Effects of Phragmites australis growth on nitrogen retention in a temporal stream

En los últimos años, en el SE ibérico con el incremento de la superficie de regadío, se ha producido un crecimiento masivo de las poblaciones de Phragmites australis que terminan invadiendo por completo las ramblas y en general los cauces de aguas superficiales. Esta situación lleva consigo la transformación física de los cauces, modificando muchas características implicadas en los procesos bióticos y abióticos de retención de N. En este estudio testamos la hipótesis de que la ocupación de los cauces por Phragmites australis afecta negativamente a la retención de N. Así comparamos las tasas de retención (%R)de N − NO−3 y N − NH+4 en diferentes subtramos de una misma rambla: un subtramo no vegetado (238 m2) y dos subtramos vegetados que diferían en superfície (480 m2 y 910 m2). Los resultados demostraron que las eficacias de retención (%R) para ambos solutos fueron superiores en el tramo no vegetado. Aunque no existen resultados concluyentes parece intuirse que estas diferencias fueron más acusadas fuera del periodo vegetativo del heófito, mientras que en los meses de primavera y verano pudiera ocurrir un incremento de las tasas de retención en los tramos vegetados. Así mismo, la capacidad de los subtramos para la retención de N-nitrato, mostró una clara dependencia de los aportes de nitrógeno, disminuyendo conforme la carga de nitrógeno aumenta. Sin embargo, el tramo no vegetado mostró una mayor capacidad de carga que el tramo vegetado de mayor superfície y este que el tramo vegetado de menor superfície. Este estudio pone de manifiesto que la ocupación de los cauces por Phragmites australis, fenómeno generalizado en muchas partes del mundo, no sólo puede suponer cambios en la estructura de la vegetación y la fauna de las ramblas sino que también afectar a su funcionamiento y muy especialmente a un proceso clave implicado en la calidad de las aguas como es la eliminación del nitrógenoIn recent years in Southeast Spain with the increase in irrigated land surface, there has been a massive growth number of Phragmites australis populations which ended up invading completely the intermittent streams (ramblas) and the shallow water channels in general. This situation brings forth the physical transformation of the channels, thus modifying many characteristics implicated in the biotic and abiotic processes involved in nitrogen retention. In this study, we tested the hypothesis that the channel invasion by Phragmites australis negatively affects nitrogen retention. Therefore, we compared the retention rates ( %R) of NO−3− N and NH+4− N in different subreaches of the same temporal stream: a unvegetated subreach (238 m2), and two vegetated subreaches that differed in surface areas (480 m2 and 910 m2). The results showed that the retention efficiency ( %R) for both solutes were higher in the unvegetated subreach. Although there are no conclusive results, it seems that the differences were more important outside the vegetated period of the helophytes, while during the spring-summer period an increase of the retention rates in the vegetated subreaches could occur. In the same way, the capacity of the subreaches for N-nitrate retention, showed a clear dependency of the nitrogen inputs, decreasing as the nitrogen load increases. However, the unvegetated subreach showed a greater load capacity than the vegetated subreach with larger surface, and this one, greater than the vegetated subreach with the smaller surface. This study reveals that channel invasion by Phragmites australis, a generalized phenomenon in many parts of the world, not only can bring about changes in the structure of the vegetation and the fauna in the streams, but can also affect its function, and especially a key process involved in water quality, such as nitrogen eliminatio

Emisión de CO2 y pérdida de biomasa, asociada a la ocurrencia de incendios forestales en la Región del Biobío, Chile: Una aproximación desde los Servicios Ecosistémicos (SE)

Fire is a phenomenon inherent to natural forests, but the management model for forest plantations may increase its frequencyand intensity, since it is an important disturbing agent which generates changes in the dynamic that governs the operationof ecosystems and the loss or reduction of many ecosystem services. The main objective of this work is to review theproblem of forest fires in Chile with special reference to the Biobío Region, quantifying the loss of some of the ecosystemservices caused by this phenomenon. The results show that on average during the last ten years, the Biobío Region hasbecome the largest national area affected by fires (179.912 ha), confirming that these events are highly correlated withforest development (r = 0.5; P < 0.05), amounting to 50.7 % of the national total. Due to limited knowledge on the effectsof fires at the local level, results are discussed in the context of direct losses of ecosystem services, particularly the effectsin the atmosphere (CO2 emissions and biomass), stressing the importance of the conservation of native forests as absorptionsystems for the effects of fire.El fuego es un fenómeno consustancial con los bosques naturales, pero el modelo de gestión y manejo de las plantacionesforestales puede incrementar su frecuencia e intensidad, convirtiéndose en un importante agente perturbador que generacambios en la dinámica ecológica que rige el funcionamiento de los ecosistemas y la pérdida o disminución de muchosservicios ecosistémicos. El principal objetivo de este trabajo es revisar la problemática de los incendios forestales enChile con especial referencia a la Región del Biobío, cuantificando la pérdida de algunos de los servicios ecosistémicosprovocada por este fenómeno. Los resultados muestran que en promedio durante los últimos diez años, la Región delBiobío ha alcanzado la mayor superficie nacional afectada por incendios (179.912 ha), constatando que dichos eventosestán altamente correlacionados con el desarrollo forestal alcanzado en la región (r = 0.5; P < 0,05), que equivale al 50,7%del nacional. Debido al escaso conocimiento de los efectos de los incendios a nivel local, los resultados se discuten en elcontexto de las pérdidas directas de los servicios ecosistémicos, particularmente los efectos en la atmósfera (emisiones deCO2, destacando la importancia de la conservación de los bosques nativos como sistemas amortiguadores de los efectosdel fuego

Spatial scale effects on taxonomic and biological trait diversity of aquatic macroinvertebrates in Mediterranean streams

We examined the effect of spatial scale on aquatic macroinvertebrate communities in Mediterranean streams from six basins distributed across southern Europe, including Spain, France, Italy, and Greece. We classified the studied streams according to their long-term aquatic regime into the three following types: (i) permanent (P), (ii) intermittent with summer pools (I-P), and (iii) intermittent with summer dry channels (I-D). For each stream type, we analyzed taxonomic and trait diversity, as well as the composition of the macroinvertebrate community, following a spatially nested design at three spatial scales of analysis: microhabitat (substratum patches), mesohabitat (pools vs. riffles), and macrohabitat (streams). In order to assess intrinsic seasonal variability in streams from the Mediterranean region, 20 Surber samples were taken from each stream according to meso- and microhabitat frequency in the wet and the dry season during 2010. Given the need for adaptation to specific hydrological conditions and the fact that microhabitats should encompass the niche requirements of particular taxa, we hypothesized that this spatial scale would have a greater influence on macroinvertebrate taxa composition and biological traits than the other two larger spatial scales in intermittent streams. We observed that patterns in the relative importance of variance components across hierarchical spatial scales changed with time because low flow or droughts altered both mesohabitat preva - lence and microhabitat composition. Our results confirm the importance of the microhabitat scale in I-P streams in the wet season but not in the dry one, when a loss of microhabitat diversity occurred. Stream-to-stream variability was more important in P and I-D streams. Our study also explored the relationships between traits and aquatic regimes. We found that aquatic macroinvertebrates inhabiting permanent streams exhibited traits related to the longer duration of life cycles in these rivers (e.g. large size of adult stages) and adaptations to flowing conditions (e.g. modes of aquatic dispersal), whereas aquatic macroinvertebrates inhabiting intermittent streams with summer pools had traits adapted to depositional conditions and ecological preferences for confined habitats (i.e. disconnected pools without flow). Finally, aquatic macroinvertebrates from intermittent streams with summer dry channels had adaptations conferring ability to survive periods with no water (e.g. modes of aerial dispersal, resistant stages). These results indicate that microhabitat conditions should not be neglected as they can play an important role in certain situations

A biological tool to assess flow connectivity in reference temporary streams from the Mediterranean Basin

Many streams in the Mediterranean Basin have temporary flow regimes. While timing for seasonal drought is predictable, they undergo strong inter-annual variability in flow intensity. This high hydrological variability and associated ecological responses challenge the ecological status assessment of temporary streams, particularly when setting reference conditions. This study examined the effects of flow connectivity in aquatic macroinvertebrates from seven reference temporary streams across the Mediterranean Basin where hydrological variability and flow conditions are well studied. We tested for the effect of flow cessation on two streamflow indices and on community composition, and, by performing random forest and classification tree analyses we identified important biological predictors for classifying the aquatic state either as flowing or disconnected pools. Flow cessation was critical for one of the streamflow indices studied and for community composition. Macroinvertebrate families found to be important for classifying the aquatic state were Hydrophilidae, Simuliidae, Hydropsychidae, Planorbiidae, Heptageniidae and Gerridae. For biological traits, trait categories associated to feeding habits, food, locomotion and substrate relation were the most important and provided more accurate predictions compared to taxonomy. A combination of selected metrics and associated thresholds based on the most important biological predictors (i.e. Bio-AS Tool) were proposed in order to assess the aquatic state in reference temporary streams, especially in the absence of hydrological data. Although further development is needed, the tool can be of particular interest for monitoring, restoration, and conservation purposes, representing an important step towards an adequate management of temporary rivers not only in the Mediterranean Basin but also in other regions vulnerable to the effects of climate change

Retos y oportunidades para la evaluación del estado ecológico en ríos temporales

Temporary rivers (TRs) are stream ecosystems in which the effects of anthropogenic disturbances are mixed with the effects of the natural disturbance imposed by flow intermittence. Despite the advances in TRs research, many gaps persist that limit the development of appropriate methodologies for the assessment of the ecological status. In this review, we identify the current challenges for the assessment of the ecological status of TRs and analyze the existing opportunities to address these challenges. These challenges focus on: the differentiation between natural and hydrologically impacted TRs, the differentiation between natural and anthropogenic disturbances, the development of biological indices for disconnected pools and dry riverbeds, the adaptation of hydrogeomorphological indices, and the application of the metacommunity theory in TRs. The opportunities are related to: the use of molecular tools, the existence of alternative indices to the traditional ones, the availability of data to be able to do modeling, and the social implication in the assessment of the hydrological and ecological status. The review focuses mainly on the scientific and management knowledge accumulated since the implementation of the Water Framework Directive in Spain but gathers experiences from TRs around the world to guide conservation and management actions in these unique ecosystems highly threatened by global change.Este estudio está financiado por el proyecto “DRY-Guadalmed: Herramientas avanzadas para la evaluación del estado ecológico de ríos temporales mediterráneos durante la fase seca” (PID2021-126143OB-C21 y PID2021-126143OB-C22) financiado por el Ministerio de Ciencia e Innovación (MCIN/AEI/10.13039/501100011033/) y por FEDER Una manera de hacer Europa.Peer reviewe

Heterogeneous contributions of change in population distribution of body mass index to change in obesity and underweight NCD Risk Factor Collaboration (NCD-RisC)

From 1985 to 2016, the prevalence of underweight decreased, and that of obesity and severe obesity increased, in most regions, with significant variation in the magnitude of these changes across regions. We investigated how much change in mean body mass index (BMI) explains changes in the prevalence of underweight, obesity, and severe obesity in different regions using data from 2896 population-based studies with 187 million participants. Changes in the prevalence of underweight and total obesity, and to a lesser extent severe obesity, are largely driven by shifts in the distribution of BMI, with smaller contributions from changes in the shape of the distribution. In East and Southeast Asia and sub-Saharan Africa, the underweight tail of the BMI distribution was left behind as the distribution shifted. There is a need for policies that address all forms of malnutrition by making healthy foods accessible and affordable, while restricting unhealthy foods through fiscal and regulatory restrictions

Sectorización ecológica de cuencas fluviales: aplicación a la cuenca del río Segura (SE España)

Se desarrolla y experimenta un método de análisis geo-ecológico aplicado a cuencas de drenaje en el que sea posible integrar coherentemente todos los aspectos del medio físico y humano dotados de significado limnológico. El ámbito escogido para su experimentación ha sido la cuenca del río segura, caracterizada por una notable heterogeneidad ambiental; dentro de ella, el método ha permitido registrar y evaluar gradientes y definir indicadores de gran importancia en la interpretación del marco físico-químico y biológico de las aguas continentales