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

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

Soil legacy nutrients contribute to the decreasing stoichiometric ratio of N and P loading from the Mississippi River Basin.

Human-induced nitrogen-phosphorus (N, P) imbalance in terrestrial ecosystems can lead to disproportionate N and P loading to aquatic ecosystems, subsequently shifting the elemental ratio in estuaries and coastal oceans and impacting both the structure and functioning of aquatic ecosystems. The N:P ratio of nutrient loading to the Gulf of Mexico from the Mississippi River Basin increased before the late 1980s driven by the enhanced usage of N fertilizer over P fertilizer, whereafter the N:P loading ratio started to decrease although the N:P ratio of fertilizer application did not exhibit a similar trend. Here, we hypothesize that different release rates of soil legacy nutrients might contribute to the decreasing N:P loading ratio. Our study used a data-model integration framework to evaluate N and P dynamics and the potential for long-term accumulation or release of internal soil nutrient legacy stores to alter the ratio of N and P transported down the rivers. We show that the longer residence time of P in terrestrial ecosystems results in a much slower release of P to coastal oceans than N. If contemporary nutrient sources were reduced or suspended, P loading sustained by soil legacy P would decrease much slower than that of N, causing a decrease in the N and P loading ratio. The longer residence time of P in terrestrial ecosystems and the increasingly important role of soil legacy nutrients as a loading source may explain the decreasing N:P loading ratio in the Mississippi River Basin. Our study underscores a promising prospect for N loading control and the urgency to integrate soil P legacy into sustainable nutrient management strategies for aquatic ecosystem health and water security.

Estimating Excreted Nutrients to Improve Nutrient Management for Grazing System Dairy Farms.

Improving nutrient management in grazing system dairy farms requires determining nutrient flows through animals, the placement of cows within farms and potential for collection, and the re-use and loss of nutrients. We applied a model incorporating data collected at a range of temporal and spatial scales to quantify nutrient excretion in all locations that lactating herds visited on five days over a year on 43 conventional and organic grazing system dairy farms. The calculated nutrient loads excreted by cows in different places were highly skewed; while N, P and K deposited loads were consistent across the year, S, Ca and Mg loads varied between sampling times and seasons. The greatest mean and range in nutrient loads were deposited in paddocks, with the smallest amounts deposited in dairy sheds. All excreted nutrient loads increased with farm and herd sizes and milk production. Mean daily loads of 112, 15, 85, 11, 22 and 13 kg of N, P, K, S, Ca and Mg were deposited by the herds which, when standardised to a 305-day lactation, amounted to 24, 4, 20, 3, 5 and 3 t excreted annually, respectively. In addition to routine manure collection in dairy sheds, ensuring collection and recycling of nutrients excreted on feed pads and holding areas would decrease potential nutrient losses by 29% on average. Non-collected, recycled nutrients were disproportionately returned to paddocks in which cows spent time overnight, and except for S and Ca, nutrient loading rates were greater than rates applied as fertilisers. These data demonstrate the extent of excreted nutrients in grazing dairy systems and indicate the need to account for these nutrients in nutrient management plans for Australian dairy farms. We propose incorporating excretion data in current budgeting tools using data currently collected on most Australian grazing system dairy farms.

Spatial patterns of nutrients balance of major crops in Argentina.

Argentina has a long tradition of agricultural systems that use few amounts of fertilizers. However, the crop nutrient balance remains unknown throughout the country. In this study, we estimated the nitrogen (N), phosphorus (P) and sulfur (S) balance at national and subnational scale of the six major grain crops: soybean, maize, wheat, sunflower, barley and sorghum. We found a negative spatio-temporal NPS balance with an annual average deficit of -22.4 kg ha-1 year-1 for N, -6.9 kg ha-1 year-1 for P and -2.1 kg ha-1 year-1 for S. Considering the whole agricultural area analyzed, the balance represented a mean annual negative net outflow of 612 thousand tons (kT) of N, 166 kT of P and 58 kT of S. The nutrient balance was not homogeneous across the country, with significant differences among the three major productive regions: i) the Pampean nucleus region (-32.2, -8.5, -2.92 kg ha-1 year-1, for N, P and S respectively) ii) the non-nucleus Pampean region (-14.3, -3.7, -2.03 kg ha-1 year-1 for N, P and S respectively), and iii) extra-Pampean region (-22.4, -6.3, -2.13 kg ha-1 year-1 for N, P and S respectively). Remarkably, despite having the highest N and P application rate, the Pampean nucleus region has the largest deficit of the analyzed nutrients. Soybean was the main driver of the nutrient mining in the country, accounting for 62 % of the NPS deficits at national scale (-418 kT N year-1, -120 kT P year-1 and -35 kT S year-1). Our findings suggest that the current fertilization practices applied to the major extensive crops in Argentina are far from being sufficient to supply the nutrients they demand, even cultivating soybean that is a N-fixing crop. These results highlight that Argentine main crops' high productivity is reached at the expense of soil nutrient depletion.

Distribution characteristics of green tides and its impact on environment in the Yellow Sea.

Large-scale outbreaks of green tides in the Yellow Sea affect the development of local tourism and aquaculture and significantly damage the coastal ecological environment. To study the distribution characteristics of green tides and to explore their impact on the environment, a coupled physical-ecological model (LTRANS-GT) based on the Lagrangian TRANSport model (LTRANS) was constructed in this paper to simulate the growth and dissipation process of Ulva prolifera and to obtain its drift trajectory and biomass. The results show that the tracks of the green tide are mainly divided into three categories, namely, northwestward, northward, and eastward. The green tide biomass showed a single-peak with seasonal variation in most years (entering a rapid proliferation period in May-June, reaching a peak biomass after developing for approximately 30 days, then dying out rapidly and basically disappearing by August), and showed a double-peak only in a few years due to extreme weather effects. In 2017, the biomass of U. prolifera was the lowest, with a maximum wet weight of only 24600 tons, while the largest biomass occurred in 2013, with a maximum wet weight of more than 560,000 tons. The interannual difference in the biomass of U. prolifera was mainly due to its initial biomass and the difference in nutrient concentration in the area where it was located. The year in which U. prolifera absorbed the most dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorus (DIP) was 2013, with absorption values of 3973 tons and 114 tons, respectively; and the year in which U. prolifera absorbed the least DIN and DIP was 2017, with absorption values of 172 tons and 5 tons, respectively. During the period of U. prolifera outbreak, the consumption of DIN and DIP in the sea area where it occurred accounted for approximately 43.65% and 0.6% of the total discharge of the rivers, and 26.86% and 6.1% of the atmospheric deposition, respectively. The impact of green tide outbreaks on the annual nitrogen and phosphorus nutrient budget of the entire Yellow Sea was relatively small, but the impact on the area where U. prolifera grows and decays can not be ignored. In dissipation period, the decay of U. prolifera may make DON and DOP double near Shandong coast.

Nutrient budgets drive the changes in shoot N and P concentrations of plants in Inner Mongolia's grasslands over the past 40 years.

The nutrient budgets of grassland ecosystems have been extensively disturbed by human activity. The aims of this study were to quantify nitrogen (N) and phosphorus (P) budgets, and evaluate their contributions to changes in shoot nutrient concentrations of dominant plants in Inner Mongolia's grasslands over the past 40 years. N and P budgets were assessed using a nutrient budget model based on flowing intensity of nutrients in and out of the grassland. Meta-analysis was then conducted to quantify changes in shoot nutrient concentrations. The N budget remained positive and continued to increase throughout the study period, while enhanced N deposition and increased supplementary feeding dominated N input (76% of the total in 2017). In contrast, the P budget was negative until 2003, and became positive thereafter. The P input was mainly attributed to supplementary feeding (88% of the total in 2017). The mean shoot N concentration in 1979-1986 was 2.25%, while an increase to 2.53% was observed in 2006-2016. In contrast, the mean shoot P concentration was 0.17% in 1979-1991, subsequently leveling off at 0.17% in 2006-2016. The mean shoot N: P ratio basically remain unchanged over time from 16.72 to 15.85. The N surplus caused major increases in the shoot N concentration of the grassland plants; also, the increased P budget to compensate for past P deficiency resulted in no significant change of shoot P concentrations. Consequently, the grassland system had been in the joint N and P co-limitation over the past 40 years.

Nutrient budgets for the Bohai Sea: Implication for ratio imbalance of nitrogen to phosphorus input under intense human activities.

Eutrophication is a global problem for coastal ecosystems, one that the Bohai Sea (BHS), China, is severely afflicted by due to rapid economic and social development over the last forty years. For sustainable nutrients management in the BHS, comprehensive budgets for Nitrogen (N) and Phosphorus (P) was characterized in 2017, and the relative contributions of river input, submarine fresh groundwater discharge, atmospheric deposition, sediment diffusion, and exchange with the Yellow Sea were quantified. The annual N and P fluxes into the BHS were 362 × 103 t and 10.4 × 103 t, respectively. The terrigenous N inputs occupied the highest proportion, while the largest P input was from sediment diffusion. The ratio of N:P was 77 for total external inputs, while that of the Yellow River was 680; both exceeded the Redfield ratio, indicating an imbalance in the nutrient structure and a P limitation in the BHS.

Spatial characteristics of nutrient budget on town scale in the Three Gorges Reservoir area, China.

Accurately quantifying nutrient budget is an essential step toward sustainable nutrient management in large watersheds increasingly disturbed by human activity. A town-scale nutrient budget framework based on the Soil and Water Assessment Tool was developed for 2010-2012 in the Three Gorges Reservoir area in China (TGRA). Moran's I spatial correlation test and Geodetector spatial heterogeneity test were employed to systematically analyze the spatial characteristics of the resulting nutrient budget. The Moran's I value of total nitrogen (TN) and total phosphorus (TP) gradually increased from input to output in the range of 0.091-0.232 and 0.102-0.484, respectively. Towns with higher TN and TP inputs were largely concentrated in the main urban area of Chongqing because of its high population density. By contrast, towns with higher TN and TP outputs were concentrated in the head of the TGRA. The Moran's I values of the TN and TP retention coefficients (R) were 0.433 and 0.524, respectively, demonstrating clear spatial consistency. Towns with a "High-high" spatial consistency pattern and positive R value were concentrated in the tail and hinterland, while those with a "Low-low" spatial consistency pattern and negative coefficient value were located mainly in the head of the TGRA. This phenomenon was mostly caused by differences in regional elevation, the normalized difference vegetation index, and soil erosion factor. The interaction effect between any two of these three factors on nutrient retention (Geodetector q-value) was greater than 60%. Therefore, future nutrient management should be based on a full understanding of regional biophysical conditions, especially in large areas. These findings provide a new perspective on fine nutrient management.

Save reservoirs of humid subtropical cities from eutrophication threat.

Reservoir water is the most important freshwater resource for many cities, especially in densely populated humid subtropical areas. Economic growth, population increase, and urbanization have been putting reservoir water of Shenzhen (China), a humid subtropical city, under severe threat of eutrophication and water supply shortage. In this study, we focused on an upstream reservoir of Shenzhen and established a 3-dimensional hydrodynamic-ecological model to investigate the water dynamics and nutrient budget. Tributaries to the reservoir were identified as the greatest contributors to nitrogen and phosphorus loads. Zones with weak flows and high nutrient concentration have high risks of causing blooms. Several mitigation measures were proposed, including improving flow by adding additional water exit locations in the reservoir, reducing nutrients in tributaries, and enhancing algal predation, and were evaluated with the established model. The strategies combining hydrodynamic improvement and phosphorus reduction were suggested to decision makers and government managers for short-term management. However, for future water safety, excessive nitrogen is a potential danger. This study provides a modeling framework that can be applied to anthropogenic-influenced reservoirs elsewhere.

Nutrient dynamics and budgeting in a semi-enclosed coastal hypersaline lagoon.

Biogeochemical and ecological responses to limited external nutrient loading are poorly understood in tropical semi-enclosed coastal lagoons which are highly influenced by hydrological and salinity regimes. With objectives towards ecosystem sustainability via better management of the nutrient inputs, investigations were carried out to estimate the water, salt, and nutrient budget of "Pulicat" hypersaline coastal lagoon for the year 2018-2019. The budget revealed that the annual rate of precipitation and evaporation are the major driving factors regulating the annual residual flow in the lagoon. Limited exchange of water and material had resulted in a hypersaline condition with high spatial and temporal variation in salinity ranging from 20 to 103. In the absence of external loading, nutrient enrichment by internal compensation had resulted in DIN enrichment. DIN constituents are mainly contributed by ammonia, indicative of remineralisation through benthic regeneration. The extended water residence time and enhanced primary production has converted the inner lagoon into a limited phosphate system. The TRIX index also indicates a decline in the trophic status transforming the lagoon from a mesotrophic to a eutrophic system.

Nutrient mass balance of a large riverine reservoir in the context of water residence time variability.

The excessive input of nitrogen (N) and phosphorus (P) from anthropogenic activities is the main reason behind the cultural eutrophication and algal blooms in freshwater ecosystems. Here, I present a comprehensive budget of N, P for a large reservoir (Lake Diefenbaker) within a highly cultivated watershed. I constructed a 4-year nutrient budget from 2011 to 2014, using grab samples and daily flow data, and a multi-decadal (1978 through 2014) budgeting to examine the effect of inter-annual variability of water residence time on retention of N and P, and if retention of N and P is affected differently. The 4-year budget showed that the reservoir was a net source of total nitrogen (TN) during 2011 and 2014, but a net sink during 2012 and 2013. This resulted in retention coefficients of - 35% and - 4% in 2011 and 2014, respectively. With respect to the total phosphorus (TP) budget, the reservoir acted as a net sink in all 4 years, with a mean retention coefficient of 87%. Consistent with findings of the 4-year budget, the results of the multi-decadal budgeting showed that the reservoir was a net sink for TP during the period of record with a mean retention of 81% (1583 t/year). Regarding TN, the mean retention was lower (49%, 4836 t/year) and more variable relative to TP over the long term. Unlike TP, the results showed that the retention of TN has been decreasing noticeably since 1978. Overall, the retention of TP in this lake is primarily controlled by in-lake sedimentation and most likely does not change substantially in response to inter-annual variation of hydraulic variables such as water residence time. For TN, the role of sedimentation could be minor in retention process in this reservoir (or similar reservoirs elsewhere), but in-lake biological processes could play a more important role. These findings are useful for understanding the role of larger reservoirs with water residence time of 1-3 years in nutrient retention and how changes in flow and water residence time due to climate variability and water management can influence the nutrient retention efficiency.

Improving the understanding of central Bohai Sea eutrophication based on wintertime dissolved inorganic nutrient budgets: Roles of north Yellow Sea water intrusion and atmospheric nitrogen deposition.

The Bohai Sea is a shallow-water, semi-enclosed marginal sea of the Northwest Pacific. Since the late 1990s, it has suffered from nutrient over-enrichment. To better understand the eutrophication characteristics of this important coastal sea, we examined four survey datasets from summer (June 2011), late autumn (November 2011), winter (January 2016), and early spring (April 2018). Nutrient conditions in the Bohai Sea were subject to seasonal and regional variations. Survey-averaged N/P ratios in estuarine and nearshore areas were 20-133. In contrast, the central Bohai Sea had mean N/P ratios of 16.9 ± 3.4 in late autumn, 16.1 ± 3.0 in winter and 13.5 ± 5.8 in early spring, which are close to the traditional N:P Redfield ratio of 16. In summer, both dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphate (DIP) were used up in the surface waters of the central Bohai Sea, suggesting that the biological consumption of DIN and DIP may also follow the Redfield ratio. Wintertime nutrient budgets of the central Bohai Sea water were then established based on a mass balance study. Our results suggest that the adjacent North Yellow Sea supplied additional DIP to the central Bohai Sea via wintertime water intrusion, balancing terrigenous excess DIN that was introduced in summer. A water-mixing simulation combining these two nutrient sources with atmospheric nitrogen deposition suggests that eutrophication in the central Bohai Sea will likely be enhanced by the large-scale accumulation of anthropogenic nitrogen in adjacent open oceans. Such changes in nutrients may have fundamentally contributed to the recent development of algal blooms and seasonal hypoxia in the central Bohai Sea.

Retention of nitrogen and phosphorus in Lake Chaohu, China: implications for eutrophication management.

Nutrient retention is an important process in lake nutrient cycling of lakes and can mitigate lake eutrophication. However, little is known about temporal lake nutrient retention efficiency and it varies due to changes in hydrological, ecological, and nutrient inputs to lake waters. Quantitative information about seasonal lake N and P retention is critical for developing strategies to reduce eutrophication in lake systems. This study investigated TN and TP retention efficiencies and retention masses using water and mass balance calculations, and statistically analyzed the seasonal variability of nutrient retention in Lake Chaohu, China, from 2014 to 2018. Lake Chaohu experienced large amounts of external loads inputs (23.2 g N m-2 year-1 and 1.3 g P m-2 year-1), and approximately 58% TN and 48% TP were retained annually. The lake acted more as a sink for N than for P. The mean annual TP retention efficiency decreased (P < 0.05) over the study period, indicating that TP retention capacity was gradually exceeded. Seasonal variability of TN and TP retention efficiency was high and ranged from - 18.7 to 144.1% and from - 58.8 to 170.7%, respectively, over the five study years. The internal P loads over the study period were equivalent to roughly 9% of the total external loads. The annual nutrient retention efficiency of TN and TP increased with hydraulic residence time, while water temperature was an essential factor for the contrasting seasonal variation patterns of TN and TP retention efficiencies.

Rational budgeting approach as a nutrient management tool for mixed crop-swine farms in Korea.

OBJECTIVE: Due to rapid economic return, mixed crop-swine farming systems in Korea have become more intensive. Intensive farming practices often cause nutrient surpluses and lead to environmental pollution. Nutrient budgets can be used to evaluate the environmental impact and as a regulatory policy instrument for nutrient management. This study was conducted to select a nutrient budgeting approach applicable to the mixed crop-swine farms in Korea and suggest an effective manure treatment method to reduce on-farm nutrient production. METHODS: In this study, we compared current and ideal gross nutrient balance (GNB) approaches of Organisation for Economic Co-operation and Development and soil system budget (SSB) approach with reference to on-farm manure treatment processes. Data obtained from farm census and published literature were used to develop the farm nutrient budgets. RESULTS: The average nitrogen (N) and phosphorus (P) surpluses were approximately 11 times and over 7 times respectively higher in the GNB approaches than the SSB. After solid-liquid separation of manure, during liquid composting a change in aeration method from intermittent to continuous reduced the N and P loading about 50% and 47%, respectively. Although changing in solid composting method from turning only to turning+aeration improved the N removal efficiency by 30.5%, not much improvement in P removal efficiency was observed. CONCLUSION: Although the GNB approaches depict the impact of nutrients produced in the mixed crop-swine farms on the overall agricultural environment, the SSB approach shows the partitioning among different nutrient loss pathways and storage of nutrients within the soil system; thus, can help design sustainable nutrient management plans for the mixed cropswine farms. The study also suggests that continuous aeration for liquid composting and turning+aeration for solid composting can reduce nutrient loading to the soil.

Biogeochemistry of dissolved inorganic nutrients in an oligotrophic coastal mariculture region of the northern Shandong Peninsula, north Yellow Sea.

Fourteen field cruises were carried out in a mariculture region of the northern Shandong Peninsula, North Yellow Sea, China from 2016 to 2017 for a better understanding of the biogeochemical behaviors, sources and export of dissolved inorganic nutrients. The spatial variations of nutrients were not obvious due to the influence of complex hydrological and biochemical conditions. Potential nutritional level was characterized in oligotrophy, and trophic status was rated at medium level. A preliminary estimation of nutrient budgets demonstrated that the dissolved inorganic nitrogen (DIN) load was mainly from atmospheric deposition and scallop excretion, accounting for 56.9% and 35.6% of its total influx. Scallop excretion and sediment release were the major source of phosphate (DIP), contributing to 25.2% and 44.3%, while dissolved silicon (DSi) was mainly from sediment release, accounting for 94.2%. In addition, about 136.7 × 103, 7.3 × 103 and 485.5 × 103 mol km-2 yr-1 of DIN, DIP and DSi could be converted into other forms, e.g. organic and particulate matter and gas species.

Non-point source pollution risks in a drinking water protection zone based on remote sensing data embedded within a nutrient budget model.

A simple, transparent and reliable method for evaluating non-point source pollution (NPSP) risks to drinking water source areas lacking observational data is proposed herein. The NPSP risks are assessed by using nutrient budget models for total nitrogen and total phosphorus, making the best use of remote sensing and field survey data. We demonstrate its potential using a case study of the Chaihe Reservoir in northeastern China. Fertilizer inputs and crop-uptake outputs were estimated based on normalized difference vegetation index, which is derived from remote sensing as indicators of crop growth and production. The nutrient balances for this area showed surpluses of both N and P within the soil system. Estimated imbalances per unit area were consistent with statistical relationships derived from all Chinese counties, demonstrating that the proposed method is reliable. The surplus P amounts were higher than the standard threshold for NPSP risks, indicating the existence of a potential contamination risk of P to this drinking water source.

A host-feeding wasp shares several features of nitrogen management with blood-feeding mosquitoes.

Adult feeding on hosts is common among parasitic wasps. The ingested host fluid is rich in nutrients, especially proteins. A study on Eupelmus vuilleti (Hymenoptera: Eupelmidae), a host-feeding parasitoid of larvae of Callosobruchus maculatus (F.) (Coleoptera: Bruchidae), showed that the carbohydrates (maybe lipids) but not proteins, gained from host feeding accounted for the increased egg production. Thus, host protein is probably utilized for general adult metabolism, allowing conservation of carbohydrate and/or lipid resources for direct allocation to oocytes. In that case, there should be increased N excretion by female parasitoids. To test this, we studied the dynamics of excretion in E. vuilleti with and without host exposure. The aim of this work was threefold: (i) to identify the major N-containing compounds in adult excreta, (ii) to assess whether protein consumption during host feeding increased the amount of N excreted, and (iii), if so, to compare the increase in N excreted with the amount taken in during a single host feeding. We found that uric acid is the predominant N-containing metabolite in excreta, although small quantities of urea and traces of allantoin were also found. A calculation of the N budget showed that the extra quantity of N excreted following a host meal corresponds to the quantity ingested, confirming that host-feeding in this species offers little or no net quantitative benefit in N allocation to oocytes, although the allocation of specific amino acids from host feeding cannot be discounted. Interestingly, host-feeding in parasitoids appears analogous to vertebrate blood-feeding in mosquitoes, both in terms of the N-containing compounds excreted and the offset of acquired N to metabolism, rather than to oocytes. Further comparative and detailed investigations of N excretion in insects living on other N-rich fluids might establish further metabolic commonalities.

Wet nitrogen and phosphorus deposition in the eutrophication of the Lagos Lagoon, Nigeria.

Air pollution is influenced by wind-aided particulate suspension, open-air waste burning, and fossil fuel combustion. The pollutants from these sources eventually deposit on ambient surfaces. Atmospheric wet deposition into Lagos Lagoon may be significant additions to the nutrient levels of the eutrophic lagoon. Precipitation was monitored at three stations in the Lagos Lagoon basin from May to November, 2012, in order to estimate the contribution of wet deposition to the nutrient cycles of the lagoon. Water samples were digested with potassium persulfate, and the species of phosphorus (P) and nitrogen (N) were analyzed by colorimetric methods. The mean [NO3-+NO2-]-N level was 0.39 ± 0.51 kg ha-1 month-1. The average total N was 3.16 ± 6.39 kg ha-1 month-1. The mean soluble reactive P was lower than the [NO3-+NO2-]-N averaging 0.06 ± 0.09 (at control site S2) to 0.24 ± 0.10 kg ha-1 month-1 (at site S1). Average total P was 1.25 ± 0.82 kg ha-1 month-1. The annual total N (May-September) was 4.55 (at S2) to 32.4 kg ha-1 year-1 (at S3). The annual total P (May-November) over Lagos Lagoon basin was 5.06 kg ha-1 year-1 (at S2). This study demonstrated that wet deposition of anthropogenically derived nutrients to the Lagos Lagoon is ongoing and may represent a considerable proportion of the total nutrient loading to it. The increased P availability in the wet deposition is likely responsible for the water hyacinths, which usually blossom on Lagos Lagoon during the late rainy season, and the reported harmattan-season bottom water hypoxia.

3D modeling of phytoplankton seasonal variation and nutrient budget in a southern Mediterranean Lagoon.

A 3D coupled physical-biogeochemical model is developed and applied to Bizerte Lagoon (Tunisia), in order to understand and quantitatively assess its hydrobiological functioning and nutrients budget. The biogeochemical module accounts for nitrogen and phosphorus and includes the water column and upper sediment layer. The simulations showed that water circulation and the seasonal patterns of nutrients, phytoplankton and dissolved oxygen were satisfactorily reproduced. Model results indicate that water circulation in the lagoon is driven mainly by tide and wind. Plankton primary production is co-limited by phosphorus and nitrogen, and is highest in the inner part of the lagoon, due to the combined effects of high water residence time and high nutrient inputs from the boundary. However, a sensitivity analysis highlights the importance of exchanges with the Mediterranean Sea in maintaining a high level of productivity. Intensive use of fertilizers in the catchment area has a significant effect on phytoplankton biomass increase.

Guava Waste to Sustain Guava (Psidium guajava) Agroecosystem: Nutrient "Balance" Concepts.

The Brazilian guava processing industry generates 5.5 M Mg guava waste year(-1) that could be recycled sustainably in guava agro-ecosystems as slow-release fertilizer. Our objectives were to elaborate nutrient budgets and to diagnose soil, foliar, and fruit nutrient balances in guava orchards fertilized with guava waste. We hypothesized that (1) guava waste are balanced fertilizer sources that can sustain crop yield and soil nutrient stocks, and (2) guava agroecosystems remain productive within narrow ranges of nutrient balances. A 6-year experiment was conducted in 8-year old guava orchard applying 0-9-18-27-36 Mg ha(-1) guava waste (dry mass basis) and the locally recommended mineral fertilization. Nutrient budgets were compiled as balance sheets. Foliar and fruit nutrient balances were computed as isometric log ratios to avoid data redundancy or resonance due to nutrient interactions and the closure to measurement unit. The N, P, and several other nutrients were applied in excess of crop removal while K was in deficit whatever the guava waste treatment. The foliar diagnostic accuracy reached 93% using isometric log ratios and knn classification, generating reliable foliar nutrient and concentration ranges at high yield level. The plant mined the soil K reserves without any significant effect on fruit yield and foliar nutrient balances involving K. High guava productivity can be reached at lower soil test K and P values than thought before. Parsimonious dosage of fresh guava waste should be supplemented with mineral K fertilizers to recycle guava waste sustainably in guava agroecosystems. Brazilian growers can benefit from this research by lowering soil test P and K threshold values to avoid over-fertilization and using fresh guava waste supplemented with mineral fertilizers, especially K. Because yield was negatively correlated with fruit acidity and Brix index, balanced plant nutrition and fertilization diagnosis will have to consider not only fruit yield targets but also fruit quality to meet requirements for guava processing.