Growth of the Brine Shrimp \u3ci\u3eAremia franciscana\u3c/i\u3e Kellogg (Anostracoda) in the Materials Dispersion Apparatus as a Sealed Microcosm

We report the hatching of brine shrimp nauplii and their growth to preadults, and occasionally adults, in vacuum grease- sealed, 0.835-1.67 cc microalgal-based, xenic microcosms. Dormant brine shrimp cysts (1-5) were added to 0.75-1.50 ml Chlorella sp. cultures in Lexan™ plastic chambers (the microcosms) of the Materials Dispersion Apparatus (MDA); the chambers were then sealed. The assembled MDA was placed in a lighted incubator with continuous illumination at ca 26-30° C, on a shaker at 100 rpm. Occasionally the MDA was vibrated for 10 sec/day and sometimes mixed with 5-10 culture inversions at one time/day to insure particulate dispersion. Adult brine shrimp developed in as little as 9 days, with survival of preadults or adults (1 or 2/chamber maximum) for 12-56 days, at which times the experiments were terminated. Cultures with human fertilizer produced better brine shrimp growth and much longer survival compared to cultures without this fertilizer. That is, the nutrient wastes from the brine shrimp themselves were not sufficient without added human fertilizer to provide for best growth or survivorship of brine shrimp when compared to similar cultures that had this fertilizer. Some cultures (those that remained transparent and yellow to green) showed rather complete and sometimes obvious cyclic mineralization of their feces and shed chitinous exoskeletons, while other cultures (cloudy, and yellow to green) had much less particulate degradation. The concepts of bioregeneration and endogenous community culture regulation in a very small, xenic, microalgal-based metazoan closed-culture system are therefore demonstrated

Inferring lake depth using diatom assemblages in the shallow, seasonally variable lakes of the Nebraska Sand Hills (USA): Calibration, validation, and application of a 69-lake training set

The Nebraska Sand Hills are a distinctive eco-region in the semi-arid Great Plains of the western United States. The water table underlying the Sand Hills is part of the High Plains/ Ogallala aquifer, an important water resource for the central Great Plains. Lake levels are affected directly by fluctuations in the water table, which is recharged primarily by local precipitation and responds quickly to climatically induced changes in regional water balance. Instrumental records are available for only 50–100 years, and paleolimnological data provide important insights into the extremes and variability in moisture balance over longer time scales. A set of 69 lakes from across Nebraska was used to establish a statistical relationship between diatom community composition and water depth. This relationship was then used to develop a diatombased inference model for water depth using weighted averaging regression and calibration techniques. Development of the inference model was complicated by strong intra-seasonal variability in water depth and the linkages between depth and other limnologic characteristics, including alkalinity, water clarity and nutrient concentrations. Analysis of historical diatom communities from eight lakes allowed for the reconstruction of lake-level fluctuations over the past several thousand years. Comparisons of the more recent portion of these reconstructions with the instrumental Palmer Drought Severity Index (PDSI) showed that sediment records may not faithfully reflect short-term fluctuations in water level, except where sedimentation rates are very high. However, large and persistent changes in moisture availability were discernible even in longer, low-resolution records. Thus, diatoms are a useful addition to the tools available for understanding past drought in the central Great Plains, especially when trajectories of change are constrained by data from multiple sites or other proxies