Diatoms in the SW Piedmont

Studi Trent. Sci. Nat., 86 (2009): 119-126 ISSN 2035-7699119 © Museo Tridentino di Scienze Naturali, Trento 2009 Atti XVIII Convegno Gadio 2008: Un mondo che cambia: successioni ecologiche, invasioni biologiche ed alterazioni antropiche Sessione 7 - Comunicazione orale: Trasformazioni, impatti e strumenti di gestione in ambienti acquatici 2

Diatoms in the SW Piedmont (N-Italy) biological river monitoring network, with particular attention to the possible expansion of distribution of the “invasive” species Didymosphenia geminata (Lyngbye) Schmidt in Italy

Maurizio Battegazzore1*, Lucio Lucadamo2 & Luana Gallo2

1 ARPA - Agenzia Regionale per la Protezione Ambientale del Piemonte, Via Vecchia di B.S. Dalmazzo 11, 12100 Cuneo, Italy 2 University of Calabria, Department of Ecology, Via Ponte Pietro Bucci, 87036 Arcavacata di Rende (CS), Italy * Corresponding author e-mail: [email protected]

SUMMARY - Diatoms in the SW Piedmont (N-Italy) biologcal river monitoring network, with particular attention to the “invasive” species Didymosphenia geminata (Lyngbye) Schmidt - Diatoms were sampled in March 2007 in 39 stations of the SW sector of the Piedmont macroinvertebrate-based biological quality monitoring network situated along 14 watercourses, among which are important rivers such as the R.Po and the R.Tanaro. D. geminata – considered to be invasive in various parts of the world - was found in 13 watercourses and in 25 stations (93% and 64% of the total, respectively). Abundances of D. geminata were generally quite low, but in 6 stations reached 3% of the individuals of the community and a peak of 12% in one station. D. geminata abundance was not significantly correlated with altitude or with European diatom indices of water quality (EPI-D, IBD and TDI). Some degree of correlation was observed between the macroinvertebrate– based IBE index and the EPI-D index (r= 0.67) and between the same IBE index and D. geminata abundance (r= 0.41). This species results to be more widespread than expected and the hypothesis of an expansion of its distribution area in Italy is plausible, but its past presence in many of these watercourses cannot be excluded. The past data, in fact, are not sufficient to reach precise conclusions regarding present trends of geographical distribution and population densities in the studied area. However, the situation deserves to be monitored.

RIASSUNTO - Le diatomee nei punti della rete di monitoraggio biologica dei fiumi del Piemonte Sud-Occidentale, con particolare atten- zione alla specie “invasiva” Didymosphenia geminata (Lyngbye) Schmidt in Italia - Nel Marzo 2007 sono state campionate le comunità diatomiche in 39 stazioni del settore Sud-Occidentale della rete di monitoraggio basata sui macroinvertebrati bentonici, ubicate in 14 corsi d’acqua fra i quali i fiumi Po e Tanaro.D. geminata – specie considerata invasiva in diverse parti del mondo – è stata osservata in 13 corsi d’acqua e 25 stazioni (93% e 64% del totale, rispettivamente). Le abbondanze di D. geminata erano generalmente basse, tranne in 6 stazioni con oltre il 3% della comunità e un picco del 12% in una stazione. L’abbondanza di D. geminata non è risultata significativamente correlata con l’altitudine o con alcuni indici diatomici europei di qualità dell’acqua (EPI-D, IBD e TDI). Un certo grado di correlazione è stato osservato fra l’indice IBE basato sui macroinvertebrati bentonici e l’indice EPI-D (r= 0,67) e fra lo stesso IBE e l’abbondanza di D. geminata (r= 0,41). Questa specie è risultata più diffusa di quanto immaginato ed è plausibile ipotizzare che il suo areale in Italia sia in espansione, ma la sua presenza passata almeno in parte dei corsi d’acqua studiati non può essere esclusa. Al momento non è quindi possi- bile raggiungere conclusioni sulle attuali tendenze nella distribuzione geografica e nella densità di popolazione della specie; pare tuttavia opportuno monitorare l’evolversi della situazione.

Key words: river diatom communities, Didymosphenia geminata, invasive species Piedmont (Italy) Parole chiave: comunità diatomee, Didymosphenia geminata, specie invasive, Piemonte (Italia)

1. Introduction of water quality with other monitoring methods. D. geminata (Fig. 1) has the capacity to form persist- Work on diatoms has a tradition in Italy starting ant mats of organic material (thanks to the massive develop- from the XIX century (Meneghini 1846). In SW Piedmont, ment of extracellurar, polysaccharidic stalks) covering river the first known study of diatoms was by Castracane degli bottoms. In recent years, massive nuisance blooms and ex- Antelminelli (1888) who studied the diatoms of the sedi- pansion outside its known geographical range on the part of ments in the hot spring waters of Valdieri. D. geminata were reported in several countries around the Only very recently, other studies were undertaken world (Kilroy 2004; Spaulding & Elwell 2007). Battegaz- in limited portions of the Province of Cuneo (Battegazzore zore et al. (2007b) referred the occurrence of the species in et al. 2004; Battegazzore et al. 2007a). One of the aims of 2006 in the Province of Cuneo, in the Po and Varaita rivers. this study was to give a picture of the diatom communities, Therefore, in this study it was decided to extend the search never systematically studied before in all the main water- of this potentially invasive species, already found in 2 riv- courses of the Province, and to compare the results in terms ers, to all of the 14 main watercourses of the Province. 120 Battegazzore et al. Diatoms and Didymosphenia geminata in SW Piedmont

2. METHODS AND STUDY AREA

In Italy, large-scale monitoring of Diatoms for river quality evaluation has not been implemented yet. Therefore, it was decided to adopt the sampling locations used in the current macroinvertebrate monitoring network, including 39 stations situated between 150 e 1380 m a.s.l. along the 14 principal watercourses of the Province of Cuneo (see Fig. 2 and Tab. 1). Sampling was undertaken in the spring of 2007 according to the procedure described by Kelly et al. (1998). Samples were cleaned using 30% hydrogen peroxide and slides were mounted using Naphrax medium. Microscopic examination of about 400 diatom frustules for each sample, in LM at 1000 X, allowed taxonomic identification according to Krammer & Lange-Bertalot (1991-1997). On all diatom taxonomic lists, the indices TDI (Kelly & Whitton 1995), IBD (Prygiel & Coste 2000) and EPI-D (Dell’Uomo 2004) were calculated. On water samples taken in the same locations and period of time, analyses of the 12 variables: dissolved oxygen % saturation, nitrites, total nitrogen, soluble phosphates, sulphates, chloride, conductivity, total hardness, suspended solids, chemical oxygen demand, trivalent chromium and dissolved iron were undertaken according to the APAT (2003) methods. Moreover, in the same reaches of the watercourses the macroinvertebrate communities were sampled and the Indice Biotico Esteso (IBE) index was calculated, following the APAT (2003) procedure. Data were elaborated using PC-ORD software (McCune & Mefford 1999). Pearson’s correlation coefficient was calculated among all variables: the chemical variables listed previously, the TDI index, altitude and distance from source. On all data, verifica- Fig. 1 - Didymosphenia geminata observed under LM at 1000x. tion of normal distribution and a Monte Carlo test were The characteristic outline and large size make it very difficult to carried out. CCA (Canonical Correspondence Analysis) confound this species with other diatom taxa. Fig. 1 - Didymosphenia geminata osservata in microscopia ottica was adopted in order to link the taxonomical data to the a 1000x. La caratteristica forma e le grandi dimensioni la rendo- environmental variables. no difficilmente confondibile con altri taxa di diatomee.

Fig. 2 - Study area with watercourses and sampling stations represented by red dots (where D. geminata was sampled) and green dots (where D. geminata was not found). Fig. 2 - Area di studio con corsi d’acqua e stazioni di campionamento rappresentati con pallini rossi (località dove D. geminata era presente) e con pallini verdi (dove non è stata campionata). Studi Trent. Sci. Nat., 86 (2009): 119-126 121

1 P-PO4 El T3 DO G2 TDI T4 M1 T6 C2 Bo2 Bo3 G1 S5 Bo4Bo5 T2 S4 P2 N-NO 2 0 T1 M2 S6 -1,5 C1 S2 P1 1,5 P5 Be2 Pe Va1 1 Bo1 Be3 G Ve Cl Cond Va2 Be N tot. Cr S1 SO4 P4 Altit P3 Axis 2

A sse 2 Fe Fig. 3 - Biplot of the samples and environmental factors for the first two axes of the CCA. For symbol meanings see tables 1 and 2. Fig. 3 - Diagramma di ordinamen- Ti to dei campioni e dei fattori am- bientali per i primi due assi della CCA. Per i significati dei simboli -2,5 si vedano le tabelle 1 e 2. Asse 1 Axis 1

3. RESULTS CCA performed on the 13 environmental factors (DO, N-

NO2, Ntot., P-PO4, SO4, Cl, Cond., S.Sol., COD, Cr, Fe, A total of 190 diatom taxa were identified in the Altit. and TDI) and 39 samples is shown in Fig. 3. The present study. The most abundant taxa in the entire study variables COD and Suspended solids and also stations M3 were Achnanthidium minutissimum (Kutzing) Czarnecki, and T5 are not shown on the biplot because they are very Achnanthidium pyrenaicum (Hustedt) Kobayasi and Coc- close to the origin of the axes. The CCA accounted for coneis pediculus Ehrenberg. The most frequent ones about 20 % of total variability in tha taxonomic data, most (i.e. those present in the highest number of stations) were of which was asociated with the first axis. The variables A.minutissimum, Navicula tripunctata (O.F. Muller) Bory altitude, Chloride and the trophic index TDI were those and Diatoma vulgaris Bory. D. geminata was present in 13 best correlated with axis 1, while soluble phosphates and watercourses out of 14 (93%), in 25 points out of 39 (64%), iron were the factors best correlated with axis 2. Some as can be observed in table 1. In 6 stations out of 39 the samples (for ex. those from the Po and Tanaro rivers) along abundance of D. geminata was at least 3% of the commu- single watercourses were spread along a wide range of the nity and reached ca. 10% in 3 stations in different water- gradients of the two axes, others (such as the R. Bormida) courses. Peak abundance was about 12%. tended to form groups in restricted areas of the biplot, in- D. geminata abundance was not significantly cor- dicating more homogeneous environmental conditions. related with altitude (r= -0.09) or with the European diatom The station along the R. Tinella was the farthest indices of water quality EPI-D, IBD and TDI (r= 0.04, 0.04 from all others and strongly correlated with the variables and -0.001, respectively). Some degree of correlation was typically associated with pollution and eutrophic state; this observed between the macroinvertebrate–based IBE and is in agreement with the values of several environmental the EPI-D indices (r= 0.67) and between the same IBE and variables (Tabs. 1, 2) which indicate a state of deterioration D. geminata abundance (r= 0.41). in this station. In all stations where D. geminata was found, average values of water quality indices were IBE= 8.1 and EPI-D= 14.4 (both second out of five water quality class). The 3 sta- 4. DISCUSSION tions with the greatest abundances of D. geminata (> 9%), C1 on the R. Corsaglia, T5 on the R. Tanaro and M1 on the D. geminata resulted to be more widespread than R.Maira, showed IBE values in the third and fourth water expected in the study area. Due to the relatively high bio- quality class (out of five). Therefore, the species does not mass of individuals of D. geminata and of the stalks with tend to be present only in clean or high-altitude waters. which they are attached to the substrate, the relative abun- Values of environmental variables are given in ta- dances observed in this study represent an even stronger ble 2. Two variables were excluded from the CCA due dominance in terms of biomass than in terms of individuals to relatively high correlation with other variables: Hard- within the community. ness (strongly correlated with conductivity, r= 0,92), and Between the end of the XIX and the first decades of Distance from source (due to its relatively high correla- the XX century it was reported in Canada, Scandinavia and tion with altitude, r= -0,73). Preliminary screening with some mountainous areas of Europe (France, Spain, Swit- the Monte-Carlo test excluded the indices IBD, EPI-D and zerland) (Cleve 1894-1896). In the final decade of ‘900 IBE from successive multivariate analysis. The 36 most Krammer & Lange-Bertalot (1991-1997) reported a distri- common taxa used in the analysis were those present in bution covering the boreal and alpine regions of Europe, at least 10 samples. The biplot of the first two axes of the Asia and, to a lesser extent, N. America. 122 Battegazzore et al. Diatoms and Didymosphenia geminata in SW Piedmont a) geminata in sediments sampled at a depth of 400 m in Lake Como. Bonardi (1883) observed D. geminata in the Val d’Intelvi in Lombardy, near Switzerland. Forti (1900) observed D. geminata in bottom samples taken 7 years earlier by Giuseppe De Agostini in Lake Bertignano, a small pre-alpine lake in N.Piedmont. This appears to be the earliest finding ofD. geminata in Piedmont. At that time, most authors identified the species as Gom- phonema geminatum (Lyngbye) Agardh 1824. Monti (1904) observed D. geminata in samples taken in Lake Devero (N.Piedmont, not far from Switzerland). In 1925 Forni (in Giaj-Levra 1927) observed D. geminata in L. Maggiore, a very large alpine lake situated in N-Pied- mont, Lombardy and Switzerland. The known historical findings of D. geminata in NW Italy and neighbouring Swiss areas (Fig. 4a) can be b) compared with the area including river basins in which the species was observed in recent years in Italy (Fig.4b). Naturally, the representation of the single points of the recent findings of D. geminata would give a very scattered picture as compared to the area represented in the figure, which, like all distribution maps, necessarily represents a simplification of reality. However, at least in part, the historical sites seem to overlap the areas of recent findings, indicating that caution is needed in order to reach conclusions regarding a possible biological invasion of this species in Italy. Until Battegazzore et al. (2007b) published their work on the rivers Po and Varaita, no past data referred to D. geminata were available for the study area. In recent years, this species has also been reported in several river basins Fig. 4 - a) Location of historical records (XIX and beginning of of the alpine range where previous records are lacking (see XX centuries) of D. geminata in Italy and neighbouring areas of Schiftner & Blatterer, 2004, Beltrami et al., 2008a, Beltrami Switzerland. b) Area within Italy in which D. geminata is curren- et al. 2008b). Mobili (pers. comm..) observed D. geminata tly distributed as can be desumed from the more recent studies. in the Valle d’Aosta Region. Arnaud (pers. comm.) reported Fig. 4 - a) Località dei ritrovamenti storici di D. geminata (secoli the presence of D. geminata in recent years in the R. Oglio XIX e inizio XX) in Italia e nelle limitrofe aree della Svizzera. b) in Lombardy. Zorza et al. (2007) reported the species in the Area di attuale distribuzione in Italia di D. geminata desumibile R. Natisone, NE Italy. The only observation in central Italy, dagli studi più recenti. referred to the R. Tiber Appennine basin in the Umbria Re- gion, was made by Mancini et al. (2008). Regarding the preferences of D. geminata in terms of chemical variables, in table 3 the average values and stand- According to Spaulding & Elwell (2007), the present ard deviations of the 12 variables are given for all sampled distribution of the species has expanded to vast areas of stations and for the stations where D. geminata was present. N.America, Iceland and N. Zealand. Rather alarmingly, the The average values in the two cases do not appear to be sig- potential distribution of the species estimated using ecolog- nificantly different. The variables have different weights ical Niche models (McNyset & Julius 2006) covers almost as factors influencing the diatom communities (see CCA all of the temperate areas of both the northern and southern diagram, Fig. 3) but, within their range of variation, none hemispheres of the world. of them appear to explain the presence, absence or relative Regarding the question as to whether in Italy and abundance of D. geminata in the sampled stations. in particular in the study area, a biological invasion by D. In the present study, the modest or poor quality shown geminata is under way, it is necessary to examine all the by the macroinvertebrate-based IBE index in the stations existing appropriate literature including information on this with particularly high abundances of D. geminata could species in Italy, particularly in Piedmont and neighbouring be ascribed to the impact of the mats on macroinvertebrate areas. Lanzi (1882) observed D. geminata in L. Bracciano benthic communities, as described by Spaulding & Elwell near Rome (in De Toni & Levi 1886a, 1886b). Closer to (2007). However, nuisance blooms with mats of D. geminata Piedmont, Brun (1880) referred the species as present in determining complete coverage of the river bottom, as seen Courmayeur (Valle d’Aosta Region) and in alpine lakes in in other areas around the world, were not observed. There Switzerland, and precisely L. Geneva, Zermatt and Great are insufficient elements to affirm that a biological invasion St. Bernard. The latter two locations are very close to the is under way in the study area. Further investigation into the border with NW Italy (Region of Valle d’Aosta). In Lom- specific effects of the presence ofD. geminata on macroben- bardy (a Region bordering both with Piedmont and Swit- thic communities in the study area seems necessary. zerland), Castracane degli Antelminelli (1883) found D. Regarding the CCA, some samples along single wa- Studi Trent. Sci. Nat., 86 (2009): 119-126 123

Tab. 1 - Watercourses, station codes, distance from the source, altitude, n.of diatom species, % of individuals of D. geminata in the sample, various diatom-based water quality indices and the macroinvertebrate quality index IBE in March 2007. Tab. 1 - Corsi d’acqua, sigle delle stazioni di campionamento, distanza dalla sorgente, altitudine, n. di specie, % di individui di D. geminata nel campione, vari indici di qualità dei corsi d’acqua basati sulle diatomee e l’indice a base macrobentonica IBE riferiti al Marzo 2007.

River Station Distance from Altitude N. species % TDI IBD EPI-D IBE source (km) m a.s.l. D. geminata Belbo Be1 21.2 570 28 0.0 32.2 16.3 16 11.7 Belbo Be2 27.7 500 19 0.0 53.9 15.7 15.2 12.0 Belbo Be3 47.2 230 22 1.0 67.8 11.9 13.0 7.7 Tinella Ti 26.5 160 18 0.0 72.9 3.7 5.0 1.0 Ellero El 41.8 290 31 1.0 64.2 16.1 11.7 7.0 Grana G1 46.2 410 31 1.0 57.6 15.7 15.5 7.7 Grana G2 51.7 315 20 0.0 38.9 18.4 15.8 11.0 Po P1 5.3 1380 21 2.1 40.3 19.8 17.2 11.0 Po P2 23.0 460 24 0.0 38.3 19.7 16.6 11.0 Po P3 41.3 265 25 0.0 53.0 15.4 13.5 6.4 Po P4 48.0 260 34 0.0 62.1 15.1 11.1 8.0 Po P5 70.1 247 34 0.0 63.1 13.6 12.7 9.7 Stura S1 23.7 955 18 0.0 25.3 19.4 17.6 10.7 Stura S2 59.6 590 23 0.0 26.3 16.9 16.9 10.7 Stura S3 69.6 483 29 0.3 36.2 17.7 17.1 9.7 Stura S4 80.0 397 18 0.0 63.0 17.0 14.7 9.0 Stura S5 96.0 290 19 0.3 55.5 15.0 15.3 8.0 Stura S6 113.3 200 22 0.5 43.0 20.0 16.1 9.0 Corsaglia C1 30.2 413 36 11.6 43.3 17.0 15.9 7.0 Corsaglia C2 41.0 350 30 5.9 49.9 19.2 15.2 7.4 Varaita Va1 68.3 315 25 0.3 33.5 16.2 15.3 8.0 Varaita Va2 90.8 240 36 0.0 44.0 17.1 15.9 11.4 Tanaro T1 42.8 525 22 0.5 53.7 17.4 16.2 9.0 Tanaro T2 65.8 360 21 0.0 56.1 17.3 15.3 7.0 Tanaro T3 89.6 290 27 4.8 73.1 13.1 9.5 6.7 Tanaro T4 124.2 210 22 1.0 55.8 15.1 13.5 7.4 Tanaro T5 137.9 180 26 10.3 61.0 13.2 13.4 5.7 Tanaro T6 157.3 150 25 4.1 71.3 13.9 12.2 7.0 Pesio Pe 46.3 285 20 0.5 53.0 15.0 15.1 8.4 Vermenagna Ve 24.6 630 17 1.3 43.4 17.3 16.2 9.7 Maira M1 63.0 422 20 9.3 40.7 18.5 16.2 5.0 Maira M2 78.5 310 27 0.5 49.1 17.3 16.3 9.4 Maira M3 94.0 255 36 0.5 55.7 14.0 15.1 11.0 Gesso Ge 30.4 635 25 0.5 70.1 17.7 13.6 9.7 Bormida Bo1 46.4 397 33 0.8 54.6 15.1 14.0 7.7 Bormida Bo2 55.6 360 32 1.7 59.2 13.5 12.7 7.0 Bormida Bo3 60.0 354 31 0.8 66.4 13.5 11.5 9.0 Bormida Bo4 70.9 310 40 0.8 59.9 14.2 12.7 8.4 Bormida Bo5 86.9 250 32 0.0 59.5 13.2 12.6 8.0 124 Battegazzore et al. Diatoms and Didymosphenia geminata in SW Piedmont

Tab. 2 - Values of the 12 chemical variables in March 2007 samples. For the 6 variables used in the CCA (see § 2), values preceded by < were conventionally transformed into the average between 0 and the indicated value (e.g. < 5 was transformed into 2.5). Tab. 2 - Valori delle 12 variabili chimiche in campioni del Marzo 2007. Per le 6 variabili utilizzate ai fini dell’analisi CCA (vedi § 2), i valori preceduti da < sono stati convenzionalmente trasformati nella media fra 0 e il valore indicato (ad es. < 5 è stato trasformato in 2,5).

Station DO COD Ntot. Cl Cond. Hard. P-PO4 SO4 S.Sol. N-NO2 Cr Fe mg l-1 % mg l-1 mg l-1 mg l-1 μS cm-1 mg l-1 mg l-1 mg l-1 mg l-1 µg l-1 µg l-1 CaCO3 Be1 92 < 5 < 1.0 11.9 543 255 < 0.05 46.4 < 10 < 0.003 < 2 73 Be2 107 < 5 1.8 9.3 499 245 < 0.05 52.4 < 10 < 0.003 < 2 72 Be3 120 < 5 1.0 1.6 561 309 0.25 37.9 < 10 0.006 < 2 < 50 Ti 86 35 12.9 24.4 1043 426 0.69 240 22 0,09 < 2 301 El 110 < 5 2.6 10 293 144 0.18 18.5 < 10 0.058 < 2 < 50 G1 93 10 2.2 5.5 385 216 < 0.05 96.5 36 0.021 < 2 < 50 G2 94 < 5 6.4 9.1 575 323 < 0.05 59.7 < 10 0.005 2.1 < 50 P1 87 < 5 1.2 1.4 203 118 < 0.05 30.1 < 10 < 0.003 2.4 < 50 P2 104 < 5 1.4 1.6 173 100 < 0.05 28.2 < 10 < 0.003 2.3 < 50 P3 93 5 4.9 72.5 472 131 0.50 25.9 < 10 0.050 < 2 < 50 P4 108 < 5 4.2 14.9 269 137 0.10 22.8 < 10 0.029 2.8 < 50 P5 98 < 5 4.4 11.6 429 222 0.07 45.0 < 10 0.028 < 2 < 50 S1 90 < 5 < 1.0 4.3 367 191 < 0.05 112 < 10 < 0.003 < 2 < 50 S2 95 < 5 < 1.0 6.5 428 234 < 0.05 127 < 10 < 0.003 < 2 < 50 S3 99 < 5 < 1.0 7.6 415 211 < 0.05 117 < 10 < 0.003 < 2 < 50 S4 123 < 5 2.6 7.3 404 215 < 0.05 61.6 < 10 0.007 < 2 < 50 S5 100 < 5 4.4 9.2 428 228 < 0.05 60.5 < 10 0.040 < 2 < 50 S6 110 < 5 4.1 9.7 422 220 < 0.05 59.9 < 10 0.046 < 2 < 50 C1 97 < 5 < 1.0 3.4 189 100 < 0.05 8.1 < 10 0.066 < 2 < 50 C2 111 < 5 < 1.0 3.9 207 110 < 0.05 9.5 < 10 0.005 < 2 < 50 Va1 91 < 5 5.2 7.5 540 236 < 0.05 54.5 < 10 0.007 2.4 < 50 Va2 77 < 5 5.6 17.9 621 244 0.05 81.5 < 10 0.056 2.6 < 50 T1 117 7 < 1.0 8.3 225 114 < 0.05 15.4 < 10 0.003 < 2 < 50 T2 114 < 5 2.4 15.2 344 174 < 0.05 27.0 < 10 0.005 < 2 < 50 T3 106 < 5 2.5 10.1 303 145 0.17 19.6 < 10 0.050 < 2 < 50 T4 104 7 2.0 9.2 306 176 < 0.05 31.8 < 10 0.016 < 2 < 50 T5 112 7 3.8 11.9 430 237 < 0.05 68.0 < 10 0.031 < 2 < 50 T6 104 5 3.6 14.2 377 218 0.06 51.2 < 10 0.033 < 2 < 50 Pe 114 < 5 2.6 5.3 293 151 < 0.05 37.7 < 10 0.016 < 2 < 50 Ve 102 < 5 1.1 2.8 298 161 < 0.05 57.2 < 10 0.012 < 2 < 50 M1 88 < 5 2.2 5.1 537 344 < 0.05 137 < 10 < 0.003 < 2 < 50 M2 92 < 5 4.5 9.2 585 339 < 0.05 112 < 10 0.024 < 2 < 50 M3 88 < 5 6.7 12.4 610 331 0.06 76.1 < 10 0.089 2 < 50 Ge 101 8 1.0 16.2 363 197 < 0.05 63.4 < 10 0.014 < 2 < 50 Bo1 94 19 1.8 27.4 418 201 < 0.05 37.0 12 0.006 2.2 67 Bo2 95 < 5 1.5 27.7 432 201 < 0.05 43.3 < 10 0.007 < 2 < 50 Bo3 103 5 1.9 28.2 442 206 < 0.05 46.8 < 10 0.008 < 2 < 50 Bo4 101 < 5 1.5 23.8 410 189 < 0.05 47.6 < 10 0.008 < 2 < 50 Bo5 101 < 5 1.2 27.5 431 207 < 0.05 50.6 20 0.005 < 2 < 50 Studi Trent. Sci. Nat., 86 (2009): 119-126 125

Tab. 3 - Average values and standard deviation (s.d.) for chemical variables in all 39 stations and in the 25 stations where D. geminata was found. As for the CCA, here too values preceded by < were conventionally transformed into the average between 0 and the indicated value. Tab. 3 - Valori medi e deviazioni standard (s.d.) delle variabili chimiche in tutte le 39 stazioni e nelle 25 stazioni dove è stata ritrovata D. geminata. Come per l’analisi CCA, I valori originali preceduti da < sono stati convenzionalmente trasformati nella media fra 0 e il valore indicato.

Variable All stations Stations with D. geminata average s.d. average s.d. DO % 100.5 10.3 101.6 9.3 COD mg l-1 4.6 5.9 4.4 3.8 N tot. mg l-1 2.8 2.4 2.4 1.7 Cl mg l-1 13.0 12.4 10.9 8.0 Cond. μS cm-1 417.2 157.7 386.9 120.6

-1 Hard. mg l CaCO3 210.0 73.8 204.0 69.6

-1 P-PO4 mg l 0.07 0.13 0.05 0.06

-1 SO4 mg l 59.4 43.9 53.5 33.5 S.Sol. mg l-1 6.8 6.1 6.5 6.3

-1 N-NO2 mg l 0.022 0.025 0.023 0.023 Cr μS cm-1 1.3 0.6 1.2 0.5 Fe μS cm-1 35.6 45.3 26.7 8.4

tercourses were spread along a wide range of the gradients part of Piedmont and to other areas in Italy, but due to the of the two axes (for ex. the Po and Tanaro rivers), others scarcity of past diatom sampling in rivers it is also pos- grouped in limited areas, indicating more homogeneous en- sible that the species was present but simply not observed. vironmental conditions (for ex. the R. Bormida). Moreover, a certain degree of fluctuation in distribution and abundance is typical of most species and, within the known distribution area, in certain conditions, peaks of abundance 5. CONCLUSIONS can occur. However, there are elements that seem to indicate a certain expansion of distribution not only in South- In the present study, compared to existing litera- ern Piedmont, but to watercourses in sectors of the Alpine ture, the distribution of D. geminata resulted to be more and Appenine ranges and relative floodplains where past widespread than expected and not restricted to clean, low records are lacking. nutrient river reaches. Regarding the hypothesis of an in- Considering the worldwide alert in recent years vasion under way in the study area, it appears that in the (Blanco & Ector 2009), in the future it seems appropriate to last decades of the XIX century and the first decades of the undertake specific monitoring of this species in watercourses XX century D. geminata was observed mostly in lacustrine with records of its presence, including those in this study. samples from the Southern Alps, including N-Piedmont, Valle d’Aosta and Lombardy. Almost all of the historical observations of D. geminata in Italy are referred to lake REFERENCES samples, in contrast to recent data obtained from rivers. The historical lake samples, as far as it is possible to know, APAT, 2003 - Metodi analitici per le acque. Manuali e linee guida were prevalently bottom samples possibly including frus- 29, 1153 pp. tules dating from even earlier. In the historical period in Battegazzore M., Morisi A., Gallino B. & Fenoglio S., 2004 - En- question, more interest was placed on lacustrine rather than vironmental quality of Alpine springs in NW Italy using ben- on river environments, which explains the rarity of past thic Diatoms. Diatom Research, 19 (2): 149-165. data on D. geminata in rivers. Battegazzore M., Bianco L., Bona F., Falasco E., Fenoglio S., Mori- Although some diatom studies were undertaken si A., Shestani L. & Badino G., 2007a - Diatomee e qualità (Giaj-Levra 1927), no known observations of the species dei corsi d’acqua in tre aree alpine e prealpine ad altimetria e in question were made in S-Piedmont until very recently substrato geologico differente. In: Lencioni V. & Occhipinti (Battegazzore et al. 2007b). From the 1930s to very recent A. (a cura di) Atti XVII Convegno Gadio, 6-8 Maggio 2006, years there is a big gap of information, due to the apparent Cetraro. Studi Trent. Sci. Nat., Acta Biol., 83: 111-116. black-out of diatom studies in Piedmont and also in most of Battegazzore M., Mogna M., Gaggino A. & Morisi A., 2007b - Italy. Therefore, it is possible that in recent years the area La diatomea Didymosphenia geminata (Lyngbye) Schmidt of distribution of D. geminata has spread to the southern nel F. Po e nel T. Varaita. Invasione preoccupante causata da 126 Battegazzore et al. Diatoms and Didymosphenia geminata in SW Piedmont

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