International Journal of Environmental Science and Technology
Many urban water bodies in Chennai, India receive untreated sewage that pollutes their waters. An... more Many urban water bodies in Chennai, India receive untreated sewage that pollutes their waters. An example is the Sembakkam lake, in which water reaches the Pallikaranai marshland, a proposed Ramsar site. In 2019, the city experienced the worst water crisis in 30 years, and many lakes were extremely dry, favoring peaks of heavy metals. Therefore, this study focuses on analysing heavy metal pollution and evaluating its potential effects on biota. In situ parameters were measured and water, sediment, and water hyacinth samples were collected during four campaigns. Al, As, Cr, Cu, Fe, Mn, Ni, Pb, and Zn were measured in all samples. Digestions for total metal content were performed in solid samples and acetic acid extractions only in sediments. The average pH (7.89–8.46) was neutral-alkaline and electrical conductivities (1559–2864 µS/cm) were high. In water, Pb (average: 2.59 µg/l) posed the highest toxicity risk according to the United Nations Economic Commission for Europe, followed ...
Distribution and Risk Assessment of Trace Elements in Sediment Cores from a Coastal Watershed: An Example from the Lian River, South China
19th Annual Meeting of the Asia Oceania Geosciences Society
Developing an improved user interface for a physically-based stream solute transport model
Environmental Modelling & Software, 2020
Abstract There is a growing need to address water pollution that demands advanced tools to predic... more Abstract There is a growing need to address water pollution that demands advanced tools to predict the fate and transport of water quality constituents. Existing stream solute transport models use simple first-order kinetics to evaluate nutrient loss, however these ignore biochemical reactions and lack a user-friendly interface. To address this shortcoming, we integrated the One-dimensional Transport with Inflow and Storage (OTIS) model and the Enhanced Stream Water Quality Model (QUAL2E) and developed an improved interface for a physically-based solute transport model. With background algal concentration as the only calibration parameter, a generalized model was developed and evaluated. The new model performed reasonably well in predicting nutrient uptake of newly collected experimental data and published data from 32 other datasets (R2 = 0.76, NSE = 0.47 and Percent Bias = −4.3%). Inclusion of biochemical reactions from QUAL2E improves model confidence and provides options for incorporating actual process-based data which is unfeasible in existing first-order decay-based models.
Transient storage models in combination with tracer tests are widely used to study solute transpo... more Transient storage models in combination with tracer tests are widely used to study solute transport dynamics in streams. Storage parameters included in such models are typically calibrated for one or more study reaches by monitoring solute concentrations and fitting breakthrough curve data. Since stream characteristics vary spatially and temporally, it is challenging to generalize these calibrated parameters for another stream reach. This study investigates the ability of simple regression models to predict transient storage parameters such as dispersion coefficient (D), transient storage area (A s) and storage exchange coefficient (). A meta-analysis of 834 tracer studies from 67 published papers was used to develop parsimonious non-linear regression models that relate storage parameters to easily available stream parameters such as discharge, velocity, flow width and flow depth. Correlation analysis showed moderate correlation of D with velocity, depth and width; and high correlation of A s with the ratio of discharge to depth. Exchange coefficient () did not show significant correlation with available stream parameters. The models were tested using a subset of meta-analysis data and experimental tracer data from Hubbard Brook Experimental Forest located in the US and Kielstau Catchment located in Germany. We predicted storage and breakthrough curves with reasonable accuracy (R 2 > 0.5) by using new regression equations and incorporating it into an advection-dispersion-storage model. These equations provide a viable alternative to approximate transient storage parameters in circumstances where time and cost-intensive reachspecific calibration is impossible. Therefore, such regression-based estimates of storage parameters can also form an integral part of larger watershed scale models by predicting solute transport and storage in stream reaches.
Understanding the connections between climate, anthropogenic impacts, and hydrology is fundamenta... more Understanding the connections between climate, anthropogenic impacts, and hydrology is fundamental for assessing future climate change. However, a comprehensive methodology is lacking to understand significant changes in the discharge regime and their causes. We propose an approach that links change point tests with hydrologic metrics applied to two Vietnamese catchments where both climatic and anthropogenic changes are observed. The change points in discharge series are revealed by six widely used change point tests. Then, 171 hydrologic metrics are investigated to evaluate all possible hydrological changes that occurred between the pre- and post-change point period. The tests showed sufficient capabilities to detect hydrological changes caused by precipitation alterations and damming. Linking the change point tests to the hydrological metrics had three benefits: (1) the significance of each detected change point was evaluated, (2) we found which test responds to which hydrologic m...
Application of the SWAT model for ecohydrological modelling in Germany
Soil hydrology, land use and agriculture: measurement and modelling
This chapter gives an overview of the application of SWAT for ecohydrological modelling in German... more This chapter gives an overview of the application of SWAT for ecohydrological modelling in Germany. Because of its importance related to the application of Soil and Water Assessment Tool (SWAT) in Europe and Germany, the next section gives an overview on the WFD programme, followed by the introduction of the SWAT model. After an overview of studies on the simulation of land management and tillage on hydrology and river water quality, the following section describes the results and challenges of model-based scenario simulations for river basin management. The two studies that are presented were carried out within the context of the WFD: one is a 3500 km2 agricultural river basin known as the Upper Ems River Basin; the other is a 50 km2 lowland catchment in northern Germany (Kielstau catchment). The following section includes supporting studies in which the work on sensitivity analyses of management parameters in SWAT and on the impact of water quality monitoring strategies and load-e...
Current capabilities and research opportunities in applied watershed modeling
Spatial factors can play important and potentially confounding roles governing the presence, the ... more Spatial factors can play important and potentially confounding roles governing the presence, the absence, and the abundance of the diatom species and consequently influence the diatom-based bioassessment. To examine how spatial factors affect diatom community and biomonitoring, diatom community was sampled in three catchments with similar river length and watershed area across a large spatial scale along the Yangtze River, China. Redundancy analysis (RDA) showed that patterns of diatom distribution could be attributed not only to environmental variables (e.g., NO 3-N, TN, WT, and COD), but also to spatial factors (e.g., elevation, latitude, and longitude). Partial RDAs partitioned the total variance of diatom data explained (64.7%) into three parts: pure spatial variables contributed the highest proportion (19.8%), followed by pure environmental variables (5.4%), and the shared effects by environmental and spatial sets explained a large proportion of diatom variance (39.5%). Recognizing the potential influences of spatial factors, further accumulations of diatom data within different regions would allow for the development of better diatom-based monitoring methods for watershed diagnosis and management.
The ecological effects of small run-of-river dams on aquatic ecosystems are poorly understood, es... more The ecological effects of small run-of-river dams on aquatic ecosystems are poorly understood, especially on downstream benthic algal communities. We examined impacts of such dams on the benthic diatom community at a regional scale in the Xiangxi River, China. A total of 90 sites were visited, which were divided into five habitats (H1-H5) according to impact extent of each dam. Using partial least squares (PLS) modeling, we developed two predictive models (diatom species richness and total diatom density) based on environmental variables of an unregulated habitat (H1). These models were then used to predict species richness and total densities at impacted habitats (H2-H5) and residuals, i.e. the differences between observed and predicted values, were used to evaluate impact strength of flow regulation. Significant impacts of flow regulation on diatom species richness were detected at three impacted habitats (H3-H5), where observed species richness were significantly higher-70.6, 63.9 and 46.6%, respectively-than predicted values. Then, possible mechanisms for observed impacts were discussed. Further research is necessary to address the potential negative impacts of cascade run-of-river dams on other aquatic organisms in different seasons, and to explore more appropriate mechanisms for such impacts, which may lead to sustainable management strategies and help to determine the optimal ecological water requirement for the Xiangxi River.
The SRTM DEM, a digital elevation model based on the Shuttle Radar Topography Mission of February... more The SRTM DEM, a digital elevation model based on the Shuttle Radar Topography Mission of February 2000 is a source of elevation data with nearly worldwide coverage. It has proven its usefulness in various regions but problems persist for densely vegetated areas where, caused by the organic matter and water content of the vegetation, the radar signal is reflected at some level between the vegetation canopy and the ground level. This level varies with different types and densities of vegetation cover and has so far not been assessed for papyrus areas. The paper describes the approach and establishment of a correction factor for a pilot area in the Sudd swamps of southern Sudan based on comparison of SRTM reference levels and ground control points collected during field surveys between 2004 and 2006. Results show a correction factor between the sensed and the real surface of 4.66 m and a average penetration depth of the radar signal into the dense papyrus vegetation of 0.34 m.
Hydrologic models of watersheds often represent complex systems which are difficult to understand... more Hydrologic models of watersheds often represent complex systems which are difficult to understand regarding to their structure and dynamics. Virtual watersheds, i.e. watersheds which exist only in the virtual reality of a computer system, are an approach to simplify access to this real-world complexity. In this study we present the virtual watershed KIELSHED-1, a 117 km 2 v-shaped valley with grassland on a "Cambisol" soil type. Two weather scenarios are delivered with the watershed: a simplified artificial weather scenario based on long-term data of a German weather station as well as an unmodified data record. The input data and parameters are compiled according to the conventions of the SWAT 2000 hydrological model. KIELSHED-1 is mainly used for education, and illustrative application examples, i.e. calculation of water balance, model calibration, development of land use scenarios, give an insight to the capabilities of the virtual watershed.
Hydrological modeling poses a particular challenge in data scarce regions, which are often subjec... more Hydrological modeling poses a particular challenge in data scarce regions, which are often subject to dynamic change and thus of specific interest to hydrological modeling studies. When a small amount of data available for a catchment is opposed by extensive data requirements by the chosen hydrologic model, ways have to be found to extract as much information from the available data as possible. In a study conducted in the Xiangxi Catchment in the Three Gorges Region in China, the use of residual analysis as well as auto-and cross-correlations for enhanced model evaluation and for the identification of key processes governing the hydrological behavior of the catchment prior to model calibration was tested. The residuals were plotted versus various variables such as time, discharge and precipitation. Also, auto-correlations were calculated for measured and simulated discharge and cross-correlations of measured and simulated discharge with precipitation were analyzed. Results show that the analysis of residuals as well as auto-and cross-correlations can provide valuable information about the catchment response to rainfall events, which can be very helpful for calibration of hydrologic models in data scarce regions.
Hydrologic comparison between a lowland catchment (Kielstau, Germany) and a mountainous catchment... more Hydrologic comparison between a lowland catchment (Kielstau, Germany) and a mountainous catchment (XitaoXi, China) using
The KIDS model (Kielstau Discharge Simulation model) is a simple rainfall-runoff model developed ... more The KIDS model (Kielstau Discharge Simulation model) is a simple rainfall-runoff model developed originally for the Kielstau catchment. To extend its range of application we applied it to a completely different catchment, the XitaoXi catchment in China. Kielstau is a small (51 km 2) lowland basin in Northern Germany, with large proportion of wetland area. And XitaoXi is a mesoscale (2271 km 2) mountainous basin in the south of China. Both catchments differ greatly in size, topography, landuse, soil properties, and weather conditions. We compared two catchments in these features and stress on the analysis how the specific catchment characteristics could guide the adaptation of KIDS model and the parameter estimation for streamflow simulation. The Nash and Sutcliffe coefficient was 0.73 for Kielstau and 0.65 for XitaoXi. The results suggest that the application of KIDS model may require adjustments according to the specific physical background of the study basin.
The Ethiopian government has selected Lake Tana basin as a development corridor due to its water ... more The Ethiopian government has selected Lake Tana basin as a development corridor due to its water resources potential. However, combined use of groundwater (GW) and surface water (SW) is still inadequate due to knowledge gaps about the flow dynamics of GW and SW. Mostly, there is no information about groundwater use. Therefore, this study aims to investigate the dynamics of GW-SW interactions on a spatio-temporal basis in three of the main catchments (Gilgelabay, Gumara and Ribb) that drain into Lake Tana. To this end, the SWAT-MODFLOW model, which is an integration of SWAT (Soil and Water assessment Tool) and MODFLOW, is used. The results reveal strong hydraulic connection between the GW and SW in all the three catchments. In the Gilgelabay catchment, the flow from the aquifer to the river reaches dominates (annual discharge from the aquifer varies from 170 to 525,000 m3/day), whereas in Gumara (annual exchange rate between −6,530 and 1,710 m3/day) and Ribb (annual exchange rate bet...
Journal of Hydrology and Hydromechanics, Jun 1, 2019
There is an emerging challenge within water resources on how, and to what extent, borrowing conce... more There is an emerging challenge within water resources on how, and to what extent, borrowing concepts from landscape ecology might help redefine traditional concepts in hydrology in a more tangible manner. A stepwise regression model was adopted in this study to assess whether the time of concentration of catchments could be explained by five landscape structure-representing metrics for land use/land cover, soil and geological patches, using spatial data from 39 catchments. The models suggested that the times of concentration of the catchments could be predicted using the measures of four landscape structure-representing metrics, which include contiguity index (r 2 = 0.46, p ≤0.05), fractal dimension index (r 2 = 0.51, p ≤0.05), related circumscribing circle (r 2 = 0.52, p ≤0.05), and shape index (r 2 = 0.47, p ≤0.05). The models indicated that the regularity or irregularity in land use/land cover patch shape played a key role in affecting catchment hydrological response. Our findings revealed that regularity and irregularity in the shape of a given patch (e.g., urban and semi-urban, rangeland and agricultural patches) can affect patch functions in retarding and/or increasing flow accumulation at the catchment scale, which can, in turn, decrease or increase the times of concentration in the catchments.
Rivers and related freshwater ecosystems are facing increasing natural disturbance and anthropoge... more Rivers and related freshwater ecosystems are facing increasing natural disturbance and anthropogenic stressors. Understanding the key ecological processes that govern the riverine biota in aquatic ecosystems under multiple pressures has crucial importance. However, there is still insufficient knowledge in quantifying of stressors interactions. Moreover, the understanding of the responses of riverine phytoplankton to multiple stressors is still scarce from catchment aspect. As an interdisciplinary study, the catchment hydrological processes were linked to ecological responses in this study, and we chose phytoplankton functional groups (PFGs) instead of taxonomic classifications of algae to examine their responses to land-use pattern (L), hydrological regime (H), and physicochemical condition (P) across two contrasting hydrological periods (dry, wet). The traits-based phytoplankton functional groups are highly suggested as robust bio-indicators for better understanding the current ecological status. The hydrological regime was described by a matrix indices of hydrological alteration based on the outputs of a well-established ecohydrological model (SWAT). The results from variation partitioning analysis showed that P and H dominate during the dry period and P in high flows. Structural equation models (SEM) showed that the skewness of 7 days discharge emerged as a key driver of H, and had always an indirect effect on functional group TB (benthic diatoms) during both hydrological periods. The functional group M (mainly composed by Microcystis) has directly related to phosphorous in both periods, while indirectly to L of urban area in high flow period, and water bodies in low flow period. This study emphasized that climate change and anthropogenic activities such as altering flow regime and land-use pattern affect directly or indirectly riverine phytoplankton via physicochemical conditions. In addition, our findings
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Papers by Nicola Fohrer