Bruna Gumiero

Geomorphic control of denitrification in large river floodplain soils

In this manuscript we investigated the relationshipsbetween the microbiological denitrification process inriver alluvial soils with structures and patterns ofthe floodplain visible at a larger scale. Wehypothesised that both topography and soil grain sizerepresent pertinent environmental factors to forecastdenitrification activity in river floodplain. Thestudy was conducted in 15 alluvial sites along a 30 kmlong stretch of the Garonne River, a seventh-orderstream of the south west of France. Sites wereselected to encompass the widest range possible ofaverage annual flood duration (0.04 to 29 days) andfrequency (return period from 0.6 to 7 years). On anannual basis, we found that average denitrificationrates did not show any significant trend along theflood frequency gradient. Although during the studythe flood frequency and duration was higher than thecalculated average, we did not find any relationshipbetween flood duration and denitrification enzymeactivity. If flood events do not last long enough tomaintain waterlogging conditions conducive to sustaindenitrification activity for long periods, theyindirectly affect the spatial distribution ofdenitrification activity through the sorting out ofsediment deposits. Indeed, we found a significantrelationship between denitrification rates in thefloodplain soils and their texture; highest rates weremeasured in fine textured soils with high silt + claycontent. Below a threshold of 65% of silt and claycontent, the floodplain soils did not present anysignificant denitrification rates. Above thatthreshold denitrification increased linearly. Theseresults demonstrate that alluvial soil texture is alandscape scale factor which has a significant effecton denitrification in floodplains.

Vegetation, soil and hydrology management influence denitrification activity and the composition of nirK-type denitrifier communities in a newly afforested riparian buffer

Soil microbial community composition and activity could be affected by suitable manipulation of the environment they live in. If correctly applied such an approach could become a very effective way to remediate excess of chemicals. The concentration of nitrogen, especially nitrate deriving from agricultural managements, is generally found to increase in water flow. Therefore, by forcing the water flow through a buffer strip specifically designed and possibly afforested with suitable plant species, may result effective in reducing high nitrogen contents. The management of a riparian buffer may definitely affect the soil microbial activities, including denitrification, as well as the composition of the community. The present study reports on the changes occurred in terms of denitrifying microbial community composition, as compared to that of a neighbouring agricultural area, as a consequence of hydraulic management coupled to the suspension of farming practices and to the development of the woody and herbaceous vegetation. With this aim, denitrification was repeatedly measured and the data obtained were related to those deriving from a specific analysis of bacterial groups involved in denitrification. nirK, encoding for nitrite reductase, an enzyme essential for the conversion of nitrite to nitric oxide and considered the key step in the denitrification process, was chosen as the target gene. The main results obtained indicated that denitrification activity changes in riparian buffer as compared to agricultural soil and it is strongly influenced by carbon availability and soil depth. Although no significant differences on the community composition between superficial (0-15 cm) and medium (40-55 cm) layers were observed, the nirK-type denitrifier community was shown to significantly differ between riparian and agricultural soils in both surface and medium layers.

Bacterial diversity of a wooded riparian strip soil specifically designed for enhancing the denitrification process

This research is part of a project aimed at verifying the potential of a specifically assessed wooded riparian zone in removing the excess of combined nitrogen from the Zero River so as to reduce nutrient inputs into the Venice Lagoon. Among the specific objectives of the project, there was the determination of change in the composition of the microbial populations of soil of the wooded riparian strip. The composition of the bacterial communities collected at different depths inside and outside the riparian strip was determined by combined approaches involving cultivation (CFU), microscopic approaches (CTC test), and DNA-based techniques (ARDRA and DGGE). The size of the living population was the same inside and outside the experimental strip, with a minor percentage of culturable bacteria. Higher numbers of metabolically active bacteria and higher bacterial diversity were detected in the internal soil, with deeper soil layers showing reduced diversity, thus indicating that soil management within the riparian strip effectively supports the viability of bacterial communities. Total operational taxonomic units (OTUs) and percentage of single OTUs were also found to be always higher in the internal soil samples for all soil layers, with the percentage of Firmicutes increasing and Actinobacteria decreasing with depth. The increasing soil organic carbon inputs due to the contribution of the growing plants were found to support bacterial diversity in all soil layers. DNA-based analysis also indicated a clear effect of the applied treatments on soil bacterial diversity and a well-defined separation of the bacterial communities related to the different soil layers of the riparian strip.

Leaf Bags and Natural Leaf Packs: Two Approaches to Evaluate River Functional Characteristics

An extensive knowledge of the functional characteristics of rivers is of basic importance to develop precise management plans with specific aims, e.g. to rehabilitate riparian ecotones or increase the retention capacity of streams. In this study man-made leaf bags (LB) and natural leaf accumulations (NLP) were used. The first method was useful in calculating breakdown rates and the second one in understanding the effective litter composition, which does not always reflect the composition of the riparian canopy. The assemblages of macroinvertebrate colonizing both LB and NLP were divided into functional feeding groups and compared. Are both methods (Leaf Bags and Natural Leaf Packs) necessary and complementary to analyse the functional characteristics of an upland river? The study was carried out in three different sites on the upper reaches of the Adige River. The breakdown rates were very similar in all three study sites but litter quality and quantity were very different. Although, in the two upper sites, the composition of invertebrates colonizing LB and NLP was the same, abundance and biomass values coincided only in the first stage of the colonization process of LBs. In the third site no invertebrates using litter as a trophic resource were found. Both NLP and LB methods are needed in the evaluation of rehabilitation programs as they take account of the different aspects of the dynamics and the composition of CPOM.

Riparian vegetation as indicator of channel adjustments and environmental conditions: the case of the Panaro River (Northern Italy)

Disturbances affecting flow and sediment transport regimes (e.g. dams, diversions, gravel mining, weirs, bank reinforcements, climate changes) can promote riverbed degradation and channel narrowing, and thus influence vegetation dynamics and composition. This study investigates the relationships and feedbacks between channel adjustments and riparian vegetation dynamics by combining an analysis of morphological channel changes with a wider phytosociology analysis of existing vegetation within the river corridor. These relationships were illustrated by using the case study of the Panaro River (located in the Northern Apennines, Italy), being a representative case of a deeply incised and narrowed river. More specifically we analyzed: (1) the relations between landforms and distributional patterns of vegetation types and characteristic plant species (index species): these provided information about the hydrogeomorphic condition of fluvial landforms and about channel adjustments; (2) the distance of riparian vegetation conditions from expected conditions as a consequence of human impact, based on the fact that each species and vegetation type has a given tolerance for specific disturbance regimes or stresses. Although some expected relations between landforms and vegetation types were found, we recorded significant deviations from the typical correlation pattern existing between morphology and vegetation, and this could be used to infer the intensity and the typology of human disturbances. In particular, the index species can indicate present ecological conditions and on past channel evolution. With this knowledge it might be possible to develop botanical recovery models in the future and, even more importantly, enable the recognition of the differences between temporal and spatial diversity.

The Italian Rivers

Few Italian rivers today can be considered to be in a natural state. Since humans have colonized this region, they have strongly interacted with the rivers and their natural dynamics by shaping their morphology and using the landscape. Exploitation of natural resources has been so extensive that today only small areas of the landscape and of the rivers that flow through it can be considered natural. Italian rivers comprise a diversity of fluvial ecosystems, ranging from Alpine glacier-fed streams to ephemeral Mediterranean streams and from large rivers, such as the Po, to spring-fed brooks and artificial canals. They all flow through densely populated areas. Although Italy is rich in water resources, the distribution is uneven, with the majority occurring in the north (65%), 15% in the centre, 12% in the south, and 8% in the main islands. Because of this variability, this chapter focuses on the Po River, which forms the largest Italian plain and covers ∼24% of Italy. Other Alpine rivers described in the chapter include the Adige, the second longest Italian river, the Tagliamento because of its relatively pristine condition, and the Brenta River because of its historical role in the region and as an example of a river with a mix of natural and regulated reaches.

Monitoring and Modeling Digestate Fate and Transport in Infiltrating Afforested Areas Versus Maize/Ray-Grass Rotation Plots

Managed aquifer recharge systems must account for the expected long-run performance from a water quality viewpoint to be considered sustainable in ameliorating not only the groundwater quantity but also its quality. Gravity-driven infiltration ditches in newly afforested areas are one of many managed aquifer recharge systems that could enhance the availability of groundwater resources in medium and short runs. Although, in highly anthropized landscapes such as in Northern Italy, the need of large areas for managed recharge systems is often controversial with respect to the classical land use, which is prevalently agricultural. For this reason, a large scale field experiment has been conducted recently to assess the potential of combining managed aquifer recharge systems with the need of maintain productive the land (Mastrocicco et al. in Ecohydrology, 9(1):167–178, 2016).

Preliminary assessment on flood mitigation potential via managed aquifer recharge in the Brenta megafan (Italy)

Managed aquifer recharge (MAR) design and operation must incorporate the expected long-term performance from a water quantity perspective to sustainably mitigate hydrologic impacts of groundwater overexploitation. Gravity driven infiltration ditches are one of many MAR schemes that could augment the available water resources. In the present study, an infiltration system (IS) consisting of 8 ditches was monitored to determine its hydrologic performance over time and its possible export to similar areas of the Brenta Megafan (Northern Italy). The IS displayed an almost constant capacity to infiltrate the diverted water with a total amount of 0.8 Mm3/ha/y. The good results suggest to promote this technique in other areas that suffer from groundwater resources depletion

Decomposition processes of alder leaves downstream of the Ridracoli Dam (Apennines, Italy)

The categorisation of stream macroinvertebrates in to functional feeding groups is a crucial factor in the study of leaf decomposition in a stream. Nevertheless, several authors reported difficulties in allocating macroinvertebrates to trophic groups many taxa are capable o f modifYing their diet an d consuming a wide range of available food sources, thus appearing to be generalists or opponunists (BouLTON & BooN 1991, PALMER et al. 1993). Shredders are reputed to feed directly on CPOM, thus hastening leaf disintegration, and they undoubtedly play an important role in leaf breakdown (STEWART & DAVIES 1989, STEWART 1992). However, changes in feeding behaviour occur during life cycles. Therefore, the small larvae of shredders (particularly Plecoptera in first life stages), being nor yet effective in leaf shredding, should be considered as collectors (CASAS 1996). Leptophlebiidae are another questionable point several authors consider them to be collectors (IMBERT & Pozo 1989, CHAUVET er al. 1993), but according to others they are likely to directly affect leaf decomposition (RoWE et al. 1996). The structure and composition of the macroinvertebrate community may be altered by the presence of impoundments. Sedimenrarion of particulare organic matter within the reservoir, f!ow regularion and modified thermal regimes alter habitat features and food availability for benrhic macroinvertebrates downstream of rhe impoundment (PErrs 1984). The aim of this study was to analyse leaf decomposirion and macroinvertebrate colonization in rwo regulared streams. Hence three quesrions were addressed: l. Can an impoundmenr modifY leaf decomposition and rhe community srrucrure of leaf substratum? 2. Are shredders rhe only functional group affecring leaf breakdown? 3. How much does seasonality influence leaf decomposition processes in similar leaf-packs? Study area

Leaf colonization by aquatic macrobenthos: a comparison between Alpine and Apennine streams

Headwaters are characterized by heterotrophic metabolism, mainly supported by leaf litter input from riparian vegetation (BENFIELD 1997, PosT & eRuz 1977). A multispecific riparian vegetation is of great importance for the macrobenthic con:munity, because i t provides a continuous supply o f h1gh q_uality food throughout the year: autumnal leaf lmer input follows a specific temporal sequence, according to abscission periods, and different species have different decomposition rates (PETERSEN & euMMINS 1974; WEBSTER & BENFIELD 1986). In spring, additional leaf litter input is sometimes represented by green leaves lost from trees during storms (LEFF & McARTHUR 1990) or by partially decomposed leaves transported by run-off (MERRITT & LAwsoN 1992). Naturalleaf-packs are thus usually multispecific in contrast with artificialleaf-packs, often used in studies in lotic environments (eAsAs 1997, VouGHT & LANNERSTAD 2000). It is likely that a naturally heterogeneous pack supports a more abundant and varied colonizing fauna than monospecific packs (BOVLTON & BooN 1991). Several studies have been carried out with artificialleaf-packs, but the environmental variables that affect the structure of the benthic community in naturalleaf-packs are still not well known. The present survey was carried out within the framework of the European eommission project ERMAS I! and with the aim of studying the influence of riparian vegetation and geographical factors on colonization of the in-stream leaves.