Freshwater Impoundments Research Articles

Nakdong estuary barrage and reclamation project: Preliminary results of the botanical, macrozoobenthic and ornithological studies

The Nakdong Estuary Barrage and Reclamation Project has been investigated by studies on the vegetation, macrozoobenthos and birds in the Nakdong river delta, Republic of Korea. This study deals with the preliminary results, obtained during October to November 1983, while the environmental impacts of the barrage were being discussed. The total biomass of Scirpus triqueter, the estuary's most important foodplant for waterfowl ( mainly for swans), was assessed at approximately 38·3 tonnes dry wt. Of this amount only the roots and rhizomes (9·6 tonnes dry wt) are expected to be consumed by birds. Aquatic weeds in the nearby fresh Jukrim branch provided another food source (5·8 tonnes dry wt). The wintering waterfowl also used other feeding areas such as farmland and freshwater impoundments—almost all herbivorous birds participated in nightly feeding migrations. At 12 stations, spread over 20·5 km 2 of intertidal flats of the estuary, a total of 40 macrozoobenthic species were found. Crustaceans dominated with 19 species, while molluscs and polychaetes were represented by 11 and 10 species, respectively. For all stations together an average biomass of 14·6 g ash-free dry wt (ADW) m −2 (range 3·1–51·9 g) was calculated, dominated by molluscs with 9·5 g, while the share of crustaceans and polychaetes was only 2·9 g and 2·2 g, respectively. In terms of weight, the bivalve Corbicula japonica was dominant with an average of 4·4 g ADW m −2. During three censuses 10 000 waders and 25 000 to 30 000 waterfowl were counted. Among them were two species not recorded before in Korea: the ruff and the canvasback. Of all nonpasserines the wigeon (with a peak of 6800) and the dunlin (with a peak of 9100) were most numerous, while the ducks proved to be the most dominant (64%) group of birds. In the beginning of October the wader density in the estuary amounted to 5·2 birds ha −1 intertidal area exposed at low tide.

Striped Bass Management in Lakes with Emphasis on Management Problems

Abstract The number of fisheries for striped bass Morone saxatilis in freshwater impoundments in the United States has increased dramatically over the last decade. A survey of fisheries agencies throughout the country was conducted to evaluate accomplishments and problems associated with management of striped bass and hybrid striped bass (male white bass Morone chrysops x female striped bass). Through 1981, fisheries for striped bass, hybrid striped bass, or both had been established in at least 279 lakes in 34 states. Mean annual harvest rates from striped bass, hybrid striped bass, and mixed (both fish in same lake) fisheries were 1.1, 0.7, and 3.0 kg/hectare, respectively. In reservoirs where they are established, these fisheries contribute an average of 13.6% to the total harvest by weight; their maximum contribution is 66.2%. Improvements in management have been limited by the lack of good objectives and of quantitative evaluations of stocking success. The most frequently cited management problem was...

Jamaica Bay studies VII: Factors affecting the distribution and abundance of ducks in a New York estuary

The abundance and distribution of ducks (Anatini, Cairinini, Aythyini, Mergini, Oxyurini) were examined at Jamaica Bay Wildlife Refuge, a coastal estuary on Long Island, New York. The refuge contains a variety of tidal habitats as well two freshwater impoundments. The largest concentrations of diving ducks were present in March and April, and from October through December; while the largest concentrations of dabbling ducks were present from June through December. Thus, diving ducks used the refuge on migration whereas dabbling ducks used the refuge during and following the breeding season. Time of year was thus the most significant factor affecting distribution and abundance. Some species were present all year, including Black Duck Anas rubripes, Mallard A. platyrhynchos, Gadwall A. strepera, and Ruddy Duck Oxyura jamaicensis. Although both dabblers and divers used all areas of the bay, dabblers used both ponds while divers used only the East Pond. Dabbling ducks concentrated in the bay at low tide, and on the ponds at high tide. There were more divers on the bay on a falling tide although tide direction did not influence the abundance or distribution of dabblers. Temperature and wind variables influenced the distribution of all ducks: they used the bay at low temperatures, and rafted in large flocks on the bay in intermediate, Northwest winds. Only the numbers and distribution of dabblers were significantly influenced by cloud cover. We conclude that abiotic factors influence the abundance and distribution of ducks on Jamaica Bay Wildlife Refuge, and that tidal factors should be considered when managing migratory or wintering populations of ducks.

Extensive culture of two mullet species in freshwater impoundments in the eastern Cape

The feasibility of using freshwater mullet Myxus capensis and flathead mullet Mugil cephalus to increase the fisheries potential of freshwater impoundments was investigated. The recruitment periods of fry of both species into the upper reaches of a number of eastern Cape estuaries were established. Techniques used to minimize mortalities during the capture, transportation and stocking of the fry are described. Data on growth and mortality of both species of mullet fry stocked into a variety of impoundments are discussed with regard to their potential for extensive aquaculture and angling purposes.

Impounded Water as a Major Producer of Culex Salinarius (Diptera: Culicidae) in Coastal Areas of New Jersey, USA12

Culex salinarius was found to be the dominant species in 9 of the 10 largest Culex populations in New Jersey, USA. Sampling revealed that larval habitats included coastal brackish and freshwater impoundments, a stop ditch and a dredge deposit zone. Virtually all of these habitats were manmade, and many were constructed to control the saltmarsh mosquito, Aedes sollicitans . These data demonstrate the need for more thorough evaluation of marsh management techniques to avoid replacing one nuisance species with another.

Temperature Variations in Deep Reservoirs

A mathematical model is developed to study the thermal behavior of freshwater impoundments. The model is formulated to simulate thermal stratification, turnover, hypolimnetic behavior, and epilimnetic behavior. Inputs to the model include meteorological data so that an energy budget relation is included. Output from the model includes the time-varying temperature distribution for the impoundment. A 315-day simulation is made of the thermal distributions in the TVA's Fontana Reservoir using the model. The results of the simulation show excellent comparison between predicted and measured quantities.

Effect of Mixing Depth and Turbidity on the Productivity of Fresh-Water Impoundments

Abstract Mixing depth and turbidity negatively affect the productivity of an aquatic environment through the control they exert on the effective energy available for photosynthesis. A feedback equation is developed that defines the interaction of these two quantities with the production by phytoplankton. The equation permits calculation of the relative productivity of any body of water provided nutrients are assumed adequate, and provided depth of mixing and turbidity are known. Calculated relative production corresponded very well with observed production for a series of 33 small shallow ponds. The possibility is advanced that the same principles apply to reservoirs when thermocline depth can be regarded as mixing depth, and further, it is suggested that the productivity of reservoirs might be increased by reducing the depth of the mixed layer by withdrawing from the surface. In addition, this practice might further enhance production by mixing deeper water, richer in nutrients, into the euphotic zone du...

Fresh-water Impoundments

Abstract Several features of impoundments and reservoirs, either inherent or the result of operations at the dam, can reduce and limit the biological productivity of an impoundment and consequently the fish production of its waters. Among these characteristics are the stagnation of large masses of water, the removal of food materials in the waters drawn out of the reservoir, the limited lateral areas of shallow water around the margin of the impoundment, extensive fluctuation of water level, and continued and often heavy silting in of the bottom. Water conditions in an impoundment usually are less stable and are often quite different from those found in comparable natural lakes. The limitations of impounded waters for fish productivity can in part be offset by: (1) Controlling the draw-off (where such regulation is compatible with the major interests for which the impoundment is created) so that fairly constant water level will be maintained during the nesting season of the most desirable species of fish....