Studies on Small Mountain Lakes in the Val Grande National Park (Central Alps, Italy)

Studi Trent. Sci. Nat., Acta Biol., 82 (2005): 43-54 ISSN 0392-0542 © Museo Tridentino di Scienze Naturali, Trento 2006

Studies on small mountain lakes in the Val Grande National Park (Central Alps, Italy)

Angela BOGGERO*, Aldo Marchetto, Marina Manca, Rosario Mosello & Gabriele A. Tartari

CNR Institute of Ecosystem Study (ISE), Largo V. Tonolli 50, I-28922 Verbania Pallanza (Italy) *Corresponding author e-mail: [email protected]

SUMMARY - Studies on small mountain lakes in the Val Grande National Park (Central Alps, Italy) - Three small mountain lakes, located at 1909-2109 m a.s.l. in the Val Grande National Park, were analysed for water chemistry, invertebrate benthic fauna, zooplankton and diatoms. The study sites receive no direct anthropogenic pollution, but they are subject to long-range transport of atmospheric pollutants, e.g. in the form of acid deposition. �Water�� chemistry was compared with previous data dating back to 1987. ��The low buffer capacity of the ponds, leading to acid pulses during snowmelt and low pH in the most sensitive of the waterbodies, is reflected in the macroinvertebrate fauna, which are poor in acid-sensitive taxa, and the zooplanktonic and algal communities, dominated by species typical of acidic water or tolerant of extreme conditions. ��Macrobenthos assemblage composition is also controlled by the presence of an outlet, which should be regarded as a key feature in the conservation of these sites.

RIASSUNTO - Studi su alcuni piccoli laghi di montagna del Parco Nazionale Val Grande (Alpi Centrali, Italia) - All’interno del Parco Nazionale Val Grande, abbiamo studiato la chimica, il macrobentos, lo zooplancton e le diatomee epilitiche di tre pozze e laghetti. Situati a un’altitudine di 1909-2109 m s.l.m, essi non sono soggetti ad alcun disturbo antropico diretto, ma ricevono gli inquinanti trasportati a lunga distanza dalla circolazione atmosferica, in particolare deposizioni acide. La composizione chimica delle loro acque è stata confrontata con quella rilevata in una precedente campagna nel 1987. La loro bassa capacità tampone li rende soggetti a bruschi incrementi di acidità nel corso dell’anno, come per esempio durante il disgelo. Questi impulsi, e il pH relativamente basso di una delle pozze, influenzano negativamente la comunità macrobentonica povera di specie acido-sensibili, lo zooplancton e le diatomee, dominati entrambi da specie tipiche di acque acide o note per la grande ampiezza della loro nicchia ecologica. La comunità macrobentonica è anche condizionata dalla presenza o assenza di un emissario: per questo occorre tener presente l’importanza del mantenimento del regime idraulico delle pozze di alta montagna nel corso della stesura di piani di conservazione ambientale.

Key words: mountain lakes, chemistry, macroinvertebrates, zooplankton, diatoms, Val Grande Parole chiave: laghi alpini, chimica, macroinvertebrati, zooplancton, diatomee, Val Grande

1. INTRODUCTION The Val Grande National Park is rich in running water, but hosts only a few small headwater lakes and Remote mountain lakes, situated above or beyond ponds. This paper focuses on three small lakes evalu- the tree-line, have great ecological and environmen- ating their sensitivity to acid deposition, and the eco- tal value: they support unique plant and animal com- logical status of their water and biota, with a view to munities, are the headwater catchments for water sup- their correct management and conservation. plies and are excellent sensors of environmental change for entire mountain environments. Although they are generally perceived to be in pristine condition, previ- 2. SITES ous studies have shown that in the Alps they are threat- ened by acid deposition and nitrogen enrichment (Mo- The three largest ponds (Tab. 1), located at 1909- sello et al. 1991), by the deposition of persistent or- 2109 m a.s.l. close to the northern border of the Val ganic pollutants (POPs) and trace metals (Carrera et Grande National Park, were sampled three times in al. 2002), and that they are very sensitive to climate 2000 (at the end of June, July and September) and once change (Psenner & Schmidt 1992). in June 2001. They are small (< 0.1 ha), shallow (less 44 Boggero et al. Small mountain lakes in Val Grande

Tab. 1 - Location of the study sites. Tab. 1 - Coordinate dei laghi studiati. Longitude E Latitude N Altitude (m a.s.l.) Lake Geccio (LG) 8° 25.150' 46° 5.750' 2109 Lake Marmo (LM) 8° 28.805' 46° 3.800' 1965 Scaredi pond (PS) 8° 28.416' 46° 3.676' 1909 than 2-m deep) and, apart from L. Geccio, do not have Axioplan microscope and identified to species level a permanent outlet. They were ice covered from No- following the nomenclature of Krammer & Lange- vember 2000 to May 2001. Bertalot (1986-91) and Krammer (2000).

3. METHODS 4. RESULTS

Water samples were collected at the surface, clo- 4.1. Hydrochemistry se to the outlet and analysed for pH, conductivity at + 20 °C, alkalinity (acidimetric titration), NH4 , total N The chemical composition of the water of the stu- (TN), reactive P (RP), total P (TP), reactive Si (RSi) dy sites is reported in table 2. Ionic content is very low, (spectrophotometry), main cations (Ca++, Mg++, Na+, and conductivity values range between 7 and 30 µS cm-1. + = - - K ) and anions (SO4 , NO3 , Cl ) (ion chromatography). Nitrate and sulphate, deriving from acid deposition, are Details of the analytical methods are reported by Tar- the main anions, while rock weathering products (Ca, tari & Mosello (1997). Si and bicarbonate, maesaured as alkalinity) are pre- Semi-quantitative benthos samples were taken by sent in increasing concentration from Scaredi pond, to kicking the substrate �(�F��rost et al. 1971; Storey et al. L. Geccio to L. Marmo. 1991). The small Scaredi pond (PS) was sampled at The study sites share a low ionic content, but they one station only, while lakes Marmo (LM) and Geccio differ in their acid neutralising capacity. Thanks to the (LG), which have respectively a temporal and a perma- presence of a marble vein in its catchment, L. Marmo nent outlet, were sampled along the littoral in the main has sufficient alkalinity (0.13-0.16 meq l-1) to stabili- basin and in the outlet. Samples were also taken from ze the pH of its water at 6.5-6.7 units. In contrast, the a pool in L. Geccio downstream of a landslide which alkalinity of L. Geccio is lower 0.06-0.03 meq l-1, and had fallen into the lake. the lake pH drifts during summer from 6.2 to 6.6 units. Field collection was performed with a long-handlet Finally, the Scaredi pond is totally unbuffered and its net (225�� µ�m�� mesh), each collection lasting for 2-3�� min- pH is clearly acid, at values of around 5, one of the utes. The samples were fixed in 80% alcohol and sieved lowest measured in the Alps. through a net in the laboratory (same mesh size as the As regard algal nutrients, the concentration of pho- sampling net). The organisms were removed from the sphorus is very low, while nitrogen and silica, deriving sediment and put under a stereo microscope (Zeiss), respectively from atmospheric depositions and from sorted in the main families and identified to genus or rock weathering, show higher concentrations. In lakes species level, when possible. The�� Raddum Acidifica- Geccio and Marmo, nitrogen is almost present as ni- tion Index (Raddum & Fjellheim 1984; Raddum et al. trate, while ammonium and organic nitrogen are also 1988; Fjellheim & Raddum 1990) was used to estab- present in the smaller Scaredi pond. In this pond, the lish the level of alteration of the benthic macrofauna low pH probably prevents the complete microbial oxi- in the lakes. dation of ammonium to nitrate. No specific sample was collected for zooplankton analysis; the samples for the macrobenthos were 4.2. Benthic fauna used, because in shallow mountain lakes during day- time zooplankton is mainly located on the bottom, The benthic fauna (4232 individuals collected) where it is less subject to excessive light and UV ra- comprises 74 taxa, 62 of which are insects and 12 diation. non-insects (Tab. 3, Appendix 1). Twenty-four taxa Diatom samples were collected by brushing small are exclusive to littorals and 18 to running waters, and stones, fixed in Lugol’s iodine solution and mount- 31 taxa are common to both habitats. Twenty taxa are ed in Naphrax. Diatoms were observed using a Zeiss common to 2 lakes, and 5 taxa to all of them. Regar- Studi Trent. Sci. Nat., Acta Biol., 82 (2005): 43-54 45

Tab. 2 - Chemical composition of the water of the study sites. Dep.= deposition chemistry at Lunecco, volume weighted mean for the year 2000. Tab. 2 - Composizione chimica delle acque dei laghi studiati. Dep.= composizione chimica delle deposizioni atmosferiche a Lunecco, concentrazioni medie ponderate sui volumi per l’anno 2000. Variable L. Geccio L. Marmo Scaredi pond Dep. 27.06 26.07 27.09 29.06 27.07 26.09 18.06 29.06 27.07 26.09 18.06 Date 2000 2000 2000 2000 2000 2000 2000 2001 2000 2000 2000 2001 pH 6.66 6.21 6.62 6.74 6.51 6.60 6.63 4.98 5.07 4.97 5.21 4.92 Cond. µS cm-1 16.2 11.95 18.71 28.1 25.0 29.5 21.3 12.3 9.0 12.9 7.1 15.5 Alk. meq l-1 0.06 0.03 0.06 0.16 0.13 0.17 0.12 0 0 0 0.01 0.02 Cl- mg l-1 0.16 0.16 0.174 0.25 0.26 0.27 0.06 0.28 0.24 0.37 0.13 0.29 = -1 SO4 mg l 2.91 1.95 3.09 4.00 3.02 3.48 1.10 3.09 1.36 2.14 0.85 1.70 - -1 NO3 mg N l 0.35 0.36 0.50 0.31 0.56 0.56 0.18 0.03 0.19 0.42 0.25 0.47 + -1 NH4 mg N l 0.01 0.01 0.01 0.02 0 0 0.01 0.01 0.04 0.15 0.16 0.53 Ca mg l-1 1.58 1.18 2.01 4.22 3.53 4.74 2.57 0.80 0.44 0.71 0.26 0.59 Mg mg l-1 0.33 0.22 0.35 0.21 0.19 0.20 0.14 0.11 0.07 0.11 0.03 0.05 Na mg l-1 0.50 0.35 0.47 0.49 0.51 0.50 0.35 0.27 0.18 0.28 0.10 0.20 K mg l-1 0.35 0.27 0.35 0.35 0.39 0.45 0.33 0.13 0.19 0.19 0.07 0.12 RP mg l-1 0.001 0.001 0.001 0.004 0 0.001 0.002 0.001 0.001 0.002 0.005 0.003 TP mg l-1 0.005 0.008 0.003 0.006 0.007 0.002 0.002 0.017 0.010 0.009 0.004 - TN mg l-1 0.35 - 0.52 0.50 - 0.60 0.58 0.26 - 0.75 0.48 - RSi mg l-1 1.34 0.99 1.36 0.42 1.14 1.22 0.98 0.32 0.29 0.26 0.19 - ding running waters, 7 taxa are common to both outlets li)), while Scaredi pond shows a greater distribution of and 13 exclusive to the outlet of L. Geccio. water boatmen (≈5%). Caddis flies were present with percentages of around 4.2.1. Lake littorals 4% in L. Geccio (mainly Allogamus sp.) and Scaredi pond (Limnephilus coenosus (Curtis)), while Hemiptera Lake littorals represent the richest habitats in ter- Heteroptera (with Arctocorisa carinata (Sahlberg)) are ms of number of individuals, with insects as the best lower than 3% in L. Marmo. A few individuals of lee- represented class (more than 90% of the whole com- ches (Erpobdella testacea (Sav.)) and mussels (P. caser- munity). tanum) are also present in L. Geccio and a few dragon- Among the insects, chironomids are the most repre- flies Aeschna( cyanea (Müller)) in Scaredi pond. sented group along the littoral (Tab. 3) forming more The number of taxa in the littoral area is 21, 28 and than 70% of the community of the three lakes. Subfa- 32 for Scaredi pond, lakes Geccio and Marmo (Tab. 3), mily Chironominae tribe Tanytarsini prevails in Scare- respectively, corresponding to 1107, 1277, and 757 indi pond and L. Geccio, representing more than 65% of dividuals. Insects provide in all cases the highest num- the chironomids, and they co-dominate with Tanypodi- ber of taxa (20/21, 18/28 and 26/32, Appendix 1), es- nae in L. Marmo (both higher than 40%). Tanypodinae pecially in Scaredi pond where the lowest species num- are second in importance in Scaredi pond (16%) and ber was observed. L. Geccio (21%), while Orthocladiinae represent less The taxa common to the three lakes belong to the than 15% of the chironomids in all the studied lakes. family Enchytraeidae and, among chironomids, to the The tribe Chironomini (subfamily Chironominae) is Tanypodinae Macropelopia nebulosa gr., the Ortho- present in low numbers (5-9%) only in L. Marmo and cladiinae Heterotrissocladius marcidus (Walker), Li- Scaredi pond. Prodiamesinae are represented by only mnophyes sp., and the Chironominae Paratanytarsus one individual in L. Geccio. laccophilus gr., which is considered the most wide- Oligochaetes are the second best represented class spread. The most abundant taxa are the chironomids in the two lakes (Tab. 3), with Enchytraeidae as the Paratanytarsus laccophilus gr. (PS), Procladius (Ho- most widespread family (percentages of around 9% lotanypus) sp. (LM) and Paratanytarsus austriacus gr. L. Geccio and ≈3% in L. Marmo). They codominate (LG), constituting more than 40% of the total fauna in in L. Marmo with mussels (Pisidium casertanum (Po- each of the three lakes studied. 46 Boggero et al. Small mountain lakes in Val Grande

Tab. 3 - Percentages of the main taxa and of the main chironomid families per lake and per habitat. Tab. 3 - Abbondanze relative (%) dei principali taxa e delle principali famiglie di chironomidi suddivise per lago e ambiente di studio.

LAKE LITTORALS OUTLETS Taxa Geccio Marmo Scaredi Taxa Geccio Marmo Plecoptera 0% 0% 1% Plecoptera 15% 0% Trichoptera 6% 0% 2% Trichoptera 5% 0% Coleoptera 5% 0% 0% Coleoptera 0% 1% Dipt. Chironomidae 84% 90% 79% Dipt. Chironomidae 57% 90% Oligochaeta 2% 5% 14% Oligochaeta 10% 8% Others 3% 4% 4% Others 12% 2% Total No. individuals 1277 757 1107 Total No. individuals 851 529

Diptera - Chironomidae Diptera - Chironomidae Tanypodinae 15% 42% 14% Tanypodinae 3% 28% Orthocladiinae 1% 10% 10% Orthocladiinae 92% 55% Chironomini 14% 4% 0% Chironomini 0% 1% Tanytarsini 70% 44% 76% Tanytarsini 5% 16% Diamesinae 1% 0% Total No. Chironomidae 1062 913 641 Total No. Chironomidae 486 474 No. of taxa (lake+outlet) 47 36 21 No. of taxa in the outlet 19 4

4.2.2. Outlets cio), the outlets present the same dominant species as are found along the littoral. Of the three lakes under investigation, Scaredi Stoneflies Nemourella( pictetii (Klapalek)) (Tab. 3), pond is a seepage lake, while lakes Geccio and Mar- followed by black flies Cnetha( latipes (Meigen)) and mo have a permanent and a temporal outlet, respec- caddis flies Plectrocnemia( conspersa (Curtis)) are pre- tively. sent in considerable quantities in the outlet of L. Gec- A total of 1091 individuals (529 in L. Marmo and cio, while they are rare in that of L. Marmo. Oligochae- 851 in L. Geccio) were registered in both outlets (Tab. tes (mainly represented by Nais elinguis/variabilis) 3), distributed among 46 taxa, 21 in L. Marmo and are the second best distributed group in both environ 34 in L. Geccio. Insects are again the most abundant ments, constituting 8% (L. Marmo) and 10% (L. Gec- and most represented group, with more than 400 indi- cio) of the community. Triclads (Crenobia alpina (Da- viduals and 15 taxa in each outlet, representing 91% na)) are present only in the outlet of L. Geccio, while (outlet of L. Marmo) and 84% (outlet of L. Geccio) occasional mussels were found at the outlet of L. Mar- of the entire community. Non-insect groups form 9% mo. Water mites and beetles are rare. and 16% (lakes Marmo and Geccio, respectively) of The total number of entities found is very different the community, with 47 and 135 individuals, and only in the three systems, from 21 in Scaredi pond to 47 in 5 taxa in each outlet. L. Geccio. However, the presence of an outlet, temporal Chironomids are well represented in both outlets in L. Marmo and permanent in L. Geccio, determines (Tab. 3), making up 90% (outlet of L. Marmo) and 57% a marked difference in species abundance in the two (outlet of L. Geccio) of the entire community. Ortho- lakes (Tab. 3). cladiinae are the best represented subfamily in both outlets, with up to 92% of the population in L. Geccio, 4.3. Zooplankton but only 55% in L. Marmo. Tanypodinae and Tanytar- sini are the other subfamilies found, but only in the A total of 7 taxa were found in the study lakes outlet of L. Marmo they are abundant (28% and 16%, (Tab. 4), 6 cladoceran and a copepod species. The lat- respectively). Apart from Tanypodinae, also represented ter was a cyclopid not identified at the species level, by Zavrelimyia sp., (L. Marmo), and from Orthocla- as it was a copepodite in the 3rd stage. The small pre- diinae, with Corynoneura lobata (Edwards) (L. Gec- sence of copepods may reflect the occasional nature Studi Trent. Sci. Nat., Acta Biol., 82 (2005): 43-54 47

Tab. 4 - Zooplankton taxa found in the study lakes. Tab. 4 - Elenco dei taxa zooplanctonici rinvenuti nei laghi studiati. L. Geccio L. Marmo Scaredi pond Cladocera Cladocera Cladocera Alona affinis Alona affinis Daphnia gr. longispina Alonella excisa Chydorus sphaericus Alona affinis Chydorus sphaericus Alona quadrangularis Chydorus sphaericus Alonella excisa Copepoda Copepoda Cyclops sp. (copepodites) Cyclops sp. (copepodites) of the samplings: more samplings would be required ts in atmospheric deposition in the area depends sub- to produce a more complete list of taxa, as various stantially on the distance of the sampling station from species quickly succeed one another during the short the Po Plain, while the effect of altitude is more limi- ice-free season. Furthermore, if sampling is perfor- ted (Della Lucia et al. 1996). The chemical composi- med close to the bottom sediments, the samples are tion of atmospheric deposition is dominated by ions of biased towards the cladocerans. For this reason, we anthropogenic origin (sulphates, nitrates and ammo- will focus on the presence rather than the absence of nium), which give to the deposition its acidity (pH = taxa in each lake. 4.4-4.9). The high ammonium concentration must be noted, as it contributes to buffering the acidity of at- 4.4. Diatoms mospheric depositions. However, in soils and waters the ammonium ion is Diatoms were sampled in L. Marmo and Scaredi quickly taken up by vegetation or undergoes microbial pond. In the former diatom assemblage was strongly oxidation to nitrate, producing further acidity. The po- dominated by Achnanthes minutissima, while A. mar- tential acidity of atmospheric depositions at Lunecco, ginulata, A. scotica, C. minuta, C. gracilis, Denticu- considering ammonium oxidation, corresponds to an la tenuis, Eunotia bilunaris, E. praerupta, E. tenella, average pH of approximately 4.0-4.2 units. Gomphonema angustatum and Navicula cf. gallica we- Differences in the chemical composition of the stu- re also found. In Scaredi pond the main species were dy lakes and atmospheric deposition are mainly due to Eunotia exigua and Achnanthes minutissima, and mi- weathering processes, which contribute base cations nor species were A. helvetica fo. minor, Gomphone- and alkalinity to the lake water. The rock weathering ma exiguum, Nitschia spp. and Pinnularia microstau- rate at Scaredi is very low and the chemical composition ron var. nonfasciata. of the pond is close to that of atmospheric deposition, while L. Marmo is characterized by a higher alkalinity because of the marble present in its catchment (Tab. 5. DISCUSSION 2). Some events carry alkaline dust of Saharan origin. In the watersheds alkaline dust and rock weathering 5.1. Hydrochemistry buffer the acidity of atmospheric deposition, but buffering is not complete in Scaredi pond, where free aci- The low pH values measured are due to the litholo- dity is still present. gical composition of the small watersheds and to the In the last 15 years, the acidity of atmospheric acidity of the atmospheric depositions. The wet air mas- deposition and sulphate concentration in the study area ses originating on the Mediterranean Sea cross the Po has decreased, due to the reductions in sulphur oxides Plain where they are enriched with pollutants before emissions in line with the international agreements for reaching the mountains of the Val Grande. Atmosphe- controlling pollution; nitrogen compounds have not ric deposition is not sampled directly in the study area, shown any significant trend. but at Lunecco, a few kilometres west of the study si- Not all the study lakes have responded to these trends. te. Deposition collected weekly at this station can be Although a continuous temporal series of analytical data considered representative of the study area, as a pre- does not exist, analyses carried out in 1987 can usefully vious study showed that the concentration of pollutan- be compared to the data collected in 2000 (Tab. 5). 48 Boggero et al. Small mountain lakes in Val Grande

Tab. 5 - Comparison of water chemical composition of the study sites in 1987 and 2000. Tab. 5 - Confronto tra la composizione chimica dei laghi nel 1987 e nel 2000.

Variable L. Geccio L. Marmo Scaredi pond Date 03.08.1987 2000 01.09.1987 2000 01.09.1987 2000 pH 5.46 6.2-6.7 6.7 6.5-6.7 4.65 4.97-5.07 Cond. µS cm-1 20.2 12.0-18.7 27.6 25.0-28.1 16.6 9.0-12.9 Alk. meq l-1 0.046 0.033-0.064 0.124 0.130-0.165 0 0 Cl- mg l-1 0.09 0.16-0.17 0.42 0.25-0.27 0.35 0.24-0.37 = -1 SO4 mg l 2.45 1.95-3.09 4.27 3.02-4.00 3.07 1.36-3.09 - -1 NO3 mg N l 0.71 0.35-0.50 0.74 0.31-0.56 0.22 0.03-0.42 + -1 NH4 mg N l 0.156 0.004-0.010 0.014 0-0.018 0.084 0.012-0.147 Ca mg l-1 1.78 1.18-2.01 4.5 3.53-4.74 0.72 0.44-0.80 Mg mg l-1 0.44 0.22-0.35 0.19 0.19-0.21 0.09 0.07-0.11 Na mg l-1 0.73 0.35-0.50 0.60 0.49-0.51 0.25 0.18-0.28 K mg l-1 0.62 0.27-0.35 0.55 0.35-0.45 0.16 0.13-0.19 RSi mg l-1 0.98 0.99-1.36 0.99 0.42-1.22 0.33 0.26-0.32

The main difference between the samples collected clude Macropelopia nebulosa gr. in L. Marmo and Za- in 1987 and in 2000 is clearly the increase in pH, both vrelimyia melanura gr. and Heterotrissocladius marci- in L. Geccio and Scaredi pond. Reduced acidity of at- dus gr. in L. Geccio. mospheric deposition from 4.7 to 5.0 allowed the alka- As shown by Wathne et al. (1995), altitude, espe- line buffer to recover in L. Geccio, leading to an evi- cially above 2000 m a.s.l., is one of the factors limiting dent improvement in lake pH from 5.5 to 6.2-6.7. Sca- benthic fauna composition. We found an increase in the redi pond closely follows the values found in atmo- number of species from 21 in Scaredi pond (1909 m) to spheric deposition, while the well-buffered L. Marmo 47 in L. Geccio (2109 m). However, Scaredi pond is a shows no change. tarn with a marked thermal excursion and very consi- In L. Geccio, with higher pH values, ammonium derable variations in the water level, drying up for short completely disappeared: in this lake the improvement periods, so that its biodiversity is lower than that of per- in the chemical characteristics of its water has allowed manent lakes (Williams 1996). The other lakes are dee- increased efficiency in the biological oxidation of am- per, with a more diversified littoral environment, with monium to nitrate. the result that the shore fauna has a different development and distribution. Moreover, the further enrichment 5.2. Benthic fauna of the community with purely orophilous species is due to the presence of a water course, which in the case Generally, high altitude lakes have a stenothermal of L. Geccio is permanent. The outlet of L. Marmo is fauna typical of cold water. Previous studies carried out temporal, and strictly depends to a high degree on the in the context of specific research projects on two hi- amount of precipitation. The composition of the fau- gh altitude lakes in the Ossola Valley confirm this fin- na found here is therefore more similar to the fauna of ding, a consequence of the extreme conditions of li- the littoral than to that of a real outlet. fe which restrict the development of benthic fauna to An analysis of the chironomids population structure a few months in the year (e.g. Boggero & Nocentini yields valuable information about the prevalent trophic 1994). The species found in these environments have conditions. The presence of Chironomus thummi gr. and a very wide geographical distribution, typical of al- C. plumosus gr., Einfeldia pagana gr. and Endochiro- pine regions where very few species are able to with- nomus dispar gr., which prefer littoral environmen- stand the extreme climatic conditions. Among the cad- ts with abundant vegetation, is an index of a medium/ dis flies, there are Allogamus sp., Plectrocnemia con- high trophic state, whereas H. marcidus gr., Tanytarsus spersa and Limnephilus coenosus. Stoneflies, which lugens gr. and, in general, most of the Tanytarsini are prefer cold and well-oxygenated water, are present in mainly distributed in oligo-mesotrophic water (lakes lakes Marmo and Geccio; water boatmen (A. carina- Marmo and Geccio) (Saether 1979; Nocentini 1985). ta) are present in L. Marmo. Chironomids found in- As regards the correlation between benthic fauna Studi Trent. Sci. Nat., Acta Biol., 82 (2005): 43-54 49 and lake water chemistry, the negative impact of low is more sensitive to physical-chemical changes; and pH, calcium and alkalinity values, in particular the mi- the shallower Scaredi pond, with abundant shoreli- nimum values measured at the ice melt, is the reason ne vegetation, and which may dry up for short perio- for the exclusive dominance of acid-tolerant species, ds, tending to have a higher trophic level and a poorer especially in Scaredi pond. The constant presence of fauna, but which is more tolerant of drastic changes in mussels in L. Marmo can be attributed to their habit the water chemistry. of living buried in soft, sandy sediment, which tends to protect them from sudden chemical drops. Following 5.3. Zooplankton Raddum’s scoring system, we found three sensitive species: one among the turbellarians (Crenobia alpina) with Juvenile specimens of Cyclops were recovered in a score of 0.5, one among the mussels (P. casertanum) Scaredi pond and in L. Marmo. It is not surprising to with a score of 0.25, and one among the chironomids find Cyclops in the acidic Scaredi pond, because it is (T. lugens gr.) with a score of 0.5. The first of these was widely reported as an acid tolerant taxon. It has diffe- found solely in the outlet of L. Geccio, while the other rent feeding behaviours in the course of its life cycle: two were present both in lakes Marmo and Geccio. Sca- a particle feeder (particles smaller than 18 µm) during redi pond presents only species tolerant of acidification. naupliar stages, it becomes a predator as an adult; co- On the basis of the scores assigned to the lakes and the pepodites are generally thought to prefer eggs, above mean values of all their respective sampling stations, L. all those of Daphnia, which are considered a food ne- Marmo scores 0.5, L. Geccio 0.17, and Scaredi pond, cessary to complete its development (Gliwicz 1994). with no acid-sensitive species, 0. The finding of a Daphnia ephippium in this pond The ratio between acid-sensitive entities and total suggests the classic succession from Cyclops to Daph- number of species highlights the low number of sen- nia already described in studies on small lakes of this sitive entities found in these lakes. Such low numbers type (Santer 1993): as the samples were collected in of sensitive species are typical of the Alps, which ha- July, they would not include Daphnia specimens of the ve been subject to the pollution of atmospheric depo- new generation, which usually appear during late sum- sition for many years now (Wathne et al. 1995). Our mer, but they did include small partenogenetic eggs observations are in agreement with the results of water (ephippia) laid in the previous autumn. chemical analysis: Scaredi pond, with alkalinity close In Scaredi pond, we also found Alona quadrangula- to zero and a pH of 5, is to be regarded as severely af- ris, a cladoceran known to be acid-tolerant, which lives fected. L. Geccio, with alkalinity close to 0.05 meq l-1 on plants feeding on epiphytic detritus particles (Tab. and a pH of around 6, is acid-sensitive, especially to 6). Another species of the same genus (Alona affinis) the acid shock at the ice melt. In contrast, L. Marmo, was found in the less acidic lakes Geccio and Marmo. with higher alkalinity and pH values, is a lake with low Similar results, with the same Alona species living in sensitivity to acidification. The three lakes in our stu- acidified and pristine lakes were obtained in a study of dy can therefore be divided into two groups: the dee- 15 high mountain lakes in the Alps (Manca & Armi- per lakes Geccio and Marmo, with clearer water, oli- raglio 2002). Finally, we found Chydorus sphaericus, go-mesotrophic, and scarce shoreline vegetation sup- a species well-known for its very wide ecological am- porting a more abundant and diversified fauna which plitude, in all three lakes.

Tab. 6 - Main trophic role of the zooplankton species found in the study lakes. Tab. 6 - Principale ruolo trofico delle specie di zooplancton riscontrate nei laghi oggetto di questo studio.

Taxon Lake Trophic role Daphnia gr. longispina Scaredi pond Macrofiltrator with very large feeding range Cyclops Scaredi pond, L. Geccio Juveniles up to copepodite III feeding on phytoplankton and fresh detritus. Older stages predators and feeling on eggs. Chydorus sphaericus Scaredi pond, Microfiltrator, feeding on detritus collected near the sediment. lakes Marmo and Geccio Alona quadrangularis Scaredi pond Microfiltrators, feedings on the detritus covering the plants on Alona affinis lakes Marmo and Geccio which they lives Alonella excisa Scaredi pond, L. Marmo 50 Boggero et al. Small mountain lakes in Val Grande

5.4. Diatoms Analyses of lake water and atmospheric depositions also show a high nitrogen load. These compounds Most of the species found in Scaredi pond are aci- might increase the trophic status of the vegetation, not dobiontic or acidophylic epilithic species, like Eunotia only in the study area, but in the entire territory of the exigua and Pinnularia microstauron var. nonfasciata Park, where they could favour the alteration of the ve- (= Pinnularia spec. 2 in Marchetto & Schmidt 1992), getal communities. Taking into account the presence with pH optima of around 5.8. The main exception is of a permanent outlet, the present hydraulic status of Achnanthes minutissima, a species normally conside- the lakes should be maintained, avoiding modifications red as typical of alkaline waters. However, this species in the outlet flow, in order to maintain a differentiated is also a very plastic species, able to grow in extreme macrobenthic community. environments such as metal polluted water. In difficult conditions it may also develop in acid waters (e.g. Rug- giu et al. 1998). In L. Marmo, the diatom community is ACKNOWLEDGMENTS composed of both acidophylic (Achnanthes marginula- ta, A. scotica, Eunotia spp.) and alkaliphylic (Denticu- The research presented here was funded by the la tenuis, Cymbella minuta and, with the previous re- Val Grande National Park, in the framework of the ported reserve, Achnanthes minutissima) species: this EU Inter-Reg II Programme “Concetto di paesaggio pattern is typical of lakes with intermediate and oscil- transfrontaliero quale sostegno per la creazione di una lating pH (Niederhauser 1993). Unlike the majority of rete di aree protette tra il Parco Nazionale Val Grande alkaline lakes in the Alps, these lakes did not contain (Italia) e l’area Centovalli-Collina di Maia-Lago Ver- any small Fragilaria spp. bano (Confederazione Elvetica)”. Thanks are due to Dr. E. Dumnicka (Institute of Na- ture Conservation - Polish Academy of Sciences, Po- land) and Dr. A. Di Sabatino (Dipartimento di Scien- 6. CONCLUSIONS ze Ambientali - Università de L’Aquila, Italy) for the taxonomical identification of oligochaetes and water The small lakes in the Val Grande National Park mites, respectively. are not affected by local pollution sources and accom- modate a relatively diversified benthic fauna and flora, considering the extreme climatic conditions that REFERENCES characterise high mountain lakes. As in many shallow alpine lakes, planktonic assemblages are poor, be- Boggero A. & Nocentini A.M., 1994 - Macrozoobentos di cause strong light intensity and high water transpa- un lago alpino d’alta quota (Lago Paione Superiore, Val rency affect phytoplankton development. The quali- Bognanco). Atti X Congr. A.I.O.L., Alassio, 4-6 Novembre ty of the benthic assemblages is strongly controlled 1992: 177-187. by physical and chemical factors, in particular by the Carrera G., Fernandez P., Grimalt J.O., Ventura M., Camarero presence of a permanent outlet and by water pH. The L., Catalan J., Nickus U., Thies H., & Psenner R., 2002 latter has been affected by the deposition of pollu- - Atmospheric deposition of organochlorine compounds tants transported from the plain towards the Alps. In to remote high mountain lakes of Europe. Environ. Sci. particular, the Scaredi pond is among the most acid Technol., 36: 2581-2588. lakes of the whole Alpine chain, because of the pe- Della Lucia M., Marchetto A., Mosello R. & Tartari culiar lithology of the area and its geographic posi- G.A.,1996 - Studies on a chemical gradient of atmos- tion, which exposes it to high amount of precipitation pheric deposition from the Po Valley to the Alps. Wat. and of acid loads. Air Soil Pollut., 87: 171-187. The acidity of its waters is reflected in the compo- Fjellheim A. & Raddum G.G., 1990 - Acid precipitation: biological monitoring of streams and lakes. Sci. Total sition of the benthic fauna, which does not include any Environ., 96: 57-66. sensitive species and has a smaller biodiversity. Acidi- Frost S., Huni A. & Kershaw W.E., 1971 - Evaluation of a fication is however regressing, because of the reduction kicking technique for sampling stream bottom fauna. of emissions following international agreements on the Can. J. Zool., 49: 167-183. control of atmospheric pollutants. Zooplanktonic and Gliwicz Z.M., 1994 - Retarded growth of cladoceran zoo- diatom communities are also strongly controlled by the plankton in the presence of a copepod predator. Oeco- extreme physical conditions and by the pH of the water, logia, 97: 458-461. as they are made up of species typical of acidic water Krammer K., 2000 - The genus Pinnularia. ��Gantner Verlag or known for their ecological amplitude. K.G., Königstein. Studi Trent. Sci. Nat., Acta Biol., 82 (2005): 43-54 51

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Appendix 1 - Macroinvertebrate taxonomical entities found in the study lakes. L= littoral, O= outlet, P= pond. Appendice 1 - Elenco dei taxa macrobentonici. L= litorale, O= emissario, P= pozza.

Taxa Geccio Marmo Scaredi TURBELLARIA Planariidae Crenobia alpina (Dana) P, O BIVALVIA Pisidiidae Pisidium casertanum (Poli) P L, O Planorbidae L OLIGOCHAETA Enchytraeidae L, P, O L, O L Lumbriculidae L, P, O L, O Naididae Nais elinguis/variabilis L, O L, O Tubificidae L, P HIRUDINEA Erpobdellidae Erpobdella testacea (Sav.) L, P HACARINA Hydryphantes sp. (Koch) P Lebertia (Hexalebertia) ��dubia (Thor) L L, O Sperchon cfr. glandulosus O Sperchon cfr. squamosus L INSECTA PLECOPTERA Nemouridae Nemourella pictetii (Klapalek) L, P, O Leuctridae O Leuctra sp. O ODONATA Aeschnidae Aeschna cyanea (Müller) L HEMIPTERA Corixidae L, O L Arctocorisa carinata (C. Sahlberg) L, O COLEOPTERA Dytiscidae P, O L Agabus sp. O Stictotarsus griseostriatus ��(De Geer) L Hydroporinae L, O L Helophoridae Helophorus (Atracthelophorus) arvernicus (Mulsant) L TRICHOPTERA Limnephilidae O L Allogamus sp. L, P, O Studi Trent. Sci. Nat., Acta Biol., 82 (2005): 43-54 53

(Appendix 1 - continued) (Appendice 1 - continua)

Taxa Geccio Marmo Scaredi Limnephilus spp. L Limnephilus coenosus (Curtis) L Phryganeidae Oligotricha striata (Linnaeus) L Polycentropodidae Plectrocnemia conspersa (Curtis) L, P, O DIPTERA Ceratopogonidae Heleinae L, P Culicidae L L Limoniidae Dicranota sp. O L Muscidae L Psychodidae Saraiella sp. O Sciaridae L Simuliidae Prosimulium latimucro (Enderlein) O Simulium (Nevermannia) vernum (Macquart) O Tipulidae Tipula sp. L Chironomidae Tanypodinae L, O Macropelopia nebulosa gr. P L, O L Procladius (Holotanypus) sp. L, O L Zavrelimyia spp. L, P, O L, O Diamesinae Pseudodiamesa nivosa (Nowicki) O Prodiamesinae Prodiamesa olivacea (Meigen) P Orthocladiinae Bryophenocladius sp. L Cardiocladius sp. O L Corynoneura lacustris (Edwards) L Corynoneura lobata (Edwards) L, P, O Corynoneura sp. P L, O Cricotopus (Isocladius) sp. L Cricotopus sp. O Eukiefferiella brevicalcar (Kieffer) O Heterotanytarsus sp. O Heterotrissocladius marcidus �(�W��alker) L, P, O O L Limnophyes sp. P, O L, O L Metriocnemus hygropetricus gr. O 54 Boggero et al. Small mountain lakes in Val Grande

(Appendix 1 - continued) (Appendice 1 - continua)

Taxa Geccio Marmo Scaredi Orthocladius (Eudactylocladius) sp. P, O Parametriocnemus sp. O Parorthocladius sp. O Psectrocladius (Allopsectrocladius) sp. L Thienemanniella cfr. clavicornis O Tvetenia calvescens (Edwards ) O O Chironominae Chironomus plumosus gr. L Chironomus thummi gr. L L Chironomus/Einfeldia L L Cladotanytarsus mancus gr. L Einfeldia pagana gr. L Endochironomus dispar gr. L, O L Micropsectra spp. L, P, O Micropsectra bidentata gr. O Paratanytarsus austriacus (Kieffer) L, P, O L Paratanytarsus laccophilus gr. L, P L, O L Tanytarsus lugens gr. L, P L, O