ALBERT

Notes: As part of an agricultural non-point-source study in the Conestoga River head waters area in Pennsylvania, different methods for collecting ground water samples from a fractured carbonate-rock aquifer were compared. Samples were collected from seven wells that had been cased to bedrock and drilled as open holes to the first significant water-bearing zone. All samples were analyzed for specific conductance, dissolved oxygen, and dissolved-nitrogen species. Water samples collected by a point sampler without pumping the well were compared to samples collected by a submersible pump and by a point sampler after pumping the well. Samples collected by using a point sampler, adjacent to major water-bearing zones in an open borehole without pumping the well, were not statistically different from samples collected from the pump discharge or from point samples collected adjacent to major water-bearing zones after pumping the well. Samples collected by using a point sampler without pumping the well at depths other than those adjacent to the water-bearing zones did not give the same results as the other methods, especially when the water samples were collected from within the well casings. It was concluded that, for the wells at this site, sampling adjacent to major water-bearing zones by using a point sampler without pumping the well provides samples that are as representative of aquifer conditions as samples collected from the pump discharge after reaching constant temperature and specific conductance, and by using a point sampler after pumping the well.

Notes: Nutritionally important food items for crayfish have been difficult to identify and little information exists for third instar (first-feeding) crayfish. In this study, three major groups of potentially-important foods were fed to communally-reared third instar crayfish (Procambarus clarkii) and weight gain and survival were measured over a 30 day period. Mean weight gain (% increase) of crayfish fed the zooplankton Daphnia magna alone or in combination with other food items, ranged 2, 277–3, 239%, while mean weight gain of crayfish fed unidentified aquatic bacteria, the aquatic macrophyte Myriophyllum spicatus, combinations of bacteria and plant, or a negative control ranged 254–767%. No significant interaction of food items was detected. Bacteria appear to be a utilizable nutritional source for juvenile crayfish, but, using the methods employed in this study, do not support maximum rates of weight gain. Thus, pond management strategies that maximize zooplankton populations at the time of crayfish hatching might be beneficial.

Notes: Culture of orconectid crayfishes in the midwestern USA offers the potential of contributing to a year-round supply of fresh product as summer/fall production would augment winterhpring production in the southern USA. However, relatively little basic biological information exists for this potential new aquaculture crop. In this study, the authors reared juvenile (third instar) Orconectes virilis and Orconectes immunis at either 10, 15, 20, 25 or 30 C and measured weight gain and survival over a 21 day period. Orconcctes immunis juveniles were larger than O. virilis at the third instar and gained weight more rapidly in this experimental system. Gains in weight and length for both species increased as temperature increased from 10 to 25 C. Both values were lower in crayfish reared at 30 C, though number of molts was the same in crayfish reared at 25 or 30 C. Thus, there appears to be a bioenergetic cost of rearing orconectid crayfishes in temperatures above 25 C. Further, incremental growth with successive molts was influenced by water temperature.

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.

Notes: SUMMARY. Mixed natural assemblages of algae and bacteria exhibited lower rates of 14C assimilation and high rates of dissimilation of recent photosynthate when amended with low concentrations (7.2 mg 1-1) of unfractioned dissolved humic materials (DHM). The extent of the inhibition or stimulation was greatest in the smaller (1–5 μm) assemblage particles. In different algal-bacterial assemblages, additions of DHM markedly enhanced community alkaline phosphatase activity (APA), particularly under low light regimes, DHM of low apparent molecular weight was much more stimulatory to both 14C assimilation and APA than DHM of high apparent molecular weight, supporting the belief that DHM molecular weight is an important determinant of DHM interactive capacity. Higher concentrations of D HM (either unfractionated, or molecular weight fractionated) produced greater APA responses. Addition of phosphate enhanced the disparity in rates of 14C assimilation of samples incubated under low and high light regimes, increased the rates of 14C assimilation, and depressed APA. There were indications of interactions between DHM and phosphorus in several experiments. Two hypotheses were invoked to explain increases in APA in response to DHM: (1) increased competition between algae and bacteria for phosphate following bacterial release from substrate limitation, or (2) DHM may have acted as a sequestering agent for organophosphorus compounds, and in so doing, gradually depleted available phosphate. In either case, it is clear that DHM alters phosphorus cycling. This DHM characteristic may be ecologically as important as its ability to complex trace metals.

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: SUMMARY. The seasonal and depth distributions of dominant phytoplankters, in situ primary productivity, organic carbon, and major chemical variables are described for Gull Lake, Michigan for the years 1971–74. Despite efforts by residents surrounding this moderately large dimictic lake to reduce phosphorus loading, all indications are of progressive eutrophication over the period. Previously dominant Cyclotella michiganiana has almost completely disappeared while araphidinean diatoms have increased greatly; certain blue-green algae that were absent previously are becoming characteristic. The ratio of araphidinean to centric diatoms in recent sediments has also increased. Primary productivity and particulate and dissolved organic carbon concentrations have also increased. Voluntary attempts to reduce nutrient loading have apparently been inadequate to arrest increasing rates of eutrophication.

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.