Rossano Bolpagni

A remote sensing approach to monitor the conservation status of lacustrine Phragmites australis beds

Phragmites australis populations in native areas have been gradually declining since the mid-20th century. We developed a logical approach based on remote sensing to monitor the conservation status of P. australis beds in response to environmental gradients and orient future management actions in Lake Garda (northern Italy). During the 2010 growing season we collected data on: (i) the structural and functional status of seven P. australis beds and (ii) land cover in a 50-m buffer around each bed, and we tested four different vegetation indices (VIs) derived from a multi-temporal and multisensor dataset. Double hierarchical clustering based on the VI statistics and environmental variables (morphological, functional and land-use) showed a good consistency between the outputs of the vigor-function analysis and the environmental classification of the P. australis beds considered. Overall, the bed’s area was the most influential factor in the data clustering procedures, followed by the descriptors derived from the enhanced vegetation index. Our results confirmed the importance of temporal characteristics of remote sensing data to assess the conservation status of common reed beds and proved the sensitivity of VIs and derived descriptors to local environmental conditions within a homogeneous littoral area. This study supports the utility of remote sensing for monitoring riparian vegetation and analyzing the spatial and temporal response of P. australis populations to human pressure and management actions.

Recognizing harmful algal bloom based on remote sensing reflectance band ratio

We present a band ratio algorithm based on remote sensing reflectance (RRS) data to detect an algal bloom composed of cyanobacteria (Planktothrix spp.) and chrysophytes in Lake Idro, a small meso-eutrophic lake situated in the subalpine region (northern Italy). The bloom started around the first week of September 2010 and persisted for about 1 month, with highest mean chlorophyll-a concentrations (17.5 ± 1.6 mgm−3) and phytoplankton cellular density (7,250,000 cell·l−1) measured on September 14, 2010. RRS data obtained from in situ measurements were first investigated to select the diagnostic wavelengths (i.e., 560 and 620 nm) of both phycoerythrin (present in the Planktothrix spp.) and other pigments (e.g., fucoxanthin, common to several species of chrysophyte). Testing the algorithm on RRS data derived from atmospherically corrected image data showed the ability of the medium resolution imaging spectrometer (MERIS) to detect the bloom also. The results demonstrate that a combination of in situ and MERIS data is a valuable tool to monitor the extent and duration of phytoplankton blooms.

Multitemporal analysis of algal blooms with MERIS images in a deep meromictic lake

Abstract MERIS images (2003–2011) were used to detect algal bloom events in Lake Idro (Northern Italy) applying a semi-empirical algorithm. From the study of an intense phenomenon occurred in late summer 2010, a retrospective analysis of similar events during late summer/early autumn period was performed. High intra-and inter-annual variability was observed and three additional bloom events were identified on 2003, 2005 and 2008. Hydrological and weather parameters were examined at different temporal intervals (August-October, September-October and monthly from August to October) to investigate the regulating factors of bloom incidence. Rather low temperatures and the persistence of clouds seem to facilitate starting and maintenance of blooms.

Fragmentation and groundwater supply as major drivers of algal and plant diversity and relative cover dynamics along a highly modified lowland river

Algae and aquatic vascular plants were investigated along a highly modified medium-sized lowland river (Oglio River, northern Italy). We focused on the role of fragmentation and groundwater supply in driving macrophyte assemblages, paying particular attention to soft-bodied benthic algae. Four different a priori stretch types (dammed, groundwater-dependent, potamal and rhithral) were identified along the river longitudinal gradient as proxies of river hydrology and relative human-induced flow alterations. Over three years (2009-2011), taxa diversity, cover data, spatial and temporal dynamics and indicator and detector species were compared with physical, chemical and hydrological variables at 30 different river sites. Data was explored by indicator species analysis, nonmetric multidimensional scaling, and PROTEST. A total of 88 taxa, of which 36 were algae (equal to 40.9% of the total diversity), 3 bryophytes (3.4%) and 49 vascular plants (55.7%), were recorded. Taxa diversity peaked at the groundwater-dependent sites for both algae and vascular plants (with a mean of 12.8±2.7 and 12.7±4.8 taxa per site, respectively). Algae cover values were one order of magnitude higher than those of vascular plants (with an overall mean of 37.0±24.2% per site). The vascular plants counterbalanced the algae coverage values exclusively at the dammed sites (27.6±23.2% vs 28.2±13.9%, respectively). A clear zonation of communities emerged from the multivariate analysis, which revealed taxa rearrangements that largely overlapped the river stretch types. Inter-annual comparisons confirmed the strong stability of the primary producer communities in the short term (three years). Our work substantiates the pivotal role played by fragmentation and hydrology, in addition to groundwater, in structuring riverine macrophyte communities. Further investigations are needed to resolve the uncertainty surrounding the non-linear responses of macrophytes to the physical and chemical conditions of rivers.

Distribution, morphology and ecological niche of Batrachospermum and Sheathia species (Batrachospermales, Rhodophyta) in the fontanili of the Po plain (northern Italy)

Abstract Twenty-three freshwater springs of the Po plain (northern Italy) were surveyed and visited multiple times during 2011–2013 to assess water quality and algal taxa present. Despite poor water conditions of this human-altered floodplain, a relatively high number of taxa referable to the freshwater red algae, Batrachospermum and Sheathia, were observed. The identity of specimens collected was based on morphology and confirmed with sequence data. The specimens belonged to Sheathia arcuata, S. boryana, Batrachospermum atrum, B. gelatinosum and B. gelatinosum f. spermatoinvolucrum. This is the first report of B. gelatinosum f. spermatoinvolucrum outside North America. Niche analysis revealed a marked difference in the physical and chemical preferences of the freshwater red algae recorded. The occurrence of S. boryana was limited to relatively low nitrate and higher oxygen concentrations. Conversely, the spatial distribution of the other four taxa indicated that they were able to tolerate high concentrations of nitrate (up to 53.6 mg l–1) and low rates of dissolved oxygen saturation (as low as 3%). All the specimens of B. gelatinosum collected had few to many trichogynes deformed by a basal protuberance or knob, a structure previously unobserved in this species. No other taxa showed any deformities. The ecological analyses confirmed the existence of a relationship between the environmental conditions of the springs and the occurrence of knobs.

Aquatic Plant Diversity in Italy: Distribution, Drivers and Strategic Conservation Actions

Italy is recognized as one of the prominent hot spot areas for plant diversity at regional and global scale, hosting a rich range of ecosystems and habitat types. This is especially true considering aquatic habitats, which represent a major portion of the total water surfaces in the Mediterranean region. Nevertheless, only a scant attention was paid to clarify the species richness of aquatic plant and its contribution to the total diversity at the country scale, despite such plants are seriously threatened at multiple scales. This paper provided the first comprehensive inventory of aquatic plants at the whole country scale, collecting data on species’ distribution, trends, and explanatory determinants of species richness. We confirmed the key contribution of Italy to the regional and global aquatic plant diversity with a total of 279 species recorded since 2005, equal to the 88.5%, 55.9% and ∼10% of the richness estimated at European/Mediterranean, Palearctic and global scale, respectively. Ten species are considered extinct in the wild [among which Aldrovanda vesiculosa L., Caldesia parnassifolia (Bassi ex L.) Parl., Helosciadium repens (Jacq.) W.J.D. Koch, and Pilularia globulifera L.], four were doubt [among which Luronium natans (L.) Raf., Utricularia intermedia Hayne, and U. ochroleuca R.W. Hartman.], and eight were erroneously reported in the past, among which Isoëtes lacustris L., Myosotis rehsteineri Wartm., and Ranunculus aquatilis L. Only 18 species – mainly helophytes (14) – were present in all the 20 Italian regions, whereas hydrophytes showed most scanty regional frequencies. Temperature, latitude, area and water resources availability are the main drivers of aquatic plant spatial arrangement and diversity. Furthermore, the number of inhabitants per km2 well described the number of “lost species” since 2000. The findings of the present survey call for an urgent elaboration of large-scale strategies to ensure the survival of aquatic plants, stressing on multiple functions played by aquatic plants in supporting national economy and human well-being. In this context, Italy can play a fundamental role guaranteeing temporary refuge for projected or expected species migrations along latitude and longitude gradients. Besides, in hyper-exploited landscapes man-made water bodies can further enhance the achievement of minimum conservation targets.