Years In Lake Research Articles

Parameters of Water Column Stability in a Small Polymictic Lake in Years of Different Weather Conditions

Parameters of Water Column Stability in a Small Polymictic Lake in Years of Different Weather Conditions

Mapping inundation extents in Poyang Lake area using Sentinel-1 data and transformer-based change detection method

Accurate and timely mapping of inundation extents during flood periods is essential for disaster evaluation and development of rescue strategies. With unique advantages over the optical sensors (e.g., little effect of clouds, and observations at day and night), Synthetic aperture radar (SAR) sensors provide an important data source for mapping inundation, particularly during flood periods. Freely available SAR images from Sentinel-1 have been increasingly used for many applications. This study applied an efficient transformer-based change detection method, bitemporal image transformer (BiT) with bitemporal Sentniel-1 images, to map inundation extents and evolution in Poyang Lake area in 2020. The transformer-based change detection method firstly adopted ResNet for high-level semantic features extraction, and applied a transformer mechanism to refine these features pixel-wise, followed by employing a FCN as the prediction head for generating the results of change detection. Besides, we constructed a water change detection dataset with spatial-and-temporal generalization from bitemporal Sentinel-1 images; this dataset consists of the seasonal variation water samples of Poyang Lake for years. We compared the results from the BiT method with other convolutional neural network (CNN) based methods (STANets and SNUNet). Mapped inundation extents were evaluated with the ground truth visually derived from high spatial resolution images. The evaluation showed the BiT method generated high accurate mapped inundation extents with the F1-score of 95.5%. The BiT model has proven its superior performance in detecting increased water. Based on the results of the BiT method, the variation of inundation extents in Poyang Lake during May-November 2020 was further analyzed. It was found that the water surface coverage of Poyang Lake is the smallest in late May; it gradually increased to the maximum on 14th July, and then began to stabilize and show a significant downward trend before November. The flood distribution map shows that cultivated land has been inundated with the largest area of approximately 600 km2.

Bluebills and bayou bivalves: Hurricane‐driven trophic cascades affect wintering abundance of Lesser Scaup in Louisiana

AbstractThe estuaries of coastal Louisiana overwinter a continentally significant proportion of Lesser Scaup (Aythya affinis; colloquially, “bluebills”), a migratory bird species of conservation concern since population declines began in the 1980s. Thirty‐eight years of aerial waterfowl surveys of Lake Pontchartrain—an oligohaline estuarine lagoon in southeast Louisiana—show that scaup abundance fluctuates between 0 and 1,194,907 birds, though the mechanisms driving this variation are unknown. Previous studies have shown that scaup feed primarily on mollusks, and so changes in the benthic prey community have the potential to strongly influence scaup dynamics on the Lake. Benthic communities are in turn shaped by both natural and anthropogenic disturbances (e.g., hurricanes and spillway openings), potentially creating a lagged bottom‐up trophic cascade that ultimately affects scaup abundance. Using 22 yr of paired benthic invertebrate and aerial waterfowl survey data, we found scaup populations increased with the abundance of medium‐sized Rangia clams (Rangia cuneata) and Dwarf Surf Clams (Mulinia lateralis). Those prey species declined in years when the Lake was hit by a hurricane, but medium‐sized Rangia rebounded strongly the year after, likely because storm‐surge salinity induces spawning. Using long‐term aerial survey data for scaup, we indeed found strong declines on the Lake in years when a hurricane made landfall, but scaup abundance increased the following year, presumably responding to large numbers of medium‐sized Rangia. Our three‐part analysis makes a strong case for a hurricane‐driven bottom‐up trophic cascade that affects scaup populations on Lake Pontchartrain. This study adds to a growing literature demonstrating not only that estuaries are tidally and seasonally dynamic, but that punctuated disturbance events can be important for maintaining ecosystem function.

Seasonal dynamics of phytoand zooplankton of an eutrophicated lake in years with different water content and temperature conditions

Seasonal dynamics of phytoand zooplankton of an eutrophicated lake in years with different water content and temperature conditions

Effects of the interannual variations in the flood pulse mediated by hypoxia tolerance: the case of the fish assemblages in the upper Parana River floodplain

The effects of the duration of the floods on abiotic variables and attributes of species tolerant and intolerant to hypoxia (STH and SIH respectively) were evaluated in rivers and lakes of the upper Paraná River. Fish were sampled once a year, in six sampling stations, during the high water period from 2000 to 2003. There were overall reductions in dissolved oxygen levels and increases in transparency of water in lakes in years of moderate floods. The duration of floods influenced species differentially based on their tolerance to hypoxia: in moderate floods, richness of STH increased and numerical abundance and biomass of SIH reduced significantly. Opposite relationships were detected between dissolved oxygen and the attributes of STH and SIH. Dissolved oxygen was the best predictor of variability of STH and SIH in years of moderate floods, whereas water transparency predicted significant amounts of STH in years of short floods. Being positively affected by dissolved oxygen reductions, STH seem to take advantages in persisting in seasonally harsh lentic habitats. The incorporation of abiotic data as well the differential tolerance of species to hypoxia would improve further investigations of the effects of interannual variations in the flood pulse on tropical fish assemblages

Phytoplankton community and their impact on water quality: An analysis of Hollingsworth Lake, UK

Algal bloom had been a problem on the Hollingworth Lake in years’ past to the locales and the lake’s biodiversity. In order to assess the status of the lake, the lake’s phytoplankton and water quality were examined during the study period of June to August 2004) at three lake depths. 49 species belonging to 7 different classes were identified including Dinophytes, Cyanophytes, Baccilariophytes, Chlorophytes, Cryptophytes, Euglenophytes and Crysophytes. The most representative class in terms of species richness was Dinophyceae (2species) and dominated by Ceratium hirudinella. Cyanobacteria had 13 species and was dominated by Microcytisflos aquae, Baccilariophytes had 10 species, Chlorophytes had 15 species, Cryptophytes (4 species), Chrysophytes (2 species) and the least of the species was Euglenophyte as it contributed with lower biovolume values. The total biovolumes of the phytoplankton species including Microcystis Flos aquae and Oscillatoria aghardii increased progressively following the increase in temperature over the summer months with a mean level of temperature was 17°C, pH-7.72; conductivity of 0.199ms/cm and Dissolved Oxygen, 87%. When the lake’s chemical components, phytoplankton composition and phytoplankton biomass were compared with international technical standards for measurement, including the World Health Organisations’ standard for water quality and the EC Directive for goodquality water, the results indicated the lake to fall within the mesotrophic-eutrophic status. At the time of this study, the lake was not susceptible to generating algal blooms.

Multidecadal variations and decline in spring discharge in the Canadian middle Arctic since 1550 AD

Annually laminated (varved) sediments from Sanagak Lake in the Canadian middle Arctic were used to reconstruct past spring discharge. Two years of sediment transport observations demonstrate that sediment delivery in this nival regime is limited primarily to the short period of maximum discharge. Interannual variability in catchment snow water equivalence (SWE) was the primary control over the length of the peak discharge period, resulting in substantially increased sediment transport and deposition in the lake in years with higher SWE. Analysis of annual sediment accumulation reveals high interannual variability with a persistent 64–80 year frequency as well as a prominent decline, particularly since 1820 AD. These spectral results suggest a linkage between the Atlantic Multidecadal Oscillation (AMO) and snowfall conditions through persistence of the characteristic frequency since 1550 AD.

Variation in the Life History of the American Smelt in Inland Waters of Maine

Abstract A survey conducted by Wardens of the Department of Inland Fisheries and Game provided information on the time and duration of smelt spawning runs in 114 Maine lakes in 1958, and in two lakes in years prior to 1958. Other phases of the Maine smelt investigation provided information on spawning sites, habitats occupied, maximum sizes, and behavior with respect to angling. Large variations in these aspects of the life history of the smelt were found. Evidence is presented which suggests that certain phases of the spawning behavior are subject to the law of heterogenous stimulus summation. Possible reasons for the different habitat types occupied, the different maximum sizes attained, and the differences in behavior with respect to angling are briefly discussed. It is suggested that these variations might be the result of speciation in progress. If so, the genetic constitution of the various smelt populations might have implications in management.