Testing the spectral variation hypothesis by using satellite multispectral images

In the present paper, a test of the spectral variation hypothesis (SVH) was performed using multispectral high resolution satellite data. The SVH was tested by comparing the relationship between the spectral heterogeneity and species richness in plots of different size (100-10000 m2) in a complex wetland ecosystem, the "Montepulciano Lake", Central Italy. The nature reserve of the Montepulciano Lake is centered on a 100 ha shallow lake surrounded on three sides by a Phragmites australis and Carex sp. pl. marsh of about 280 ha. The monitoring program for the reserve vegetation started in 2002 and is based on the analysis of 1, 100 m2 and 1 ha (10000 m2) plots, organized in such a manner that four of the smaller size plots are nested, following a random design, within a larger one. Data on species composition and community structure were collected in the plots and stored in a GIS-linked archive. A multispectral Quickbird satellite image (3 m spatial resolution) acquired of the wetland and lake ecosystem during the same period was radiometrically and geometrically corrected. We performed an analysis to examine the use of spectral heterogeneity using the four visible and infrared wavebands of the satellite image to predict species richness at the different spatial scales. The spectral heterogeneity was found to explain about 20% of the variance of species richness at the 100 m2 scale and about 50% at the 1 ha scale. It was concluded that multispectral high resolution satellite data can contribute to the biodiversity assessment of complex wetland ecosystem

The contribution of volunteer-based monitoring data to the assessment of harmful phytoplankton blooms in Brazilian urban streams

Urban streams are vulnerable to a range of impacts, leading to the impairment of ecosystem services. However, studies on phytoplankton growth in tropical lotic systems are still limited. Citizen science approaches use trained volunteers to collect environmental data. We combined data on urban streams collected by volunteers with data obtained by professional scientists to identify potential drivers of phytoplankton community and determine thresholds for Cyanobacteria development. We combined datasets (n = 117) on water quality and environmental observations in 64 Brazilian urban streams with paired data on phytoplankton. Sampling activities encompassed dry (July 2013 and July 2015) and warm (February and November 2014) seasons. Volunteers quantified phosphate (PO43 −), nitrate (NO3−) and turbidity in each stream using colorimetric and optical methods and recorded environmental conditions in the immediate surroundings of the sites through visual observations. We used non-parametric statistics to identify correlations among nutrients, turbidity and phytoplankton. We also looked for thresholds with respect to high Cyanobacteria abundance (> 50,000 cells/mL). The streams were characterized by relatively high nutrient concentrations (PO43 −: 0.11 mg/L; NO3−: 2.6 mg/L) and turbidity (49 NTU). Phytoplankton densities reached 189,000 cells/mL, mainly potentially toxic Cyanobacteria species. Moderate but significant (p < 0.05) correlations were observed between phytoplankton density and turbidity (ρ = 0.338, Spearman) and PO43 − (ρ = 0.292), but not with NO3−. Other important variables (river flow, temperature and light) were not assessed. Volunteers' observations covaried with phytoplankton density (p < 0.05, Kruskal-Wallis), positively with increasing number of pollution sources and negatively with presence of vegetation in the riparian zone. Our results indicate that thresholds for PO43 − (0.11 mg/L) can be used to separate systems with high Cyanobacteria density. The number of pollution sources provided a good indicator of waterbodies with potential cyanobacteria problems. Our findings reinforced the need for nutrient abatement and restoration of local streams and highlighted the benefits of volunteer-based monitoring to support decision-making

L’uso dell’eterogeneità spettrale per la massimizzazione dell’efficienza del censimento di specie vegetali

Il presente studio ha come scopo quello di testare il potenziale uso di immagini telerilevate nella massimizzazione dell’efficienza del censimento di specie vegetali. L’area di studio è la Riserva Naturale “Lago di Montepulciano”, una delle più importanti zone umide del centro Italia. Il campionamento, basato su un disegno campionario casuale stratificato, è stato eseguito nel giugno 2002. La composizione di specie vegetali è stata rilevata in unità di campionamento di 100 m2 (plot) e 1 ha (macroplot). Un’immagine multispettrale Quickbird del giugno 2002 è stata acquisita e corretta sia geometricamente che radiometricamente. Curve di accumulazione delle specie basate sull’informazione spettrale sono state ottenute ordinando le unità di campionamento sulla base della loro massima distanza spettrale. L’efficienza di tali curve è stata testata rispetto a una curva di rarefazione derivata dalla media di 10000 curve basate su un ordinamento casuale delle unità di campionamento. La curva derivata dalla massima distanza spettrale tra i siti ha mostrato una rapida accumulazione delle specie e un andamento molto al di sopra della curva di rarefazione, sia a scala di plot che di macroplot. Il presente studio ha dimostrato che l’ordinamento delle unità di campionamento basato sull’informazione telerilevata può portare a una massimizzazione dell’efficienza del censimento di specie vegetali