The effects of the oligochaete Branchiura sowerbyi Beddard (Tubificidae) on the biological and chemical characteristics of overlying water and soil in a submerged ricefield soil systemKikuchi, E.; Kurihara, Y.
doi: 10.1007/BF00007108pmid: N/A
Submerged ricefield soils, outdoors, and with and without the tubificid Branchiura sowerbyi Beddard, were used to study the effects of tubificids on some biotic and abiotic variables. Measurements of chemical and biological features showed that the tubificids accelerated the diffusion of dissolved substances, increased the release of soil bacteria and enhanced the production of algae and a duckweed (Lemna paucicostata) in the overlying water. In the presence of tubificids, increased numbers of Cladocera (Moina sp., Simocephalus sp.) and ostracods in the overlying water, and higher number of sulfate-reducing bacteria in the soil were observed. The tubificids further enhanced the microbial activity in the upper soil layer, which in turn produced large amounts of organic matter.
Overturn in a hypertrophic, warm, monomictic impoundment (Hartbeespoort Dam, South Africa)Robarts, R.; Ashton, P.; Thornton, J.; Taussig, H.; Sephton, L.
doi: 10.1007/BF00007109pmid: N/A
A major decrease in air temperature with an increase in wind stress created thermal instability resulting in overturn. Surface oxygen values decreased from 12.6 (170% saturation) prior to overturn to 0.4 mg · l−1 (5.7%) after overturn. Recovery of surface oxygen concentrations to supersaturation took approximately three months. Changes in the nitrogen balance after overturn indicated that extremely high rates of nitrification occurred. Little change in phosphorus concentration was observed. Surface chlorophyll concentrations decreased from 235 to approximately 2 mg · m−3, resulting in very low primary production values (Amax = 12.4 mg C m−3 h−1). Reduced rates of primary production were maintained for several months after overturn, mainly owing to the low ratio of Zeu/Zm (0.17). No significant changes occurred in the total bacterial population other than a redistribution within the water column. Significant changes occurred in the distribution and density of the zooplankton population. No fish kills were observed although fish populations were oxygen-stressed.
Seasonal variation of egg size and number in a Daphnia pulex populationBrambilla, Donald
doi: 10.1007/BF00007111pmid: N/A
Seasonal variation of egg size and number was examined in a Daphnia pulex population inhabiting a vernal pond. In this population, size at maturity declines at midseason, probably as an adaptive response to size-selective predation by larvae of the salamander Ambystoma. The larger early season individuals produce more and larger eggs than the smaller late season individuals. Age at maturity does not vary between seasons. Laboratory experiments indicate that temperature may affect egg size, egg number and size at maturity. However, field data suggest that temperature accounts for only a small fraction of the total variation in egg size and number. Indirect measures of nutrition indicate that food limitation does not cause the seasonal decline in egg size and number. The seasonal change in reproductive traits is well correlated with changes in invertebrate and vertebrate predation. Examination of predator feeding preferences and their impact on Daphnia mortality indicate that variation of reproductive traits is most likely a complex adaptation to changing predation regimes.
Periphyton production in an Appalachian riverHill, B.; Webster, J.
doi: 10.1007/BF00007114pmid: N/A
Periphyton primary production was measured by 14C uptake on natural substrates in two sections of the New River, Virginia, U.S.A. Production ranged from 6.71 ± 0.43 mg C g−1 h−1 in summer to 1.47 ± 0.22 mg C g−1 h−1 in late autumn in the hardwater reach and from l.90 ± 0.10 mg C g−1 h−1 to 0.12 ± 0.08 mg C g−1 h−1 in the softwater reach. Production in the hardwater reach was 3–5 times greater than in the softwater reach and significantly correlated with dissolved inorganic carbon (DIC) concentration (r2 = 0.506). No significant correlation was found between periphyton production and photosynthetically active radiation (PhAR). Extrapolation of periphyton production to a 135 km reach of the New River yielded an estimated annual input of 2 252 T AFDW from this source. Estimates of allochthonous (excluding upstream contributions) and aquatic macrophyte inputs to this same reach were 64 T AFDW and 2 001 T AFDW, respectively. While periphyton is not a large source of organic matter, its high food quality and digestibility make it an important component of the New River energy dynamics.
Instar sizes, life cycles, and food habits of five Rhyacophila (Trichoptera: Rhyacophilidae) species from the Appalachian Mountains of South Carolina, U.S.A.Manuel, Kenneth; Folsom, Todd
doi: 10.1007/BF00007115pmid: N/A
The larval head widths at each instar, life cycles, and food habits of late instars were determined for five species of Rhyacophila from two Appalachian mountain streams in South Carolina, U.S.A. Rhyacophila acutiloba Morse & Ross was univoltine with two cohorts, one emerging in the spring and another presumably emerging in early autumn. Rhyacophila fuscula (Walker), R. nigrita Banks, and R. carolina Banks were apparently multicohort, univoltine species with extended flight periods. Rhyacophila minor Banks was univoltine with a spring emergence. All species were predaceous and consumed mainly Plecoptera nymphs and Trichoptera larvae.