Associate Editor: A. Flores.
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Despite the fair and extensive floristic and taxonomic knowledge on the European freshwater diatoms, the diatom flora of the Iberian Peninsula is rather poorly known. The freshwater diatoms of Galicia —NW Spain— have never been thoroughly investigated and there are few works related to some selected localities. The first floristic studies on freshwater diatoms in the region date back to the first half of the 20th century (Gamundi
This paper reports the results of a systematic survey of the diatom assemblages in Galicia —NW Spain—. The paper describes diatoms collected from running waters in rivers and streams of the Galicia-Costa basin. The study has three main goals: 1) to present a floristic catalogue of the freshwater diatoms living in the rivers of the study area; 2) to provide data on their distribution and autoecology; and 3) to give descriptions of unusual taxa.
Galicia is located in the NW of Iberian Peninsula, situated in a transitory zone between the Atlantic and Mediterranean regions under an oceanic climate (
Map of Galicia sampling sites studied. Sites numbered from 1 to 34 are those included within the Galicia-Costa basins (HDGC). The Macizo Central Gallego (MCG) localities are numbered from 35 to 41.
One of the key elements of the Galician landscape is the existence of a large and dense river network controlled by climate and tectonic and the morphological configuration. Galicia-Costa has mild winters and cool summers with precipitation exceeding 1,500 mm per year while well distributed throughout the year. As a result most of the Galician rivers have an Atlantic or oceanic climate characterized by an abundant and regular flow, with high waters in winter and a moderate drought in the summer. The mountainous geomorphology and regular precipitation influences the occurrence and permanence of many small and medium-sized rivers with regular discharge throughout the year.
The river systems occurring within the area of Galicia-Costa include all Galician river basins that flow into the Bay of Biscay and to the Atlantic Ocean. The rivers of the Bay of Biscay slope flow to the north. These rivers are short with steep gradients. These rivers undergo an oceanic climate with a reduced variation in annual temperature and rain patterns. The Atlantic slope comprises all the rivers flowing west to the Atlantic Ocean. These rivers show a higher environmental and spatial variability, with two groups easily differentiated: the rivers of the Arco Ártabro-Fisterra and the rivers of the Rias Baixas. The proximity of the mountains to the coast and the oceanic climate of the basins of the Arco Ártabro-Fisterra make all rivers in this area short and quite fast flowing, although they have a summer drought more pronounced than those of the Bay of Biscay. The Rías Baixas rivers are subject to significant Mediterranean influences and undergo severe droughts during summer months.
This study was carried out in 41 localities (
Temperature, pH, conductivity, and dissolved oxygen were measured in situ in each locality with a HANNA HI 9024C microcomputer pH-meter, a HANNA HI 9033 multi-range conductivity meter and a CRISON oxi 45 oxymeter. Water samples for chemical analyses were collected into polypropylene bottles and transported chilled to the laboratory. Water chemistry analyses were carried out at the Department of Physical Chemistry —USC— and included: temperature —ºC—, pH, potassium —mg∙L-1—, magnesium —mg∙L-1—, manganese —mg∙L-1—, chloride —mg∙L-1—, sulphate —mg∙L-1—, ammonium —mg∙L- 1—, conductivity —μS∙cm-1 at 20 ºC—, nitrates —mg∙L-1—, nitrites —mg∙L-1—, phosphates —mg∙L-1—, dissolved oxygen —mg∙L-1—, TOC (mg∙L-1), BOD5, suspended solids —mg∙L-1—, turbidity —NTU; nephelometric turbidity units—, and alkalinity —mEq∙L-1—. Standard methods for chemical water analysis were carried out following American Public Health Association (APHA
Localities were sampled between 2002 and 2007 at different moments of the year but more frequently at the end of spring and summer. Diatoms were collected with a brush, from medium-size stones chosen from well lightened and flowing streams. Samples were preserved in a cool-box in the field, until being carried to the laboratory. Diatoms frustules were cleaned with 30% H2O2 in hot during 6‒7 h. The cleaned frustules were mounted on glass-slides using Naphrax® (CEN
Weighted averaging regression and calibration were perfomed to calculate pH, conductivity, nitrates and phosphates optima of diatom species using the computer program C2 (Juggins
Characteristics of studied localities are given in
Localities and physicochemical values. [C, rivers of the Bay of Biscay; AAF, rivers of the Arco Ártabro-Fisterra; ARB, rivers of the Rias Baixas; MCG, rivers of the Macizo Central Gallego.]
CODE | RIVER | LOCALITY | COORDINATES | Tª | PH | CONDUCTIVITY | O2 | HARDNESS | DRANAIGE |
---|---|---|---|---|---|---|---|---|---|
ºC | μS/cm | mg/L | mg CO3Ca/L | ||||||
1 | MASMA | MASMA | 29T0634761 4815296 | 16.1 | 7.6 | 147.9 | 9.6 | 53.2 | C |
2 | OURO | S ACISCLO | 29T0631412 4824765 | 15.9 | 7.0 | 93.3 | 9.6 | 18.7 | C |
3 | LANDRO | NASEIROS | 29T0613811 4830530 | 15.6 | 6.8 | 69.9 | 10.0 | 11.4 | C |
4 | SOR | COTO RIBEIRAS | 29T0605538 4835129 | 16.3 | 6.6 | 66.8 | 9.9 | 10.4 | C |
5 | MERA | MERA DE ABAIXO | 29T0588129 4832636 | 15.1 | 7.3 | 123.5 | 10.1 | 38.3 | C |
6 | FORCADAS | VILABOA | 29T0576983 4826378 | 19.8 | 7.4 | 109.9 | 9.0 | 28.2 | C |
7 | XUBIA | S. SADURNIÑO | 29T0573708 4808503 | 15.8 | 7.4 | 153.2 | 9.3 | 41.3 | AAF |
8 | BELELLE | VILADONELLE | 29T0571126 4815639 | 15.8 | 6.5 | 74.0 | 8.8 | 11.5 | AAF |
9 | EUME | RIBADEUME | 29T0591148 4820458 | 16.1 | 6.5 | 46.2 | 9.7 | 8.7 | AAF |
10 | EUME | OMBRE | 29T0571870 4808503 | 13.0 | 6.4 | 126.2 | 10.7 | 41.8 | AAF |
11 | MANDEO | MUNIFERRAL | 29T0576677 4789040 | 16.6 | 7.0 | 83.0 | 9.9 | 14.9 | AAF |
12 | MERO | MABEGONDO | 29T0560483 4789644 | 16.0 | 7.0 | 112.7 | 9.6 | 25.2 | AAF |
13 | MERO | CAMBRE | 29T0554293 4793045 | 20.1 | 7.1 | 195.0 | 9.5 | 58.7 | AAF |
14 | BARCÉS | RIBEIRA | 29T0551899 4784011 | 16.5 | 7.1 | 456.7 | 9.8 | 167.0 | AAF |
15 | ANLLONS | ANLLÓNS | 29T0509358 4786303 | 16.9 | 7.3 | 173.1 | 10.0 | 40.8 | AAF |
16 | GRANDE | PONTE DO PORTO | 29T0491863 4776196 | 17.2 | 6.7 | 93.4 | 9.7 | 15.8 | AAF |
17 | CASTRO | SENANDE | 29T0489192 4765965 | 16.6 | 6.3 | 85.7 | 9.6 | 10.8 | AAF |
18 | XALLAS | PTE OLVEIRA | 29T0498653 4756899 | 18.7 | 6.7 | 74.5 | 9.0 | 16.9 | ARB |
19 | DUBRA | PORTOMOURO | 29T0529113 4756357 | 14.9 | 7.2 | 90.1 | 10.4 | 26.8 | ARB |
20 | TAMBRE | CHAIÁN | 29T0538222 4754950 | 17.0 | 7.0 | 98.3 | 9.9 | 27.3 | ARB |
21 | TAMBRE | PORTOMOURO | 29T0528303 4758349 | 17.6 | 7.2 | 98.6 | 10.2 | 23.9 | ARB |
22 | TRABA | NOIA-PORTOBRAVO | 29T0510919 4737178 | 16.4 | 6.2 | 72.3 | 9.9 | 10.7 | ARB |
23 | ULLA-FURELOS | PONTE BARAZÓN | 29T0580147 4745726 | 15.7 | 7.3 | 122.1 | 9.0 | 38.4 | ARB |
26 | ULLA-DEZA | CIRA | 29T0554401 4736284 | 16.9 | 7.2 | 106.5 | 10.1 | 26.5 | ARB |
27 | ULLA-SAR | BERTAMIRÁNS | 29T0530247 4745287 | 17.6 | 7.4 | 310.8 | 8.3 | 55.3 | ARB |
24 | ULLA | SANTISO (MOURAZOS) | 29T0579849 4744500 | 15.6 | 7.2 | 77.9 | 9.8 | 20.1 | ARB |
25 | ULLA | PTE LEDESMA | 29T0554492 4738488 | 16.5 | 7.3 | 93.7 | 9.7 | 27.9 | ARB |
28 | ULLA | CARCACÍA | 29T0532844 4732618 | 18.3 | 7.3 | 93.9 | 9.9 | 25.1 | ARB |
29 | UMIA | COTO DE CALDAS | 29T0527579 4716262 | 18.3 | 6.8 | 55.8 | 8.9 | 9.5 | ARB |
31 | LEREZ | CUTIÁN | 29T0538023 4708198 | 17.4 | 6.7 | 40.1 | 9.1 | 7.4 | ARB |
30 | LEREZ | BORA | 29T0534017 4699819 | 19.1 | 6.7 | 37.9 | 10.7 | — | ARB |
32 | VERDUGO | SOUTOMAIOR | 29T0536405 4688537 | 18.5 | 6.8 | 39.2 | 9.5 | 4.9 | ARB |
33 | OITAVEN | SOUTOMAIOR | 29T0536676 4687826 | 17.1 | 6.5 | 35.0 | 9.6 | 5.0 | ARB |
34 | ZAMÁNS | ZAMÁNS | 29T0523794 4667710 | 19.7 | 6.9 | 61.7 | 9.1 | 11.3 | ARB |
35 | SAN LÁZARO | 29T644962 4686175 | 6.3 | 7.5 | 60.0 | — | — | MCG | |
36 | TORNOS-PALLEIRAS | 29T636432 4683447 | 12.7 | 6.6 | 12.7 | 88.5 | — | MCG | |
37 | CANEIRO-REQUEIX0 | 29T647398 4687699 | 18.6 | 6.8 | 89.3 | 9.7 | — | MCG | |
38 | CENZA | 29T647250 4671662 | 24.5 | 7.1 | 20.2 | 79.1 | — | MCG | |
39 | PRADOALBAR-CONSO | 29T641788 4670533 | 16.7 | 6.9 | 15.0 | 9.8 | — | MCG | |
40 | INVERNADEIRO SUR | 29T636900 4664375 | 17.5 | 7.0 | 128.3 | 9.1 | — | MCG | |
41 | INVERNADEIRO NORTE | 29T640350 4665600 | 18.4 | 6.7 | 43.3 | 9.3 | — | MCG |
Results of the diatom analysis are divided into three parts. First, we provide a narrative on some taxa and their distribution to examine relationships between the occurrences of diatom taxa. Second, we establish a provisional taxon checklist for Galicia freshwater diatoms. Finally we give an account of unusual taxa with distribution restricted mostly to Galicia or northwest Iberia.
Galicia river diatoms are a diverse component of the ecosystem, although very distinctive of the Iberian Peninsula diatom flora. Compared with some other geographically and climatically similar areas in northern Spain, Galician running waters are quite distinctive. The geology in the Galician coastal area is homogeneously siliceous, thus rivers and streams are characteristically softwater. Consequently, diatom taxa characteristic of acidic waters were usually well-represented in Galician rivers (
Optima calculated for the most common and abundant diatoms. Values were calculated using Weighted Averages as implemented in C2 (Juggins
pH | Conductivity | Nitrates | Phosphates | |
---|---|---|---|---|
μS cm-1 | mg L-1 | mg L-1 | ||
6.7 | 72.3 | 1.519 | 0.041 | |
6.1 | 43.5 | 1.338 | 0.024 | |
6.9 | 78.1 | 2.887 | 0.113 | |
6.7 | 55.1 | 1.252 | 0.026 | |
6.6 | 43.3 | 0.837 | 0.020 | |
6.8 | 45.7 | 0.826 | 0.054 | |
7.0 | 78.9 | 1.373 | 0.059 | |
7.0 | 79.1 | 1.442 | 0.044 | |
6.1 | 48.2 | 0.487 | 0.019 | |
6.7 | 81.3 | 0.503 | 0.032 | |
6.7 | 35.1 | 1.885 | 0.017 | |
7.1 | 67.1 | 2.522 | 0.059 | |
6.8 | 50.0 | 1.377 | 0.027 | |
6.3 | 38.7 | 0.538 | 0.003 | |
6.3 | 38.5 | 0.941 | 0.022 | |
6.5 | 31.9 | 0.384 | 0.003 | |
6.3 | 51.1 | 0.824 | 0.026 | |
6.3 | 31.8 | 0.284 | 0.004 | |
6.2 | 35.1 | 0.847 | 0.011 | |
6.3 | 38.2 | 1.065 | 0.030 | |
6.1 | 34.0 | 0.842 | 0.005 | |
6.4 | 51.2 | 1.016 | 0.015 | |
6.6 | 36.0 | 1.497 | 0.007 | |
6.1 | 38.6 | 0.842 | 0.021 | |
6.6 | 42.7 | 0.528 | 0.006 | |
6.8 | 51.5 | 2.938 | 0.035 | |
6.6 | 55.9 | 1.176 | 0.017 | |
7.0 | 70.5 | 1.554 | 0.056 | |
6.4 | 41.9 | 1.395 | 0.039 | |
6.5 | 60.9 | 2.520 | 0.119 | |
6.6 | 59.3 | 3.374 | 0.072 | |
6.5 | 45.5 | 0.960 | 0.048 | |
6.5 | 44.1 | 0.691 | 0.030 | |
6.9 | 75.5 | 2.118 | 0.120 | |
6.7 | 68.8 | 1.693 | 0.089 | |
6.9 | 52.9 | 1.724 | 0.020 | |
6.8 | 49.0 | 1.214 | 0.038 | |
6.0 | 44.0 | 0.761 | 0.002 | |
6.4 | 39.9 | 0.637 | 0.010 | |
6.7 | 60.8 | 1.450 | 0.070 | |
7.0 | 75.2 | 1.277 | 0.042 | |
6.7 | 67.3 | 2.113 | 0.149 | |
7.0 | 71.1 | 3.885 | 0.093 | |
6.9 | 82.8 | 3.146 | 0.085 | |
6.9 | 115.0 | 3.436 | 0.381 | |
6.8 | 66.3 | 1.433 | 0.060 | |
6.8 | 54.5 | 2.111 | 0.046 | |
6.9 | 86.2 | 2.404 | 0.266 | |
6.5 | 51.6 | 1.273 | 0.010 | |
6.8 | 92.1 | 0.283 | 0.046 | |
6.3 | 38.8 | 1.391 | 0.044 | |
6.7 | 59.0 | 0.734 | 0.009 | |
6.9 | 62.0 | 1.633 | 0.024 | |
6.1 | 38.7 | 1.154 | 0.007 | |
6.6 | 64.3 | 1.735 | 0.014 |
Diatom communities showed a high degree of similarity among sites and were comparable in all upstream stretches of these rivers draining siliceous substrates. Dominant epilithic diatom taxa were
Overall, 141 taxa have been found which can be classified in 48 genera and six families. The taxa that are new records for Iberian Peninsula are marked with three asterisk (***), for Spain with two asterisk (**), the records which are new to Galicia with an asterisk (*). Locality numbers for the new records and figures are indicated after each taxon within brackets.
Epilithic diatoms
Epilithic diatoms
Epilithic diatoms
Epilithic diatoms
Epilithic diatoms
Epilithic diatoms
Epilithic diatoms
Epilithic diatoms
Epilithic diatoms
Epilithic diatoms
1.
Valves 14‒130 × 9.5‒40 μm, linear-lanceolate or linear-elliptical to elliptical, with wedge-shaped or obtuse to broadly rounded endings, often a bit concave in the middle. Raphid valves with a moderately strong to weak curved raphe and equilateral-turning terminal branches. Axial area narrow, linear, while central area is fairly narrow, reaching to the edges forming a transverse fascia. Rapheless valves with narrow axial area, often running curved, mostly. Ends not wedge-shaped, but rather broadly rounded. Stria mostly 9‒10 in 10 μm and less coarse than
2.
Valves 25‒33 × 5‒6.5 μm, outline very variable, strictly lanceolate, although gradually narrowing early to almost pointed ends. Striae 26–30 in 10 μm, mostly from two to three composed lineolae, radial, and only at the ends sometimes parallel to slightly convergent. The Voigt unconformity is clearly visible on one side by truncated stria. Central area is small and indistinct rhombic, and clearly separated from the narrow linear axial area. Raphe filiform with small, clearly marked central pores.
3.
Valves 110‒200 × 26‒35 μm, moderately to distinctly dorsiventral, dorsal margin evenly arched. Ventral margin slightly protuberant at the central part. Valve ends not protracted and broadly rounded. Axial area moderately wide, linear, widening at mid-valve to form a widened central area. Raphe filiform near the proximal ends with moderately large roundish central pores which are moderately distant and slightly ventrally deflected. Distal ends slightly reverse-lateral, terminal fissures sickle-shaped. Striae slightly radiate. Puncta distinctly visible and more or less roundish. Striae 6.5‒8 in 10 μm.
4.
Valves are asymmetric to the apical axis and variably asymmetric to the transapical axis. Dorsal margins are moderately arched. Ventral margins are weakly concave. The apices are broadly rounded, with a deep notch on the ventral side. Terminal raphe fissures are very short at the junction of the valve face and mantle. Striae are radiate and very finely punctate. Areolae are difficult to resolve in LM.
5.
Valves 20‒40 × 3‒6 μm. Ventral margin is weakly concave, while dorsal margin is distinctly convex. Frequently, this dorsal margin presents two shallow undulations. Valve somewhat narrower at the ends than at the centre. The ends of the valve are rounded, narrowing slightly but they do not set off from the main body of the valve. The terminal nodes are located near but not at the end of the valve. Striae in the middle around 14‒16 in 10 μm, about 22 in the ends; striae straight and almost perpendicular to the ventral side in the center of the valve.
6.
Valves 15‒50 × 4‒7 μm. Striae 13‒17 in 10 μm, more distant at the centre of the valve than at the ends. Ventral margin straight in smaller specimens but weakly concave in larger specimens. Dorsal margin is convex. Apices are acutely rounded, with a “nose-like” appearance. Raphe distal ends lie on the valve mantle and the terminal raphe nodules are well set in from the apices. Frustules are rectangular to quadratic in girdle view.
7.
Valves 14‒45 × 3.5‒5 μm, thickened midway between the center and the ends. Striae 14‒19 in 10 μm, getting closer to the ends. The ventral side of the valve is almost straight or weakly concave at most. The dorsal margin is convex. The apices hardly differ from the body of the valve. The terminal nodes are clearly differentiated, and located near the ends.
8.
Valves 10‒140 × 5‒10 μm, dorsiventral and symmetric to the transapical axis. Striae 7‒15 in 10 μm, extending across the entire surface of the valve. Ventral margin straight or slightly concave, can appear biarcuate due to inflated central region. The apices of the valves have a rounded end. Raphe runs mainly on the valve mantle and at the poles and it is curved slightly over the face of the valve at the apices. Terminal nodes are clearly distinctive. Rectangular frustules in girdle view.
9.
Valves 20‒100 × 4‒15 μm. Striae at mid-valve 6‒13 in 10 μm, irregularly and distantly spaced, and slightly more dense at valve ends, parallel, becoming strongly radiate at valve apices. Valves weakly to strongly curved with clearly protracted, broadly rostrate or abruptly terminated ends. The dorsal margin is convex; narrowed, and the ends are truncate-rostrate. The terminal nodules are distinct, at the ends of the valve, extending upwards along the apices. The frustles in the girdle view are rectangular.
10.
Valves 6‒35(40) × 2.7‒4.5 μm, curved dorsiventrally and symmetric to the transapical axis. Dorsal margin consistently strongly convex, smooth, rarely linear. Ventral valve margin consistently weakly concave. Valve slightly narrowed towards the end. Apices rounded to slightly (sub-) rostrate. Striae 18‒23 in 10 μm, extending across the entire valve face. Raphe slightly developed mainly on the valve mantle and restricted to the poles. Terminal nodules small, dot-like, positioned slightly distant from both valve apices and ventral valve margin. Frustules box-like or rectangular in girdle view. Raphe often only visible in girdle view.
11.
Valves 28‒105 × 10‒18 μm, generally rhomboid in shape, although valves at the small end of the size range are not strongly rhomboid. Striae 29‒32/10 μm, parallel in the middle to gradually strongly convergent to the end, radiate at the apices; longitudinal striae are present, but may be disorganized at the valve center. The apices are slightly constricted and narrowly rounded. The longitudinal ribs are slightly curved. Both the thickness of the ribs and size of the central nodule are variable in relation to valve size. The porte-crayon is relatively small.
12.
Valves 6–14 × 4–5 μm, elliptical in the smaller specimens and linear in the larger, and centrally inflated. Striae 24–30 in 10 μm. Flat valves with large sternum raphe, and two rows of elongated areolae that are only visible in LM. A longitudinal row of areolae runs over the mantle along the margin of the valve, interrupted at the ends.
13.
Valves 12–26 × 4.5–5.5 μm. Striae 16–23 in 10 μm, parallel in the central part, soon becoming moderately radial, becoming parallel again towards the apices. Raphe branches straight, filiform; central endings only very slightly bent; proximal raphe ends relatively close to each other, and only very slightly bent in the same direction which is opposite to that one towards which the terminal fissures are curved. Faint longitudinal lines visible on both sides of the raphe. Axial area narrow and straight, slightly widening towards the central area that is just a small unilateral expansion of the axial area.
14.
Valves 50‒126 × 12‒22 μm, linear, lanceolate, linear-elliptical, sides parallel, slightly convex or triundulate, ends broadly rounded or broadly rostrate to subcapitate. Raphe lateral, outer fissure somewhat curved, commonly filiform in the middle, central pores with lateral annexes, terminal fissures broadly bayonet-shaped. Axial area linear or linear-lanceolate and rhombic to rounded-rhombic central area extending to a small fascia that reaches the valve margin. Striae 9‒14 in 10 μm, moderately to strongly radiate in the middle, moderately to strongly convergent at the ends, longitudinal bands absent, the alveoli completely open to the inside. Two conical spots which appears dark in the light microscope, each one at the edges of the central area which correspond to wall thickenings.
15.
Valves 17‒52 × 4‒6.5 μm. Striae (11)13(14) in 10 μm. The central area consists of a moderately broad, often asymmetric, fascia. The specimens have valve ends broadly protracted and subrostrate nearly as wide as the valve.
16.
Valves 82‒133 × 18‒20 μm, linear, with sides almost parallel to slightly convex. Striae 7‒9 in 10 μm, radiate in the centre zone, becoming slightly convergent close to the poles, and crossed by a small longitudinal strip. Apex broadly rounded and slightly narrowed. Longitudinal area is linear and moderately wide. Central area is asymmetric and rounded, often reduced or absent on one side. Raphe strongly undulated with central pores small, round and close standing.
17.
Valves 7‒12 × 3.8‒6 μm, elliptical or widely lanceolate in outline with clearly capitated ends. Striae 14‒16 in 10 μm. The raphe valve has a narrow linear or lanceolate axial area generally with a distinct central area. Striae are strongly radiate on all sides, with striae at the centre more clearly shorter than the others. The rapheless valve is similar, but the straie are nearly parallel in the centre of the valve, changing to radiate near the poles.
18.
Valves 30‒100 × 3.5‒9 μm, linear to linear-lanceolate with generally convex or parallel sides. Striae 18‒27 in 10 μm, clearly visible, interrupted in the middle by a narrow hyaline area. Frustules weakly silicified with narrow-linear isopolar longitudinal axis. Apices strongly narrowed, stretched and bluntly rounded. Easily distinguished of other related taxa by their sigmoid outline.
19.
Valves 20‒120 × 9‒25 μm, bilaterally symmetrical, isopolar, generally linear-lanceolate, lanceolate or even elliptical with cuneate or rounded poles; alar wings 2‒3 in 10 μm. Striae 20‒22 in 10 μm fine and parallel at the center, becoming radiant ends, visible but not distinct. Pseudo-raphe narrow and straight. The most obvious features of the valve are the corrugations of the surface associated with the formation of windows beneath the raphe system which give the valve a semblence of a series of transverse tubes opening under the raphe.
The financial support for this work has been provided by Augas de Galicia (Xunta de Galicia) through a contract with the University of Santiago de Compostela for the assessment of the stream water quality in rivers of Galicia-Costa using diatom metrics (2005‒2007). We are indebted to Juan Manuel Antelo Cortizas (Department of Química-Física) and Teresa García Bernadal (researcher of Santiago de Compostela University) for their assistance during fieldwork and insightful comments on stream chemistry and ecology. Special thanks are to Maria Penalta for the photomicrographs in this study. We also thank the reviewers for their very helpful and constructive comments. Finally, we also would like to acknowledge Dr. Alejandro Quintanar for the corrections and improvements made to the original manuscript.