Italian Volcanic lakes: a diversity hotspot and refuge for European charophytes

Macrophytes are one of the most important components of primary producers in lacustrine environments. Charophytes represent the most threatened group of macrophytes and are included in many European Red-Lists. Thus, finding and preserving charophyte diversity hotspots is important for European macrophyte conservation strategies. Within the framework of a general project aimed at investigating aquatic plant diversity of Italian volcanic lakes (IVL), a field survey carried out in 2009-2010 recognized high charophyte diversity. Overall, 17 species of charophytes, which correspond to 50% of Italian stoneworts and 30% of the European species, were recorded. Nevertheless, only four IVL out of the nine lakes investigated can be considered Chara-dominated lakes. Three Chara-vegetation belts characterized the Chara dominated IVL, as in other pristine deep calcareous European lakes. A Chara aspera belt grew at a lower depth, followed by a Chara polyacantha belt at a medium depth and a Chara globularis dominated belt at a higher depth, up to the maximum growing depth. The most common species was Chara globularis, whereas seven species were rare. Sixteen of the 17 species found belong to the IUCN threatened categories throughout Europe. The most interesting taxa are Nitella hyalina, Nitella gracilis and Lychnothamnus barbatus. Nitella hyalina is extinct in Switzerland and Great Britain, critically endangered in the Balkans and in Germany. Nitella gracilis is extinct in Denmark and endangered in the Balkans, Sweden and Switzerland. The Lychnothamnus barbatus population found in Martignano is the only one known in Italy. Lakes Vico, Martignano, Bolsena and Bracciano host from 18% to 44% of European charophytes. The high number of species in each lake allows the selection of these lakes as European hotspots of charophyte diversity. Therefore, the IVL can be a reference system for the conservation of aquatic species that are typical of Italian and European deep lakes

Measuring freshwater aquatic ecosystems: The need for a hyperspectral global mapping satellite mission

AbstractFreshwater ecosystems underpin global water and food security, yet are some of the most endangered ecosystems in the world because they are particularly vulnerable to land management change and climate variability. The US National Research Council's guidance to NASA regarding missions for the coming decade includes a polar orbiting, global mapping hyperspectral satellite remote sensing mission, the Hyperspectral Infrared Imager (HyspIRI), to make quantitative measurements of ecosystem change. Traditionally, freshwater ecosystems have been challenging to measure with satellite remote sensing because they are small and spatially complex, require high fidelity spectroradiometry, and are best described with biophysical variables derived from high spectral resolution data. In this study, we evaluate the contribution of a hyperspectral global mapping satellite mission to measuring freshwater ecosystems. We demonstrate the need for such a mission, and evaluate the suitability and gaps, through an examination of the measurement resolution issues impacting freshwater ecosystem measurements (spatial, temporal, spectral and radiometric). These are exemplified through three case studies that use remote sensing to characterize a component of freshwater ecosystems that drive primary productivity. The high radiometric quality proposed for the HyspIRI mission makes it uniquely well designed for measuring freshwater ecosystems accurately at moderate to high spatial resolutions. The spatial and spectral resolutions of the HyspIRI mission are well suited for the retrieval of multiple biophysical variables, such as phycocyanin and chlorophyll-a. The effective temporal resolution is suitable for characterizing growing season wetland phenology in temperate regions, but may not be appropriate for tracking algal bloom dynamics, or ecosystem responses to extreme events in monsoonal regions. Global mapping missions provide the systematic, repeated measurements necessary to measure the drivers of freshwater biodiversity change. Archival global mapping missions with open access and free data policies increase end user uptake globally. Overall, an archival, hyperspectral global mapping mission uniquely meets the measurement requirements of multiple end users for freshwater ecosystem science and management

Functional traits in macrophyte studies: Current trends and future research agenda

The use of functional traits (FTs) can provide quantitative information to explain macrophyte ecology more effectively than traditional taxonomic-based methods. This research aims to elucidate the trait-based approaches used in recent macrophyte studies to outline their applications, shortcomings, and future challenges. A systematic literature review focused on macrophytes and FTs was carried out on Scopus database (last accessed May 2020). The latest 520 papers published from 2010 to 2020, which represent 70 % of the whole literature selected since 1969, were carefully screened. Reviewed studies mainly investigated: 1) the role of FTs in shaping communities; 2) the responses of macrophytes to environmental gradients; 3) the application of FTs in monitoring anthropic pressures; and 4) the reasons for success of invasive species. Studied areas were concentrated in Europe (41 %) and Asia (32 %), overlooking other important biodiversity hotspots, and only 6.2 % of the world macrophytes species were investigated in dedicated single species studies. The FTs most commonly used include leaf economic and morphological traits, and we noticed a lack of attention on root traits and in general on spatial traits patterns, as well as a relatively poor understanding of how FTs mediate biotic interactions. High-throughput techniques, such as remote sensing, allow to map fine-scale variability of selected traits within and across systems, helping to clarify multiple links of FTs with ecological drivers and processes. We advise to promote investigations on root traits, and to push forward the integration of multiple approaches to better clarify the role of macrophytes at multiple scales

Impacts of Climate Change on Physical Characteristics of Lakes in Europe

One of the tasks of the EEWAI action is the assessment of the impacts of climate change on ecological water quality in order to support the implementation of the Water Framework Directive. This task requires development of comprehensive knowledge base, models, and databases to provide tools for the evaluation of the adaptation needs of the EU water resources management with respect of the anticipated changes in water quality due to climate change. In 2008, EEWAI initiated a service contract between Joint Research Centre and Helsinki University of Technology in order to develop further a Decision Support System elaborated within the EU project CLIME into a new tool called CLIME Maps. The aim was to extend the central lake database, to update the computational basis of lake physical parameters by applying the newest achievements in this field of science, and enable creating map views of the projected changes of physical parameters of basic lake types. Based on the model results, this report gives an overview of the impacts that climate change may have on physical properties of lakes and demonstrates further implications that these changes have on lake ecosystems. The technical report on CLIME Maps and the users¿ manual are included in annexes of the report.JRC.H.5-Rural, water and ecosystem resource

Impact of nutrients and water level changes on submerged macrophytes along a temperature gradient: A pan-European mesocosm experiment

Submerged macrophytes are of key importance for the structure and functioning of shallow lakes and can be decisive for maintaining them in a clear water state. The ongoing climate change affects the macrophytes through changes in temperature and precipitation, causing variations in nutrient load, water level and light availability. To investigate how these factors jointly determine macrophyte dominance and growth, we conducted a highly standardized pan-European experiment involving the installation of mesocosms in lakes. The experimental design consisted of mesotrophic and eutrophic nutrient conditions at 1 m (shallow) and 2 m (deep) depth along a latitudinal temperature gradient with average water temperatures ranging from 14.9 to 23.9 degrees C (Sweden to Greece) and a natural drop in water levels in the warmest countries (Greece and Turkey). We determined percent plant volume inhabited (PVI) of submerged macrophytes on a monthly basis for 5 months and dry weight at the end of the experiment. Over the temperature gradient, PVI was highest in the shallow mesotrophic mesocosms followed by intermediate levels in the shallow eutrophic and deep mesotrophic mesocosms, and lowest levels in the deep eutrophic mesocosms. We identified three pathways along which water temperature likely affected PVI, exhibiting (a) a direct positive effect if light was not limiting; (b) an indirect positive effect due to an evaporation-driven water level reduction, causing a nonlinear increase in mean available light; and (c) an indirect negative effect through algal growth and, thus, high light attenuation under eutrophic conditions. We conclude that high temperatures combined with a temperature-mediated water level decrease can counterbalance the negative effects of eutrophic conditions on macrophytes by enhancing the light availability. While a water level reduction can promote macrophyte dominance, an extreme reduction will likely decrease macrophyte biomass and, consequently, their capacity to function as a carbon store and food source

Benthic metabolism and denitrification in a river reach: a comparison between vegetated and bare sediments

This study aims at comparing biogeochemical processes in a Vallisneria spiralis meadow and in unvegetated sediments in the upper reach of the Mincio River (Northern Italy). The main hypothesis of this work is that meadows of rooted macrophytes affect benthic metabolism, enhancing capacity to retain nutrients (assimilation) and dissipate (denitrification) nitrogen loadings. In order to highlight how plants affect benthic processes in the riverbed, oxygen, dissolved inorganic carbon (DIC), soluble reactive phosphorus (SRP) and inorganic nitrogen fluxes, together with denitrification rates, were measured from February to November 2007 in intact cores collected from stands of V. spiralis and bare sediments. V. spiralis biomass, elemental composition and growth rates were concurrently measured. Macrophyte biomass ranged from 60 to 120 g m-2 (as dry matter); growth rates followed a seasonal pattern from 0.001 in winter up to 0.080 d-1 in summer. On an annual basis, the macrophyte meadow was autotrophic with net O2 production and dissolved inorganic carbon uptake, while the bare sediment was net heterotrophic. The concurrent N assimilation by macrophytes and losses through denitrification led to similar N uptake/dissipation rates, up to 2500 mmol m-2 y-1. Under the very high NO3 - concentrations of the Mincio River, the competition between primary production and denitrification processes was also avoided. A significant ammonium regeneration from sediments to the water column occurred in the V. spiralis meadow, where plant debris and particulate matter accumulated. Here, SRP was also released into the water column, whilst in the bare sediment SRP fluxes were close to zero. Overall, V. spiralis affected the benthic metabolism enhancing the ecosystem capacity to control nitrogen contamination. However, the actual N removal rates were not sufficient to mitigate the pollution discharge

Ecology of Periphyton in a Subtropical River Floodplain

The Atchafalaya River Basin (ARB) in southcentral Louisiana, USA, is a large and biologically diverse floodplain surrounding the Atchafalaya River (AR), which is the largest distributary of the Mississippi River, receiving 30% of the combined daily discharge of the Mississippi and Red Rivers. Annual flooding facilitates exchange between the AR and its floodplain and is thought to give rise to the high productivity of the river-floodplain system. Primary production within the aquatic ARB is driven by periphytic algae, phytoplankton, and aquatic macrophytes, however, very little is known about periphytic algal assemblages in floodplain systems. In this study, artificial substrates were used to sample periphytic algae from several areas across the ARB between 2017- 2019, and environmental variables measured along a spatiotemporal gradient were used to better understand the factors influencing periphytic algal assemblages. Lake Verret, which did not have active AR connections, was also sampled to provide a natural control for the purpose of investigating the effect of an annual flood pulse on periphyton assemblage composition. Algae were classified into seven groups that included chrysophytes, centric diatoms, pennate diatoms, chlorophytes, euglenoids, xanthophytes, and cyanobacteria. Periphytic algal assemblages were dominated by chlorophytes in 2017, but then shifted to mainly diatoms in 2018 and 2019. Canonical correspondence analyses (CCAs) indicated this may have been due to differences in macrophyte abundance among years. Overall, algal densities were higher early in the year and lower during the summer, likely related to greater nutrient levels associated with inundation of the floodplain by the AR. CCAs also indicated spatial effects on ARB periphyton with diatoms dominating assemblages near river water inputs and other groups such as chlorophytes increasing in relative abundance further into the floodplain. This is likely related with associated spatial gradients in nitrogen sources, particularly ammonium. During 2019, the ARB experienced intense flooding, which lasted an unprecedented 329 days. Total algal cell abundance increased substantially during the high magnitude flood but diminished as floodwaters receded during the summer. Although variable across years, the AR flood pulse strongly influenced the composition and dynamics of the ARB periphyton assemblage, with spatial and temporal patterns reflecting interactions of nutrient availability, temperature, distance from source water, macrophyte abundance and composition, and shading

Remote sensing in shallow lake ecology

Shallow lakes are an important ecological and socio-economic resource. However, the impact of human pressures, both at the lake and catchment scale, has precipitated a decline in the ecological status of many shallow lakes, both in the UK, and throughout Europe. There is now, as direct consequence, unprecedented interest in the assessment and monitoring of ecological status and trajectory in shallow lakes, not least in response to the European Union Water Framework Directive (2000/60/EC). In this context, the spatially-resolving and panoramic data provided by remote sensing platforms may be of immense value in the construction of effective and efficient strategies for the assessment and monitoring of ecological status in shallow lakes and, moreover, in providing new, spatially-explicit, insights into the function of these ecosystems and how they respond to change. This thesis examined the use of remote sensing data for the assessment of (i) phytoplankton abundance and species composition and (ii) aquatic vegetation distribution and ecophysiological status in shallow lakes with a view to establishing the credence of such an approach and its value in limnological research and monitoring activities. High resolution in-situ and airborne remote sensing data was collected during a 2-year sampling campaign in the shallow lakes of the Norfolk Broads. It was demonstrated that semi-empirical algorithms could be formulated and used to provide accurate and robust estimations of the concentration of chlorophyll-a, even in these optically-complex waters. It was further shown that it was possible to differentiate and quantify the abundance of cyanobacteria using the biomarker pigment C-phycocyanin. The subsequent calibration of the imagery obtained from the airborne reconnaissance missions permitted the construction of diurnal and seasonal regional-scale time-series of phytoplankton dynamics in the Norfolk Broads. This approach was able to deliver unique spatial insights into the migratory behaviour of a potentially-toxic cyanobacterial bloom. It was further shown that remote sensing can be used to map the distribution of aquatic plants in shallow lakes, importantly including the extent of submerged vegetation, which is central to the assessment of ecological status. This research theme was subsequently extended in an exploration of the use of remote sensing for assessing the ecophysiological response of wetland plants to nutrient enrichment. It was shown that remote sensing metrics could be constructed for the quantification of plant vigour. The extrapolation of these techniques enabled spatial heterogeneity in the ecophysiological response of Phragmites australis to lake nutrient enrichment to be characterised and assisted the formulation of a mechanistic explanation for the variation in reedswamp performance in these shallow lakes. It is therefore argued that the spatially synoptic data provided by remote sensing has much to offer the assessment, monitoring and policing of ecological status in shallow lakes and, in particular, for facilitating the development of pan-European scale lake surveillance capabilities for the Water Framework Directive (2000/60/EC). It is also suggested that remote sensing can make a valuable contribution to furthering ecological understanding and, most significantly, in enabling ecosystem processes and functions to be examined at the lake-scale

Remote sensing of inland waters: challenges, progress and future directions

Monitoring and understanding the physical, chemical and biological status of global inland waters are immensely important to scientists and policy makers alike. Whereas conventional monitoring approaches tend to be limited in terms of spatial coverage and temporal frequency, remote sensing has the potential to provide an invaluable complementary source of data at local to global scales. Furthermore, as sensors, methodologies, data availability and the network of researchers and engaged stakeholders in this field develop, increasingly widespread use of remote sensing for operational monitoring of inland waters can be envisaged. This special issue on Remote Sensing of Inland Waters comprises 16 articles on freshwater ecosystems around the world ranging from lakes and reservoirs to river systems using optical data from a range of in situ instruments as well as airborne and satellite platforms. The papers variably focus on the retrieval of in-water optical and biogeochemical parameters as well as information on the biophysical properties of shoreline and benthic vegetation. Methodological advances include refined approaches to adjacency correction, inversion-based retrieval models and in situ inherent optical property measurements in highly turbid waters. Remote sensing data are used to evaluate models and theories of environmental drivers of change in a number of different aquatic ecosystems. The range of contributions to the special issue highlights not only the sophistication of methods and the diversity of applications currently being developed, but also the growing international community active in this field. In this introductory paper we briefly highlight the progress that the community has made over recent decades as well as the challenges that remain. It is argued that the operational use of remote sensing for inland water monitoring is a realistic ambition if we can continue to build on these recent achievements.Output Type: Editoria