Lakes and Reservoirs: Research and Management最新文献

Blue catfish (Ictalurus furcatus), channel catfish (Ictalurus punctatus) and flathead catfish (Pylodictis olivaris) are popular sport fishes throughout North America, and are therefore intensively managed by some natural resource agencies. Although catfish fisheries rely on sufficient natural reproduction and recruitment to sustain these populations, few studies have evaluated the variables affecting catfish recruitment. Thus, the objectives of this study were to describe population characteristics (age, size structure, condition, growth, mortality and recruitment) of blue catfish, channel catfish and flathead catfish in Thunderbird Reservoir, Oklahoma, and evaluate the effects of hydrology, water quality and temperature on year-class strength. During 2017 and 2018, 235 blue catfish, 194 channel catfish and 120 flathead catfish were collected and aged using otoliths. In general, these catfish species in Thunderbird Reservoir were slow growing, long-lived, had low mortality rates and experienced variable recruitment. Blue catfish recruitment was lower in years with higher average January air temperatures. Channel catfish recruitment was higher in years with increased average annual and spring/summer exchange rate and increased spring/summer average reservoir water volume (ha-m). Conversely, higher annual average total hardness (mg/L) resulted in decreased recruitment for channel catfish. Flathead catfish recruitment exhibited a minimal negative impact with increased annual reservoir volume (ha-m). The present study is among the first to describe potential variables influencing year-class formation of blue catfish, channel catfish and flathead catfish in reservoirs. Although the variables found to influence catfish recruitment are outside the control of fisheries managers, biologists should promote downstream angling opportunities for blue catfish that escape during reservoir water release events and stock channel catfish in systems with consistently high total water hardness in order to maximize fishing opportunities. Further, they can use the results of this study to manage angler expectations following periods of low recruitment.

Lake Victoria, like many other lakes in Africa, is affected by water hyacinth that reside in several bays for the majority of the year. The weed affects several economic activities of the local communities and denies revenue to the government from blue economic activities related to the lake. The present study examined the interaction of water hyacinth with biotic and abiotic factors and the efficiency of introduced weevils to better control this invasive weed. Water quality samples were collected and compared from the time of water hyacinth re-emergence and sinking within the Winam Gulf of Lake Victoria. The present study was divided into three phases with an interval of 2 months. Water hyacinth was collected, and the damages resulting from the weevils to the hyacinth, as well as the number of weevils, was recorded and analysed. Fish samples were collected with experimental gill nets. The collected water samples was analysed for the aquatic plant nutrient ammonium, soluble reactive phosphorus, nitrates and nitrites. Data were analysed using R package. The results of the present study indicated that the weevils inhibited nutrient uptake by hyacinth by 17% within the first 4 weeks. The hyacinth subsequently increased the nutrient levels in the gulf by threefold after their decay and sinking. Weevils also increased the sinking rate of water hyacinth through the destruction of their petioles and leaves. One hundred and ninety-four more fish were observed in the experimental nets during the weed infestation, compared to periods when the weed was absent within the gulf. The major conclusions were that water hyacinth impacts both biotic and abiotic factors, and that the weevils alone are unable to eradicate the weed.

Exploitation of mineral resources can result in dramatic multidirectional changes in the natural environment in mining areas, with the changes being particularly evident in the form of land degradation. One of the consequences of underground mining is subsidence of the overlying surface of the land area. The greatest subsidence typically occurs when the mining operation is carried out with a longwall top coal caving process, which can result in subsidence basin deformation developing on the surface. This development can lead to a change in natural landforms. As a consequence of the development of subsidence basins in the present study, the maximum depth in the Upper Silesian Coal Basin may exceed 30-m, which can also change the hydrological conditions of the area. Development of subsidence basins can often lead to changes in the morphometric parameters of the existing hydrographic objects, a phenomenon that also applies to dam reservoirs. As a result of land subsidence, the depth and surface area of hydrographic objects can increase, with the maximum depth point moving deeper into the reservoir outside the frontal barrage zone, with changes also occurring in the reservoir tank morphometry. In extreme cases, the barrage may stop water damming, being located outside the reservoir zone, meaning the tank's water management function is lost. All the reservoirs in the current study are located in the Upper Silesian Coal Basin in southern Poland, which is currently the only significant coal-mining centre in Europe, with the surface area of the basin being 7490 km².

Shallow lakes favour the development of aquatic macrophytes that can influence the limnological characteristics of these environments. In addition to macrophytes, allochthonous organic matter contributes to the metabolism of lakes through the bed of decomposing detritus. Among the decomposing microorganisms, bacteria can be important in the processing of organic matter when the abundance of fungi and invertebrates is low. The present study evaluated the effects of macrophyte coverage on bacterial-mediated leaf decomposition of allochthonous debris in shallow subtropical lakes. Litter bags were incubated with senescent leaves of Erythrina crista-galli in six shallow lakes, three with high (HML) and three with low (LML) macrophyte coverage. After 2, 7, 15 and 35 days of incubation, a set of litter bags was removed from each lake for bacterial, environmental and mass-loss analyses. Decomposition rates were higher in the LML (49% of remaining mass), compared to the HML (63% of remaining mass). The bacterial density and biomass were higher in the LML. Limnological variables influenced bacterial morphotypes, especially branched filament. Thus, the high coverage of aquatic macrophytes can be a main factor influencing the bacterial colonization in the debris, delaying the decomposition process in these ecosystems.

Invasive fish species pose considerable threats to aquatic biodiversity. The fishery of Lake Naivasha was enhanced by introduction of invasive fish species, including carp. The present study examined factors driving successful carp invasions, and their ecological impacts, knowledge of both being essential for management purposes. The present study revealed that carp invaded the lake, probably due to its adaptive traits such as environmental tolerance, fast growth, high fecundity, early sexual maturation and food flexibility. It reduced the biomass of Oreochromis leucostictus, Coptodon zillii and Micropterus salmoides which initially contributed to the fishery through competition and habitat degradation. It is noteworthy that the biomass of Oreochromis niloticus in the lake has recently increased and surpassed carp, attributable to a reduction in its predator (M. salmoides) and its biological traits. In terms of ecological effects, carp enhance water turbidity and stimulate algal growth by resuspending sediments and associated nutrients through its foraging activities. Although direct removal has been a useful practice for controlling carp in other places, this approach might be impractical for Lake Naivasha, since carp is the main species sustaining the lake fishery. Instead, implementation of effective management measures, including control of fishing effort, pollution control and protection of surrounding wetlands, would promote recovery and long-term sustainability of the fishery resources of this lake.

Previous studies have indicated certain environmental variables such as rainfall, nutrient concentrations and mixing events can be strong drivers of the phytoplankton community structure in reservoirs. Shifts in the phytoplankton community composition of Puerto Rican reservoirs, however, are not well understood. The present study identified the spatial and temporal changes in the phytoplankton community structure of two reservoirs in Puerto Rica, and which environmental parameters determined the structure. Whether or not the main environmental variables varied on the basis of the initial trophic status of the reservoirs was also explored. Two Puerto Rican reservoirs, one classified as mesotrophic and the other as eutrophic, were sampled on three sampling dates, with the reservoirs into three zones (dam; transition; riverine). Physical parameters were recorded at each sampling site, nutrient concentrations were measured, and the phytoplankton community biomass and diversity were determined. A canonical correspondence analysis (CCA) was run for each reservoir to explore which variables determined the phytoplankton community composition. Temperature, pH and total phosphorus concentration were the main drivers of the phytoplankton community composition for the mesotrophic reservoir, while specific conductance, pH, total phosphorus and nitrate were the main explanatory variables. Although the driving variables changed between the reservoirs, the temporal shifts observed in the phytoplankton community structure were consistent for both reservoirs regardless of their trophic status. The findings of the present study suggest that, although shifts in the phytoplankton community structure are similar in reservoirs with differing initial trophic status, the environmental variables driving community composition may nevertheless vary. Accordingly, tropical reservoirs managers should consider a reservoir's initial trophic status when evaluating what environmental parameters may lead to changes in its phytoplankton community structure. The present study represents a first step at examining the variables driving phytoplankton community structure in Puerto Rican reservoirs.

Periodically flooded environments in the Amazon River basin are recognized as being highly productive because of their limnological dynamics and ecological heterogeneity. They also have been historically impacted by fishery activities, therefore being crucial ecosystems to be considered in small-scale conservation policies. Previous studies, however, did not detect or assess significant or consistent positive effects of combinations between protected areas or environmental variables on ichthyofauna. Accordingly, the present study analysed the effects of fishery management (hereafter categorization of lakes) and environmental characteristics on the attributes of fish assemblages in 20 floodplain lakes (eight categorized as open access; 12 categorized as protected lakes) inserted in a legally protected area, the Reserva de Desenvolvimento Sustentável Piagaçu-Purus (RDS-PP) in the lower Purus River, Amazonas State, Brazil. The results of the present study indicated depth, surface area and lake categorization synergistically influenced the ichthyofauna of these floodplain lakes. It also suggests this influence should not be treated separately in management policies. It was concluded that the potential effectiveness of fishery management in floodplain lakes is closely related to small-scale (i.e. local) interventions, with emphasis on the role of the lakes as a unit of effective management of ichthyofauna in floodplains. Furthermore, participatory decisions during the process of elaborating management plans for floodplain lakes should consider environmental attributes relevant to biological communities and traditional knowledge.

Macrobenthos are important bioindicators of organic and nutrient pollution. The present study used the macrobenthos-based rapid bioassessment protocol (RBP II) to study the effects of treated textile effluent inputs into a natural stream ecosystem connected to a wetland marsh. Three reference sites and three sites receiving point source inputs from a textile effluent treatment plant were selected. The physical and chemical parameters, and the abundance and diversity of macrobenthos at each site, were assessed during the rainy and dry seasons of 2020. Although the water quality parameters at the sites representing the point source inputs did not exceed the standard textile effluent discharge limits, a significant influence on the macrobenthic community composition was observed at the effluent discharge receiving sites. The dominant macrobenthos in the ecosystem (Baetis sp., Leptophlebia sp; Tubifex sp.) exhibited significant correlations with lead, copper, chromium and cadmium concentrations of the water and sediments. The Shannon–Weiner Diversity Index, Family Biotic Index, EPT Index and EPT/C ratio used in the rapid bioassessment protocol indicated significantly strong correlations with the water and sediment quality parameters, demonstrating their suitability to be used as a tool for biological measurements in aquatic ecosystems receiving textile effluents.