1,721,078 research outputs found
Microhabitat patterns of soft-bodied benthic algae in a lowland river largely fed by groundwater
No full textIn lowland rivers largely fed by groundwater, the aquifer resurgence plays a major role in supporting local plant diversity. However, large knowledge gaps exist with regard the role of groundwater on algal diversity and spatial arrangement. In this context, our main aim was to evaluate the distributive gradients of soft-bodied benthic algae across a mid-size lowland river with a bottom dominated by hard substrate (Oglio River, north Italy). Along the investigated river sector, a clear segregation both for taxa and for environmental data was observed, especially in terms of pH, hydrological variables and nutrient availability. Overall, we recorded an important contribution of groundwater supply in shaping the structure and complexity of algal communities at the microhabitat level (in the meter range) during the river base flow. All these considerations shed new light on the response of algal taxa to a relevant groundwater ingression in a lowland river
Fragmentation and groundwater supply as major drivers of algal and plant diversity and relative cover dynamics along a highly modified lowland river
No full textAlgae 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
A remote sensing approach to monitor the conservation status of lacustrine Phragmites australis beds
No full textRole of ephemeral vegetation of emerging river bottoms in modulating CO2 exchanges across a temperate large lowland river stretch
No full textRivers and marginal wetlands contribute significantly to the carbon (C) exchange rate per unit area compared to adjacent terrestrial ecosystems, due to high C inputs, metabolic activity and CO2 supersaturation. Within riverscapes, the contribution of emerging bottoms (i.e. parafluvial zones) and ephemeral vegetation (i.e. microphytobenthos or annual vascular plant communities) to the C metabolism is understudied. The aim of this study was to evaluate the CO2 exchange rates at the water- and emergent sand bar-atmosphere interfaces within a lowland large temperate river stretch. CO2 fluxes were measured seasonally, in summer (August 2007) and winter (March 2008) via static closed chambers, together with the primary producers’ biomass (microphytobenthos and vascular macrophytes). Our results showed that the river was a CO2 source (between 0.2 and 7.6 mmol CO2 m−2 day−1), whilst the vegetated parafluvial zones acted as a net sink, with assimilation rates peaking at 623.4 mmol CO2 m−2 day−1. Emerging bare sediments were on the contrary net emitting CO2 systems (2.7–60.1 mmol CO2 m−2 day−1). Within lotic environments, seasonally emergent vegetated sand bars may represent important C fixation hot spots, with summer primary production particularly contributing to offsetting CO2 emissions and counterbalancing the heterotrophic metabolism of the saturated zones. Based on these outcomes, we suggest that studies addressing the strictly aquatic fluvial environment, which is generally a CO2 emitter, should be linked to those from transitional areas in order to better integrate terrestrial and aquatic C budgets
Soil system budgets of N, Si and P in an agricultural irrigated watershed: surplus, differential export and underlying mechanisms
No full textOngoing socio-economic and climatic changes can differentially affect the biogeochemistry of the key nutrients nitrogen (N), silica (Si), and phosphorus (P) by altering their soil budgets, their transfer to aquatic environments and their ecological stoichiometry. This may lead to cascade consequences for aquatic communities and biogeochemical processes. Soil budgets, river export, and N, Si, and P ecological stoichiometry were assessed in a heavy impacted basin (Mincio River, Italy) in two decades (1991–2000; 2001–2010). The main aim was to analyse element-specific mechanisms of terrestrial-aquatic transport and retention within aquatic habitats. Budget results suggest a net accumulation (inputs exceeding outputs) of all nutrients in agricultural lands, mainly due to livestock manure, with a reduction for N (196 kg N ha−1year−1in 2000, and 132 kg N ha−1year−1in 2010), and constant values for Si (up to 3 kg Si ha−1year−1) and P (43 kg P ha−1year−1) along the study period. River export of N and P accounted for 3–27% and ~ 2% of N and P soil net accumulation, respectively, while Si export was significantly greater (25 kg Si ha−1year−1) than Si net accumulation on farmlands. The stoichiometry of net nutrient accumulation in soils was not reflected by the stoichiometry of nutrient riverine export, due to element-specific mechanisms. We speculate that N and Si vertical and horizontal mobilization is increased by the irrigation loop, while P retention is favored by limited erosion due to limited slopes in the Mincio River basin. The simultaneous analysis of N, Si and P allows us to better understand the different paths, transformation and retention mechanisms at the watershed scale
Do oxic–anoxic transitions constrain organic matter mineralization in eutrophic freshwater wetlands?
No full textThis study aims at investigating decomposition processes in wetlands that are daily or seasonally exposed to intermittent oxic and anoxic conditions. We hypothesized that in wetland ecosystems where anoxia regularly establishes, decomposition rates are not affected by oxygen shortage, especially when nitrates are available. Monitoring and experiments were performed from December 2003 to January 2005 in one of the widest (81 ha) freshwater wetlands in the Po river floodplain (Natural Reserve Paludi del Busatello, Italy). Intact sediment cores were sampled on a seasonal basis. Sediment–water fluxes of oxygen, dissolved inorganic carbon, methane, and inorganic nitrogen were determined under oxic and anoxic conditions. Oxic–anoxic transitions always resulted in enhanced ammonium, dissolved inorganic carbon, and methane effluxes. At high temperatures, the methane release from sediments was inversely related to both nitrate concentrations and uptake. Likely, nitrate can compensate for the oxygen deficiency while maintaining an oxidative metabolism, either supporting microbial decomposition as an electron acceptor or stimulating the oxidation of the byproducts of the anaerobic metabolism, e.g., methane. This is a key point as the number of temperate wetlands with concurrent nitrate pollution and oxygen shortage is increasing throughout the world
Aquatic Plant Diversity in Italy: Distribution, Drivers and Strategic Conservation Actions
Full text linkItaly 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
Greenhouse gas (CO2, CH4 and N2O) within an agricultural impacted watershed (Po River Plain, Northern Italy)
No full textIn the Po River Plain, nitrogen surplus in permeable soils results in elevated downward nitrogen fluxes, mostly as nitrate. Lowland springs, aligned along interfaces between gravel and sandy soils, recycle part of this nitrogen to the surface and we hypothesised that they may be hot spots of N 2 O and other greenhouse gases, due to incomplete denitrification in the suboxic environment. In early and late summer 2009, water flow was measured and water samples were collected at the outlet and ~1 km downstream at 14 springs; physico-chemical parameters [temperature, pH, dissolved inorganic nitrogen (DIN) and dissolved gases (O 2 , N 2 O, CH 4 , CO 2 )] were analysed. All springs were characterised by elevated nitrate concentrations (154 1411 μM) and recycled to the surface inorganic nitrogen (~180 kg N-NO3- day-1 on average). Spring waters were suboxic (40 60% of O 2 saturation) and CO 2 , CH 4 and N 2 O supersaturated (26.6 2399.0, 0.002 1.02 and 0.02 1.02 μM, respectively). CO 2 and N 2 O underwent a significant degassing process from the supersaturated waters to the atmosphere. Calculated N 2 O emissions (up to 0.646 g N 2 O m-2 d-1, among the highest reported for aquatic environments) highlight the role of lowland springs as hotspots of N 2 O. We conclude that lowland springs located in heavily impacted watersheds recycle groundwater nitrate and have an extremely elevated potential as greenhouse gas emitters
First time in Italy. Is the elusive aquatic megadrile Sparganophilus Benham, 1892 (Annelida, Clitellata) accelerating its dispersal in Europe?
No full textDuring field studies in River Mincio, northern Italy, populations of the aquatic megadrile Sparganophilus tamesis Benham, 1892 were discovered, the worms being particularly abundant among the roots of Vallisneria spiralis L. This finding represents the first record of Sparganophilidae in Italy. A morphological account, with photographs of worms and cocoons, as well as field and laboratory remarks on density, behaviour and habitat, are provided. The view of S. tamesis being senior synonym to S. eiseni Smith, 1895 is favoured, as is the hypothesis of the arrival and spreading of Sparganophilus in Europe amongst the roots of water plants. </p
How do low-abundance taxa affect river biomonitoring? Exploring the response of different macroinvertebrate-based indices
No full textThe contribution of rare taxa to aquatic bioassessments remains a subject of debate, and generates contrasting positions among researchers. Very little is known about the effect of low-abundance taxa (LAT) for calculating both single and multimetric macroinvertebrate-based indices, as well as the ecological status classification. In this study, we aimed to: i) identify the aquatic macroinvertebrates that need special attention during index applications given their low abundance; ii) analyse the effect of excluding LAT on single (IBMWP and IASPT) and multimetric (STAR_ICMi) biological indices; and iii) investigate the influence of LAT on river ecological status assessments. To this end, two different river basins in SE Spain and N Italy with contrasting climatic conditions and river types were selected. Our results showed that almost all the taxa at the family level can act as low-abundance taxa. In particular, the LAT belonged mainly to orders Diptera, Trichoptera, Coleoptera, Gastropoda and Hemiptera. The IndVal analysis stressed Tabanidae, Cordulegasteridae and Hydroptilidae as the most characteristic low-abundance families in the Spanish data set, while Dryopidae and Athericidae were identified mostly in N Italy. Excluding LAT affected the studied index values and the resulting bioassessment classification, except for the IASPT index. Loss of the entire LAT pool reduced the ecological status for 78% of the samples for the IBMWP index. Changing took place in 41% of the samples when considering the STAR_ICM index. Relevant changes were detected even when considering loss of 50% of the LAT, especially with the IBMWP index. Similar values and patterns were obtained in each considered quality class and river type. Our results provide useful information about controversial taxa and stress the significance of LAT in river biomonitoring. Excluding LAT is discouraged, although different responses according to the considered index were detected. The IBMWP index always obtained lower values (coupled mainly with an underestimation of ecological classes), while STAR_ICMi and, especially the IASPT index, were less affected by excluding LAT. Paying special attention to all the protocol application stages is recommended, with emphasis placed when using the IBMWP index
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