Total Nutrient Inputs Research Articles

Wheat bran addition methods in Pacific white shrimp (Litopenaeus vannamei) biofloc systems

Incorporating non-starch polysaccharides (NSP) as a slowly degradable carbohydrate source in pelleted feed can simplify biofloc system management, compared to external carbon addition. NSP-containing ingredients like wheat bran synchronizes carbon input with the system organic matter dynamics compared to simple sugars. This study evaluated the effect of two methods of addition of an NSP-rich carbon source, wheat bran, to a Pacific white shrimp (Litopenaeus vannamei) biofloc system; supplementation via feed (wheat bran diet; WBdiet) and direct addition to the water (CONdiet+WB). The amount and composition of the total nutrient input to each mesocosm of the treatments was the same. A digestibility and a growth experiment were carried out separately for 35 and 42 days, respectively. The nutrient digestibility was overall lower in shrimp fed the WBdiet compared to the CONdiet, but without an effect on shrimp final weight, production, and survival. When comparing the methods of addition, neither of the approaches altered the shrimp nutritional quality. As expected, a difference in faecal C:N ratio was observed; 21 vs. 17 for WBdiet and CONdiet, respectively. The difference in faeces composition did not affect biofloc quantity, quality, and chlorophyll-a concentrations, and resulted in comparable water quality and microbial activity. Our study concluded that both NSP-addition methods, either via feed or via the water, were equally effective. When compared to the traditional addition of carbohydrate to the water, supplementing NSP-containing carbon sources via the feed can be a more efficient approach in terms of labour and feeding management practices.

Status quo of fertilization strategies and nutrient farm gate budgets on stockless organic vegetable farms in Germany

Fertilizer management in stockless organic vegetable production is strongly affected by external nutrient purchases due to the high nitrogen (N) and potassium (K) requirements of vegetables. However, the database on nutrient flows and budgets in organic vegetable farming in Europe is very limited. Therefore, a survey based on semi-structured interviews was carried out comprising 12 organic horticultural farms in Germany. The results show that three different main fertilizer categories are used as inputs in different ratios by the inventoried farms: (1) base fertilizers (e.g., composts, solid farmyard manures), (2) commercial organic N fertilizers (e.g., keratins or plant products from food production or fermentation processes), and (3) commercial mineral fertilizers (e.g., potassium sulfate), all of which are approved for organic production. Ninety percent of the total nutrient inputs to the farms came from these fertilizers and biological N2 fixation, with the remaining 10% coming from other inputs, such as seeds or growing media. The estimated yearly average total farm budgets were nearly balanced across all farms with moderate surpluses (67.5 kg N ha−1, 2.06 kg P ha−1, and 0.26 kg K ha−1). However, large imbalances were found for most of the individual farms. These imbalances indicate the risk of nutrient accumulation or nutrient depletion in the soil, depending on the fertilization strategy and productivity of the farm. More specifically, increasing N share from base fertilizers led to increased P and K budgets, while strategies based on the use of large amounts of keratins led to the opposite—K and P depletion. We concluded that balanced nutrient management in organic vegetable production systems requires a thorough calculation and should combine the use of base fertilizers, commercial fertilizers with low P content, and increased N supply via BNF.

Assessing nutrient budgets and N2O emission of newly constructed rice-giant freshwater prawn co-culture on reclaimed land

In recent years, newly constructed rice-giant river prawn (Macrobrachium rosenbergii) co-culture has been widely applied on reclaimed land in southeast China. Raising M. rosenbergii in paddy fields can alter nutrient budgets and have environmental impacts. However, the exact impacts remain unclear. Here, a field experiment was conducted using M. rosenbergii and Macrobrachium nipponense in reclaimed paddy fields to assess and compare the nutrient budgets and N2O emissions of the two ecosystems, henceforth referred to as RS1 and RS2, respectively. Each ecosystem was stocked with 150,000 post-larvae per ha and then compared with a rice monoculture system (RM) to evaluate the environmental impacts of rice-shrimp co-culture. In RS1, the main inputs for N and P were fertilizer and artificial feed, accounting for 59.35% and 34.01% of the total N inputs and 53.15% and 41.43% of the total P inputs, respectively. In RS2 and RM, fertilizers dominated the nutrient budget, accounting for more than 79.28% of the total nutrient input. Nutrient exports were dominated by rice (straw+grain) and commercial shrimp in RS1, accounting for 33.44% and 18.66% of N and 55.56% and 20.02% of P, respectively. The wastewater drainage, NH3 volatilization, and N2O emissions contributed to the remainder nutrient budget. Particularly, the N2O emission fluxes in RS1 (2.21 ± 0.32 kg·ha−1·yr−1) were significantly higher than those in RS2 (1.78 ± 0.24 kg·ha−1·yr−1) and RM (1.56 ± 0.17 kg·ha−1·yr−1) over the one-year experiment. Changes in environmental variables (including NH4+-N, NO2--N, DO, pH, SP, etc.) significantly contributed to the enhanced N2O emissions following the conversion from the reclaimed paddy field to RS1. These results implied that RS1 improved the yields of shrimp and rice grains but at the cost of increasing N2O emissions. Considering the wide distribution of reclaimed paddy fields in southeast China, M. rosenbergii could serve as an ideal alternative species in rice-shrimp co-culture systems to increase nutrient utilization efficiency, although N2O emissions still need to be reduced to mitigate the negative environmental impacts.

Budidaya Hidroponik Pakcoy (Brassica Rapa L) dan Ikan Nila dengan Sistem Aquaponik (Studi Kasus Desa Losari Nganjuk)

Aquaponics is a combined system of fish farming techniques and hydroponic plant cultivation. Fish manure and feed residues are very dependent on the supply of nutrients in the aquaponic system of red tilapia (Oreochromis niloticus) aquaculture. The level of production of vegetable crops in a certain area is also influenced by the total nutrient input ratio of feed to domestic fish per day. The aquaponic system utilizes optimum water supply for each commodity by utilizing a recirculation system. The type of fish used is fish that live in freshwater, a type of tilapia. Fish farming includes the maintenance of fish, which pays attention to the growth and development of fish. Hydroponics itself is a way of farming without using soil as a medium but using water which contains controlled nutrients containing the essential elements needed for plant growth. The location of this research was conducted in Losari Village, Kec. Gondang, Kab. sleepy. It aims to increase the demand for vegetables, limited land and space, efficiency in land use, and decoration. In addition, this cultivation system allows for increased production of cultivated products with limited land and water sources, and creates its own beauty. (9 pt).

Macronutrients (NPK) balance in rice field and dryland maize cropping systems

Fertilisers, especially those containing NPK nutrients, have become a necessity in farming both rice fields and dry land. Most of the application of fertilisers is based on plant commodities and less based on the nature of the diversity of the soil or growing media. This study aimed to determine the balance of NPK nutrients and the nutrient elements that became the limiting factor in the rice and dryland maize cropping systems. The study was conducted at a rice field in Jember District and on dry land in Bogor District with maize plants. The fertiliser used is organic fertiliser. Nutrient balance is obtained by calculating the difference between the total input of nutrients N, P, and K given and the total output of nutrients N, P, and K transported by plants. The results showed that the combination of fertilizing treatment with biochar (50%), fish waste (25%), and chicken manure (25%) up to 10 t/ha on rice field soil at the experimental location in Jember had to limit factors for plant growth: low organic matter content, trace elements essential nutrients N and P are also low. Likewise, the combination of inorganic NPK fertiliser treatment with organic fertiliser up to 600 kg/ha on dry land in Bogor has not been able to improve its fertility status with limiting factors: low organic matter content, low N-total, and low exchangeable K.

Eutrophication Assessment Using Phytodiversity at the Land-Water Interface of Lake Anasagar of Ajmer

Since most of the water, silt, nutrients, and organic inputs from the catchment areas must pass through theland-water interface before reaching the water body, the biota of this zone and the ecosystem processesoperating therein play a significant role in regulating water quality, biodiversity and productivity of inlandwaters. Therefore, this zone can be considered as a biological frame of the aquatic ecosystem. As the effectof pollutants coming from various anthropogenic activities and factors operating on land are morepronounced at the interface, the aquatic flora growing here may be indicative of trophic state of the waterbody. The present study deals with phytoplankton and macrophytes as a criterion for trophic evaluation ofAnasagar- a perennial freshwater lake of Ajmer which is being influenced by a number of anthropogenicactivities on its margin. Human settlements and construction activities in the catchment areas lead todeterioration of the water quality of the lake. The study indicates that rather than physico-chemicalcharacteristics used to classify wetlands under oligo- and eutrophic scales, Phytodiversity is a potent criterionfor trophic evaluation. As a major element of aquatic biota, the algal community often exhibits dramaticchanges in response to different types of pollutants. Hence, the diversity of algal component in the aquaticecosystem serves as a reliable index for biomonitoring of pollution load. Land-water interface is rich inalgal diversity, in all 123 algal species belonging to Cyanophyceae (41), Chlorophyceae (48),Bascillariophyceae (22) and Euglenophyceae (12) were recorded. On the basis of number of algal speciesbelonging to various groups, Nygaard Trophic State Indices were calculated which indicate hypereutrophicstatus of wetland. Wetland plants in land-water interface play an important role in nutrient dynamics. Thecontribution of some dominant macrophytes in nutrient enrichment at the land-water interface was alsoassessed. It was estimated that among the macrophyte species, Azolla pinnata and Trapa bispinosa contributedmaximum to the total nutrient inputs into the lake waters. If these macrophyte species are removed beforedecomposition Starts, nutrient enrichment of the lake may be checked to a large extent. Recently manyinitiatives have been taken to restore Lake Anasagar under National Lake Conservation Program throughinstallation of water treatment plant and by providing aeration in the water body. This will favourablyaffect the biological components including algal flora and macrophytes. Data on the physico-chemicalanalysis state that the water quality is still not improved because inputs of fertilizers and detergents havenot been checked so far.

Superior residual fertiliser value in soil with phosphorus recycled from urine in layered double hydroxides

Layered double hydroxides (LDHs) of magnesium (Mg) and aluminium (Al) are ion exchangers that can be used as slow release phosphorus (P) fertilisers. These LDHs can be used successfully to concentrate P from waste streams such as urine. This study was set up to test the fertiliser potential of P derived from urine and concentrated on LDHs. Ryegrass was grown in a pot trial using a P- and N-deficient soil where different urine derived fertilisers, i.e. LDH-P, stored urine and urine mixed with sludge as a source of P were compared to different mineral N and P doses in a full factorial design. Plants were grown for 75 days with four cuttings and did not exhibit salinity stress in stored urine treatments. Plant growth and P uptake responded to N, P doses in mineral fertilizer treatments with significant N-P interaction. The fertiliser use efficiency of urine fertilisers was lower than that of mineral fertilisers at equivalent total nutrient input for stored urine, due to lower N availability, and for urine mixed with sludge due to lower P availability. In contrast, the yield and P uptake of ryegrass grown on LDH loaded with P from urine (LDH-P) showed equal fertiliser P use as mineral fertiliser. Interestingly, the residual soil P after harvest, scored by the sum of isotopically exchangeable P in soil and the P uptake, was higher for LDH-P than for mineral P, confirming slow release properties of LDH that limit loss of P by fixation in soil.

Replacing 30 % chemical fertilizer with organic fertilizer increases the fertilizer efficiency, yield and quality of cabbage in intensive open-field production

ABSTRACT: The combined application of chemical fertilizer and organic fertilizer is an effective way to improve soil fertility, crop yield and quality. In this study, a field experiment was conducted to evaluate the yield, quality and fertilizer use efficiency of cabbage (Brassica oleracea var. capitata L.) grown under different ratios of organic fertilizer replacing chemical fertilizer at a rate of 225 kg N ha-l in 2019 and 2020. The fertilizer treatments included N0 (non nitrogen fertilizer), CK (only compound fertilizer was applied, N:P:K=15.0 %:6.5 %:12.4 %), T1, T2 and T3 (organic fertilizer replaced 15 %, 30 % and 45 % chemical fertilizer, respectively), and T4 (total nutrient input was reduced by 10 % under T2). Results showed that T2 had the highest marketable yield and fertilizer use efficiency, as well as the best quality. The marketable yield, vitamin C content, soluble sugar content, REN (apparent uptake efficiency of fertilizer N) and AEN (agronomic N use efficiency) of T2 increased by 32.2 %, 14,9 %, 5.5 %, 97. % and 55.6 %, respectively, in contrast, the crude fibers decreased by 34.0 %, compared with CK in the two years. In addition, T4 guaranteed the yield and moderately improved the quality of cabbage, compared with CK. Therefore, we can alternatively apply fertilization according to the purpose of capturing the highest yield or properly declining fertilizer to sustain soil texture and productivity.

Effect of Intensity and Mode of Artificial Upwelling on Particle Flux and Carbon Export

Reduction of anthropogenic CO2 emissions alone will not sufficiently restrict global warming and enable the 1.5°C goal of the Paris agreement to be met. To effectively counteract climate change, measures to actively remove carbon dioxide from the atmosphere are required. Artificial upwelling has been proposed as one such carbon dioxide removal technique. By fueling primary productivity in the surface ocean with nutrient-rich deep water, it could potentially enhance downward fluxes of particulate organic carbon (POC) and carbon sequestration. In this study we investigated the effect of different intensities of artificial upwelling combined with two upwelling modes (recurring additions vs. one singular addition) on POC export, sinking matter stoichiometry and remineralization depth. We carried out a 39 day-long mesocosm experiment in the subtropical North Atlantic, where we fertilized oligotrophic surface waters with different amounts of deep water. The total nutrient inputs ranged from 1.6 to 11.0 μmol NO3– L–1. We found that on the one hand POC export under artificial upwelling more than doubled, and the molar C:N ratios of sinking organic matter increased from values around Redfield (6.6) to ∼8–13, which is beneficial for potential carbon dioxide removal. On the other hand, sinking matter was remineralized at faster rates and showed lower sinking velocities, which led to shallower remineralization depths. Particle properties were more favorable for deep carbon export in the recurring upwelling mode, while in the singular mode the C:N increase of sinking matter was more pronounced. In both upwelling modes roughly half of the produced organic carbon was retained in the water column until the end of the experiment. This suggests that the plankton communities were still in the process of adjustment, possibly due to the different response times of producers and consumers. There is thus a need for studies with longer experimental durations to quantify the responses of fully adjusted communities. Finally, our results revealed that artificial upwelling affects a variety of sinking particle properties, and that the intensity and mode with which it is applied control the strength of the effects.

Throughfall and stemflow are major hydrologic highways for particulate traffic through tree canopies

For one‐third of Earth’s land surface, precipitation passes through tree canopies (as throughfall or stemflow) before entering watersheds. Over a century of research has described fluxes of water and solutes along these “hydrologic highways”, yet little is known about their “traffic” – that is, the organisms and nonliving particulates frequently discarded from water samples after filtration in the lab. A comprehensive understanding of the composition of sub‐canopy precipitation is necessary to estimate the total nutrient and pollutant inputs to watersheds for redistribution downstream, as well as to systematically investigate precipitation effects on organismal exchanges along the atmosphere–plant–soil continuum. Here, we review current concepts and research showing that the hydrologic highways from tree canopies to soil carry ecologically relevant quantities of biologic (viruses, microbes, microfauna, and meiofauna) and abiotic particulates. Their fate may have important consequences for the biogeochemistry and biodiversity of terrestrial systems.

Submarine groundwater discharge-driven nutrient fluxes in a typical mangrove and aquaculture bay of the Beibu Gulf, China

To understand the role of submarine groundwater discharge (SGD) in a mangrove combined aquaculture ecosystem, groundwater samples and timeseries observations (27 h) of 224Ra, 223Ra, and nutrients were obtained during wet and dry seasons in Zhenzhu Bay, a typical mangrove and aquaculture ecosystem along the Beibu Gulf in China. The SGD rates in Zhenzhu Bay were estimated to be 22.3–44.5 cm/d in the wet season and 41.1–58.1 cm/d in the dry season, which were 0.8–1.6 and 9.8–14.1 times higher than the corresponding river water discharge values, respectively. Furthermore, SGD-driven dissolved inorganic nitrogen, dissolved inorganic orthophosphate, and dissolved inorganic silicate accounted for 72%, 56%, and 60% of the total nutrient input, respectively, during wet season, which increased to 93%, 98%, and 89% during dry season. The findings highlight that SGD plays an important role in the dissolved inorganic nutrient sources of Zhenzhu Bay, and that the effective utilization and management of the bay should consider SGD.

Effects of nutrient-rich submarine groundwater discharge on marine aquaculture: A case in Lianjiang, East China Sea

Submarine groundwater discharge (SGD) and associated nutrient have long been received insufficient attention in the aquaculture areas of Lianjiang, East China Sea. In this study, we used 224Ra mass balance model to evaluate the importance of SGD in the aquaculture areas of Lianjiang in different seasons. The results showed that SGD fluxes were 0.14 ± 0.070 m3 m−2 d−1 in July and 0.077 ± 0.040 m3 m−2 d−1 in October 2019, which corresponded to approximately 22% and 32% of the river discharge, respectively. Nevertheless, the dissolved inorganic nitrogen (DIN) and phosphorus (DIP) fluxes contributed by SGD over total nutrient inputs were approximately 58% and 73%, respectively in July, 11% and 33%, respectively in October 2019. The ratio of DIN to DIP in seawater was slightly higher than that derived from SGD in July and significantly lower than that derived from the river and SGD in October, which was prone to profound modulated by shellfish (e.g., clam Ruditapes philippinarum and Sinonovacula constricta) and nori (e.g., Pyropia haitanensis) that selectively acquire nitrogen and phosphorous, suggesting that SGD could affect the nutrient structure and aquaculture activities in Lianjiang. Moreover, the new primary production via SGD yielded (2.47 ± 1.32) × 103 mg C m−2 d−1 in July and (3.52 ± 1.76) × 102 mg C m−2 d−1 in October 2019, which were approximately 8–25% and 10–31% of the production in the entire study area. These meaningful discoveries indicated that SGD and associated nutrient are the predominant regulator of nutrient and aquaculture structure under significant seasonal differences.

Nutrient accumulation from excessive nutrient surplus caused by shifting from rice monoculture to rice-crayfish rotation.

The potential environmental risk associated with nutrient surplus after switching from rice monoculture (RM) to rice-crayfish rotation (RCR) was assessed in the Jianghan Plains in China. Nutrient surplus was achieved by surveying 32 RM and 69 RCR and determining their nutrient inputs and outputs, and the soil nutrient status for different soil properties were recorded for 0-23 years. The annual average input of N, P2O5, and K2O in RCR was 536, 185, and 253kgha-1, respectively, wherein fertilizer and feed accounted for the major fraction of the total nutrient input. For instance, they accounted 58% and 18% of N, 74% and 24% of P2O5, and 70% and 30% of K2O, respectively. The annual apparent surplus of N, P2O5, and K2O was 397, 145, and 225kgha-1, respectively, leading to low apparent nutrient use efficiency. Consequently, compared with RM, the total N and soil readily oxidized organic carbon in the upper soil surface (0-20cm) for the RCR field significantly increased by 0.42-0.96gkg-1 and 1.63-3.19gkg-1, respectively. The available N, Olsen P, and exchangeable K of the RCR in the upper soil layer also increased significantly. In the RCR system, a significant positive linear relationship between the apparent accumulated nutrient surplus of N, P, and K elements and the total N, Olsen P, and exchangeable K present in the 0-60cm soil profile was observed. In RCR, the soil pH in 0-60cm soil profile and cation exchange capacity in the 0-20cm soil layer increased as the cultivation time progressed. Nutrient accumulation in the soil not only enhanced soil fertility but also negatively influenced the environment. Therefore, several measures (e.g., new fertilization technologies, new fertilizer, legislation approaches for nutrient surplus, and technical training) should be adopted to control the nutrient surplus.

Timing of dietary switching by savannah elephants in relation to crop consumption

Tree and grass quality on the African savannah shows seasonal variation, driving mixed-feeding herbivores to switch between browsing and grazing. During this switch, crop consumption could be an attractive alternative to browsing. We analysed elephant diet variability in the Okavango Delta, Botswana, using faecal stable isotope ratios of carbon (δ^13C) and frequencies of elephant crop consumption, to determine the extent to which crop consumption relates to this potential switch. Although elephants did increase their relative grass consumption in the wet season, browse dominated the annual diet. After February, the proportion of grass in the diet dropped considerably, and continued decreasing through April when farmers reported most crop consumption. Generalized Linear Models revealed that the occurrence of elephant crop consumption increased with the proportion of grass consumed and with decreasing grass quality. The proportion of grass in elephant faeces increased with increasing crop consumption intensity. As crop consumption could also be related to nutrient deficiencies in elephant diet, we calculated the total dietary input of nutrients to reveal potential deficiencies. Elephant diet contained insufficient levels of sodium year-round, and insufficient phosphorus from February to July. As the latter coincides with the timing of crop consumption, we consider our results an indication that phosphorus –and potentially sodium - deficiencies, could play a role in elephant dietary choices, including crop consuming behaviour. Further experimental research is required to show whether supplying elephants with supplementary phosphorus and sodium sources could reduce this micro-nutrient deficiency, and could play a role in reducing elephant crop consumption.

Machine-learning-based simulation and fed-batch control of cyanobacterial-phycocyanin production in Plectonema by artificial neural network and deep reinforcement learning

In this paper, a model-free deep reinforcement learning (DRL) strategy is presented with an artificial neural network (ANN) as reaction simulation environment, to obtain a fed-batch control strategy for an experimental bioreactor. The proposed method is a fundamental attempt to control reactions by employing state-of-the-art machine learning tools without the aid of well-established mechanistic understanding of the reaction system. This application utilizes the Asynchronous Advantage Actor-Critic (A3C) algorithm, a member of the DRL family, that takes advantage of actor-critic algorithm and asynchronous learning by parallel learning agents to achieve stability and efficiency of the learning process. The resulting controller demonstrates robust performance in the fed-batch bioreactor since it can be adjusted to meet varying constraining factors including nutrient limitations and culture lengths. Results are presented for a bioreactor that produces cyanobacterial-phycocyanin (C-PC) in Plectonema sp. UTEX 1541. Experimental validations show a 52.1% increase in the product yield, and a 20.1% increase in C-PC concentration compared to a control group with the same total nutrient input replenished in a non-optimized manner.

The role of upwelling intermittence in the development of hypoxia and nitrogen loss over the Oregon shelf

Abstract Coastal upwelling regions represent less than 2% of the marine biosphere's volume. Nonetheless, local biogeochemical processes have a considerable impact on the structure and functioning of the global oceans. In this study we characterize the evolution of biogeochemical properties during the upwelling seasons of 2009 and 2010 in the coastal ecosystem off central Oregon (west coast of USA). Both years displayed similar cumulative upwelling favorable winds and total input of preformed nutrients into the midshelf despite of their marked differences in the timing of the onset of the upwelling season, its duration and the number of upwelling relaxation events. However, these differences in upwelling forcing induced inter-annual variability in oxygen and nitrogen deficiencies, particulate matter accumulation and nutrient regeneration. Our results suggest that the summer evolution of nitrogen loss and oxygen depletion over the shelf does not follow a simple relationship with the cumulative upwelling index. We hypothesize that other factors, such as the intensity and persistence of the upwelling, which affect the residence time of water masses over the continental shelf, play a key role in the cumulative effect of biological processes leading to hypoxia in these coastal environments.

Aquaculture Production is a Large, Spatially Concentrated Source of Nutrients in Chinese Freshwater and Coastal Seas.

As Chinese aquaculture production accounts for over half of the global aquaculture production and has increased by 50% since 2006, there is growing concern about eutrophication caused by aquaculture in China. This paper presents a model-based estimate of nutrient flows in China's aquaculture system during 2006-2017 using provincial scale data, to spatially distribute nutrient loads with a 0.5° resolution. The results indicate that with the increase in fish and shellfish production from 30 to 47 million tonnes (Mt) during 2006-2017, the nitrogen (N) release increased from 1.0 to 1.6 Mt/year and that of phosphorus (P) from 0.1 to 0.2 Mt/year. Nutrient release from freshwater aquaculture was concentrated in Guangdong, Jiangsu, and Hubei, and that from mariculture in Shandong, Fujian, and Guangdong. Aquaculture is an important strongly concentrated nutrient source in both freshwater and marine environments. Its nutrient release is >20% of total nutrient inputs to freshwater environments in some provinces, and nutrients from mariculture are comparable to river nutrient export to Chinese coastal seas. Aquaculture production and nutrient excretions are now comparable to those of livestock production systems in China and need to be accounted for when analyzing causes of eutrophication and harmful algal blooms and possible mitigation strategies.

Natural groundwater nutrient fluxes exceed anthropogenic inputs in an ecologically impacted estuary: lessons learned from Mobile Bay, Alabama

In this study we evaluated the magnitude and seasonal variations of natural and anthropogenic fluxes of inorganic (NO3−, NH4+, and PO43−) and organic (DON and dissolved organic carbon) nutrients delivered by submarine groundwater discharge (SGD) and rivers to the fourth largest estuary in the USA, Mobile Bay in Alabama. To identify the sources of SGD-nutrient in the estuary and their subsurface biogeochemical transformation, we applied a multi-method approach that combines geochemical nutrient (N and P) mass-balances, stable isotopes (nitrate $$\updelta^{15} {\text{N}}_{{{\text{NO}}_{3} }}$$ and $$\updelta^{18} {\text{O}}_{{{\text{NO}}_{3} }}$$ and sediment organic matter δ13Corg and δ15Norg) signatures, microbial sequencing analyses, dissolved organic matter source-composition, and shallow estuarine sediment lithological analyses. We found that during dry seasons SGD delivered nearly a quarter of the total nutrient inputs to Mobile Bay. These SGD fluxes were anoxic and N was delivered to the bay almost entirely as NH4+ and DON, which represented more than half of the total NH4+ and almost one fifth of the total DON inputs to the bay. We further observed that these significant SGD-derived N fluxes occurred exclusively to the east shore of Mobile Bay, historically impacted by hypoxia and large-scale fish kills known as “Jubilees”. We demonstrate here that although the Mobile Bay coastal area is largely developed and anthropogenic influences are well documented, a shallow peat layer identified only on the east shore serves as the main source of the exceptionally high NH4+ and DON fluxes. We found that the high groundwater NO3− concentrations observed further inland from over-fertilization also identified by previous studies, decreased dramatically as groundwater percolated through the intertidal zone of the coastal aquifer. The microbial community identified in the coastal sediments suggests that denitrification and dissimilatory nitrate reduction to ammonium (DNRA) were the main processes responsible for this extensive removal and transformation of anthropogenic N, respectively. Furthermore, we found no significant anthropogenic inputs from manure or sewage waste to the bay. These findings show that natural sources of nutrients can outcompete anthropogenic inputs despite extensive development of the coastal area. We hypothesize that similar subsurface biogeochemical nutrient transformations can occur in other shallow estuaries of the northern Gulf of Mexico and worldwide.

Fertile cities: Nutrient management practices in urban agriculture

Cities are increasingly targeted as centers for sustainable development and innovation of food systems. Urban agriculture (UA) is advocated by some as a multi-faceted approach to help achieve urban sustainability goals as it provides possible social, economic and environmental benefits. The role of UA in restoring resource cycles receives increasing attention, especially with regard to assimilating urban waste. However, there is little information on how nutrients are managed in UA in industrialized countries. To examine nutrient management in UA, data was collected from a total of 25 ground-based UA initiatives in the Netherlands on i) preferences for types of fertilizers, and ii) quantity and quality of fertilizers used including nutrient composition and organic matter content. The main inputs at urban farms were compost and manure, high in organic matter content. The total nutrient inputs were compared to nutrient demand, based on crop nutrient uptake, in order to determine nutrient balances. Results show that mean nutrient inputs exceeded mean crop demand by roughly 450% for total nitrogen, 600% for phosphorus and 250% for potassium. Mean inputs for plant-available nitrogen were comparable to crop uptake values. The surpluses, particularly for phosphorus, are higher than fertilizer application limits used for conventional farming in The Netherlands. While nutrient input calculations were subject to several uncertainties, e.g., due to lack of accuracy of the data supplied by the farmers, results show a salient indication of over-fertilization and thus a suboptimal nutrient use. If UA continues to expand across cities these observed nutrient surpluses may pose a risk for local surface waters and groundwater as well as soil quality. The need to improve nutrient management in UA is evident. Soil tests, harvest logging and book keeping of nutrient inputs would improve data quality and may help balance nutrient inputs with nutrient outputs.

Nutrient budgets in a small-scale freshwater fish pond system in Indonesia

Over the past several years, Indonesian freshwater aquaculture has intensified, with a concomitant increase in the use of commercial pellets. To assess the effects of pond aquaculture intensification on nutrient dynamics, we monitored nutrients and fish production in a small-scale fish farm in West Java province. The studied system consisted of semi-intensive giant gourami (Osphronemus goramy) production in four small earthen ponds (353–482 m2 each and 0.46–0.55 m deep). Nitrogen (N) and phosphorus (P) fluxes through the ponds were monitored, and data on fish production were collected during a 5-month production cycle. Results showed that, on average, 61% total N and 77% P inputs were trapped in the accumulated sediments. Only 15% of total N and <3% P inputs introduced into ponds were recovered in harvested fish. Sediment nutrient accumulation increased linearly with total nutrient input. The consequences of intensification of giant gourami aquaculture using this production model are explored in terms of nutrient use efficiency and environmental impact.