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Comparing the performance of flat and hierarchical Habitat/Land-Cover classification models in a NATURA 2000 site
No full textThe increasing need for high quality Habitat/Land-Cover (H/LC) maps has triggered considerable research into novel machine-learning based classification models. In many cases, H/LC classes follow pre?defined hierarchical classification schemes (e.g., CORINE), in which fine H/LC categories are thematically nested within more general categories. However, none of the existing machine-learning algorithms account for this pre-defined hierarchical structure. Here we introduce a novel Random Forest (RF) based application of hierarchical classification, which fits a separate local classification model in every branching point of the thematic tree, and then integrates all the different local models to a single global prediction. We applied the hierarchal RF approach in a NATURA 2000 site in Italy, using two land-cover (CORINE, FAO-LCCS) and one habitat classification scheme (EUNIS) that differ from one another in the shape of the class hierarchy. For all 3 classification schemes, both the hierarchical model and a flat model alternative provided accurate predictions, with kappa values mostly above 0.9 (despite using only 2.2-3.2% of the study area as training cells). The flat approach slightly outperformed the hierarchical models when the hierarchy was relatively simple, while the hierarchical model worked better under more complex thematic hierarchies. Most misclassifications came from habitat pairs that are thematically distant yet spectrally similar. In 2 out of 3 classification schemes, the additional constraints of the hierarchical model resulted with fewer such serious misclassifications relative to the flat model. The hierarchical model also provided valuable information on variable importance which can shed light into "black-box" based machine learning algorithms like RF. We suggest various ways by which hierarchical classification models can increase the accuracy and interpretability of H/LC classification maps
Estimating. Satellite-Derived Bathymetry (SDB) with the Google Earth Engine and Sentinel-2
No full textBathymetry mapping forms the basis of understanding physical, economic, and ecological processes in the vastly biodiverse coastal fringes of our planet which are subjected to constant anthropogenic pressure. Here, we pair recent advances in cloud computing using the geospatial platform of the Google Earth Engine (GEE) with optical remote sensing technology using the open Sentinel-2 archive, obtaining low-cost in situ collected data to develop an empirical preprocessing workflow for estimating satellite-derived bathymetry (SDB). The workflow implements widely used and well-established algorithms, including cloud, atmospheric, and sun glint corrections, image composition and radiometric normalisation to address intra- and inter-image interferences before training, and validation of four SDB algorithms in three sites of the Aegean Sea in the Eastern Mediterranean. Best accuracy values for training and validation were R2 = 0.79, RMSE = 1.39 m, and R2 = 0.9, RMSE = 1.67 m, respectively. The increased accuracy highlights the importance of the radiometric normalisation given spatially independent calibration and validation datasets. Spatial error maps reveal over-prediction over low-reflectance and very shallow seabeds, and under-prediction over high-reflectance (<6 m) and optically deep bottoms (>17 m). We provide access to the developed code, allowing users to map bathymetry by customising the time range based on the field data acquisition dates and the optical conditions of their study area
Remote sensing of beta diversity: evidence from plant communities in a semi?natural system
No full textQuestion Do remote sensing signals represent beta diversity? Does beta diversity agree with community types?. Location UNESCO Man and Biosphere Reserve, La Palma, Canary Islands. Methods We recorded perennial, vascular plant species abundances in 69 plots (10 m x 10 m) in three pre?defined community types along an elevational gradient of 2400 m: succulent scrubland, Pinus canariensis forest and subalpine scrubland. The remote sensing data consists of structural variables from airborne Light Detection and Ranging (LiDAR) and multispectral variables from a time series of Sentinel?2 (S2) images. Non?metric Multidimensional Scaling was used to assess beta diversity between plots. K?means unsupervised clustering was applied to remote sensing variables to distinguish three community types. We subsequently quantified the explanatory power of S2 and LiDAR variables representing beta diversity via the Mantel test, variation partitioning and Multivariate Analysis of Variance. We also investigated the sensitivity of results to grain size of remote sensing data (20, 40, 60 m). Results The beta diversity between the succulent and pine community is high, whereas the beta diversity between the pine and subalpine community is low. In the wet season, up to 85% of beta diversity is reflected by remote sensing variables. The S2 variables account for more explanatory power than the LiDAR variables. The explanatory power of LiDAR variables increases with grain size, whereas the explanatory power of S2 variables decreases. Conclusion At the lower ecotone, beta diversity agrees with the pre?defined community distinction, while at the upper ecotone the community types cannot be clearly separated by compositional dissimilarity only. The high beta diversity between the succulent scrub and pine forest results from positive feedback switches of Pinus canariensis being a fire?adapted, key tree species. In accordance with the spectral variation hypothesis, remote sensing signals can adequately represent beta diversity over large extent, in short time and at low costs. However, in?situ sampling is necessary to fully understand community composition. Nature conservation requires such interdisciplinary approaches
Spatial congruence between multiple stressors in the Mediterranean Sea may reduce its resilience to climate impacts
No full textClimate impacts on marine ecosystems may be exacerbated by other, more local stressors interacting synergistically, such as pollution and overexploitation of marine resources. The reduction of these human stressors has been proposed as an achievable way of retaining ecosystems within a "safe operating space" (SOS), where they remain resilient to ongoing climate change. However, the operability of an SOS requires a thorough understanding of the spatial distribution of these climate and human impacts. Using the Mediterranean Sea as a case study, we illustrate the spatial congruence between climate and human stressors impacting this iconic "miniature ocean" synergistically. We use long-term, spatially-explicit information on the distribution of multiple stressors to identify those highly impacted marine areas where human stressors should be prioritized for management if the resilience to climate impacts is to be maintained. Based on our spatial analysis, we exemplify how the management of an essential supporting service (seafood provision) and the conservation of a highly impacted Mediterranean sub-region (the Adriatic Sea) may benefit from the SOS framework
Ecosystem Services in a Protected Mountain Range of Portugal: Satellite-Based Products for State and Trend Analysis
No full textMountains are facing strong environmental pressures, which may jeopardize the supply of various ecosystem services. For sustainable land management, ecosystem services and their supporting functions should thus be evaluated and monitored. Satellite products have been receiving growing attention for monitoring ecosystem functioning, mainly due to their increasing temporal and spatial resolutions. Here, we aim to illustrate the high potential of satellite products, combined with ancillary in situ and statistical data, to monitor the current state and trend of ecosystem services in the Peneda-Ger?s National Park, a protected mountain range in Portugal located in a transition climatic zone (Atlantic to Mediterranean). We focused on three ecosystem services belonging to three broad categories: provisioning (reared animals), regulating (of water flows), and cultural (conservation of an endemic and iconic species). These services were evaluated using a set of different satellite products, namely grassland cover, soil moisture, and ecosystem functional attributes. In situ and statistical data were also used to compute final indicators of ecosystem services. We found a decline in the provision of reared animals since year 2000, although the area of grasslands had remained stable. The regulation of water flows had been maintained, and a strong relationship with interannual precipitation pattern was noted. In the same period, conservation of the focal iconic species might have been affected by interannual fluctuations of suitable habitat areas, with a possible influence of wildfires and precipitation. We conclude that satellite products can efficiently provide information about the current state and trend in the supply of various categories of ecosystem services, especially when combined with in situ or statistical data in robust modeling frameworks
Setting up a water quality ensemble forecast for coastal ecosystems: a case study of the southern North Sea
No full textPrediction systems, such as the coastal ecosystem models, often incorporate complex non-linear ecological processes. There is an increasing interest in the use of probabilistic forecasts instead of deterministic forecasts in cases where the inherent uncertainties in the prediction system are important. The primary goal of this study is to set up an operational ensemble forecasting system for the prediction of the Chlorophyll-a concentration in coastal waters, using the Generic Ecological Model. The input ensemble is generated from perturbed model process parameters and external forcings through Latin Hypercube Sampling with Dependence. The forecast performance of the ensemble prediction is assessed using several forecast verification metrics that can describe the forecast accuracy, reliability and discrimination. The verification is performed against in-situ measurements and remote sensing data. The ensemble forecast moderately outperforms the deterministic prediction at the coastal in-situ measurement stations. The proposed ensemble forecasting system is therefore a promising tool to provide enhanced water quality prediction for coastal ecosystems which, with further inclusion of other uncertainty sources, could be used for operational forecasting
Caratterizzazione del campo fluidodinamico su un profilo NACA 0015 tramite vernici termosensibili
No full text-si sono svolte presso l\u27Istituto INM-CNR, utilizzando un profilo alare investito da una corrente fluida (acqua) avente numero di Reynolds costante e pari a 180000, per quattro angoli d\u27attacco (3?, 5?, 7? e 10?), caratteristici in quanto rappresentativi delle condizioni di esercizio di turbine marine ed eoliche. Sono stati raccolti quattro set di 10916 immagini (per ogni angolo d\u27attacco), con vista dall\u27alto della superficie in depressione del profilo. Su di essi sono state realizzate le procedure di ortorettificazione, registrazione, calibrazione e filtraggio (nel tempo e nello spazio). In questo modo sono state ottenute immagini rappresentanti per ogni pixel non pi? un valore di intensit? luminosa, bens? di temperatura. Quindi si ? proceduto al calcolo dei punti e delle linee medie di separazione e transizione, relative alla bolla, valutandone anche il comportamento temporale. Inoltre ? stato calcolato l\u27andamento della deviazione standard media (nel tempo e lungo l\u27apertura alare) della temperatura per ogni angolo d\u27attacco. In particolare ? stato osservato una bassa variabilit? delle linee caratteristiche della bolla per un angolo di attacco pari a 10?, rispetto agli altri angoli di attacco. Inoltre ? stata trovata un\u27ottima corrispondenza fra i picchi dei profili di deviazione standard e le posizioni dei punti di transizione. A partire dalle mappe medie di temperatura, tramite l\u27analogia dell\u27equazione dell\u27energia con il flusso ottico, sono state ricavate le mappe medie di sforzo di taglio a parete. Da queste, grazie alla verifica delle condizioni di convergenza e divergenza delle linee di sforzo di taglio a parete (Surana, et al., 2006), ? stato possibile individuare i punti medi e le linee medie di riattacco. Come per la separazione e la transizione, ? stato indagato il loro andamento temporale. I risultati hanno mostrato come le linee di separazione, transizione e riattacco si spostino sempre pi? verso il bordo d\u27attacco all\u27aumentare dell\u27angolo d\u27incidenza, confermando la tendenza gi? osservata in letteratura. Inoltre mentre per piccoli angoli d\u27attacco il loro andamento spaziale e temporale comporta delle evidenti oscillazioni, per valori pi? grandi queste si riducono in entit?, giungendo ad un angolo di 10? dove si osserva una situazione quasi stazionaria. La linea di transizione ? stata trovata giacere, concordemente con i risultati in letteratura, a cavallo fra la dead water region e la regione di flusso inverso della bolla. Infine sono state analizzate le mappe di temperatura e sforzo di taglio istantanee. Da queste sono state individuate, lungo la linea di separazione, delle strutture a forma d\u27onda che congiungono i nodi di convergenza ai punti di sella delle linee di sforzo di taglio. La loro evoluzione dipende dall\u27angolo d\u27attacco, all\u27aumentare del quale esse risultano sempre pi? schiacciate. Dalle mappe di temperatura ? stata osservata l\u27assenza di bubble flapping a 10?, confermando la tendenza quasi stazionaria descritta in precedenza. Inoltre sono stati individuati degli eventi intermittenti per i quali si assiste alla propagazione di una regione fredda a forma di cuneo all\u27interno della zona pi? calda, in prossimit? della separazione. Viene quindi data una giustificazione al loro innesco tramite l\u27osservazione di getti locali d\u27acqua fredda che precedono di poco l\u27evento
The effect of microbial activity on soil water diffusivity
No full textIn this study, we explored the effects of microbial activity on the evaporation of water from cores of a sandy soil under laboratory conditions. We applied treatments to stimulate microbial activity by adding different amounts of synthetic analogue root exudates. For comparison, we used soil samples without synthetic root exudates as control and samples treated with mercuric chloride to suppress microbial activity. Our results suggest that increasing microbial activity reduces the rate of evaporation from soil. Estimated diffusivities in soil with the largest amounts of added root exudates were one third of those estimated in samples where microbial activity was suppressed by adding mercuric chloride. We discuss the effect of our results with respect to water uptake by roots
Chlorophyll a interference in phycocyanin and allophycocyanin spectrophotometric quantification
No full textThe accurate quantification of cyanobacteria phycobiliproteins is an important aspect in various research topics, such as cyanobacteria ecology and physiology studies, and especially to calibrate algorithms used in remote sensing of cyanobacterial blooms. Here we present a spectroscopic approach, exploiting spectrophotometric equations, aimed at improving the phycocyanin and allophycocyanin quantification when chlorophyll a is present in the phycobiliprotein aqueous extract
Seeking alternative stable states in a deep lake
No full text1. Hysteresis linked to alternative stable states may explain delays in water quality recovery despite reduced nutrient loadings in shallow lakes. Because deep lakes are assumed to be less prone to critical transitions, similar delays are attributed to the confounding effects of additional environmental disturbances, such as climate warming. Herein, we hypothesised that the lack of evidence of nutrient?driven alternative stable states in a deep lake arises from the fact that the nutrient threshold that causes the critical transition is lower than the nutrient threshold in shallow lakes. Thereby, it might have been crossed much earlier in the lake history. 2. To test this hypothesis, we focused on the palaeo?ecological trajectory of Lake Varese, which is a deep, hypereutrophicated peri?alpine lake undergoing restoration. Proxies for drivers of ecological state (i.e. total phosphorus-TP-through diatoms and pigments) and ecological responses (Cladocera), as well as a repeatable analysis, were used to identify transitions and to distinguish hysteretic delays from those of the ecosystems responding to additional constraints over the past century. 3. Our results suggest spatial heterogeneity in the ecological response. The littoral habitats changed abruptly and prematurely for a low TP threshold, causing a shift that met many criteria of a flickering?type critical transition. Soon after the littoral shift, a striking increase in the lake phosphorous concentration was recorded and drove the pelagic assemblage towards a new state. This transition was abrupt, and the pelagic communities exhibited limited evidence of recovery; however, we found no evidence of hysteresis. Therefore, the modern ecological trajectory of the pelagic communities is currently driven by climate warming. 4. This detailed analysis allowed us to go beyond the general pattern that links ecological responses to drivers and suggest that a nonlinear transition following eutrophication can take place in a deep lake synchronously with linear transitions. Instead of triggering a new regime shift, climate warming, to which pelagic habitats are more sensitive than littoral ones, has driven the lake further from its safe operating space