Groundwater Nitrate Pollution Sources Assessment for Contaminated Wellfield

Nitrates are one of the most common groundwater contaminants and they come from different sources. The paper presents a study of groundwater quality at Varaždin wellfield in the north part of Croatia. The nitrate concentration at this location has been above the maximum allowed concentration for several decades, which has made the opening of new wellfields costly. Based on the previously developed groundwater flow model, a model that covers the narrow area of the wellfield is developed. The influential zone of the observed wellfield in working conditions is determined. Based on the developed model, the sources of nitrate pollution are located, which can be generally divided into non-point and point sources. Considering the time of groundwater retention in the horizontal flow, it is concluded that the water protection zones are marked following the applicable ordinance. Based on the developed groundwater flow model at the observed wellfield, a simulation of nitrate pollution propagation by advection and dispersion processes is performed. The simulation results point out the location of the poultry landfill as the largest source of nitrate pollution. However, poultry farms, which are located in the influence area of the wellfield, also contribute significantly to the nitrate concentration at the wellfield.

NITRATE REMOVAL IN WOODCHIP DENITRIFICATION BIOREACTOR – AN APPROACH COMBINING MATHEMATICAL MODELLING AND PI CONTROL

A mathematical model of nitrate removal in woodchip denitrification bioreactor based on field experiment measurements was developed in this study. The approach of solving inverse problem for nonlinear system of differential convection-reaction equations was applied to optimize the efficiency of nitrate removal depending on bioreactor’s length and flow rate. The approach was realized through the developed algorithm containing a nonlocal condition with an incorporated PI controller. This allowed to adjust flow rate for varying inflow nitrate concentrations by using PI controller. The proposed model can serve as a useful tool for bioreactor design. The main outcome of the model is a mathematical relationship intended for bioreactor length selection when nitrate concentration at the inlet and the flow rate are known. Custom software was developed to solve the system of differential equations aiming to ensure the required nitrate removal efficiency.

Antarctic meltwater-induced dynamical changes in phytoplankton in the Southern Ocean

IIt has been suggested that the freshwater flux due to the recent melting of the Antarctic ice-sheet/shelf will suppress ventilation in the Southern Ocean. In this study, we performed idealized earth system simulations to examine the impacts of Antarctic meltwater on surface phytoplankton biomass in the Antarctic Ocean. The enhanced stratification due to the meltwater leads to a decrease in the surface nitrate concentration but an increase in the surface dissolved iron concentration. These changes are associated with the reduced upwelling of nitrate-rich deep water and the trapped iron exported from the terrestrial sediment. Because of the limited iron availability in the Southern Ocean, the trapped iron in surface water enhances the chlorophyll concentration in the open ocean. However, in the marginal sea along the Antarctic coastline where the iron is relatively sufficient, a nitrate reduction induces a chlorophyll decrease, indicating a regime shift from iron-limited to nitrate-limited conditions.

ПАЛОЧНИКИ КАК ФАКТОР ПОЧВООБРАЗОВАНИЯ

Изучение существ – создателей важнейшего компонента жизни на планете – почвы, скорее всего, важная часть подготовки межпланетных космических команд. Работа представляет собой многоплановое исследование, где главным объектом выступает насекомое – Палочник аннамский. Автором проведены наблюдения за пищевой активностью и получены данные о количестве помета, то есть скорости формирования будущего гумуса. Проведено выращивание комнатного растения хлорофитум и оценено влияние смеси песка и гуано палочника на рост листьев и корней. Автору удалось провести серию химических анализов на количество нитратов в полученной «почве». Оценка концентрации нитратов в грунте проводилась как с помощью реагентов, так и с использованием прибора «Соэкс Эковизор F4». С их помощью получены данные о разных по времени формирования «почвах». The study of the creatures - creators of the most important component of life on the planet - the soil, first of all, is an important part of the preparation of interplanetary space teams. The work is a multifaceted study, where the main object is the insect – the Annam stick insect. The author carried out observations of food activity and obtained data on the amount of litter, that is, the rate of formation of future humus. A chlorophytum houseplant was grown and the effect of a mixture of sand and stick insect guano on the growth of leaves and roots was evaluated. The author managed to conduct a series of chemical analyses for the amount of nitrates in the resulting "soil". The assessment of the nitrate concentration in the soil was carried out both with the help of reagents and with the use of the device "Soex Ecovisor F4". With their help, data on "soils" of different formation times were obtained.

Reconstructing Missing and Anomalous Data Collected from High-Frequency In-Situ Sensors in Fresh Waters

In situ sensors that collect high-frequency data are used increasingly to monitor aquatic environments. These sensors are prone to technical errors, resulting in unrecorded observations and/or anomalous values that are subsequently removed and create gaps in time series data. We present a framework based on generalized additive and auto-regressive models to recover these missing data. To mimic sporadically missing (i) single observations and (ii) periods of contiguous observations, we randomly removed (i) point data and (ii) day- and week-long sequences of data from a two-year time series of nitrate concentration data collected from Arikaree River, USA, where synoptically collected water temperature, turbidity, conductance, elevation, and dissolved oxygen data were available. In 72% of cases with missing point data, predicted values were within the sensor precision interval of the original value, although predictive ability declined when sequences of missing data occurred. Precision also depended on the availability of other water quality covariates. When covariates were available, even a sudden, event-based peak in nitrate concentration was reconstructed well. By providing a promising method for accurate prediction of missing data, the utility and confidence in summary statistics and statistical trends will increase, thereby assisting the effective monitoring and management of fresh waters and other at-risk ecosystems.

Nutrient Deficiency Affects the Growth and Nitrate Concentration of Hydroponic Radish

In hydroponics, a continuous supply of mineral nutrients is essential for plant growth. However, constitutive nutrient-rich conditions also increase the nitrate content in the plants, which can be harmful to human health. Here, we investigated the effect of nutrient deficiency on the growth and component composition of hydroponic radish by changing the timing of nutrient removal from the hydroponic solution. Radish plants that were 14 days old were transferred to four different nutrient conditions for 14 days: nutrient deficiency for 14 days (WW), full nutrient for 14 days (NN), nutrient deficiency for the last 7 days (NW), and nutrient deficiency for the first 7 days (WN). After the treatments, the NW plants had similar taproot growth to NN plants. In contrast, the WN plants significantly reduced taproot growth. The WW plants reduced the shoot and taproot weight and their water contents. The nitrate content in the taproots was reduced in the NW and WW plants. The WW plants contained lower total phenol and higher ascorbic acid and sugar contents. These results suggest that the uptake of nutrient minerals at the young growth stage is important for the growth of radish taproot. Nutrient deficiency management can be one of the most effective tools for regulating radish growth and composition.

Integrated Surface-Groundwater Modelling of Nitrate Concentration in Mediterranean Rivers, the Júcar River Basin District, Spain

High nutrient discharge from groundwater (GW) into surface water (SW) have multiple undesirable effects on river water quality. With the aim to estimate the impact of anthropic pressures and river–aquifer interactions on nitrate status in SW, this study integrates two hydrological simulation and water quality models. PATRICAL models SW–GW interactions and RREA models streamflow changes due to human activity. The models were applied to the Júcar River Basin District (RBD), where 33% of the aquifers have a concentration above 50 mg NO3−/L. As a result, there is a direct linear correlation between the nitrate concentration in rivers and aquifers (Júcar r2 = 0.9, and Turia r2 = 0.8), since in these Mediterranean basins, the main amount of river flows comes from groundwater discharge. The concentration of nitrates in rivers and GW tends to increase downstream of the district, where artificial surfaces and agriculture are concentrated. The total NO3− load to Júcar RBD rivers was estimated at 10,202 tN/year (239 kg/km2/year), from which 99% is generated by diffuse pollution, and 3378 tN/year (79 kg/km2/year) is discharged into the Mediterranean Sea. Changes in nitrate concentration in the RBD rivers are strongly related to the source of irrigation water, river–aquifer interactions, and flow regulation. The models used in this paper allow the identification of pollution sources, the forecasting of nitrate concentration in surface and groundwater, and the evaluation of the efficiency of measures to prevent water degradation, among other applications.