An annual fossil record of production,planktivory and piscivory during whole-lake manipulations

Annual and subannual paleolimnological records of pigments and zooplankton were used to analyze three whole-lake manipulations. The relative abundance of cladoceran remains in recent seasonal laminae was significantly correlated with the relative abundance of species in the plankton (r ²=0.59,P<0.001). Comparison of food-web structure after piscivore introduction showed that there are multiple outcomes of predation and that final food-web structure depended on the strength of interaction between piscivorous and planktivorous fish. Intense predation on cyprinids (Phoxinus eos, P. neogaeus, Umbra limi) by largemouth bass (Micropterus salmoides) allowed large herbivores (Daphnia pulex) and invertebrate predators (Chaoborus punctipennis) to dominate. Analysis of fossil invertebrate morphology suggested that small grazers (Bosmina longirostris, Diaphanosoma birgei) were eliminated by invertebrate predators. Under moderate predation by rainbow trout (Oncorhynchus mykiss), cyprinids remained, only intermediate-size herbivores (D. rosea) increased in abundance, andBosmina persisted. In contrast to food-web manipulations, increased algal abundance resulting from watershed disturbance (road construction) did not alter the species composition or size-structure of fossil Cladocera.     

The effects of changing solar angles,cloud regimes,and air temperatures on the temperatures of contrasting surfaces

A steady-state energy budget and a solar radiation-cloud attenuation model have been linked. This has permitted a systematic examination of the changing relative surface temperatures and differences between surface and air temperatures as functions of varying solar altitudes, selected cloud types, cloud covers, and air temperatures. This analysis was performed for two contrasting surfaces: barren and grassy. The results are presented in a series of three-dimensional graphs. The grassy landscape reacted more conservatively to changing solar altitudes (for all cloud types and amounts) compared with the barren surface. The results are assumed to encompass most of the possible extremes encountered in real landscapes exposed to similar changes in solar angle, air temperatures, and cloud regimes.Dr. O'Rourke is currently a Post-Doctoral Scholar at UCLA.     

An urban radiation obstruction model

An urban street canyon radiation obstruction model has been developed. The model can describe community structure in terms of the type and dimensions of every building, block, road, park, etc. The need for massive data acquisition in regard to obstruction modeling calls for computerized algorithms, relieving the researcher of the needless tedium of hand calculations and the accompanying high degree of error and labor costs. The model program OBSTRUCT was written in FORTRAN IV for use on the IBM 3033. To facilitate changes or modifications, OBSTRUCT was written in modular form.     

A revised species list and commentary on the macroalgae of the Chesapeake Bay in Maryland

Macroscopic marine algae were collected at a variety of intertidal sites and on cruises throughout the Maryland Chesapeake Bay in 1972–73, and numerous specimens from the University of Maryland herbarium were examined. The revised species list contains 62 taxa as follows: 26 Rhodophyceae, 1 Xanthophyceae, 6 Phaeophyceae, 29 Chlorophyceae. Grinnellia americana, Neoagardhiella baileyi, Porphyra sp.,Vaucheria sp.,Desmotrichum undulatum, Ectocarpus confervoides, Enteromorpha compressa var.lingulata, E. linza, Entocladia viridis andUrospora sp. are new records for the flora of the upper Bay. Records ofAscophyllum are believed to represent discarded bait-packing material rather than an endemic population in the upper Bay. Ceramium, Polysiphonia, Cladophora, Enteromorpha andUlva are the genera most likely to be encountered in the upper Bay. In winter, brown algae, mainlyEctocarpus species, become a more conspicuous component of the flora. Comments on distribution, seasonality, taxonomic problems, and invalid or questionable records are included. Literature pertinent to the Delmarva region is reviewed briefly.     

Dissolved aluminium in interstitial waters of recent terrigenous marine sediments from the North Atlantic Ocean

The vertical distribution of dissolved Al in interstitial waters of recent marine sediments has been determined using a fluorimetric analytical method adapted for interstitial water analysis. The results suggest that diagenetic reactions occur in the sediment soon after deposition. A narrow depth zone acting as a source of dissolved Al is found in each core. Outside this zone Al appears to be removed from solution and its concentration decreases to values of 1.5 μgAl/l or less, comparable to those of open ocean waters. Dissolved Al and SiO₂ concentrations in interstitial waters close to the sediment-seawater interface are linearly correlated in most cases, suggesting that the geochemistry of Al may be related to the behaviour of biogenic silica in marine sediments.     

Methane solubilities in multisalt solutions

Solubilities of methane in multisalt solutions at 550 psia and 25°C can be predicted from single-salt salting coefficients. The ionic strength contribution of the ith salt, I_i, is multiplied by its molal salting coefficient, k_mi, in the following summation over all salts:

$\text{log}\text{M}{}_{\mathrm{o}}\text{M}{}_{\mathrm{s}}\text{= ∑}{}_{\mathrm{i}}\text{k}{}_{\mathrm{m}}{}_{\mathrm{i}}\text{I}{}_{\mathrm{i}}$

where m_o and m_s are molal methane solubilities in distilled water and the salt solution, respectively, at the T, P and methane fugacity of interest.This equation predicts methane solubility in multisalt brines containing Na⁺, K⁺, Mg⁺², Ca⁺², Cl^?, SO₄^?2 and CO₃^?2 ions. k_mi values reported by Stoessell and Byrne (1982b) can be used in solubility predictions in brines at earth surface conditions. Prediction in reservoir brines would require determination of k_mi, for the different salts at reservoir temperatures and pressures.     

Predation by the ctenophoreMnemiopsis leidyi in Narragansett Bay,Rhode Island

The impact ofMnemiopsis leidyi as a predator was studied quantitatively to determine their feeding rates on mixed natural zooplankton. These studies showed that feeding rate was independent of food concentration, but a function of both temperature and size of ctenophore. The feeding rate (liters cleared per mg dry weight per day) ranged from about 0.01 for larger ctenophores at lower temperatures (10–15°C) to about 0.1 for smaller ctenophores at higher temperatures (20–25°C). Combining these results with ctenophore biomass estimates from three years of sampling, numerical estimates were made of zooplankton mortality due to ctenophore predation. The maximum summer cropping byM. leidyi was calculated to be an average of 5–10% per day for the bay as a whole. Although substantial, this predation pressure alone does not account for the observed summer decline of zooplankton.     

Stage-specific spatial and temporal variability in the diets of larval winter flounder (<Emphasis Type="Italic">Pseudopleuronectes americanus</Emphasis>) in a northeastern U.S. estuarine nursery

Collections of winter flounder (Pseudopleuronectes americanus) larvae were made biweekly from March to May in 1999 and 2000 in the Navesink River-Sandy Hook Bay estuarine system, New Jersey, to determine stage-specific spatial and temporal variability in diets. Relatively high percentages of larvae with empty guts were found at low water temperatures. Percentages of empty guts did not differ by larval stage (preflexion and postflexion) or region of collection (river and bay). There was high intraregional variability in percentages of larvae with empty guts. Nauplii, invertebrate eggs, and polychaete larvae were dominant prey items followed by tintinnids, bivalve and gastropod veligers, and diatoms. Ontogenetic dietary shifts were evident in both years. Preflexion winter flounder largely consumed nauplii, invertebrate eggs, and tintinnids; postflexion winter flounder consumed the largest prey (polychaete larvae) but also retained small prey items in their diets. Water temperature significantly affected the percentages of larvae feeding on nauplii (p<0.05) and tintinnids (p<0.08) in 2000. Region of collection was not significantly related to diets because of high intraregional variability. Fine scale spatial (within regions, stations were approximately 3 km apart) and temporal (weeks) dietary variation of larval winter flounder could result in accompanying variation in development, growth stage duration, and survival.     

Pampean Orogen: An Intraplate Component of Early Paleozoic Deformation?

After accretion of the Pampean continental fragment to the western Rio de la Plata craton margin (530 Ma), subsequent deformation, crustal anatexis and plutonism may have been intraplate responses to Brasiliano-PanAfrican collisional tectonism on the eastern margin during the amalgamation of Gondwana. Investigations of intraplate orogens such as the Tien Shan and the Ancestral Rocky Mountains, as well as of analogue and numerical models, permit discrimination of two early Paleozoic tectonomagmatic phases in the Sierras Pampeanas. The first involved marginal trough subduction and calc-alkaline magmatism, culminating in accretion of the Pampean terrane to the western craton edge; the second was characterized by crustal anatexis and peraluminous plutonism, penetrative deformation and high-angle reverse faulting resulting from continental collision on the eastern craton margin.Field observations from modern (Tien Shan) and ancient (Ancestral Rocky Mountains) intraplate chains, deep seismic and borehole data, radiometric and fission-track data constitute control for analogue and numerical models of intraplate deformation resulting from continental collision. Near-simultaneous continent-wide deformation, regularly spaced ranges/buckles, reverse-fault initiation at fold hinges of buckles, and doubling of crustal thickness are replicated in structural arrays formed in four-layer analogue models of lithospheric buckling. These data have significant implications for the ductile deformation, crustral thickening and post-subduction plutonism that spanned central South America in Late Cambrian time.