ECOLOGICAL, EVOLUTIONARY, AND SYSTEMATIC SIGNIFICANCE OF DIATOM LIFE HISTORIES 1

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65431/1/j.0022-3646.1997.00897.x.pd

A 200,000‐year, high‐resolution record of diatom productivity and community makeup from Lake Baikal shows high correspondence to the marine oxygen‐isotope record of climate change

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/109793/1/lno20004540948.pd

AULACOSEIRA SKVORTZOWII SP. NOV. (BACILLARIOPHYTA), A POORLY UNDERSTOOD DIATOM FROM LAKE BAIKAL, RUSSIA 1

Aulacoseira skvortzowii sp. nov. is a diatom taxon present in modern plankton assemblages and sedimentary deposits from Lake Baikal, Russia. It has been previously reported as A. islandica (O. MÜll.) Simonsen, A. islandica ssp. helvetica (O. MÜll.) Simonsen, a sporangial frustule of A. baicalensis (K. Meyer) Simonsen, and Aulacoseira “spore”. However, its microstructure, ecology, and ability to form true resting spores provide ample criteria to describe this diatom as Aulacoseira skvortzowii sp. nov.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65810/1/j.0022-3646.1996.00165.x.pd

(1234) Proposal to conserve the name Acanthoceras Honigm. (Bacillariophyceae) against Acanthoceras Kütz. (Rhodophyceae)

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/149724/1/tax05073.pd

RECOGNITION OF TAXONOMICALLY SIGNIFICANT CLUSTERS NEAR THE SPECIES LEVEL, USING COMPUTATIONALLY INTENSE METHODS, WITH EXAMPLES FROM THE STEPHANODISCUS NIAGARAE COMPLEX (BACILLARIOPHYCEAE) 1

Since the early 1960s, numerical techniques have produced a wide variety of methods to suggest classifications of organisms based on quantitative measurements. A long-recognized shortcoming of these methods is that they will suggest classifications for any group of organisms and any set of measurements, whether or not the clusters in the suggested classification have any natural meaning or significance. Some progress has been made in assessing the reality of clusters determined by various methods. Data simulated to reflect known cluster structure have been used to test the accuracy of different methods, Various methods have been applied to the same data sets to compare how well they realize various desirable properties. Here we define a data-based model of randomness to represent what might be meant by “no natural basis for subdivision into clusters” and use it to compare an observed measure of cluster distinctness to the distribution of this measure predicted by this model of randomness. In this way, unwarranted subdivision can be statistically avoided, and significant subdivisions can be investigated with confidence. Our methods are illustrated with some examples from the Stephanodiscus niagarae Ehrenb. species complex. Significant differences in morphologic expression are identified in S. reimerii Theriot and Stoermer in Theriot, S. superiorensis Theriot and Stoermer and S. yellowstonensis Theriot and Stoermer. In addition, statistically significant clusters are identified in S. niagarae populations from different geographic locations and in members of the same population grown in different environments. These results suggest current criteria for resolving diatom taxa may not be sufficient to discern subtle differences that occur between real species.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65691/1/j.0022-3646.1997.01049.x.pd

Siliceous microfossil succession in the recent history of two basins in Lake Baikal, Siberia

As part of the international cooperative Baikal Drilling Project, siliceous microfossil assemblage succession was analyzed in two short (∼ 30-cm) sediment cores from Lake Baikal. One core was recovered from the north basin (Core 324, 55°15′N, 109°30′E), a second from between the central and southern basins (Core 316, 52°28′N, 106°5′E). The northern core had higher amounts of biogenic silica (40 g SiO 2 per 100 g dry weight sediment) compared to the southern core, and increased deposition in the more recent sediments. Weight percent biogenic silica was lower in the southern core, ranging from approximately 20–30 g SiO 2 per 100 g dry weight sediment throughout the entire core. Trends in absolute microfossil abundance mirror those of biogenic silica, with generally greater abundance in the northern core (86–275×10 6 microfossils g −1 dry sediment) compared to the southern core (94–163×10 6 microfossils g −1 dry sediment).Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43073/1/10933_2004_Article_BF00735480.pd

Water Quality (2000-08) and Historical Phosphorus Concentrations from Paleolimnological Studies of Swamp and Speckled Trout Lakes, Grand Portage Reservation, Northeastern Minnesota

This is a technical study to determine reference conditions for water quality on the Grand Portage Reservation. It has some historical interest related to human settlement, as well as data useful for monitoring water quality in the future. Reston, VA: U.S. Department of the Interior, U.S. Geological Survey.A paleolimnological approach was taken to aid the Grand Portage Reservation, in northeastern Minnesota, in determining reference conditions for lakes on the reservation. The U.S. Geological Survey, in cooperation with the Grand Portage Band of Chippewa Indians and the Science Museum of Minnesota, conducted a study to describe water quality (2000–08) and historical total phosphorus concentrations (approximately 1781–2006) for Swamp and Speckled Trout Lakes. Results from this study may be used as a guide in establishing nutrient criteria in these and other lakes on the Grand Portage Reservation. Historical phosphorus concentrations were inferred through paleolimnological reconstruction methods involving diatom analysis and lead-210 dating of lake-sediment cores. Historical diatom-inferred total phosphorus concentrations in Swamp Lake ranged from 0.017 to 0.025 milligrams per liter (mg/L) based on diatom assemblages in sediment samples dated 1781–2005. Historical diatom-inferred total phosphorus concentrations in Speckled Trout Lake ranged from 0.008 to 0.014 mg/L based on diatom assemblages in sediment samples dated 1825–2006. In both lakes, historical changes in diatom-inferred total phosphorus concentrations did not exceed model error estimates, indicating that there has been minimal change in total phosphorus concentrations in the two lakes over about two centuries. The pH and alkalinity values of waters in both lakes indicate that general water-quality conditions likely are not threatening fish or acid-intolerant forms of aquatic life. Lake-sediment cores from Swamp and Speckled Trout Lakes were collected in 2006 and dated back to 1781 for Swamp Lake and 1825 for Speckled Trout Lake. A large increase in sediment accumulation rate after 1960 likely was a result of logging along the northeastern shore of Swamp Lake in 1958. The diatom flora of Swamp Lake is very diverse with more than 280 diatom taxa found in the core samples. These diatoms included many rare or uncommon species and several unknown taxa. Minor increases in sediment accumulation rates in the Speckled Trout Lake core occurred between 1840 and 1880. These increases may have resulted from fires following droughts in northeastern Minnesota. Heinselman (1973) identified five periods of fire in the 1800s for the Boundary Waters Canoe Area, Minnesota: 1801, 1824, 1863–64, 1875, and 1894. Most of these fire periods followed prolonged droughts of subcontinental extent, including the 1864 drought. Similar to the Swamp Lake core, the diatom flora of the Speckled Trout Lake core was very diverse and dominated by softwater diatoms. More than 215 diatom taxa were found in the core samples including many rare or uncommon species and several unknown taxa. Results of loss-on-ignition analyses indicated that sediment from Swamp Lake historically has been dominated by the inorganic component with a shift to an organic component in modern sedimentation. Median values of recent (2000–08) total phosphorus concentrations in water-quality samples and diatom-inferred phosphorus in recent sedimentation in Swamp and Speckled Trout Lakes were similar. These similarities, coupled with strong analogues for subfossil diatom communities for both lakes within the 89 Minnesota lakes diatom transfer function, indicate that recent and historical diatom-inferred phosphorus reconstructions might be used to help establish reference conditions and nutrient criteria for Grand Portage Reservation lakes when a sampling program is designed to ensure representative phosphorus concentrations in water samples are comparable to diatom-inferred concentrations

Response of boreal lakes to changing wind strength: coherent physical changes across two large lakes but varying effects on primary producers over the 20th century

Near‐surface wind speeds have changed over recent decades, raising questions about the extent to which these changes are altering the vertical thermal structure of lakes and affecting lake food webs. Neo‐ and paleolimnological techniques were used to assess wind‐driven changes in lake thermal habitat and resulting effects on primary producers in two lakes in Isle Royale National Park, an island archipelago located in Lake Superior, where wind speed has increased in recent decades. Responses in Siskiwit Lake, a large (16 km2 surface area), deep (Zmax = 49 m), oligotrophic lake, were compared to those of Lake Desor, a moderately large (4.3 km2) but shallower (Zmax = 13 m), mesotrophic lake. High‐frequency sensor data suggested that changes in wind speed affected epilimnion thickness in both lakes synchronously (ρ = 0.7, p [less than] 0.001). Diatom‐inferred mixing depths suggested a coherent shift in both lakes to deeper mixing (an increase of 3 and 6 m) since 1920 (ρ = 0.8), which was correlated with an increase in regional wind speed during the 20th century at the decadal‐scale in Lake Desor and Siskiwit Lake (ρ = 0.6 and 0.4, respectively). In Lake Desor, algal biomass declined as mixing deepened from 1920 to 1980, and then cyanobacteria and cryptophyte pigments increased from 1980 to present, a period of inferred stable and deep mixing. Algal pigment concentrations in Siskiwit Lake were unchanged as mixing depth deepened. Although changes in wind speed altered lake physical structure similarly, the ecological consequences of these changes differed between lakes and were most likely influenced by lake‐specific variability in nutrient and light availability

Lake–landscape connections at the forest–tundra transition of northern Manitoba

To better understand aquatic–terrestrial linkages in the sub-Arctic, and specifically the relative importance of landscape position versus land cover, we surveyed lakes, soils, land cover, and lake/basin characteristics in a 14 000 km2 region of acidic forest–tundra landscape near northern Manitoba, Canada (59.56°N, 97.72°W) in 2009. We analyzed 39 different biological, chemical, and physical variables for lakes and soils. We used a remote-sensing–based classification to determine that the landscape was 21% water, 46% peat-forming lowland, and 24.9% open tundra, and we assigned lake order to all lakes based on the order of the outlet stream for each lake. Lakes were oligotrophic to mesotrophic (median total phosphorus: TP = 11.8 µg L−1), N-limited (median dissolved inorganic nitrogen: TP = 1.6), acidic (median pH 5.7), and had moderate amounts of dissolved organic carbon (median DOC = 5.2 mg L−1). We identified 2 principle groups of variables represented by DOC and conductivity/cations, respectively, that captured major axes of lake variation. DOC, 2 measures of DOC quality (a250/a365 [a proxy for molecular weight and aromaticity] and specific ultraviolet absorbance), and Fe and were significantly correlated with percent cover of lowland forest, but conductivity/cations were not correlated with variation in land cover. Soils were generally acidic (pH 2.7–4.4) and nutrient-poor, and wetland soils contained more carbon and higher concentrations of calcium, magnesium, and other cations than upland open tundra. Landscape position of lakes (measured as lake order) did not capture systematic differences in land cover or lake biogeochemistry. Our results highlight the importance of lowland export of DOC to lakes and further suggest the need for additional regional studies of aquatic–terrestrial connections in Arctic and sub-Arctic landscapes

Morphology, ecology and biogeography of Stauroneis pachycephala P.T. Cleve (Bacillariophyta) and its transfer to the genusEnvekadea

Stauroneis pachycephala was described in 1881 from the Baakens River, Port Elizabeth, South Africa. Recently, it was found during surveys of the MacKenzie River (Victoria, Australia), the Florida Everglades (USA) and coastal marshes of Louisiana (USA). The morphology, ecology and geographic distribution of this species are described in this article. This naviculoid species is characterised by lanceolate valves with a gibbous centre, a sigmoid raphe, an axial area narrowing toward the valve ends, and capitate valve apices. The central area is a distinct stauros that is slightly widened near the valve margin. The raphe is straight and filiform, and the terminal raphe fissures are strongly deflected in opposite directions. Striae are fine and radiate in the middle of the valve, becoming parallel and eventually convergent toward the valve ends. The external surface of the valves and copulae is smooth and lacks ornamentation. We also examined the type material of S. pachycephala. Our observations show this species has morphological characteristics that fit within the genus Envekadea. Therefore, the transfer of S. pachycephala to Envekadea is proposed and a lectotype is designated