ALBERT

Notes: Organic and inorganic carbon and nitrogen parameters were sampled simultaneously at 6 h intervals over a diurnal period at seven stations in a small hardwater stream in southern Michigan. Concentrations and budget values (kg/day) varied up to 10-fold at individual stations and between stations. The most constant parameters were total dissolved organic carbon and nitrogen. The most variable parameter was particulate organic carbon.Significant changes were noted in all parameters as the stream passed through different stream-side habitats. Budget values facilitated interpretation of these changes over time between stations. High variability in the concentration values was introduced by large allochthonous inputs of dissolved organic matter (DOM) and water alternately adding to or diluting parameters. Distance from upstream terrestrial DOM sources, DOM residence time, the pulsed nature of DOM inputs and biological utilization of DOM have important effects on the quality and quantity of DOM that enters recipient lakes and rivers. The importance of ground-water flux and DOM content is stressed. The DOM input and turnover within hardwater streams appears t o be in rapid, dynamic equilibrium.

Notes: A typical marl lake of the Upper Great Lakes region has very few quantitatively important aquatic macrophytes. The macrophytes, however, dominate the total primary production of the lake. Submersed vegetation is extremely sparse on the shallow (less than I m) marl bench that characterizes the littoral of these lakes, and is completely dominated by one. little-known species (Scirpus subterminalis Torr.) between 1 and 7 m.A detailed investigation of the spatial and seasonal distribution of macrophytic species and biomass showed that S. subterminalis strongly dominated the lake (79% of total biomass). S. suhterminalis represented an almost pure stand (to 200 g m−2 mean annual ash-free dry weight) at all times of the year at intermediate depths of macrophytic growth (1–6 m). Two species of Chara (of eight varieties and forms) were present in significant quantities (12% of total biomass; to 100 g m−2) but were severely limited to shallow depths (0-S-l m) and protected areas. Several annual submersed angiosperms were present (9% of total biomass), but only two species were quantitatively important. Potamogeton illinoensis Morong. and P. praelongus Wulfen formed brief summer peaks (less than 100 g m−2) at 3 and 4–6 m, respectively.A striking feature of the seasonal biomass distribution of Scirpus subterminalis was the higher, viable biomass (to 150g m−2) throughout the winter under ice cover. Cyclic fluctuations of the S. subterminalis populations were discerned at different depths, each with different periodicities. The population at 2 m exhibited a fall peak; that at 4 m had a summer maximum. The lowest overall biomass of S. subterminalis occurred in the 2 m population in June. Chara populations at 0–2 m also exhibited a relatively constant biomass throughout the year. The appearance of Nitella at 7 m in July-October and of Chara at 5 m in September-October was interpreted as an interaction between light, thermal, and carbon stratification.Estimates of macrophytic productivity of perennial (‘evergreen’) species populations whose biomass remains relatively constant throughout the year were made employing several different methods of calculation and turnover factors. All methods resulted in productivity estimates in good agreement with the conservative value of 178 g m−2 year−1 for the entire lake. In comparison to the other components (phyto-planktonic, epiphytic and epipelic algae) of the primary production of Lawrence Lake, the aquatic macrophytes constituted a major portion (anuual mean 82·77 g C m−2 year−1 or 48·3 %) of the total production of the lake.The low diversity but relatively high quantitative importance of macrophytes in marl lakes is attributed to an adverse dissolved inorganic and organic chemical milieu which inhibits phytoplanktonic production and allows only certain adapted macrophytes to develop strongly. The phenomenon of perennial biomass levels throughout the year is believed to be much more common than previously suspected and has iikely resulted from adaptations of submersed macrophytes to ameliorated conditions of water and temperatures relative to the terrestrial situation in winter.

Notes: 1. Pelagic trophic structure and energy fluxes are evaluated predominantly on the basis of ingestion of particulate organic matter by living organisms and the effects of consumption on the population dynamics of trophic levels.2. Population fluxes are not representative of the material and energy fluxes of either the composite pelagic region or the lake ecosystem. Metabolism of particulate and especially dissolved organic detritus from many pelagic and non-pelagic autochthonous and from allochthonous sources dominates both material and energy fluxes. Because of the very large magnitudes and relative chemical recalcitrance of these detrital sources, the large but slow metabolism of detritus provides an inherent ecosystem stability that energetically dampens the ephemeral, volatile fluctuations of higher trophic levels.3. The annual time period is the only meaningful interval in comparative quantitative analyses of material and energy fluxes at population, community, and ecosystem levels.4. Non-predatory death and metabolism by prokaryotic and protistian heterotrophs dominate. Continued application of animal-orientated relationships to the integrated, process-driven couplings of the aquatic ecosystems impedes understanding of quantitative ecosystem pathways and control mechanisms.

Notes: Three independent studies were conducted in which supplemental food was provided to juvenile Orconectes virilis reared at varying densities. One study was conducted in fiberglass tanks (densities of either 13, 27 or 54 individuals/m2) and two were conducted in outdoor pools (densities of either 2.5, 5, 10, 20 or 30 individuals/m2). Crayfish were offered a variety of foods ranging from a formulated diet to agricultural forages. Weight gain of crayfish fed a formulated diet and reared at varying densities was similar in the study conducted in tanks, but survival was significantly lower at the two highest densities (27 and 54/m2). Weight gain, survival and yield decreased as density increased in the studies conducted in outdoor pools. The highest weight gain and survival were at a density of 2.5/m2. Wheat straw was used as the source of nutrients. Use of formulated diets did not result in rapid weight gain when crayfish were reared at higher densities.