Vegetation and Water of Some Spring-Wells of Po Valley (Northern Italy): Ecological Features and Management Proposals


 Spring-wells (lowland springs, “fontanili”) are elements of Po Valley (Northern Italy) with ecological and historical importance: they provide water at a relatively constant temperature, generating unique ecosystems dependent on the groundwater outflow. Despite their importance, they are endangered by degradation processes as the expansion of urban areas and/or the intensification of agriculture, very marked in Po Valley. This research describes four spring-wells of Po Valley from a botanical and ecological perspective through phytosociological relevés and different ecological indexes. Water chemical-physical features are also considered (pH, temperature and ammonium ion, nitrite, nitrate, orthophosphate, chloride and organic matters contents). Plant communities of the spring-well beds shows a low number of species (5.8 ± 2.9) but also no exotic species while the vegetation of the banks has a high number of species (32.4 ± 9.8) but several of them are exotic/ornamental, with a low ecological value of the Ecological Index of Maturity (EIM = 4.4 ± 1.5) indicating disturbances, however moderate compared to the surrounding corn fields (EIM = 0.002 ± 0.001). All the water samples has high ammonium content (>0.50 ppm), the water of the spring-well B results the most polluted and both algae and Callitriche obtusangula (rare native species) grow largely in it, while spring-well C has less phosphates and more nitrite and is marked by the abundance of Equisetum telmateia. Exotic but historically important species as Morus alba were considered in the discussion, where management proposals to protect and enhance the studied spring-wells and others with similar characteristics are discussed.


Introduction
Wetlands play an important role in providing ecosystem goods and services to human society. However, the neglection of their importance intensi ed their loss due to the widespread conversion of wetlands because of shortages of land that is suitable for agriculture and urban settlement (He et al, 2015). They are very often environments rich in species, local climate regulators as well as elements that enrich the landscape and the historical-cultural heritage of the territory in which they are located (Ramsar Convention Bureau 2001; Mitra et al. 2003). Although they provide important services, wetlands are declining faster than any other ecosystems (MEA 2005) and this phenomenon affects the whole Globe, in particular those territories where the expansion of urban areas and agricultural activities is more marked (Hu et al. 2017). In fact, recent studies estimated that at least 33% of global wetlands has been lost since 2009 (Hu et al. 2017) and 64-71% since the early 1900 (Davidson 2014), and that this loss is mainly due to land conversion as well as to climate change (Lin and Yu 2018).
The Po Valley (or Po Plain) is the largest plain in Italy and in southern Europe (47.800 km²). It is bordered to the north and west from the Alps, to the south from the Apennines and to the east from the Adriatic Sea. Today much of the territory of Po Valley is farmed according to intensive farming methods and occupied by large, urbanized areas that grew rapidly during the last century and are still in expansion.
Considering the geological, pedological and environmental characteristics, Po Valley is divided into two main areas: the "high plain" and the "low plain" (Martinis et al. 1976; Andreis 2002). The "high plain" is at the base of the slopes of the Alps and the Apennines (over 100-150 m a.s.l.) and is characterized by very permeable soils whose particles size consists mainly of coarse elements (stones, gravel, and sand). In the "high plain", rainwater penetrates the soil in depth until it reaches waterproof rocks/sediments on which it ows and then resurfaces at lower altitudes (100-80 m a.s.l.), giving rise to resurgences (Toniolo 1933;Minelli et al. 2002;De Luca et al. 2014). The resurgences are located along a large part of Po Valley forming a belt from west to east parallel to the foothills (about 800 km long and 25 km wide) which is known as the "resurgence belt" and which delimits the "high plain" from the "low plain" (Martinis et al. 1976;De Luca et al. 2014). The soils of the "low plain" have ner and impermeable particles (silt and clay) that allow the water to stagnate and generate swamps (covered by hygrophilous forests) which, however, were reclaimed by man (from the Roman age up to the last century) to promote agriculture (Frattini 2008;De Luca et al. 2014). Human work transformed the resurgences of Po Valley into springwells (lowland springs, "fontanili") (Corbetta 1969;De Luca et al. 2014), concentrating their points of emergence. The spring-wells were obtained by enlarging the natural valleys in the land, encouraging the water to surface, forming a more or less rounded "head", that can collect more springs. The water collected is channelled into a canal or "central axis" of the watercourse (Corbetta 1969 Balestrini et al. 2016Balestrini et al. , 2021. In 2018 the ANBI Association (Associazione Nazionale Boni che, Irrigazioni e Miglioramento Fondiario, https://www.anbi.it) and Lombardy Region nanced the "AcquaPluSS" project (https://www.anbilombardia.it/portfolio-items/progetto-acquapluss/) to preserve/improve and enhance the spring-wells of Lombardy. This project proposes a series of activities/work to be carried out in some areas of Po Valley including study, enhancement, and restoration of four spring-wells located in Brescia province (Lombardy) in the territory managed by the Oglio Mella Reclamation Consortium.
This research is part of the "AcquaPluSS" project and aims at analysing the vegetation (from a oristic and ecological point of view) of four spring-wells in the plain of the province of Brescia. In particular, phytosociological relevés of the vegetation of the "heads" of the spring-wells were carried out and a system of ecological indices (Taffetani and Rismondo 2009;Rismondo et al. 2011;Giupponi et al. 2015) was applied in order to highlight elements of biological value and evaluate the state of conservation/degradation of these environments. Furthermore, the chemical-physical characteristics of the waters from the spring-wells were analysed to assess their level of pollution and highlight any relationships with the presence/absence of hygrophilous plants. The results of the vegetation and water analyses were nally processed to provide good practices to the Oglio Mella Reclamation Consortium (and other territorial managers of environments with similar characteristics) useful to preserve, restore and enhance the vegetation of these wetlands.

Study areas
The four springs considered in this research are in Po Valley within the province of Brescia (Lombardy region, Italy) ( Table 1, Fig. 1). Some of them (A and C) are surrounded by maize elds (corn cultivated according to intensive farming techniques) while others (B and D) are in urban areas and are adjacent to houses/gardens and/or roads. At the edge of some spring-wells there are recreational areas where various exotic/ornamental species were planted such as: Eryobotrya japonica, Aesculus hippocastanum, Hibiscus spp., Rosa spp., Musa spp. Since 2012 the ordinary management work (cleaning the spring-well riverbed, cutting dangerous trees, etc.) of this spring-wells has been carried out by the Oglio Mella Reclamation Consortium.

Vegetation analysis
Data on the current vegetation of the four spring-wells were collected by performing 20 phytosociological relevés according to the method of Braun-Blanquet (1964) and using his conventional abundance/dominance scale (r, rare species in the relevé; +, coverage < 1%; 1, coverage 1-5%; 2, coverage 5-25%; 3, coverage 25-50%; 4, coverage 50-75%; 5, coverage 75-100%). In detail, 5 relevés for each spring-well "head" were performed: one in the bed of spring-well (zone I) and four in the banks/edges (zone II) ( Fig. 1). In addition to the relevés of the spring-well, 5 phytosociological relevés were carried out in the maize elds adjacent to the spring-well A and C in order to compare the vegetation of the springwell and of the most common farming system of Po Valley.
The relevés were performed during summer months (June-July) of 2020 and an area of 30 m 2 was studied for the vegetation of the banks/edges and that of the bed of spring-well, while for the maize elds  Table 2). The IE provides the percentage of exotic species of a plant community considering exotic species coverage compared to total coverage while IL gives the percentage of endemic species (Giupponi et al. 2015).

Water analysis
Three water samples of 1 L were collected in each spring-wells in three different months: May, July and September 2020. The water samples were collected at the "head" of the spring-wells after measuring the water temperature with a digital thermometer (Checktemp® 1 -HI98509 Hanna Instruments). The 12 water samples were stored in dark bottles placed in the laboratory at a temperature of 4°C until their chemical analysis. The ammonium ion, nitrite, nitrate, orthophosphate and chloride contents were evaluated for each water sample using a spectrophotometric method. In detail, the ammonium ion content in the water was assessed using Nessler's reagent while the nitrite was quanti ed using the Griess reagent (CNR-IRSA 2003; Kruse and Mellon 1953). The nitrate content of each water sample was obtained according to Tartari and Mosello (1997) while the water-soluble orthophosphate ion was determined in accordance with Menzel and Corwin (1965). The determination of chloride was carried out by the Mohr method (Vollenweider 1962). A digital pH meter (BASIC, Denver Instrument) was used to measure the pH of each water sample and the concentration of oxygen in the water (indicator of organic matters) was determined using permanganate value method (Kubel method) (Heukelekian et al. 1954). Each chemical analysis was performed in triplicate.
The results of the chemical-physical analyses of the water and the data of the relevés carried out in the riverbeds of the spring-wells were analysed used canonical correspondence analysis (CCA) to highlight the most important variables that differentiate the spring-wells and the presence/absence of species.
CCA was performed using "vegan" package of R (R Development Core Team 2015).

Flora and vegetation
During the study 141 species were identi ed ( Table S1). Most of them (73%) are perennial terrestrial plants (hemicriptophytes, phanerophytes, geophytes and nano-phanerophytes) while the therophytes (annual/ephemeral plants) are 26% of the biological spectrum (Fig. 2). The latter are mostly species of Stellarietea mediae phytosociological class, typical of urban/anthropic environments (such as: Anisantha sterilis, Hordeum murinum, Lamium purpureum and Avena fatua). The aquatic plants (hydrophytes), that are mainly located along the bed of the spring-wells, make up 1% of the ora list. 20% of the identi ed species are exotic (Fig. 2). Most of these are ornamental/garden plants not very common or rare in the natural environments of Lombardy (Nandina domestica, Spirea chamaedryfolia, Iris orientalis, Oxalis articulata etc.) but there are also naturalized and invasive species very common in northern Italy such as Robinia pseudoacacia, Morus alba, Ailanthus altissima, Ambrosia artemisiifolia and Erigeron canadensis.
No endemic species were identi ed while some uncommon or rare native species of Lombardy were found, such as Callitriche obtusangula (aquatic species presents in A, B and D spring-wells) (Fig. 2), Prunus domestica, Carex riparia, Poa palustris, Lemna minor and Helosciadium nodi orum.
The dendrogram resulting from the cluster analysis (Fig. 3) shows three groups (clusters) of relevés corresponding to the three different vegetation types present in the three zones were the relevés were carried out: I, hydrophilic vegetation of the bed of spring-wells: characterized by aquatic/helophytic species of Lemnetea monoris, Potametea pectinati and Phragmito australis-Magnocaricetea elatae phytosociological classes (Table S1) (Table S1); III, vegetation of maize elds: characterized by Zea mays and some cosmopolitan weeds including Cynodon dactylon and Sorghum halepense (Table S1).
DCA biplot (Fig. 3) con rms the results of the cluster analysis that does not show oristic differences among the banks/edges vegetation of the four spring-wells. indicates disturbances affecting this plant community. However, these disturbances are moderately low if compared to those affecting corn elds (III) where there is a dominant exotic species (Zea mays) and ruderal weeds able to survive in disturbed and/or degraded environments.
Water Table 3 shows the chemical-physical features of the spring-wells water. All the water samples have high (and similar) ammonium content, over the legal quality thresholds for groundwater. The water of the spring-well B results the most polluted. In fact, it has high concentration of orthophosphate and organic substance (concentration of oxygen due to the presence of organic oxidisable substance) in addition to the high concentration of ammonium. Moreover, the water of B has a higher concentration of nitrate but within the legal limit and coherent with the results in Balestrini et al. (2021). The oxygen concentration of water in spring-well B was over the threshold only in May (5.37 ppm) while the water of the spring-well C exceeded the threshold for nitrite only in September (0.70 ppm) and the water of the spring-well A had exceeded the threshold for orthophosphate only in July (1.18 ppm). The chloride and nitrate values of all spring-wells are below the quality thresholds for groundwater. The results returned by CCA are shown in Fig. 5. The biplot shows a main ecological gradient along the rst axis (CCA1) which explains most of the variance in the dataset. In particular, along the CCA1 ammonium and nitrite in water decrease while nitrate, orthophosphate and organic substance increase. The water of spring-well B is the most polluted and both algae (indicators of eutrophic water) and Callitriche obtusangula are abundantly present in it (Table S1). The same plants also grow in the bed of A and D spring-wells but with less coverage values (Table S1). Spring-well C differs from the others for water with less phosphates and more nitrite, moreover in its bed (and on its banks) Equisetum telmateia is abundant (Fig. 5, Table S1). Helosciadium nodi orum is also abundant in C but is present, with lesser coverage, also in A and D while it is absent in B. The spring-well A is characterized by some hygrophilous species that are little or not present in the other study sites, such as: Poa palustris, Hypericum tetrapterum, Phalaroides arundinacea and Lythrum salicaria. Agrostis stolonifera is the only species found in all the beds of the spring-wells considered in this research.  (Cavagnis and Orsini 1992). Also, the chloride content, also if far below the threshold, (250 ppm), resulted slightly higher (Table 3)

Vegetation and water
The oristic-vegetational results of the four spring-wells show signs of environmental degradation but also valuable elements that are common to all four study areas at various level. The high number and/or coverage of ruderal therophytes of Stellarietea mediae class living in the spring-wells banks/edges, and even more in the corn elds, is a clear sign of disturbance as suggested by the low EIM value (far lower than the maximum value of 9 related to a mature wood free from exotic species) (Fig. 4). Such disturbance is caused by human activities, more precisely it is due to the intensive management of the surrounding elds and to the presence of urban areas around the considered spring-wells. These wetlands are deeply in uenced by the adjacent highly disturbed areas as corn elds where IM and EIM values are extremely low (Fig. 4). that some exotic species (as white mulberry) can have if present in determined environments (agro-ecosystems). The limit of these indexes is to consider every exotic species as a degradation and disturbance element, aspect that could be overcome integrating these indexes or creating new ones able to consider the historical-cultural value of these kind of exotic species in the plant communities where they are present.
Beyond the ruderal spontaneous species and the exotic invasive/naturalized species that naturally colonized the banks of the spring-wells, ornamental (exotic) species planted out of controls by local inhabitants (oral communication) were detected. These species, although not invasive, contribute to the degradation of the spring-wells either from an ecological (they lower EIM values) and physiognomic/landscaping point of view and their presence suggests the necessity of involving the local community in outreach/formative activities (Schild 2016). This would empower people awareness on the value and biological, scenic, and cultural importance of spring-wells and to know the basic concepts of nature conservation.
Together with the ruderal and exotic species, the oristic analysis allowed the identi cation of native species typical of Po Valley wetlands, as the ones of Lemnetea minoris, Potametea pectinatii, Phragmito australis-Magnocaricetea elatae and Salici purpureae-Populetea nigrae phytosociological classes (Table  S1). These species present in areas I and II, represent the biological-naturalistic valuable element of the spring-well analysed. This applies particularly for spring-well A that is the richest in wetland species some of which found exclusively (such as: Carex riparia and Lythrum salicaria) and/or that have noteworthy coverage (such as: Poa palustris, Phalaroides arundinacea and Populus nigra) on the banks/edges of this speci c spring-well. Spring-well A could be then employed as "source" area where to collect plant material (seeds or other propagation organs) to employ in possible re-introduction/re-population or ecological restoration initiatives of this or nearby spring-wells banks/edges ("sink" areas).
The riverbed of the spring-wells (zone I), although it has much less species comparing to banks/edges, does not present exotic species, and in fact its EIM and IM values are higher comparing to the ones of banks/edges vegetation (Fig. 4). Such value is however far from the maximum EIM value (9) for the reason that in zone I, a series of biotic and abiotic disturbances more or less recent (among which the constant presence of running water and the excavation and cleaning initiatives of the riverbed and springwells) hamper the establishment of a soil layer able to host species of the mature forest typical of Po Valley. In zone I, additionally to the absence of exotic species, there are some species uncommon/rare in Lombardy and in general in Italy as Callitriche obtusangula. From the analysis of the chemical-phyisical features of spring-wells (Table 3) and from CCA (Fig. 5) it might seem that Callitriche obtusangula needs eutrophic waters with a high nitrate, phosphates, and organic substance concentration as in spring-well B in which Callitriche obtusanguala has interesting values of coverage and algae are abundant (Table S1; Fig. 1). Conversely, in waters poorer in phosphates, nitrate and organic substance, Callitriche obtusanguala is less abundant (as well as algae) till being totally absent in spring-well C, that is the one with the least eutrophic water and that presents the minor number of species (3) in the riverbed (Table  S1). The presence of Callitriche obtusangula in polluted waters is explained by being a nitrophilous and salt dependent species ("ss" Leuschner (2010). Hence its presence, associated to algal uncontrolled growth, it is to consider an indicator of slow running waters particularly rich in nutrients/pollutants (eutrophic waters). Equisetum telmateia abundance in the riverbed and riverbanks of spring-well C could be instead due to minor nutrient requirements comparing to Callitriche obtusangula and to the fact that this species is not salt tolerant (Ellenberg and Leuschner (2010); Landolt et al. 2010). This only partially explains the results of the research, since spring-well C waters have low nitrate, orthophosphate and organic substance content, but a high content in nitrite (0.29 ppm). So, tailor made studies would be necessary to understand if the presence of nitrite in the water (and/or in the soil) can be or not a factor able to favour Equisetum telmateia or if this species is instead favoured by the low concentration of nitrate, phosphate and organic substance.

Management proposals
Considering ). Once the young native trees/shrubs have taken seeds and after they created a dense shrubland, it will be possible to eliminate the highest exotic trees and the ones dangerous for people and goods ( Fig. 6). Passing the years, the young native trees and shrubs will go on growing and expanding, thus improving the oristic and ecological features of the spring-wells vegetation. At this stage the management operations of trees/shrubs would be limited to the removal of dead/unstable plants (Fig. 6) and to the vegetation destruction after landslides on the riverbanks (often very steep, Table S1) in extraordinary circumstances. The intervention with low-impact soil stabilization works as soil bioengineering based on plants (or parts thereof) as building materials in combination with dead materials (such as stones, steel, iron, timber, etc.) would be advisable (Bischetti et al. 2014).
While the control of exotic/ornamental trees/shrubs on the riverbanks represents an operation relatively easy, the removal of ruderal and exotic herbaceous species could be much more For what concerns the riverbeds of the spring-wells (zone I), given the absence of exotic species, possible interventions of re-introduction/re-colonization are the only actions to consider. In this zone, changes of the physical-chemical characteristics of the water and removing/upset the mud layer of the riverbed where hydrophytes as Callitriche obtusangula can root are to avoid. While the mechanic disturbance of the spring-well riverbeds is an action relatively easy to control as it is mainly attributable to human cleaning intervention, controlling the chemical-physical water and mud features is more di cult as they depend on both climatic and land use factors (Kløve et al. 2014;Balestrini et al. 2021). In the case study the high nitrogen content (in particular ammonium and nitrite), phosphates and organic substance is reasonably ascribable to the use of frequently employed intensive agriculture products (as ammonium nitrate) or possible industrial/urban discharges. Considering the di culties of depurating groundwaters (Balestrini et al. 2008(Balestrini et al. , 2018, this issue could be at least reduced identifying and stopping possible uncontrolled spills of discharge water in the spring-wells or nearby areas, and/or limiting the use of polluting chemicals in the elds adjacent the study areas. This last action could be facilitated by instituting one or more protected areas (as local park of supra-municipal interest -PLIS) able to protect spring-wells creating also buffer areas where only low-input agricultural techniques (as organic agriculture) can be employed. If land managers want to start the depuration and/or protect spring-well groundwaters against pollution in accordance with the European directive (EC 2006), the trade-off showed in this research will be to take into consideration: polluted/eutrophic waters favour the growth (and conservation) of Callitriche obtusangula while oligotrophic waters limit this rare species. In this case, a situation of compromise would seem ideal, meaning waters moderately eutrophic (with nutrients/pollutants values possibly under the legal threshold) that however allow the growth of The study area where the four spring-wells are located (a) and the three zones where the phytosociological relevés were carried out (b): I, bed of the spring-well; II, banks and edges; III, maize elds close to the spring-well. The code of the spring-wells (A, B, C and D) is the same reported in Table 1 Figure 2 Biological spectrum of spring-wells ora (a), percentage of exotic and native species (b) and abundance de nition of the species found in the spring-wells referring to Lombardy region according to Martini et al. (2012) (c). The photographs show Callitriche obtusangula (rare native species) (d) and Oxalis articulata (uncommon exotic species) (e). Key: G, geophytes; T, therophytes; H, hemicryptophytes; P, phanerophytes; NP, nano-phanerophytes; I, hydrophytes; RR, very rare in Lombardy; R, rare; U, uncommon; C, common; CC, very common   Scheme of the work to carry out over ten years to improve the ecological characteristics of the vegetation (trees and shrubs) of the spring-wells banks/edges Supplementary Files