest and orchard soils. LWLI values exhibit significant positive correlations with antibiotic seasonality in soils (R2: 0.33–0.58). Furthermore, landscape source–sink structures have a significant influence on antibiotic seasonality between winter and other seasons in farmland soils; however, these structures affect antibiotic seasonality between summer and other seasons in forest and orchard soils. The results of this study indicate that water movement regulated by landscape structure may play a crucial role in influencing antibiotic seasonality in soils at the watershed scale, and the landscape source–sink model can be used to quantitatively evaluate antibiotic seasonality in soil environment.

Quantifying Landscape Pattern–Hydrological Process Linkage in Northwest Iran

The enormous heterogeneity and complexity of landscape patterns and their linkage with the hydrological responses have rarely been quantified and cataloged, especially in ungauged regions. This research therefore linked the landscape characteristics to hydrological processes using a newly developed runoff landscape index (RLI) at the watershed scale in Ardabil Province, northwest Iran. First, 11 common landscape metrics were calculated using Fragstats 4.2.1 software. Then, a runoff landscape index (RLI) was developed based on land cover (λC), soil (λK), and topography (λS) factors in 28 watersheds. Correlation and regression analyses were also conducted to determine the relationship between RLI, commonly used landscape metrics, and mean base flow. The spatial variations of all meaningful landscape metrics and RLI were considerable throughout the study watersheds. The mean values of λC, λK, and λS were found to be 2.78 ± 1.08, 0.50 ± 0.10, and 1.22 ± 0.30, respectively. The mean RLI varied from 0.00009 in the Lay Watershed with an area of 19.09 km2 to 0.28 in the Boran Watershed with 10,268.95 km2. The correlation coefficient (r &gt; 0.42; p-value &lt; 0.05) was obtained significantly between RLI and only five landscape metrics, including the largest patch index (LPI), landscape shape index (LSI), landscape division index (DIVISION), splitting index (SPLIT), and Shannon’s diversity index (SHDI). In addition, a regression model with R2 of 0.97 and 0.67, respectively, in calibration and validation steps was established between river base flow as the dependent variable and main waterway length, LPI, LSI, SPLIT, modified Simpson’s diversity index (MSIDI), and λS as independent variables. The result confirms the significant interdependence of RLI and landscape characteristics, which can be used to interpret the landscape’s dynamic and its effects on hydrological processes.

Muddied Waters: The Use of "Residual" And "Legacy" Phosphorus.

Phosphorus (P) inputs to the biosphere have quadrupled in less than a century due to intensification of rock phosphate mining and the use of P fertilizers for crop production. Accumulation of P in soils can increase P transfers across the soil-water continuum that impair aquatic ecosystem function and water resource quality for society. However, what this accumulated P is called, and subsequent connotations of magnitude versus mechanism at pedon versus watershed scale, varies in the literature. We argue that the two commonly used terms of "residual" and "legacy" P, though often used interchangeably, hold distinct meanings and connotations. Tracing the historical origins and trajectories of these terms reveals that "residual P" refers to the magnitude of fertilizer P that remains in the soil after crop harvest, whereas "legacy P" refers to the mechanism of P transfer across the watershed and its long-term impacts on water quality. The use of "legacy P" in many cases refers to the residuality of anthropogenic P inputs, and thus should be "residual P". We recommend that the term "residual P" be used when referring to the accumulation of P in soils under agricultural management from past inputs, and the term "legacy P" be used when referring to the transfer of P within watersheds. The intentional and thus consistent use of residual versus legacy P stands to provide important nuance in the environmental sciences and overlapping fields of agronomy and biogeochemistry.

Dual stable isotopes to rethink the watershed-scale spatiotemporal interaction between surface water and groundwater

The interaction between groundwater and surface water, including their recharge relationship and ratio, is crucial for water cycling, management, and pollution control. However, accurately estimating their spatiotemporal interaction at the watershed scale remains challenging. In this study, we used dual stable isotopes (δ18O, δ2H, d-excess, and lc-excess) and hydrochemistry methods to rethink spatiotemporal interaction at the Yiluo River watershed in central China. We collected 20 groundwater and 40 surface water samples over four periods in two seasons (dry and wet). Our results showed that in the downstream region, groundwater recharged surface water in the dry season while surface water recharged groundwater in the wet season, with average recharge ratios of 89.82% and 90.02%, respectively. In the midstream region, surface water recharged groundwater in both seasons with average ratios of 93.79% and 91.35%. In contrast, in the upstream region, groundwater recharged surface water in both seasons with ratios of 67.35% and 76.89%. Seasonal changes in the recharge relationship between surface water and groundwater in the downstream region also been found. Our findings provide valuable insights for watershed-scale water resource and pollution management.

Combining Hydrological Modeling and Regional Climate Projections to Assess the Climate Change Impact on the Water Resources of Dam Reservoirs

Climate change may significantly impact the availability and quality of water resources in dam reservoirs by potentially altering the hydrological regime of lake tributaries and the corresponding flow–duration curves. Hydrological models driven by climate projections (downscaled to the watershed scale and bias corrected to eliminate systematic errors) are effective tools for assessing this potential impact. To assess the uncertainty in future water resource availability, resulting from the inherent uncertainty in climate model projections, an ensemble of climate models and different climate scenarios can be considered. The reliability and effectiveness of this approach were illustrated by analyzing the potential impact of climate change on the water availability at Brugneto Lake in northern Italy. This analysis was based on climate projections derived from an ensemble of 13 combinations of General Circulation Models and Regional Climate Models under two distinct scenarios (RCP4.5 and RCP8.5). The semi-distributed HEC-HMS model was adopted to simulate the hydrological response of the basin upstream of the lake. The hydrological model parameters were calibrated automatically via the PEST software package using the inflows to the lake, estimated through a reverse level pool routing method, as observed values. Future water availability was predicted for short- (2010–2039), medium- (2040–2069), and long-term (2070–2099) periods. The results indicate that the uncertainty in reservoir inflow is primarily due to the uncertainty in future rainfall. A moderate reduction in water availability is expected for Brugneto Lake by the end of the current century, accompanied by modifications in the flow regime. These changes should be considered when planning future adaptation measures and adjusting reservoir management rules.

Nitrate losses from forest during snowmelt: An underestimated source in mid-high latitude watershed

The forest nitrate cycle is a crucial part of the watershed nitrate load but has received limited attention compared to that of agricultural and residential land. Here, we analyzed the status and sources of riverine nitrate fluxes and identified the characteristics and contribution of forest nitrate loss to the riverine system in a mid-high latitude forested watershed using monthly field sampling and a modified Soil and Water Assessment Tool (SWAT) with enhanced forest nutrient cycle representation. The results indicate that nitrate losses in the headwater stream and downstream exhibit different seasonal characteristics. The nitrate losses in the headwater stream show a bimodal pattern due to lower temperatures and snowmelt runoff. Redundancy analysis (RDA) revealed that, unlike nitrogen (N) fertilizer-induced nitrate loss in the rainy season, forest loss has a positive effect on headwater stream nitrate concentration during the snowmelt season. The modified SWAT was then utilized to simulate nitrate losses in forest lands. The forest nitrate export per unit area of the headwater stream (1.58 ± 1.78 kg/ha/yr) was observed to be higher than that of the downstream (0.67 ± 0.74 kg/ha/yr) due to high snowmelt and mineralization of active organic N. At watershed scale, forest lands contributed 8.18 ± 3.94 % of the total nitrate losses to the water system in the headwater watersheds during the snowmelt season, representing the highest level within the entire basin. A comparison with forest streams in similar low-temperature conditions worldwide revealed that increasing nitrate loss occurred after extreme cold weather or soil freezing events, with an average increment of 6.32 kg/ha/yr. Therefore, forest nitrate losses should be better characterized and included in future watershed N budgets in low-temperature regions, which might help to reduce the N budget uncertainty and improve watershed management.

Spatiotemporal Analysis of Extreme Rainfall and Meteorological Drought Events over the Angat Watershed, Philippines

Understanding the spatiotemporal distribution of extreme rainfall and meteorological drought on a watershed scale could be beneficial for local management of any water resources system that supports dam operation and river conservation. This study considered the watershed of Angat as a case, given its economic importance in the Philippines. A series of homogeneity tests were initially conducted on each rainfall dataset from monitoring stations in and near the watershed, followed by trend analysis to determine the rate and direction of change in the annual and seasonal rainfall extreme indices in terms of intensity, duration, and frequency. Three indices, using the rainfall deviation method (%DEV), percent of normal rainfall index (PNRI), and Standardized Precipitation Index (SPI), were also used to identify meteorological drought events. Generally, rainfall in the watershed has an increasing annual PCPTOT (4–32 mm/year), with increasing frequency and intensity in heavy rainfall and wet days. A significant increasing trend (α = 5%) in the seasonal PCPTOT (7–65 mm/year) and R10mm (1.7–10.0 days/decade) was particularly observed in all stations during the Amihan Monsoon Season (Dec–Feb). The observed increasing rainfall intensity and frequency, if it continues in the future, could have an implication both for the water resources operation to satisfy the multiple objectives of Angat Reservoir and for the flood operation that prevents damage in the downstream areas. The effect of each ENSO (El Niño- Southern Oscillation) phase on the rainfall is unique in magnitude, intensity, and duration. The seasonal reversal of the ENSO in the extreme rainfall and meteorological drought signals in Angat Watershed was also evident. The identified meteorological drought events in the watershed based on SPI-12 persisted up to 12–33 months, could reduce more than 60% (PNRI &lt; 40%) of the normal rainfall. Insights from the study have implications for the hydrology of the watershed that should be considered for the water resources management of the Angat Reservoir.

Multi-Scale Remote Sensing Assessment of Ecological Environment Quality and Its Driving Factors in Watersheds: A Case Study of Huashan Creek Watershed in China

The Huashan Creek watershed is the largest water source and the main production area of honeydew in Pinghe County, whose extensive cultivation of honeydew has exacerbated soil and water pollution. However, the spatial application of remote sensing ecological index (RSEI) in this watershed and key driving factors are not clear considering the applicability of data quality and the diversity of methodological scales. To explore the RSEI and driving factors at distinct scales in Huashan Creek watershed, this study constructed the RSEI based on the environmental balance matrix at seven scales in 2020, revealed its spatial response characteristics at different scales, and analyzed the key drivers. The results show that the 240 m grid as well as rural and watershed scale convergence analyses satisfy the assessment of RSEI, whose Moran indexes are 0.558, 0.595, and 0.146, respectively. The RSEIs at different scales have significant spatial aggregation characteristics, but the overall status is moderate. The central town–riparian area with poor RSEI contrasts with the western mountainous area, which has comparatively better quality. Population has a major influence on RSEI at multiple scales (0.8), with elevation and patch index acting significantly at the village and grid scales, respectively. These findings help to identify the spatial distribution of quality and control mechanisms of RSEI in the Huashan Creek watershed and provide new insights into key scales and drivers of ecological restoration practices in the watershed.

The temporal variation of sediment connectivity from 1982 to 2020 in the Wei River basin, China

AbstractSediment connectivity is a valuable metric that characterizes the relationship between sediment transport from the source to the sink, and the ease of sediment erosion. Over the past four decades, changes in land use types and vegetation cover have significantly altered sediment dynamics in the Wei River basin. In this study, we used the index of connectivity (IC) to assess the temporal changes in sediment connectivity at a watershed scale. We employed Landsat images to analyse the relationship between changes in vegetation cover or land use type and sediment connectivity. We used factor detector and interaction detector in Geodetector to analyse the importance and impact of vegetation and slope on IC changes. We assessed the correlation of sediment yield and connectivity to validate our results and it shows that IC has strong or moderate positive correlation with sediment yield from eight out of nine stations in the Wei River Basin. Our findings demonstrate that soil and water conservation measures, as well as the grain for green project, have led to the transformation of cropland and grassland into woodland. This change is reflected in the decrease of the maximum IC value from 6.24 to 5.72 in the Beiluo sub‐basin, indicating a decreasing trend in sediment connectivity. Although the maximum IC value increased from 5.76 to 5.08 in the Jing sub‐basin, driven by human activity, showing an increasing trend. Furthermore, the IC value decreased in the western part of the Wei sub‐basin. Overall, sediment connectivity exhibits a weak decreasing trend in most regions of the Wei River basin, while it shows an increasing trend slightly in the Jing sub‐basin. The correlation coefficients ranged from 0.47 to 0.86, with sediment yield being moderately or strongly correlated with IC. Our study identified vegetation, human activity, and slope as the main influencing factors of IC. The results of factor detector showed that the q value of vegetation was 0.63 and the slope was 0.1, Vegetation played a major role in the change of IC. The results of interaction detector showed that interaction between vegetation and slope was greater than the single factor. The temporal variability of sediment connectivity in the basin provides valuable insights for sediment transport management. Our research highlights the importance of studying sediment connectivity and offers proposals for measures that can be taken to address sediment transport challenges in the Wei River basin.