Eduardo Aguilera

Gaseous emissions from management of solid waste: a systematic review.

The establishment of sustainable soil waste management practices implies minimizing their environmental losses associated with climate change (greenhouse gases: GHGs) and ecosystems acidification (ammonia: NH3). Although a number of management strategies for solid waste management have been investigated to quantify nitrogen (N) and carbon (C) losses in relation to varied environmental and operational conditions, their overall effect is still uncertain. In this context, we have analyzed the current scientific information through a systematic review. We quantified the response of GHG emissions, NH3 emissions, and total N losses to different solid waste management strategies (conventional solid storage, turned composting, forced aerated composting, covering, compaction, addition/substitution of bulking agents and the use of additives). Our study is based on a meta-analysis of 50 research articles involving 304 observations. Our results indicated that improving the structure of the pile (waste or manure heap) via addition or substitution of certain bulking agents significantly reduced nitrous oxide (N2O) and methane (CH4) emissions by 53% and 71%, respectively. Turned composting systems, unlike forced aerated composted systems, showed potential for reducing GHGs (N2O: 50% and CH4: 71%). Bulking agents and both composting systems involved a certain degree of pollution swapping as they significantly promoted NH3 emissions by 35%, 54%, and 121% for bulking agents, turned and forced aerated composting, respectively. Strategies based on the restriction of O2 supply, such as covering or compaction, did not show significant effects on reducing GHGs but substantially decreased NH3 emissions by 61% and 54% for covering and compaction, respectively. The use of specific additives significantly reduced NH3 losses by 69%. Our meta-analysis suggested that there is enough evidence to refine future Intergovernmental Panel on Climate Change (IPCC) methodologies from solid waste, especially for solid waste composting practices. More holistic and integrated approaches are therefore required to develop more sustainable solid waste management systems.

Yield-scaled mitigation of ammonia emission from N fertilization: the Spanish case

Synthetic nitrogen (N) fertilizer and field application of livestock manure are the major sources of ammonia (NH3) volatilization. This N loss may decrease crop productivity and subsequent deposition promotes environmental problems associated with soil acidification and eutrophication. Mitigation measures may have associated side effects such as decreased crop productivity (e.g. if N fertilizer application is reduced), or the release of other reactive N compounds (e.g. N2O emissions if manure is incorporated). Here, we present a novel methodology to provide an integrated assessment of the best strategies to abate NH3 from N applications to crops. Using scenario analyses, we assessed the potential of 11 mitigation measures to reduce NH3 volatilization while accounting for their side effects on crop productivity, N use efficiency (NUE) and N surplus (used as an indicator of potential N losses by denitrification/nitrification and NO3− leaching/run-off). Spain, including its 48 provinces, was selected as a case study as it is the third major producer of agricultural goods in Europe, and also the European country with the highest increase in NH3 emissions from 1990 to 2011. Mitigation scenarios comprised of individual measures and combinations of strategies were evaluated at a country- and regional level. Compared to the reference situation of standard practices for the year 2008, implementation of the most effective region-specific mitigation strategy led to 63% NH3 mitigation at the country level. Implementation of a single strategy for all regions reduced NH3 by 57% at the highest. Strategies that involved combining mitigation measures produced the largest NH3 abatement in all cases, with an 80% reduction in some regions. Among the strategies analyzed, only suppression of urea application combined with manure incorporation and incorporation of N synthetic fertilizers other than urea showed a fully beneficial situation: yield-scaled NH3 emissions were reduced by 82%, N surplus was reduced by 9%, NUE was increased by 19% and yield was around 98% that of the reference situation. This study shows that the adoption of viable measures may provide an opportunity for countries like Spain to meet the international agreements on NH3 mitigation, while maintaining crop yields and increasing NUE.

The Spanish Transition to Industrial Metabolism: Long‐Term Material Flow Analysis (1860-2010)

The aim of this work is to reconstruct the main economy‐wide/material flow accounting indicators for the Spanish economy between 1860 and 2010. The main results indicate that from 1960 onward, the country saw a very rapid industrial transition based on the domestic extraction of quarry products and the import of fossil fuels and manufactured goods. Direct material consumption rose from 58.7 million tonnes (Mt) in 1860 to 570.2 Mt in 2010. In per capita terms, it rose from 2.76 tonnes per capita per year (t/cap/yr) to 11.61 t/cap/year. Of the decennial years studied in this article, a peak of 15.23 t/cap/yr occurs in the year 2000; the subsequent fall is explained by the crisis of 2008. Until 1930, Spain was a net exporter of resources, but since that year, and especially since 1960, it began to depend heavily on overseas resources. The physical trade balance per inhabitant in Spain was -0.01 t/cap/year in 1860 and today it is 2.45 t/cap/year. This process also reveals the change in consumption patterns, which became increasingly dependent on abiotic resources. In 1860, 98.1% of resources consumed was biomass, whereas today the figure is 16.2%. In all events, this article shows how, although the great transformation did not occur until 1960, before that date the country saw significant qualitative transformation, which did not involve relevant changes in the mobilization of resources.

Spanish agriculture from 1900 to 2008: a long-term perspective on agroecosystem energy from an agroecological approach

According to the agroecological approach, energy analyses applied to agriculture should provide information about the structure and functions of the agroecosystem; in other words, about the maintenance of its fund elements, which sustain the flow of ecosystem services. To this end, we have employed a methodological proposal that adds agroecological EROIs to the existing economic EROIs. This methodology is applied here for the first time at the country level, and over a long-term historical period. The Spanish agroforestry sector, which is representative of Mediterranean agroclimatic conditions, has been studied on a decadal basis from 1900 to 2008, fully spanning its process of industrialization and modernization. The results show the loss of energy efficiency brought about by the industrialization of Spanish agriculture. The economic EROIs (FEROI, EFEROI and IFEROI) fell by 42, 93 and 12%, respectively. The shift towards livestock production and the dramatic increase in industrial inputs are the causes of this decline. With regard to agroecological EROIs, NPPact EROI and Biodiversity EROI fell by 6 and 15%, respectively. This suggests that the fund elements are being degraded and alerts us to low returns to nature in the form of un-harvested biomass available to aboveground and underground wildlife. Finally, Woodening EROI increased by 48%. Sixty percentage of this increment was due to the growth of woodland in areas freed from agricultural activities. However, this change in land use was partly due to feed imports from third countries where deforestation processes may well be taking place, an effect that has not been considered in the analysis.

Soil carbon sequestration is a climate stabilization wedge: Comments on Sommer and Bossio (2014)

Sommer and Bossio (2014) model the potential soil organic carbon (SOC) sequestration in agricultural soils (croplands and grasslands) during the next 87 years, concluding that this process cannot be considered as a climate stabilization wedge. We argue, however, that the amounts of SOC potentially sequestered in both scenarios (pessimistic and optimistic) fulfil the requirements for being considered as wedge because in both cases at least 25 GtC would be sequestered during the next 50 years. We consider that it is precisely in the near future, and meanwhile other solutions are developed, when this stabilization effort is most urgent even if after some decades the sequestration rate is significantly reduced. Indirect effects of SOC sequestration on mitigation could reinforce the potential of this solution. We conclude that the sequestration of organic carbon in agricultural soils as a climate change mitigation tool still deserves important attention for scientists, managers and policy makers.

A historical perspective on soil organic carbon in Mediterranean cropland (Spain, 1900–2008)

Soil organic carbon (SOC) management is key for soil fertility and for mitigation and adaptation to climate change, particularly in desertification-prone areas such as Mediterranean croplands. Industrialization and global change processes affect SOC dynamics in multiple, often opposing, ways. Here we present a detailed SOC balance in Spanish cropland from 1900 to 2008, as a model of a Mediterranean, industrialized agriculture. Net Primary Productivity (NPP) and soil C inputs were estimated based on yield and management data. Changes in SOC stocks were modeled using HSOC, a simple model with one inert and two active C pools, which combines RothC model parameters with humification coefficients. Crop yields increased by 227% during the studied period, but total C exported from the agroecosystem only increased by 73%, total NPP by 30%, and soil C inputs by 20%. There was a continued decline in SOC during the 20th century, and cropland SOC levels in 2008 were 17% below their 1933 peak. SOC trends were driven by historical changes in land uses, management practices and climate. Cropland expansion was the main driver of SOC loss until mid-20th century, followed by the decline in soil C inputs during the fast agricultural industrialization starting in the 1950s, which reduced harvest indices and weed biomass production, particularly in woody cropping systems. C inputs started recovering in the 1980s, mainly through increasing crop residue return. The upward trend in SOC mineralization rates was an increasingly important driver of SOC losses, triggered by irrigation expansion, soil cover loss and climate change-driven temperature rise.

The agrarian metabolism as a tool for assessing agrarian sustainability, and its application to Spanish agriculture (1960-2008)

Agrarian metabolism applies the social metabolism framework to agriculture. It focuses on the study of the exchange of material and energy flows between a society and its environment for producing useful biomass. These flows must maintain the fund elements of the agroecosystem in sufficient quantity and of sufficient quality for them to continue providing ecosystem services. This methodology was applied to Spanish agriculture between 1960 and 2008, a period characterized by a deep process of intensification based on external inputs (EIs). We specifically focused on nitrogen (N), phosphorus (P), potassium (K), carbon (C), and energy flows, and on the three fund elements that they sustain such as soil, biodiversity, and woodland. The results show that the growing incorporation of EIs has broken the equilibrium between land and biomass uses required by traditional farming, lowering the density of internal energy loops. On cropland, the relative fall in unharvested biomass had a negative effect on both biodiversity and the soil, which reduced the replenishment of organic C between 1960 and 1990. The sharp increase in internal and external flows of biomass for animal feed hardly contributed to increasing soil organic carbon (SOC) between 1990 and 2008 because of the fact that these flows had increasingly lower C:N ratios. The massive importation of N in feed and mineral fertilizers (553 and 1150 Gg in 2000, respectively) increased the surplus and the losses of N, which in turn could have a negative impact on biodiversity, water, and the atmosphere. The scenario constructed without imported animal feed would allow a reduction in the environmental impacts related to the excess of N, with hardly any negative effect on SOC replenishment, and improving energy return rates in the form of total, unharvested, and accumulated phytomass.

The Making of Olive Landscapes in the South of Spain. A History of Continuous Expansion and Intensification

The objective of this work is to make an additional contribution that reveals new evidence about the nature of Mediterranean landscapes, their historical construction and the consequences of their transformation process. For this, we want to study the case of what is perhaps the most representative crop of the region: olive groves. The study area is the south of Spain which, for more than a century, has had the main concentration of olive trees in the Mediterranean and currently has the highest concentration of cultivated trees in the continent, with a continuous wood of more than 200 million trees. In the study period, between 1750 and 2010, we will outline the change in the social function of the crop, the management applied, the resulting landscapes and the socio-ecological consequences of the change. As we will see, historically, olive groves have not presented a constant image, but have changed from being a widespread crop, similar to exploitation systems such as dehesas and montados, to the industrial monoculture that they are today. The reconstruction of the geography of their expansion and the change in the morphology of olive grove landscapes and its causes, enable us to rebuild one of the most representative fragments of traditional Mediterranean landscapes, the olive groves of the south of Spain, and, with it, to participate in some of the debates that still persist about this matter.

Agroecosystem energy transitions: exploring the energy-land nexus in the course of industrialization

Agriculture and forestry are integral parts of the socioeconomic energy system, not only in the recent context of biofuel production, but also from a fundamental, long-term socio-ecological perspective (Rappaport 1971; Bayliss-Smith 1982; Sieferle 2001). For most of human history, biomass was humanity’s major source of primary energy, and since the Neolithic Revolution, agriculture and forest use have been society’s mainmechanism for harnessing energy. Even though fossil fuels and other modern energy forms became dominant in the last two centuries, biomass remains vital to the current energy regime (Krausmann et al. 2008). Humanity continues to rely on agriculture for food supply. Taken together, food and feed constitute the energy sources essential for the reproduction of human and livestock populations and the provision of human and animal labor (Kander et al. 2014). In the future, we will need to feed a growing population while also moving away from fossil energy and toward a new type of low-carbon energy system. Both goals will require an efficient and sustainable agricultural production system, one with high biomass output but which does not deplete soil fertility or depend on high inputs of non-renewable resources. Understanding the energy dynamics of agroecosystems is thus crucial to feeding the people of the world in the face of an uncertain energy future. Industrialization had profound and long-term impacts on both societal and ecological processes far beyond agriculture. From a socio-ecological perspective, industrialization resulted from technological innovations enabling the mobilization of previously untapped fossil energy sources, conceptualized in the notion Benergy transition^ (Grübler 2008). The increasing technical energy availability fostered unprecedented economic growth (Ayres and Warr 2010) and the emergence of modern political structures (Mitchell 2009; Scheffer et al. 2017). The ecological impacts of industrialization were equally substantial and have led researchers to propose a new geological era, the BAnthropocene,^ in which, they argue, humans have become a global geological force (Crutzen 2006; Steffen et al. 2007). One important effect of industrialization was the partial separation of energy provision from land use: pre-industrial societies relied on local, land-based resources for their energy provision, e.g., fuelwood for cooking, heating, and manufacturing or draught animals, fed on biomass, for transport (Fernandes et al. 2007). Industrializing societies, on the other hand, supplemented their energy supplies with modern energy carriers (Pachauri and Jiang 2008) that require much less land for extraction or generation. Paradoxically, industrialization processes have usually resulted in increasing total biomass extraction and consumption, as has been demonstrated in long-term socioecological research (LTSER, see Haberl et al. 2006; Singh et al. 2013). Various case studies around the globe have studied increasing biomass extraction and use at different scales, ranging * Simone Gingrich simone.gingrich@boku.ac.at