Philippe Massicotte

Spatial connectivity in a large river system: resolving the sources and fate of dissolved organic matter.

Large rivers are generally heterogeneous and productive systems that receive important inputs of dissolved organic matter (DOM) from terrestrial and in situ sources. Thus, they are likely to play a significant role in the biogeochemical cycling of the DOM flowing to the oceans. The asymmetric spatial gradient driven by directional flow and environmental heterogeneity contributes to the fate of DOM flowing downstream. Yet, the relative effects of spatial connectivity and environmental heterogeneity on DOM dynamics are poorly understood. For example, since environmental variables show spatial heterogeneity, the variation explained by environmental and spatial variables may be redundant. We used the St. Lawrence River (SLR) as a representative large river to resolve the unique influences of environmental heterogeneity and spatial connectivity on DOM dynamics. We used three-dimensional fluorescence matrices combined with parallel factor analysis (PARAFAC) to characterize the DOM pool in the SLR. Seven fluorophores were modeled, of which two were identified to be of terrestrial origin and three from algal exudates. We measured a set of environmental variables that are known to drive the fate of DOM in aquatic systems. Additionally, we used asymmetric eigenvector map (AEM) modeling to take spatial connectivity into account. The combination of spatial and environmental models explained 85% of the DOM variation. We show that spatial connectivity is an important driver of DOM dynamics, as a large fraction of environmental heterogeneity was attributable to the asymmetric spatial gradient. Along the longitudinal axis, we noted a rapid increase in dissolved organic carbon (DOC), mostly controlled by terrestrial input of DOM originating from the tributaries. Variance partitioning demonstrated that freshly produced protein-like DOM was found to be the preferential substrate for heterotrophic bacteria undergoing rapid proliferation, while humic-like DOM was more correlated to the diffuse attenuation coefficient of UVA radiation.

Googling trends in conservation biology.

Web-crawling approaches, that is, automated programs data mining the internet to obtain information about a particular process, have recently been proposed for monitoring early signs of ecosystem degradation or for establishing crop calendars. However, lack of a clear conceptual and methodological framework has prevented the development of such approaches within the field of conservation biology. Our objective was to illustrate how Google Trends, a freely accessible web-crawling engine, can be used to track changes in timing of biological processes, spatial distribution of invasive species, and level of public awareness about key conservation issues. Google Trends returns the number of internet searches that were made for a keyword in a given region of the world over a defined period. Using data retrieved online for 13 countries, we exemplify how Google Trends can be used to study the timing of biological processes, such as the seasonal recurrence of pollen release or mosquito outbreaks across a latitudinal gradient. We mapped the spatial extent of results from Google Trends for 5 invasive species in the United States and found geographic patterns in invasions that are consistent with their coarse-grained distribution at state levels. From 2004 through 2012, Google Trends showed that the level of public interest and awareness about conservation issues related to ecosystem services, biodiversity, and climate change increased, decreased, and followed both trends, respectively. Finally, to further the development of research approaches at the interface of conservation biology, collective knowledge, and environmental management, we developed an algorithm that allows the rapid retrieval of Google Trends data.

Colorful Niches of Phytoplankton Shaped by the Spatial Connectivity in a Large River Ecosystem: A Riverscape Perspective

Large rivers represent a significant component of inland waters and are considered sentinels and integrators of terrestrial and atmospheric processes. They represent hotspots for the transport and processing of organic and inorganic material from the surrounding landscape, which ultimately impacts the bio-optical properties and food webs of the rivers. In large rivers, hydraulic connectivity operates as a major forcing variable to structure the functioning of the riverscape, and–despite increasing interest in large-river studies–riverscape structural properties, such as the underwater spectral regime, and their impact on autotrophic ecological processes remain poorly studied. Here we used the St. Lawrence River to identify the mechanisms structuring the underwater spectral environment and their consequences on pico- and nanophytoplankton communities, which are good biological tracers of environmental changes. Our results, obtained from a 450 km sampling transect, demonstrate that tributaries exert a profound impact on the receiving river’s photosynthetic potential. This occurs mainly through injection of chromophoric dissolved organic matter (CDOM) and non-algal material (tripton). CDOM and tripton in the water column selectively absorbed wavelengths in a gradient from blue to red, and the resulting underwater light climate was in turn a strong driver of the phytoplankton community structure (prokaryote/eukaryote relative and absolute abundances) at scales of many kilometers from the tributary confluence. Our results conclusively demonstrate the proximal impact of watershed properties on underwater spectral composition in a highly dynamic river environment characterized by unique structuring properties such as high directional connectivity, numerous sources and forms of carbon, and a rapidly varying hydrodynamic regime. We surmise that the underwater spectral composition represents a key integrating and structural property of large, heterogeneous river ecosystems and a promising tool to study autotrophic functional properties. It confirms the usefulness of using the riverscape approach to study large-river ecosystems and initiate comparison along latitudinal gradients.

Global distribution of dissolved organic matter along the aquatic continuum: Across rivers, lakes and oceans

Based on an extensive literature survey containing more than 12,000 paired measurements of dissolved organic carbon (DOC) concentrations and absorption of chromophoric dissolved organic matter (CDOM) distributed over four continents and seven oceans, we described the global distribution and transformation of dissolved organic matter (DOM) along the aquatic continuum across rivers and lakes to oceans. A strong log-linear relationship (R2=0.92) between DOC concentration and CDOM absorption at 350nm was observed at a global scale, but was found to be ecosystem-dependent at local and regional scales. Our results reveal that as DOM is transported towards the oceans, the robustness of the observed relation decreases rapidly (R2 from 0.94 to 0.44) indicating a gradual decoupling between DOC and CDOM. This likely reflects the decreased connectivity between the landscape and DOM along the aquatic continuum. To support this hypothesis, we used the DOC-specific UV absorbance (SUVA) to characterize the reactivity of the DOM pool which decreased from 4.9 to 1.7m2 × gC-1 along the aquatic continuum. Across the continuum, a piecewise linear regression showed that the observed decrease of SUVA occurred more rapidly in freshwater ecosystems compared to marine water ecosystems, suggesting that the different degradation processes act preferentially on CDOM rather than carbon content. The observed change in the DOM characteristics along the aquatic continuum also suggests that the terrestrial DOM pool is gradually becoming less reactive, which has profound consequences on cycling of organic carbon in aquatic ecosystems.

Towards a Tool Supporting Integration Testing of Aspect-Oriented Programs

Aspect-Oriented Programming is an emerging software engineering paradigm. It offers new constructs and tools improving separation of crosscutting concerns into single units called aspects. AspectJ, the most used aspect-oriented programming language, represents an extension of Java. In fact, existing object-oriented programming languages suffer from a serious limitation in modularizing adequately crosscutting concerns in a program. Many concerns crosscut several classes in an object-oriented system. However, new dependencies between aspects and classes result in new testing challenges. Interactions between aspects and classes are new sources for program faults. Moreover, existing object-oriented testing methods (unit and integration testing) are not well adapted to the aspect technology. As a consequence, new testing techniques must be developed for aspect-oriented programs. We present, in this paper, a new aspects-classes integration testing strategy and the associated tool. The adopted approach consists of two main phases: (1) static analysis: generating testing sequences based on dynamic interactions between aspects and classes, (2) dynamic analysis: verifying the execution of the selected sequences. We focus, in particular, on the integration of one or more aspects in the control of collaborating classes.

Riverscape heterogeneity explains spatial variation in zooplankton functional evenness and biomass in a large river ecosystem

Ecologists have long focused on local-scale phenomena (i.e. local environment variables) and assumed that spatial processes were unimportant factors influencing both the community structure and the functional diversity of aquatic communities. In this paper we used zooplankton assemblages in a typical large river (St. Lawrence River) as a biological model to examine the roles of (1) local environmental conditions (physicochemical characteristics of the water column), (2) broad-scale connectivity (a proxy for dispersion potential), and (3) habitat heterogeneity (a proxy for niche diversity) on the structure and the diversity of lotic communities. Together, these three sets of descriptors explained respectively 52, 49 and 59 % of the variation in zooplankton total biomass, functional diversity and community structure. After partialling out the roles of local environmental conditions and broad-scale connectivity, we demonstrated that habitat heterogeneity alone is a key driver of zooplankton total biomass and functional evenness at the riverscape level. In homogeneous and temporally stable habitats, zooplankton communities had higher biomass and functional evenness but lower species richness. Conversely, zooplankton had lower biomass and higher species richness in heterogeneous and unstable habitats, suggesting that zooplankton species can coexist because disturbances prevent competitive exclusion from occurring. This is the first study to reveal how local environmental conditions, spatial connectivity and habitat heterogeneity operate jointly to determine the functional diversity and structure of aquatic communities in a natural ecosystem.

Generating aspects-classes integration testing sequences a collaboration diagram based strategy

Aspect-oriented software development is an emerging software engineering paradigm. It provides new constructs and tools to improve separation of crosscutting concerns into single units called aspects. The aspect paradigm introduces, in fact, new abstractions in software development. AspectJ is an aspect-oriented extension for Java. Actually, existing object-oriented programming languages suffer from a serious limitation in modularizing adequately crosscutting concerns. Many concerns crosscut several classes in an object-oriented system. However, the aspect paradigm introduces new dimensions in terms of control and complexity. New dependencies between aspects and classes result in new testing challenges. In fact, aspects can interact with any class in a program. Interactions between aspects and classes are new sources for program faults. Object-oriented testing techniques do not cover the new dimensions introduced by aspects. Thus, new aspect-oriented testing techniques must be developed. We propose, in this paper, a new technique to generate test sequences based on the dynamic interactions between aspects and classes. We focus, in particular, on the integration of one or more aspects in a collaboration between a group of objects. The paper also introduces associated testing criteria. The proposed approach follows an iterative process.

Comparison of Lake Ontario and St. Lawrence River hydrologic droughts and their relationship to climate indices

Five characteristics (intensity or magnitude, duration, frequency, timing, and variability) of drought, defined using the threshold level method (TLM) and recorded in mean annual water levels in Lake Ontario and the St. Lawrence River from 1918 to 2010, were compared. Timing is the only characteristic that is different for the two water bodies. For Lake Ontario, the most intense drought occurred in the 1930s, whereas in the St. Lawrence River, intense droughts took place in the 1960s and 2000s. The Lake Ontario drought produced two shifts in mean before (decrease) and after (increase) the 1930s. The change in variance that took place in the 1960s is thought to be related to the construction of locks during the digging of the seaway. The droughts that affected the St. Lawrence River had no impact on the stationarity (mean and variance) of the annual mean water level series. Analysis of the correlation between drought severity and climate indices revealed that years characterized by very weak to moderate drought are significantly correlated with PDO (Pacific Decadal Oscillation), while those characterized by intense drought are correlated with NAO (North Atlantic Oscillation). Both climate indices are negatively correlated with Lake Ontario water levels, while they are positively correlated with St. Lawrence River levels. The study suggests that NAO may be used to predict the driest years for the two water bodies.

Aspects-classes integration testing strategy: an incremental approach

Aspect-Oriented Programming is an emerging software engineering paradigm. It provides new constructs and tools improving separation of crosscutting concerns into single units called aspects. In fact, existing object-oriented programming languages suffer from a serious limitation in modularizing adequately crosscutting concerns. Many concerns crosscut several classes in an object-oriented system. However, new dependencies between aspects and classes result in new testing challenges. Interactions between aspects and classes are new sources for program faults. Existing object-oriented testing methods (unit and integration testing) are not well adapted to the aspect technology. Thus, new testing techniques must be developed for aspect-oriented software. We present, in this paper, a new aspects-classes integration testing strategy. The adopted approach consists of two main phases: (1) static analysis: generating test sequences based on the dynamic interactions between aspects and classes, (2) dynamic analysis: verifying the execution of the selected sequences. We focus, in particular, on the integration of one or more aspects in the control of collaborating classes.

Comparison of the Characteristics (Frequency and Timing) of Drought and Wetness Indices of Annual Mean Water Levels in the Five North American Great Lakes

In this study, we compared the frequency and timing of drought and wetness indices of annual mean water levels in the North American Great Lakes as they relate to teleconnection indices over the period from 1918 to 2012. In terms of timing, drought occurred in the Great Lakes watershed during the 1920, 1930 and 2000 decades, and was very intense in the East during the 1930’s and in the West during the 2000 decade. The main cause of extreme drought episodes in the 1920’s and 1930’s was a decrease in precipitation, while the 2000 decade drought is thought to be caused by increased water temperature (enhanced evaporation) due to a significant decrease in winter ice cover. The 1970 and 1980 decades were very wet over the whole watershed as a result of increased precipitation in the region. The succession of these dry and wet episodes did not have the same impacts on the stationarity of annual mean water levels in the five Great Lakes. Lake Superior shows an abrupt shift in mean in 1999, but a smoothed shift in variance since 1994, whereas Lake Erie shows four abrupt shifts in mean. Lake Ontario also shows the two first abrupt shift in mean and one abrupt change in variance. Extreme drought indices are negatively correlated with the North Atlantic Oscillation (NAO) for the two shallowest lakes (Ontario and Erie). In contrast, extreme wetness indices are positively correlated with PDO (positive correlation) and SOI (negative correlation) for Lake Superior only.