International Journal of Ecology

Lake Tana is Ethiopia’s largest body of fresh water, covering approximately 3,200 km². Despite its multidisciplinary applications in Ethiopia and neighboring countries, water hyacinth (Eichhornia crassipes (Mart.) Solms) is a significant problem in this large lake. This invasive weed first appeared in Lake Tana in 2011 and quickly spread to the water’s surface over the next two to three years. In this background, this article aims at reviewing the existing knowledge on the occurrence, impact, and management options for water hyacinths in Lake Tana. Water hyacinth is one of the most dangerous water weeds, causing a wide range of problems in bodies of water and water resources, including ecological, environmental, economic, and social consequences. Due to the weed species’ rapid spread via sexual and asexual reproduction, it covers a wide range of water bodies, and appropriate management options must be implemented before seriously affecting the water body and spreading to the Nile Basin.

Background. Aquatic insect community structure is dynamic due to threats by anthropogenic activities coupled with changing climatic conditions. The insect’s survival is dependent on the substrate, water quality, and environmental effects. The changes in water quality influence their distribution and abundance and are reflected in spatial and temporal trends. This study sought to document the effects of spatial variation on aquatic insects in Winam Gulf of Lake Victoria, Kenya. Materials and Methods. Systematic random design was used in sampling, and water quality parameters were assessed. Insects were sampled by profundal lake procedure, pooled, sorted, and identified based on the morphological approach and diversity indices analyzed. The relationship between insects and water quality was established. Results. Statistical homogeneity in water quality parameters was documented with the exception of nitrates, nitrites, soluble reactive phosphorus, ammonium, and silicates, which displayed significant variation at . A total of 383 individual insects representing 19 species, 19 genera, 16 families, and six orders were obtained from Winam Gulf. Hemiptera, Ephemeroptera, and Diptera were the most predominant orders, respectively. Chironomus spp. and Ablebesmyia spp. were representatives of the Chironomidae family. Species distribution and water quality were determined using cluster analysis (CA) and conical correspondence analysis (CCA). Conclusion. The findings of this study demonstrated that spatial variations were associated with change in water quality and had a corresponding influence on insect community structure.

The abandonment of seminatural Molinia meadows observed in Central and Eastern Europe during the 20^th century started the secondary succession and threatened the state and persistence of populations of numerous meadow species. Considering this, the aims of the presented investigations were to study the abundance and selected traits of individuals of Gladiolus imbricatus L. in extensively used (EM) and unmanaged for at least 15 years (UM) Molinia meadows (Southern Poland, Central Europe). Altogether, 125 juvenile individuals, 21 vegetative individuals, and 119 generative individuals of Gladiolus imbricatus were investigated. The field studies showed positive correlation among the height of shoots and other traits of generative individuals in both study patches. Moreover, the greater abundance of population of Gladiolus imbricatus (especially the greater number of juveniles), as well as the greater dimensions of leaf blades, shoots, inflorescence, and number of capsules in the patch UM, indicates the appropriate state of the population. These data indicate a positive influence of abandonment and evolving secondary succession on the Gladiolus imbricatus population within the Molinia meadows.

Fish habitat degradation, such as water pollution due to the rapid expansion of incompatible land uses, is one of the noteworthy challenges to freshwater ecosystems. Elevated contents of nutrients and contaminants in water are some of the imperative challenges. This research was conducted to investigate the link between water qualities and fish productivity in the Nyumba ya Mungu Dam, whose fishery potential had decreased by 95% between 1972 and 2018. Physicοchemical characteristics, namely, temperature, pH, dissolved oxygen (DO), turbidity, total nitrogen, total phosphorus, chlorophyll a, and the water depth of fishing net location, were assessed following standard procedure. Fish catches per unit effort representing fish biomass/productivity were monitored for twelve months from January to December 2019. Pearson’s correlation analysis indicated that fish catch per unit effort was positively and significantly correlated with turbidity (r = 0.461,  < 0.01) and TP (r = 0.405,  < 0.01). Stepwise multiple regression model results indicated that turbidity, dissolved oxygen, and the depth of the fishing net location are the statistically significant predictors of fish catch per unit effort which represented fish biomass. Findings further indicated that the model combining turbidity and dissolved oxygen predicted a 24% change in fish catch per unit effort, whereas turbidity, dissolved oxygen, and the depth of fishing net location contributed a 28.9% change in fish catch per unit effort. In conclusion, fish productivity in the NMD is limited by organic matter availability and nutrient levels that cause algae bloom occurrence. Turbidity is an indicator of organic matter availability and the effect of algae bloom on fish productivity. Inflow of nutrients to the dam nourishes the algae biomass, thus creating vicious cycles on fish productivity as fish species in the dam failed to take advantage of high primary production by algae.

This research aims to evaluate the water quality status and pollution load-carrying capacity of the Way Umpu River based on land use. This was carried out using the survey method by directly measuring the river water debit, pH, temperature, and dissolved oxygen (DO) on-site, taking the water sample to analyze the parameters of water quality such as total dissolved solid (TDS), total suspended solid (TSS), water color, turbidity, salinity, biochemical oxygen demand (BOD), chemical oxygen demand (COD), fecal coli, total coliform, and plankton in the lab, and monitoring the land use. The results showed that the use of land for illegal mining and the settlement of inhabitants in station-4 (ST-4) caused water pollution. Furthermore, based on Class III water use, the parameters in ST-4 exceeded the standards for TSS, color, and BOD, while other stations such as ST-1, ST-2, ST-3, ST-5, and ST-6 showed clean and good water quality statuses. It was also found that the pollution load-carrying capacity of the Way Umpu River has not yet been exceeded for Class III and the quality of the water may be improved when the river water debit increases. In addition, the plankton community structure on ST-1, ST-2, and ST-3 showed the number of species and individuals, and the diversity index was relatively high compared to ST-4, ST-5, and ST-6. It was concluded that the integrated evaluation was based on water quality status, plankton community structure, and pollution load analyses. The land use for illegal mining will decrease the water quality and the plankton community structure compared to other land uses.

Silphium perfoliatum (cup plant) is native to North America and is increasingly used as a bioenergy crop in Germany. Spontaneous occurrences of this species have already been detected in several European countries. To assess the possible risk to biodiversity by spreading of S. perfoliatum, we investigated the competitiveness of this species against the native and highly competitive Urtica dioica over four years in a field experiment in Bayreuth (Germany). S. perfoliatum grew well among U. dioica, although its biomass was strongly reduced by surrounding U. dioica. Projection area, plant height, and reproductive potential were less or similarly reduced by surrounding U. dioica as by the intraspecific competition. Moreover, S. perfoliatum significantly suppressed the growth of the competitive U. dioica. A settlement and establishment of S. perfoliatum in the native flora of Central Europe and a suppression of uncompetitive plant species are therefore conceivable.