Treatment by enhanced denitrification of forecasted nitrate concentrations under different climate change scenarios.

Climate change has a decisive influence on future water resources and, consequently, on future nitrate (NO3-) concentrations. Due to decreasing water resources, in addition to decreasing and finite NO3- degradation capacities of the aquifers, higher NO3- concentrations are expected in the future. Likewise, NO3- pollution is expected to become more frequent. However, enhanced denitrification by addition of organic carbon (C) as an electron donor is a promising treatment method. This study describes the first model using NO3- projections based on climate projections, combined with the treatment method of enhanced denitrification. The exemplary study area is the Lodshof water catchment which is located in the Lower Rhine Embayment. The model illustrates the considerable potential of enhanced denitrification as an effective treatment. The expected increase in NO3- concentrations by the end of the 21st century, resulting from climate chance and a decreasing water resource, can be reduced by 38-58% in this model. In all projections, the limit value of 50 mg/L can be complied by this treatment. A projection with 20% lower NO3- input and the described treatment highlights the effectivity of combining measures to be able to manage the NO3- problem. Furthermore, this publication critically discusses the transfer of denitrification rates from laboratory experiments to the field scale and finally into models like this.

Modified microbiology through enhanced denitrification by addition of various organic substances-temperature effect.

Worldwide, the environmental nitrate (NO3-) problem is increasingly coming into focus. These increases in NO3- concentration result mainly from agricultural inputs and are further exacerbated by decreasing and finite geogenic NO3- degradation capacity in aquifers. Thus, treatment methods are becoming more and more important. In this study, the effects of enhanced denitrification with addition of organic carbon (C) on thereby autochthonous occurring microbiology and compared at room temperature as well as 10 °C were investigated. Incubation of bacteria and fungi was carried out using natural sediments without degradation capacity and groundwater with high NO3- concentrations. Addition of the four applied substrates (acetate, glucose, ascorbic acid, and ethanol) results in major differences in microbial community. Cooling to 10 °C changes the microbiology again. Relative abundances of bacteria are strongly influenced by temperature, which is probably the explanation for different denitrification rates. Fungi are much more sensitive to the milieu change with organic C. Different fungi taxa preferentially occur at one of the two temperature approaches. Major modifications of the microbial community are mainly observed whose denitrification rates strongly depend on the temperature effect. Therefore, we assume a temperature optimum of enhanced denitrification specific to each substrate, which is influenced by the microbiology.

Denitrification in the vadose zone: Modelling with percolating water prognosis and denitrification potential.

Transport and transformation processes of nitrogen in the soil are an essential part of understanding the relationship between agricultural input and nitrate (NO3-) concentrations in groundwater. The presented study describes these transformation processes around NO3- degradation at a water catchment in the Lower Rhine Embayment, Germany. Despite intensive agriculture, extracted groundwater at a depth of 21 to 22 m shows unexpectedly very low NO3- levels, below 3 mg/L NO3- for all wells. The local water supplier therefore carried out investigations in this area and generated soil data from 22 representative areas (142 soil samples from 82 drilling meters from the surface to a max. depth of 5.5 m) and groundwater analyses from 17 groundwater monitoring wells (from 3 to 5 m below ground surface). Soil types are predominantly luvisol and gleysol. The substrate in the topsoil is mainly clayey silt; underneath there are mostly medium-grained sands with partial silt intercalations which appear as a separate layer. Based on this dataset, the percolating water residence times and the NO3- leaching potential were calculated in this study. Together with the nitrogen surplus and with the help of reactive transport modelling, the denitrification potential in the vadose zone was simulated. The comparison of simulation results with laboratory-measured data shows a high correlation. Substantial NO3- reduction in the vadose zone was observed: dependent on soil type, reduction capacity and water residence time, up to 25% of the NO3- was reduced here. The applied modelling is considered an improvement in NO3- degradation potential assessment because it considers many relevant variables such as precipitation, soil parameters (grain size, field capacity, available water capacity, coarse fragments) and nitrogen input. Therefore, a transfer to other sites with comparable hydro(geo)logical conditions is possible, also due to relatively easily determinable input data. This assessment of nitrogen degradation in the vadose zone will be a useful tool for NO3- levels forecast in groundwater.

Forecasting nitrate evolution in an alluvial aquifer under distinct environmental and climate change scenarios (Lower Rhine Embayment, Germany).

When investigating future nitrate (NO3-) concentrations in groundwater, climate change has a major role as it determines the future water budget and, in turn, the conditions in the aquifer which will finally have a decisive effect on NO3- concentrations. In this study, the different effects on water balance and NO3- concentration under three projected climate scenarios - RCP 2.6, RCP 4.5, and RCP 8.5 - are analysed in a water protection area in the Lower Rhine Embayment in Germany. Recharge values were calculated from downscaled precipitation and temperature data for the 21st century in a water budget that considers land use in the evapotranspiration term. Nitrate concentration evolution is estimated using recharge and expected fertilization rates with a lumped-parameter model. In order to be able to map the NO3- concentration, the investigation area is divided into 1000 × 1000 m cells. Each cell is assigned a specific NO3- input and a NO3- degradation capacity. Results show significant variations in NO3- development projected with the different climate scenarios due to different temperatures and consequently actual ET, and precipitation. Nevertheless, nitrate concentrations clearly increase in all projections. The total NO3- mass increases most strongly with RCP 8.5 until 2099 (by 89% compared to 2020) and least with RCP 4.5 (by 50%). Further projections show a 20% reduction in agricultural NO3- input can reduce NO3- concentrations, but insufficiently to comply with drinking water guidelines in all regions and aquifers. The model indicates that NO3- input loads should be defined according to future recharge variations governed by climate change. Consequently, a time-varying fertilization rate specific for each region, with their own turnover time and degradation rate, must be estimated to meet pollution environmental goals.