1,720,977 research outputs found
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
Mesohabitat mosaic in lowland braided rivers: Short-term variability of macroinvertebrate metacommunities
No full textBraided rivers are among the most variable and dynamic riverine systems. Changes in these environments are sudden and frequent, driven by the high hydrological variability. They host high levels of local heterogeneity, with many different habitats in close proximity establishing a mosaic of patches. This provides the conditions for high levels of biodiversity, with strong community variability in particular among the different habitats at the stream-reach level. Nevertheless, these systems are still poorly studied and their complexity is often not taken into account in biomonitoring protocols. We applied mixed effects modelling, spatial ordination techniques and beta-diversity partitioning (into nestedness and turnover components) with the aim of improving the knowledge of braided rivers, investigating: i) the organization of macroinvertebrate communities among the different habitats of a river reach, and ii) the temporal variability of this organization (both among seasons and during summer). We predicted a differentiation of macroinvertebrate communities between distinct habitats within rivers, with this differentiation increasing during the low-flow period. We carried out our study in four braided rivers and streams of the Po River basin (Northern Italy) sampling three different kinds of mesohabitats (main channel, secondary channel and pool) in eight stations during seven campaigns from June 2015 to April 2016. We found a high variability of taxa richness, abundance and community structure among mesohabitats, with marginal ones accounting for the greater part of macroinvertebrate diversity. Secondary channels resulted as being the habitat hosting greater taxa diversity, with 10 exclusive taxa. Surprisingly the mesohabitat communities differed greatly during the seasonal phase, whereas their dissimilarity decreased during summer. This could be explained considering the summer flow reduction as a homogenizing force, leading to a general loss of the most sensitive taxa. However, the summer taxa turnover value resulted higher than nestedness, suggesting a strong environmental control on community organization, with taxa well adapted to the different conditions of mesohabitats and able to manage the effects of flow reduction. Our work represents a remarkable issue for biomonitoring protocols, highlighting the importance of taking into account the whole complexity of braided rivers for a more realistic evaluation of macroinvertebrate communities.</p
Daphnia diversity in water bodies of the Po River Basin
Full text linkShallow water bodies dominate the areal extent of continental waters and host a proportion of biodiversity higher than the percentage of Earth’s surface they cover. Daphnia is a key component of small aquatic ecosystems food webs. Here we present the result of a survey in 24 ponds located in the core of Po river Basin, to assess the actual spreading of Daphnia species in one of the most productive areas of the Northern hemisphere. By using diagnostic genetic markers (12S rRNA and ND5 genes) we identified five Daphnia species: D. ambigua, D. curvirostris, D. longispina, D. obtusa and D. pulex in fourteen ponds. Additional analyses of two nuclear genes (LdhA and Rab4) revealed that D. pulex in the study area is native European strain. In opposite, D. ambigua shared haplotype with the North-Eastern American lineage that was introduced to Europe by long-distance dispersal. In the Po river Basin we identified a highly divergent lineage of D. longispina group that formed a clade with individuals from northern European Russia and might represent a new Daphnia species. Daphnia species in the Cremona province have European origin, except for D. ambigua which is a North American species spreading across Europe. Future attention will require monitoring of invasive species, particularly D. ambigua and the North American invasive clone of D. pulex that is already present in Northern Italy. </p
Rare but large bivalves alter benthic respiration and nutrient recycling in riverine sediments
No full textBioturbation studies have generally analyzed small and abundant organisms while the contribution to the benthic metabolism by rare, large macrofauna has received little attention. We hypothesize that large, sporadic bivalves may represent a hot spot for benthic processes due to a combination of direct and indirect effects as their metabolic and bioturbation activities. Intact riverine sediments with and without individuals of the bivalve Sinanodonta woodiana were collected in a reach with transparent water, where the occurrence of the mollusk was clearly visible. The bivalve metabolism and its effects on sedimentary fluxes of dissolved gas and nutrients were measured via laboratory incubations of intact cores under controlled conditions. S. woodiana contributed significantly to O2 and TCO2 benthic fluxes through its respiration and to NH4+, SRP and SiO2 regeneration via its excretion. The bivalve significantly stimulated also microbial denitrification and determined a large efflux of CH4, likely due a combination of bioturbation and biodeposition activities or to anaerobic metabolism within the mollusk gut. This study demonstrates that a few, large individuals of this bivalve produce significant effects on aerobic and anaerobic benthic metabolism and nutrient mobilization. Random sediment sampling in turbid waters seldom catches these important effects due to low densities of large fauna
New physical and chemical perspectives on the ecology of Thorea hispida (Thoreaceae)
No full textIn the last decade, many new records for Thorea hispida (Thore) Desvaux 1898 emend. Sheath, Vis et Cole 1993 (Rhodophyta) have been collected from Europe as a probable result of the enactment of the Water Framework Directive which has fueled a renewed interest in the characterization of the macroscopic primary producers of river systems. Despite this, the species remained poorly documented, especially regarding habitat requirements and related physical and chemical drivers. To further add to the knowledge of these parameters, a three-year survey (2009-2011) was conducted along the southern reach of the Oglio River, a mid-size tributary of the Po River in Northern Italy that hosts three newly recorded populations of T. hispida. In parallel, a comprehensive review of the literature was performed. In this work, we present the first records for T. hispida from Italy, and a first detailed physical, chemical and hydromorphological characterization of its habitat. We confirm the predilection of T. hispida for turbid waters (> 80 mg L -1 of total suspended solids) with high nutrient (up to 9.4 mg L -1 for nitrates and up to 173 μg L -1 for soluble reactive phosphorous) and high conductivity levels (up to 660 µS cm -1 for conductivity). In addition, our data extended the range of tolerance of the species for temperature (5.1–26.2 °C) and pH (7.1–8.6). In general, our results and previously published data corroborate with the idea that T. hispida can not be considered a sensitive species (i.e., a taxon scarcely adapted to increasing levels of pollution), showing a preference for rivers characterized by high nutrients availability. Moreover, its rarity must be traced to the low detectability of the thallus due to species life cycle and the very limited accessibility of colonized habitats
Agricultural practices regulate the seasonality of groundwater-river nitrogen exchanges
No full textSoil System Budgets (SSB) of nutrients are generally performed annually over arable land to infer their use efficiency and water pollution risk in highly exploited agricultural watersheds. They are seldom partitioned into seasonal budgets and matched with seasonal nutrient transport in adjacent river reaches. We calculated seasonal soil nitrogen (N) budgets in a Mincio River sub-basin (Italy), and we analyzed the dissolved inorganic N net export in the river reach draining such sub-basin. Our results show seasonal differences of SSB with N excess in winter and even more in spring, equilibrium among sources and sinks during autumn and N deficit during summer. Seasonal inorganic N loads transported by the river were not correlated with SSB as they peaked in late summer and were at their minimum in early spring. Fertilization uncoupled to significant uptake supports N excess in winter and spring, whereas crop uptake uncoupled to N inputs supports summer N deficit. Nitrification cannot explain nitrate accumulation in the river reach, suggesting alternative dynamics driving the local hydrology. Flood irrigation results in large soil nitrate solubilization, transport and in upward migration of the groundwater piezometric head during spring and summer periods. River water is likely replaced by nitrate-rich groundwater when the groundwater recharge exceeds a certain threshold coinciding with late summer. Irrigation is then interrupted and the piezometric head, together with nitrate exchange, decreases. This work suggests that a deep understanding of N dynamics in agricultural watersheds with flooding irrigation on permeable soils needs the reconstruction of the vertical pathways of nitrate and of river-groundwater interactions. Moreover, the partitioning of annual into seasonal N budgets and their combination with irrigation practices allows the identification of hot moments in N cycling. Agricultural practices minimizing nitrate excess, its mobility and the risk of surface and groundwater pollution are suggested for this area
Vegetated canals mitigate nitrogen surplus in agricultural watersheds
No full textWithin irrigated agricultural watersheds, canal networks may play a crucial role as nitrogen (N) sink. This is due to the intertwined action of macrophytes and microbial communities occurring in the dense net of small watercourses. We hypothesize that vegetated canals may buffer relevant fractions of excess N from agriculture via microbial denitrification, and that vegetation provides multiple interfaces that greatly support the activity of bacteria. To test these hypotheses, we measured net dinitrogen (N2) fluxes in bare sediments and at the reach-scale in vegetated ditches. As study areas we selected canals subjected to diffuse N pollution, laying in a lowland sub-basin of the Po River (northern Italy). Denitrification was evaluated on the basis of changes in dissolved N2:Ar, measured by Membrane Inlet Mass Spectrometry. Complementary data were obtained via upstream-downstream inorganic N balances and intact core incubations targeting sedimentary N fluxes. Denitrification was the major pathway for N removal, with rates at the reach-scale (5-25mmolNm-2d-1) up to one order of magnitude higher than in sediment alone (3-7mmolNm-2 d-1). Results highlighted that N uptake by macrophyte stands was quantitatively small; however, aquatic vegetation provided multiple interfaces for microbial growth and N-related processes. Our data suggest that 1ha of vegetated canal may remove between 150 and 560kgNyr-1. In the study area, an average canal density of ~0.05 linear kmha-1 of agricultural land has the potential to buffer 5-17% of the excess N from agriculture (~60kgNha-1yr-1).The results of this study suggest the central role of emergent vegetation in promoting microbial N-transformation and canal self-depuration. Innovative management of the canal networks should couple hydraulic needs with the maintenance of emergent vegetation
Benthic nitrogen metabolism in a macrophyte meadow (Vallisneria spiralis L.) under increasing sedimentary organic matter loads
No full textOrganic enrichment may deeply affect benthic nitrogen (N) cycling in macrophyte meadows, either promoting N loss or its recycling. This depends upon the plasticity of plants and of the associated microbial communities, as those surrounding the rhizosphere. Rates of denitrification, dissolved inorganic N fluxes and N uptake were measured in sediments vegetated by the submerged macrophyte Vallisneria spiralis L. under increasing organic matter loads. The aim was to investigate how the combined N assimilation and denitrification, which subtract N via temporary retention and permanent removal, respectively, do vary along the gradient. Results showed that V. spiralis meadows act as regulators of benthic N cycling even in organic enriched sediments, with negative feedbacks for eutrophication. A moderate organic load stimulates N uptake and denitrification coupled to nitrification in the rhizosphere. This is due to a combination of weakened competition between macrophytes and N cycling bacteria and enhanced radial oxygen loss by roots. An elevated organic enrichment affects N uptake due to hostile conditions in pore water and plant stress and impairs N mineralisation and its removal via denitrification coupled to nitrification. However, the loss of plant performance is almost completely compensated by increased denitrification of water column nitrate, resulting in a shift between the relative relevance of temporary and permanent N removal processe
Exotic species, rather than low flow, negatively affect native fish biomass in the Oglio river, Northern Italy
No full textTesting the response of macroinvertebrate communities and biomonitoring indices under multiple stressors in a lowland regulated river
No full textRiver systems and their communities are exposed to diverse and multiple threats. Understanding how these threats affect the behaviour of biomonitoring indices is essential in order to provide reliable tools for the management and conservation of watercourses. To this purpose we tested the relationship of the STAR_ICMi index and its metrics, LIFE index and macroinvertebrate community with hydrology, water chemistry and land use in 8 sites located along the Oglio River course (Northern Italy), a watercourse originating from a large and deep lake. Macroinvertebrates and water samples were collected seasonally from summer 2013 to summer 2015 and daily discharge data were used to calculate several indices of hydrological alteration. A subset of these variables was selected by principal component analysis for using in the data analysis. The influence of hydrology, water chemistry and land use on macroinvertebrate community structure was explored with the variance partitioning method, while their influence on biomonitoring indices was analysed in a linear mixed effect model framework. Temporal and spatial constraints were explicitly considered in both analyses. Macroinvertebrate community structure was mainly related to these last two factors and to their joint effects with water chemistry and hydrology. STAR_ICMi, its metrics (with the exception of the Shannon index) and LIFE were related to the distance from the lake outlet, a proxy of mean annual discharge, groundwater input and artificial land use. STAR_ICMi, ASPT and EPT richness were also inversely related to the flow variability in the 3 months preceding sample collection. Surprisingly LIFE index was not related to any of the hydrological variables. The results of this study highlight weakness in the current biomonitoring tools and support the need for further investigations on macroinvertebrate interrelations with environmental drivers and their spatial and temporal structure. This is essential to overcome the limitations that may affect the reliability of macroinvertebrate-based indices in aquatic biomonitoring
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