Nutrient Cycling

Constructed wetlands are built to meet a number of regulatory requirements, including compensatory mitigation for wetland losses, treatment of wastewater, and reduction of non-point-source pollution. Natural processes in the wetland stabilize the substrate, enhance permeability, remove organic, inorganic and microbiological contaminants and facilitate the flux of gases between the sediments and atmosphere. Here we present the results of an ongoing study to evaluate the nutrient retention efficiency of a constructed wetland at the Mansfield Campus of the Ohio State University, built to mitigate the loss of stream and wetlands resulting from the construction of the Riedl Hall in 2005. The wetland is also used for stormwater retention, draining 190,000 m2 of campus uplands. Water samples have been collected monthly since April, 2009 and used for determination of organic and inorganic nutrients. Samples were collected at both the inflow and the outflow. Water temperature, pH, and concentration of total dissolved solids were also measured in situ using portable meters. Although there was considerable variability in the dataset, the mean values for all variables but pH were higher in the inflow compared to the outflow (Total Dissolved Solids = 11% higher; Total Oxidized Nitrogen (NO3 + NO2) = 46% higher; NH4 = 51% higher; PO4 = 122% higher; Total Nitrogen = 37% higher; Total Phosphorus = 43% higher; pH = 1% lower). These downstream changes in the studied variables were attributed primarily to biogeochemical processes in the wetland, which removes excess nutrients and improves water quality. The nutrient removal efficiency of the wetland varied considerably between seasons. Highest nutrient removal was observed during the summer (~40% efficiency), while the lowest was observed in the fall (~25% efficiency). Higher efficiency was observed in the removal of PO4 (65% in summer), while TON had the lowest removal efficiency (22% in the fall). There is a positive significant correlation between precipitation and DIN concentrations in both the inflow and outflow stations. Precipitation events explain 73% of the variability in DIN concentrations on the inflow and 87% of the variability on the outflow. On average, a reduction of 14% in the nutrient removal efficiency of the Riedl wetland was observed after rainfall events.

Agricultural nutrient balances have been receiving increasing attention in both historical and nutrient management research. The main objectives of this study were to further develop balance methodologies and to carry out a comprehensive assessment of the functioning and nutrient cycling of 1950s agroecosystems in Portugal. Additionally, the main implications for the history of agriculture in Portugal were discussed from the standpoint of soil fertility. We used a mass balance approach that comprises virtually all nitrogen (N), phosphorus (P) and potassium (K) inputs and outputs from cropland topsoil for average conditions in the period 1951-56. We found a consistent deficit in N, both for nationwide (-2.1 kg.ha(-1).yr(-1)) and arable crops (-1.6 kg.ha(-1).yr(-1)) estimates, that was rectified in the turn to the 1960 decade. P and K were, in contrast, accumulating in the soil (4.2-4.6 kg.ha(-1).yr(-1) and 1.0-3.0 kg.ha(-1).yr(-1), respectively). We observed that the 1950s is the ver...

Plants can develop novel adaptations for nutrient acquisition in nutrient-limited ecosystems. These adaptations include colonization by roots of tree trunks and logs that can act as nutrient reservoirs. Termites may facilitate this root colonization by digging tunnels and accelerating decomposition in logs and tree trunks. We measured the frequency with which above-ground tree root colonization co-occurs with the presence of termites or their tunnels inside living trees above 20 cm dbh (n = 178) and dead tree trunks and logs at least 15 cm in diameter (n = 146) in a Bornean tropical forest. Roots above the soil surface co-occur with termite tunnels 39% more frequently than expected by chance in trunks of living trees and 17% more frequently than expected by chance in logs. By categorizing logs according to hardness through ease of penetration, we found that softer logs at a late stage of decay did not show co-occurrence of termite activity and roots to the same extent as harder logs. This suggests that trees forage where termites have removed physical barriers to colonization. In this fashion, termites may accelerate nutrient cycling in tropical rain forests.

In this study, we investigate phosphorus (P) and iron (Fe) cycling in sediments along a depth transect from within to well below the oxygen minimum zone (OMZ) in the northern Arabian Sea (Murray Ridge). Pore-water and solid-phase analyses show that authigenic formation of calcium phosphate minerals (Ca-P) is largely restricted to where the OMZ intersects the seafloor topography, likely due to higher depositional fluxes of reactive P. Nonetheless, increased ratios of organic carbon to organic P (Corg/Porg) and to total reactive P (Corg/Preactive) in surface sediments indicate that the overall burial efficiency of P relative to Corg decreases under the low bottom water oxygen concentrations (BWO) in the OMZ. The relatively constant Fe/Al ratio in surface sediments along the depth transect suggest that corresponding changes in Fe burial are limited. Sedimentary pyrite contents are low throughout the ~25 cm sediment cores at most stations, as commonly observed in the Arabian Sea OMZ. However, pyrite is an important sink for reactive Fe at one station in the OMZ. A reactive transport model (RTM) was applied to quantitatively investigate P and Fe diagenesis at an intermediate station at the lower boundary of the OMZ (bottom water O2: ~14 μmol L−1). The RTM results contrast with earlier findings in showing that Fe redox cycling can control authigenic apatite formation and P burial in Arabian Sea sediment. In addition, results suggest that a large fraction of the sedimentary Ca-P is not authigenic, but is instead deposited from the water column and buried. Dust is likely a major source of this Ca-P. Inclusion of the unreactive Ca-P pool in the Corg/P ratio leads to an overestimation of the burial efficiency of reactive P relative to Corg along the depth transect. Moreover, the unreactive Ca-P accounts for ~85% of total Ca-P burial. In general, our results reveal large differences in P and Fe chemistry between stations in the OMZ, indicating dynamic sedimentary conditions under these oxygen-depleted waters.

Three levels of N (40,80,120 kg N ha-1) and P (0,17.5,35 kg P ha-1), and 2 levels of K (0,33 kg K ha-1) were tested for 19 years in rice and wheat crops of a rice-wheat cropping system in a fixed layout of 3×2×2 factorial partially confounded design along with one control and 3 replications. From this trial, data of 7 treatments, i.e. 0-0-0, 40-35-33, 80-35-33, 120-35-33, 120-0-0, 120-35-0 and 120-0-33 kg ha-1 N-P-K respectively were compared for yield trends, changes in response functions, soil organic -C and available N,P,K status. Soil organic - C decreased in unfertilized plots by 62% (over initial value of 0.45%) but increased by 44, 40 and 36% in plots receiving 120-35-33, 120-35-0 and 80-35-33 kg ha-1 N-P-K respectively. Available N was also greatest in these same three treatments. Available soil P increased by about 5 fold in 15 years in treatments supplied with fertilizer P, but no significant change was detected in treatments without P addition. Yields of rice and wheat ex...

Reforestation is an important tool for reducing or reversing biodiversity loss and mitigating climate change. However, there are many potential compromises between the structural (biodiversity) and functional (carbon sequestration and water yield) effects of reforestation, which can be affected by decisions on spatial design and establishment of plantings. We systematically review the environmental responses to reforestation and show that manipulating the configuration of plantings (location, size, species mix and tree density) increases a range of environmental benefits. More extensive tree plantings (> 10 ha) provide more habitat, and larger improvements to carbon and water cycling. Planting a mixture of native trees and shrubs is best for biodiversity while traditional plantation species, generally non-native species, sequester C faster. Tree density can be manipulated at planting or during early development to accelerate structural maturity and to manage water yields. A diversity of habitats will be created by planting in a variety of landscape positions and imitating the patchy distribution of forest types, which historically has characterized many regions. Areas with shallow aquifers can be planted to reduce water pollution or avoided to maintain water yields. Reforestation should be used to build forest networks that are surrounded by low-intensity land use and that provide links within regions and between biomes. While there are adequate models for C sequestration and changes in water yields after reforestation, the quantitative understanding of changes in habitat resources and species composition is more limited. Development of spatial and temporal modelling platforms based on empirical models of structural and functional outcomes of reforestation is essential for deciding on how to reconfigure agricultural regions. To build such platforms, we must quantify: (a) the influence of previous land uses, establishment methods, species mixes and interactions with adjacent land uses on environmental (particularly biodiversity) outcomes of reforestation; and (b) the ways in which responses measured at the level of individual plantings scale up to watersheds and regions. Models based on this information will help widespread reforestation for carbon sequestration improve native biodiversity, nutrient cycling and water balance at regional scales.

The use of fertilizers in agriculture is a possible source of soil and water pollution. The aim of the study was to evaluate leaching of N, Ca and Mg in a pot experiment under two fertilizers rates, in the presence and absence of plants and with two different soil types (loamy and clay loam soil). Half of the pots were planted with Italian ryegrass (Lolium multiflorum) in order to evaluate effect of the presence of the plants on the leaching process. Results show a relatively high amount of N and Ca leached especially from the loamy soil and in absence of the plants. The presence of ryegrass plants decreased the amount of N and Ca leached significantly. Mg was leached in smaller amounts compared with the other two elements.

A B S T R A C T Late 18th century agriculture was under social and economic pressures, emanating from unprecedented population growth and establishing world markets. Farmers met these challenges successfully and largely without external energy subsidies and mineral fertilizers. Our research asks (1) if and how performance gains were achieved by improving traditional nutrient management through advanced, organic farming and (2) whether this early agrarian intensification compromised the natural capital of agro-ecosystems. We present a long-term socio-ecological perspective on nutrient cycling in the historical agro-ecosystem of the estate Bruck in eastern Austria, from 1787 to 1906. Focal point is the development of different patterns in nutrient cycling, tracing the transition from traditional, organic to industrial farming. We used nutrient balances and input-output analysis for a quantitative assessment of nitrogen and phosphorus flows. To investigate the correlation between growing system performance and improved internal nutrient cycling, we applied the Finn cycling index (FCI), which represents the fraction of nutrients recycled on-farm before leaving the system. Improving nutrient cycling entailed the operational integration of livestock, the utilization of ecological nutrient replenishment processes through legume intercropping and optimizing nutrient transfers from extensive land-use systems. Nitrogen recycling grew steadily from 20% in 1787 to 36% in 1906. Phosphorus recycled on farm grew accordingly from 33% in 1787 to 46% in 1840, before dropping to 31% in 1906 due to increased application of mineral fertilizers. We show, that cereal yields more than doubled through improved traditional nutrient management. In the long-run, however, advanced organic farming induced an unsustainable use of phosphorus and the loss of ecological buffer capacity from traditional mixed land-use systems.

There is high confidence that the anthropogenic increase of atmospheric greenhouse gases (GHGs) is causing modifications in the Earth's climate. Coastal waterbodies such as estuaries, bays and lagoons are among those most affected by the ongoing changes in climate. Being located at the land-sea interface, such waterbodies are subjected to the combined changes in the physical-chemical processes of atmosphere, upstream land and coastal waters. Particularly, climate change is expected to alter phytoplankton communities by changing their environmental drivers (especially climate-related), thus exacerbating the symptoms of eutrophication events, such as hypoxia, harmful algal blooms (HAB) and loss of habitat. A better understanding of the links between climate related drivers and phytoplankton is therefore necessary for projecting climate change impacts on aquatic ecosystems. Here we present the case study of the Zero river basin in Italy, one of the main contributors of freshwater and nutrient to the salt-marsh Palude di Cona, a coastal waterbody belonging to the lagoon of Venice. To project the impacts of climate change on freshwater inputs, nutrient loadings and their effects on the phytoplankton community of the receiving waterbody, we formulated and applied an integrated modelling approach made of: climate simulations derived by coupling a General Circulation Model (GCM) and a Regional Climate Model (RCM) under alternative emission scenarios, the hydrological model Soil and Water Assessment Tool (SWAT) and the ecological model AQUATOX. Climate projections point out an increase of precipitations in the winter period and a decrease in the summer months, while temperature shows a significant increase over the whole year. Water discharge and nutrient loads simulated by SWAT show a tendency to increase (decrease) in the winter (summer) period. AQUATOX projects changes in the concentration of nutrients in the salt-marsh Palude di Cona, and variations in the biomass and species of the phytoplankton community.

The climatic conditions of North East India are favorable for trees to produce biomass in the form of foliage and twigs that are very rich in essential plant nutrients. Effective recycling of this biomass would help meet the nutritional requirement of crops. Field experiment was conducted in kharif (June–November) seasons for consecutive 3 years (2003, 2004, and 2005) at a lowland farm, subtropical Meghalaya (950 m asl), India, to study the effect of incorporating N-fixing tree biomass (leaves and twigs) on productivity and economics of rice (Oryza sativa L.). Fresh biomass from five tree species including erythrina (Erythrina indica), acacia (Acacia auriculiformis), alder (Alnus nepalensis), tree bean (Parkia roxburghii), and cassia (Cassia siamea) were applied at a rate of 10 t/ha. A plot with recommended NPK rate (80:60:40 kg/ha) and a control plot were also maintained for comparison. Among the tree species used, the biomass of E. indica was superior in terms of N (3.2%), P (0.47%), K (1.5%), and organic C (18.8%) contents. In the first and second year, productivity of rice was high with recommended NPK rate (4.82 t/ha in 2003 and 5.08 t/ha in 2004) followed by rice with incorporation of E. indica biomass. In the third year of the experiment, effects of tree biomass incorporation on growth, yield and yield attributes surpassed those of the recommended NPK rate, with the exception of A. nepalensis biomass. In that year, the maximum grain yield was recorded under E. indica treatments, exceeding yields under the recommended NPK rate and control by 10.5 and 69.3%, respectively. Incorporation of tree biomass significantly improved (14–19% N and 62–83% P over control) the stocks of soil available N and P. Treatment with A. auriculiformis and E. indica biomass resulted in significantly higher soil organic C content which exceeded that under the recommended NPK rate by 10.3 and 9.2% and that under the control by 15.2 and 14%, respectively higher by species. The highest net return was recorded with the recommended NPK rate ($ 381/ha) followed by E. indica ($ 303/ha). Since the local farmers are resource poor and rarely use chemical fertilizers, application of plant biomass, particularly that of E. indica, to lowland rice is a recommendable option to improve productivity and income, and to sustain soil health.

Humus forms are the seat of most biological transformations taking place in terrestrial ecosystems, being at the interface between plants, animals and microbes. The diversity of terrestrial humus forms (mor, moder and mull) can be attributed to the existence of different patterns (strategies) for the capture and use of resources by ecosystems, in ascending order of biodiversity and bioavailability. Arguments are found in the parallel development of humus forms and terrestrial ecosystems, in exclusion mechanisms between organisms living in different humus forms, and in palaeontological studies. The diversification of terrestrial life forms in the course of Earth history, concomitant with an improvement in resource availability due to the development of sedimentary layers at the surface of continents, may explain the successive appearance of more active humus forms enabling the coexistence of an increasing number of organisms. Contradictory reports about the relationships between biodiversity and stability of ecosystems can be explained by the existence of different belowground pathways making ecosystems more stable.

Cocoa agroforestry systems have the potential to conserve biodiversity and provide environmental or ecological benefits at various nested scales ranging from the plot to ecoregion. While integrating organic practices into cocoa agroforestry may further enhance these potentials, empirical and robust data to support this claim is lacking, and mechanisms for
biodiversity conservation and the provision of environmental and ecological benefits are
poorly understood. A field study was conducted in the Eastern Region of Ghana to evaluate the potential of organic cocoa agroforests to conserve native floristic diversity in comparison with conventional cocoa agroforests. Shade tree species richness, Shannon, Simpson’s
reciprocal and Margalef diversity indices were estimated from 84 organic and conventional cocoa agroforestry plots. Species importance value index, a measure of how dominant a species is in a given ecosystem, and conservation status were used to evaluate the conservation potential of shade trees on studied cocoa farms. Organic farms recorded higher mean shade tree species richness (5.10 ± 0.38) compared to conventional farms (3.48 ± 0.39). Similarly, mean Shannon diversity index, Simpson’s reciprocal diversity index and Margalef diversity index were significantly higher on organic farms compared to conventional farms. According to the importance value index, fruit and native shade tree species were the most important on both organic and conventional farms for all the cocoa age groups but more so on organic farms. Organic farms maintained 14 native tree species facing a conservation issue compared to 10 on conventional cocoa farms. The results suggest that diversified organic cocoa farms can serve as reservoirs of native tree species, including those currently facing conservation concerns thereby providing support and contributing to the conservation of tree species in the landscape.

Invasive species that alter ecosystems are often successful competitors due to their effects on nutrient cycling. Sphaeropteris cooperi (Cyatheaceae; Australian tree fern) has been invading intact Hawaiian rainforests for decades and displacing the dominant native tree fern Cibotium glaucum (Cibotiaceae). S. cooperi produces more leaves that grow faster, contain more N and P, and decompose faster than C. glaucum leaves. Our experiment tested the effects of additions of leaf litter from native and non-native tree ferns on the growth and nutrient content of four native angiosperm species in forest (N-rich) and landslide (P-rich) soils. Both litter treatments inhibited growth initially in all species, but subsequent responses were species-specific. Compared to control treatments, the increase in biomass was highest in the fast-growing Carex wahuensis and Hibiscus arnottianus with S. cooperi litter in landslide soil. Leaf N in C. wahuensis was higher with S. cooperi litter and in forest soil, as expected, but other leaf nutrient responses showed some evidence of nutrient immobilization from litter addition. Several growth measures were higher with S. cooperi than C. glaucum litter and in forest than landslide soil, suggesting that N availability is the strongest driver of growth. Our results show that S. cooperi can alter nutrient cycling in Hawaiian plants, sometimes with positive effects on growth. However, under natural conditions, native plants must compete for these additional nutrients with S. cooperi and other invasive species. This study contributes to invasion biology as the first to examine the impact of leaf litter of an invasive fern on native species.

Abrupt sunlight reduction scenarios (ASRS) following catastrophic events, such as a nuclear war, a large volcanic eruption or an asteroid strike, could prompt global agricultural collapse. There are low-cost foods that could be made available in an ASRS: resilient foods. Nutritionally adequate combinations of these resilient foods are investigated for different stages of a scenario with an effective response, based on existing technology. While macro- and micronutrient requirements were overall met, some—potentially chronic—deficiencies were identified (e.g., vitamins D, E and K). Resilient sources of micronutrients for mitigating these and other potential deficiencies are presented. The results of this analysis suggest that no life-threatening micronutrient deficiencies or excesses would necessarily be present given preparation to deploy resilient foods and an effective response. Careful preparedness and planning—such as stock management and resilient food production ramp-up—is ind...