2003. Haberyan, K.A., S.P. Horn, and G. Umana V. Basic limnology of fifty-one lakes in Costa Rica. Revista de Biologia Tropical 51(1):107-122. View as PDF file

2003. Thomas, D.S.G., G. Brook, P. Shaw, M. Bateman, K. Haberyan, C. Appleton, D. Nash, S. McLaren, and F. Davies. Late Pleistocene wetting and drying in the NW Kalahari: an integrated study from the Tsodilo Hills, Botswana. Quaternary International 104(1):53-67.

2003. Haberyan, K.A. Do weekly quizzes improve student performance on General Biology exams? The American Biology Teacher 65(2):110-114.

2001. Haberyan, K.A. Coring and extruding sediments from shallow lakes with the simple, inexpensive VolksCorer and VolksExtruder. Journal of Paleolimnology 26:219-223. Parts list

1999. Haberyan, K.A. and S.P. Horn. Chemical and physical properties of seven volcanic lakes in Costa Rica. Brenesia 51:85-95.

1999. Horn, S.P., K.H. Orvis, and K.A. Haberyan. Investigación limnológica y geomorfológica de lagos glaciares del Parque Nacional Chirripó, Costa Rica. Informe Semestral, Instituto Nacional Geográphico de Costa Rica 35: 95-106.

1999. Umaña, G., K.A. Haberyan, and S.P. Horn. Limnology in Costa Rica. In Wetzel, R.G. and B. Gopal (editors), Limnology in Developing Countries 2: 33-62.

1999. Haberyan, K.A. and S.P. Horn. A 10,000-year diatom record from a glacial lake in Costa Rica. Mountain Research and Development 19: 63-70.

1998. Haberyan, K.A. The effect of volcanic ash influx on the diatom community of Lake Tanganyika, East Africa. Transactions, Missouri Academy of Sciences 32: 102-105.

1998. Haberyan, K.A. A hypothesis concerning vertically-migrating zooplankton and their fecal pellets. Transactions, Missouri Academy of Sciences 32: 99-101.

1998. Robbins, L.H., M.L. Murphy, A.C. Campbell, G.A. Brook, D.M. Reid, K.A. Haberyan, and W.S. Downey. Test excavations and reconnaissance palaeoenvironmental work at Toteng, Botswana. South African Archaeological Bulletin 53:125-132.

1997. Chavez, L., and K.A. Haberyan. Diatoms from the Camastro Diatomite, Costa Rica. Revista de Biología Tropical 44:857-860.

1997. Haberyan, K.A., S.P. Horn, and B.F. Cumming. Diatom assemblages from Costa Rican lakes: an initial ecological assessment. Journal of Paleolimnology 17: 263-274.

1996. Porter, K.G., P.A. Saunders, K.A. Haberyan, A.E. Macubbin, T.R. Jacobsen, and R.E. Hodson. Annual cycle of autotrophy and heterotrophy in a small, monomictic, piedmont lake (Lake Oglethorpe, GA): analog for the effects of climatic warming on dimictic lakes. Limnology and Oceanography 41: 1041-1051.

1996. Robbins, E.I., Y.-Y. Chen, M.C. Cuomo, K.A. Haberyan, E. Head, and P.J. Mudie. Fecal pellets. Chapter 17 in Jansonius, J. and D.C. McGregor (editors), Palynology: Principles and applications 3: 1085-1097. American Association of Stratigraphic Palynologists.

1996. Robbins, L.H., M.L. Murphy, N.J. Stevens, G.A. Brook, A.H. Ivester, K.A. Haberyan, R.G. Klein, R. Milo, K.M. Stewart, D.G. Matthiesen, and A.J. Winkler. Paleoenvironment and archaeology of Drotsky's Cave: western Kalahari Desert, Botswana. Journal of Archaeological Science 23: 7-22.

1995. Haberyan, K.A., G. Umaña V., C. Collado, and S.P. Horn. Observations on the algae of some Costa Rican lakes. Hydrobiologia 312: 75-85.

1992. Horn, S.P. and K.A. Haberyan. Costa Rican lakes: physical and chemical properties. National Geographic Research and Exploration 9: 86-103.

1992. Brook, G.A., K.A. Haberyan, and S. De Filippis. Evidence of a shallow lake at Tsodilo Hills, Botswana, 17,500 to 15,000 B.P.: further confirmation of a widespread late Pleistocene humid period in the Kalahari. Palaeoecology of Africa 23: 165-175.

1992. Halfman, J.D., D.F. Jacobson, C.M. Cannella, K.A. Haberyan, and B.P. Finney. Fossil diatoms and the mid to late Holocene paleolimnology of Lake Turkana, Kenya: a reconnaisance study. Journal of Paleolimnology 7: 23-35.

1991. Haberyan, K.A. and O.K. Mhone. Algal communities near Cape Maclear, southern Lake Malawi, Africa. Hydrobiologia 215: 175-188.

1990. Haberyan, K.A. The misrepresentation of the planktonic diatom assemblage in traps and sediments: southern Lake Malawi, Africa. Journal of Paleolimnology 3: 35-44.

1988. Haberyan, K.A. Phycology, sedimentology, and paleolimnology near Cape Maclear, southern Lake Malawi, Africa. Ph.D. Dissertation, Duke University, Durham N.C. 246 pp.

1987. Haberyan, K.A. and R.E. Hecky. The late Pleistocene and Holocene stratigraphy and paleolimnology of Lakes Kivu and Tanganyika. Palaeogeography, Palaeoclimatology, Palaeoecology 62: 169-197.

1987. Haberyan, K.A. Fossil diatoms and the paleolimnology of Lake Rukwa, Tanzania. Freshwater Biology 17: 429-436.

1985. Robbins, E.I., K.G. Porter, and K.A. Haberyan. Pellet microfossils: possible evidence for metazoan life in Early Proterozoic time. Proceedings of the National Academy of Science 82: 5809-5813.

1985. Haberyan, K.A. The role of copepod fecal pellets in the deposition of diatoms in Lake Tanganyika. Limnology and Oceanography 30: 1010-1023.

1984. Haberyan, K.A. Copepod fecal pellets and microfossil deposition in Lake Tanganyika. M.S. Thesis, University of Georgia, Athens. 151pp.

1983. Livingstone, D., B. Rosendahl, R. Dunseath, J. Maley, P. Bailey, K. Haberyan, D. Burney, G. Sugihara, M. Patterson, C. Ebinger, F. Spy-Anderson, J. Nelson, M. Crow, J. LeFournier, C. Stager, R. Kendall, J. Melack, M. LaBarbera, C. LeMut, W. Cromie, J.J. Tiercelin, M. Mvumbi, and J. Chorowitz. Potential sites for a long core in the East African Rift. Bulletin des Centres des Recherches, Exploration, et Production, Elf Aquitaine 7: 443-448.

We suspended sediment traps at 2m, 4m, and 6m near the deepest point (8.7m) in a 30 ha eutrophic lake in Georgia, U.S.A., for 13 consecutive months. Aside from one depth collection (2m in August), the inorganic fraction was always greater than the organic fraction, by a ratio of 7:2 for the year. Inorganic flux reflected rainfall and peaked in December and March, while virtually all of the organic flux took place in March and April. During winter turnover (October through March), sedimentation rates increased linearly with depth. However during the summer, when the lake was stratified, sedimentation rates in traps below the thermocline were essentially constant and less than fluxes in the uppermost trap. The data suggest, therefore, that the thermocline acts as a barrier to sedimentation, and allows microscopic heterotrophs to consume detritus that has paused during its descent. As a consequence, nutrient loss to the hypolimnion is reduced, epilimnetic recycling is increased, and inorganic sediments seem to be redirected to the lake's stream outflow rather than deposited on the bottom.

We visited 51 lakes in Costa Rica as part of a broad-based survey to document their physical and chemical characteristics and how these relate to the mode of formation and geographical distribution of the lakes. The four oxbow lakes were low in elevation and tended to be turbid, high in conductivity and CO2, but low in dissolved O2; one of these, L. Gangoca, had a hypolimnion essentially composed of sea water. These were similar to the four wetland lakes, but the latter instead had low conductivities and pH, and turbidity was often due to tannins rather than suspended sediments. The thirteen artificial lakes formed a very heterogenous group, whose features varied depending on local factors. The thirteen lakes dammed by landslides, lava flows, or lahars occurred in areas with steep slopes, and were more likely to be stratified than most other types of lakes. The eight lakes that occupy volcanic craters tended to be deep, stratified, clear, and cool: two of these, L. Hule and L. Rió Cuarto, appeared to be oligomictic (tending toward meromictic). The nine glacial lakes, all located above 3440m elevation near Cerro Chirripó, were clear, cold, dilute, and are probably polymictic. Cluster analysis resulted in three significant groups of lakes. Cluster 1 included four calcium-rich lakes (average 48 mg/l), Cluster 2 included fourteen lakes with more Si than Ca+2 and higher Cl- than the other clusters, and Cluster 3 included the remaining thirty-three lakes that were generally less concentrated. Each cluster included lakes of various origins located in different geographical regions; these data indicate that, apart from the high- altitude glacial lakes and lakes in the Miravalles area, similarity in lake chemistry is independent of lake distribution.

The sediments and landforms at the Tsodilo Hills, in the northwestern Kalahari desert, provide an opportunity to directly investigate the late Quaternary wetting and drying of the region from evidence at a single site. Lacustrine carbonates, including incorporated molluscs and diatoms, a lake shoreline feature and stabilised linear dunes were investigated for their constituent palaeoenvironmental signals. Chronometric control is provided by calibrated 14C, AMS and OSL dating. The evidence suggests that linear dune construction has not occurred since the Last Glacial Maximum, with particular development from 36 to 28 ka. Lake stands indicating wetter regional conditions than present occurred at 40-32 ka, with more seasonal conditions from 36 ka, and at 27-12 ka with a possible drying out at 22-19 ka. Data are consistent with other independent studies from the region, and with recent evidence obtained from Atlantic cores off the cost of Namibia. It is concluded that careful consideration of multi-proxy data from a single location can assist in resolving discrepancies that arise from independent studies of lake, cave and dune records in the Kalahari.

© 2003 Elsevier Press and International Union for Quaternary Research (INQUA).

Note:The article has no official "abstract;" here is a summary.
Hourly exam averages were compared for four sections of General Biology, two of which experienced weekly quizzes. On identical exams, the quizzed sections performed -1.5 to +4.0% better, but none of these differences were significant. Therefore, quizzes did not seem to improve student performance on hourly exams, nor apparently did they improve learning. Each faculty should carefully evaluate the costs and benefits of quizzes in their classes.

Materials for constructing a simple piston corer are available at most well-stocked hardware stores, primarily using galvanized fence post for the barrel and pipe for the drive rod and head. These are assembled with a modicum of machinist skills. In the field, this VolksCorer operates like similar corers; it is limited to relatively shallow water (about 10-15 m) and is poorly suited for down-the-hole coring, but it requires few specialized tools. Likewise, materials to construct the VolksExtruder are widely available; this extruder, although simple, allows very precise extrusion control. The very low cost of the corer and extruder (less than US$50 each) make them suitable for investigators operating with low budgets without sacrificing sample quality. Parts list.

1999. Haberyan, K.A. and S.P. Horn. Chemical and physical properties of seven volcanic lakes in Costa Rica. Brenesia 51:85-95.

We made twelve visits to seven volcanic lakes in Costa Rica to determine their basic physics and chemistry. Lake waters were low in alkalinity (< 130 mg/l CaC03), conductivity, (<150 mS/cm), and most major ions. Three of the lakes -- Botos, Barva, and Cerro Chato -- occupy craters atop Quaternary volcanoes. All have very low alkalinities (<10 mg/l CaCO3) and conductivities (>80 mS/cm), but differ strongly in ionic composition, transparency, and pH. The remaining four lakes occupy Holocene maars or explosion craters (Laguna Río Cuarto in the Río Cuato explosion crater, and Lagunas Hule, Congo, and Bosque Alegre in the Hule explosion crater). We made repeated visits to Laguna Río Cuarto and Laguna Hule and found remarkable variation over time. These lakes often remain stratified throughout the year, but they turned over in January 1997, as evidenced by homogenization of chemical and physical parameters, turbidity, and reported fish kills. Thus these lakes are oligomictic rather than meromictic.

Horn, S.P., K.H. Orvis, and K.A. Haberyan. 1999. Investigación limnológia y geomorfológica de lagos glaciares del Parque Nacional Chirripó, Costa Rica. Informe Semestral, Instituto Geográphico de Costa Rica 35:95-106.

More than 30 lakes of glacial origin exist in Chirripó National Park in the Cordillera de Talamanca, Costa Rica. In February-March 1998 an investigation was carried out on the limnology and geomorphology of nine lakes in three glaciated valleys, including five lakes that had not been studied previously. Temperature measurements indicate an increase of 4-7 C in water temperatures in the lakes, owing to the effects of the strong El Niño of 1997-1998.

Umaña, G., K.A. Haberyan, and S.P. Horn. 1999. Limnology in Costa Rica. In Wetzel, R.G. and B. Gopal. Limnology in Developing Countries 2: 33-62.

Costa Rica occupies part of the Central American Isthmus near 10^oNorth latitude, and its topography includes a central spine of volcanic and tectonic highlands that separates Caribbean and Pacific lowlands. Temperature and rainfall (including amount and timing) vary strongly by location, and consequently the country supports a large diversity of habitats. Its lakes are equally diverse, and probably exceed 500 in number; they range from oxbow lakes near sea level to cirque and moraine-dammed lakes above 3300 m on the country's highest peak. These glacial lakes tend to be clear, cold, very dilute, and polymictic. Similar are the crater lakes on extinct volcanic cones (1000 m to 3000 m in elevation), but about half of these are stratified in the wet season (northern summer), and their chemical composition varies more widely. Most of the natural lakes in the middle elevations (300 m to 1000 m) occupy former stream valleys dammed by landslides, lahars, volcanic mudflows, or lava; these can be unusually deep for their area and are more often stratified (7 of 9 lakes in this group). Low elevation lakes include oxbow lakes and swamp lakes, which are often stratified, tannin-stained, and more concentrated. The deepest lake in the country, Laguna de Río Cuarto, reaches 66 m of depth in its volcanic explosion crater (maar); it is probably oligomictic, mixing irregularly on a decadal time scale.

Rivers are more poorly known, but are attracting increasing attention as human impacts increase. Rivers have traditionally served as waste-removal systems and sites for hydroelectric projects. Most rivers are low in dissolved minerals owing to the igneous terrain and copious rainfall, but many become more concentrated in the dry season. Some rivers, e.g. the Río Agrio, bear unique chemical composition as a result of localized volcanic features.

© 1999 International Association for Limnology (SIL).

1999. Haberyan, K.A. and S.P. Horn. A 10,000-year diatom record from a glacial lake in Costa Rica. Mountain Research and Development 19: 63-70.

Note: There was no abstract in the original article; here's an off-the-cuff summary.

We counted 21 diatom slides from a 10,000-year-old core from a glacial lake, Lago de las Morrenas (elevation 3480 m) in Costa Rica, and scanned slides from 31 additional levels (sample interval 20 cm). At each level, at least ninety-five percent of all diatoms belong to a species of Aulacoseira (apparently a new species in the A. alpigena / A. lirata complex). This taxon is common in other lakes on the Cerro Chirripó, and in high altitude lakes in the Andes.

The diatom flora of the lake apparently has been dominated by this taxon since the lake was formed, so presumably the lake has always been cold, polymictic, and clear; in fact the great Secchi depth (7.5 m) may allow these Aulacoseira filaments adequate illumination while they lay on the bottom. Two peaks in diatom deposition rate seem to correlate to charcoal in this core and in cores from nearby lakes, but the diatoms of the lake seem insensitive to local drought, if any.

1998. Haberyan, K.A. The effect of volcanic ash influx on the diatom community of Lake Tanganyika, East Africa. Transactions, Missouri Academy of Sciences 32: 102-105.

I examined diatoms in the vicinity of a 56m ash layer, deposited around 11,850 years ago, in a core from Lake Tanganyika, East Africa, to assess the impacts of ashfall on a large lake. Immediately after the ashfall, diatoms concentrations fell by an order of magnitude, and Nitzschiadominated the flora instead of Stephanodiscus. The strong decrease in Aulacoseira abundance suggests that the ashfall probably occurred in the calm season (now November through April). The diatom community had recovered to pre-ash status within a decade.

1998. Haberyan, K.A. A hypothesis concerning vertically-migrating zooplankton and their fecal pellets. Transactions, Missouri Academy of Sciences 32: 99-101.

Vertical migration and pelletization of feces provide separate, intrinsic evolutionary advantages to zooplankton. Fecal pellets are a valuable source of nutrition, and sink at rates that place them in the depth range of migrators in the daytime. Consequently, migrators at depth can ingest the pellets that were excreted the previous night in surface waters, perhaps providing an important supplement to daily nutrition.

1998. Robbins, L.H., M.L. Murphy, A.C.Campbell, G.A. Brook, D.M. Reid, K.A. Haberyan, and W.S. Downey. Test excavations and reconnaissance palaeoenvironmental work at Toteng, Botswana. South African Archaeological Bulletin 53:125-132.

Recent interdisciplinary research near Lake Ngami has revealed Later Stone Age occupation dated to between c. 3930+ 100 BP and 2400 + 80 BP. Detailed study of the sediments, dated by radiocarbon and thermoluminescence (TL) methods, as well as the identification of 19 species of diatoms provides new evidence about the water conditions and the past nature of Lake Ngami during the Holocene. These findings suggest that the main Later Stone Age occupation occurred during a period when an arm of Lake Ngami extended into the valley north of the site. The Holocene palaeoenvironmental record for Lake Ngami compares favourably with other regional data, especially cave speleothem and tufa evidence obtained from the summer rainfall zone of southern Africa.

1997. Chavez, L., and K.A. Haberyan. Diatoms from the Camastro Diatomite, Costa Rica. Revista de Biología Tropical 44:857-860.

Note: translated from the Spanish

We studied diatoms in 23 samples from three lacustrine deposits (Pliocene) in the vicinity of Loma Camastro near Liberia, Guanacaste, Costa Rica. The primary species were Aulacoseira ambigua, Cyclotella meneghiniana, Fragilaria brevistriata, Fragilaria pinnata, Navicula menisculus, Nitzschia amphibia, Stephanodiscus dubius, and Synedra ulna. We recognized seven assemblages, all suggesting that the lake was shallow, eutrophic, slightly basic (pH 7.8 to 8.5), with low to medium concentrations of silica, and low conducitivity. Some slight variations may suggest changes in trophic status.

1997. Haberyan, K.A., S.P. Horn, and B.F. Cumming. Diatom assemblages from Costa Rican lakes: an initial ecological assessment. Journal of Paleolimnology 17: 263-274.

We compared the distributions of 59 diatom species in surface sediments of 25 Costa Rican lakes with 21 environmental variables using canonical correspondence analysis (CCA). The distribution of taxa was related to the chemical and physical characteristics of the lakes. The most influential chemical variables were cation concentrations (especially magnesium) and related variables such as water hardness, pH, and temperature. Lake area and lake depth were among the most important physical variables.

A number of taxa were identified as potential environmental indicators. The diatoms Brachysira serians var. brachysira and Frustulia rhomboides seem to be associated with low values of alkalinity, hardness, Ca, Mg, and SiO₂. Cymbella minuta var. silesiaca is associated with low to moderate values of alkalinity, hardness, Ca, and Mg. Nitzschia cf. amphibia may be an indicator of moderate-to-high concentrations of Mg. Pinnularia braunii var. amphicephala seems to prefer low values of hardness, Ca, Mg, and SiO₂.

In many closed lakes, these environmental variables (Mg/Ca/hardness/ alkalinity) increase with effective evaporation. Consequently, these diatoms my be indirectly tracking P:E ratios. Results from this initial, small data set indicate the potential of diatoms for inferring lake paleochemistry, and perhaps P:E ratios, in Costa Rica.

1996. Porter, K.G., P.A. Saunders, K.A. Haberyan, A.E. Macubbin, T.R. Jacobsen, and R.E. Hodson. Annual cycle of autotrophy and heterotrophy in a small, monomictic, piedmont lake (Lake Oglethorpe, GA): analog for the effects of climatic warming on dimictic lakes. Limnology and Oceanography 41: 1041- 1051.

Lake Oglethorpe, Georgia, is a small, monomictic impoundment in the southeastern U.S. Piedmont region. Seasonal differences in ecological processes correspond to the two major stratification patterns and result in seasonal differences in pelagic community structure. The winter mixed period (November-March) provides light and temperatures suitable for active nutrient regeneration and uptake, population growth of edible phytoplankton and crustacean zooplankton, and low bacterial abundance and production. Monthly estimates of daily primary productivity are in the mesoeutrophic range (40-1,420 mg C m^-2 d^-1); however, mean annual primary productivity is in the eutrophic range (500 g C m^-2 yr^-1) because of greater activity in winter and an extended "growing season." The stratified period (April-October) is characterized by rapid development of hypolimnetic anoxia, high bacterial production, cyanobacteria and large algae, heterotrophic flagellatese, ciliates, rotifers, small cyclopoid copepods, and Chaoborus. Heterotrophic activity, HPLC chlorophyll a, and grazer activity were highest at the epilimnetic-metalimnetic boundary. Bacterial abundances (1.5-32 x 10⁶ cells ml^-1) increased in the hypolimnion during the stratified period. Long-term (1978-1994) warming within the water column (0.061-0.10 ^oC yr^-1) follows midwinter (January) air temperature trends. Using Lake Oglethorpe as an analog, we predict as consequences of climatic warming in northern dimctic lakes: increses in nutrient cycling rates, winter primary and secondary productivity, summer heterotrophic production, and microbial components of the food web.

1996. Robbins, E.I., Y.-Y. Chen, M.C. Cuomo, K.A. Haberyan, E. Head, and P.J. Mudie. Fecal pellets. Chapter 17 in Jansonius, J. and D.C. McGregor (editors), Palynology: Principles and applications 3: 1085-1097. American Association of Stratigraphic Palynologists.

Note: There was no abstract in the original article; here's one of the introductory paragraphs.

The purpose of this chapter is to explore methods by which fecal pellets can be identified in rocks and to suggest techniques for the preparation of samples for pellet identificaiton. This chapter also presents four case studies, three of which were designed to extend our understanding of the role of fecal pellets in concentrating dinoflagellates, diatoms and pollen grains. The last case study explores the difference between pellets from planktonic and benthic animals and how the pellet type affects the petroleum source potential of rocks.

© 1996 American Association of Stratigraphic Palynologists Foundation.

1996. Robbins, L.H., M.L. Murphy, N.J. Stevens, G.A. Brook, A.H. Ivester, K.A. Haberyan, R.G. Klein, R. Milo, K.M. Stewart, D.G. Matthiesen, and A.J. Winkler. Paleoenvironment and archaeology of Drotsky's Cave: western Kalahari Desert, Botswana. Journal of Archaeological Science 23: 7-22.

Test excavations conducted at Drotsky's Cave have provided important new information on the paloeoenvironment and archaeology of the western Kalahari desert during the late and terminal Pleistocene. An occupation layer dated to the terminal Pleistocene was rich in Late Stone Age artefacts, pieces of ostrich egg shell, the remains of carnivorous bullfrogs, springhare, and other fauna. A detailed sediment study, along with the evidence of Angoni vlei rat, climbing mouse, an aquatic Xenopus frog, and side neck turtle confirms that conditions were for the most part, substantially more moist than at present between approximately 30,000 and 11,000 years ago. Analysis of a diatom assemblage dated to the terminal Plesitocene implies that the currently-dry Gwihaba Valley was mostly likely flowing for much of the year. Our evidence supports findings made at other localities in the Kalahari documenting the existence of especially moist conditions during the terminal Pleistocene.

1995. Haberyan, K.A., G. Umaña V., C. Collado, and S.P. Horn. Observations on the algae of some Costa Rican lakes. Hydrobiologia 312: 75-85.

We sampled 30 lakes in Costa Rica in the wet season (July-August) of 1991 for phytoplankton (with integrated and whole water samples), and 17 for zooplankton (with net tows). Taxa of plankton and community richness were poorly related to geography, morphology, chemistry, and other biota. Neither the zooplankton nor the phytoplankton appeared to influence the composition of the other, and neither were apparently influenced by the presence of fish.

Phytoplankton richness reflected primarily sampling method, but also tended to decrease with elevation and with Secchi disk depth, and tended to increase with pH and alkalinity. Chlorophytes were the most abundant division in 14 lakes; these lakes tended to be unstratified, turbid, and located at higher elevation. Diatoms were common in 4 of the 7 lakes with elevated silica (over 30 ppm). Each lake showed at least a 3:1 dominance by copepods, cladocera, or insect larvae. Copepods dominated 7 of the 17 lakes, most of which were shallow, turbid, and had low alkalinity. Cladocera dominated 7 lakes that were typically deeper and located at low- to mid- elevations. Insect larvae dominated two small, turbid lakes.

1993. Horn, S.P. and K.A. Haberyan. Costa Rican lakes: physical and chemical properties. National Geographic Research and Explorations 9: 86-103

Volcanic eruptions, landslides, rivers, glaciers, and human activity in Costa Rica have formed hundred of lakes. We surveyed 30 natural and artificial lakes ranging in elevation from near sea level to 3520m. All are fresh (mean alkalinity, 62 ppm CaC0₃; standard deviation, 55) and circumneutral in pH (mean, 6.5+1.3), regardless of location or elevation; the strongest correlate with elevation was temperature. Nationwide, lake chemistries show low diversity, but we found that neighboring lakes can be surprisingly different in physical structure and chemistry, even when similar in morphology and setting. Ten lakes, all below 1700 m, were stratified, albeit weakly; all are fairly deep or well-protected from wind. These 10 lakes are probably oligomictic, although 1 of them (Laguna Río Cuarto) tends towards meromixis. Most lakes in Costa RIca are probably polymictic.

1992. Brook, G.A., K.A. Haberyan, and S. De Filippis. Evidence of a shallow lake at Tsodilo Hills, Botswana, 17,500 to 15,000 B.P.: further confirmation of a widespread late Pleistocene humid period in the Kalahari. Palaeoecology of Africa 23: 165-175.

Two lacustrine carbonates containing freshwater diatoms were deposited immediately south of Tsodilo Hills at ca. 17,500 yr BP and at ca. 15,000 yr BP in an area which today is dry year-round. Although the lake was probably influenced by evaporative concentration at both times, differences in sedimentology and in diatom assemblages suggest a more permanent, deeper water body at 17,500 yr BP. The lake at 15,000 yr BP may have dried out seasonally and received wind-blown sand. Greater humidity in late glacial times may have been caused by an increase in summer precipitation due to the more southerly position of the Inter Tropical Convergence Zone, coupled with lower temperatures and evapotranspiration rates.

1992. Halfman, J.D., D.F. Jacobson, C.M. Cannella, K.A. Haberyan, and B.P. Finney. Fossil diatoms and the mid to late Holocene paleolimnology of Lake Turkana, Kenya: a reconnaissance study. Journal of Paleolimnology 7: 23-35.

A 12 m sediment core recovered from the south basin of Lake Turkana, northwestern Kenya, reveals four major diatom assemblages that span approximately 5450 to 1070 years BP based on AMS radiocarbon analyses. The oldest assemblage, Zone D (5450 to 4850 yr BP), is dominated by Melosira nyassensis and Stepanodiscus spp. and is interpreted to reflect higher lake levels, fresher water and more variable seasonal mixing of the water column than the modern lake. Melosira dominates the assemblage in Zone C (4850 to 3900 yr BP) with some Surirella engleri and Stephanodiscus. This assemblage indicates a continuation of relatively high lake levels and seasonal mixing of a stratified lake. The brief peak of Surirella, interpreted as benthic, suggests an episode of slightly lower lake level. Thalassiosira rudolfi and Surirella predominate since the beginning of Zone B (3900 to 1900 yr BP), reflecting a decrease in lake level and increase in water column salinity. Increasing dominance of Surirella in Zone A (1900 to 1070 yr BP) may suggest that the lake continued to decrease in depth. Salinity probably rose to levels comparable with the modern lake. These results are consistent with paleoclimatic interpretations based on carbonate abundance, lamination thickness, oxygen isotope and bulk geochemistry profiles from this core and cores recovered from the north basin. It extends the known paleolimnology beyond 4000 yr BP of the earlier research to 5450 yr BP and into the early to mid Holocene pluvial phase in northern intertropical east Africa.

1991. Haberyan, K.A. and O.K. Mhone. Algal communities near Cape Maclear, southern Lake Malawi, Africa. Hydrobiologia 215: 175-188.

Algal communities were compared among benthic and net plankton samples from Cape Maclear, Lake Malawi. In the cool mixing season (from May to August), rocks were overgrown by Cladophora or Calothrix, accompanied by the diatoms Rhopalodia, Cymbella, and Navicula. These diatoms, together with Epithemia and Cocconeis, were epiphytic on Cladophora and macrophytes. In sandy areas, the common diatoms were Rhopalodia, Fragilaria, Epithemia, Navicula, Surirella, and Melosira.

In all phytoplankton samples, taken with a 10 m m mesh net, cyanophyte cells were the most common (70 to 80%), especially those of Oscillatoria. Biomass, however, was dominated by Peridinium from November to April and by Anabaena and Oscillatoria from September to April when the mixolimnion was stratified. Among the chlorophytes, Oedogonium was the most common, especilly from May into December when Pleodorina became more common.

Diatoms dominated the biomass in the mixing season (May to September): Stephanodiscus in May, followed by Melosira nyassensis and lanceolate Nitzschia species from mid-June through August. For the rest of the year the epilimnion was stratified and the Nitzschia species were virtually the only diatoms present.

Benthic and planktonic communities share few taxa: benthic taxa never made up more than 2% of cells in offshore tows. This conclusion contrasts with previous reports, especially regarding Surirella. Consequently, an abundance of benthic taxa in sediment cores may be interpreted as lower lake level if sediment redistribution can be excluded. The seasonality of the planktonic diatoms is compatible with current ecological hypotheses, and therefore increases their value as paleolimnological indicators.

1990. Haberyan, K.A. The misrepresentation of the planktonic diatom assemblage in traps and sediments: southern Lake Malawi, Africa. Journal of Paleolimnology 3: 35-44.

Sediment trap collections near Cape Maclear, Lake Malawi, were compared to phytoplankton and surface sediment diatoms to assess taphonomic variations. The sedimenting diatom coummunity became progressively different from the diatom plankton with increasing depth: long Nitzschia species were strongly under-represented in the traps (annually, 53% among planktonic diatoms vs. 14% in the offshore 29 m trap; p << 0.005 by Kruskal-Wallis test), while Melosira was greatly over-represented in traps (32% vs. 57%; p < 0.005). The abundance of the minor taxa (Rhopalodia, Fragilaria, Cymbella, and Surirella) were greatly enhanced in traps relative to the plankton, but they were still relatively uncommon (<3% of all diatoms each). Differences in grazing, dissolution, and sinking rates alone are insufficient to account for these distortions; a combination of these, plus perhaps unknown factors, strongly influence the deposited assemblage.

These misrepresentations were also present at the sediment surface. The greatest discrepancy was noted for Melosira (32% of plankton vs. 53% of sediment surface diatoms; p < 0.005). In Lake Malawi, at least, paleolimnologists must not assume a straightforward correlation of modern and fossil assemblages.

1988. Haberyan, K.A. Phycology, sedimentology, and paleolimnology near Cape Maclear, southern Lake Malawi, Africa. Ph.D. Dissertation, Duke University, Durham N.C. 246 pp.

Southern Lake Malawi was sampled thoroughly to determine algal distributions, the effects of sedimentary process, and paleolimnology. Rocks were covered with mats of the chlorophyte Cladophora or the cyanophyte Calothrix, accompanied by the diatoms Rhopalodia, Cymbella, and Navicula. Common diatoms among sand grains were Rhopalodia, Navicula, Epithemia, Fragilaria brevistriata, and Surirella.

The planktonic biomass was dominated during the stratified (calm) season by Peridinium, Anabaena, and Nitzschia cf. spiculum. In the mixing (windy) season, diatoms dominate the biomass, including approximately equal cell abundances of Stephanodiscus, Nitzschia cf. spiculum, and Melosira. The chlorphyte Oedogonium was also common.

Sediment trap collections revealed strong misrepresentation among diatoms. Melosira accounted for 32% of planktonic diatom cells, but 57% of the diatoms in the deeper (29 m) sediment trap (Kruskal-Wallis test, p < 0.005). Nitzschia cf. spiculum was dramatically under-represented in traps: 53% of planktonic diatom cells but only 14% in the deeper trap (p << 0.005). These data demonstrate that sedimenting diatom assemblages are sometimes a distorted representation of the living community.

The surface sediment assemblage was also different from the plankton. Melosira rose from 32% in the plankton to 53% of the deposited assemblage (p < 0.005). The abundance of Nitzschia cf. spiculum plummeted from 53% of the plankton to 0.8% in the surface mud (p< 0.005).

Grab samples were used to develop transfer functions for paleodepth estimation. The microfossil assemblage was more strongly correlated with depth rather than distance from shore. Seven depth functions resulted in r² values exceeding 0.59 and 95% confidence limits of 5 ot 27 m; the best was total percent planktonic diatoms (r² = 0.73, + 7-16 m).

These paleodepth transfer functions were applied to Core MK-1, and the results match the historical record rather poorly. Because of its strong dependence on the southeasterly trade winds, Melosira suggests relatively consistent wind strength since about 1700 A.D. Benthic diatoms show little change as well, so it seems unlikely that lake level has varied substantially (i.e. < 20 m) from modern since 1700.

In Core 6P, Melosira was relatively uncommon in sediments representing approximately the third and fifth millenia BP. Local upwelling must have been quite reduced. Abundant Stephanodiscus there suggests that southerly trade winds were weaker, not absent. The benthic diatom Rhopalodia may indicate a slight lowering of lake level in the last two to three millenia. Therefore, the predominant signal recorded in the sediments is one of varying wind strength. Lake level apparently has not been more than 40 m lower than modern in the last six millenia.

Large-lake paleolimnologists must not assume fair representation of diatoms in sediments. Major misrepresentations cause Nitzschia to be virtually absent from surface sediments, although it is the most common genus among the planktonic diatoms.

1987. Haberyan, K.A. and R.E. Hecky. The late Pleistocene and Holocene stratigraphy and paleolimnology of Lakes Kivu and Tanganyika. Palaeogeography, Palaeoclimatology, Palaeoecology 62: 169-197.

Evidence from diatoms, chemistry, and sedimentology shows that Lakes Kivu and Tanganyika experienced late Pleistocene low stands, -86 to -300 m for Kivu and -250 to -350 m for Tanganyika. Both lakes had higher (2-10 fold) sedimentation rates prior to 11,500 yr B.P. About 9900 yr B.P., upwelling become important in southern Lake Tanganyika, which had been deepening for at least several millenia. By 9400 yr B.P., Kivu had become deep and dilute, with overflow via the Ruzizi River to Lake Tanganyika. Southern Lake Tanganyika became more stably stratified about 5200 yr B.P. Volcanism and hydrothermal activity in Kivu began about 5000 yr B.P., and the salinity reached 3 ppt and the lake became strongly stratified. The Ruzizi River outflow was interrupted from 3500 yr B.P. until recently. The sedimentary record implies that sudden hydrothermal activity and sublacustrine volcanism in Kivu has probably been the cause of its impoverished fauna.

These results show that high lake levels in the Eastern Rift of Africa from 10,000 to 7000 yr B.P. were paralleled in the Western Rift. Given the great volumes of these lakes, climate has not caused great variations in salinity; the diatom floras, however, have been remarkably sensitive to changes in stratification and nutrient supply. Volcanism has been a major force in the limnological and biological evolution of Lake Kivu, while both Kivu and Tanganyika have responded to changes in preciptation and wind stress.

1987. Haberyan, K.A. Fossil diatoms and the paleolimnology of Lake Rukwa, Tanzania. Freshwater Biology 17: 429-436.

1. A 23.1 m sediment core from Lake Rukwa, southwest Tanzania, records 13,000 years of climatic change in five diatom assemblage zones. Zone E (13,000 - 12,700 BP) reflects the transition from the waning lake glacial arid phase to pluvial conditions, as indicated by the co-occurrence of diatoms associated with fresh and relatively saline conditions. Zone D (12,700 - 4400 BP) represents a moist period with frequent stratification, indicated by the halophobic genera Melosira and Stephanodiscus, which also represent alternating silica-rich and silica-depleted waters. Beginning with Zone C (4400 - 3900 BP) the lake became much more saline with Thalassiosira predominating. This drying trend was reversed slightly in Zone B (3900 - 3300 BP). During the last three millenia (Zone A), lake salinity was further reduced, while tranistory moist phases were occurring in more northerly lakes such as Victoria and Kivu.

2. Lake Rukwa was relatively stable over a time scale of centuries, but on an annual basis is quite variable in salinity depending on the local rainly season.

3. These results agree well with the generalized paleoclimatic chronology of East Africa and suggest that the Holocene climatic regime of East Africa extended to at least 8^oS.

1985. Robbins, E.I., K.G. Porter, and K.A. Haberyan. Pellet microfossils: possible evidence for metazoan life in Early Proterozoic time. Proceedings of the National Academy of Science 82: 5809-5813.

Microfossils resembling fecal pellets occur in acid-resistant residues and thin sections of Middle Cambrian to Early Proterozoic shale. The cylindrical microfossils average 50 x 110 mm and are the size and shape of fecal pellets produced by microscopic animals today. Pellets occur in dary gray and black rocks that were deposited in the facies that also preserves sulfide minerals and that represent environments analogous to those that preserve fecal pellets today. Rocks containing pellets and algal microfossils range in age from 0.53 to 1.9 gigayears (Gyr) and include Burgess Shale, Greyson and Newland Formations, Rove Formation, and Gunflint Iron-Formation. Similar rock types of Archean age, ranging from 2.68 to 3.8 Gyr, were barren of pellets. If the Proterozoic microfossils are fossilized fecal pellets, they provide evidence of metazoan life and a complex food chain at 1.9 Gyr ago. This occurrence predates macroscopic metazoan body fossils in the Ediacaran System at 0.67 Gyr., animal trace fossils from 0.9 to 1.3 Gyr, and fossils of unicellular eukaryotic plankton at 1.4 Gyr.

1985. Haberyan, K.A. The role of copepod fecal pellets in the deposition of diatoms in Lake Tanganyika. Limnology and Oceanography 30: 1010-1023.

Fecal pellets from a 16,000-year sediment core from southern Lake Tanganyika account for over 40% of all diatom deposition and about 30% of total bulk sedimentation. Comparison of diatoms inside pellets with those in the surrounding sediment indicates that small, blunt species like Fragilaria brevistriata and Gomphonema clevei are preferentially ingested by grazing copepods. Long, fragile species like Nitzschia spiculum are strongly avoided. Filamentous Melosira spp. seem to be an important food of copepods.

This grazing selectivity, coupled with the enhanced sinking rates and preservation of fecal pellets, could distort the fossil diatom record. Relative diaotm abundances in pelletized, nonpelletized, and pooled stratigraphes indicate that pellets actually cause shifts of < 4% of total diatom abundance in Lake Tanganyika. Even with selective grazing, F. brevistriata and G. clevei are rare in sediments (<2% of all diatoms).

1984. Haberyan, K.A. Copepod fecal pellets and microfossil deposition in Lake Tanganyika. M.S. Thesis, University of Georgia, Athens. 151pp.

Copepod fecal pellets sink at rates appropriate to place them at depths occupied by their producers after their predawn migration. Coprophagy of these pellets increases net energy intake.

A large volcanic ash influx at the south end of Lake Tanganyika 11,800 years ago greatly reduced the diatom community, but affected the genus Nitzschia least severly. Abundance and frequencies of all taxa had returned to pre-ash values within 25 years.

Surface water and sedimented plankton communities are quite similar in northern Lake Tanganyika. For Lake Malawi, similar comparisons indicate that seasonality, possible abrasion, and even occasional exposure to oxic waters reduce fecal pellet abundances. The accuracy of the sediment record must be evaluated on a case-by-case basis.

Fecal pellets in southern Lake Tanganyika account for 30% of all sediment flux and 40% of all diatom flux. Since 4300 yBP, diatoms are less common in sediments and in pellets, indicating a feeding shift by grazing copepods as diatoms became less common in surface waters. Small round diatoms (Fragilaria, Gomphonema) are four to eight times more common inside pellets and long, sharp forms (Nitzschia) are strongly avoided by grazers. Overall, only very slight shifts in the relative abundances of diatoms are caused by fecal pellet deposition of preferred species.

1983. Livingstone, D., B. Rosendahl, R. Dunseath, J. Maley, P. Bailey, K. Haberyan, D. Burney, G. Sugihara, M. Patterson, C. Ebinger, F. Spy-Anderson, J. Nelson, M. Crow, J. LeFournier, C. Stager, R. Kendall, J. Melack, M. LaBarbera, C. LeMut, W. Cromie, J.J. Tiercelin, M. Mvumbi, and J. Chorowitz. Potential sites for a long core in the East African Rift. Bulletin des Centres des Recherches, Exploration, et Production, Elf Aquitaine 7: 443-448.

The sediment under Lake Malawi is 1000 meters thick in places. It is much faulted and folded and is interrupted by a widespread angular unconformity overlain by a thin sedimentary veneer. One of the Lake Tanganyika basins contains at least 2900 m of sediment, without any seismically visible sign of hiatus or disturbance.

Lake Malawi has experienced very little change in either diatom or pollen assemblages over the past 30,000 years. Lake Tanganyika provides a more sensitive record of climatic change over the same period of time.

Coring to basement in such large lakes would be very expensive. Maar lakes would be much more manageable. Because their sediment comes from a simple catchment that is small in relation to the size of the lake, proxy climatic records from maars would present fewer complications than those of a large graben.