An integrated multi-level watershed-reservoir modeling system for examining hydrological and biogeochemical processes in small prairie watersheds

Eutrophication of small prairie reservoirs presents a major challenge in water quality management and has led to a need for predictive water quality modeling. Studies are lacking in effectively integrating watershed models and reservoir models to explore nutrient dynamics and eutrophication pattern. A water quality model specific to small prairie water bodies is also desired in order to highlight key biogeochemical processes with an acceptable degree of parameterization. This study presents a Multi-level Watershed-Reservoir Modeling System (MWRMS) to simulate hydrological and biogeochemical processes in small prairie watersheds. It integrated a watershed model, a hydrodynamic model and an eutrophication model into a flexible modeling framework. It can comprehensively describe hydrological and biogeochemical processes across different spatial scales and effectively deal with the special drainage structure of small prairie watersheds. As a key component of MWRMS, a three-dimensional Willows Reservoir Eutrophication Model (WREM) is developed to addresses essential biogeochemical processes in prairie reservoirs and to generate 3D distributions of various water quality constituents; with a modest degree of parameterization, WREM is able to meet the limit of data availability that often confronts the modeling practices in small watersheds. MWRMS was applied to the Assiniboia Watershed in southern Saskatchewan, Canada. Extensive efforts of field work and lab analysis were undertaken to support model calibration and validation. MWRMS demonstrated its ability to reproduce the observed watershed water yield, reservoir water levels and temperatures, and concentrations of several water constituents. Results showed that the aquatic systems in the Assiniboia Watershed were nitrogen-limited and sediment flux played a crucial role in reservoir nutrient budget and dynamics. MWRMS can provide a broad context of decision support for water resources management and water quality protection in the prairie region.     

Factors affecting the export of nitrate-nitrogen from drainage basins in southern Ontario

The export of nitrate-N from 21 watersheds near Toronto, Ontario was measured over a 25-month period. The annual average loss ranges from 1.41 to 7.31 kg ha⁻¹. Analysis of these data indicated a very significant correlation between nitrate exports and percentage of each watershed in crops and abandoned agricultural land. A number of soil and topographic variables also had significant correlations with stream nitrate levels. The causal relationships underlying these simple correlations are difficult to evaluate because of considerable multicollinearity between land use and watershed physiography. The separate analysis of stream discharge indicated that agricultural watersheds have lower mean annual discharges (1 s⁻¹ km⁻²) than those watersheds containing extensive areas of forest and abandoned agricultural land. Variations in annual discharge therefore tended to reduce the contrast in nitrate exports between agricultural and non-agricultural watersheds. The influence of watershed characteristics on nitrate levels exhibited considerable seasonal contrasts. During summer low flow conditions nitrate concentration and loss were not correlated with watershed land use, and instead were affected primarily by localised pollution sources and by biological processes within the streams.     

Long-term sodium and chloride surface water exports from the Dallas/Fort Worth region

Sodium and chloride in surface water are typically related to urbanization and population density and can have a significant impact on drinking water sources and the subsequent salinity of aquatic ecosystems. While the majority of research has focused on the impact of deicing salts on urban surface waters in colder climates, the effect of urbanization on sodium and chloride concentrations has been found to occur in warmer climates. This study investigated long-term exports of sodium and chloride from watersheds with increasing urbanization in the humid subtropical Dallas-Fort Worth region. We compared exports to characteristics of urbanization: urban land cover, impervious surface area, and calculated contributions from wastewater discharges. Long-term data (1980-2008) were obtained from five USGS gages located in and around the cities. Exports were calculated by regression analysis between concentrations and discharge and normalized for time and the watershed area. Grab samples were collected from June 2009 to May 2010 and sodium and chloride concentrations quantified. Our results show a strong positive relationship between the mean annual sodium and chloride exports from each watershed and the percent urban land cover and impervious surface area. Long-term increases in sodium and chloride fluxes were found for the three watersheds with the highest percentage of urban land cover. The single largest contributor was wastewater effluent that was estimated to contribute approximately half of the total loads in the three urbanized watersheds. Atmospheric deposition and deicing salts accounted for small amounts of the total export for urbanized watersheds. The source of the remaining salt load is still unknown and may be a combination of non-point sources. Estimates of urban salt exports were similar to estimates from northern watersheds affected by deicing salts.     

Buffer zone versus whole catchment approaches to studying land use impact on river water quality

Secondary databases, GIS and multivariate analysis tools were used to determine whether there was a correlation between water quality and landscape characteristics within three local southern Ontario watersheds. Whole catchment and 100 m buffer zone influences on water quality over three seasons were compared. Chemical fluxes were also calculated and used to compare the loading of pollutants to downstream environments. Urban land use had the greatest influence on water quality. The influence of agricultural land use was variable and did not agree with the results of other studies. The only natural landscape variables that appeared to have an influence on water quality were slope and silt-clay surficial geology deposit. There was a clear trend of increased chemical fluxes with increasing urban land use intensity within a watershed. Forested land use appeared important in mitigating water quality degradation. The catchment landscape characteristics appeared to have slightly greater influence on water quality than the 100 m buffer. The results of this study may have been influenced by the scale and accuracy of databases used. The secondary data were useful in determining major trends in water quality and possible non-point origins of surface water pollution, and in identifying areas that are in need of further investigation.     

Impacts of climate and land‐cover changes on water resources in a humid subtropical watershed: a case study from East Texas,USA

This study investigates the response of water resources regarding the climate and land‐cover changes in a humid subtropical watershed during the period 1970–2009. A 0.7°C increase in temperature and a 16.3% increase in precipitation were observed. Temperature had a lower increase trend, and precipitation showed definite increasing trend compared to previous studies. The main trend of land‐cover change was conversion of vegetation and barren lands to developed and crop lands affected by human intervention, and forest and grass to bush/shrub which considered to be caused by natural climate system. Hydrologic responses to climate and land‐cover changes resulted in increases of surface run‐off (15.0%), soil water content (2.7%), evapotranspiration (20.1%) and a decrease in groundwater discharge (9.2%). We found that surface run‐off is relatively stable with precipitation, whereas groundwater discharge and soil water content are sensitive to changes in land cover, especially land cover brought about by human intervention.     

Nonpoint source pollution: a distributed water quality modeling approach

A distributed water quality model for nonpoint source pollution modeling in agricultural watersheds is described in this paper. A water quality component was developed for WATFLOOD (a flood forecast hydrological model) to deal with sediment and nutrient transport. The model uses a distributed group response unit approach for water quantity and quality modeling. Runoff, sediment yield and soluble nutrient concentrations are calculated separately for each land cover class, weighted by area and then routed downstream. With data extracted using Geographical Information Systems (GIS) technology for a local watershed, the model is calibrated for the hydrologic response and validated for the water quality component. The transferability of model parameters to other watersheds, especially those in remote areas without enough data for calibration, is a major problem in diffuse modeling. With the connection to GIS and the group response unit approach used in this paper, model portability increases substantially, which will improve nonpoint source modeling at the watershed-scale level.     

Relationship between small dam efficiency and gully erodibility of the lithologic formations covering their watershed

Soil conservation strategy in the semi-arid areas of central Tunisia has focused on the construction of numerous hill reservoirs. However, limited rainfall combined with severe soil erosion is jeopardizing the usefulness of hill reservoirs such that there is an urgent need to undertake further studies into the location and efficiency of small dams. The paper reports investigations into the relationship between location of the dam and the underlying lithology of the catchment areas with the dam efficiency. A gully erodibility factor has been proposed for nine groups of lithological formations identified and a watershed lithologic number was computed as the product of seven watersheds for which 1:50,000 scale lithological maps were available. A significant linear relationship was determined between the watershed lithologic number and the efficiency of the small dams, indicating that an accurate lithological survey prior to small dam planning can be used to indicate the dam's likely efficiency and to plan any necessary soil and water conservation works in the catchment areas.     

The ecosystem‐watershed concept in the environmental sciences — a review

The ecosystem‐watershed concept, which originated with the Hubbard Brook Watershed Ecosystem study, provides an important framework for research into contemporary processes in many environments. Integration of freshwater lakes into the basic model allows such studies to be extended back in time, and the typicality of present‐day landscapes and processes to be adjudged. In many ecosystem‐watersheds, inputs, outputs and processes are dominated by cultural factors. Many effects of Man upon environmental systems are thus transmitted and expressed via the material pathways of ecosystem‐watersheds. The ecosystem‐watershed concept is thus uniquely suited to integrative and interdisciplinary analysis of many environmental problems.     

Weathering and erosion fluxes of arsenic in watershed mass budgets

Arsenic in natural waters and in soils represents a serious health hazard. Natural sources of this element in soil are the subject of this communication. Weathering mass balance of As and rates of weathering in soils are evaluated from monitored inputs and outputs in two small watersheds. These watersheds are located within the Celina-Mokrsko gold district, Czech Republic. Annual chemical weathering fluxes of As are calculated from the monthly weighted means of stream water and groundwater. The fluxes are corrected for atmospheric precipitation, agrochemical inputs, and biological uptake. Mechanical and chemical weathering rates of the arsenopyrite-bearing rocks in the watersheds were estimated from mass balance data on sodium and silica. The input of As due to total weathering of bedrock was estimated to be 1369 g ha(-1)yr(-1) in the Mokrsko watershed (MW) and 81 g ha(-1)yr(-1) in the Celina watershed (CW). These results indicate that the annual weathering rate of As in the watersheds represents more than 95% of the total As input to the soil. Accumulation rate of As in the soil was estimated at 311 g ha(-1)yr(-1) in MW and 69 g ha(-1)yr(-1) in CW. The mass balance method for calculation of weathering rate of As was used, and the results suggest that weathering could be the most important process in the As biogeochemistry of the areas with elevated As content in the bedrock. Simple model of weathering and erosion can be used successfully in estimating their role in As pollution on the scale of small watershed. The method is also useful for indicating the mass balance of As in soils that is controlled by both the natural and anthropogenic inputs and outputs of As.     

Relationship between dissolved organic and inorganic compounds in tributaries of the Lake Baikal

It was shown that the balance between organic and inorganic compounds is mostly conditioned by watershed size and relief, rather than chemistry. The rise and fall of dissolved organic carbon concentration are irreversely proportional to those of acid neutralizing capacity and follow the changes in water flowpaths. This relationship was used to distinguish between dissolved matter sources, and to characterize quantitatively and qualitatively their contribution to surface water chemistry. The proposed approach has restricted applicability to the watersheds composed of sedimentary materials and to the watersheds with high percentage of wetlands. The applicability of the approach is also limited to a variety of environmental conditions. Big watersheds should be divided into lower order subcatchments to reduce uncertainty in interpretation of results. In small and medium watersheds, the proposed approach can be used for predicting water chemistry under different environmental conditions and for tracing contaminants.     

Impact of fertilizer on a small watershed of Lake Biwa: use of sulfur and strontium isotopes in environmental diagnosis

Sulfur and strontium isotopes (delta(34)S and (87)Sr/(86)Sr) were determined in 39 river water samples collected over three different cultivation periods (April, May, and June), and in several materials used for comparison (fertilizers, detergents, soils, irrigation and agricultural waters), to evaluate the impact of fertilizers on a small agricultural watershed of Lake Biwa, in central Japan. delta(34)S values in river water decreased (from +5.8 to -2.0 per thousand) with increasing SO(4) concentrations (3.8 to 93.2 ppm) from upstream to downstream of the watershed. Comparison of river water S isotopes with those of possible source materials indicates that the enrichment of SO(4) can be attributed to the dissolution of two kinds of fertilizers: (1) compound fertilizers commonly used in this area and (2) ammonium sulfate which is applied on a small scale. In contrast, (87)Sr/(86)Sr values of river water decreased with time from April (avg. 0.71163), through May (avg. 0.71139), to June (avg. 0.71127). The tendency of the sample plots on the (87)Sr/(86)Sr vs. 1/Sr diagram suggests a time-dependent increase in the contribution of soil water to the river, which is partly affected by the Sr-bearing fertilizers. It is suggested that a maximum of 25% of dissolved Sr is derived from these fertilizers, while more than 75% of it is of rock origin. Mass balance calculations permitted us to evaluate the proportion of fertilizer contribution in each river. Combined use of S and Sr isotopes together with concentration data could be a new environmental diagnosis technique for rivers and soils in localized watersheds.     

SENEQUE: a multi-scaling GIS interface to the Riverstrahler model of the biogeochemical functioning of river systems

The Riverstrahler model describes the biogeochemical functioning of an entire river system, from 100 to 100,000 km(2) or more, taking into account the constraints set by the morphology of the drainage network, the meteorological/hydrological conditions, and the inputs of material from point and non-point sources in the watershed. This tool has been applied for research purpose to several river systems differing in terms of hydrological regime and anthropogenic influences. In order to improve its capabilities and its generic dimension, as well as to develop a user-friendly interface allowing its transfer to non-specialist users including managers, the model has been coupled to a GIS interface. This gives the user the possibility to visualize the available geospatial database, to select the best geographical representation of the drainage network, to automatically prepare the corresponding input files required for the model, to pilot the model calculation and to visualize the results. The coupling with a GIS interface has considerably improved the capabilities of the Riverstrahler model. The code of the model is now entirely generic and can be run on any river system for which a suitable database is available. Its spatial resolution can be adapted to the requirement of the relevant problem, from the highest level, where each elementary watershed is individualized, to the lower level, where the whole basin is idealized as one basin with tributaries of each order having the same characteristics. As an illustration of the new potentialities offered by the coupling of Riverstrahler with a GIS through the SENEQUE interface, the results of a same modeling scenario are compared at different spatial resolutions. For the first time, with on-line coupling to a geodatabase, the effect of increasing the spatial resolution of the drainage network representation on the performance of the Riverstrahler model has been examined. At the outlet of the basin, the water quality results were found invariant to a large degree, whatever the details of its representation in the calculations. This result justifies the use of a low resolution representation of the upstream watershed when results are required only at the outlet of the basin.     

Timing of organic carbon release from mountain pine beetle impacted ponderosa pine forests in South Dakota

The decay of mountain pine beetle (MPB) (Dendroctonus ponderosae) affected ponderosa pine (Pinus ponderosa) forests has increased organic carbon (OC) loading within the Rapid Creek watershed in the Black Hills of South Dakota, with total OC (TOC) concentrations up to 6.2 mg L^?1 observed in 2015. The impacts of large‐scale tree mortality on water quality were delayed. OC concentrations in the watershed correlated with recent MPB impact stage progression. Regional ponderosa pine forests that were 3 and 6 years after MPB infection (grey and snagfall phases) exhibited increased OC loading within the Rapid Creek watershed. A better understanding of regional watershed response patterns for MPB tree mortality may assist with mitigating ancillary water quality impacts.     

大型露天矿山边坡岩体稳定性分级分析方法

基于大型露天矿山边坡的构成要素与规模大小,将其划分为总体边坡、组合台阶边坡、台阶边坡3个层次;根据结构面规模与各层次边坡规模的几何关系,将结构面划分为贯穿结构面、非贯穿结构面、小规模结构面3个层次。从岩体结构控制论角度,认为不同空间位置、不同规模结构面对不同层次边坡的岩体稳定性影响存在差异性,提出结构面空间位置与边坡部位相匹配、结构面规模与边坡规模相匹配开展大型露天矿山边坡岩体稳定性分级分析的新思路。重点介绍大型露天矿山边坡岩体工程稳定性分级分析方法,按照结构面空间位置与边坡部位的匹配性、结构面规模与边坡规模的匹配性,依次对露天矿山的总体边坡、组合台阶边坡、台阶边坡进行分层次的岩体稳定性分析,系统全面地找出控制边坡稳定的关键性结构面及其组合,实现露天矿山边坡岩体稳定性的精细分析。结合具体案例,分别从整体稳定性、局部稳定性两方面评价了露天矿山的总体边坡、组合台阶边坡、台阶边坡的稳定性。大型露天矿山边坡岩体工程稳定性分级分析为开展边坡岩体稳定性的精确计算创造了必要的条件。     

THOUGHTS ON ECOLOGICAL WATERSHED PLANNING UNDER THE TERRITORIAL SPATIAL PLANNING

The author firstly points out several problems that commonly exist in China’s watersheds and the urgent need for multidisciplinary collaboration in ecological planning. The theories and practices on watershed ecological planning are reviewed respectively from the aspects of waterway planning, natural river and wetland protection, ecological baseflow recovery, nonpoint source pollution reduction, and biodiversity protection. The author suggests that if we could reserve multi-functional ecological zone in the new territorial spatial planning by multidisciplinary collaboration, ecological goals including flood control, water quality improvement, ecological base flow provision, and biodiversity protection could be achieved. In this comprehensive solution, only when water bodies and associated habitats such as the ground and underground, upstream and downstream, and rivers and banks are coordinated as a whole, it will generate multiple ecological benefits. Finally, the author believes that planners and designers have the ability to solve ecological problems. To fulfill this vision, we must call for collaboration between land planning and ecological watershed planning in the process of territorial spatial planning.     

Estimation of monthly diffuse nutrient loads for a watershed in Turkey

Diffuse pollution has a complex nature depending on various land‐use activities like agriculture, livestock breeding and forestry. In this study, an alternative methodology is applied for decreasing the spatial uncertainty of diffuse nutrient load estimations. It is applied in the Melen Watershed, Turkey, which is an important watershed from where additional water will be supplied for the megacity Istanbul via interbasin water transfer. Monthly diffuse nutrient loads were estimated for each subwatershed by utilizing remote sensing (RS) and geographical information systems (GIS). Estimated nutrient loads were considerably different in various months due to the temporally irregular fertilizer application and meteorological conditions. Temporal differences were also predicted in the spatial distribution of the nutrient loads. The methodology is applicable in watershed protection studies, especially where necessary etudes should be conducted in the short term and with limited data. Such efforts in identifying and determining the diffuse loads are important for sustainable management of the watershed.     

Adaptation of the Natural Resources Conservation Service (NRCS) curve number (CN) model in estimating direct run‐off from humid tropical forest catchments

Suitability of the Natural Resources Conservation Service (NRCS) curve number (CN) model of run‐off prediction was evaluated on three humid tropical forested catchments in Kimakia, Kenya. The catchments were dominated by Pinus patula (catchment A), Arundinaria alpina (catchment C) and Pennisetum clandestinum (catchment M). The study used discharge and rainfall data collected between 1958 and 1986. Seventy‐three (73) isolated storms were graphically separated into baseflow, interflow and surface run‐off. Forest cover types significantly improved catchments characteristics that influence baseflow and interflow generation in catchment C but not those that influence surface run‐off production. In its original form, the NRCS CN model resulted in direct run‐off estimates that deviated from observed ones by between 43.8% and 55.3%. These discrepancies were minimized through modification of the β and CN parameters. CN generated empirically using storm rainfall predicted the direct run‐off satisfactorily. Therefore, the modified NRCS CN model adequately estimates direct run‐off from humid tropical forested catchments.     

非平稳随机场下饱和渗透系数空间变异性的无限长边坡稳定概率分析

土体饱和渗透系数表现为天然的空间强变异性,其均值通常沿土层深度方向呈递减趋势,但目前鲜有文献考虑这一特性。为此,以FLAC为平台,利用fish语言基于局部平均法建立了表征土体饱和渗透系数均值随深度递减的一维非平稳随机场模型,采用FLAC两相流模块模拟雨水的入渗过程,以蒙特卡罗法为框架,结合考虑正孔隙水压力的广义有效应力无限边坡稳定模型,探讨了饱和渗透系数空间变异性在不同降雨时刻下对边坡最危险滑裂面分布规律以及相应的边坡破坏概率的影响。结果表明：忽略饱和渗透系数的空间变异性的确定分析方法将不能真实反映边坡的安全性;随着降雨持时的增加,边坡最危险滑裂面发生在坡底基岩处的概率逐渐降低;随着饱和渗透系数竖向相关距离的增加,边坡最危险滑裂面发生在坡底的概率逐渐增加,而相应的边坡破坏概率却随竖向相关距离的增加而逐渐降低。     

Spatial and inter-annual variability of specific sediment yield: case of hillside reservoirs in Central Tunisia

Water erosion is the major process responsible for soil loss in Central Tunisia. It represents a main risk of sedimentation which threatens the lifetime of water and soil conservation works in the region, such as hillside reservoirs. This paper focuses on the study of spatial and inter-annual variability of specific sediment yield (SSY) estimated from sediment yield (SY) of 23 small watersheds of hill reservoirs located in the Tunisian Dorsal and the Cap Bon regions. The calculated values of mean inter-annual specific sediment yield varied from 180 to 3298 t/km²/year, over a period of 12 years (from 1994 to 2006). The selected catchments were classified into three groups according to their SSY data. The SSY map, elaborated with a geographical information system (GIS), showed an important spatial variability between watersheds of the same group. Moreover, analyses of the coefficient of variation (CV) showed that 70% of the considered sites demonstrate a tendency to moderate and high inter-annual variability of SSY. In order to identify the principal factors governing variability of erosion and sedimentation, a multiple regression analysis was carried out using nine parameters characterizing morphology, topography, land cover, climate and protection works of the 23 considered sites. The generated model revealed that 85% of SSY variability is correlated to seven principal factors, which are drainage area (A), rainfall intensity recorded in 30 min (I ₃₀), percentage of water and soil conservation works, percentage of clay and carbonate in soils, vegetation land cover, overall slope index (I _G) and rainfall amount (R _a). The obtained SSY results were compared to others cited in a large bibliographical synthesis of studies carried out at the planet scale. We deduced that the SSY values obtained in this study are among the relatively high series in the world. The high variability of specific erosion rates in Central Tunisia is believed to be related to the semi-arid climate, characterized by the irregularity and the severity of storms and the spatial and temporal variability of other multiple factors affecting erosion processes.