For particle-bound substances such as phosphorus, erosion is an important input pathway to surface waters. Therefore, knowledge of soil erosion by water and sediment inputs to water bodies at high spatial resolution is essential to derive mitigation measures at the regional scale. Models are used to calculate soil erosion and associated sediment inputs to estimate the resulting loads. However, validation of these models is often not sufficiently possible. In this study, sediment input was modeled on a 10 × 10 m grid for a subcatchment of the Kraichbach river in Baden-Wuerttemberg (Germany). In parallel, large-volume samplers (LVS) were operated at the catchment outlet, which allowed a plausibility check of the modeled sediment inputs. The LVS produced long-term composite samples (2 to 4 weeks) over a period of 4 years. The comparison shows a very good agreement between the modeled and measured sediment loads. In addition, the monitoring concept of the LVS offers the possibility to identify the sources of the sediment inputs to the water body. In the case of the Kraichbach river, it was found that around 67% of the annual sediment load in the water body is contributed by rainfall events and up to 33% represents dry-weather load. This study shows that the modeling approaches for calculating the sediment input provide good results for the test area Kraichbach and the transfer for a German wide modeling will produce plausible values.

Changes in land-use, agricultural management and climate affect the turnover and storage of organic carbon in soils (SOC) as well as the nitrogen mobilization from soil organic matter (SOM), with potential side effects on nitrogen availability and leaching. When addressing the requests for increased carbon storage in soil as well as for the reduction of nitrogen losses, integrated approaches on regional scales are required that take into account the actual changes in agricultural management and climate. This study investigated the arable land (7345 km(2)) of Saxony (Germany) with regard to the following: (1) the trends of SOC storage and organic matter-related nitrogen fluxes, including their subregional and annual dynamics, (2) changes in the carbon input to arable soils and the turnover of organic matter, and (3) the contribution of different drivers (climate, crop production and fertilization, tillage system) to the simulated SOM changes for the period 1998-2014 on a 500 m grid. The model CANDY carbon balance (CCB) was specifically adapted for large-scale simulations of SOM turnover to link spatial data on soils and climate with regional statistics on agricultural management. This new 'regional mode' of CCB has been validated using data from 391 plots across different European locations. The initial SOC levels for Saxony assumed steady state conditions at the beginning of the simulation period and have been validated using data from 667 monitoring sites. The results showed an increase in the SOC stocks of the arable soils of Saxony of 785 x 10(3) t C (1.24%o annually) during the simulation period. At the same time, the model simulated an average increase in organic nitrogen stored in SOM of approximately 7.5 kg N ha(-1) a(-1), with considerable differences between individual years and subregions. Both the increase in carbon inputs to soil (+8%) and the reduction of carbon turnover rates (-10%) had positive effects on SOC storage. While the increased use of conservation tillage was the most important driver for the overall increase in SOM storage in Saxony, climate variability and crop production and fertilization had the largest effect on its annual dynamics.

The paper presents an improved approach for investigating submarine groundwater discharge (SGD) based on radon mapping and radon mass balancing in the coastal sea. While the use of radon as an environmental tracer in SGD studies is well-established, we identified based on our longstanding experience six methodical shortcomings of the conventional approach and suggest corresponding developments. The shortcomings include: (1 and 2) inadequate consideration of both detection equipment response delay and influence of tidal stage; (3 and 4) incorrect quantification of radon losses, due to offshore mixing and degassing resulting in a potentially incorrect radon mass balance; (5) inaccurate determination of the terrestrial groundwater endmember, due to inhomogeneous radon distribution in the coastal aquifer; and (6) difficulties in distinguishing between discharged fresh groundwater and recirculated seawater. The improved approach is practically demonstrated in a step by step manner in a large-scale field study, which was carried out in False Bay (South Africa) and which consisted of two parts, namely (i) qualitative SGD localization along the entire False Bay coastline based on coastal radon distribution patterns and (ii) quantitative SGD investigation within a defined coastal area of interest (AOI) based on a radon mass balance (RMB). The plausibility of the AOI related results was evaluated by a hydrogeological model, used for qualitative SGD localization, and a hydrological model, applied for estimating groundwater recharge within the AOI catchment.

Since the 1990’s, the groundwater quality along the southern coast of the Western Cape Province of South Africa has been affected by increasing land use activities. Groundwater resources have become increasingly important in terms of providing good quality water. Polluted coastal groundwater as a source of submarine groundwater discharge also affects the quality of coastal water. For this study, land use activities causing groundwater pollution and areas at particular risk were identified. An assessment approach linking land use/land cover, groundwater and submarine groundwater discharge on a meso-scale was developed and the methods applied to two study regions along the southern coastal area. Dryland and irrigated crop cultivation, and urbanized areas are subject to a “high” and “very high” risk of groundwater nitrogen pollution. Application of fertilizer must be revised to ensure minimal effects on groundwater. Practice of agricultural activities at locations which are not suited to the environment’s physical conditions must be reconsidered. Informal urban development may contribute to groundwater nitrogen pollution due to poor waste water disposal. Groundwater monitoring in areas at risk of nitrogen pollution is recommended. Land use activities in the submarine groundwater discharge contribution areas was not found to have major effects on coastal water.

The inclusion of biogas production into the agricultural system has modified crop management and as a result the soil organic carbon (SOC) cycle of the agricultural landscape. To evaluate the effects for the German federal state of Saxony this study determines: (1) the share of agricultural land required for biogas production, (2) the change in regional carbon input fluxes to soil during the time of the establishment of the biogas production considering also the quality of sources of different fresh organic matter (FOM) for the formation of SOC and (3) the differences in carbon input to SOC between the area influenced by biogas production (here "biogas fingerprint area" (BFA)) and the surrounding arable land. Based on the location of biogas plants the region was subdivided into biomass providing units (BPUs) where a part of the arable land was considered as affected by biogas production (BFA). We hypothesized that each biogas plant uses a specific substrate mix according to its capacity. The carbon fluxes for each BPU were estimated for the years 2000 (without biogas plants) and 2011 (with biogas plants). For the year 2011, the analysis included the area demand for production of biogas feedstock and digestate recycling. On average 17.6% of the BPU agricultural land was required to supply the biogas plants and dispose of their digestate. Per kilowatt installed electrical capacity this equates to 2.0 ha, including inter alia 0.4 ha for energy crops. Highest area requirements have been observed for biogas plants with < 500 kW installed capacity. Between 2000 and 2011 the total carbon flux into soil increased by 2.1%. When considering the quality of different FOM sources the gain in carbon input was 2.8%. The BFAs showed higher carbon input to soil than the surrounding agricultural land due to high contributions from digestate and crop residues (esp. agricultural grass). This compensated the low carbon input from crop by-products (e.g. straw).

A major challenge for water resource management in Western Cape, South Africa, is the reduction of the growing sediment and nutrient loads in coastal areas, which belong to the areas most affected by land use change. We used the WebGIS based software STOFFBILANZ to simulate runoff, soil loss, sediment, phosphorus, and nitrogen input in the surface water and groundwater of study area (ca. 6,450 km²). The simulated runoff shows a large regional variability caused by the heterogeneous distribution of rainfall. For the reference catchment Klein River simulated total daily runoff fit the observed values of the reference year 2012. The calculation of potential input of sediment, phosphorus, and nitrogen into waters is based on aggregated or generalized information on climate data, land use types, crop and fruit types, yields, mineral fertilizers, farm manure, nitrogen fixing by leguminous plants, atmospheric nitrogen deposition, and soil denitrification. Critical source areas for potential sediment input, particulate P input and diffuse N input are mainly agricultural areas. Additionally, point sources of high relevance for N and P are found in urban areas. Based on the potential input of sediment and nutrients the impacts of current land use change on water resources were estimated. We used the web-based information system WebLand for the simulation aiming at the provision of stakeholders with information for decision making in water resource management.

Change of land use and agricultural management, combined with severe droughts during the last two decades, are the main reasons for a strong decrease of water quality and quantity in the Miyun reservoir (China). Due to semi-arid monsoon climate, episodic water fluxes have to be considered adequately in an integrated water resources management in the total catchment area. To get insight into runoff generation processes, sediment and nutrient source areas and transfer dynamics, a monitoring approach was established in the Miyun catchment area spanning from plot measurements with weighable gravitation lysimeters and in situ measurements to a subcatchment scale of approx. 10 km2. One of these subcatchments (Sheyuchuan) was selected to adapt the methodologies to the regional runoff pattern using the web GIS-based modeling tool STOFFBILANZ. Calibration of the daily runoff modeling is based on the lysimeter observations from Shixia station and runoff observations in Sheyuchuan subcatchment for the reference year 2011. Despite the fact that the climatic water balance in the region is negative, the precipitation event on 24 July 2011 with a rainfall of 107 mm caused a significant leachate at the lysimeter. The daily modeling for the lysimeter core by the FAO-ETc-adj approach showed a similar deep percolation and a similar distribution of evapotranspiration for the year considered. In the next step, the calibrated model was applied to the subcatchment Sheyuchuan to compare the results of direct runoff and groundwater runoff (deep percolation) with the runoff observations at the weir. Deep percolation was extremely small (1.7 mm yr-1), and direct runoff was 26.9 mm yr-1 in 2011. In comparison to the monitoring results at the weir, a disagreement in the quantity of runoff was found between the observation on the one hand and the simulation on the other hand, which can be explained by water storage in reservoirs for irrigation purposes. Additionally, the water fluxes in the total catchment area were simulated at meso-scale, obtaining a good correlation with observed values.

Changes in land use and agricultural management have caused a strong increase in sediment and particulate phosphorus input into the Miyun reservoir. The simulation of the relevant runoff and sediment fluxes at the mesoscale needs adequate procedures, adapted to a semiarid monsoon climate and regional land-use pattern.

The production of energy crops in Germany is a growing agronomic sector and is expected to occupy a substantial share of farmland in the near future. At the same time, there are concerns that energy crops might cause increased nitrogen pollution of soil water, surface water and groundwater. Therefore, the Federal State of Saxony, Germany, funded a study on potential effects of an intensified cultivation of energy crops. In frame of this study, we used the Web GIS-based model STOFFBILANZ to simulate N leaching from the rooting zone and N loads of surface water for a reference scenario and an energy crop scenario. For the reference scenario, we used data representing the crop cultivation for the year 2005 at municipality level. We found that the total loads for N leaching from the rooting zone of cropland are highest for the loess region (8,067 t year−1), followed by mountainous region (6,797 t year−1) and lowland (5,443 t year−1). However, highest N fluxes in the leachate from rooting zones have been simulated for lowland (40.6 kg ha−1 year−1) and mountainous region (37.1 kg ha−1 year−1), while nitrate concentrations of leachate were highest for the lowland (101.8 mg l−1). In terms of diffuse N input into surface water, the mountainous region is the most important source area (total N load 6,380 t year−1, flux 34.6 kg ha−1 year−1). Retention by in-stream processes accounts for 15 % (3,784 t year−1) of the total N load leaving the study area (25,136 t year−1). In the 2020 energy crop scenario, shares of rape and silage maize (id., ensiled corn) were limited for each municipality to a maximum of 25 and 33 %, respectively. The conversion of grasslands to crop farming was not allowed. Under these conditions, we found slight to substantial reductions of nitrogen loads for leachate from the rooting zone and for surface waters. The simulated reduction depends strongly on local conditions. Only small reductions (ca. 4–8 %) were found for the lowlands and mountainous regions of Saxony, while reductions for the loess region were substantial (ca. 22 %). A major outcome of our study is that the cultivation of energy crops might reduce N loss if certain preconditions are assumed, for example, without conversion of grasslands to crop farming. However, effects might vary widely depending on local conditions.