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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Assessing macrophyte seasonal dynamics using dense time series of medium resolution satellite data.
No full textThe improved spatial and temporal resolution of latest-generation Earth Observation missions, such as Landsat 8 and Sentinel-2, has increased the potential of remote sensing for mapping land surface phenology in inland water systems.
The ability of a time series of medium-resolution satellite data to generate quantitative information on macrophyte phenology was examined, focusing on three temperate shallow lakes with connected wetlands in Italy, France, and Romania.
Leaf area index (LAI) maps for floating and emergent macrophyte growth forms were derived from a semi-empirical regression model based on the best-performing spectral index, with an error level of 0.11 m2 m−2. Phenology metrics were computed from LAI time series using TIMESAT to analyze the seasonal dynamics of macrophyte spatial distribution patterns and species-dependent variability. Particular seasonal patterns seen in the autochthonous and allochthonous species across the three study areas related to local ecological and hydrological conditions.
How characteristics of the satellite dataset (cloud cover threshold, temporal resolution, and missing acquisitions) influenced the phenology metrics obtained was also assessed. Our results indicate that, with a full-resolution time series (5-day revisit time), cloud cover introduced a bias in the phenology metrics of less than 2 days. Even when the temporal resolution was reduced to 15 days (like the Landsat revisit time) the timing of the start and the peak of macrophyte growth could still be mapped with an error of no more than 2–3 days
Upscaling nitrogen removal processes in fluvial wetlands and irrigation canals in a patchy agricultural watershed
No full textThe evaluation of nitrogen (N) removal in aquatic ecosystems within human exploited watersheds may allow the setting of upper limits of N use in agriculture. However, such an evaluation is complex owing to the small scale heterogeneity of aquatic ecosystems, including dominant vegetation and inherent N-related processes. In this work, microbial denitrification and primary producer assimilation were estimated in fluvial wetlands and irrigation canals of the Mincio River watershed (~ 850 km2, Italy), and scaled-up to the whole watershed using GIS and remote-sensing techniques. Denitrification in the fluvial wetland area which covered only ~ 3% of the watershed was estimated to permanently remove 80% of the excess N, defined as N soil surplus (~ 5500 t N y−1) minus N river export (~ 1300 t N y−1). Adding the estimated N uptake by primary producers in the wetland system, approximately all the N excess produced in adjacent agricultural land of the Mincio watershed can be retained or removed by internal processes. In contrast, the canal network had a linear extent of over 1770 km but its estimated denitrification capacity was comparatively much smaller (up to 7% of the excess N). Combinations of N-budgeting at the whole basin scale, experimental data, GIS and remote sensing techniques offer the possibility to analyze N retention capacity in heterogeneous aquatic environments. The application of such approach to the Mincio watershed stresses the functional relevance of even small wetland areas in agricultural settings
Reactive silica traces manure spreading in alluvial aquifers affected by nitrate contamination: A case study in a high plain of Northern Italy
No full textIn the northern sector of the Po River Plain (Italy), widespread intensive agriculture and animal farming are supported by large amounts of water from Alpine lakes and their emissaries. Flood irrigation and excess fertilization with manure affect both the hydrology and the chemical quality of surface and groundwater, resulting in diffuse nitrogen pollution. However, studies analyzing the mechanisms linking agricultural practices with vertical and horizontal nitrogen paths are scarce in this area. We investigated groundwater quality and quantity in an unconfined, coarse-grained alluvial aquifer adjacent to the Mincio River (a tributary of the Po River), where steep summer gradients of nitrate (NO3-) concentrations are reported. The effects of manure on solutes' vertical transport during precipitation events in fertilized and in control soils were simulated under laboratory conditions. The results show high SiO2 and NO3- leaching in fertilized soils. Similarly, field data are characterized by high SiO2 and NO3- concentrations, with a comparable spatial distribution but a different temporal evolution, suggesting their common origin but different processes affecting their concentrations in the study area. Our results show that SiO2 can be used as a conservative tracer of manure spreading, as it does not undergo biogeochemical processes that significantly alter its concentrations. On the contrary, nitrate displays large short-term variations related to aquifer recharge (i.e., flood irrigation and precipitation). In fact, aquifer recharge may promote immediate solubilization and stimulate nitrification, resulting in high NO3- concentrations up to 95.9 mg/L, exceeding the Water Framework Directive (WFD) thresholds. When recharge ends, anoxic conditions likely establish in the saturated zone, favoring denitrification and resulting in a steep decrease in NO3- concentrations
Corrigendum to “a rule-based approach for mapping macrophyte communities using multi-temporal aquatic vegetation indices” (Remote Sensing of Environment (2015) 171 (218–233), (S0034425715301711) (10.1016/j.rse.2015.10.020))
No full textThe authors regret to inform the readers that Fig. 6 at page 228 of this article contained some errors in four of the classification rules outlined. The correct version of this Figure is the following: [Figure presented] Figure caption is not changed. As the errors were only of graphical nature, any other part of results, discussion and conclusions contained in the original article are not affected by this correction. The authors would like to apologise for any inconvenience caused
A rule-based approach for mapping macrophyte communities using multi-temporal aquatic vegetation indices
No full textMacrophytes are important components of freshwater ecosystems, playing a relevant role in carbon and nutrient cycles. Notwithstanding their widespread diffusion in temperate to subtropical shallow lakes, little effort has been performed so far in extensively mapping macrophyte communities at regional to continental scale. A rule-based classification scheme was implemented for mapping four macrophyte community types (helophyte, emergent rhizophyte, floating, and submerged-floating association). Input features were selected among multi-spectral reflectance and multi-temporal vegetation indices, based on Landsat data acquired over four test sites: Lake Taihu (China), Kis-Balaton wetland (Hungary), Lake Trasimeno and Mantua Lakes system (Italy). The best performing features were derived from Water Adjusted Vegetation Index (WAVI) computed at: early spring, maximum growth, and late autumn conditions. Overall accuracy (OA) and Kappa coefficient (k) of macrophyte maps produced with our approach over the ensemble of four sites were 90.1% and 0.865, respectively, with best performance in European temperate areas (OA = 93.6-94.2%, k = 0.887-0.916), and lower scores for subtropical Lake Taihu (OA = 82.8%, k = 0.762). Per-class accuracies were higher than 80% for all target classes, except for the submerged-floating association, with misclassifications concentrated in Taihu site. The robustness of the approach was tested over two independent validation cases: a different site (i.e. Lake Varese, Italy), and a different input dataset (i.e. AVNIR-2 data, for Mantua Lakes system). Consistent accuracy results were achieved: OA = 94.3% (k = 0.922) and OA = 85.6% (k = 0.766), with some misclassification due to spatial resolution of AVNIR-2 data. (C) 2015 Elsevier Inc. All rights reserved
Assessment of potential algal blooms in a shallow fluvial lake through hydrodynamic modelling and remote-sensed images
No full textLeaf reflectance can surrogate foliar economics better than physiological traits across macrophyte species
No full textBackground: Macrophytes are key players in aquatic ecosystems diversity, but knowledge on variability of their functional traits, among and within species, is still limited. Remote sensing is a high-throughput, feasible option for characterizing plant traits at different scales, provided that reliable spectroscopy models are calibrated with congruous empirical data, but existing applications are biased towards terrestrial plants. We sampled leaves from six floating and emergent macrophyte species common in temperate areas, covering different phenological stages, seasons, and environmental conditions, and measured leaf reflectance (400–2500 nm) and leaf traits (dealing with photophysiology, pigments, and structure). We explored optimal spectral band combinations and established non-parametric reflectance-based models for selected traits, eventually showing how airborne hyperspectral data could capture spatial–temporal macrophyte variability. Results: Our key finding is that structural—leaf dry matter content, leaf mass per area—and biochemical—chlorophyll-a content and chlorophylls to carotenoids ratio—traits can be surrogated by leaf reflectance with normalized error under 17% across macrophyte species. On the other hand, the performance of reflectance-based models for photophysiological traits substantively varies, depending on macrophyte species and target parameters. Conclusions: Our main results show the link between leaf reflectance and leaf economics (structure and biochemistry) for aquatic plants, thus envisioning a crucial role for remote sensing in enhancing the level of detail of macrophyte functional diversity analysis to intra-site and intra-species scales. At the same time, we highlighted some difficulties in establishing a general link between reflectance and photosynthetic performance under high environmental heterogeneity, potentially opening further investigation directions
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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