SPATIAL STRUCTURE OF VEGETATION OF LARGE LAKES OF THE ONEGA PENINSULA (ON THE EXAMPLE OF MURAKANSKOE AND BOLSHOE VYGOZERO LAKE)

Studying the vegetation of freshwater lakes remains a topical subject in the national parks of the Arkhangelsk Region. It is in particular important for the Onega Pomorie National Park, which is located along the coasts of the Onega and Dvinskoy bays (of the White Sea) in the northern part of the Onega Peninsula. This article examines the spatial structure of aquatic and coastal-aquatic vegetation of Murakanskoye and Bolshoye Vygozero – two large lakes of the Onega Peninsula. The spatial structure is presented in the form of ecological series of associations of plant communities. A comparative characteristic of the lakes’ vegetation is given in the discussion of the article. The littoral zone is poorly developed in both lakes mentioned above. It depends on the openness of the water areas to the winds from the north. It is indicated that the species composition and vegetation structure of the Bolshoye Vygozero Lake mostly depends on water transparency and high acidity; these factors determine the development of the Phragmitetum australis fontinaliosum dalecarlicae, Phragmitetum australis caricosum aquatilis, Caricetum aquatilis associations. In the Murakanskoe Lake, high water transparency and slightly alkaline pH values contribute to the development of communities of pondweeds – such as Potamogeton alpinus, Potamogeton praelongus, and communities of the Lobelietum dortmannae isoëtosum echinosporae association.

The waters transparency model of Lake Laut Tawar, Aceh, Indonesia

Lake Laut Tawar in Aceh Province, Indonesia is an important ecosystem that has several endemic biotas such as Rasbora tawarensis and Poropuntius bargensis. Eutrophication is a potential problem in Lake Laut Tawar. To evaluate the trophic state needed the value of water transparency. This study aims to formulate a model for estimating the transparency of Lake Laut Tawar waters. The dependent variable was water transparency, and the predictors variable was the chlorophyll-a concentration, total suspended solids, and total dissolved solids. Observations and sampling were conduct starting from October 2016 to September 2017. Data analysis was using simple regression, multiple regression, and one-way ANOVA. The result showed a decrease in waters transparency (SD) was caused by increased phytoplankton density (Chl-a), suspended material (TSS), and dissolved material (TDS). But the dissolved matter did not have a partial effect if the values of other variables are constant. The model to estimate the water transparency of Lake Laut Tawar is Log SD = 1.414 – 0.322 Log Chl-a – 0.406 Log TSS. The average values of water transparency did no differential between the seven observation stations. It is presumably because the waters of Lake Laut Tawar are easily mixed.

Long-Term Changes in the Land–Ocean Ecological Environment in Small Island Countries in the South Pacific: A Fiji Vision

Small island countries in the South Pacific are ecologically fragile areas, vulnerable to climate change, and the long-term ecological changes in the sea and land have an important impact on their sustainable development. This study takes Fiji, a typical small island country in the South Pacific, as an example, to analyze the change and connection of marine and terrestrial ecosystem environments based on 30 years of multi-source, satellite, remote-sensing data. From 1991 to 2019, according to the change in forest area in Fiji, three stages were delineated: first was a period of stability, then a decrease, and then a recovery in recent years. From 1991 to 2002, Fiji’s vegetation accounted for 73% of the total area; sea environment surrounding the islands, such as sea level height and sea surface temperature, were relatively low, with high water transparency. From 2002 to 2014, with the development of forestry and tourism, vegetation decreased by 6.89% and bare land increased, which changes the runoff erosion in the drainage basin; correspondingly, the chlorophyll a concentration in three major estuaries was found to be slightly increased with low water transparency. Meanwhile, coupled with the rising sea temperature, the area of Fiji’s coral reefs shrank significantly, with 51.13% of the total loss of coral reefs occurring in the Vanua Levu, where bare land and runoff were more distributed in its drainage basin. From 2014 to 2019, Fiji’s vegetation and coral reef areas recovered from the former stage; affected by short-term climate oscillations such as El Niño-Southern Oscillation (ENSO), the sea surface temperature showed a significant abnormal drop and the water transparency decreased. In the past 30 years (1993–2018), the sea level rise rate around Fiji reached 4 mm/year, and the temperature increased by 0.3 °C, which threatens the coastal ecosystem environment, including coral reefs and mangrove; inappropriate land-use change would worsen the situation in these ecologically fragile areas.

WATER QUALITY RESTORATION: THE EFFECT OF ZOOPLANKTON ON CYANOBACTERIA DEVELOPMENT IN TWO EUTROPHIC PONDS

Based on a study of the dimensional structure of phytoand zooplankton, it is demonstrated that fi trophic press leads to a decrease in the population and size of zooplankton. Th isolation of fi zooplankton from planktoneating fi favors the development of largesize fi in particular, Daphnia magna and Daphnia longispina, which can consume cyanobacteria. In cases of high abundance, zooplankton breaks up large colonies and improves its food base. Planktoneating fi and hatchlings eat fi zooplankton, thereby indirectly contributing to the development of cyanobacteria. In cases of higher nutrient input in the absence of planktoneating fi fi zooplankton can regulate the development of phytoplankton, contributing to higher water transparency. Th main consumers of colonial cyanobacteria are largesize fi D. magna, D. longispina, etc.

Water Transparency Prediction of Plain Urban River Network: A Case Study of Yangtze River Delta in China

Water transparency is commonly used to indicate the combined effect of hydrodynamics and the aquatic environment on water quality throughout a river network. However, how water transparency responds to these indicators still needs to be explored, especially their complicated nonlinear relationship; thus, this study represents an analysis of the Suzhou civil river network. Using an artificial neural network (ANN) hydrological model and a multiple linear model (MLR) with in-situ data between 2013–2019, we investigated the Suzhou River’s sensitivity to the six factors and water transparency, which including flow velocity and data from five categories of water-quality monitoring data: total suspended matter (TSS), water temperature (TE), dissolved oxygen (DO), chlorophyll (Chl) and chemical oxygen demand (COD). The results suggest that the ANN model can achieve better performance than the MLR model. Furthermore, results also show a well-established correlation between enhanced hydrodynamics and improved water transparency when the flow velocity ranged from 0.22 to 0.45 m/s. Overall, COD is a vital factor for the SD prediction because including the COD can see a notable improvement in the ANN model (with a correlation coefficient of 0.918). This study demonstrates that the ANN model with hydrodynamic and water quality parameters can achieve a better prediction of water transparency than other discussed models for a coastal plain urban river network.

Patterns, Trends and Drivers of Water Transparency in Sri Lanka Using Landsat 8 Observations and Google Earth Engine

Addressing inland water transparency and driver effects to ensure the sustainability and provision of good quality water in Sri Lanka has been a timely prerequisite, especially under the Sustainable Development Goals 2030 agenda. Natural and anthropogenic changes lead to significant variations in water quality in the country. Therefore, an urgent need has emerged to understand the variability, spatiotemporal patterns, changing trends and impact of drivers on transparency, which are unclear to date. This study used all available Landsat 8 images from 2013 to 2020 and a quasi-analytical approach to assess the spatiotemporal Secchi disk depth (ZSD) variability of 550 reservoirs and its relationship with natural (precipitation, wind and temperature) and anthropogenic (human activity and population density) drivers. ZSD varied from 9.68 cm to 199.47 with an average of 64.71 cm and 93% of reservoirs had transparency below 100 cm. Overall, slightly increasing trends were shown in the annual mean ZSD. Notable intra-annual variations were also indicating the highest and lowest ZSD during the north-east monsoon and south-west monsoon, respectively. The highest ZSD was found in wet zone reservoirs, while dry zone showed the least. All of the drivers were significantly affecting the water transparency in the entire island. The combined impact of natural factors on ZSD changes was more significant (77.70%) than anthropogenic variables, whereas, specifically, human activity accounted for the highest variability across all climatic zones. The findings of this study provide the first comprehensive estimation of the ZSD of entire reservoirs and driver contribution and also provides essential information for future sustainable water management and conservation strategies.

Pervasive decline of subtropical aquatic insects over 20 years driven by water transparency, non-native fish and stoichiometric imbalance

Insect abundance and diversity are declining worldwide. Although recent research found freshwater insect populations to be increasing in some regions, there is a critical lack of data from tropical and subtropical regions. Here, we examine a 20-year monitoring dataset of freshwater insects from a subtropical floodplain comprising a diverse suite of rivers, shallow lakes, channels and backwaters. We found a pervasive decline in abundance of all major insect orders (Odonata, Ephemeroptera, Trichoptera, Megaloptera, Coleoptera, Hemiptera and Diptera) and families, regardless of their functional role or body size. Similarly, Chironomidae species richness decreased over the same time period. The main drivers of this pervasive insect decline were increased concurrent invasions of non-native insectivorous fish, water transparency and changes to water stoichiometry (i.e. N : P ratios) over time. All these drivers represent human impacts caused by reservoir construction. This work sheds light on the importance of long-term studies for a deeper understanding of human-induced impacts on aquatic insects. We highlight that extended anthropogenic impact monitoring and mitigation actions are pivotal in maintaining freshwater ecosystem integrity.