Nitrogen Export Research Articles

Analyses of the inputs and exports of carbon and nitrogen organics by mangroves’s litterfall in the coastal area of Tinanggea, South Konawe Regency

This study aimed to elucidate the inputs and exports of carbon and nitrogen organics by mangrove of Tinanggea, Southeast Sulawesi. The contents of carbon and nitrogen organics in mangrove litters were determined from twice monthly of litterfall collection at the Biology Laboratory of FMIPA, UHO. The inputs and exports of carbon and nitrogen organics by mangroves were calculated based on the monthly litterfall production of mangroves in each stasiun. The input of carbon and nitrogen organics from mangrove litter ranges from 11,72 to 14,30 ton/ha/year for carbon, and ranges from 0,007 to 0,16 ton/ha/year for nitrogen, while they were higher at station T5 and the lower on the T2 station. The mangrove exports organic carbon ranging from 3,52 to 4,29 ton/ha/year, while its organic nitrogen export ranges from 0,07-0,16 ton/ha/year. This study results realized that the inputs and exports of carbon and nitrogen organics are very dynamic in the mangrove ecosystem that indicated their important role on maintaining the productivity of the coastal environment in the Tinanggea and its surrounding areas.

Съдържание и износ на основни макроелементи с биомасата и зърното на ечемик (Hordeum Vulgare L.) отглеждан като последействие

A field study with spring barley (Hordeum vulgare L.) was conducted on the area of long-term balance experiment in Tsalapitsa village near Plovdiv (Bulgaria), on alluvial-meadow soil. Mineral fertilization was not applied to this crop in order to equalize the area regarding nutrient content. The crop grown before barley was maize with 4 variants of fertilization and one control variant: N0P0, N100Р50, N150Р100, N200Р150, and N250P200. The present study aimed to evaluate the productivity, content and uptake of macronutrients (N, P, K, Ca and Mg) with the biomass of barley, grown as aftereffect. Due to the fertilization of the previous crop, different residual amounts of nutrients in soil lead to significant variability in barley yields. The highest grain yield was obtained in variant N250P200 - 3978.8 kg/ha, approximately four times higher than the yield in the control. Nitrogen content in the grain of barley is also influenced by the variants, being the lowest in the control - 1.25%, and the highest in variants N250P200 and N200P150 - 2.13% and 2.09%, respectively. The variability of P, K, Ca and Mg contents by variants is lower. With the total biomass of barley, depending on the variants of the experiment, between 23.2 - 132.7 kg N/ha; 26.6 - 146.3 kg K/ha and 9.3 - 36.5 kg P/ha were exported from the field. A good regression relationship was found between barley grain yield and nitrogen export with the total biomass (R2 = 0.859, P≤0.001).

Exploring river nitrogen and phosphorus loading and export to global coastal waters in the Shared Socio-economic pathways

This global spatially explicit (0.5 by 0.5 degree) analysis presents the nitrogen (N) and phosphorus (P) inputs, processing and biogeochemical retention and delivery to surface waters and river export to coastal seas according to the five shared socioeconomic pathways (SSP). Four systems are considered: (i) human system; (ii) agriculture; (iii) aquaculture; (iv) nature. Exploring the changes during 1980–2015 and 2015–2050 according to the SSPs shows that the natural nutrient sources have been declining in the past decades and will continue to decline in all SSPs in future decades due to massive land transformations, while agriculture, human sewage and aquaculture are becoming increasingly dominant (globally up to 80% of nutrient delivery). More efforts than those employed in any of the SSPs are needed to slow down the global nutrient cycles. One of the drivers of the proliferation of harmful algal blooms is the tendency towards increasing N:P ratios in global freshwaters and export to the global coastal seas; this is the result of increasing N:P in inputs in food production, more efficient biogeochemical retention of P than of N in river basins, and groundwater N legacies, which seems to be most pronounced in a united world that strives after sustainability. The diverging strategies to achieve UN Sustainable Development Goals 14 (life below water), 2 (zero hunger) and 6 (clean water and sanitation) therefore require a balanced management system for both N and P in all systems, that accounts for future nutrient legacies.

Diffuse nutrient export dynamics from accumulated litterfall in forested watersheds with remote sensing data coupled model

Nutrients exported from forest litterfall significantly contribute to the global cycling of elements and the water quality in watersheds. Simulating the watershed discharge load is challenging because of the combined effects of the decomposing litterfall and topographic heterogeneity. We quantified the contribution of diffuse nutrient export from forest litterfall in a low temperature watershed using artificial rainfall experiments and watershed territorial modeling with remote sensing data, and therefore, the critical spatial factors and corresponding nutrient export dynamics were identified. Rainfall intensity and terrain slope were found to be the key factors for nutrient export under different litterfall decomposition conditions. Based on the moderate resolution imaging spectroradiometer data and field observations, the temporal patterns of litterfall biomass of two types of dominant forests (broad-leaved and mixed) were interpreted. The spatial patterns of total organic carbon (TOC), total nitrogen (TN), and total phosphorus (TP) exports from watershed litterfall were simulated by coupling the observed discharge parameters under artificial rainfall conditions and watershed surface flow modeling with the hydrological characteristics of the forested areas. The average watershed TOC, TN, and TP loads exported from the litterfall were approximately 58.22, 7.89, and 0.37 kg ha−1 a−1, respectively. The exported loads of TOC, TN, and TP varied with the forest types, and the loads from the litterfall of deciduous broad-leaved forest were found to be ∼50–70% of loads from the litterfall of mixed forest. A comparison with similar studies worldwide also indicated that low temperature decreased the litterfall decomposition rate and diffuse nutrient export. This study indicated that litterfall nutrients were a key contributor to watershed water pollution, and their spatial discharge trend varied intensively with the terrestrial conditions. The modified simulation methods were found to accurately assess the cycling of nutrients from the forest litterfall on a watershed scale.

Assessment of coordinative relationship between comprehensive ecosystem service and urbanization: A case study of Yangtze River Delta urban Agglomerations, China

Understanding the coordinative relationship between urbanization and ecosystem services (ESs) has a great significance in sustainable development in urban agglomeration. In this paper, InVEST model was firstly used to assess the spatio-temporal evaluation of four types of ESs (water yield, carbon storage, soil retention and nitrogen export) in the Yangtze River Delta Urban Agglomerations (YRDUA) of China from 2000 to 2020. Then comprehensive evaluation index system of urbanization was established from the multi-dimensions of economy, population and land to analyze the urbanization level during the study period. Finally, a comprehensive ecosystem service (CES) index was developed to explore the coordinative relationship between ESs and urbanization by using coupling coordinating degree model (CCDM). The results revealed that: 1) Urbanization has led to greatly land use/ land cover change, which caused the degradation of carbon storage and water purification, and the improvement of water yield and soil retention. The higher water yield and nitrogen export mainly clustered around urban areas, while higher carbon storage and soil retention were distributed in forest-rich cities in the Zhejiang and the southern of Anhui. There were positive correlations between different ESs. And the CES of cities in the YRDUA had deteriorated during the study period. 2) The urbanization levels of almost all cities showed an overall upward trend, with Shanghai the highest urbanization, followed by Nanjing and Hangzhou, and rapid urban expansion mainly occurred in developed urban areas. 3) The coordinative relationship between CES and urbanization in the YRDUA was always in mild incoordination, showing an obvious spatial distribution pattern of “higher in the south, but lower in the north”. The coordinative relationship between CES and urbanization in most cities in the north of YRDUA has not achieved coordination development, with the state of moderate or mild incoordination, while the cities in the south has attained coordination development, with the state of primary or even superior coordination. Therefore, our study suggested that differentiated urban space management and control policies should be made for the YRDUA to improve the overall coordinative relationship between CES and urbanization.

Evolution and determinants of ecosystem services: insights from South China karst

The South China Karst (SCK), the world's largest contiguous karst region, has undergone severe ecological degradation associated with the interaction of fragile natural attributes and human activities. Understanding the causes of changes in ecosystem services (ES) is essential to prevent and control ecosystem degradation and support sustainable development. However, existing studies have not comprehensively explored the impact of natural systems and human activities on karst ES and have failed to consider their spatiotemporal heterogeneity. Here, we used regression analysis to study the spatiotemporal evolution of ES in diverse landscapes (karst and non-karst) of SCK and the impact of human activity on them. Random forest regression and geographically weighted regression analysis were used to explore the key factors and driving forces in different landscape ES. The results show that from 1982 to 2018, ES, such as soil conservation (+8.12%), net primary productivity (+21.14%), carbon storage (+0.86%), nitrogen export (−5.89%), and phosphorus export (−1.46%), were improved, mainly due to re-greening and rewilding, which optimizes the structure of the ecosystem. However, large-scale afforestation led to a decrease in water yield (−13.23%). Urban development worsened habitat quality (−0.50%) and biodiversity (−1.91%). With the intensification of human activities, ES in the karst region showed lower maintenance capacity than in non-karst regions. The study found that the driving factors of ES varied with the differing landscapes. Population distribution in the karst region was the biggest threat to ES, whereas farming in the non-karst region was the main ES threat in this region. In these regions, the improvement in vegetation coverage was helpful in plant-carbon sequestration, and the increase of precipitation increased water yield. Importantly, we found that biodiversity maintenance plays a crucial role in ES. Nature-based solutions combined with proper management strategies can counter ecosystem degradation and help achieve sustainable development.

Measuring and modeling nitrogen export from cranberry farms

AbstractNitrogen (N) pollution is arguably the single greatest threat to coastal water quality in the United States. In the state of Massachusetts, sustainable management of cranberry agriculture requires detailed understanding of potential sources and losses of N, which can contribute to impaired coastal waters. Given the complexity of N transport processes, models are often used to quantify the amount of N delivered from cranberry farms to coastal waters. However, ambiguities in model parameters, inconsistencies in deriving N loading rates, and inaccuracies in spatial coverages leave open questions about the contribution of cranberry agriculture to impaired coastal waters. In this study, we synthesize the methods, assumptions, and results of all N budget studies conducted in cranberry farms from 1995 to 2019. We propose a new analytical framework for measuring N fertilizer export from cranberry farms which includes our best understanding of N retention and transport in cranberry farms. We then apply our results to two watershed land‐use models (Massachusetts Estuaries Project Linked Watershed‐Embayment Model, LM; the Waquoit Bay Nitrogen Loading Model, NLM) to quantify N loads contributed by cranberry farms to the highly eutrophic Wareham River estuary. We find that the LM and NLM are in close agreement with respect to the amount of N delivered from cranberry farms to the Wareham River estuary. In our application of the LM, we estimated that 7791 kg N·yr−1 from cranberry farms, or 15% of the total N load, reached the estuary. By comparison, we found that the NLM estimated slightly higher N loads contributed by cranberry farms to the estuary: 8365 kg N·yr−1, or 16% of the total N load. However, the models gave contrasting estimates of unattenuated N loads from cranberry farms (9670 kg N·yr−1, LM; 12,870 kg N·yr−1, NLM) and the amount of N transmitted through the watershed to the estuary (81% LM; 65% NLM).

Impact of landscape pattern change on water-related ecosystem services: Comprehensive analysis based on heterogeneity perspective

The transformation of surface landscapes by human activities is the main driving factor that affects changes in ecosystem functions and ecological processes, significantly influencing the ability of regional water ecosystems to deliver products and services to human society. However, the relationship between landscape heterogeneity and multiple water ecosystem services and the mechanisms of dynamic change remain unclear, posing challenges for managing and enhancing ecosystem services through landscape management decisions. Taking the Zishui basin as an example, this study aimed to clarify the impact of landscape heterogeneity on water-related ecosystem services and relationships by analyzing the relative importance and comprehensive impacts of landscape structure composition and landscape spatial configuration changes on three ecosystem services (water production, soil conservation, and water purification). These services were quantified for the years 2000, 2005, 2010, 2015, and 2018 using the InVEST model. Furthermore, quantitative indices were constructed to assess the impact of landscape heterogeneity on water ecosystem services. The results show that annual water yield and soil conservation increased at first and then decreased from 2000 to 2018, with 24.48% and 22.50% overall decreases, respectively. In contrast, the total export of N and P decreased at first and then increased, with 3.65% and 5.18% overall increases, respectively. The contribution indices of landscape pattern changes to water yield, soil conservation, nitrogen export, and phosphorus export were 0.04%–2.02%, 0.08 × 10−2%–0.32 × 10−2%, 13.57%–70.05%, and 11.01%–68.22%, respectively, showing interannual and spatial differences. The impact of landscape pattern change on water-related ecosystem services mainly reflects intensity change, which does not change the dominant relationships. Both landscape composition and configuration have impacts on water-related ecosystem services, but the effects of composition are larger than those of configuration. Among them, the proportions of cultivated land, woodland, and construction land, along with changes in Shannon’s diversity index (SHDI), patch density (PD), and edge density (ED) have obvious influences on water-related ecosystem services and show nonlinear relationships. In summary, the impacts of landscape heterogeneity indicators on water-related ecosystem services have obvious category differences, interannual changes, and spatial differences. This study provides new insight into the driving effects of landscape pattern change on the supply of water-related ecosystem services and will provide a reference for practical land management applications and policy formulation of water ecosystem services.

Stacked conservation practices reduce nitrogen loss: A paired watershed study

Combinations of best management practices (BMPs) are needed to achieve nutrient reduction goals in the Mississippi/Atchafalaya River Basin (MARB), but field results are crucial to encourage stacked adoption of BMPs. A paired catchment-scale study (2015–18) was done to assess the impact of (i) BMPs, (ii) precipitation patterns, and (iii) seasonality on nitrogen (N) export. Flow-weighted samples were collected and analyzed for total ammonia nitrogen (TAN), nitrate (NO3–N), and total nitrogen (TN). Catchments Low-BMP 11 and High-BMP 12 had 27.6% and 87.6% areal coverage of BMPs, respectively. No significant difference (p > 0.05) in TAN concentrations was found between Low-BMP 11 (0.023 mg L−1) and High-BMP 12 (0.020 mg L−1). However, NO3–N and TN concentrations were significantly higher (p < 0.05) at Low-BMP 11 (NO3–N: 26.0 mg L−1, TN: 28.7 mg L−1) than at High-BMP 12 (NO3–N: 8.8 mg L−1, TN: 9.2 mg L−1). Two precipitation factors that affected N export patterns were observed. First, N flushing could continue for several years after a drought as elevated NO3–N concentrations were observed in 2015 (i.e., two years after the 2011–2013 drought). Second, higher annual N export was observed when more precipitation occurred during the pre-planting or early-growing season versus later periods. For both catchments, the highest 50% of flows were responsible for majority of the NO3–N export. We estimated that 33–37%, 61–62%, and 82–85% of the NO3–N loads occurred in the 90th, 75th, and 50th flow percentiles, respectively. As demonstrated in High-BMP 12, stacked BMP application effectively lowered NO3–N and TN loads by 60.3% and 59.1%, respectively, relative to Low-BMP 11. Although 27.6% BMP coverage area in Low-BMP 11 was considered low for this study, this coverage area is higher than many other parts of the MARB. This research highlights the importance of joint efforts between landowners in a watershed to meet downstream water quality goals.

Efficiency and feasibility of Best Management Practices to reduce nutrient loads in an agricultural river basin

Excessive use of mineral fertilizers and inappropriate tillage operations are two main drivers of land degradation. The European Green Deal (EUGD) aims to restore the natural functions of ground and surface soil by 2030. EU Member States will be called upon to include mitigation measures in their own management programs. In this context, the current work aimed to evaluate the feasibility of Best Management Practices (BMPs), generally used to counteract soil erosion, in achieving nutrient load reduction, and evaluate their economic convenience in the private and public sector. The Soil and Water Assessment Tool (SWAT) was used to model point and diffuse nutrient sources in the Carapelle basin (Apulia, Italy) and to simulate BMP scenarios. Contour farming (CF), no tillage (NT), reforestation (RF), and two additional scenarios, including the 20% reduction of fertilizers in CF and NT, (CFR) and (NTR), were simulated following the EUGD strategy. For the current land uses, the riverine export of nitrogen (TN) and phosphorous (TP) were ∼49 kg ha-1y-1 and ∼0.044 kg ha-1y-1, respectively. CF and NT increased N-NO3 load both into surface runoff and in terms of leaching. Conversely, RF showed a reduction of N-NO3 losses. CFR and NTR scenarios decreased N-NO3 load both in surface runoff and leached of ∼20%. CFR and NTR represented the best alternative among the analyzed scenarios both for their lower production costs at the farm level and for their savings in terms of nutrient and soil losses. RF was economically profitable in sloped areas, thus representing BMPs that may be implemented in combination with other practices to have a greater impact at the basin scale. BMP implementation requires significant investments (public and private). The results of this study provide the scientific basis for decision-making for agriculture and watershed management.

Impacts of reclamation derived land use changes on ecosystem services in a typical gulf of eastern China: A case study of Hangzhou bay

Reclamation activities can achieve considerable economic benefits, but also cause negative effects on regional ecosystems. Exploring the ecosystem services (ESs) in an economically developed but eco-environment fragile gulf region, and providing decision-making basis for the formulation of land use (LU) policies and ecological protection planning in the gulf region. Based on multi-year land use, meteorological and soil datasets, we analyzed spatiotemporal changes of ESs in Hangzhou Bay (HZB), China, and explored the impact of reclamation activities on ESs. The results showed that the LU change in HZB was marked by a fast increase of urban land and a large transfer of farmland to urban land. Per ES in HZB, water yield and carbon storage increased, while soil retention, habitat quality, and nitrogen export tended to decline. Various ESs failed to achieve coordinative development. The trade-off relationship of ESs was concentrated between carbon storage, nitrogen export, and water yield, and between habitat quality, water yield, and nitrogen export. With the intensification of reclamation activities in HZB, shoreline shrank; morphology tended to be more complicated; and reclamation activities had a significant impact on ESs. Based on the research results, four methods (policies and measures) to promote the coordination development of HZB ecosystem and social economy were proposed, so as to contribute to the high-quality development of the HZB Greater Bay Area.

Seasonal River Export of Nitrogen to Guanting and Baiyangdian Lakes in the Hai He Basin

AbstractEutrophication refers to the nutrient enrichment, leading to blooms of algae. Such blooms in lakes can happen throughout the year because of the changes in nutrient and hydrological cycles. Nutrient export to lakes from rivers is the main cause of eutrophication problems. Seasonal trends in nitrogen (N) export by rivers to lakes are still not well understood. The objective of this study is, therefore, to better understand the seasonal trends in river export of dissolved inorganic N (DIN) to lakes of the Hai He Basin. To this end, we selected Guanting and Baiyangdian as representative lakes, whose drainage areas include various cropping systems. We developed a seasonal version of the Model to Assess River Inputs of Nutrients to lAkes (MARINA‐Lakes) model for Guanting and Baiyangdian while assessing N flows from the land to the lakes. The model accounts for the seasonality in human activities (e.g., cropping systems and fertilizer practices), climate, and hydrology. The effective seasons are winter (December–February), spring (March–May), summer (June–August), and fall (September–November). The model results for the year 2012 indicate that river export of DIN was highest in winter and lowest in summer. Point sources accounted for over 50% of DIN exports to Guanting and Baiyangdian across seasons. Avoiding direct discharges of animal manure (point source) in winter is needed to reduce future lake pollution. We argue that effective lake pollution control requires accounting for seasonal N cycles. Our study can support effective nutrient management and environmental policies.

Spatial Pattern Analysis of a Water-Related Ecosystem Service and Evaluation of the Grassland-Carrying Capacity of the Heihe River Basin under Land Use Change

A key challenge to the sustainability and security of grassland capacity is the protection of water-related ecosystem services (WESs). With the change of land use, the supply of aquatic ecosystem services has changed, and the grassland-carrying capacity has been affected. However, the correlation mechanism between WESs and the grassland-carrying capacity is not clear. In this study, we used the InVEST (Integrated Valuation of Ecosystem Services and Tradeoffs) model to evaluate the impact of land-use change on WESs, and made a tradeoff analysis between WESs and grassland-carrying capacity. Considering that the Heihe River Basin (HRB) was an important grassland vegetation zone, which was a milestone for the development of animal husbandry in China, HRB was taken as a case. The main findings are as follows: (1) the spatial distribution of WESs shows the dissimilation rule, the upper reaches are the main water yield area, the soil retention is weakening in the middle and lower reaches, and the pollution has further increased in the middle and upper reaches. (2) The carrying capacity of animal husbandry decreased in the upper reaches, increased in Shandan County and Zhangye City in the middle reaches, and decreased sharply in other regions. (3) There was a positive correlation between the livestock-carrying capacity and nitrogen export in 2018, which was increasing. As the change of land use has changed the evapotranspiration structure, WESs have undergone irreversible changes. Meanwhile, the development of large-scale irrigated farmland and human activities would be the source of a further intensification of regional soil erosion and water pollution. Therefore, it is necessary to trade off the WESs and animal husbandry under land-use change. This paper revealed how WESs changed from 2000 to 2018, the characteristics of the changes in the spatial and temporal distribution, and the carrying capacity. It aims to provide a scientific basis for coordinating the contradiction between grassland and livestock resources, improving the regional ecological security situation, and carrying out ecosystem management.

Ecosystem Services Evaluation of Nature-Based Solutions with the Help of Citizen Scientists

Ecosystem services are increasingly being considered in decision-making with respect to mitigating future climate impacts. In this respect, there is a clear need to identify how nature-based solutions (NBS) can benefit specific ecosystem services, in particular within the complex spatial and temporal dynamics that characterize most river catchments. To capture these changes, ecosystem models require spatially explicit data that are often difficult to obtain for model development and validation. Citizen science allows for the participation of trained citizen volunteers in research or regulatory activities, resulting in increased data collection and increased participation of the general public in resource management. Despite the increasing experience in citizen science, these approaches have seldom been used in the modeling of provisioning ecosystem services. In the present study, we examined the temporal and spatial drivers in nutrient delivery in a major Italian river catchment and under different NBS scenarios. Information on climate, land use, soil and river conditions, as well as future climate scenarios, were used to explore future (2050) benefits of NBS on local and catchment scale nutrient loads and nutrient export. We estimate the benefits of a reduction in nitrogen and phosphorus export to the river and the receiving waters (Adriatic Sea) with respect to the costs associated with individual and combined NBS approaches related to river restoration and catchment reforestation.

Organic inputs to reduce nitrogen export via leaching and runoff: A global meta-analysis

Organic inputs as a substitution for, or addition to, chemical fertilizers can potentially mitigate N losses. However, it is not well known how their effects on N leaching and runoff depend on application approaches. We conducted a global meta-analysis of 129 studies to compare the effects of organic inputs on N export via leaching and runoff. We compared three application approaches: chemical fertilizer N substituted by organic fertilizer with: 1) equal amounts of total N or, 2) equal amounts of mineral N and 3) additional organic fertilizer N on top of chemical fertilizer. The meta-analysis showed that organic inputs reduced overall N leaching and runoff by 15% and 29%, respectively, without compromising crop yield, and that this effect was significantly influenced by the application approach taken. Organic substitution of chemical fertilizer N with equal amounts of total N decreased both leaching and runoff by more than 30% and hardly affected crop yield. Substitution with equal amounts of mineral N generally increased crop yield by 6% but also increased N leaching by 21%. Organic inputs in addition to chemical fertilizer N did not affect leaching and runoff. The differences between application approaches were reinforced with increased treatment duration. The loss ratios of leaching and runoff were 14% and 4.5%, respectively, from chemical fertilizer, and 9.2% and 2.6%, respectively, from organic fertilizer. The optimal substitution rates differed between leaching (40–60%) and runoff (60–100%) when substitution was based on equal amounts of total N. We conclude that substitution of chemical for organic fertilizer at equal amounts of total N is most effective in reducing N export via leaching and runoff without compromising crop production.

Campylobacterota dominate the microbial communities in a tropical karst subterranean estuary, with implications for cycling and export of nitrogen to coastal waters.

Subterranean estuaries (STEs), the zones in which seawater and subsurface groundwater mix, are recognized as hotspots for biogeochemical reactions; however, little is known of the microbial communities that control many of those reactions. This study investigated the potential functions of microbes inhabiting a cenote and an offshore submarine spring (Pargos) in the near-coastal waters of the Yucatan Peninsula, Mexico. The inland cenote (Cenote Siete Bocas; C7B) is characterized by a chemocline that is host to an array of physicochemical gradients associated with microbial activities. The chemocline includes an increasing gradient in sulfide concentrations with depth and a decreasing gradient in nitrate concentrations. The microbial community within the chemocline was dominated by Sulfurimonas and Sulfurovum of the Campylobacteria, which are likely responsible for sulfide oxidation coupled with nitrate reduction. Although C7B has not been directly connected with Pargos Spring, water discharging from the spring has physicochemical characteristics and microbial community structures similar to C7B, strongly suggesting biogeochemical processing in the STE impacts groundwater composition prior to discharge. This work yields insight into the microbial communities and biogeochemical reactions in STEs in karstic aquifers and provides evidence for the importance of Campylobacteria in controlling nitrate concentrations exported to marine springs.

Dissolved Inorganic Nitrogen Input via Net Nitrogen Mineralization under Antibiotics and Warming from the Water Level Fluctuation Zone of a Three Gorges Tributary

The water level fluctuation (WLF) zone is one of the dominant sources of total dissolved inorganic nitrogen (TDN) export via net nitrogen (N) mineralization in the Three Gorges Reservoir (TGR). However, antibiotics pollution may impact the process of TND exports from WLF zone in the TGR, especially under drying-rewetting processes and climate warming, and thus increasing the risk of eutrophication in the tributaries of the TGR. The effects of the antibiotics Griseofulvin (GIN) and Fosfomycin (FIN) with 0, 0.2 and 0.4 g kg−1 net N mineralization rate (NMR) from WLF-zone soil in the Pengxi river, a typical tributary of the Yangtze River, under 25 and 35 °C were estimated in 30-day flooding and drying incubations. The results showed that GIN concentrations, temperatures and their interaction significantly affect net-nitrification rates (NNR) and NMR under drying and did not significantly affect NNR under flooding. FIN concentrations and temperatures solely influenced the NNR under flooding. The amounts of TDN exports via NMR without antibiotics from the WLF zone of Pengxi River are 6883.8 (flooding, 25 °C), 9987.3 (flooding, 35 °C), 9781.6 (drying, 25 °C), and 27,866.5 (drying, 35 °C) t year−1, which is 21.0, 29.8, 30.4 and 84.8 times of the permissible Class A discharge in China according to (GB18918-2002). Thus, the NMR of WLF zone should be controlled whether there is antibiotics pollution or not, especially during the dry period for alleviating water eutrophication. This study will be helpful for the assessment of nitrogen budgets in the WLF zone to eutrophication in the Three Gorges Reservoir.

Controls of Organic Carbon and Nutrient Export from Unmanaged and Managed Boreal Forested Catchments

Understanding the anthropogenic and natural factors that affect runoff water quality is essential for proper planning of water protection and forest management, particularly in the changing climate. We measured water quality and runoff from 10 unmanaged and 20 managed forested headwater catchments (7–12,149 ha) located in Finland. We used linear mixed effect models to test whether the differences in total organic carbon (TOC), total nitrogen (TN) and total phosphorus (TP) export and concentrations observed can be explained by catchment characteristics, land use, forest management, soil fertility, tree volume and hydrometeorological variables. Results show that much of variation in TOC, TN and TP concentrations and export was explained by drainage, temperature sum, peatland percentage and the proportion of arable area in the catchment. These models explained 45–63% of variation in concentrations and exports. Mean annual TOC export in unmanaged catchments was 56.4 ± 9.6 kg ha−1 a−1, while in managed it was 79.3 ± 3.3 kg ha−1 a−1. Same values for TN export were 1.43 ± 0.2 kg ha−1 a−1 and 2.31 ± 0.2 kg ha−1 a−1, while TP export was 0.053 ± 0.009 kg ha−1 a−1 and 0.095 ± 0.008 kg ha−1 a−1 for unmanaged and managed, respectively. Corresponding values for concentrations were: TOC 17.7 ± 2.1 mg L−1 and 28.7 ± 1.6 mg L−1, for TN 420 ± 45 µg L−1 and 825 ± 51 µg L−1 and TP 15.3 ± 2.3 µg L−1 and 35.6 ± 3.3 µg L−1. Overall concentrations and exports were significantly higher in managed than in unmanaged catchments. Long term temperature sum had an increasing effect on all concentrations and exports, indicating that climate warming may set new challenges to controlling nutrient loads from catchment areas.

The influence of landscape spatial configuration on nitrogen and phosphorus exports in agricultural catchments

ContextNitrogen (N) and phosphorus (P) exports from rural landscapes can cause eutrophication of inland and coastal waters. Few studies have investigated the influence of the spatial configuration of nutrient sources—i.e. the spatial arrangement of agricultural fields in headwater catchments—on N and P exports.ObjectivesThis study aimed to (1) assess the influence of the spatial configuration of nutrient sources on nitrate (NO3−) and total phosphorus (TP) exports at the catchment scale, and (2) investigate how relationships between landscape composition (% agricultural land-use) and landscape configuration vary depending on catchment size.MethodsWe analysed NO3− and TP in 19 headwaters (1–14 km², Western France) every two weeks for 17 months. The headwater catchments had similar soil types, climate, and farming systems but differed in landscape composition and spatial configuration. We developed a landscape configuration index (LCI) describing the spatial organisation of nutrient sources as a function of their hydrological distance to streams and flow accumulation zones. We calibrated the LCI’s two parameters to maximise the rank correlation with median concentrations of TP and NO3−.ResultsWe found that landscape composition controlled NO3− exports, whereas landscape configuration controlled TP exports. For a given landscape composition, landscape spatial configuration was highly heterogeneous at small scales (< 10 km2) but became homogeneous at larger scales (> 50 km2).ConclusionsThe spatial configuration of nutrient sources influences TP but not NO3− exports. An ideal placement of mitigation measures to limit diffuse TP export should consider both the hydrological distance to streams and flow accumulation zones.

Phosphorus concentrations into a subtropical lake strongly influence nitrogen accumulation, nitrogen export, and Chl a concentrations

We measured water quality monthly for 22 years in water entering, within, and exiting a 65 km2 shallow polymictic and eutrophic freshwater lake in the northern Gulf of Mexico. Fertilizer use in the watershed is the dominate source of phosphorous (P) going into the lake and controls the lake’s P concentrations, but nitrogen (N) fertilizer use was not related to total nitrogen concentration in the lake. Half of the particulate P entering the lake is trapped within it and there is a net accumulation of N that appears to be from the stimulation of nitrogen fixation. The lake’s concentration of Chlorophyll a (µg Chl a l−1) and increase in N in the lake was directly related to the concentration of P in water entering the lake. Variations in the Chl a concentration within a freshwater lake downstream are also directly related to the annual use of P fertilizer, but not to N fertilizer use. Reducing agriculture-sourced P runoff will lower (but not eliminate) both the frequency of algal blooms within Lac des Allemands and the amount of N delivered to the estuary.