Nutrient Inputs Research Articles

Paleolimnological evidence for primary producer change linked to hydrologic connectivity and human impacts in Lake Carlton, Florida, USA

Hypereutrophic conditions in lake ecosystems are generally associated with nutrient inputs from surrounding terrestrial landscapes. However, some systems can receive primary nutrient inputs through hydrologic connections such as rivers or canals. Lake Carlton, Florida, USA is a small, shallow, polymictic lake that ends a hydrologically connected string of lacustrine systems with hypereutrophic lakes Beauclair and Apopka. Lake Beauclair and Lake Apopka were connected hydrologically when a system of canals was constructed beginning in 1893 CE. These lakes have maintained hypereutrophic conditions despite extensive management to reduce nutrient inputs. Here, we collected a sediment core from Lake Carlton to accomplish two primary research objectives: 1) reconstruct the nutrient input for Lake Carlton throughout the last ~ 150 years to conduct source assessment, and 2) link primary producer changes with management actions between lakes Apopka, Beauclair, and Carlton. Paleolimnological tools were applied to a 165-cm sediment core and analyzed for bulk density, organic matter content, nutrients (C, N, P), photosynthetic pigments, and total microcystins. Sediments were dated using 210Pb and results indicate that the core represents over 150 years of sediment accumulation. Sedimentary nutrient concentrations show that the primary driver of nutrient inputs resulted from canal construction, beginning in 1893 CE, which corresponded to increased nutrient deposition. Photosynthetic pigment data indicate dramatic increases in most primary producer groups coinciding with the hydrologic modification. However, around ~ 1970 CE, primary producer communities shifted from diatom dominance to cyanobacterial dominance, which appeared to be linked to internal nutrient dynamics and competition among phytoplankters within the lake ecosystem. Cyanotoxin production records show a significant lag between cyanobacterial dominance and peak cyanotoxin production with toxins increasing in the last 30 years. These data demonstrate that local nutrient inputs do not govern all phytoplankton dynamics in shallow lake systems but must be interpreted considering hydrologic alterations and management practices.

Use of geotechnologies to promote the sustainable expansion of fish farming: an analysis for the municipality of Chopinzinho, Brazil

The expansion of fish production in a sustainable way in small municipalities has become an objective for both fish farmers and consumers, whether for nutritional and/or environmental appeal. The objective of this work was to map natural resources in the municipality of Chopinzinho/Pr using geotechnology to subsidies the planning of fish production in the municipality. The methodology used was based on geoprocessing and remote sensing tools. Results indicate annual growth in fish production, an amount of 53.1 hectares of water depth and 242 excavated ponds, the majority (81.8%) measuring less than 3,000 meters. The estimated nutrient input, due to fish farming, in excavated ponds, during the cultivation cycle was 104.14 tons of Total Nitrogen and 12.78 tons of Total Phosphorus and during harvesting 3.95 tons of Total Nitrogen and 0,85 tons of Total Phosphorus. Therefore, the use of geotechnology tools to map natural resources and excavated ponds, for subsequent estimation of nutrient input, has the potential to become a methodology to promote the expansion of fish production in a sustainable manner.

The effect of drainage on fine‐root biomass, production, and turnover in hemiboreal old‐growth forests on organic soils

AbstractInformation on the capacity of organic soils to capture and store carbon in old‐growth forests in the hemiboreal forest zone is scarce and fragmented. However, fine‐root data can provide valuable insights into soil carbon fluxes. Thus, the aim of the current study was to provide estimates of the fine‐root biomass (FRB), fine‐root production (FRP), and fine‐root turnover (FRT) rate by tree species and other functional groups in old‐growth (stand age 131–179 years) forests on mesotrophic organic soils dominated by Scots pine (Pinus sylvestris L.), with and without the effects of forest drainage. The sequential soil coring method was used to estimate the FRB and FRP. The total FRB was significantly higher in the undrained sites (6.8 ± 0.3 t ha−1) than in the drained sites (3.97 ± 0.1 t ha−1). The FRB of Scots pine in the undrained forest was significantly higher (1.7 ± 0.1 t ha−1) than in the drained forest (0.5 ± 0.1 t ha−1), supporting an extensive foraging strategy. The significantly higher mean FRB of Norway spruce (Picea abies [L.] Karst.) (1.4 ± 0.1 t ha−1) in the drained sites than the undrained sites (0.7 ± 0.2 t ha−1) can be explained by there being a higher proportion of spruce in the stand compositions, thus a higher standing volume of this species and an increased FRB. The FRB of dwarf shrubs (2.43 ± 0.2 t ha−1) formed the largest part of the total FRB in the undrained sites and the second largest (1.16 ± 0.1 t ha−1), following Norway spruce, in the drained sites. The total FRP was similar between the undrained (2.05 ± 0.31 t ha−1 year−1) and drained (1.82 ± 0.26 t ha−1 year−1) stands. However, considerable variability in the FRP was observed between different sites of the same forest site type. The FRT rate of Scots pine was twice as high in the drained sites than the undrained sites, suggesting faster nutrient and carbon input into the drained soil compared with the undrained soil. Estimates of FRB, FRP, and FRT rates for different functional groups can be used in carbon‐cycle modeling and in further calculations to estimate the carbon budget (balance) in forests on organic soils.

Multiple enrichment mechanisms of organic matter in the Fengcheng Formation of Mahu Sag, Junggar Basin, NW China

Based on core and thin section data, the source rock samples from the Fengcheng Formation in the Mahu Sag of the Junggar Basin were analyzed in terms of zircon SIMS U-Pb geochronology, organic carbon isotopic composition, major and trace element contents, as well as petrology. Two zircon U-Pb ages of (306.0±5.2) Ma and (303.5±3.7) Ma were obtained from the first member of the Fengcheng Formation. Combined with carbon isotopic stratigraphy, it is inferred that the depositional age of the Fengcheng Formation is about 297–306 Ma, spanning the Carboniferous–Permian boundary and corresponding to the interglacial period between C4 and P1 glacial events. Multiple increases in Hg/TOC ratios and altered volcanic ash were found in the shale rocks of the Fengcheng Formation, indicating that multiple phases of volcanic activity occurred during its deposition. An interval with a high B/Ga ratio was found in the middle of the second member of the Fengcheng Formation, associated with the occurrence of evaporite minerals and reedmergnerite, indicating that the high salinity of the water mass was related to hydrothermal activity. Comprehensive analysis suggests that the warm and humid climate during the deposition of Fengcheng Formation is conducive to the growth of organic matter such as algae and bacteria in the lake, and accelerates the continental weathering, driving the input of nutrients. Volcanic activities supply a large amount of nutrients and stimulate primary productivity. The warm climate and high salinity are conducive to water stratification, leading to water anoxia that benefits organic matter preservation. The above factors interact and jointly control the enrichment of organic matter in the Fengcheng Formation of Mahu Sag.

Litter Decomposition of a Deciduous Tectona philippinensis and an Evergreen Parashorea malaanonan Across Contrasting Sites

Litter traits and site conditions alter nutrient inputs from deciduous and evergreen forests by influencing litter decomposition processes. Here, we investigated the leaf and stem mass loss rate (MLR) of a deciduous (Tectona philippinensis) and an evergreen (Parashorea malaanonan) tree species and the factors influencing it through an intersite experiment and litterbag method in secondary forests in Lobo, Batangas and Mount Makiling Forest Reserve (MMFR). Variations in initial litter quality (leaf area, specific leaf area (SLA), leaf thickness, vein density), and site factors (light intensity and temperature) were assessed. P. malaanonan has a lower SLA and vein density than T. philippinensis. The leaf and stem MLR were significantly higher in the mixed litter (44.09–57.83%) than that of a single-species litter of either T. philippinensis (28.16–41.83%) or P. malaanonan (33.60–47.66%). The leaf MLR of T. philippinensis was greater when placed in Lobo (where the litter originated) than at a different site (i.e., MMFR). Moreover, leaf litter decomposition was faster in T. philippinensis than in P. malaanonan, particularly during the rainy season. Overall, the study showed that litter decomposition in deciduous and evergreen differed across sites due to variations in litter quality and environmental variables. Keywords: decomposability traits, home-field advantage (HFA), intersite experiment, litter quality, mass loss rate

Quantification of Major Inorganic Contaminants in a Mediterranean Coastal Lagoon with a Large Dystrophic Crisis.

In August 2021, the Mar Menor, a saltwater lagoon located in the Region of Murcia (Spain), suffered a tragic environmental episode of dystrophic crisis and anoxia. The appearance of numerous dead fish in different areas of the lagoon over the course of days put all the authorities and the population of the area on alert. This paper shows a case study of what happened in the lagoon in terms of the presence of the most common inorganic pollutants. Measurements of the concentration of nitrogen species, phosphates and main heavy metals were carried out at different sampling sites in the Mar Menor from May 2021 to November 2022. Chemical analyses were carried out for each of the species under study. These analyses provide valuable information about the dystrophic crisis caused by a classic eutrophication process that began with the excessive nutrient input into the Mar Menor. Ion chromatography and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) were used as instrumentation for the quantification of these samples. The species whose values were greatly increased after the tragic episode described above were nitrates. The concentration varied significantly at the different sampling sites throughout the study. On the last sampling date, decreased concentrations of all the species were measured at each of the sampling sites, coinciding with the apparent good state of the lagoon.

Synergistic effects of coal waste derived humic substances and inorganic fertilizer as soil amendments for barley in sandy soil

Increasing pressures on land resources requires increased land use efficiency. Over 900 million ha of sandy soils throughout the world are extensively used for agricultural crop production, most requiring nutrient inputs. Although use of humic substances together with inorganic fertilizer as soil amendments has been introduced, their synergistic effects on plant growth in sandy soils are not well addressed. We assessed the efficacy of a lignite waste derived humic substance on barley (Hordeum vulgare L.) growth, with and without inorganic fertilizer. Ten treatments were applied to sandy soils, comprising sole application of the humic product at four rates (NH1, NH2, NH3, NH4), sole application of fertilizer (F), and their combinations (F + NH1, F + NH2, F + NH3, F + NH4). Synergistic effects of nano humus and fertilizer were more notable than the corresponding sole application, particularly on plant biomass and seed production. Combined application with inorganic fertilizer increased root biomass by 92 % (0.1 g per plant), shoot biomass by 80 % (0.5 g per plant), root length by 24 % (3.6 cm), and seed production by 38 % (5 seeds per head) averagely relative to the untreated control, suggesting a strong synergistic effect. The increased seed production was particularly important from an agricultural perspective. Four application rates of nano humus all showed beneficial effects on barley growth with no significant differences. The most distinct positive effect of the humic product as a sole application was on root growth. Our study confirmed that a lignite waste derived humic product, nano humus, together with fertilizer may be an effective soil amendment to enhance agricultural plant growth in sandy soil regions.

A novel approach to identify priority areas for optimal nutrient management in mixed land-use watersheds through nutrient budget assessment

Excessive nutrient supply in agricultural regions has led to various environmental issues, thereby requiring concentrated management owing to its persistent upward trend. Nutrient budgets (NBs), a vital agricultural environmental indicator, are employed for nutrient management in agricultural areas, using data surveyed by administrative agencies. However, the spatial extent of nutrient data for nutrient budgeting is limited by administrative boundaries according to the surveying organization, posing challenges in interpreting spatial patterns at the watershed level. In this study, a novel approach was developed to identify priority nutrient management areas by applying hot spot spatial analysis to watershed-level NBs, considering hydrological characteristics. This method was applied to approximately 850 subwatersheds across the Republic of Korea, where land cover characteristics are complex. Reassessing nutrient budgets at the watershed scale, accounting for overlapping administrative boundary areas and crop cultivation ratios, indicated similar levels between the two methods. Hot spot analysis revealed that watersheds with elevated NBs mirrored the spatial patterns of livestock excreta and cropland. The spatial distribution characteristics of watersheds with high nutrient levels in rivers corresponded with the concentration characteristics of industrial and commercial areas. Therefore, applying watershed-level NBs based on land cover ratios that consider nutrient input characteristics in agricultural regions is deemed appropriate for selecting priority nutrient management areas. Collectively, this study presents a method for selecting nutrient management priority areas by simultaneously considering the spatial characteristics of various environmental factors, such as land cover, livestock excreta, river water quality, and land area-based watershed-specific NBs. The proposed approach, considering mixed land cover characteristics, is anticipated to be valuable for selecting priority management areas in watersheds with diverse pollution sources. Future research is needed to explore nutrient budgets within watersheds, the influence of land use on pollution sources, and their correlation with water quality.

Losses of low-germinating, slow-growing species prevent grassland composition recovery from nutrient amendment.

Nutrient enrichment often alters the biomass and species composition of plant communities, but the extent to which these changes are reversible after the cessation of nutrient addition is not well-understood. Our 22-year experiment (15 years for nutrient addition and 7 years for recovery), conducted in an alpine meadow, showed that soil nitrogen concentration and pH recovered rapidly after cessation of nutrient addition. However, this was not accompanied by a full recovery of plant community composition. An incomplete recovery in plant diversity and a directional shift in species composition from grass dominance to forb dominance were observed 7 years after the nutrient addition ended. Strikingy, the historically dominant sedges with low germination rate and slow growth rate and nitrogen-fixing legumes with low germination rate were unable to re-establish after nutrient addition ceased. By contrast, rapid recovery of aboveground biomass was observed after nutrient cessation as the increase in forb biomass only partially compensated for the decline in grass biomass. These results indicate that anthropogenic nutrient input can have long-lasting effects on the structure, but not the soil chemistry and plant biomass, of grassland communities, and that the recovery of soil chemical properties and plant biomass does not necessarily guarantee the restoration of plant community structure. These findings have important implications for the management and recovery of grassland communities, many of which are experiencing alterations in resource input.

Modeling and Forecasting the Removal of Biogenic Elements from Agricultural Lands Depending on the Soil Agrophysical Properties

Introduction. Environmental pollution prevention, including prevention of water bodies, with nutrients (nitrogen and phosphorus) when they are removed from agricultural lands with possible runoff is a topical problem that requires a timely solution. The studies have found that the removal of nutrients is a result of geochemical processes, fertilization, and other factors. In this regard, mathematical modeling of the process of removal of nutrients from agricultural lands and their possible entry into water bodies is an urgent task. Aim of the Study. The study is aimed at modeling and predicting the process of possible removal of nutrients from agricultural lands to water bodies. Materials and Methods. When conducting the study, there were used well-known modeling methods. They are the methods for calculating the removal of nutrients from agricultural objects into water bodies, based on the minimum amount of initial information for predicting the eutrophication of water bodies and agrochemical methods taking into account the structure and size of field and agricultural areas, crop yields, and removal nutrients with the harvest. Results. Based on an analysis of the literature and expert judgment, a list of the most significant indicators influencing the process of nitrogen and phosphorus removal was justified. There have been developed mathematical models to determine and predict the input of nutrients from agricultural lands to water bodies. There have been found significant indicators influencing the amount of input of nutrients, such as the amount of applied fertilizers, the volume of moisture, soil water capacity, field area, depth of cultivation, etc. There is given an example of calculating the amount of input of nutrients into water bodies with a rainfall intensity of 50 mm per hour. Discussion and Conclusion. The essence of the proposed mathematical models comes down to the synthesis of numerous indicators in the complex process of removal of nutrients and their impact on water quality. The proposed mathematical models make it possible to predict the removal of nutrients from agricultural lands and to develop and implement technical and technological solutions to prevent environmental pollution.

The Impact of Canopy on Nutrient Fluxes through Rainfall Partitioning in a Mixed Broadleaf and Coniferous Forest

Rainfall constitutes the primary input in the nutrient flux within forest ecosystems. The forest canopy modulates this flux by partitioning rainfall and selectively absorbing or adding nutrients. In mixed forests, variation in tree species composition regulates rainwater chemical composition, potentially leading to spatial heterogeneity in nutrient distribution and influencing nutrient cycling processes. This study examined the partitioning of rainfall into throughfall and stemflow, as well as their associated nutrient concentrations and fluxes, in a mixed broadleaf and coniferous forest on Changbai Mountain in Northeast China. We observed a rising trend in nutrient contents from rainfall to throughfall and then stemflow. The nutrient contents of stemflow varied largely with tree species due to the differences in canopy structure and bark morphological characteristics. The nutrient input contributed by throughfall and stemflow was 92.30 kg ha−1 during the observation period, and most elements underwent passive leaching through washout except for F− and Na+. We note that the nutrient fluxes in stemflow differed among tree species, with Pinus koraiensis (PK) delivering more acid group anions and Quercus mongolica (QM) providing more cations. Our research provides new insights into nutrient cycling within mixed forest canopies, sparking a transformative advancement in forest management and protection strategies through hydrochemistry-driven solutions.

Submerged macrophyte root oxygen release reduces sediment oxygen demand: A positive feedback loop in shallow lakes

Shallow lakes have two stable ecological states, macrophyte dominated or algal dominated. The macrophyte dominated state is the more desired state as it generally has clearer water that is safe for contact recreation. Whereas the algal dominated state is considered degraded, resulting from high anthropogenic nutrient inputs, with turbid water that is often unsafe for contact recreation. These ecological states are somewhat resilient due to in-lake feedback loops that maintain or enhance conditions for the dominate primary producer. For the macrophyte dominated state, many of these feedback loops are theoretically plant density dependent, but rarely has the plant density required to initiate these feedback loops been identified. Here we illustrate the plant density dependence of a previously unstudied feedback loop present in the macrophyte dominated state. Increased densities of Isoëtes kirkii were able to reduce sediment oxygen demand through their root oxygen releases. This reduction in sediment oxygen demand occurred at 32 plants m−2 in a garden soil and 63 plants m−2 in the sediment of a hypo-eutrophic lake, a disparity likely due to the higher initial sediment oxygen demand present in the lake sediments. In a shallow lake, plants present in the hypolimnion will reduce sediment oxygen demand, increasing the amount of time required before anoxic conditions are created and the resulting release of dissolved reactive phosphorus. This will likely decrease the potential for subsequent algal blooms and the associated shading of submerged macrophytes, thus maintaining in-lake conditions that favour macrophytes.

Ecosystem metabolism in the deep and oligotrophic Lake Tanganyika

This study investigated variability in ecosystem metabolism in the meromictic, oligotrophic, and deep Lake Tanganyika. A large buoy equipped with a weather station, oxygen and temperature sensors for every 10 m down to 102 m depth and an irradiance sensor at 0 and 22 m depth, provided a three-month data with one-minute frequency. These data enabled us to derive detailed description of water column mixing and light conditions along with daily depth specific rates of gross primary production, ecosystem respiration and net production over a 3-month period. We applied a mass balance approach which included dissolved oxygen exchange between depth layers driven by mixed-layer deepening and eddy diffusivity from a one-dimensional hydrodynamic model. The vertical extent of the upper mixed layer varied between 21–40 m and the extent of the metalimnion varied between 48–75 m, with the euphotic zone (20–38 m) extending into the metalimnion on several days, providing enough light for primary production to occur below the upper mixed layer. Vertical profiles of metabolism showed several periods with elevated primary production in the metalimnion around the deep chlorophyll maximum. This deep productivity may compensate for the decreasing primary production in the epilimnion caused by climate change induced reductions in nutrient inputs from deeper waters.

Assessment of aquatic ecosystem quality in Dharoi Reservoir using Sentinel-2 satellite imagery

Background: Dharoi Reservoir, located in Gujarat, India, is a vital freshwater resource supporting agriculture, industry, and local communities. Chl-a, a key indicator of water quality, reflects the trophic state and ecological balance of aquatic systems. Objective(s): This study aims to provide comprehensive insights into the water quality dynamics of Dharoi Reservoir, offering valuable information for environmental management and sustainable water resource planning. Methods: This study employs high-resolution Sentinel-2 satellite imagery to analyze Chl-a concentrations in the reservoir during October 2020. The Chl-a index, calculated by dividing Sentinel-2 bands B5 and B4, reveals a spatial distribution of Chl-a concentrations. Results: The Chl-a index ranges from 73.78 to 100. The mean Chl-a index is 91.6 with a standard deviation of 3.27, indicating elevated and variable Chl-a concentrations. Conclusions: The findings contribute to the understanding of the reservoir’s ecological health and assist in making informed decisions for water quality management. This research exemplifies the integration of remote sensing technology and environmental stewardship, promoting sustainable water management practices in the region. Policy recommendations: No policy recommendations are explicitly stated in the abstract, but they could be inferred from the conclusions. For example, one possible policy recommendation is to monitor and regulate the sources of nutrient inputs into the reservoir, such as agricultural runoff, sewage, and industrial effluents, to reduce the risk of eutrophication and algal blooms. Another possible policy recommendation is to implement adaptive management strategies that consider the seasonal and spatial variability of Chl-a concentrations and their impacts on water quality and availability.

Existing wetland conservation programs miss nutrient reduction targets.

Restoring wetlands will reduce nitrogen contamination from excess fertilization but estimates of the efficacy of the strategy vary widely. The intervention is often described as effective for reducing nitrogen export from watersheds to mediate bottom-level hypoxia threatening marine ecosystems. Other research points to the necessity of applying a suite of interventions, including wetland restoration to mitigate meaningful quantities of nitrogen export. Here, we use process-based physical modeling to evaluate the effects of two hypothetical, but plausible large-scale wetland restoration programs intended to reduce nutrient export to the Gulf of Mexico. We show that full adoption of the two programs currently in place can meet as little as 10% to as much as 60% of nutrient reduction targets to reduce the Gulf of Mexico dead zone. These reductions are lower than prior estimates for three reasons. First, net storage of leachate in the subsurface precludes interception and thereby dampens the percent decline in nitrogen export caused by the policy. Unlike previous studies, we first constrained riverine fluxes to match observed fluxes throughout the basin. Second, the locations of many restorable lands are geographically disconnected from heavily fertilized croplands, limiting interception of runoff. Third, daily resolution of the model simulations captured the seasonal and stormflow dynamics that inhibit wetland nutrient removal because peak wetland effectiveness does not coincide with the timing of nutrient inputs. To improve the health of the Gulf of Mexico efforts to eliminate excess nutrient, loading should be implemented beyond the field-margin wetland strategies investigated here.

Cross-shore transport and eddies promote large scale response to urban eutrophication

A key control on the magnitude of coastal eutrophication is the degree to which currents quickly transport nitrogen derived from human sources away from the coast to the open ocean before eutrophication develops. In the Southern California Bight (SCB), an upwelling-dominated eastern boundary current ecosystem, anthropogenic nitrogen inputs increase algal productivity and cause subsurface acidification and oxygen (O2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{2}$$\\end{document}) loss along the coast. However, the extent of anthropogenic influence on eutrophication beyond the coastal band, and the physical transport mechanisms and biogeochemical processes responsible for these effects are still poorly understood. Here, we use a submesoscale-resolving numerical model to document the detailed biogeochemical mass balance of nitrogen, carbon and oxygen, their physical transport, and effects on offshore habitats. Despite management of terrestrial nutrients that has occurred in the region over the last 20 years, coastal eutrophication continues to persist. The input of anthropogenic nutrients promote an increase in productivity, remineralization and respiration offshore, with recurrent O2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{2}$$\\end{document} loss and pH decline in a region located 30–90 km from the mainland. During 2013 to 2017, the spatially averaged 5-year loss rate across the Bight was 1.3 mmol m-3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{-3}$$\\end{document} O2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{2}$$\\end{document}, with some locations losing on average up to 14.2 mmol m-3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{-3}$$\\end{document} O2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{2}$$\\end{document}. The magnitude of loss is greater than model uncertainty assessed from data-model comparisons and from quantification of intrinsic variability. This phenomenon persists for 4 to 6 months of the year over an area of 278,40 km2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{2}$$\\end{document} (∼\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim$$\\end{document}30% of SCB area). These recurrent features of acidification and oxygen loss are associated with cross-shore transport of nutrients by eddies and plankton biomass and their accumulation and retention within persistent eddies offshore within the SCB.

Enhancing long-term river water quality prediction: Construction and validation of an improved hybrid model

To prevent eutrophication of river caused by excessive inputs of nutrients, accurately predicting these nutrient concentrations is of utmost importance. However, long-term accurate predictions of nutrients concentrations remain a challenge. In this study, an improved hybrid algorithm combining adaptive variational mode decomposition and multi-functional recurrent fuzzy neural network (AVMD-MFRFNN) was proposed. Firstly, whale optimization algorithm (WOA) was developed to identify the optimal number of modes for variational mode decomposition (VMD). Then VMD was employed to decompose input data into intrinsic mode fractions (IMFs), benefiting for reducing the noise effect and non-stationarity of data. Then, MFRFNN with the capability of characterizing complex data was developed to train and test the IMFs. The proposed AVMD-MFRFNN achieved impressive results with the root mean square errors (RMSEs) of 0.036 mg/L, 0.758 mg/L and 1.435 mg/L for predicting total phosphorus (TP), chemical oxygen demand (CODMn) and total nitrogen (TN) after 168 hours. These results signify a decrease of 5.3%, 14.1% and 30.1% compared to the second-best compared method. Moreover, this study demonstrates the potential that integrating the proposed AVMD with other methods can enhance the modeling performance of time series. Furthermore, sensitivity analysis results further validate the effectiveness of WOA in optimizing VMD parameter. Finally, the applicability of AVMD-MFRFNN was confirmed by the data from another river section. These results provide new insights and technical support into the management and preservation of river water environment.

Nutrient runoff and leaching under various fertilizer treatments and pedogeographic conditions: A case study in tobacco (Nicotiana tabacum L.) fields of the Erhai Lake basin, China

To ensure water security, it is crucial to understand the characteristics of nitrogen (N) and phosphorus (P) in water and to reduce their inputs. We conducted a 2-year trial (2021–2022) in tobacco fields across three sites in the Erhai Lake basin, China, to comprehensively measure and summarize N and P loss through runoff and leaching for four fertilizer treatments: no fertilizer (CK); farmers' traditional organic fertilizer (FP); chemical fertilizer (CF); and a combination of organic and inorganic fertilizer (OIC). The highest N concentrations were detected in leachate in the early tobacco growth stage, whereas the highest P concentrations occurred in runoff in the middle growth stage. Compared to FP, the OIC treatment improved nutrient uptake in flue-cured tobacco, while also reducing N loss through runoff and leaching by 45.37% and 19.34%, and reducing P loss by 7.22% and 8.26%, respectively. Correlation analyses revealed positive relationships of nutrient loss with soil organic matter content and nutrient inputs; elevation and soil water content exhibited varying correlations with different nutrients. These findings provide a theoretical foundation for the effective management of agricultural non-point source pollution in the Erhai Lake basin and shed light on water pollution pressures worldwide.

Fertilisation strategies and their influence on nutrient flows in organic apple orchards

AbstractIn organic fruit production, permitted fertilisers contain multiple nutrients with stoichiometries differing from the nutrient offtakes of the fruit trees. Furthermore, some pesticides contain nutrients resulting in additional inputs. These conditions may cause unbalanced nutrient supplies and thereby influence the long-term sustainability of the system. An analysis of nutrient management practices in organic apple farms was conducted in three Southern and one Northern German apple-growing region. Data on nutrient inputs (via fertilisers and pesticides) and outputs (via fruit) per orchard were collected along with soil samples from up to five orchards per farm on 19 farms. On average, farmers fertilised 37 kg N and harvested 23 Mg apples per ha and year. Nutrient budgets showed imbalances for N (+ 25 kg ha−1 year−1), P (+ 3 kg), K (− 4 kg), Ca (+ 37 kg), Mg (+ 4 kg), S (+ 53 kg), Na (+ 4 kg) and Cl (+ 3 kg). Base fertilisers like compost or manure contributed to higher nutrient inputs due to a larger P and K-to-N-ratio. Commercial organic fertilisers such as keratins or vinasse contained much lower ratios. The main S input sources were pesticides (46 kg). N inputs by base (p = 0.06) and commercial (p = 0.37) fertilisers had no significant effect on the yield. Balanced nutrition can best be achieved by applying a combination of 20% of the total N demand via base fertilisers, complemented with commercial fertilisers with low element-to-N-ratios (e. g. keratin fertilisers, vinasse or biological N2 fixation). No correlation was found between soil nutrient status and nutrient budgets. Site conditions and internal field nutrient flows (transfer of the inter-row biomass via mulching into the tree row) had a stronger influence on the soil nutrient content than fertilisation strategy. In addition, fruit orchards showed a spatial differentiation of soil nutrient contents. Elevated P and K contents above the recommended range in the tree row were found in 67% of the orchards, while tendencies of depletion were found in the inter-row area. Mulching schemes which transfer biomass from the inter-row area to the tree row need to be adapted to this condition.

Increasing cascade dams in the upstream area reduce nutrient inputs to the Three Gorges Reservoir in China

The upstream cascade dams play an essential role in the nutrient cycle in the Yangtze. However, there is little quantitative information on the effects of upstream damming on nutrient retention in the Three Gorges Reservoir (TGR) in China. Here, we aim to assess the impact of increasing cascade dams in the upstream area of the Yangtze on Dissolved Inorganic Nitrogen and Phosphorus (DIN and DIP) inputs to the TGR and their retention in the TGR and to draw lessons for other large reservoirs. We implemented the Model to Assess River Inputs of Nutrients to seAs (MARINA-Nutrients China-2.0 model). We ran the model with the baseline scenario in which river damming was at the level of 2009 (low) and alternative scenarios with increased damming. Our scenarios differed in nutrient management. Our results indicated that total water storage capacity increased by 98 % in the Yangtze upstream from 2009 to 2022, with 17 new large river dams (>0.5 km3) constructed upstream of the Yangtze. As a result of these new dams, the total DIN inputs to the TGR decreased by 15 % (from 768 Gg year−1 to 651 Gg year−1) and DIP inputs decreased by 25 % (from 70 Gg year−1 to 53 Gg year−1). Meanwhile, the molar DIN:DIP ratio in inputs to the TGR increased by 13 % between 2009 and 2022. In the future, DIN and DIP inputs to the TGR are projected to decrease further, while the molar DIN:DIP ratio will increase. The Upper Stem contributed 39 %–50 % of DIN inputs and 63 %–84 % of DIP inputs to the TGR in the past and future. Our results deepen our knowledge of nutrient loadings in mainstream dams caused by increasing cascade dams. More research is needed to understand better the impact of increased nutrient ratios due to dam construction.