Lakes and Reservoirs: Research and Management最新文献

This brief review describes the major causes of lake cultural eutrophication and assesses different strategies applied to control or reduce the negative consequences of this eutrophication. Excessive nutrient inputs, particularly from agricultural lands through non-point source runoff, are among the main causes of cultural eutrophication on a global scale. Reducing nutrient inputs from agricultural lands through management of lake catchment areas, therefore, is an integral part of any effort to control lake eutrophication. Nutrient enrichment results in algal blooms and creates favourable condition for the invasion of a lake by alien aquatic weeds, making this invaluable freshwater resource unsuitable for many purposes, including drinking, agricultural and industrial water resources, fishing, transportation and recreational purposes. A major part of this review addresses attempts made to address the negative impacts of eutrophication by restoring water quality. Several research outputs discussing bottom-up and top-down control mechanisms were utilized for the present review. Much emphasis has been given in the literature regarding the use of biomanipulation as a promising and sustainable solution for controlling eutrophication. Biomanipulation tools used to control cyanobacteria and algal bloom have involved zooplanktivorous fish removal, piscivorous fish stocking, daphnia stocking, benthivorous fish removal, planktivorous fish stocking and mussel stocking. Further, some insect and fungal species have been used as biological control agents in an effort to control invasive aquatic weeds in tropical lakes. Although this review is limited in its analysis and explanation of the drawbacks associated with each described biomanipulation method, it can be deduced that biomanipulation generally exhibits considerable potential for controlling or reducing phytoplankton overgrowth and aquatic weed invasions, assuming it is also integrated with strategies to control external nutrient loadings to lakes.

Lake Naivasha is a tropical freshwater body in Kenya, providing a source of livelihoods to the surrounding communities. The lake ecosystem, however, has become degraded over time because of increasing pollutant loads from multiple sources, including human settlements and agricultural and surface runoff in its basin. Thus, it is vital to study the lake's water quality to determine its current status to inform appropriate management measures. Accordingly, the present study analysed water quality parameters and the trophic state of Lake Naivasha on the basis of water samples collected at eight sampling sites during the dry and wet seasons from December 2019 to May 2020. The physico-chemical parameters were measured in situ, while nutrients were analysed in the laboratory. The results indicated high turbidity, total nitrogen (TN), ammonium-nitrogen (NH₄⁺-N), nitrate-N (NO₃-N) and total phosphorus (TP) levels during the wet season, and at the Malewa and Karati River mouths, while pH, electrical conductivity (EC) and chlorophyll-a values were relatively high during the dry season. The water temperature and dissolved oxygen (DO) concentration, however, did not vary between sampling sites or seasons. Cluster analysis (CA) classified the sites into three clusters based on water quality spatial and seasonal variations. Cluster 1 was comprised of the isolated region (Crescent), while clusters 2 and 3 mainly comprised sites sampled during wet and dry seasons, respectively. Similarly, principal component analysis (PCA) revealed spatial and seasonal physico-chemical variations, indicating nutrient parameters (TN, TP, NO₃-N and NH₄⁺-N), pH, Secchi depth and turbidity are the major variables influencing water quality variations. Furthermore, factor analysis (FA) identified nutrients, sediment and organic sources as the main lake pollution sources. The trophic state index (TSI = 60–72) indicated the lake varied from a eutrophic to hypertrophic state during the study period. The lake was found to be more eutrophic than reported in previous studies, indicating a progressive deterioration of its water quality. The overall results demonstrated some of the sampling sites in the lake are heavily contaminated with pollutants from various sources, attributable primarily to land use patterns and anthropogenic activities. The results of the present study are useful to inform decisions regarding management of the lake water quality.

The reliability and impact of several regulation policies on Lake Victoria in East Africa were investigated using the Water Rights Analysis Package (WRAP). Its reliability is determined by establishing the risk of policies failing to meet water demands. The impacts on the lake are evaluated by assessing the effect of policies for lake levels. Policies are based on (i) the lake's firm and safe water yields and (ii) dam turbine configurations at the lake's outlet. The present study demonstrated the applicability of WRAP in modelling large complex reservoirs and determined that constant release policies with a maximum limit of 1015 m³/s have low risks of failure and improve lake water-level stability.

Dependent on the specific fishery, green sunfish (Lepomis cyanellus) can be viewed as a benefit or a detriment. Regardless, effective management of this species relies on precise age estimation, which is critical to detail age structure, growth and recruitment rates of their populations. To determine the most precise method for age estimation, estimated ages of whole and cracked otoliths of 422 green sunfish were compared from three small impoundments (0.6–16.2 ha) in Oklahoma. Green sunfish ages ranged from 0 to 7 for cracked otoliths and 0 to 6 for whole-viewed otoliths, depending on the population. High precision between readers was observed for whole (per cent agreement = 85%–96%; mean CV = 3.4%–4.8%; and average per cent error = 2.4%–3.4%) and cracked otoliths (per cent agreement = 92%–96%; mean CV = 0.3%–6.3%; and average per cent error = 0.3%–4.4%). Limited bias was observed for young fish (≤age 3) for evaluating between-reader precision using whole otoliths. When bias was present, ages generally exceeded the 1:1 line of equivalency. Final consensus ages for older fish (≥age 5) were sometimes underestimated using whole otoliths, compared to cracked otoliths. Fair agreement for final consensus ages (73%–87%) between whole and cracked otoliths was observed, compared to other otolith ageing studies in the literature. However, the results of the present study indicated no significant differences in growth or age-frequency estimates using ages derived from whole and cracked otoliths, suggesting the moderate level of consensus agreement was not sufficiently low to significantly impact population characteristics and subsequent management decisions. Green sunfish growth rates in Oklahoma appear sufficiently high to allow the use of whole otoliths for age estimation to age seven, unless slow growth is expected. To ensure precise age estimation, however, it is suggested that otoliths from green sunfish ≥age 5 be cracked, regardless of growth rates.

The present study analyses civic and community-based initiatives in conserving urban ecological commons in India, which have been increasingly polluted, encroached upon and degraded because of rapid land-use transformations. Bangalore, a city in south India, has one of the largest networks of manmade lakes, some of which are restored and managed by citizen groups, civil society, environmental activists and voluntary private bodies. The restoration process interfaces with urban policy making, shaping predominant management agendas in association with the State. Community initiatives in conserving the lakes are not only well-organized, but also play a crucial role in making city commons vibrant and integral nodes of cultural and social identification. However, the contemporary management system involving citizen groups in lake conservation is largely at odds with the tradition of community-managed lake systems previously existing in the city, which have eroded as the city became industrialized and increased in size and population, resulting in rapid landscape transformations. Against this background, the present study aims to illustrate that a seemingly representative community management of city ecologies is often embedded in an overwhelming political context. It also discusses the need for an urgent deconstruction to better understand how overtly flexible and dynamic restoration actions interact with inequality, power and conflicts. The results of the present study emphasize that the current participatory and community-driven initiatives of ecological restoration in Indian cities unfortunately accord limited significance to the overarching questions of social justice and relations of power.

The present study describes the length-weight relationships (LWRs) of 12 dominant finfish species from Vembanad Lake, India, from June 2015 to May 2016. Samples were carried out using a wide range of fishing gears such as gill nets (mesh sizes 20–60 mm), seine nets (mesh sizes 8–16 mm), cast nets (mesh sizes 6–8 mm) and hook and lines. The values of the exponent b ranged from 2.506 (Glossogobius giuris) to 3.305 (Heteropneustes fossilis) and regression parameters R² from .960 (Carinotetraodon travancoricus) to .995 (G. giuris). The study reports the new maximum total length (TL_max) for Hyporhamphus xanthopterus and first reference regarding length-weight relationships for Mystus oculatus, Ompok malabaricus and C. travancoricus. The results provide useful information for preparing sustainable resource management plans and conservation strategies for these species in the lake and similar ecosystems.

Environmentally sustainable aquaculture depends on accurate understanding of the impacts of aquaculture-derived organic matter (AOM) and the ability of aquaculture systems to absorb and dilute perturbations. To this end, the present study assessed the impacts of AOM from cage culture of Nile tilapia on the ecology of Lake Victoria, Kenya, using fish cages near Anyanga Beach in Siaya County from December 2018 to October 2019. Four locations were surveyed for organic loadings from cage cultures, located 0, 50, 150 and 500 m (as a control site) away from the cages. The cage aquaculture produced increased P and N concentrations near the cages and a decreased N:P molar ratio. These changes stimulated algal growth which, in turn, affected the water quality. The organic material accumulated on the bottom under the cages, increasing the benthic BOD (BOD, >10 mg/g), a sensitive indicator of the ecological footprint of the cage aquaculture. Further, the negative ORP observed in the benthic layer suggested anoxic bacterial metabolism, possibly causing build-up of sulphides and methane. These changes altered the abundance and composition of both limnetic and benthic communities. At the beginning of the study, 22 zoobenthic taxa existed around the cages and 18 at the reference sites. Only 3 saprophilous taxa, chiefly gastropods (Physella spp.), bivalves (Sphaerium spp.) and oligochaetes (Tubifex spp.) were present at the cage site and 17 at the reference site at the end of the culture period. The Shannon diversity index exhibited a declining tendency with the length of culture period at the cage site, signifying a negative impact of aquaculture on biodiversity. The water quality recovery after cage disturbance is rapid (<4 months), noting there was no significant difference in the water quality recorded at the cage site and the other sampling sites after a fallow period of 4 months. However, the recovery of the sediment and meiofauna was far from complete at the end of this period. Moving the cages slightly (50–100 m) away from the former location may allow the benthic communities to recover and alleviate the problem. Further, the fallowing period, particularly for the Anyanga Beach site, should be extended from four to at least 5 months to allow for the environment to recover. With the rapid increase of cage fish farming in the African Great Lakes Region and with the potential for its occurrence in other lakes, there is a need to develop regulations to guide the industry, as well as the need for continuous monitoring of the environment, in order to provide information to guide investments and ensure sustainable cage farming.

Oreochromis leucostictus is a commercially important tilapiine in Lake Naivasha, with its stocks having declined because of the effects of fishing, habitat degradation and pollution. The present study investigated its length–weight relationship, condition factor, sex ratio and maturity. Fish samples (233) were collected during 2017, with each fish measured (cm), weighed (g) and analysed for maturity in the laboratory. The mean (±SD) total length and weight were 21.3 ± 0.3 cm TL and 187.4 ± 8.3 g, respectively. The fish exhibited a negative allometric growth pattern (b = 2.33). The mean condition factor was 1.06, 0.99 and 1.04 for male, female and combined sexes, respectively. The condition factor was significantly higher in September (1.70 ± 0.15) and October (1.63 ± 0.15) than in other months. Males were significantly more dominant than females (male:female sex ratio = 2.19:1.0). Females (21.0 cm TL) matured at smaller lengths, compared to males (26.0 cm TL). Comparisons with earlier studies suggested the length–weight relationship, condition factor, sex ratio and size at first maturity of O. leucostictus in Lake Naivasha varied significantly from other tilapiines in various water bodies. The results of the present study provide insights into the biological attributes of O. leucostictus useful for its sustainable management.

The relationships between fish size, weight and otolith morphometry are useful for fisheries management, predator–prey studies and feeding habits. Accordingly, the main purpose of the present study was to determine the relationships between body length, body weight and otolith dimensions, and to calculate the length-weight relationship and condition factor for a Sciaenid fish Pama croaker, Otolithoides pama (Hamilton, 1822) from the Lower Meghna estuary, Bangladesh. Field sampling was conducted from September 2019 to March 2020. The length, breadth and weight were measured for each pair of sagittae, as well as the total length (TL), standard length (SL) and body weight (BW) for each specimen. A total of 246 fish samples were collected. The TL and BW of collected individuals ranged from 14.40 to 27.40-cm and 21 to 175-g, respectively. The calculated growth coefficient (b = 3.018 for males; 3.052 for females) were >3, indicating the fish follow a positive allometric growth. The mean Fulton's condition (Kn) values ranged from 0.674 ± 0.06 to 0.776 ± 0.07, exhibiting similar trends for all size classes. The relationships for fish size and otolith morphometry were described by linear regression models as TL = 0.048OL – 0.308 (r² = 0.921); BW = 0.047OL + 6.252 (r² = 0.929); TL = 0.003OW – 0.414 (r² = 0.836); BW = 0.003OW + 0.039 (r² = 0.81). The otolith length and weight exhibited a strong correlation (0.929 > r² > 0.805) with total length and body weight, while the otolith breadth exhibited a weak correlation. No significant differences between left and right otolith were observed (p > .05). Because the results of the present study indicated fish length and otolith growth have a positive relationship, this finding can be a valuable tool to evaluate fish growth by back-calculating the length of a fish from its otolith characteristics.

Studies addressing the macrobenthic diversity and their potential as bioindicators in water quality assessment programs are sparse for Sri Lanka. The present study investigated the macrobenthic diversity in relation to water quality parameters in some urban reservoirs in the Western Province of Sri Lanka, assessing their potential as bio-indicators in water quality assessment programs. The six study reservoirs included the Ihalagama Tank, Peralanda Tank, Kesbewa Tank, Boralesgamuwa Tank, Bolgoda Lake and Beira Lake. The microbenthic fauna abundance at randomly selected locations (n = 9) in each reservoir and selected water quality parameters (temperature; pH; electrical conductivity; total dissolved solids; BOD₅; dissolved nitrates; total dissolved phosphate and alkalinity of the overlying water at each location were measured between July 2020 and January 2021, using standard data collection methods). The species richness (SR), species heterogeneity (H′) and species evenness (J) of the macrobenthic fauna in each reservoir were calculated, and the abundance and water quality data analysed using ANOVA and PCA as appropriate. A total of 13 macrobenthic taxa (Glyphidrilus sp., Limnodrilus socialis, Dero sp., Stratiomyd larva, Chironomid larva, Bellamya sp., Melanoides tuberculata, Gyraulus sp., Lymnaea sp., Paludomus sp., Thiara sp., Ancylus sp. and Mesostoma sp.) were observed from the six study reservoirs. The oligochaete tubificid worm L. socialis dominated the sediment samples, accounting for more than 94.7% of the total macrobenthic abundance, with the highest relative abundance of this species observed in Beira Lake (99.3%). The species richness of the macrobenthic community was highest in the Ihalagama and Kesbewa tanks (SR = 5), while it was the lowest in the Peralanda Tank (SR = 2). Since the benthic community was mainly dominated by L. socialis, the lowest species heterogeneity and species evenness values were observed in Beira Lake (H′ = 0.05; J = 0.03). The values of the water quality parameters among the study reservoirs varied, with Beira Lake exhibiting significantly high BOD₅, dissolved nitrate, and total dissolved phosphate values (p < .05) than the other reservoirs, indicating a higher degree of eutrophication. Furthermore, the SR, J and H′ values for the study reservoirs decreased with increasing BOD₅, dissolved nitrate and total dissolved phosphate levels. Thus, it was concluded that the abundance and diversity of macrobenthic fauna are primarily governed by water quality parameters. Furthermore, L. socialis can be used as a potential bioindicator organism in water quality assessment programs in urban reservoirs.