Internal Nutrient Recycling Research Articles

Arctic cyanobacterial mat community diversity decreases with latitude across the Canadian Arctic.

Cyanobacterial mats are commonly reported as hotspots of microbial diversity across polar environments. These thick, multilayered microbial communities provide a refuge from extreme environmental conditions, with many species able to grow and coexist despite the low allochthonous nutrient inputs. The visibly dominant phototrophic biomass is dependent on internal nutrient recycling by heterotrophic organisms within the mats; however, the specific contribution of heterotrophic protists remains little explored. In this study, mat community diversity was examined along a latitudinal gradient (55-83°N), spanning subarctic taiga, tundra, polar desert, and the High Arctic ice shelves. The prokaryotic and eukaryotic communities were targeted, respectively, by V4 16S ribosomal RNA (rRNA) and V9 18S rRNA gene amplicon high-throughput sequencing. Prokaryotic and eukaryotic richness decreased, in tandem with decreasing temperatures and shorter seasons of light availability, from the subarctic to the High Arctic. Taxonomy-based annotation of the protist community revealed diverse phototrophic, mixotrophic, and heterotrophic genera in all mat communities, with fewer parasitic taxa in High Arctic communities. Co-occurrence network analysis identified greater heterogeneity in eukaryotic than prokaryotic community structure among cyanobacterial mats across the Canadian Arctic. Our findings highlight the sensitivity of microbial eukaryotes to environmental gradients across northern high latitudes.

Evaluation of the impact of aquatic-animal excretion on nutrient recycling and retention in stormwater treatment wetlands

The relative contribution of aquatic animals to phosphorus (P) and nitrogen (N) cycles of water bodies can be substantial. Excretion rates can be affected by seasonal environmental conditions, physiology, and body size. Determining the importance of particular species or size classes to total fauna-driven internal recycling of nutrients requires measurements of seasonal mass-specific excretion rates (MSER). We used short-term incubation experiments to estimate the contribution of excretion and egestion by eight species of fish and one macroinvertebrate to water column P and N in Stormwater Treatment Areas (STAs) used to retain P from water flowing to the Everglades in Florida, U.S.A. To account for environmental conditions and fish physiology, excretion was estimated during day and night in the wet and dry seasons for nine of the most abundant fish and invertebrates found in the STAs. To yield measurable contributions of analytes in short-duration incubations, large-fish species were incubated individually, whereas small-fish species and invertebrates were incubated in single-species groups. For large-fish species, total excreted nutrients were positively correlated with the mass of individual fish, but MSER decreased with increased individual size. All four small species, three fish and invertebrate, excreted P and N at greater MSERs than all five large-fish species. Most MSERs were not correlated with incubated mass (stocked density) of small animals (80%), indicating that there were no density-dependent effects on excretion rates. Most species excreted more N and less P during the South Florida wet season (May to October) though this was not the case for one or more analytes for three of the large species. Most species excreted more during the day, except large herbivores that excreted more at night. Small species excreted higher proportions of particulate P and N, while the larger species had higher proportions of dissolved nutrients. Using measured MSERs and areal biomass estimates for the nine species, we estimated mass of P and N excreted annually. Based on known inflow P and N loads for four STAs, a preliminary and conservative estimate is that fish excretion can recycle between 50% to 92% of the annual total P entering the system and 15% to 29% of the annual total N entering the system. These preliminary results underestimate the actual amounts because they do not account for STA cells that were not sampled, nor known under-estimation of large-fish biomass, as well as other animal effects on nutrient cycles such as bioturbation. Though preliminary, our results suggest that altering aquatic animal abundance or species composition could improve the efficiency of STAs to remove and retain nutrients from inflowing waters.

Aboveground Carbon Fixation and Nutrient Retention in Temporary Spontaneous Cover Crops in Olive Groves of Andalusia

In Southern Spain, olive trees have traditionally been cultivated in marginal areas with relatively shallow and bare soils under rainfed conditions, resulting in heavy soil losses and soil degradation. The implementation of temporary spontaneous cover crops in the inter-rows of olive groves, has proven to be a suitable diversification strategy to reduce soil erosion but it can also contribute to climate change mitigation and the boosting of internal nutrient recycling. However, information on the contribution of cover crops to atmospheric CO2 fixation and on nutrient retention in olive groves is scarce, which is a major drawback when it comes to modelling on larger spatial scales. In this study, we aimed to assess the potential effects of temporary spontaneous cover crops in olive groves on CO2 fixation and nutrient retention. The aerial biomass of cover crops (0.25m2 frames) and contents of carbon and nitrogen (CNHS analyser), phosphorus and potassium (IPC-MS) were analyzed in 46 commercial olive groves with different tree densities and cover crop layouts; the whole farm (WCC), the whole farm except the area below the tree canopy (CCC) or in bands of a given width in the inter-row area (BCC). Cover crops of 56% of the olive groves were under BCC whereas only 17% were under WCC. The annual net primary production of cover crops under WCC (1,707.4 kg DM ha−1 y−1) was significantly higher than that of CCC (769.5 kg DM ha−1 y−1) and with intermediate values for BCC (1,186.4 kg DM ha−1 y−1). Similarly, the annual rate of C-CO2 fixation in the annual net primary production of olive groves with WCC (642.1 kg C ha−1 y−1) was 1.35 and 2.1 times higher than the olive groves with BCC and CCC, respectively. On average, 19.5 kg N ha−1 y−1, 2.48 kg P ha−1 y−1 and 24.30 kg K ha−1 y−1 was accumulated in the biomass of the cover crops. This study demonstrates that cover crops contribute significantly to CO2 reduction and the retention of significant amounts of tree-unused nutrients. In addition, the higher the area covered by cover crops, the higher the contribution to these ecosystem services.

Fish Feeds in Aquaponics and Beyond: A Novel Concept to Evaluate Protein Sources in Diets for Circular Multitrophic Food Production Systems

With the general objective of optimizing internal nutrient recycling, circular multitrophic food production systems, e.g., combining fish, plant, and insect larvae production, rely on the quality and composition of sustainable nutritional inputs. Therefore, differences in dissolved and solid nutrient excretion patterns produced by Nile tilapia (Oreochromis niloticus) reared in recirculating aquaculture systems (RAS) with 5% daily water exchange and fed black soldier fly meal (BSFM), poultry by-product meal (PM), poultry blood meal (PBM) and fish meal (FM) as single protein sources were investigated to evaluate the potential for creating specific fish meal-free diets. Fish fed the FM and PM diet showed the significantly best (p < 0.05) and among each other similar (p > 0.05) growth performance (specific growth rate (SGR): 2.12 ± 0.04/2.05 ± 0.11; feed conversion ratio (FCR): 0.86 ± 0.03/0.92 ± 0.01), whereas the PBM diet caused significantly reduced performance (SGR: 1.30 ± 0.02; FCR: 1.79 ± 0.05) in comparison to the FM/PM diet as well as the BSF diet (SGR: 1.76 ± 0.07; FCR: 1.11 ± 0.05). The FM and PM diet resulted in a faster increase and significantly higher dissolved nitrogen and phosphorus levels, while the BSF diet caused faster accumulation and significantly elevated levels of dissolved potassium, magnesium, and copper. The PBM diet resulted in the feces with the significantly highest nutrient density (gross energy, crude protein, and amino acids) but overall much lower dissolved nutrient levels in the water. Results are discussed with regard to implications for developing circular multitrophic food production systems.

Interspecific interactions alter plant functional strategies in a revegetated shrub-dominated community in the Mu Us Desert, China.

Previous studies investigating plant-plant interactions have focused on plant growth, context dependence and shifts in interactive outcomes. However, changes in functional traits in the context of interactions have been inadequately explored; few studies have focused on the effects of interactions on the plasticity of functional strategies. We conducted a 4-year removal experiment for the xeric shrub Artemisia ordosica and perennial graminoids (PGs) in the Mu Us Desert, northern China. Soil nutrient content, biomass and 12 functional traits related to plant morphology and nutrient status were measured for the shrub species and a dominant PG species (i.e. Leymus secalinus) in the presence and absence of shrubs and PGs. Shrubs affected the functional traits of L. secalinus, reducing leaf dry matter content and increasing plant height, which probably promoted the functional strategy of L. secalinus towards a more resource-acquisitive and competitive strategy. In contrast, when the shrubs were affected by PGs, they shifted towards a resource-conservative and stress-tolerative strategy, by increasing leaf dry matter content and decreasing specific leaf area. Moreover, the shrub species relied more on internal nutrient recycling (higher nitrogen resorption efficiency) rather than on external nitrogen uptake under nitrogen competition; instead, L. secalinus tended to exhibit higher external nitrogen uptake from soil during nitrogen shortages. This study indicated that the functional strategies and nutrient cycling of the shrub species and the dominant PG were altered by each other. The shifts in functional traits may help plants to coexist in the community for a relatively long time. Our findings highlighted that interspecific interactions alter plant functional strategies and provided new insights into community assembly and succession mechanisms in a revegetated shrubland for ecological restoration of drylands.

Key drivers structuring rotifer communities in ponds: insights into an agricultural landscape.

Understanding the influence of environmental and spatial factors on the structure of aquatic communities remains a major challenge in community ecology. This study aims to identify main drivers of rotifer abundance and diversity in ponds embedded in an intensive agricultural landscape in Northeast Germany. We studied 42 ponds of glacial origin (kettle holes) covering a wide range of environmental parameters. The predominant factors structuring the rotifer metacommunity shifted from abiotic environmental filtering in spring to unstudied factors in autumn, while spatial factors remained less important. Fertilizer-driven salinization, internal nutrient recycling, primary productivity and sediment phosphorus release were the prevalent biogeochemical processes in the ponds. Both fertilizer-driven salinization and primary productivity negatively affected rotifer alpha diversity, and positively affected beta diversity. This impact was lower in forest ponds than in those surrounded by arable fields or grassland. However, rotifer diversity did not significantly differ among land-use categories. Our results indicate that the long-term impact of intensive agriculture in the region and the associated widespread eutrophication overrides the direct influence of land use on rotifer diversity but point to an indirect effect via fertilizer-driven salinization. Furthermore, this study highlights the role of ponds in enhancing regional biodiversity in agricultural landscapes.

Towards New Soil Management Strategies for Improving Soil Quality and Ecosystem Services in Sustainable Agriculture: Editorial Overview

The major issues related to indiscriminate land use are overall related to topsoil depletion, groundwater contamination, plant disease outbreaks, air pollution and greenhouse gas emissions. Currently, global vision focused on the environmental impact and use of eco-friendly strategies are increasing. The design of new agroecosystems and food systems are fundamental to make more sustainability in soil management systems by improving the release of advanced ecosystems services for farmers. Sustainable agriculture utilizes natural renewable resources in the best way due to their intrinsic features by minimizing harmful impact on the agroecosystems. Farmers should sustain or even increase the soil organic matter (SOM) content overall in depleted, semiarid and arid soils. Nutrients recycled from agro-waste into the soil using residual biomass sources should be endorsed by diversified agriculture and governmental policies in which livestock and crop production are spatially integrated. Many good agricultural practices that growers may use to promote soil quality and soil health by minimizing water use and soil pollution on farms are yet available from past years. Exploration of the natural soil biodiversity and manipulation of soil microbiota by continuous amendment with compost, biochar and digestate represents a pre-requisite to develop more efficient microbial consortia useful for soils and crops. On the other hand, more attention is proven regarding the sustainable use of useful microorganisms employed as pure inoculants in rhizosphere. Among them, plant growth-promoting rhizobacteria and biological control agents cover the major groups of tailored inoculants in order to rationalize the internal recycling of nutrients and their energy recovery, or to improve the soil quality and plant health thanks to their diversified mechanisms of action and complex interactions between SOM, microbiota and plant roots in the rhizosphere.

Nitrogen, Phosphorus, and Potassium Resorption Responses of Alfalfa to Increasing Soil Water and P Availability in a Semi-Arid Environment

In semi-arid areas, alfalfa (Medicago sativa L.) is widely grown, but its growth is often restricted due to limited rainfall and soil nutrients, particularly phosphorus (P). Nutrient resorption is an effective strategy for dealing with nutrient shortages. Alleviation of these limited resources using film mulch and P fertilization—which are common practices in semi-arid areas—can affect the internal recycling of such nutrients. Little is known about such effects in alfalfa and the relationship between resorption efficiency and forage yield. We conducted a two-year field experiment in the semi-arid Loess Plateau of China using film mulch and P fertilization to investigate the response to long-term increasing soil water and P availability on leaf nitrogen (N), P, and potassium (K) concentrations and nutrient resorption characteristics in alfalfa. In green leaves, mulching significantly increased P concentration by an average of 5.5% but it had no significant effect on N concentration over two years, and it decreased K concentration by 16.1% in 2017. P fertilization significantly increased N concentrations to a greater degree in 2018 (8.1%) than 2017 (1.6%). P fertilization also significantly increased P concentrations by an average of 34.1% over two years. In contrast, P fertilization significantly decreased K concentration in the mulched treatment by an average of 17.3% in 2017 and 21.8% in 2018, but it had no effect in the no-mulch treatment. In senescent leaves, mulching significantly increased N concentration by an average of 3.9% and P concentration by an average of 16.7%, but it had no significant effect on K concentration over two years, while P fertilization significantly decreased N and K concentrations over two years by an average of 7.5%, and 32.8%, respectively. P fertilization significantly increased senesced P concentration by an average of 11.9% in 2017 and 17.5% in 2018; and year × mulching × P fertilization had a significant interaction on senesced leaf P concentration. For resorption efficiency, mulching decreased P resorption efficiency by an average of 3.0%, but it had no impact on N or K resorption efficiency, while P fertilization increased the N, P, and K resorption efficiencies in alfalfa by an average of 6.8%, 6.2%, and 76.4% over two years, respectively. Interactive effects of mulching and P fertilization were found on P and K resorption efficiencies over time. In addition, N and K resorption efficiencies were significantly higher in 2018 than in 2017. The application of P fertilizer without mulching resulted in positive correlations between forage yield and N, P, and K resorption efficiencies, but no correlations were observed under film mulch. That is, mulching changed the relationship between forage yield and N, P, and K resorption efficiencies in alfalfa, suggesting that N, P, and K resorption efficiencies may not be related to high yield. Our results provide new insights into the role of nutrient resorption in alfalfa in response to increasing soil water and P availability and the relationship between resorption efficiency and forage yield, which will help us to improve alfalfa yield in semi-arid regions.

Quantifying trade-offs among on-farm and off-farm fertility sources to make vegetable organic farming systems more sustainable

A core principle of organic farming is the reliance on internal nutrient recycling, favoring nutrient sources produced on farms (e.g.,manures) as opposed to those that are not (e.g., processed fertilizers, municipal compost). Soil fertility management varies tremendously among organic vegetable production systems, potentially with large effects on crop productivity, the environment, and trade-offs between them. We compared four certified organic systems using manure, municipal waste compost, and/or processed fertilizers to grow a mix of vegetable crops with variable nutrient demand. The four systems added nutrients to meet recommended nitrogen (N) inputs, estimated phosphorus (P) removal, or both, with different trade-offs expected between crop yields and environmental impacts depending on the imbalance in N:P ratio between fertility sources and crop removal. Municipal compost minimized trade-offs between yields and environmental impacts for crops with a low N demand (e.g.,beet). In these systems, we observed higher carbon inputs (2–6 fold), and lower residual soil N (40–50%) and nitrous oxide (N2O) emissions (50–75%) compared to systems based on manures or processed fertilizers. In contrast, the manure-based system had the highest crop yields when N demand was high (e.g., cauliflower), but also the highest environmental impacts. Using processed fertilizers instead of manure typically lowered N2O emissions (45%) and P surpluses (85%), but it also reduced yields (10%). Overall, our results confirm the need to develop high-yielding organic vegetable systems that minimize environmental impacts and the challenge of minimizing farm-scale yield-environment trade-offs without relying on off-farm fertility sources.

An Integrated Analysis of the Eutrophication Process in the Enxoé Reservoir within the DPSIR Framework

The Enxoé reservoir in southern Portugal has been exhibiting the highest trophic state in the country since its early years of operation. The problem has attracted water managers’ and researchers’ attention as the reservoir is the water supply for two municipalities. Extensive research was thus conducted over the last few years, including field monitoring and modelling at the plot, catchment, and reservoir scales. This study now frames all partial findings within the Driver-Pressure-State-Impact-Response (DPSIR) framework to better understand the eutrophication process in the Enxoé reservoir. Agriculture and grazing were found to have a reduced role in the eutrophication of the reservoir, with annual sediment and nutrient loads being comparably smaller or similar to those reported for other Mediterranean catchments. Flash floods were the main mechanism for transporting particle elements to the reservoir, being in some cases able to carry up three times the average annual load. However, the main eutrophication mechanisms in the reservoir were P release from deposited sediment under anoxic conditions and the process of internal recycling of organic matter and nutrients. Reducing the P load from the catchment and deposited sediment could lead to a mesotrophic state level in the reservoir. However, this level would only be sustainable by limiting the P internal load ability to reach the photic zone.

Nitrogen allocation and recycling in peri-urban mixed crop\u2013livestock farms in Ethiopia

Mixed crop–livestock (MC–LS) farms are assumed to be more environmental friendly than specialized livestock systems, due to their better options for internal nutrient recycling. However, there are large differences among MC–LS farms in nutrient allocation and recycling. Here, we posit that the relative allocation of nitrogen to crop and livestock compartments, expressed as crop–livestock ratio (CLS), determines the performance of MC–LS farms. Among 300 urban and peri-urban farms studied in 2014, 42 MC–LS farms (Addis Ababa: 20; Jimma: 22) were re-interviewed in 2016, using MonQIt (monitoring tool) questionnaire. The performances of these farms were evaluated using partial nitrogen balance (PNB), N use efficiency (NUE), N recycling index and net farm income (NFI). CLS was negatively related to N input, PNB and NFI. Livestock oriented MC–LS farms had 4–5 times higher N input and 7 times higher PNB than crop oriented MC–LS farms, because they had 2–4 times higher NFI and purchased more external N input. This indicated that N allocation has significant environmental and economic implications. Sensitivity analyses suggested that NUE at farm system level can be improved by 20–25% and N recycling (NR) by 10–20% over the current condition. In conclusion, MC–LS farms are diverse, and much of the diversity can be captured by the CLS indicator. NUE and NR of peri-urban MC–LS farms in Ethiopia can be significantly improved through NUE enhancing measures: targeted exchange of crop residues and manure between crop and livestock activities within and between farms and improving animal NUE through breeding and precision feeding.

Poplar leaf rust reduces dry mass accumulation and internal nitrogen recycling more markedly under low soil nitrogen availability, and decreases growth in the following spring.

Rust is one of the most important biotic stress factors that affect poplars. The aims of this work were: (i) to analyze the changes in growth and nitrogen (N) accumulation in Populus deltoides W. Bartram ex Marshall plants infected with rust (Melampsora medusae Thümen.) and to determine how internal N stores are affected by the disease, in plants growing under two N availabilities in the soil; and (ii) to evaluate the impact of rust in the early sprout in the following growing season and the cumulative effect of the disease after repeated infections. Two clones with different susceptibility to rust were analyzed. At leaf level, rust reduced gas exchange capacity, water conductance in liquid phase and photosynthetic rate in both clones. At plant level, rust reduced plant growth, accelerated leaf senescence and abscission occurred with a higher concentration of leaf N. Even though N concentration in stems and roots were not significantly reduced by rust, total N accumulation in perennial tissues was reduced in infected plants. The vigor of the early sprout of plants infected by rust in the previous season was lower than that of non-infected plants. Therefore, rust affects plant growth by reducing the photosynthetic capacity and leaf area duration, and by decreasing internal nutrient recycling. As nutrient reserves in perennial tissues are lower, rust infection reduces not only the growth of the current season, but also has a cumulative effect on the following years. The reduction of growth was similar in both clones. High availability of N in the soil had no effect on leaf physiology but increased plant growth, delayed leaf senescence and abscission, and increased total N accumulation. If fertilization increases plant growth (stem and root dry mass) it can mitigate the negative effect of the pathogen in the reduction of nutrient storages and future growth.

Assessing human impact on Rostherne Mere, UK, using the geochemistry of organic matter

This study investigates recent changes in the geochemistry of organic material from a hypereutrophic lake (Rostherne Mere, United Kingdom) using the geochemical and molecular composition of radiometrically dated sediment cores. Modern samples suggest that recent sedimentation is dominated by algal production; however, a minor component of allochthonous organic material is present. Sediment cores reveal that absolute proxy values and the magnitude of observed changes are broadly homogenous across the lake basin. A transition to environmental conditions favouring enhanced algal productivity in recent sediments is suggested by higher total organic carbon (TOC) and lower carbon to nitrogen ratio (C/N), carbon isotope composition of organic matter (δ13Corg), and average n-alkane chain length. A strong covariance between TOC and Rock-Eval Hydrogen Index implies this transition is driven by an increasing algal contribution rather than being a response to variations in the source of organic matter. Decadal trends and abrupt shifts in organic geochemical proxies are suggested to be directly related to changes in external anthropogenic nutrient loading following the construction and decommissioning of sewage treatment plants. The development of hypereutrophic conditions likely occurred in stages, where rapid transitions are associated with the commencement of sewage effluent input in the 1930s, population increases in the 1980s, and a dramatic reduction in external nutrient loads in the 1990s. Recovery of the lake ecosystem is limited by internal nutrient recycling, and organic proxies indicate that the geochemistry of sediments has remained relatively constant since effluent diversion. This study highlights the utility of organic geochemical parameters in tracing recent eutrophication processes in lakes to provide evidence for the timing and scale of anthropogenic environmental change.

Water Quality and Plankton Communities in Hybrid Catfish (♀ Channel Catfish,Ictalurus punctatus× ♂ Blue Catfish,Ictalurus furcatus) Ponds After Partial Fish Harvest

Twelve 0.4‐ha ponds were stocked with 10,000 hybrid catfish fingerlings in March 2015. Six ponds were partially harvested in August to remove fish larger than ∼0.57 kg. All remaining fish were removed in October and November. Partial harvest of faster‐growing fish removed ∼26% of the fish initially stocked; feeding rate (and therefore external nutrient loading) was reduced by about the same amount. However, reduced nutrient loading after partial fish harvest had no meaningful effects on water quality, phytoplankton biomass, phytoplankton and zooplankton community structure, or supplemental aeration. Lack of ecosystem change was caused by persistent internal recycling of nutrients added to the system before partial harvest and continued high (albeit reduced) external nutrient loading after partial harvest. Decisions to employ partial fish harvest to manage single‐cropped hybrid catfish ponds should be based on economic considerations and risk reduction rather than the expectation that fish biomass reduction will improve water quality.

Soil improvement and mitigation of greenhouse gas emissions for integrated crop–livestock systems: Case study assessment in the Pantanal savanna highland, Brazil

Greenhouse gas emissions and climate change has been partially attributed to agricultural expansion by deforestation, while the pressure to assure food, fiber and energy for the future generations leads to the intensification of agricultural systems. The transition to more efficient systems is actually considered an important strategy to reduce deforestation and to spare land for other uses, including the recovery of environmental services and ecohydrological processes in the drainage basin such as carbon sink and water regulation. The Brazilian Federal Program for Low Carbon Agriculture (ABC Program) intends to reduce carbon emissions by stimulating technological processes that neutralize emissions or enhance the sinking of greenhouse gases. A pilot farm has been established to assess an intensive animal-plant farming system that incorporates anaerobic digestion for biogas, power generation and organic fertilizer production. Emergy Synthesis was chosen as a methodological tool to assess and to diagnosis the farm system design. The modified emergy assessment including externalities (greenhouse gas emissions) improves the understanding of integrated crop–livestock systems efficiency in internal recycling of nutrients and power conversion. The adoption of manure treatment in intensified agricultural systems can effectively contribute to enhance environmental and economic performances.

Benchmarking the economic, environmental and societal performance of Dutch dairy farms aiming at internal recycling of nutrients

Several dairy farms in the Netherlands aim at reducing their environmental impact by improving the internal nutrient cycle (INC) at farm level. Practices to improve nutrient cycling at these INC farms, however, might not only reduce the environmental impact on-farm, but alter also the off-farm environmental impact associated with supply chain processes (production and transport) related to inputs entering the farm, such as purchased feed or fertilizer or the economic or societal performance of these farms. We compared, therefore, a set of sustainability indicators of nine INC farms with a group of benchmark farms, comparable in terms of farm size, intensity and site-specific circumstances. This benchmark group was composed using statistical matching to exclude the effect of these characteristics on economic, environmental and societal performance. Economic indicators used were: farm income per unpaid annual working unit and the costs to revenues ratio. Environmental indicators used were derived from a cradle-to-farm-gate life cycle assessment: land occupation (LO), non-renewable energy use (NREU), global warming potential (GWP), acidification potential (AP) and eutrophication potential (EP), expressed per kg fat-and-protein-corrected milk (FPCM). In addition, we quantified the soil content of organic carbon and phosphorus, and the soil nitrogen supply. Societal indicators used were: payments for agri-environmental measures, grazing hours and penalties for aberrant milk composition. Results showed that INC farms had a lower non-renewable energy use per kg FPCM, higher soil organic carbon content and received higher annual payments for agri-environmental measures, whereas economic and other environmental, societal indicators did not differed. Furthermore, we demonstrated the need for a sound benchmark to assess the effect of INC-farming on the economic, environmental and societal performance. Statistical matching enabled us to define, for each INC farm, a benchmark group with similar farm characteristics, which are known to affect sustainability indicators. Observed differences in sustainability indicators between both farm groups, therefore, truly resulted from aiming at internal nutrient cycling, and not from differences in other farm characteristics.

A synergistic combination of algal wastewater treatment and hydrothermal biofuel production maximized by nutrient and carbon recycling

This study introduces and analyzes a novel system for algal biofuel production that synergistically integrates algal wastewater treatment with hydrothermal liquefaction (HTL) of wastewater biosolids and algae into bio-crude oil. This system maximizes the biofuel potential of wastewater inputs by internally capturing and recycling carbon and nutrients – a powerful concept referred to as multi-cycle nutrient reuse, which amplifies waste nutrients into multiple cycles of algal biomass and bioenergy production. We call this system “Environment-Enhancing Energy” (E2-Energy) because it can simultaneously improve conventional wastewater treatment by nutrient removal and production of a large amount of biofuel co-products. Moreover, E2-Energy resolves several key bottlenecks commonly associated with large-scale algal biofuel production including: contamination of target high-oil algal cultures, high nutrient costs/usage, unsustainable fresh water usage, and large energy inputs for dewatering/extraction. A series of algal cultivation and HTL experiments were conducted to confirm the primary steps and performance characteristics of the E2-Energy system. These experiments showed: (1) low-oil, mixed algal–bacterial biomass can be successfully cultured with the recycled HTL aqueous product; (2) both organics and nutrients are removed from wastewater during algal–bacterial biomass production (63–95% reduction); (3) this low-oil, algal–bacterial biomass can be converted into bio-crude oil via HTL with a high yield (∼50%) and a net positive energy balance; and (4) the HTL step re-releases nutrients to an aqueous phase product that can be recycled back to step (1). This repeating loop of steps 1–4 facilitates multi-cycle reuse of nutrients and thus provides biomass amplification. A mathematical model was also developed using STELLA® to simulate mass balances for long-term E2-Energy operations with internal recycling of nutrients and carbon. The model results showed that E2-Energy can amplify the biomass and biofuel production from wastewater by up to 10 times, which gives it the potential to replace all US petroleum imports using only current wastewater feedstocks and carbon dioxide from the atmosphere or point sources. Thus, E2-Energy represents a major paradigm shift—where wastewater treatment systems become optimized biofuel producers with enhanced effluent quality, which provides a viable and advantageous pathway to sustainable, carbon-neutral energy independence.

Potential and realized nutrient resorption in serpentine and non-serpentine chaparral shrubs and trees

Low-nutrient adapted species have numerous mechanisms that aid in nutrient conservation. Hypothetically, species adapted to nutrient-poor soils should have tighter internal nutrient recycling, as evidenced by greater resorption. However, literature results are mixed. We suggest methodological factors may limit our understanding of this process. We hypothesized that plants adapted to serpentine soils would be more proficient in resorbing N and P than plants adapted to non-serpentine soils, although there would be differences among functional groups within each soil type. For six growing seasons, we sampled senescent leaf tissue from the dominant and co-dominant shrubs and trees found in serpentine and non-serpentine chaparral communities in the California Coast Range. Our study also explicitly included congener pairs found on both soil types. Most species were highly N proficient, but species adapted to serpentine soils were more P proficient. Surprisingly, two of the three potential N-fixing species were also highly N proficient. Evergreen Quercus congeners were more N proficient than their deciduous congener pairs, although there was no difference in P resorption proficiency. Overall, large inter-annual variation was observed among most species sampled, but at least in some years, maximum potential resorption likely was reached. However, climate (temperature and precipitation) was not strongly correlated with either N or P resorption proficiency. Our data suggest that controlling for phylogeny can aid in interpretation of resorption patterns. More importantly, our study clearly shows that resorption patterns can only be discerned through long-term datasets, of which few exist in the literature.

Controls of hydrochemical fluxes via stemflow in tropical lowland rainforests: Effects of meteorology and vegetation characteristics

summary So far stemflow has been underrepresented in studies of ecosystem ecology as it usually contributes less than 10% to hydrological input to the forest floor. However, in terms of nutrient cycling, stemflow may constitute an important pathway for the localized input of highly enriched solutes to the forest floor. We measured stemflow hydrology and biogeochemistry in three different ecosystem types (primary forests on ridge and ravine, as well as secondary forest) in South-West Costa Rica. Stemflow hydrochemistry was mainly controlled by meteorology (precipitation magnitude and duration), ecosystem characteristics (topography and plant area index) and species-specific traits (stem diameter and tree height). Stemflow was enriched 7.5-fold in nutrients compared to bulk precipitation and 2.9-fold compared to throughfall. In net stemflow most solutes (especially DOC and K) were leached, while inorganic nitrogen and phosphorus (i.e. NO3 and PO4) were retained along the stemflow pathway. Computation of multiple regression models allowed dissecting the contributions of canopy exchange and dry deposition processes to net stemflow fluxes. Net stemflow was dominated by canopy exchange processes and to a lesser extent by dry deposition fluxes. Including throughfall and litterfall nutrient flux data we calculated that stemflow comprised 1–10% of dissolved internal recycling of nutrients and up to 1.5% of total aboveground nutrient returns. However, dissolved returns by canopy exchange via throughfall plus stemflow contributed up to 50% of total aboveground nutrient return. This demonstrates that stemflow per se represents a small but localized proportion of total above nutrient recycling but that total dissolved returns of (highly available) nutrients and DOC can be important as a part of the internal nutrient cycle of tropical rainforests.

Using successional theory to measure marine ecosystem health

Marine ecosystems are diverse and complex, providing significant challenges to the development of generalizable metrics of ecosystem health. Of particular concern is the varied form of change caused by multiple human activities, which limits the capacity to generate a single measure to encapsulate the overall condition of the ecosystem. Here we consider how successional theory can help to simplify our understanding of marine community structure, especially when viewed in context of human disturbance. During succession, the emergent properties of communities change in predictable ways. As communities mature, there is an increase in total production and biomass, the mean size of organisms, the level of internal recycling of food and nutrients, and the mean trophic level. Using a set of multi-species trophic models, we explore the changes in community structure that are likely to occur during succession. These changes include increases in biomass within trophic levels due to decreased rates of energy and food loss through trophic and production inefficiencies, and potential shifts from top-down control early in succession to bottom-up later. Because human activities disproportionately favor early-successional species, we can gain insights by considering community degradation in the context of succession being played in reverse. Indicators of health based on ecological succession thus provide a mechanistic view to measure the impact of human activities (both positive and negative) on marine ecosystems.