Inferential evaluation and revision in L1 and L2 text comprehension: An eye movement study

Text comprehension frequently demands the resolution of no longer plausible interpretations to build an accurate situation model, an ability that might be especially challenging during second language comprehension. Twenty-two native English speakers (L1) and twenty-two highly proficient non-native English speakers (L2) were presented with short narratives in English. Each text required the evaluation and revision of an initial prediction. Eye movements in the text and a comprehension sentence indicated less efficient performance in the L2 than in L1 comprehension, in both inferential evaluation and revision. Interestingly, these effects were determined by individual differences in inhibitory control and linguistic proficiency. Higher inhibitory control reduced the time rereading previous parts of the text (better evaluation) as well as revisiting the text before answering the sentence (better revision) in L2 comprehenders, whereas higher proficiency reduced the time in the sentence when the story was coherent, suggesting better general comprehension in both languages.This research was supported by the grant with ref. 754446-AT3i funded by a MSCA-COFUND Athenea3i and the research project with ref. PSI 2017-89324-C2-2-P funded by MCIN, both to Ana Pérez. Funding for open access charge: Universidad de Granada

Effects of riparian vegetation removal on nutrient retention in a Mediterranean stream

We examined the effects of riparian vegetation removal on algal dynamics and stream nutrient retention efficiency by comparing NH4-N and PO4-P uptake lengths from a logged and an unlogged reach in Riera Major, a forested Mediterranean stream in northeastern Spain. From June to September 1995, we executed 6 short-term additions of N (as NH4Cl) and P (as Na2HPO4) in a 200-m section to measure nutrient uptake lengths. The study site included 2 clearly differentiated reaches in terms of canopy cover by riparian trees: the first 100 m were completely logged (i.e., the logged reach) and the remaining 100 m were left intact (i.e., the shaded reach). Trees were removed from the banks of the logged reach in the winter previous to our sampling. In the shaded reach, riparian vegetation was dominated by alders (Alnus glutinosa). The study was conducted during summer and fall months when differences in light availability between the 2 reaches were greatest because of forest canopy conditions. Algal biomass and % of stream surface covered by algae were higher in the logged than in the shaded reach, indicating that logging had a stimulatory effect on algae in the stream. Overall, nutrient retention efficiency was higher (i.e., shorter uptake lengths) in the logged than in the shaded reach, especially for PO4-P. Despite a greater increase in PO4-P retention efficiency relative to that of NH4-N following logging, retention efficiency for NH4-N was higher than for PO4-P in both study reaches. The PO4-P mass-transfer coefficient was correlated with primary production in both study reaches, indicating that algal activity plays an important role in controlling PO4-P dynamics in this stream. In contrast, the NH4-N mass-transfer coefficient showed a positive relation-ship only with % of algal coverage in the logged reach, and was not correlated with any algal-related parameter in the shaded reach. The lack of correlation with algal production suggests that mechanisms other than algal activity (i.e., microbial heterotrophic processes or abiotic mechanisms) may also influence NH4-N retention in this stream. Overall, this study shows that logging disturbances in small shaded streams may alter in-stream ecological features that lead to changes in stream nutrient retention efficiency. Moreover, it emphasizes that alteration of the tight linkage between the stream channel and the adjacent riparian zone may directly and indirectly impact biogeochemical processes with implications for stream ecosystem functioning

Multiple stressors in Mediterranean freshwater ecosystems: The Llobregat River as a paradigm

Hydrological modifications drive other ecological stressors of freshwater ecosystems and interact with them. The present paper examines the relevance of hydrological disturbances resulting from global change by presenting the case of the Llobregat River, a highly disturbed system in NE Spain. The Llobregat is a clear example of a Mediterranean river suffering from multiple stressors. Both the distribution and abundance of organisms and ecosystem functioning as a whole are greatly determined by water scarcity, water salinity, nutrient concentration, and organic (and inorganic) pollution. Structural drought exacerbates these problems, as the capacity to dilute pollutants is compromised. Controlling water abstraction and limiting nutrient and pollutant inputs downstream are essential to the structural and functional recovery of biological communities and to maximizing the ecosystem services provided by the Llobregat River. [Contrib Sci 10:161-169 (2014)

Multiple stressors in Mediterranean freshwater ecosystems: The Llobregat River as a paradigm

Hydrological modifications drive other ecological stressors of freshwater ecosystems and interact with them. The present paper examines the relevance of hydrological disturbances resulting from global change by presenting the case of the Llobregat River, a highly disturbed system in NE Spain. The Llobregat is a clear example of a Mediterranean river suffering from multiple stressors. Both the distribution and abundance of organisms and ecosystem functioning as a whole are greatly determined by water scarcity, water salinity, nutrient concentration, and organic (and inorganic) pollution. Structural drought exacerbates these problems, as the capacity to dilute pollutants is ompromised. Controlling water abstraction and limiting nutrient and pollutant inputs downstream are essential to the structural and functional recovery of biological communities and to maximizing the ecosystem services provided by the Llobregat River

Drought effects on resource quality in a Mediterranean stream: fatty acids and sterols as indicators

Seasonal droughts in Mediterranean streams shape their physical, chemical, and biological characteristics. Thus, droughts have the potential to alter resources at the base of the food web, which in headwater streams are primarily allochthonous and secondarily autochthonous organic matter (OM). In the present study we assessed the quality of basal resources in a Mediterranean stream during a drought episode before and after a non-flow period (NF). Fatty acids (FA) and sterols were analyzed in the benthic substrata (leaves and sand and cobbles biofilm) and transported OM (particulate and dissolved fractions). FA and sterols were selected as indicators of resource quality because they include essential molecules for consumers and may be used as biomarkers of OM sources. The drying-rewetting process determined a general reduction in the total and essential FA of benthic substrata and transported particulate OM, and a shift from predominantly autochthonous to allochthonous OM. Furthermore, the sterol composition did not change between the drying and rewetting phases and the rewetting did not cause the leaching of FA in dissolved OM. The epilithic biofilm and leaves were the most important sources of essential FA and sterols, while the sand biofilm was the poorest source of these lipids. Our conclusions enhance the understanding of the mechanisms underlying the effects of droughts on basal resource quality in streams

Trophic mechanisms underlying bentho-demersal community recovery in the north-east Atlantic

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Energy limitation or sensitive predators? Trophic and non-trophic impacts of wastewater pollution on stream food webs

Impacts of environmental stressors on food webs are often difficult to predict because trophic levels can respond in divergent ways, and biotic interactions may dampen or amplify responses. Here we studied food-web-level impacts of urban wastewater pollution, a widespread source of degradation that can alter stream food webs via top-down and bottom-up processes. Wastewater may (1) subsidize primary producers by decreasing nutrient limitation, inducing a wide-bottomed trophic pyramid. However, (2) wastewater may also reduce the quality and diversity of resources, which could decrease energy transfer efficiency by reducing consumer fitness, leading to predator starvation. Additionally, (3) if higher trophic levels are particularly sensitive to pollution, primary consumers could be released from predation pressure. We tested these hypotheses in 10 pairs of stream sites located upstream and downstream of urban wastewater effluents with different pollutant levels. We found that wastewater pollution reduced predator richness by ∼34%. Community size spectra (CSS) slopes were steeper downstream than upstream of wastewater effluents in all except one impact site where predators became locally extinct. Further, variation in downstream CSS slopes were correlated with pollution loads: the more polluted the stream, the steeper the CSS. We estimate that wastewater pollution decreased energy transfer efficiencies to primary consumers by ∼70%, limiting energy supply to predators. Additionally, traits increasing vulnerability to chemical pollution were overrepresented among predators, which presented compressed trophic niches (δ15 N-δ13 C) downstream of effluents. Our results show that wastewater pollution can impact stream food webs via a combination of energy limitation to consumers and extirpation of pollution-sensitive top predators. Understanding the indirect (biotically mediated) vs. direct (abiotic) mechanisms controlling responses to stress may help anticipating impacts of altered water quantity and quality, key signatures of global change

Biochemical quality of basal resources in a forested stream: effects of nutrient enrichment

We studied biochemical changes in biofilm and suspended particulate and dissolved organic matter (OM) during the leaf emergence period (March-May 2008) in a forested headwater stream in response to a long-term (4 years, 2004-2008) experimental nutrient enrichment study. This study compared results from one reach upstream of the enrichment point and one reach downstream using moderate nutrient concentrations (nitrogen, N, from 388 to 765 μg L−1 and phosphorus, P, from 10 to 30 μg L−1, resulting in N:P ratios of 85-56). During the spring of 2008, we analysed the chlorophyll content, elemental composition (carbon, C, and N), bacterial density, and extracellular enzyme activities along with their biochemical composition (amino acids, fatty acids and sterols) on biofilm and OM. Nutrients caused changes in the biochemical composition of the biofilm, while changes in the OM were subtle. The C:N ratio of the biofilm decreased with nutrient enrichment likely due to the increase in protein (non-essential amino acids). The polysaccharide and total and essential fatty acid contents were higher when nutrient enrichment coincided with greater light availability. The peptidase extracellular activity was higher in the fertilised reach at early spring, while phosphatase activity decreased at late spring. The suspended and dissolved OM composition did not change due to the nutrient addition, likely due to the lower water residence time in the reach. Headwater systems are highly dynamic, and the biochemical composition of the biofilm changed in response to changes in nutrients but also to light in this study. These changes, although moderate, could influence higher trophic levels through modifications in their diet. This experiment exemplifies how small land use shifts may affect headwater streams

Dam regulation and riverine food-web sructure in a Mediterraenan river

Flow regimes are a major driver of community composition and structure in riverine ecosystems, and flow regulation by dams often induces artificially-stable flow regimes downstream. This represents a major source of hydrological alteration, particularly in regions where biota is adapted to strong seasonal and interannual flow variability. We hypothesized that dam-induced hydrological stability should increase the availability of autochthonous resources at the base of the food web. This, in turn, should favour herbivorous over detritivorous strategies, increasing the diversity of primary consumers, and the food-web width and length. We tested this hypothesis by studying the longitudinal variation in food-web structure in a highly-seasonal Mediterranean river affected by an irrigation dam. We compared an unregulated reach to several reaches downstream of the dam. Hydrological and sedimentological stability increased downstream of the dam, and altered the type and quantity of available resources downstream, prompting a change from a detritus-based to an algae-based food web. The fraction of links between top and intermediate species also increased, and the food web became longer and wider at the intermediate trophic levels. Food-web structure did not recover 14 km downstream of the dam, despite a partial restitution of the flow regime. Our results advance the notion that hydrologic alteration affects riverine food webs via additions/deletions of taxa and variation in the strength and distribution of food-web interactions. Thus, flow regulation by dams may not only impact individual facets of biodiversity, but also food-web level properties across river networks