Diatoms (Bacillariophyceae) from the Valley of the Great Lakes in Western Mongolia
Mark B. Edlund1, Avery L.C. Shinneman2 and Soninkhishig Nergui3
1St. Croix Watershed Research Station, Science Museum of Minnesota, Marine on St. Croix Minnesota 55047, USA
2St. Croix Watershed Research Station, Science Museum of Minnesota, Marine on St. Croix Minnesota 55047, USA
3Faculty of Biology National University of Mongolia, Ulaanbaatar 210646, Mongolia
The Valley of the Great Lakes (VOGL) in western Mongolia is dominated by two main (Uvs, Khyargas) and many minor closed basin lake systems. In 2004 and 2005, we sampled diatom communities from the surfi cial sediment of 64 lakes in the western Mongolian provinces of Uvs, Khovd, Zavkhan, and Bayan-Ulgii. Lakes ranged in water chemistry from fresh to hypersaline, oligotrophic to hypertrophic, and from low elevation VOGL lakes to high elevation lakes in the Altai Mountains. Over 300 diatom species were identifi ed in the sediment samples including a diverse fl ora limited to saline lakes, many widespread taxa, many new reports for the Mongolian diatom fl ora, and several new and possibly endemic species. We also review recent diatom literature from Mongolia including fl oristic surveys, paleo-ecology, and water quality studies.
Keyword: diatoms,Bacillariophyceae,Valley of Great Lakes,paleoecology,taxonomy
Researchers have been studying the Mongolian diatom fl ora for over 100 years. The fi rst published investigation of diatom distribution was a report on species found in Lake Hovsgol by Dorogostaпsky in 1904 (Edlund et al., 2001). Diatom studies by Russian, Mongolian and international scientists have proceeded through the last century (e.g., Skvortzow, 1937; Morales & Edlund, 2003; Edlund et al., 2003; Metzeltin et al., 2009); however, work has been largely focused on occurrence and distribution with little ecological or applied focus. In recent decades, interest has been building in Mongolia and surrounding regions to use diatoms in paleoclimatological (Tarasov et al., 2000; Peck et al., 2002; Soninkhishig et al., 2003; Fedotov et al., 2000, 2004; Rudaya et al., 2008; Shinneman et al., 2009b, c), paleo-ecological (Shinneman et al., 2009a, b; Mackay et al., in press), and ecosystem health assessments (Soninkhishig et al., 1999, Soninkhishig and Edlund, 2001); making an understanding of the distribution and taxonomy of diatoms in Mongolia an important line of study for applied research. Here we expand on the known diversity and distribution of diatoms in Mongolia with a checklist of over 300 diatom taxa identifi ed from 64 surfi cial sediment samples from western Mongolian lakes. Mongolia, and much of Central Asia, have not been well surveyed and continued exploration has yielded many new species, new reports, and broader distributions in the Mongolian diatom fl ora. The importance of Mongolian diatom studies is also being realized with recent large-scale research programs using diatoms in biogeography, taxonomy, bioassessment, and paleolimnology studies.
Material and Methods
Study region - The Valley of the Great Lakes lies in the far west of Mongolia, bounded by the Mongol Altai Mountains to the west, the Khangai Mountains to the east, and the Gobi Desert to the south (Fig. 1).
The Great Lakes region is part of the endorheic Central Asian Basin and includes several smaller closed drainage basins with lakes ranging from fresh to hypersaline (Dulmaa, 1979; Shinneman et al., 2009a). Many of the large terminal basins in the valley are believed to be remnants of large Tertiary or Quaternary paleolakes (Grunert et al., 2000). Sample sites included three large terminal basins in the area, Khyargas, Uvs, and Uureg. There are additionally numerous large and small ephemeral ponds, playa lakes, fl oodplain lakes, and dune-blocked lakes. During two fi eld seasons (August 2004 and August 2005) we sampled 64 lakes in the western Mongolian provinces of Uvs, Khovd, Zavkhan, and Bayan-Ulgii. At each lake a surface sediment sample (0-1 cm sediment depth) was collected from the deepest site accessible by canoe using a line-operated “Wiegner” gravity corer. The sediment was preserved in 10% formaldehyde solution and prepared for microscopy following Renberg (1990). Cleaned material was mounted on microslides with Zrax and random transects examined with an Olympus BX50 microscope capable of 1250x and n.a. 1.40 until 400 valves were counted. Data handling and analysis are described in Shinneman et al. (2009a).
Over 300 species were identifi ed in 64 sampling sites across the region, including new distributional reports for nearly 100 taxa in the VOGL and/or the Mongolian fl ora, in addition to the identifi cation of several new species (Appendix 1; Fig. 1). Some of the new distributional records in the VOGL have also been reported in other studies of Mongolian waterbodies, notably the studies from Buir Nuur, Khugnu Khaan, and the Khentii Mountains (Soninkhishig & Edlund, 2001; Soninkhishig et al., 2002; Metzeltin et al., 2009). Five VOGL lakes were sampled and found to have no diatoms present; these had a specifi c conductance greater than 170,000 #S cm-1 and were presumably too saline to support or preserve a diatom community. In lakes where diatoms were present, either salinity or trophic status had any apparent effect on total species richness; however, community assemblages were linked strongly with both salinity and trophic status (Shinneman et al., 2009a). In deep, freshwater lakes, Cyclotella and Discostella species (Cyclotella ocellata Pantocsek, Discostella pseudostelligera (Hust.) Houk & Klee) were most common, as were several species of the genus Staurosirella. Highly saline lakes had abundant Amphora fl oras; Anomoeoneis sphaerophora (Ehrenb.) Pfi tzer and its varieties and Chaetoceros spores were also common, though typically low in relative abundance. In more dilute waters the community was shifted to high percentages of Pseudostaurosira elliptica (Schumann) Edlund, Morales & Spaulding and Staurosirella pinnata (Ehrenb.) D.M.Williams & Round as well as a number of Cyclotella species found in lower abundance. Highly eutrophic systems were typically characterized by several nitzschioid diatoms (Nitzschia bacillum Hust., Nitzschia constricta (Kьtz.) Ralfs) as well as Stephanodiscus minutulus (Kьtz.) Cleve & J.D.Mцll. and an unknown Gomphonema species, which were not found in abundance in the more nutrient-poor systems. Because surface sediments are often biased toward planktonic assemblages, much greater diversity would be expected if diatoms from littoral and wetland areas had been systematically sampled. Large, saline terminal basins, while retaining high overall diversity, were often dominated (20- 60%) by a single taxon including several unknown and apparently endemic species. These included the terminal basins of Khyargas Nuur and Uureg Nuur. The sole member of the Khyargas Nuur plankton community is the endemic species Puncticulata khyargasiana Shinneman, Edlund & Soninkhishig, whereas the sole member of the Uureg Nuur plankton community is the endemic Cyclotella uuregensis Shinneman, Edlund & Soninkhishig.
The fi rst assessment of diatom diversity in Mongolia was published nearly 10 years ago (Edlund et al. 2001) and reported 547 diatom taxa based on review of the published literature and new distributional reports. A revision of that checklist (including other algal groups) has been published by Dorofeyuk and Tsetsegmaa (2002). Since the original checklist, other studies have expanded sampling efforts to new regions, including the western Valley of the Great Lakes (Soninkhishig et al., 2003; Shinneman et al., 2009a, b, c; Edlund et al., 2009, this study), the Buir Nuur region (Soninkhishig & Edlund, 2001), the Lake Hovsgol region (Edlund et al., 2006; Levkov, 2009), the Khugnu Khaan region (Soninkhishig et al., 2002), the Kharaa River basin (Bukhchuluun et al., this volume), an overall lake survey (Tsetsegmaa, 2008), the Khentii Mountain region (Metzeltin et al., 2009), and Nur bog (Kulikovskiy et al., 2010). These surveys have added considerably to the diversity and documented distributions of diatoms in Mongolia. Other studies have focused on specifi c elements of Mongolia’s diatom fl ora for their taxonomic or biodiversity interest. Edlund et al. (2000, 2001, 2006) used Mongolian material to study uncommon diatom groups such Eunotia clevei Grunow ex Cleve, Biremis zachariasii (Reichelt) Edlund, Andresen & Soninkhishig, and Decussata placenta (Ehrenb.) Lange-Bertalot & Metzeltin. Shinneman et al. (submitted) monographed the Cyclotella sensu lato fl ora of western Mongolian lakes. Some diatom groups, such as Hannaea arcus (Ehrenb.) R.M. Patrick and its allies have especially high diversity in and near Mongolia (Bixby 2001; Bixby et al. 2005). Levkov et al. (2009) used material from Lake Hovsgol as part of his monograph of the genus Amphora sensu lato. Yoshitake et al. (2009) also used Hovsgol material to identify multiple forms of Gomphonema ventricosa W. Greg. and to compare Hovsgol’s populations to other collections. Other examples of high or interesting diversity in Lake Hovsgol include the small fragilarioid taxa (Morales & Edlund, 2003; Morales et al., 2010), the plankton (Edlund et al. 2003), and the Navicula reinhardtii Grunow in Cleve & J.D.Mцller complex (Edlund et al. 2006; Edlund & Soninkhishig, 2009). With so much work focused on the diversity and taxonomy of Mongolia’s diatoms, many new species have been discovered and described in the last decade. The largest addition to the fl ora was Metzeltin et al. (2009), in which 64 new species were formally described and 615 total taxa were reported from collections made primarily in the Khentii Mountains. Kulikovskiy et al. (2010) described 18 new species from a Mongolian bog and used Mongolian material to support the description of one new genus. Williams and Reid (2006) described a new taxon from a Mongolian spring, Amphorotia stoermeri Williams & Reid, in their monograph of the new genus Amphorotia. Lake Hovsgol continues to be a Mongolian biodiversity hotspot. Edlund et al. (2003) described two new Stephanodiscus species and Pappas & Stoermer (2003) described a new Asterionella from the Hovsgol plankton. Morales & Edlund (2003) and Morales et al. (2010) described three new small fragilarioid species from the Hovsgol region. Levkov (2009) described four new Amphora species and identifi ed strong connections between the Amphora fl oras of Lake Hovsgol and Lake Baikal. Finally, Edlund and Soninkhishig (2009) formally described the members of the Hovsgol Navicula reinhardtii species flock. New species have also been discovered in Mongolia’s VOGL region. Edlund et al. (2009) described a small Amphora species, A. soninkhishigae Edlund, Shinneman & Levkov, found in two saline lakes, Uvs Nuur and Oigon Nuur. Shinneman et al. (submitted) described three new cyclotelloid species from western Mongolian lakes. Two of the species, Puncticulata khyargasiana Shinneman, Edlund & Soninkhishig and Cyclotella uuregensis Shinneman, Edlund & Soninkhishig, appear to be endemic to their type localities, Khyargas and Uureg Nuur, respectively. Notable within the list of diatom species found in western Mongolia are the large numbers of provisionally named taxa (Appendix 1), such as the Opephora spp. Diatoms given provisional identifi ers represent taxa that are likely undescribed. Efforts have been made to formally describe provisional taxa that were found in relatively high abundance (Edlund et al. 2009; Shinneman et al., submitted), but the minor provisionally named taxa are a testament to the undiscovered diatom diversity that awaits researchers working in Mongolia. Diatoms are increasingly being used in Mongolia in applied studies such as indicator species for water quality assessments (Soninkhishig et al., 1999, 2001). Importantly, several studies over the last decade have made use of diatoms as paleo-ecological and paleoclimate studies (Tarasov et al., 2000; Peck et al., 2002; Soninkhishig et al., 2003; Fedotov et al., 2000, 2004; Rudaya et al. 2008; Shinneman et al., 2009a, b,c), highlighting the need for a continued dialog on the taxonomy and ecological distributions of the group. Sampling for the current VOGL survey was designed to develop a diatom calibration model that could be used to interpret historical ecological change in sediment records (Shinneman et al., 2009a). Diatom abundance and distribution in western Mongolian lakes were strongly controlled by specifi c conductance, bicarbonate ion, and total phosphorus; as such, subfossil diatom assemblages could be used to quantitatively reconstruct trophic state and lake salinity (Shinneman et al., 2009a, b, c). Diatoms in recent sediment records record an increase in nutrients in fi ve western Mongolian lakes; these recent changes could be attributed to both increased intensity of grazing and recent climatic warming (Shinneman et al., 2009b). Diatoms in longer sediment records record a negative correlation between temperature and effective moisture (Shinneman et al., 2009c). Assemblage changes in the most recent decades in the long cores indicate a more complex set of drivers are likely affecting lakes in western Mongolia including landscapelevel changes in nutrient dynamics (livestock), and climate change, which is primarily manifested as an ecological response to warmer winters. The recent changes in diatom assemblages in western Mongolian lakes are unprecedented in the longer core records (Shinneman et al., 2009c) and convey a critical need to better understand the connections between aquatic biodiversity, water quality, and the landscape and climate drivers that are impacting Mongolia’s lakes.
We thank our Mongolian colleagues, Drs. Y. Khand and G. Tserenkhand, and especially our drivers, cooks, and fi eld crew for their help and generosity during two fi eld expeditions. This material is based upon work supported by the National Science Foundation (NSF) under grants DEB-0316503 and DEB-0431529 to MBE. Any opinions, fi ndings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily refl ect the views of the NSF.
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