Factors Driving the Spatiotemporal Variation of Dissolved Organic Carbon Flux from Croplands in the Midwestern USA

Improving understanding of dissolved organic carbon (DOC) cycling from farmlands to rivers is a challenge due to the complex influence of farming practices, the hydrology of predominantly flat lowlands, and seasonal snowpack effects. Monthly field DOC concentrations were measured throughout the year at sub-basin scale across the Chippewa River Watershed, which falls within the Corn Belt of the Midwestern United States. The observations from croplands were benchmarked against the data sampled from hilly forested areas in the Connecticut River Watershed. The Soil Water Assessment Tool (SWAT) was used to simulate daily soil water properties. This method tests for a framework for using the combination of new field data, hydrological modelling, and knowledge-based reclassification of Land Use/Land Cover (LULC) to analyze the predictors of both the spatial and temporal changes of DOC over farmlands. Our results show: 1) DOC concentrations from cropland baseflow were substantially high throughout the year, especially for spring runoff/snowmelt scenarios, 2) gradient analysis with spatial factors only was able to explain ~82% of observed annual mean DOC concentrations, and 3) with both spatial and temporal factors: [Evapotranspiration, Soil Water, and Ground Water], the analysis explained ~81% of seasonal and ~54% of daily variations in observed DOC concentrations.

GROUNDWATER RUNOFF IN THE PIVDENNYI BUH RIVER BASIN IN CONDITIONS OF GLOBAL WARMING

This paper analyses changes in the calculated values of the specific runoff of unconfined and confined groundwaters to the rivers Pivdennyi Buh (Khmilnyk town) and Zhar (a tributary of the Pivdennyi Buh; Vinnytsia and Khmelnytsky regions) by seasons and long-term stages, for a total of 38 years (1980-2017). Regularities of seasonal changes in groundwater runoff in areas with different relief and average long-term groundwater levels (0.5-1.5; 0.8-2.5 and 2.7-4.5 m) are revealed. These changes have been shown to be closely related to abnormal air temperature fluctuations. There are four stages of successive changes in the regime of groundwater and in the volume of their runoff to rivers: I. 1980-1989 (1990) — traditionally minimal winter and autumn underground runoff, moderate summer and predominant spring runoff, dominance of runoff from the area with high GWT; ІІ. 1990-1998 — growth and advantages of groundwater runoff from the area with low GWT, reduction to the long-term minimum of groundwater runoff in the area with high GWT (0.8-2.5 m); III. From 1999 to 2014 — the predominant dominance of winter runoff over spring, slow growth of groundwater runoff in a limited area of the catchment with levels of 0.8-2.5 m; high-amplitude fluctuations of runoff and GWT with the achievement of long-term maximums in the area with GWT = 2.5-4.0 m; IV. 2015-2019 — the most intense reduction of GWT, and in the upper reaches of small rivers — of underground runoff to rivers.There is a progressive decrease in the specific flow of groundwater to rivers, and consequently of their resources — primarily for the aquifers in the upper reaches of rivers with GWT 0.5-1.5 m with no pressure recharge. Aquifers of ground water fed by confined aquifers (mainly within floodplains and the first low terraces of rivers) in the studied area of the Ukrainian massif of fracture waters have greater stability of the level regime on the background of rising temperatures and decreasing precipitation (recorded by 2020) than shallow water (0.5-2.0 m) without signs of such recharge.

Method to identify composition and production phases of spring runoff in high-latitude mid-temperate regions: a case study in the Second Songhua River Basin, China

Simulation and forecasting of runoff play an important role in the early warning and prevention of drought and flood disasters. To improve the accuracy of spring runoff simulations, it is important to identify spring runoff production patterns under the combined effect of snow and frozen soil. Based on the theory of the hydrological cycle, three important parameters, which include surface and subsurface runoff, precipitation and temperature, were selected for this study. The trend analysis, statistical analysis and Eckhardt's recursive numerical filtering method were used to qualitatively identify the production patterns of spring runoff, the start and end dates and stage periods of the production patterns. Based on the qualitative identification results, the contribution of each production runoff to the total annual runoff and the total annual spring runoff is quantitatively assessed. The results of the study show that the spring runoff production patterns in the Second Songhua River Basin can be divided into snowmelt runoff, frozen soil conditions of snowmelt–rainfall runoff and rainfall runoff under frozen soil conditions; the snowmelt production is from 21 March, the frozen soil conditions production is from 21 April and the frozen soil ablation ended on 15 June; the shortest phases of each production pattern last 28, 20 and 18 days and the longest last 31, 26 and 24 days. This research provides the basis for improving the principles of production runoff calculation in spring runoff simulation methods.

Hydrological Similarity-Based Parameter Regionalization under Different Climate and Underlying Surfaces in Ungauged Basins

Hydrological similarity-based parameter regionalization is the dominant method used for runoff prediction in ungauged basin. However, the application of this approach depends on assessing hydrological similarity between basins. This study used data for runoff, climate, and the underlying surface of the Hulan River Basin and Poyang Lake Basin to construct a novel physical hydrological similarity index (HSI). The index was used to compare the efficiency of transfer of the parameters of commonly used regionalization methods and to finally apply parameters to ungauged basins. The results showed that: (1) Precipitation is the main climatic factor regulating magnitude of runoff in the Poyang Lake Basin. Spring runoff in Hulan River Basin was regulated by precipitation and temperature. (2) The GR4J and CemaNeigeGR4J models achieved reasonable simulations of runoff of Poyang Lake Basin and Hulan River Basin. Although CemaNeigeGR4J considers snowmelt, the model simulations of spring runoff in the Hulan River Basin were not accurate. (3) There was a significant correlation between climate, the underlying surface, and hydrological model parameters. There were fewer significant correlations between environmental factors and between environmental factors and hydrological model parameters in the Hulan River Basin compared to those in the Poyang Lake Basin, possibly due to less sub-basins in the Hulan River Basin. (4) The HSI based on a combination of principal component analysis and the entropy method efficiently identified the most similar gauged basin for an ungauged basin. A significant positive correlation existed between the HSI and parameter transfer efficiency. The relationship between the HSI and transfer efficiency could be represented by logistic regression and linear regression in the Poyang Lake Basin and Hulan River Basin, respectively. The HSI was better able to quantify the hydrological similarity between basins in terms of climate and underlying surface and can provide a scientific reference for the transfer of hydrological model parameters in an ungauged basin.

STUDY OF CONDITIONS OF GULLY FORMATION IN MOUNTAIN REGIONS OF SOUTH-EAST KAZAKHSTAN WITH USE OF GIS-TECHNOLOGIES

In the article the results of field and laboratory researches of gully erosion in the mountains of Zhetysu Alatau of south-east Kazakhstan are considered. Mountain ridge Malaisary was chosen for study of gully erosion. Malaisary ridge is the western ridge of Zhetysu Alatau mountains in the south-east Kazakhstan. Foothills and plain territories of southeast Kazakhstan are characterized by favorable conditions for the development of erosion processes. There was conducted stationary monitoring (yearly in October from 2013 to 2018) of gully erosion development on the Malaisary ridge from 2013 to 2018. Most of gullies of studied ridge show development in the top part and extend in the width mainly due to fluvial processes. There were studied the natural-anthropogenic factors influencing development of gully erosion; the morphometric characteristic received using the modern devices and satellite images are provided. The determined factors of development of gullies on Malaisary ridge are mechanical substratum composition, atmospheric precipitation (spring runoff, summer rainfalls), steepness and length of the slopes. The received materials allow concluding that gully erosion is the most active factor of the ridge relief transformation. Intensive gully erosion development increases ecological tension of natural-anthropogenic environment in the region. Growth of gully net and its active development deteriorates quality of agricultural lands and create threat to road objects and residential area infrastructure in the region.