Search Results (129)

Due to its long-term and high-frequency observation capabilities, remote sensing is widely recognized as an indispensable and preferred technology for large-scale and cross-regional water quality monitoring. This paper comprehensively reviews the recent progress of remote sensing for water environment monitoring, predominantly focusing on remote sensing data sources, inversion indices, and inversion models. Specifically, we summarize the inversion methods for commonly monitored water quality parameters, including optically active constituents (such as chlorophyll-a, colored dissolved organic matter, total suspended solids, and water clarity) and non-optically active constituents (including total nitrogen, total phosphorus, and chemical oxygen demand). Furthermore, the applications of remote sensing in the field of environmental sciences such as spatiotemporal evolution and driver factor analysis of water quality, carbon budget research, and pollution source identification are also systematically reviewed. Finally, we propose that atmospheric correction algorithm improvement, multi-source data fusion, and high-precision large-scale inversion algorithms should be further developed to reduce the current dependence on empirical observation algorithms in remote sensing and overcome the limitations imposed by temporal and spatial scales and that more inversion models for non-optically active parameters should be explored to realize accurate remote sensing monitoring of these components in the future. This review not only enhances our understanding of the critical role of remote sensing in inland water quality monitoring but also provides a scientific basis for water environment management. Full article

Nitrogen (N) derived from the decomposition of litter from cover crops can contribute to the mineral nutrition of citrus trees. This study aimed to assess the prior contribution of N derived from the decomposition of forage radish (Raphanus sativus) and black oats (Avena strigosa) to Satsuma mandarin tree N demand. Forage radish and black oats were grown and enriched with ¹⁵N stable isotope. Two studies were conducted on (1) non-bearing, potted satsuma mandarin seedlings for 120 days in the greenhouse (Experiment 1) and (2) bearing field-growing Satsuma mandarin trees for 270 days (Experiment 2). Tree growth and total N and ¹⁵N concentrations were determined in annual and perennial organs of citrus and soil. The highest value of N derived from the decomposition of cover crop root residues was observed in the leaves and roots of non-bearing trees, while the highest amount of N derived from shoot residue decomposition was observed in the leaves of bearing trees. The results showed little contribution of the decomposition of residues of forage radish and black oats on the total N budget of annual and perennial organs of both bearing and non-bearing Satsuma mandarin trees, probably because the climatic conditions promoted a fast N mineralization and possible losses through volatilization and leaching. Full article

This study evaluated water quality, growth, and partial budget analysis (PBA) for Penaeus vannamei, comparing super-intensive Biofloc Technology (BFT) and Recirculating Aquaculture Systems (RAS). The 69-day trial used 100 L units with two treatments (RAS and BFT), each with three replicates. Shrimp were initially reared in a 30-day nursery to a weight of 0.10 ± 0.04 g and then stocked at 500 shrimp m⁻³. Biofloc growth in BFT was promoted by maintaining a C:N ratio of 15:1, adding dextrose when total ammonia nitrogen (TAN) reached 1 mg L⁻¹. Probiotics (3 g m⁻³) were administered daily to both groups. TAN levels in BFT initially spiked but stabilized after 36 days. Vibrio abundance was initially higher in RAS, but by the end of the trial, it was higher in BFT. Final weight, weekly growth ratio, and yield were greater in BFT, whereas feed conversion ratio (FCR) and water use were higher in RAS. Survival rates were 83.33% in BFT and 88% in RAS. BFT achieved a superior net benefit/cost compared to RAS. Although RAS more effectively controlled nitrogenous compounds, BFT exhibited better growth performance, with higher final weights, lower FCR, and better Vibrio management. The partial budget analysis indicated an economic advantage for BFT, with a net positive benefit of $2270.09 when shifting from RAS to BFT due to lower operating costs and higher shrimp yield. Among these two sustainable production systems, BFT was more productive while utilizing less natural resources. Full article

This study employs an integrated numerical modeling approach using MODFLOW and MT3D to simulate groundwater flow and nitrate transport in the alluvial aquifer of Hennaya plain. The groundwater flow model was calibrated and validated against observed hydraulic heads, showing excellent agreement in both steady-state and transient conditions, with a correlation coefficients (R²) of 0.99 and 0.987, respectively. Meticulous calibration yielded adjusted hydraulic conductivity values between 10⁻¹ and 10⁻¹¹ m/s, with effective porosity ranging from 0.03 to 0.34 and total porosity values varying from 0.29 to 0.38 across the aquifer. Water budget analysis revealed that the aquifer’s primary recharge occurs from the southern side. Nitrate transport modeling indicated that advection is the dominant process, with contaminants migration predominantly occurring from south to north, following the groundwater flow direction. Pollution levels were found to decrease gradually with distance from sources, confirming agricultural activities and sewage disposal as primary contributors to nitrate contamination. Predictive scenarios over a 40-year period explored various management strategies, which suggest that maintaining current nitrogen input rates will lead to continued increases in nitrate pollution, while a 50% reduction in agricultural inputs could significantly improve groundwater quality. However, even with substantial reductions, nitrate concentrations are not expected to reach levels safe for drinking within the simulation timeframe. This study underscores the need for immediate and sustained action to address nitrate pollution in the Hennaya Plain aquifer, emphasizing the importance of stringent nitrogen management practices, particularly in the agricultural sector. Full article

Natural superabsorbent polymers (SAPs) were essential coating materials for developing slow-release fertilizers (SRFs) due to low cost and biodegradability. However, conventional natural SAPs were unsuitable for rice systems due to low stability and short slow-release period. Herein, a natural SAP with a semi-interpenetrating polymer network was prepared by poly (γ-glutamic acid) (PGlu), diatomite, and pullulan polysaccharide and combined with biochar to develop double-layer co-coated slow-release urea for rice systems. The results indicated that diatomite and pullulan modification significantly improved the slow-release capacity of SAP, with a significant increase in the average fertilizer ¹⁵N content of the soil profile by 37.9 ± 7.4% in 14–56 days. The improved slow-release capacity had significant benefits for the sustainability of the rice system, which increased plant N uptake by 17.2 ± 4.8%, decreased fertilizer N losses by 30.4 ± 7.2%, and increased rice grain yield by 9.88 ± 3.6%. More importantly, this natural SAP was fully degradable and its decomposition products are large amounts of small-molecule nutrients that could provide additional C, N, and Si to rice. Therefore, novel co-coated SRF may emerge as a greatly promising candidate for future intensive paddies. Full article

Lake Trafford, a 600-ha subtropical lake in southwestern Florida, has suffered from over 50 years of cultural eutrophication, resulting in the invasion of Hydrilla verticillata and organic sediment accumulation due to herbicide treatments. This study aimed to assess the effects of dredging on nutrient dynamics. A pre-dredging nutrient budget, developed using land use models and climatic data, estimated nutrient loads of 190 kg d⁻¹ for total nitrogen (TN) and 18.6 kg d⁻¹ for total phosphorus (TP), with total maximum daily loads (TMDLs) of 70.4 kg d⁻¹ for TN and 4.15 kg d⁻¹ for TP. Post-dredging analysis, using detailed spatiotemporal data, showed higher nutrient loads of 274.3 kg d⁻¹ for TN and 24.2 kg d⁻¹ for TP. While dredging reduced legacy nutrient accumulation, it led to increased nutrient influx from groundwater, caused by the exposure of organic sediment, as evidenced by increased lake water electrical conductivity. These findings demonstrate the importance of conducting thorough pre-dredging assessments to mitigate unintended consequences, offering practical insights for managing nutrient loads and improving restoration strategies in eutrophic lakes. Full article

Sustainability in agroecosystems relies on the optimized use of resources to achieve consistent yields while maintaining or improving soil health. The monitoring of soil quality is crucial when changes from rainfall-fed to irrigated crop systems occur. The objective of this study was to assess the impact of different crop successions in the Mediterranean area under irrigation and different technical practices. The soil nitrogen–phosphorous–potassium (NPK) and soil organic carbon (SOC) balances were observed in four fields with irrigated annual crops in a two-year succession timeframe, namely, sunflower–maize (P1), sunflower–clover (P2), maize–sunflower (P3), and alfalfa–alfalfa (P4). The SOC and nutrient balance, integrating the total irrigation, mineral fertilizers, and exported yield, was calculated for each farm. Except for maize–sunflower succession (P3), all fields presented a negative SOC balance at the end of the two-year crop succession, indicating losses from 2.84 to 4.91 Mg SOC ha⁻¹ y⁻¹. While in N-fixing plants the soil N decreased, in the remaining crops a surplus was observed, possibly leading to future N losses. The continuous depletion of soil P revealed a potential underestimation of this nutrient. Soil K appears to be related to specific crop management practices, namely, crop residue incorporation after harvest. In annual irrigated crops under Mediterranean conditions, crop succession can induce soil fertility degradation if conservation practices are absent. Full article

To understand potential sources and losses of nitrogen from farming systems in Darusa, Bangladesh, a detailed survey of farming practices was conducted. A total of 100 households were randomly selected using demographic and agricultural information about the farmers in the study area. Data were used to stratify the farmers according to their operational land holding, livestock numbers (tropical livestock unit), use of irrigation, age, and educational level. Four clusters of farm households were identified, and nine households were randomly selected from each cluster for a total of 36 households. These 36 households completed more detailed surveys about their cropping and livestock. The surveys identified local practices of nitrogen management in different crops and types of livestock. Further information on traditional practices for soil fertility management was obtained by interviewing selected farmers. The results show that the major use for organic residues from crops and livestock is to provide fuel. Crop residues were used as fuel by 84% of farmers, with 23% using all of their crop residues as fuel. Some manure was used as fuel by all farmers, with 56% of farmers using most of their manure as fuel. As a result, 23% used no crop residues and 56% used less than half of their manure to improve soil fertility. This suggests that recycling of nitrogen in the study area is low. Soil analysis indicates that the organic matter and nitrogen contents of the soil in the study area were only 1.43% and 0.08%, respectively. Therefore, further recycling of organic residues should be practiced in order to reduce losses of available nitrogen from the system. More research is needed to quantify nitrogen lost by these practices and to draw up a full nitrogen budget for the study area. Full article

While the biogeochemical properties of the Israeli coastal shelf (ICS) are similar to adjacent pelagic waters, the external sources of inorganic nitrogen (N) are very different. The main source of ‘new’ N to the pelagic zone is deep winter mixing, with minor contributions from atmospheric deposition and eddy diffusion across the nutricline. For the ICS, major N sources include offshore water advection (260 × 10⁶ mol N y−¹), atmospheric input (115 × 10⁶ mol N y−¹), and riverine input (138 × 10⁶ mol N y−¹), which primarily consists of treated wastewater and stormwater runoff. Direct pollutant discharge from sewage outfalls and submarine groundwater discharge are relatively minor. Key N sinks are new production (420 × 10⁶ mol N y−¹) and sediment deposition and uptake (145 × 10⁶ mol N y−¹). Inputs of nitrate and ammonium were similar and dominant in winter. Unlike temperate shelves, where riverine input is dominant, here it was only slightly higher than atmospheric input, with net N advection onto the shelf being significant. External N inputs did not change net primary production (NPP) by more than ~30% or affect dominant pico and nanophytoplankton genera, except in localized patches. This study offers baseline values for future climate and environmental change assessments. Full article

Water pollution with nitrogen (N) from agriculture constitutes a persisting environmental problem in intensive farming regions worldwide. Understanding the spatio-temporal interconnection between agricultural N emissions and N inputs to water bodies is key to evaluating and improving existing mitigation policies. Nitrogen flux models are an indispensable tool for addressing these complex research questions in the land use–water nexus, requiring adequate data on agricultural N surpluses. However, high-resolution farm management data are not readily available to the scientific community. We develop a municipality-level agricultural N budget model for Germany based on farm-level administration data from the Integrated Administration and Control System (IACS) and regional expert knowledge. We estimate a total agricultural N surplus of 58 kg N ha⁻¹ of utilised agricultural area as the three-year average for 2014–2016. About 90% of municipalities exhibit N surpluses between 21 and 99 kg N ha⁻¹. Evaluation with collected farm accountancy data revealed a good fit of the modelled (with observed) mineral N quantities applied. Our results highlight the potential of farm-level data for N flux models. Due to the ubiquitous reporting of land use and farming structures in the IACS, our approach can be adapted in other countries of the EU to serve as a harmonised backbone of monitoring and policy impact assessments. Full article

Little is known about the effect of the long-term application of organic and inorganic fertilizers on P-use efficiency, P budget, and the residual effect of P fertilizer. To clarify the effect of different fertilization on soil P balance in a rice (Oryza sativa L.)–wheat (Triticum aestivum L.) rotation system is helpful to promote the sustainable development of agriculture. Thus, a thirty-five-year fertilizer experiment was conducted with eight treatments, including an unfertilized control (CK); chemical nitrogen (N), phosphorus (P), and potassium (K) fertilizers; and organic manure (M) either alone or in combination treatments (N, NP, NPK, M, MN, MNP, and MNPK). The results indicated that crop yields and P uptake were higher in the combined application of manure and chemical fertilizer treatments than in the manure or chemical fertilizer alone treatments. Soil P budget indicated a 23.4–55.4 kg P ha⁻¹ yr⁻¹ surplus in the organic combined with or without mineral fertilizer treatments, but the soil P budget indicated a 20.0 and 21.9 kg P ha⁻¹ yr⁻¹ deficit in the control and N treatments. The proportion of residual fertilizer P converted to soil available P in NP, NPK, M, MN, MNP, and MNPK treatments was 4.5%, 4.8%, 19.1%, 19.0%, 11.5%, and 13.3%, respectively, over a 35-year period. Furthermore, according to the higher P content and crop uptake in organic manure treatment compared with chemical P fertilizer alone, an organic addition could effectively reduce the use of chemical fertilizer and become an effective way of sustainable development in practice. Therefore, the combined application of organic and inorganic fertilizer will be a practical method to increase crop yields and soil P status in a rice–wheat planting system. Full article

Intensifying soil health means managing soils to enable sustainable crop production and improved environmental impact. This paper discusses soil health intensification by reviewing studies on the relationship between soil structure, soil organic matter (SOM), and ecosystem carbon budget. SOM is strongly involved in the development of soil structure, nutrient and water supply power, and acid buffering power, and is the most fundamental parameter for testing soil health. At the same time, SOM can be both a source and a sink for atmospheric carbon. A comparison of the ratio of soil organic carbon to clay content (SOC/Clay) is used as an indicator of soil structure status for soil health, and it has shown significantly lower values in cropland than in grassland and forest soils. This clearly shows that depletion of SOM leads to degradation of soil structure status. On the other hand, improving soil structure can lead to increasing soil carbon sequestration. Promoting soil carbon sequestration means making the net ecosystem carbon balance (NECB) positive. Furthermore, to mitigate climate change, it is necessary to aim for carbon sequestration that can improve the net greenhouse gas balance (NGB) by serving as a sink for greenhouse gases (GHG). The results of a manure application test in four managed grasslands on Andosols in Japan showed that it was necessary to apply more than 2.5 tC ha⁻¹ y⁻¹ of manure to avoid reduction and loss of SOC in the field. Furthermore, in order to offset the increase in GHG emissions due to N₂O emissions from increased manure nitrogen input, it was necessary to apply more than 3.5 tC ha⁻¹y⁻¹ of manure. To intensify soil health, it is increasingly important to consider soil management with organic fertilizers that reduce chemical fertilizers without reducing yields. Full article

Aquaculture is increasing globally, providing protein to a growing population, but little is known regarding the nutrient budgets in aquaculture. To obtain insight into how management practices impact nutrient fluxes in freshwater aquaculture earthen ponds worldwide, we conducted a literature review. Our literature search yielded 23 papers in which nutrient budgets were reported. Our results showed that the main nutrient inputs are inlet water, feed, and fertilizers, but they varied according to location and management practices. Overall, feed and fertilizers constituted the predominant nutrient sources, accounting for up to 99% of the total inputs. The most quantified outputs were outlet water, fish, and sedimentation. Our findings indicate that only up to 20% of carbon, 45% of nitrogen, and 60% of phosphorus are assimilated by the fish. In some systems, up to 80% of carbon, 80% of nitrogen, and 60% of phosphorus accumulate in pond bottoms; in other systems, the outflow represents substantial losses of up to 16% of carbon, 76% of nitrogen, and 55% of phosphorus. More insight into nutrients’ fate in fishponds is crucial from a sustainability perspective, as feed and fertilizer use can likely be optimized, reducing operational costs and the potential impact on the surrounding environment and atmospheric greenhouse gas concentrations. Full article

This study presents a county-level analysis and visual assessment of Iowa’s Food–Energy–Water systems (IFEWs), focusing on the interdependencies of agricultural practices, nitrogen management, and energy production. We use data from the USDA National Agricultural Statistics Service and other sources to assess cropland-nitrogen sources, animal-based-nitrogen contributions, and ethanol production capacity across Iowa’s counties. Our methodology leverages geoprocessing and interpolation tools to address data availability challenges and refine nitrogen surplus (Ns) estimates. The results reveal spatial–temporal dynamics of cropland-nitrogen, quantify non-point nitrogen sources at the county level, and evaluate the impact of energy systems on the IFEWs balance. We discuss the implications of our findings for sustainable agriculture, environmental management, and energy production in Iowa. The study highlights the need for integrated approaches to address the complex interactions within the IFEWs and informs policy development for sustainable resource management. Full article