William Y. B. Chang

Dynamics of dissolved oxygen and vertical circulation in fish ponds

Chang, W.Y.B. and Hai Ouyang, 1988. Dynamics of dissolved oxygen and vertical circulation in fish ponds. Aquaculture, 74: 263-276. Dissolved oxygen dynamics and vertical water circulation in high density integrated fish culture ponds were monitored monthly at 2-h intervals for 26 h from March through September at the Pearl River Delta, China. Stable thermal stratification was found almost daily in May-September. Vertical circulation began daily between 8 and 10 p.m. The average depth for this turnover in summer can be as great as 0.7-l m. Complete vertical circulation occurs only during major storms. A convection turbulence model was used to examine the vertical mixing process and showed that light wind ( < 100 cm/s) and surface cooling ( < 2OC) after sunset can substantially influence the depth of mixing. Photosynthesis by algae is the most important natural mechanism contributing oxygen to ponds; compared to photosynthesis, net oxygen gain and loss due to diffusion during daylight is small. The compensation depth corresponded to twice the Secchi disk depth, ranging from 50 to 80 cm. The dissolved oxygen (D.O.) concentration in the hypolimnion was usually less than 2 mg/l, but increased at night during the period of vertical circulation. Hypolimnion oxygen deficit (HOD) was explored with the in situ D.O. concentration. HOD was found to increase during the daylight period and decrease at night after destratification.

Large Lakes of China

China contains 28 of the worlds large lakes (> 500 km2). Information on these lakes is considerably limited. This paper describes in greater detail the origin, location, and the physical, chemical, and biological characteristics of the Chinese lakes and discusses the prevalant lake fish management methods in China. Elements which have influenced changes in Chinese large lakes are discussed. Climatic condition and tectonic uplift have strongly influenced the large lakes in the Tibet-Qinghai-Sinkiang region while sediment loading and human impacts continue to be the major concern for the large lakes in the Pacific basin.

Taihu Lake, lower Yangtze drainage basin: evolution, sedimentation rate and the sea level

Abstract The present study focuses on two Holocene sediment boreholes in Taihu Lake, sunk to examine the lake sediment including sedimentary texture and structure, microfossils, magnetic susceptibility and radiocarbon-dated Holocene stratigraphy. Results demonstrate that the early Taihu Lake area consisted primarily of West Taihu Lake depression and a low floodplain in the East Taihu Lake area. No hydraulic connection existed between the two sectors during the early Holocene when sea level stood at lower level. Core sediments, microfossil and magnetic evidence records that West Taihu Lake began to be inundated by brackish water prior to 6000 years ago, while East Taihu Lake still remained a freshwater setting. After 6000 B.P., a further rise in freshwater table in response to sea-level fluctuation progressively drowned the entire lake, coalescing the two parts after 4600–3500 B.P. Our coring revealed that the lacustrine sediment began to form in West Taihu Lake as early as 11,000 years ago, while it happened much later (only after 5700 B.P.) to form in East Taihu Lake. High sedimentation rates (0.42–0.35 mm/year) in lacustrine deposits of West Taihu Lake occurred between ~11,000 and 5000 B.P. In contrast, the high sedimentation rates (1.54 mm/year) in East Taihu Lake occurred only within a very short time period, from ~6500 to 5500 B.P. Since then, sedimentation rates have decelerated to a very low value (

Changes in the abundance of blue-green algae related to nutrient loadings in the nearshore of Lake Michigan

Nutrient loadings to the nearshore of southeastern Lake Michigan have undergone a remarkable reduction. This reduction can affect the nutrient supply and result in biological changes. Changes in phytoplankton community, particularly the blue-green algae, can be related to nutrient changes. After thermal stratification, sudden increases in the blue-green algae population were significantly correlated to soluble reactive phosphorus concentrations. Phosphorus-stimulated low dissolved silica and phosphorus limitations after stratification appear to be primary factors contributing to the success of these algae.

Determining the density dependence of immigration and emigration of benthic stream invertebrates: theoretical considerations

Simple mathematical models are formulated to describe density independent and density dependent dispersal. These models clarify hypotheses of density dependence and may be manipulated easily to suit particular applications. The models demonstrate that the initial composition of a species aggregate must be controlled before valid conclusions can be drawn about the density dependency of the aggregates dispersal. Stochastic models of emigration are derived to assess the power of particular experimental designs and statistical techniques to discriminate a known form of density dependent emigration.

The influence of phytoplankton composition on the relative effectiveness of grinding and sonification for chlorophyll extraction

The chlorophyll recovery efficiency was compared between control, ground, and sonified samples. The results showed significant improvement between control and ground samples but not between control and sonified samples. Neither prolonging time of sonification nor using an ice bath during filter grinding improved efficiency. Higher chlorophyll a recovery was obtained from ground samples than from sonified ones, when the water samples contained centric diatoms and filamentous blue-green algae. When total phytoplankton numbers were high, there was a distinct advantage in using grinding rather than sonification for chlorophyll c recovery.

Path Analysis and Factors Affecting Primary Productivity

Abstract No cause-effect relationship of light and nutrients on primary productivity was found in Lake Monroe, Indiana, using path analysis, but sufficient light was indispensable to an increase in productivity during nutrient enrichment. The lack of sufficient light can explain why primary productivity was low in December, January, February, and early March despite high levels of nutrients in the lake. Lack of significant increase in algal productivity in summer may be attributed the deficiency in available phosphate.

Effects of Water Management Policy on the Formation of Lakes Hongtze and Kaoyu, Two Large Chinese Lakes

Water management policy ordinarily has only a limited impact on the formation of large lakes. This note describes a unique example in which the water management policies enacted in China for more than 700 years to protect the national capital from inundation by the Yellow River and to ensure the shipping and transportation function of the Grand Canal were directly instrumental in the formation of large lakes Kaoyu and Hongtze.

Primary productivity and nutrients in the sediment retention basin of Lake Monroe

Lake Monroe is the largest body of water in Indiana with a daily mean productivity of 220 mg · C · m−2 · day−1 in an observed range from 26 to 714 m · C · M−2 day−1. It is a medium soft reservoir; the acid combining capacity varies from 0.28 to 0.71 meq · l−1 with a mean slightly above 0.5 meq · l−1. The results of diurnal changes in major nutrients, the C, N, and P ratios, and bioassay experiments indicated that phosphorus is the major limiting nutrient on algal photosynthesis in this lake. Surface photo-inhibition may be used to indicate the sufficiency of light for the species of algae in the water. The low productivity in December, January, February, and early March can be attributed to light limitation due to low water transparency.

A numerical simulation of trichromatic equations in chlorophyll estimation using the spectrophotometric technique

A numerical simulation of trichromatic pigment equations is made with the aid of a computer utility program. Significant quantitative differences in the estimates of pigment concentration result from using different sets of trichromatic equations. Estimates of chlorophylls a, b, and c were found highly correlated with the application of the equations, even though the absorbance values used as input for the stimulation are not correlated.