Influences of land use changes on the dynamics of water quantity and quality in the German lowland catchment of the Stör

Understanding the impacts of land use changes (LUCCs) on the dynamics of water quantity and quality is necessary for the identification of mitigation measures favorable for sustainable watershed management. Lowland catchments are characterized by a strong interaction of streamflow and near-surface groundwater that intensifies the risk of nutrient pollution. In this study, we investigated the effects of long-term changes in individual land use classes on the water and nutrient balance in the lowland catchment of the upper Stör in northern Germany. To this end, the hydrological model SWAT (Soil and Water Assessment Tool) and partial least squares regression (PLSR) were used. The SWAT model runs for three different land use maps (1987, 2010, and 2019) were conducted, and the outputs were compared to derive changes in water quantity (i.e., evapotranspiration – ET; surface runoff – SQ; base flow – BF; water yield – WYLD) and quality variables (i.e., sediment yield – SED; load of total phosphorus – TP; load of total nitrogen – TN). These changes were related to land use changes at the subbasin scale using PLSR. The major land use changes that significantly affected water quantity and quality variables were related to a decrease in arable land and a respective increase in pasture and urban land during the period of 1987–2019. Changes in landscape indictors such as area size, shape, dominance, and aggregation of each land use class accounted for as much as 61 %–88 % (75 % on average) of the respective variations in water quantity and quality variables. [...] The cause–effect results of this study can provide a quantitative basis for targeting the most influential change in landscape composition and configuration to mitigate adverse impacts on water quality in the future

When is a hydrological model sufficiently calibrated to depict flow preferences of riverine species?

Riverine species have adapted to their environment, particularly to the hydrological regime. Hydrological models and the knowledge of species preferences are used to predict the impact of hydrological changes on species. Inevitably, hydrological model performance impacts how species are simulated. From the example of macroinvertebrates in a lowland and a mountainous catchment, we investigate the impact of hydrological model performance and the choice of the objective function based on a set of 36 performance metrics for predicting species occurrences. Besides species abundance, we use the simulated community structure for an ecological assessment as applied for the Water Framework Directive. We investigate when a hydrological model is sufficiently calibrated to depict species abundance. For this, we postulate that performance is not sufficient when ecological assessments based on the simulated hydrology are significantly different (analysis of variance, p < .05) from the ecological assessments based on observations. The investigated range of hydrological model performance leads to considerable variability in species abundance in the two catchments. In the mountainous catchment, links between objective functions and the ecological assessment reveal a stronger dependency of the species on the discharge regime. In the lowland catchment, multiple stressors seem to mask the dependence of the species on discharge. The most suitable objective functions to calibrate the model for species assessments are the ones that incorporate hydrological indicators used for the species prediction

Representation of hydrological processes in a rural lowland catchment in Northern Germany using SWAT and SWAT+

The latest version of the Soil and Water Assessment Tool (SWAT+) features several improvements compared with previous versions of the model, for example, the definition of landscape units that allow for a better representation of spatio-temporal dynamics. To evaluate the new model capabilities in lowland catchments characterized by near-surface groundwater tables and extensive tile drainage, we assess the performance of two SWAT+ model setups in comparison to a setup based on a previous SWAT model version (SWAT3S with a modified three groundwater storage model) in the Kielstau catchment in Northern Germany. The Kielstau catchment has an area of about 50 km2, is dominated by agricultural land use, and has been thoroughly monitored since 2005. In both SWAT+ setups, the catchment is divided into upland areas and floodplains, but in the first SWAT+ model setup, runoff from the hydrologic response units is summed up at landscape unit level and added directly to the stream. In the second SWAT+ model setup, runoff is routed across the landscape before it reaches the streams. Model results are compared with regard to (i) model performance for stream flow at the outlet of the catchment and (ii) aggregated as well as temporally and spatially distributed water balance components. All three model setups show a very good performance at the catchment outlet. In comparison to a previous version of the SWAT model that produced more groundwater flow, the SWAT+ model produced more tile drainage flow and surface runoff. Results from the new SWAT+ model confirm that the representation of routing processes from uplands to floodplains in the model further improved the representation of hydrological processes. Particularly, the stronger spatial heterogeneity that can be related to characteristics of the landscape, is very promising for a better understanding and model representation of hydrological fluxes in lowland areas

Modelagem hidrológica em uma bacia hidrográfica rural na Alemanha

O uso de modelagem eco hidrológica em estudos de balanço hídrico, descarga de sedimentos e de nutrientes tem aumentado em todo o mundo. Importante na modelagem é a calibração e validação do modelo para que possa ser usado como ferramenta de estudo de mudança de cenários de uso e manejo. O objetivo deste estudo é calibrar e validar o modelo SWAT (Soil and Water Assessment Tool) e estimar os principais componentes da vazão do rio em uma bacia de planície rural. Foi investigada uma área de 462 km² da parte superior da bacia hidrográfica do rio Stör, localizada no norte da Alemanha. Os resultados da modelagem revelaram boa performance da calibração e validação da vazão diária do rio em três estações de medição da bacia Stör superior. De acordo com o modelo SWAT, os componentes da vazão são representados por 34,3% de fluxo de drenagem, 52,8% de fluxo de águas subterrâneas, de 7,7% de fluxo lateral e 5,2% de fluxo de escoamento superficial de água nesta bacia hidrográfica de planície.El uso de modelado eco-hidrológico en estudios de balance hídrico, descarga de sedimentos y de nutrientes ha aumentado en todo el mundo. Importante en el modelado es la calibración y validación del modelo para que pueda ser utilizado como herramienta de estudio de cambio de escenarios de uso y manejo. El objetivo de este estudio es calibrar y validar el modelo SWAT (Soil and WaterAssessment Tool) y estimar los principales componentes del caudal del río en una cuenca de llanura rural. Se investigó un área de 462 km² de la parte superior de la cuenca hidrográfica del río Stör, ubicada en el norte de Alemania. Los resultados de la modelaje revelaron un buen desempeño de la calibración y validación del flujo diario del río en tres estaciones de medición de la cuenca Stör superior. De acuerdo con el modelo SWAT, los componentes del caudal son representados por el 34,3% de flujo de drenaje, el 52,8% de flujo de agua subterránea, el 7,7% de flujo lateral y el 5,2% de flujo superficial de agua en esta cuenca hidrográfica de llanura.The use of ecohydrological modeling in studies of water balance, sediment and nutrient load is increasing worldwide. Important in modeling is a good calibration and validation of the model in order to use it as a tool to study land use change. The aim of this study is to calibrate and validate the model Soil and Water Assessment Tool (SWAT) and to estimate the main components of river discharge in a rural lowland catchment. 462 km² of the upper part of the Stör catchment, located in Northern Germany was investigated. The results of modeling showed a good performance for calibration and validation of daily discharge at three gauging stations of the upper Stör catchment. SWAT calibration shows that discharge components are represented by 34.3% of drainage, 52.8% of groundwater flow, 7.7% of lateral flow and 5.2% of surface runoff in this rural lowland catchment

Comparison of water balance method and alternative evaporation methods applied to the Aswan High Dam Reservoir

Aswan High Dam Reservoir (AHDR) is a large human-made reservoir situated in southern Egypt and northern Sudan. The reservoir is located in a typical arid zone so that evaporation results in a significant water loss from the reservoir. To quantify these evaporation water losses, different methods can  be applied. The water balance method was used to estimate water losses of the AHDR during 43 open-water seasons. Compared to earlier publications, this study used longer time series data and more evaporation approaches. Moreover, we evaluated the deviation between evaporation rates as derived from the water balance method and as calculated using 16 evaporation/evapotranspiration formulas. Five approaches are not well suited for use at the AHDR because they underestimated evaporation rates (e.g. Stephens-Stewart model), or overestimated evaporation rates (e.g. de Bruin model). Annual evaporation rates obtained by the Bowen ratio energy balance method at the three floating stations Raft, Allaqi and Abu Simbel were estimated at 7.9, 6.9 and 6.7 mm d-1, respectively. The monthly water losses of the years 1978 to 1984, a period with reasonable evaporation rates, are used to estimate the evaporation losses. The results of the study show a systematic deviation between the monthly average values determined using the water balance method through the period 1978 to 1984 and the monthly mean values determined by the 16 evaporation calculation approaches at three floating stations. This deviation is particularly clear in the months of May, June and September (primarily lower estimates) as well as in July (primarily higher estimates). The deviation can be attributed to the simplicity of the water balance method as well as to its limited suitability for large reservoirs as the AHDR over short periods like a month. Among the 16 evaporation calculation approaches the mass transfer method provided the most reasonable results under the given site conditions

Enhancing hydrologic modelling through the representation of traditional rainwater harvesting systems: A case study of water tanks in South India

Water tanks as traditional rainwater harvesting systems for agriculture are widely distributed in South India. They have a strong impact on hydrological processes, affecting streamflow in rivers as well as evapotranspiration. This study aims at an accurate representation of water harvesting systems in a hydrologic model to improve model performance and assessment of the catchment water balance. To this end, spatio-temporal variations of water bodies between the years 2016 and 2018 and the months of January and May 2017 were derived from Sentinel-2 satellite data to parameterize the water tanks (reservoir) parameters in the Soil and Water Assessment Tool (SWAT+) model of the Adyar basin, Chennai, India. Approximately 16% of the basin is covered by water tanks. The initial model performance was evaluated for two model setups, with and without water tanks. The best model run was selected with a multi-metric approach comparing observed and modelled monthly streamflow for 5000 model runs. The final model evaluation was carried out by comparing estimated water body areas by the model and remote sensing observations for January to May 2017. The results showed that representing water tanks in the hydrologic model led to an improvement in the representation of the seasonal variations of streamflow for the whole simulation period (2004–2018). The model performance was classified as good and very good for the calibration (2004–2011) and validation (2012–2018) periods as NSE varies between 0.67 and 0.85, KGE varies between 0.65 and 0.72, PBIAS varies between −24.1 and −23.6, and RSR varies between 0.57 and 0.39. The best fit was shown for the high and middle flow segments of the hydrograph where the coefficient of determination (R2) ranges from 0.81 to 0.97 and 0.75 to 0.81, respectively. The monthly variation of water body areas in 2017 estimated by the hydrologic model was consistent with changes observed in remote sensing surveys. In summary, the water tank parametrization using remote sensing techniques enhanced the hydrologic model's efficiency and applicability for future studies

A guideline for spatio‐temporal consistency in water quality modelling in rural areas

To summarize, we suggest a guideline for water quality modelling: 1. Spatial and temporal patterns of land use and land management are critical to adequately represent water quality in models. Remote sensing and land use models are very useful resources to be exploited. 2. The transfer of a model diagnostic analysis to water quality leads to a better understanding of how water quality variables are controlled by model structures and corresponding model parameters. 3. Assessing multiple model outputs regarding their temporal, spatial and process performance using observed time series, remotely sensed spatial patterns, knowledge about transport pathways and even soft data can significantly enhance model consistency. 4. Multi-metric calibration using performance metrics and signature measures both for discharge and water quality, such as FDC and NDC, leads to more balanced model simulations that represent all magnitudes of discharge and water quality accurately. 5. Scenarios and storylines should be co-developed with stakeholders in the river basin to make them more realistic and increase the acceptance of model results. They should be realistic in space and time, and provide a mix of available management options. 6. The interpretation of BMPs can be supported by diagnostic tools to show the effectiveness of measures and their combinations while considering their costs and impacts on ecosystem services

Untersuchung und Erfassung des Einflusses unterschiedlicher Bewirtschaftung auf Bodeneigenschaften an Boden-Dauerbeobachtungsflächen in Schleswig-Holstein

Um den Einfluss unterschiedlicher Bewirtschaftungspraktiken auf Bodeneigenschaften an Boden-Dauerbeobachtungsflächen Schleswig-Holsteins zu erfassen, wurden sechs BDF hinsichtlich ihrer Bewirtschaftungsweise sowie bodenchemischen, -physikalischen und –biologischen Bodeneigenschaften paarweise miteinander verglichen. Im Ergebnis hat nur bei einem von drei Vergleichspaaren die ökologisch bewirtschaftete Fläche bessere Bodeneigenschaften aufzuweisen als die konventionell bewirtschafteten Vergleichs-BDF. Die anderen beiden ökologisch bewirtschafteten Flächen sind die des Versuchsguts Lindhof und erst seit 1993 ökologisch bewirtschaftet. Biologische Bodeneigenschaften reagieren unmittelbar auf Bewirtschaftungsänderungen. Änderungen der Nährstoffverfügbarkeit haben einen starken Einfluss auf die Zusammensetzung der Strategietypen der Enchyträen. Die Messintervalle der biologischen Parameter sollten für eine bessere Interpretation des Einflusses der Bewirtschaftung verkürzt werden. Um den Einfluss unterschiedlicher Bewirtschaftungspraktiken auf chemische und physikalische Bodeneigenschaften beur-teilen zu können, sind mehr Messperioden notwendig

Environment regimes play an important role in structuring trait‐ and taxonomy‐based temporal beta diversity of riverine diatoms

A sound understanding of the community changes over time and its driving forces is at the centre of biodiversity conservation and ecology research. In this study, we examined: (i) the relative roles of turnover and nestedness components to trait‐ and taxonomy‐based temporal beta diversity of riverine diatoms; (ii) whether trait‐based temporal beta diversity provides complementary information to taxonomy‐based temporal beta diversity; (iii) the relative roles of hydrology (e.g. discharge, antecedent precipitation index), metal ions (e.g. Mg²⁺, Si²⁺) and nutrients (e.g. nitrogen, orthophosphate) to the both facets of temporal beta diversity and their components (i.e. total beta diversity, turnover and nestedness); and (iv) whether inclusion of environment regimes increase their explained variations. A total of 338 daily samples of riverine diatom communities were collected. We employed Mantel tests to evaluate the complementarities between trait‐ and taxonomy‐based temporal beta diversity. Using distance‐based redundancy analysis (db‐RDA) and variation partitioning, we investigated the relative roles of hydrology, metal ions and nutrients to each facet of temporal beta diversity and its components. Correlations between trait‐ and taxonomy‐based temporal beta diversity and their components were weak, which showed their complementary ecological information. Taxonomy‐based total beta diversity had a high contribution by turnover component, whereas trait‐based total beta diversity was largely driven by nestedness component. Results of variation partitioning demonstrated that the pure and shared fractions of hydrology, metal ions and nutrient differed among the components of trait‐ and taxonomy‐based temporal beta diversity. Furthermore, addition of environment regimes could dramatically increase the explained variation of temporal beta diversity and its components. Synthesis. Our results highlighted the importance of the two facets of temporal beta diversity as well as their decomposition for exploring diversity patterns of riverine diatoms in relation to abiotic factors, particularly the environment regimes. Although a high temporal taxonomic divergence was detected, the high level of temporal trait convergence indicated that species turnover with similar biological traits occurred during our study period. Our study, for the first time, provides a new perspective into temporal beta diversity of daily riverine diatom communities, which has not yet been documented by previous freshwater studies

Hydrological and environmental variables outperform spatial factors in structuring species, trait composition, and beta diversity of pelagic algae

There has been increasing interest in algae-based bioassessment, particularly, trait-based approaches are increasingly suggested. However, the main drivers, especially the contribution of hydrological variables, of species composition, trait composition, and beta diversity of algae communities are less studied. To link species and trait composition to multiple factors (i.e., hydrological variables, local environmental variables, and spatial factors) that potentially control species occurrence/abundance and to determine their relative roles in shaping species composition, trait composition, and beta diversities of pelagic algae communities, samples were collected from a German lowland catchment, where a well-proven ecohydrological modeling enabled to predict long-term discharges at each sampling site. Both trait and species composition showed significant correlations with hydrological, environmental, and spatial variables, and variation partitioning revealed that the hydrological and local environmental variables outperformed spatial variables. A higher variation of trait composition (57.0%) than species composition (37.5%) could be explained by abiotic factors. Mantel tests showed that both species and trait-based beta diversities were mostly related to hydrological and environmental heterogeneity with hydrological contributing more than environmental variables, while purely spatial impact was less important. Our findings revealed the relative importance of hydrological variables in shaping pelagic algae community and their spatial patterns of beta diversities, emphasizing the need to include hydrological variables in long-term biomonitoring campaigns and biodiversity conservation or restoration. A key implication for biodiversity conservation was that maintaining the instream flow regime and keeping various habitats among rivers are of vital importance. However, further investigations at multispatial and temporal scales are greatly needed