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Paleolimnologists have utilized lake sediment records to understand historical lake and landscape development, timing and magnitude of environmental change at lake, watershed, regional and global scales, and as historical datasets to target watershed and lake management. Resurrection ecologists have long recognized lake sediments as sources of viable propagules (“seed or egg banks”) with which to explore questions of community ecology, ecological response, and evolutionary ecology. Most researchers consider Daphnia as the primary model organism in these efforts, but many other aquatic biota, from viruses to macrophytes, similarly produce viable propagules that are incorporated in the sediment record but have been underutilized in resurrection ecology. The common goals shared by these two disciplines have led to mutualistic and synergistic collaborations—a development that must be encouraged to expand. We give an overview of the achievements of paleolimnology and the reconstruction of environmental history of lakes, review the untapped diversity of aquatic organisms that produce dormant propagules, compare Daphnia as a model of resurrection ecology with other organisms amenable to resurrection studies, especially diatoms, and consider new research directions that represent the nexus of these two fields.

Ecological shifts in shallow lakes from clear-water macrophyte-dominated to turbid-water phytoplankton-dominated are generally thought of as rapid short-term transitions. Diatom remains in sediment records from shallow lakes in the Prairie Pothole Region of North America provide new evidence that the long-term ecological stability of these lakes is defined by the legacy of large regime shifts. We examine the modern and historical stability of 11 shallow lakes. Currently, four of the lakes are in a clear-water state, three are consistently turbid-water, and four have been observed to change state from year to year (transitional). Lake sediment records spanning the past 150-200 yr suggest that (1) the diatom assemblage is characteristic of either clear or turbid lakes, (2) prior to significant landscape alteration, all of the lakes existed in a regime of a stable clear-water state, (3) lakes that are currently classified as turbid or transitional have experienced one strong regime shift over the past 150-200 yr and have since remained in a regime where turbid-water predominates, and (4) top-down impacts to the lake food-web from fish introductions appear to be the dominant driver of strong regime shifts and not increased nutrient availability. Based on our findings we demonstrate a method that could be used by lake managers to identify lakes that have an ecological history close to the clear-turbid regime threshold; such lakes might more easily be returned to a clear-water state through biomanipulation. The unfortunate reality is that many of these lakes are now part of a managed landscape and will likely require continued intervention.

A 7-year-old spayed female German Wirehaired Pointer was presented with difficulty breathing after being found seizing in a water-filled drainage ditch while out hunting. Aspirates from a tracheal wash contained numerous degenerate neutrophils, fewer macrophages, some of which contained basophilic debris, low numbers of extracellular diatoms, and a single intracellular short bacterial rod. As the dog continued to clinically decline and could not be weaned from oxygen support, the owners chose euthanasia. The major necropsy finding was a severe granulomatous bronchopneumonia that was likely due to aspiration of foreign material based on the microscopic presence of plant-like material, bi-refringent crystalline material, non-cellular debris, and occasional fungal structures. Diatoms are a class of algae that live primarily in water. Diatom analysis has been used, with some controversy, in human forensics to assist in documenting drowning as the cause of death. In this case, given the clinical history, the presence of diatoms and inflammation in the tracheal wash were interpreted as a likely result of the aspiration of surface water. To our knowledge, this is the first reported case of diatoms observed in a cytologic specimen in a nonhuman mammal with aspiration pneumonia.

SUMMARY Several populations identified and reported from North America and Mongolia under the names Fragilaria elliptica Schumann or Staurosira elliptica (Schumann) Williams et Round were analyzed in detail using light microscopy (LM) and scanning electron microscopy (SEM). The analysis yielded three variants that can not be ascribed to ‘elliptica’ of the type. Furthermore, two of the variants could not be related to published taxa and we describe them as new species, Staurosira ambigua sp. nov. and Staurosira dimorpha sp. nov. A third variant was identified as Pseudostaurosira trainorii Morales, a taxon originally reported from ponds and a river in the north-eastern USA. The combined LM and SEM analysis used here allowed for a more thorough circumscription of taxonomic boundaries among morphologically similar taxa and for better delimitation of their geographic distributions. A discussion of the taxonomy and ecology of these taxa based on literature and recent ecological data is presented.

SUMMARY The name Navicula hasta is regularly applied to large, heavily silicified Navicula specimens with lanceolate outlines, protracted ends, and relatively coarse, radiate, and lineolate striae that are more irregularly spaced around the central area. As such, Navicula hasta has been reported from numerous localities such as brackish water fossil sediments, oligotrophic ancient lakes and postglacial lakes. When the data for distribution of Navicula hasta are summarized, this species appears to be geographically and temporally widespread with a broad range of ecologic tolerances. Published reports for size range show that diatomists during the last century have differing concepts of the species starting with the disagreement between the protologue and one of the figures given by Pantocsek. Furthermore, an informal ‘type’ of Navicula hasta reported in 1980 does not match the protologue and is not unambiguously based on material Pantocsek had in his hands when describing his new species. We studied published reports of Navicula hasta and investigated material reported to contain Navicula hasta and its allies from the type locality (Kopecz), one of the fossil deposits reported to contain N. hasta (Bodos) and from ancient and other younger lakes worldwide. From our analyses, we document the variation and underappreciated diversity within the Navicula hasta group and set the stage for formal recognition of new species in subsequent papers. Herein, we formally propose a lectotype from among the original illustrations and designate an epitype for Navicula hasta based on Pantocsek's Kopecz material. Additionally, two new species, Navicula krenneri spec. nov. and Navicula pseudohasta spec. nov. are described and a lectotype of Navicula superhasta Lange-Bertalot and Metzeltin is proposed.

SUMMARY Three fragilarioid diatom taxa were studied in detail at the light microscopy and scanning electron microscopy levels from samples collected from Lake Hovsgol, Mongolia. Two of the taxa are new to science, described here as Staurosirella minuta Morales et M. B. Edlund and Pseudostaurosira tenuis Morales et M. B. Edlund, and may be endemic to Lake Hovsgol. The third taxon has been identified as Fragilaria polonica Witak et Lange-Bertalot and it is transferred to the genus Pseudostaurosira (Grunow) D. M. Williams et Round as Pseudostaurosira polonica (Witak et Lange-Bertalot) Morales et M. B. Edlund comb. nov. based on the ultrastructural features of its valves. The relationship of the above taxa to others reported in the literature is included herein, and the nomenclatural transfer, Pseudostaurosira naveana (Le Cohu) Morales et M. B. Edlund comb. nov., is proposed.

Siliceous microfossil succession was analyzed in a 200,000-yr sediment sequence recovered from the Buguldeika Saddle in Lake Baikal, Russia. Siliceous microfossil abundance varied among core depths from no preserved microfossils during inferred colder climate conditions to recent interglacial sediments containing over 300 3 10 6 microfossils per g dry sediment. Depth-age microfossil assemblage zones (CA-I to CA-IV) identified using correspondence analysis had high correspondence to stages in the marine d 18 O isotope record and could be partially aligned with Late Pleistocene glacial‐interglacial cycling models from the mid-Siberian Highland. These observations suggest that Lake Baikal phytoplankton communities have responded to climatic changes driven by insolation parameters and global ice volumes on temporal scales similar to tropical and polar oceans. Microfossil zone CA-I (0‐11.4 kyr B.P.) corresponded to the Holocene interglacial or d 18 O stage 1 (0‐11.4 kyr B.P.), a period of higher production in Lake Baikal during a climatic optimum. Microfossil zone CA-II (12.3‐18.7 kyr B.P.) corresponded to the Sartan glaciation and d 18 O stage 2 (12‐24 kyr B.P.). Zone CA-III (21.3‐73.2 kyr B.P.) comprised d 18 O stages 3 and 4. However, within zone CA-III, subzones CA-IIIa and IIIb (21.3‐56.8 kyr B.P.) grouped were well aligned with d 18 O stage 3 and contained sediments deposited during the inferred Karginskiy interstade. Microfossil zone CA-IVa (77.4‐129.2 kyr B.P.) and CA-IVb (130.3‐172.5 kyr B.P.) included d 18 O stages 5 and 6, respectively, with sediments that were most likely deposited during the Taz glaciation and the Kazantsevo interstade. Climate-induced changes are reflected in production differences and in community composition specificity within microfossil zones or climate stages. This suggests that climate change drives major historical successional patterns in Lake Baikal’s primary producer community; changes in primary producers must have further impacted the system’s entire biota.

Since the early 1960s, numerical techniques have produced a wide variety of methods to suggest classifcations of organisms based on quantitative measurements. A longrecognized shortcoming of these methods is that they will suggest classifications for an9 group of organisms and an9 set of measurements, whether or not the clusters in the suggested classification have an9 natural meaning or signif icance. 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 diffent methods, Various methods have been applied to the same data sets to compare how well they realize various desirable p-operties. 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 sub division can be statistically avoided, and signifcant sub divisions can be investigated with confidence. Our methods are illustrated with some examples fi-om the Stephanodiscus niagarae Ehrenb. species complex. Signifcant dif ferences in morphologzc expression are identz$ed in S. reimerii Thm‘ot and Stoermer in Then‘ot, S. superiorensis Thot and Stomnq and S. yellowstonensis Theriot and Stow. In addition, statistically significant clusters are identified in S. niagarae populations @om dzfferent geographic locations and in members of the same population grown in dzfferent environments. These results suggest current m‘h’a fm resolving diatom taxa may not be sufficient to discern subtle dafferences that occur between real species.

Aulacoseira skvortzowii sp. nov. is a diatom taxon present in modern plankton assemblages and sedimentary deposits from Lake Baikal, Russia. It has been preuiously reported as A. islandica (0. Mull.) Sirnonsen, A. islan- late fall pelagic plankton community. C~~clotella min- uta dominates the modern assemblage whereas C. ornata and C. baicalensis have become much less abundant in recent years (Popovskaya 199 1, Flower 1993). The vernal phytoplankton is usually domi- nated by Aulacoseira baicalensis (K. Meyer) Simonsen. This filamentous centric taxon begins its develop- ment beneath clear ice as early as February and continues to dominate the plankton through May or June. Population numbers vary greatly from year to year, producing what are known as "Aulacoseira" years every 3-4 years, when A. baicalensis dominates the pelagic plankton. The endemic Cyclotella typi- cally have greater development during "Aulacoseira- poor" years. The controlling factors governing this cycling of populations are poorly understood but may be related to reproductive cycles.

We observed sexual reproduction in a clonal culture of Stephanodiscus niagarae Ehrenb. and used light and scanning electron microscopy to absent flagellated male cells, auxospore growth, initial valve structure and production, and subsequent daughter cell division. Free auxospores were spherical and nonsiliceous throughout growth, producing hemispherical initial valves devoid of spines and with nonfasciculate striae. Pregametangial cells averaged 43% of the diameter of the daughter cell population and were 1/9 the biovolume of initial, cells. This paper is the first confirmed report of sexual reproduction in S. niagarae, although it appears that specimens of Actinocyclus niagarae H. L. Smith, described from Lake Erie in 1878, are actually initial valves of S. niagarae.

The final 37 km of the St. Croix River were naturally dammed by the Mississippi River to form Lake St. Croix approximately 9500 years ago. The St. Croix River is currently regarded as having ‘exceptional resource value’, as one of the least impacted large Midwest river systems. Twenty-four 2-m piston cores were recovered in 1999–2001 from Lake St. Croix sub-basins to identify post-European settlement signals of land use, trophic change, and sedimentation using a whole-basin approach to reconstruct loading history of nutrients, sediments, heavy metals, and organics. Dating chronologies based on 210Pb inventories indicated both cores recovered a sediment sequence dating from pre- and post-European settlement (c. 1850) in the St. Croix River basin. Select cores were subjected to magnetic susceptibility, loss-on-ignition, and diatom microfossil analysis. Sedimentary increases in magnetic susceptibility were indicative of increased erosion and transport of ferromagnetic mineral grains due to initiation of settlement, logging, and agricultural activities in the basin. A three-fold increase in sediment accumulation began in the mid-1800s in the northern basin and by 1900 in the southern basin. Diatom accumulation increased 20–50-fold since settlement with a shift from benthic- to planktonic-dominated assemblages. Simultaneous with the assemblage shift were the introduction and establishment of many planktonic diatoms considered ubiquitous indicators of eutrophy. The fossil diatom assemblages were further analyzed using weighted-averaging calibration and reconstruction of historical water column total phosphorus (TP). Reconstructed TP values showed that water column nutrient values have increased 2.5–3-fold since presettlement times. Presettlement values of about 0.02 mg/L TP were found in both cores with TP increases beginning c. 1910 and especially dramatic increases after World War II. Modern reconstructed TP values (about 0.055 mg/L) were similar to TP concentrations reported from monitoring during the last few decades; however, the river was clearly impacted well before monitoring efforts were begun.