NO3-N Concentrations Research Articles

Determining the likelihood and cost of detecting reductions of nitrate‑nitrogen concentrations in groundwater across New Zealand

Nitrate‑nitrogen (NO3-N) is a contaminant of concern in groundwater worldwide. Stakeholders need information on the ability to detect changes in NO3-N concentrations to prove that land management practices are meeting water quality aims. We created a database of quarterly to monthly NO3-N measurements in 948 sites across New Zealand; 186 of those sites had mean residence time (MRT) data. New Zealand has set a target of sufficient land use mitigations in the next 30 years to ensure steady state surface water concentrations do not exceed 2.4 mg L−1. Here we assess whether the current monitoring network could identify the impacts of these mitigations, assuming that the mitigations are successfully implemented at the source. Only 41 % of the network could detect statistically significant reductions with the current standard quarterly sampling after 30 years of monitoring. The percentage of sites increased to 60 % with increased monitoring frequency (often weekly) but this required a 100–300 % increase in monitoring costs. However, policy makers and stakeholders typically require information on policy and mitigation effectiveness within 5–10 years. Detection within 5–10 years was very unlikely (0–20 % of sites) regardless of the sampling frequency. Importantly, these analyses include the impacts of groundwater lag and temporal dispersion on the likelihood of detecting change, ignoring these impacts, incorrectly, yields a much higher likelihood of detecting reductions. We conclude that the current monitoring network is unlikely to be fit for the purpose of detecting NO3-N reductions within practical timeframes or budgets. Furthermore, we conclude that lag and temporal dispersion effects must be included in detection power calculations; we therefore recommend that MRT data is regularly collected. We also provide a python package to enable easy detection power calculations with lag and temporal dispersion impacts, thereby supporting the development of robust change-detection monitoring networks.

Nutrient characteristics driven by multiple factors in large estuaries during summer: A case study of the Yangtze River Estuary

Nutrients directly control the level of primary productivity and are crucial for the stability of marine ecosystems. Focusing on the survey results in August 2020 of the Yangtze River Estuary, this study elucidated the distribution characteristics and controlling factors of three nutrients: NO3-N, PO4-P, SiO3-Si. The results showed that the concentrations of NO3-N, PO4-P, SiO3-Si in the study area were generally higher near the shore than far shore, with average concentrations of 11.40, 0.70, and 23.73 μmol/L, respectively. The ocean currents drove the distribution of nutrients, and the transport of CDW and YSCC increased the nutrient levels. The resuspension of sediment caused by factors such as terrain and weather may lead to an abnormal increase in nutrients in the bottom waters. The main controlling factors of the three nutrients were different. NO3-N was significantly affected by human activities, PO4-P and SiO3-Si were mainly affected by natural factors.

Precipitation impacts the physicochemical water quality and abundance of microbial source tracking markers in urban Texas watersheds

This study investigated the sources of fecal pollution in surface and groundwaters collected from three urban watersheds in Texas during dry and wet weather and identified the impact of precipitation on water quality. Water samples (n = 316 and 107 for dry and wet events, respectively) were collected biweekly from eight sampling sites (6 sites from creeks and ponds, and 2 well sites) during two-year monitoring and analyzed for six physico-chemical parameters and ten qPCR-based assays targeting general (E. coli, Enterococcus, and universal Bacteroidales), human (BacHum and HF183), animal (Rum2Bac, BacCow, BacCan), and avian (Chicken/Duck-Bac and GFD) fecal markers. Elevated concentrations of NO3-N and NO2-N were observed in ponds and creeks sites during wet weather. Fecal markers analysis indicated higher concentrations of Rum2Bac, BacCow, and BacCan markers in most of pond and creek sites under wet weather, suggesting stormwater runoff contributed to non-point sources of fecal contamination by animal sources. Furthermore, sporadically higher concentrations of these markers were detected at groundwater sampling sites, demonstrating the significant human health risk. Multivariate statistical analysis such as cluster analysis (CA) and principal coordinate analysis (PCoA) was performed to identify relationship between sampling sites; while CA majorly classified ponds, creeks, and well sites separately, PCoA identified similarities in water quality characteristics between waters of wells with ponds and creeks. Overall, results indicate ruminant and dog fecal contamination is a major concern during storm events, consequently impacting surface and groundwater quality of the study.

Impact of Nitrogen Fertilization on Soil Nitrate Concentrations in an Onion Field in the Saiss Basin

High nitrogen (N) fertilizer rates can result in excessive nitrate (NO3-N) in soils and groundwater. The Saiss basin is an agricultural area in Morocco, where substantial increases in nonpoint source pollution from excessive N fertilization is commonly observed. The purpose of this study was to determine the short-term effect of N fertilizer application rates on soil NO3-N and soil water contents (SWC) in an onion (Allium cepa L.) field over two consecutive years (2021 and 2022). The field experiment was conducted in a randomized complete block design. Six N rates, namely 0, 90, 135, 180, 225, and 270 Kg N/ha were considered in drip-irrigated onion crops. Soil samples were collected from five consecutive soil layers, namely 0-20, 20-40, 40-60, 60-80, and 80-100 cm, and analyzed for NO3-N contents and SWC. SWC were lower before irrigation and increased significantly after irrigation for both seasons. There was no significant effect of N rates on SWC. Soil NO3-N decreased significantly with time. In the first season, lowest NO3-N levels was observed after harvest for all N rates. Visually, a marked accumulation of nitrate in soil was observed in the three highest N rates after harvest. Statistically, N rates did not show significant effect on soil NO3-N (p>0,05) in 2021 and 2022. This finding may be explained by the predominance of the denitrification process at Douyet station.

Urea and Trichoderma harzianum Loaded Clay-Polymer Composite in Conjunction with Farmyard Manure Sustains Soil Moisture and Nitrogen Availability to Manage Fusarium-Meloidogyne Disease Complex in Lentil (Lens culinaris)

ABSTRACT The present investigation reports the development and characterization of a clay-polymer composite loaded with urea and Trichoderma harzianum (UTCPC) to enhance soil moisture and nitrogen availability and manage wilt-nematode complex in lentil grown in residual moisture after rainfed rice. The Fourier transform infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM) characterization proved successful synthesis of UTCPC. The bentonite clay (8% w w−1) and Th concentration (10% w w−1) were optimized based on the maximum spore count of the UTCPC and viability of the Th spores at one month of storage at room temperature. The incubation and pot culture experiments were laid out in a completely randomized design (CRD) with six N levels replicated thrice in combinations with UTCPC. Under incubation experiment, the treatment of 100% N through farmyard manure (FYM) along with UTCPC application (T3) resulted in the highest soil moisture (18.5%) and lowest nitrate (NO3-N) content (42%) at 6 and 10 days after incubation, respectively, suggesting its sustained moisture-retaining and slow nitrate (NO3-N) release properties of the UTCPC. Under pot experiment, the treatment T3 expressed the highest soil moisture (28.8%) and NO3-N (17.6 kg ha−1) content even at 60 days after sowing. The disease severity index of all the treatments comprising UTCPC with or without nutrient application was significantly lower than the untreated soil. The lowest population of Fusarium spp. (13.8%) and Meloidogyne spp. (8%) were observed in T3. Therefore, UTCPC can be considered as an eco-friendly agri-input in enhancing moisture retention and sustaining nutrient release to the soil as well as providing biocontrol agents to manage Fusarium-Meloidogyne complex in lentil.

Atmospheric deposition and soil water chemistry in Swedish forests since 1985 – Effects of reduced emissions of sulphur and nitrogen

Trends for the atmospheric deposition of sulphur (S) and inorganic nitrogen (inorg-N) to forests and changes in the forest soil water chemistry in Sweden have been assessed since 1985, with special focus on the last 25 years, based on measurements within the Swedish Throughfall Monitoring Network (SWETHRO). The reductions in the deposition of S and inorg-N in the southern part of Sweden corresponded relatively well with the pollutant emission reductions for S and inorg-N from both EU27 + UK and Sweden during 1996/97–2021/22. For northern Sweden the deposition of S and inorg-N decreased to a lesser extent than both European and Swedish emissions. The bulk deposition of NO3-N has decreased more than the deposition of NH4-N over the last 25-year period, which is consistent with the much larger emission reductions for NOx compared to NH3 from EU27 + UK and Sweden. The S concentrations in the soil water, at 50 cm below soil surface, have decreased during the last 25 years, however somewhat less than the S deposition. At sites with low ANC and pH in the beginning of the period, the increase in ANC was generally greater and the increase in pH was smaller, but at sites with high pH and ANC above zero, the increase in pH was dominant, in line with the nonlinear relationship between pH and ANC in the soil water. The incidence of elevated concentrations of NO3-N in the soil water was highest in southwest Sweden, ranging between 4 and 19 % of all measuring occasions since 1985/86. The reduced deposition of N over the 35-year period was not reflected in the incidence of elevated concentrations of NO3-N in the soil water over time.

The Impact of Plant Spatial Patterns on Nitrogen Removal in the Naolihe Wetlands of Northeast China

The impact of the spatial pattern of wetland plants on nitrogen removal is a hot research topic. Ten water samples were collected from separate sampling points in mid-August and at the end of October 2021, and the concentrations of TN, NH4-N, and NO3-N in the water were measured to calculate the removal rates for the three forms of nitrogen in Naolihe wetlands. The spatial indices were interpreted for various plants based on images from samples taken in August. Step-by-step eliminations and function fitting methods were performed to determine the relationships between the spatial index and the removal rates for three forms of nitrogen. The results show that both Deyeuxia angustifolia (DA) and Phragmites australis (PA) ranked first for the functions between the order of sampling points of spatial indices (areas and shapes) and the removal rates for the three forms of nitrogen during the elimination process, indicating that DA and PA were the main forces determining nitrogen removal, which was dependent on plants covering the largest areas (DA: 31.2% and PA: 24.3%), with some large patches (largest plants index: DA (0.26) and PA (0.21)) and strong connectivity (patch edge density: DA (16.79) and PA (15.70)). These results have value for studying the relationship between spatial patterns and water purification functions.

Simultaneous removal of nitrate nitrogen and orthophosphate by electroreduction and electrochemical precipitation

Electrochemical methods can effectively remove nitrate nitrogen (NO3-N) and orthophosphate phosphorus (PO4-P) from wastewater. This work proposed a process for the simultaneous removal of NO3-N and PO4-P by combining electroreduction with electrochemically-induced calcium phosphate precipitation, and its performance and mechanisms were studied. For the treatment of 100 mg L–1 NO3-N and 5 mg L–1 PO4-P, NO3-N removal of 60–90% (per cathode area: 0.25–0.38 mg h–1 cm–2) and 80–90% (per cathode area: 0.33–0.38 mg h–1 cm–2) could be acquired within 3 h in single-chamber cell (SCC) and dual-chamber cell (DCC), while P removal was 80–98% (per cathode area: 0.10–0.12 mg h–1 cm–2) in SCC after 30 min and 98% (per cathode area: 0.37 mg h–1 cm–2) in DCC within 10 min. The faster P removal in DCC was due to the higher pH and more abundant Ca2+ in the cathode chamber of DCC, which was caused by the cation exchange membrane (CEM). Interestingly, NO3-N reduction enhanced P removal because more OH– can be produced by nitrate reduction than hydrogen evolution for an equal-charge reaction. For 10 mg L–1 PO4-P in SCC, when the initial NO3-N was 0, 20, 100, and 500 mg L–1, the P removal efficiencies after 1 h treatment were < 10%, 45–55%, 86–99%, and above 98% respectively. An increase in Ca2+ concentration also promoted P removal. However, Ca and P inhibited nitrate reduction in SCC at the relatively low initial Ca/P, as CaP on the cathode limited the charge or mass transfer process. The removal efficiency of NO3-N in SCC after 3 h reaction can reduce by about 17%, 40%, and 34% for Co3O4/Ti, Co/Ti, and TiO2/Ti. The degree of inhibition of P on NO3-N removal was related to the content and composition of CaP deposited on the cathode. On the cathode, the lower the deposited Ca and P, and the higher the deposited Ca/P molar ratio, the weaker the inhibition of P on NO3-N removal. Especially, P had little or even no inhibition on nitrate reduction when treated in DCC instead of SCC or under high initial Ca/P. It is speculated that under these conditions, a high local pH and local high concentration Ca2+ layer near the cathode led to a decrease in CaP deposition and an increase in Ca/P molar ratio on the cathode. High initial concentrations of NO3-N might also be beneficial in reducing the inhibition of P on nitrate reduction, as few CaP with high Ca/P molar ratios were deposited on the cathode. The evaluation of the real wastewater treatment was also conducted.

Aeration strategies and total nitrogen removal in a hybrid aerated treatment wetland

Abstract This study investigates the impact of aeration strategy on the performance of total nitrogen (TN) removal in a compact hybrid aerated treatment wetland (TW), called Rhizosph'air®. The system combines a single-stage French vertical flow wetland with an aerated horizontal-flow wetland, offering a unique and flexible approach for optimizing TN removal. In total, seven experimental conditions were tested, with different aeration modes, hydraulic loading rates and ammonium addition. The wetland system demonstrated high performance in terms of chemical oxygen demand removal (&amp;gt;85%) and solids removal (&amp;gt;90%), regardless of the experimental condition. However, TN removal was found to be directly impacted by operational changes. Increasing the hydraulic loading rate from 0.15 to 0.25 m/day led to an improvement in TN removal, achieving over 60%. Furthermore, when ammonium was added to the inlet and when the aeration timing was synced with the timing of the influent batch load, the environmental conditions facilitated the denitrification process, resulting in TN removal of approximately 70% and the lowest effluent NO3-N concentrations (8.70 ± 4.40 mg/L). In summary, the timing of the aeration strategy according to influent batch loading improved TN removal, suggesting its potential for optimization in future studies.

Identification of surface water - groundwater nitrate governing factors in Jianghuai hilly area based on coupled SWAT-MODFLOW-RT3D modeling approach

A comprehensive understanding of the key controlling factors on NO3-N spatiotemporal distribution in surface and groundwater is of great significance to nitrogen pollution control and water resources management in watershed. Hence, the coupled SWAT-MODFLOW-RT3D model was employed to simulate nitrate (NO3−) fate and transport in Huashan watershed system. The model was calibrated using a combination of stream discharge, groundwater levels, NO3-N in-stream loading and groundwater NO3-N concentrations. The simulation revealed the significant spatiotemporal variations in surface water-groundwater nitrate interactions. The annual average percolation of NO3− from rivers to groundwater was 171.5 kg/km2 and the annual average discharge NO3− content from groundwater into rivers was 451.9 kg/km2 over the simulation period. The highest percolation of NO3− from rivers to groundwater occurred in April and the highest discharge NO3− content from groundwater into rivers occurred in July. Grassland and agriculture land contributed more nitrate contents in river water and groundwater compared to bare land and forest in the study area and the water exchange was the primary driving force for nitrate interactions in the surface water-groundwater system. Sensitivity analysis indicated that river runoff and groundwater levels were most influenced by the SCS runoff curve number f (CN2) and aquifer hydraulic conductivity (K), which, in turn, significantly affected nitrate transport. Regarding water quality parameters, the denitrification exponential rate coefficient (CDN) had the most pronounced impact on NO3-N in-stream loading and groundwater NO3-N concentrations. This study underscores the central role of surface-groundwater (SW-GW) interactions in watershed-scale nitrate research and suggests that parameters with higher sensitivity should be prioritized in analogous watershed modeling.

Evaluating the Effects of Controlled Drainage on Nitrogen Uptake, Utilization, Leaching, and Loss in Farmland Soil

Controlling drainage during the growth stage is one of the means to provide suitable water and fertilizer conditions for crops, alleviate environmental pollution, and increase crop yield. Therefore, in this study, we studied three drainage treatments: free drainage (FD) and growth-stage subsurface controlled drainage (CD) at depths of 40 cm (CWT1) and 70 cm (CWT2). We used the HYDRUS-2D model to simulate the dynamic changes of NO3-N in the 0–100 cm soil layer as well as NO3-N uptake by crops, leaching after irrigation and fertilization, and loss through subsurface pipes in 2020 (model calibration period) and 2021 (model validation period). The degree of agreement between the simulated and measured values was high, indicating a high simulation accuracy. CD increased the soil NO3-N content and crop NO3-N uptake, and decreased NO3-N leaching and loss. We observed significant differences in the soil NO3-N content after irrigation at the budding stage of oilseed sunflower between CD and FD, with the largest difference seen for the 0–40 cm soil layer. CD increased crop yield, and the average oilseed sunflower yield of the CWT1 and CWT2 treatments increased by 4.52% and 3.04% relative to the FD treatment (p &lt; 0.05). CD also enhanced nitrogen use efficiency. In moderately salinized soil, CD at 40 cm (CWT1) reduced the nutrient difference in vertical and horizontal directions while retaining water and fertilizer. CWT1 stabilized the groundwater depth, reduced the hydraulic gradient of groundwater runoff, and decreased the drainage flow rate. The NO3-N leaching and loss dropped, which promoted crop nitrogen uptake and utilization, improved nitrogen use efficiency, reduced nitrogen loss, and had a positive effect on protecting the soil and water environment. The results demonstrate that CD is a suitable drainage method for the experimental area.

Potential of algal oil production from secondary treated sewage: a study using Chlorella vulgaris and synthetic wastewater

ABSTRACTTo assess the potential of using the secondary treated wastewater for the production of algal biofuel, batch experiments were carried out in photobioreactors using indigenous Chlorella vulgaris isolated from the natural freshwater body. Secondary treated wastewater with partial nitrification was simulated using various proportions of NO3-N and NH4-N while keeping the total nitrogen the same. Experiments with similar concentrations of nitrate without the NH4-N were used for comparison. In the presence of only NO3-N in the concentration range of 9–37 mg/L, the growth and fatty acid methyl ester (FAME) production was similar to the literature reports. When NH4-N was present along with NO3-N, the biomass growth was adversely affected, indicating an impact on the metabolic activity. For the same initial concentrations of nitrate in the culture, the maximum biomass concentration was reduced by 50–60% in the presence of NH4-N. The FAME profile changed significantly and a new FAME was identified, suggesting an impact on the lipid synthesis pathway. Comparison and analysis with the help of existing literature indicated that the adverse effect due to NH4-N was a function of pH. The growth, biomass yield, and FAME production were unaffected by a wide range of phosphorus concentrations. Maximum fatty acid methyl ester (FAME) suitable for biodiesel production (fatty acid carbon chain length C16 to C18) was 381.01 mg/L (224.58 mg/g of dry biomass), produced at NO3-N concentration of 18.5 mg/L and initial nitrogen loading per unit biomass of 0.37 g NO3-N/g of dry biomass.

Structures and compositions of biofilms in moving bed biofilm reactors pretreated by four drying methods

Research has so far paid little attention to the impact of the drying method on the structural and compositional analyses of biofilms from moving bed biofilm reactors (MBBRs). To ensure that the biofilm was derived from a steady operation phase of the MBBR, in this study, stable values of the chemical oxygen demand (COD), PO43-, total nitrogen (TN), ammonia–nitrogen (NH4-N), NO3-N and NO2-N concentration, and the biofilm dry weight were obtained after 22 d of operation. Four drying methods (supercritical CO2 drying, vacuum freeze-drying, heat drying, and natural drying) were used to pretreat the biofilms, and the changes in biofilm structures and compositions were investigated in detail. The supercritical CO2 drying and vacuum freeze-drying both maintained the biofilm compositions, while vacuum freeze-drying increased the average pore diameter of the biofilm more than five times that of the biofilm obtained by supercritical CO2 drying. In addition, heat drying and natural drying both damaged the structures and compositions of the biofilms, and heat drying in particular could cause structural collapse, surface charge declines of at least 20%, C and N elemental losses, and biomacromolecule (proteins, polysaccharides, and lipids) losses. The results from this investigation will aid in elucidating the appropriate drying methods for analyzing biofilm structures and compositions.

Optimizing water and nitrogen management can enhance nitrogen heterogeneity and stimulate root foraging

ContextThe root development and soil nitrogen distribution in cotton fields under varying water and nitrogen supplies have rarely been reported in Xinjiang, Northwest China. MethodsTo address this gap, a two-year field experiment was conducted during the 2019 and 2020 growing seasons to determine the impact of two irrigation amounts (I400, conventional irrigation, 400 mm; and I267, limited irrigation, 267 mm) and three N fertilizer rates (N320, 320; N272, 272; and N224, 224 kg N ha−1) on the soil NO3-N distribution, root distribution, aboveground nitrogen accumulation, and water and nitrogen use efficiency. ResultsUnder the I400 condition, soil NO3-N exhibited a 30.4% higher horizontal heterogeneity in the N272 plots compared to the N320 plots. The root length and number in the N272 plots increased by 29.0% and 85.0%, respectively, compared with those in N320. Additionally, the N272 plots exhibited higher root length density and root dry weight in the 40–80 cm soil layers. These advantages of the N272I400 combination resulted in the highest seed cotton yield, nitrogen accumulation, and nitrogen use efficiency. Under the I267 condition, the N320 plots showed significantly increased yield and aboveground N content, enhanced horizontal soil NO3-N heterogeneity, and substantially accelerated root growth in deep soil compared with the N reduction plots. A quadratic correlation was observed between root length and soil NO3-N content. Root length was positively correlated with nitrogen accumulation in aboveground leaves and negatively correlated with soil NO3-N residue. These findings suggest that enhancing the development and distribution of roots promotes plant nitrogen accumulation and photosynthesis and facilitates the soil NO3-N absorption. ConclusionsIn conclusion, nutrient heterogeneity can enhance nutrient uptake and improve plant performance, which have important implications for plant productivity and ecosystem functioning.

Water and soil quality respond to no-tillage and cover crops differently through 10 years of implementation

Addressing the global problem of eutrophication will require better management of inorganic nitrogen (N) on the agricultural landscape. This study investigates the impacts of no-tillage (NT), no tillage with winter cereal rye (NTr), and conventional tillage with rye (CTr), and a perennial (P) in comparison to a control system of conventional tillage without a cover crop (CT). All plots are individually drained and, except for P, in a corn/soybean rotation which dominates much of the Midwestern U.S. Drainage quantity and nitrate-N concentration were measured from individually drained plots 2011–2020. Treatments P, CT, and CTr began in 2004 and we report on years 7–11 (phase 1) and years 12–16 (phase 2). Treatments NT and NTr began in 2010 and we report on years 2–6 (phase 1) and 7–11 (phase 2). CTr and P functioned similarly throughout with consistent reductions in NO3-N concentration in leachate and loading. In contrast to initial expectations, when comparing NT to CT, there were consistent reductions in NO3-N concentration in leachate and loading in phase 1, but not in phase 2. Similarly, NTr did not reduce NO3-N concentration compared to NT in phase 1, but it did in phase 2. These results both indicate that there were possible changes to soil properties in the NT and NTr systems that influenced N cycling that could be unique to high carbon artificially drained environments. Soil quality improvements were detected in these mollisols after 15 years of cover crops in the conventional system, and after 10 years of NT and NTr. In this study, CTr was more consistent at improving water quality and maintaining cash crop yields than NTr. Both NTr and CTr had greater cover crop growth when the cover crop seeding method changed from drill-seeding after harvest in phase 1 to broadcast seeding in a standing crop in phase 2 due to a longer growth period. That water and soil quality responses changed over the years emphasizes the need for long-term studies.

Estimating the impact of temperature and streamflow change on river nitrogen pollution using the land-river integrated modeling system

The high nitrogen load in most rivers across the globe causes various environmental issues. Non-point source (NPS) pollution within a watershed has a significant impact on water quality management and prediction accuracy in rivers. Temperature and streamflow, as the most important environmental indicators, significantly affect water pollution management. This study takes the Rappahannock River Basins (RRB) as a case and adopts the method of coupling land and river models to improve the simulation accuracy of river pollution, outputs and analyzes the temporal and spatial distributions of nitrogen pollution in RRB, assesses the impact of temperature and streamflow changes on nitrogen pollution in water bodies. The results show that NPS pollution is mainly affected by topography and land use, and the annual output is more correlated with the watershed area. Temperature is negatively correlated with NH4-N and NO3-N in the Rappahannock River. Nitrogen is more susceptible to streamflow in winter; but in summer, it was stable and even showed the opposite changing tendency to winter. Changes in temperature of 1.5 ∼ 2℃ and streamflow of 20 ∼ 50% have similar effects on NH4-N, while increasing streamflow can significantly increase the concentration of NO3-N, and most of these changes are very evident. NH4-N and NO3-N concentrations will increase in RRB when the summer temperature is below the long-term average. NH4-N concentration will increase when upstream streamflow (such as the amount of mountain snowmelt) decreases in winter, while NO3-N concentration will decrease. The establishment of the integrated model can provide the nitrogen pollution load of each sub-watershed and each segment, which can be used to develop the TMDL for the Rappahannock River.

Invasive species interactions affect nutrient cycling in a shallow reservoir: a mesocosm experiment

Shivers SD, Golladay SW, Waters MN, Wilde SB, Marzolf NS, Covich AP. 2023. Invasive species interactions affect nutrient cycling in a shallow reservoir: a mesocosm experiment. Lake Reserv Manage. 39:278–290.Nonnative species’ introductions can affect nutrient dynamics as new combinations of species form novel ecosystems. This experiment investigated how combinations of 3 invasive species, one submerged macrophyte (Hydrilla) and 2 benthic invertebrates (Corbicula and Pomacea), affected nutrient cycling in a shallow reservoir, Lake Seminole, Georgia, United States. To assess these effects, an in-reservoir mesocosm array was installed using different combinations of the invasive species. Eight physical and chemical parameters of water quality were measured in all the mesocosms (1 control, 7 treatments) weekly for the duration of the 5 wk experiment. Nitrogenous compounds were strongly affected by Hydrilla and Pomacea presence, with NO3-N concentrations decreasing in Hydrilla mesocosms and NH4-N and total nitrogen (TN) increasing in Pomacea mesocosms. Corbicula, when present, helped to mitigate increases in N concentrations, presumably as filter feeding reduced water column TN concentration. Overall, Hydrilla growth reduced inorganic N concentration. Pomacea grazing converted stored N to available organic and particulate N. Total phosphorus concentrations were not impacted by the invasive species treatments and increased in all mesocosms during the experiment. In short, Hydrilla and Corbicula are contributing to the uptake, conversion, and sequestration of nutrients that may increase eutrophication, while Pomacea is releasing potentially eutrophying nutrients. As climate change and human influence continue to create new combinations of species, it is important to understand the effects produced by novel combinations of species.

Improving model capability in simulating spatiotemporal variations and flow contributions of nitrate export in tile-drained catchments

It is essential to identify the dominant flow paths, hot spots and hot periods of hydrological nitrate-nitrogen (NO3-N) losses for developing nitrogen loads reduction strategies in agricultural watersheds. Coupled biogeochemical transformations and hydrological connectivity regulate the spatiotemporal dynamics of water and NO3-N export along surface and subsurface flows. However, modeling performance is usually limited by the oversimplification of natural and human-managed processes and insufficient representation of spatiotemporally varied hydrological and biogeochemical cycles in agricultural watersheds. In this study, we improved a spatially distributed process-based hydro-ecological model (DLEM-catchment) and applied the model to four tile-drained catchments with mixed agricultural management and diverse landscape in Iowa, Midwestern US. The quantitative statistics show that the improved model well reproduced the daily and monthly water discharge, NO3-N concentration and loading measured from 2015 to 2019 in all four catchments. The model estimation shows that subsurface flow (tile flow + lateral flow) dominates the discharge (70–75%) and NO3-N loading (77–82%) over the years. However, the contributions of tile drainage and lateral flow vary remarkably among catchments due to different tile-drained area percentages and the presence of farmed potholes (former depressional wetlands that have been drained for agricultural production). Furthermore, we found that agricultural management (e.g. tillage and fertilizer management) and catchment characteristics (e.g. soil properties, farmed potholes, and tile drainage) play important roles in predicting the spatial distributions of NO3-N leaching and loading. The simulated results reveal that the model improvements in representing water retention capacity (snow processes, soil roughness, and farmed potholes) and tile drainage improved model performance in estimating discharge and NO3-N export at a daily time step, while improvement of agricultural management mainly impacts NO3-N export prediction. This study underlines the necessity of characterizing catchment properties, agricultural management practices, flow-specific NO3-N movement, and spatial heterogeneity of NO3-N fluxes for accurately simulating water quality dynamics and predicting the impacts of agricultural conservation nutrient reduction strategies.

Agronomic and environmental performance of 6 energy crops in a close loop with digestate fertilization

ABSTRACT This study examines the growth performances, nutrient uptake and potential methane yield of six energy crops fertilized with the digestate liquid fraction (DLF) with or without arbuscular mycorrhizal fungi (AMF) inoculation. The 3-year-experiment involved the four perennial (Arundo donax L. Miscanthus × giganteus Greef et Deu, Heliantus tuberosus L. Lolium perenne L.) and two annual (Zea mays L. and Sorghum bicolor (L.) Moench × sudanense Stapf.) crops. The cumulative highest yield was observed for A. donax (128.1 ± 8.4 Mg ha−1), followed by M. × giganteus and S. bicolor (83.0 ± 8.0 Mg ha−1), H. tuberosus and Z. mays (66.2 ± 7.7 Mg ha−1) and L. perenne (31.4 ± 2.9 Mg ha−1). A. donax showed the highest estimated methane yield per hectare (11.030 Nm3 ha−1). After 3 years, the fertilization with DLF increased the initial soil Na+ content by 76.9%. During the experiment, only temporary and marginal effects were shown by AMF inoculation, which did not affect biomass production by any crop. Interestingly, AMF significantly increased the NO3-N concentration (+70%) while it reduced the NH4-N concentration in percolation water (−32.8%). DLF could be considered a viable organic fertilizer for biomass production, but the soil Na+ concentration should be carefully monitored.

Use of legacy nitrogen as a resource: Unfertilized lotus fields contribute to water quality improvement and biodiversity conservation

Managing legacy nitrogen (N) that has accumulated over decades of intensive agriculture is necessary to balance agricultural production and environmental conservation. Using legacy N as a resource can reduce extant legacy N. The uplands of Japan's Lake Inba watershed are dominated by agroecosystems, and spring waters in the lowlands contain high NO3-N concentrations. We focused on an unfertilized, commercial lotus (Nelumbo nucifera) farm where paddy fields are irrigated with spring waters. We hypothesized that the lotus field could reduce the export of legacy N and provide habitat for fish (co-benefit). Dating of spring waters using sulfur hexafluoride revealed that the residence time of water at the study site was 12.5 years and suggested that the spring waters contained legacy N. We found large reductions of NO3-N and total nitrogen (TN) concentrations in water that passed through the lotus fields. A meta-analysis revealed that the reductions of NO3-N concentrations were highest in unfertilized lotus fields, and reductions of TN concentrations were higher in unfertilized paddy and lotus fields than in fertilized fields. The N removal by harvesting lotus roots 38.7 kg N/ha/year was smaller than the literature-based rate of N removal by denitrification. We used environmental DNA metabarcoding to identify the fish fauna in the lotus fields and an adjacent stream. The native fish richness was a little lower in the lotus fields than in the stream, but the presence of two endangered fish species in the lotus field suggested a moderate biodiversity conservation function. Our case study could be a good example of a nature-based solution to harness ecosystem functions to reduce legacy N.