Periods Of High Winds Research Articles

Wind Influences phytoplankton biomass and composition in a shallow, productive lake

Factors that regulate phytoplankton dynamics in shallow, productive lakes are poorly understood. Water-column phytoplankton chlorophyll (avg 105 µg liter−1) determined on 39 occasions over a 22-month period in shallow (mean depth, 1.7 m) Lake Apopka, Florida, correlated best with average daily windspeed compared with other environmental variables. High phytoplankton biomass reflects wind-induced resuspension of a meroplanktonic algal maximum (MAM) that exists on the aphotic lake bottom in a layer ~5 cm thick; this assemblage is dominated by microplankton-sized diatoms (>60% of total biomass) that can occur in cellular resting stages. Experiments demonstrate that the MAM can grow and photosynthesize at rates similar to surface populations when exposed to moderate irradiances. Direct inoculation of this meroplanktonic assemblage into surface waters during periods of high wind can account for a doubling in surface phytoplankton and diatom biomass as well as an increase in algal community size. A conceptual model outlines the influence that resuspension of the MAM has on ecosystem structure and function in the lake.

Physicochemical properties of aerosols over the northeast Atlantic: Evidence for wind‐speed‐related submicron sea‐salt aerosol production

Physicochemical characteristics of submicron aerosol particles over the Northeast Atlantic (63°N, 8°W) during October/November 1989 have been examined using a thermal analytical technique and are classified according to air mass origin. Aerosol associated with anthropogenically influenced air masses contained typically 80% sulphate particles by number, the remainder being soot carbon and sea salt. For Arctic air masses the contribution of sulphate to the total aerosol was reduced to around 65%, due to low concentrations relative to sea salt which is dependent on wind speed. In situations with clean maritime air and high wind speeds, sulphate aerosol accounted for less than 25% of the total accumulation mode particles, the remainder consisting predominantly of sea salt. Arctic air masses and clean maritime air during periods of high winds were consistently acidic with inferred molar ratios of NH4+/SO4= near 0.2. The continental and modified maritime aerosol encountered was found to have molar ratios of about 0.8. Soot carbon was present in all air masses to a similar degree (5–13%). In clean air masses, submicron sea salt aerosol concentrations showed a strong exponential increase with wind speed (correlation coefficients cc ≥ 0.8), down to a dry particle radius of 0.05 μm. Under these “clean air” conditions and high winds the sea salt aerosol dominated all particle sizes for r > 0.05 μm and accounted for approximately 75% of the total concentration, suggesting that under these conditions, sea salt aerosol would comprise the primary source of cloud condensation nuclei (CCN) in stratiform clouds.

Low‐frequency vibrational motion of Arctic pack ice

The mechanisms responsible for vibrational motions of Arctic ice at frequencies below about 100 Hz are know to be a combination of wave types, namely, gravity waves, flexural waves, and a variety of acoustic and/or elastic waves. Surface motion measurements using geophones and accelerometers on multiyear pack ice are used to establish the energy level of these motions and to differentiate between the different modes of propagation. Gravity waves are dominant below about 0.05 Hz, with their direction and dispersion relation being confirmed with vector measurements of acceleration from two stations. Motions driven by surface pressure fluctuations in the local wind appear at somewhat higher frequencies up to about 0.3 Hz and are particularly evident on thinner first‐year ice during periods of high wind. The band from 0.1 to 10 Hz comprises mainly flexural waves, as determined by their dispersion relation, and these are prominent during local ridge building events. At frequencies above 10 Hz, there is a combination of acoustic and flexural modes of propagation, with one or the other being dominant during specific environmental events. The probability density function of power in octave wide bands is approximately lognormal as a result of the high level of intermittence of local events. The variance in power level is significantly smaller for waterborne noise from more distant sources. Specific examples are used to illustrate the nature of the events.

Influence of sea spray and rainfall on the surface wind profile during conditions of strong winds

Janin and Cermak (1988) have: determined that airborne sediment in a wind tunnel substantially alters the low-level wind profile. This material apparently causes a reduction in wind speed since the pressure gradient force must accelerate both the air and the sediment, against the force of surface shearing stress. In this brief paper, we explore whether atmospheric wind profiles would be expected to be modified during periods of high winds as a result of heavy rainfall or sea spray. Although there has been controversy regarding the effect of sediment load on pressure drop (e.g., Rangaraju, 1988), our assumption that the wind profile rem~ins logarithmic is based on the physical modeling of Janin and Cermak (1988) in which even with sand loading in the atmosphere, the square root of the total kinetic energy profile remains logarithmic. This means that a given pressure ~adient force can accelerate either air, or a combination of air and a suspended material but when suspended material is present, the actual air velocity will be less. This Note represents an extension of Janin's study of sediment to the suspension of water in the atmosphere. If the effect of the suspended water mass were significant, there could be substantial effects on the aerodynamic response of buildings and other structures in high winds.

The seasonal cycle of arsenic in estuarine and nearshore waters of the South Atlantic Bight

Arsenic concentrations vary with season on the continental shelf of the South Atlantic Bight. During periods of high winds in the winter and early spring, inorganic arsenic concentrations are reduced to as little as 20% of typical open ocean concentrations by sorption onto resuspended sediments or incorporation into phytoplankton. In the early fall, arsenic sequestered in sediments in the spring is regenerated and returned to the water column, creating elevated arsenic concentrations in the nearshore zone that are up to 50% greater than open ocean concentrations. Arsenic in the adjacent estuaries is nearly conservative over the seasonal cycle, although its distribution in the estuaries is greatly affected by the seasonal changes in arsenic concentrations in the nearshore waters.

Dynamics of bottom currents in a small lake1

The dynamics of bottom currents in Baldeggersee, Switzerland, were investigated with a specially designed recording current meter sensitive to current velocities of 0.3–2.5 cm s−1. Supporting information was obtained from thermistor‐chain temperature recordings and from records of atmospheric boundary‐layer parameters measured in the center of the lake. During 1980–1981 bottom currents recorded for 1‐week periods on the central bottom plateau of the lake (65‐m water depth) were highly variable. The mean speed was slightly > 1 cm s−1 with no seasonal trend. Speeds >2.5 cm s−1 occurred after periods of high wind; quiescent periods were rare and seldom lasted more than 1 h. Spectral analysis shows that the primary mechanism generating bottom currents during stratification is internal gravity waves in the thermocline. During winter mixing when chemical stratification is observed below 30 m, the wind stress distribution is directly reflected in the bottom current pattern. In both periods wind‐induced disturbances were felt in the bottom layer with little time delay, indicating the event‐dominated structure of bottom current dynamics. Bursts of particle transport in the bottom layer are observed during periods of high wind, suggesting episodic particle resuspension. Such events may be important for the control of mass exchange at the sediment‐water interface.

A simplified analysis of various types of wind-induced road vehicle accidents

In periods of high wind three types of wind-induced vehicle accidents can be expected to occur: 1. (1) overtuning accidents, 2. (2) sideslip accidents, 3. (3) rotation accidents, This paper sets out a general analysis which throws some light on these types of accident and their interrelation. Simplifying assumptions have to be made for the problem to be tractable and these are discussed in some detail. For the Leyland Atlantean bus it is shown that overturning accidents are much more likely to occur than the other types of accident.

A dissolved oxygen budget model for Lake Erie in summer

SUMMARY. In this paper we extend a vertical mixing model of Lake Erie with an oxygen budget model. The model was tested against data gathered in the summers of 1979 and 1980 with good results, showing that it is capable of simulating vertical distributions of temperature and dissolved oxygen over relatively short time periods. The results underline the importance of turbulent mixing in distributing oxygen throughout the water column in the Central Basin of the lake. In addition, the results indicate that production and respiration processes dominate the budget under the influence of low wind speeds, while surface fluxes dominate during periods of high wind. Bottom mixing delays the onset of anoxic conditions at the sediment/water interface by distributing the sediment demand over the 5–6 m depth of the bottom mixed layer.

Sediment Resuspension and Currents in Lake Manitoba

The physical resuspension of bottom sediment during periods of high winds is thought to be important for nutrient recycling in large shallow lakes. In order to study resuspension, prototype instrumentation designed to collect gram quantities of suspended sediment at 38.1-cm intervals in the water column was deployed in 4.2 m of water in the shallow southern basin of Lake Manitoba for 1-month periods in 1978 and 1981. At about 2.7 m depth a sharp discontinuity was observed in the vertical distribution of total mass of suspended sediment collected. The mean current speed varied linearly with depth above the discontinuity but was more uniform near bottom. Although the water column was not thermally stratified, drogues frequently displayed a two-layer structure in the currents with a high skew in direction between layers. The particle size distributions were similarly discontinuous in the vertical, with large quantities of sand in the upper layer samples and a high silt load in the lower. The unusual particle size distribution, which was explained in terms of the origin of resuspended sediments and subsequent transport by lake currents, suggests a decoupling of lake turbulence between the two layers during high winds.

The influence of waves and seagrass communities on suspended particulates in an estuarine embayment

Resuspension of bottom sediments by waves, corresponding changes in suspended particulate material (SPM) concentrations in the overlying water column, and transport pathways of SPM were investigated in a shallow estuarine embayment colonized by seagrass communities in Chesapeake Bay. In shallow (<2 m), unvegetated regions significant resuspension of bottom sediments was evident when northerly winds exceeded 25 km h −1, increasing SPM concentrations up to 10-fold. High concentrations of SPM generated by resuspension dissipated rapidly (within 24 h) after winds became calm. Patterns of SPM along the embayment's depth gradient suggest that part of this resuspended material was transported offshore into deeper reaches of the estuary. In areas of the embayment colonized by seagrasses, wave energy was attenuated by the vegetation, suppressing resuspension and enhancing deposition. As a result, SPM concentrations were significantly lower inside seagrass beds than in adjacent unvegetated areas. During periods of high winds when wave induced resuspension occurred in unvegetated areas, SPM concentrations remained unchanged inside the bed at normal water levels. However, when water levels were elevated by spring tides or storm surges, plants were less effective at attenuating wave energy, and SPM concentrations increased inside the seagrass bed due to resuspension and advective processes. Calculations based on the results of this study indicate that sedimentation rates are substantially higher in seagrass communities than in unvegetated areas.

Environmental Control of Phytoplankton Patchiness

The relative importance of the various biological, chemical, and physical factors for the control of the phytoplankton patchiness in the environment has been studied for the near-surface waters of a small coastal embayment. It was found that during periods of low turbulent mixing (wind speed [Formula: see text]), the phytoplankton patchiness was induced by local differences (taxonomic or physiological) in its production efficiency which was linked to the dynamic fluctuation in the physicochemical characteristics of the medium. For periods of high winds [Formula: see text] it is indicated that the physical turbulent transport processes were responsible for damping out the spatial variations in the phytoplankton distribution.Key words: phytoplankton biomass, P/B ratio, spatial distribution, turbulence, wind stress

Anolis Cupreus: The Response of a Lizard to Tropical Seasonality

Seasonal changes in the population ecology of Anolis cupreus, a sexually dimorphic lizard, were studied over a 2—yr period in a deciduous and riparian forest ecosystem in western Costa Rica. This tropical environment undergoes strong seasonal changes, including a 6—mo yr dry season during which maximum air temperatures, hours of daily sunshine, and heavy winds occur. Many aspects of the ecology of A. cupreus undergo striking seasonal changes in response to this climatic seasonality. Both sexes were sexually active for about 6 mo of the year, with the ♀ cycle coinciding with the wet season. Fat body cycles in both sexes were inversely related to the reproductive cycles. Males and ♀ ♀ attain sexual maturity at 1 yr or less, and the population apparently undergoes an annual turnover. Population density was high (&gt; 1,200 anoles/ha) in the dry season, but in part because of changes in the structural habitat of ♂ ♂ and territorial behavior, density was much lower in the wet season. In the dry season social interactions were rarely seen, both sexes perched at or near ground level, and ♀ ♀. In contrast, in the wet season social interactions occupied a majority of the ♂ ♂ time as they defended territories and courted ♀ ♀. At this time of the year ♂ ♂ perched much higher than ♀ ♀ fed primarily on the ground; ♂ ♂ obtained at least half their food up to 6 m aboveground in the wet season. Because of seasonal changes in perch heights and size of prey items eaten, intrasexual (seasonal) values of place x food niche overlap were lower than intersexual values. The response of this anole to stressful climatic conditions is analogous to that of its Temperate Zone congener, Anolis carolinensis. Whereas A. carolinensis hibernates to avoid low winter temperatures, A. cupreus becomes inactive during periods of high winds and air temperatures.

Effects of location on responses of male melon flies to fiberboard blocks impregnated with cue-lure, a male attractant.

In tests on Oahu, Hawaii, in 1967-68, fiberboard blocks saturated with cue-lure, an attractant for male Dacus cucurbitae Coquillet, were suspended above ground or planced on bare soil to evalaluate the 2 methods of use in male annihilation programs. A baffle that reduced air circulation around a block on the soil (to simulate the shielding effects of vegetation around air-dropped blocks) reduced catches about 50%. During rainy periods with little wind, the suspended blocks caught more flies than the fully exposed ground blocks; this phenomenon was reversed during periods of high winds. Catches were about equal during light winds in dry periods.

Bottom Fauna of a Shallow Eutrophic Lake, Lizard Lake, Pocahontas County, Iowa

The State of Iowa is carrying on a dredging program in an attempt to rehabilitate many of the lakes in the northern part of the state. Most of these lakes are of glacial origin and are in the later stages of succession. They are of little value for boating and swimming because of the shallow depth and heavy growths of aquatic vegetation. The fish populations in many of them cannot be maintained because of their vulnerability to winter kill. By means of dredging, the life of these lakes is prolonged and sufficient depth is provided to support a fish population throughout the year. The increased depth and decrease in aquatic vegetation makes them more suitable as recreational areas. Conditions in these lakes are radically altered as a result of dredging and it is desirable to know what effect this has on the biological productivity. The bottom organisms are directly affected by dredging and it is believed that they can be used as an index to measure any changes in the productivity of these lakes. Lizard Lake was selected for a bottom fauna study because it will be dredged in the near future. This paper deals with the data gathered from Lizard Lake in the summer of 1951, before dredging of the lake, and will provide a basis for comparing the productivity in terms of bottom fauna after the lake has been dredged. Several sampling techniques were used to determine which would give the best results in dcifferent types of habitat. Lizard Lake, located in Lake Township, Pocahontas County, Iowa, has a surface area of approximately 268 acres (fig. 1). The maximum depth found in July, 1951, was 5 feet and much of the lake was between 4 and 5 feet deep. There are no docks or cottages around the lake and the surrounding land is devoted entirely to agriculture. Most of the land in the immediate vicinity of the shoreline is wooded or open pasture. The main inlet flowing into the shallow bay at the southwest corner of the lake provided water throughout the summer of 1951. The outlet is at the north end of the lake and drains into the west fork of Lizard Creek and thence to the west fork of the Des Moines River. Chemical and temperature readings indicated very little stratification from top to bottom during most of the summer. By the middle of August most of the surface of the central part of the lake was covered with a dense growth of sago pondweed, Potomogeton pectinatus. Methyl orange alkalinity ranged from 180 to 230 parts per million during the summer. Turbidity was almost entirely due to silt suspended in the water after periods of high wind. 0n calm days the Ekman sampler could be seen on the bottom at a depth of 4 feet.