Open Water Surface Area Research Articles

Watershed DOC uptake occurs mostly in lakes in the summer and in rivers in the winter

AbstractRiver networks transport dissolved organic carbon (DOC) from terrestrial uplands to the coastal ocean. The extent to which a reach or lake within a river network uptakes DOC depends on the stream order, the seasonal conditions, and the flow. At the watershed scale, it remains unclear whether DOC uptake is dominated by biological processes such as respiration, or abiotic processes like photomineralization. The partitioning of DOC uptake in lakes vs. rivers is also unclear. In this study, we present a new model that unifies year‐round controls on DOC cycling for an entire river network, including river–lake connectivity, to elucidate the importance of biotic vs. abiotic controls on DOC uptake. We present the Catchment UPtake and Sinks by Season, Order, and Flow for DOC (CUPS‐OF‐DOC) model, which quantifies terrestrial DOC loading, gross primary productivity, and uptake via microbes and photomineralization. The model is applied to the Connecticut River Watershed, and accounts for cascading reach‐ and lake‐scale DOC cycling across 98 scenarios spanning combinations of flows, seasons, and stream orders. We show that riverine DOC uptake is nearly constant with stream order, but the proportion of DOC uptake from photomineralization varies. Photomineralization dominates in rivers in most flow conditions and stream orders, especially in winter, accounting for at least half of whole‐watershed DOC uptake in February across all flows. Whole‐watershed summer DOC uptake occurs mostly via biomineralization in lakes, accounting for 80% of DOC uptake during the growing season, despite accounting for less than 6% of watershed open water surface area.

Interannual and Seasonal Variations of Hydrological Connectivity in a Large Shallow Wetland of North China Estimated from Landsat 8 Images

Hydrological connectivity is an important characteristic of wetlands that maintains the stability and functions of an ecosystem. This study investigates the temporal variations of hydrological connectivity and their driving mechanism in Baiyangdian Lake, a large shallow wetland in North China, using a time series of open water surface area data derived from 36 Landsat 8 multispectral images from 2013–2019 and in situ measured water level data. Water area classification was implemented using the Google Earth Engine. Six commonly used indexes for extracting water surface data from satellite images were compared and the best performing index was selected for the water classification. A composite hydrological connectivity index computed from open water area data derived from Landsat 8 images was developed based on several landscape pattern indices and applied to Baiyangdian Lake. The results show that, reflectance in the near-infrared band is the most accurate index for water classification with >98% overall accuracy because of its sensitivity to different land cover types. The slopes of the best-fit linear relationships between the computed hydrological connectivity and observed water level show high variability between years. In most years, hydrological connectivity generally increases when water levels increase, with an average R2 of 0.88. The spatial distribution of emergent plants also varies year to year owing to interannual variations of the climate and hydrological regime. This presents a possible explanation for the variations in the annual relationship between hydrological connectivity and water level. For a given water level, the hydrological connectivity is generally higher in spring than summer and autumn. This can be explained by the fact that the drag force exerted by emergent plants, which reduces water flow, is smaller than that for summer and autumn owing to seasonal variations in the phenological characteristics of emergent plants. Our study reveals that both interannual and seasonal variations in the hydrological connectivity of Baiyangdian Lake are related to the growth of emergent plants, which occupy a large portion of the lake area. Proper vegetation management may therefore improve hydrological connectivity in this wetland.

Change Detection of Lake Chad Water Surface Area Using Remote Sensing and Satellite Imagery

The Lake Chad located in the west-central Africa in the Sahel region at the edge of the Sahara experienced severe drought during 1970s and 1980s and overexploitation (unintegrated and unsustainable use), which is a result of variant land uses and water management practices during the last 50 years. This resulted in a decline of the water level in the Lake and surrounding rivers. The present study analyzed satellite images of Lake Chad from Landsat-MSS, Landsat-OLI to investigate the change of the open water surface area during the years of 1973, 1987, 2001, 2013, and 2017. Supervised classifications were performed for the land cover analysis. The open water area in 1973 was covering 16,157.34 km2 approximately, and that was 64.6% of the total lake area in the 1960s. As an ultimate result of the extreme drought that the study area witnessed through 1970s-1980s, the open water area has decreased to 1831.44 km2, i.e. around 11.33%, compared to that in 1973. The dilemma that the study area is suffering from is believed to be a catastrophic complication of the aforementioned drought crisis, which arose as an ultimate result the climate change, global warming, and the unintegrated and unsustainable use of water challenges the study area is still encountering.

DESENVOLVIMENTO HIDROLÓGICO E FENOLOGIA DE LAGOS DA PENÍNSULA FILDES – ANTÁRTICA

Este artigo avalia a dinâmica de congelamento e descongelamento dos lagos da península Fildes, utilizando imagens TerraSAR-X (TSX) entre fevereiro e abril de 2011, e a correlação da área de superfície líquida com as variáveis temperatura, precipitação e vento. A área de superfície líquida foi obtida a partir de classificação de imagem TSX, utilizando o classificador MAXVER, para 12 imagens do ano de 2011. A correlação de temperatura do ar atmosférico com a área, determinada pelo método de correlação de Spearman e Pearson, demonstra padrão de correlação significativa em 7 dos 15 lagos, enquanto a precipitação é uma importante variável na formação da superfície líquida em 11 dos 15 lagos. Todos os lagos voltados para a passagem de Drake mostram correlação significativa coma direção do vento que atua causando ondas na superfície líquida e que, por sua vez, provocam a quebra do gelo na superfície. Quanto à direção dos ventos, esta variável pode estar ligada à mudanças na duração do período de ablação para a península Fildes. De forma geral, as imagens TSX permitiram um detalhamento temporal inédito para a área de estudo, possibilitando mapear os lagos no período entre fevereiro e abril de 2011.

Economic value of wetlands services in the Central Rift Valley of Ethiopia

This study estimates the economic values of wetlands services in the Central Rift Valley of Ethiopia. A choice experiment valuation method was used to quantify monetary value of wetlands. The study used data collected from 405 households complemented with data collected using Participatory Rural Appraisals. Multinomial logit and random parameter logit models were used to analyze the data. The results have demonstrated the economic values of wetlands in the study area. Households ascribe the highest value for biodiversity (marginal willingness to pay value of US $1.26 per percentage of biodiversity conserved), followed by water availability (US $0.87 per ha increase in open water surface area). The statistical inferences, however, showed significant heterogeneity among households in their preference for wetland management alternatives. The probability of choosing improved wetland management is significantly reduced by age of the household head and distance; while, it is increased by education, income and location. The finding also revealed an average and aggregate willingness to pay of US $7.5 and 694,141, respectively, for a change from status quo to high impact improvement scenario. It is, thus, recommended to take rehabilitation and conservation measures to ensure sustainable use and management of wetland resources in the area.

Arctic Fog Detection Using Infrared Spectral Measurements

AbstractThe rapid increase in open-water surface area in the Arctic, resulting from sea ice melting during the summer likely as a result of global warming, may lead to an increase in fog [defined as a cloud with a base height below 1000 ft (~304 m)], which may imperil ships and small aircraft transportation in the region. There is a need for monitoring fog formation over the Arctic. Given that ground-based observations of fog over Arctic open water are very sparse, satellite observations may become the most effective way for Arctic fog monitoring. We developed a fog detection algorithm using the temperature difference between the cloud top and the surface, called ∂T in this work. A fog event is said to be detected if ∂T is greater than a threshold, which is typically between −6 and −12 K, depending on the time of the day (day or night) and the surface types (open water or sea ice). We applied this method to the coastal regions of Chukchi Sea and Beaufort Sea near Barrow, Alaska (now known as Utqiaġvik), during the months of March–October. Training with satellite observations between 2007 and 2014 over this region, the ∂T method can detect Arctic fog with an optimal probability of detection (POD) between 74% and 90% and false alarm rate (FAR) between 5% and 17%. These statistics are validated with data between 2015 and 2016 and are shown to be robust from one subperiod to another.

Effect of changes in the fractal structure of a littoral zone in the course of lake succession on the abundance, body size sequence and biomass of beetles.

Dystrophic lakes undergo natural disharmonic succession, in the course of which an increasingly complex and diverse, mosaic-like pattern of habitats evolves. In the final seral stage, the most important role is played by a spreading Sphagnum mat, which gradually reduces the lake’s open water surface area. Long-term transformations in the primary structure of lakes cause changes in the structure of lake-dwelling fauna assemblages. Knowledge of the succession mechanisms in lake fauna is essential for proper lake management. The use of fractal concepts helps to explain the character of fauna in relation to other aspects of the changing complexity of habitats. Our 12-year-long study into the succession of water beetles has covered habitats of 40 selected lakes which are diverse in terms of the fractal dimension. The taxonomic diversity and density of lake beetles increase parallel to an increase in the fractal dimension. An in-depth analysis of the fractal structure proved to be helpful in explaining the directional changes in fauna induced by the natural succession of lakes. Negative correlations appear between the body size and abundance. An increase in the density of beetles within the higher dimension fractals is counterbalanced by a change in the size of individual organisms. As a result, the biomass is constant, regardless of the fractal dimension.

A Hydrologic Restoration Attempt of the Dried Akgöl Wetland (Central Anatolia, Turkey)

The Akgol Wetland has been subject to extensive drainage processes by anthropogenic factors that have almost caused the wetland to disappear since the 1970s. In this contribution, as a one of the pioneering work on wetland restoration in Turkey, we present hydrological studies aiming to restore the natural function of the Akgol wetland and post-restoration observations. Considering the water budget of the wetland, three scenarios focusing on restoring the wetland hydrology were developed. The open water surface area and volumetric water storage relations for each scenario were simulated using GIS-based tools. The most appropriate scenario for restoration of the Akgol Wetland was chosen by taking the original state of the wetland prior to drainage as the primary criterion. As the first stage, functioning of the central channel draining the wetland was ceased by refilling it. Following this, an artificial bank was constructed at the narrowest part of the wetland, which resulted in an open water surface that cover all current and former ponds. The wetland has start to hold surface runoff and groundwater inflows since September 2011. Since rewetting, the Akgol Wetland is regaining its ecosystem functions and the increase in avian population indicate the proposed restoration effort was successful.

Biotic responses to extreme hypersalinity in an arid zone estuary, South Africa

The Groen Estuary does not function as a typical temporarily open/closed estuary for much of the time, due primarily to the high variability of its physico-chemical attributes. Extreme states are represented by an open mouth following a flood (low salinity) and extreme hypersaline conditions that develop after a prolonged period (years) of mouth closure and a high rate of evaporation from the water body. Available information suggests that biotic recruitment from the marine environment follows mouth breaching, but species disappear progressively as salinity increases and threshold salinity values are reached. A field survey in February 2015 indicated that at the time, salinity ranged from 223 in the lower reaches and <10 upstream over a distance of <1km. The study provided new information on the estuary that includes the revised delineation of the lateral boundary. Habitat mapping from past aerial photographs showed that the open water surface area has decreased over time but the vegetated areas have remained stable. No benthic macroinvertebrates, mesozooplankton or fish were present. Together with low avian species counts and abundance it was concluded that the Groen Estuary represented a small, naturally stressed ecosystem in February 2015. Main stressors were extreme hypersalinity, relatively low water volume, anoxic sediments and a mouth that had remained closed for a relatively long period of time (years).

Present-day evolution of coastal lakes based on the example of Jamno and Bukowo (the Southern Baltic coast)

Abstract This study presents the directions and the rate of changes occurring in the coastal lakes Jamno and Bukowo, located in northern Poland. Based on the cartographic materials and aerial photographs of those water bodies, it was established that in 1909–2012, the area of the lakes decreased by 183.6 ha (7.7%) and 250.7 ha (13.6%) for Jamno and Bukowo, respectively. Another component of lake disappearance — shallowing of lake basins — was analyzed using bathymetric plans. It turned out that water supplies of Jamno during more than 100 years decreased by 2.4 million m3 (5.9%), while in the case of Bukowo, it was 5.9 million (17.5%). Unfavorable location (inflow of pollutants from the basin) and morphometry of both lakes should be considered as the main causes of such major changes. The lakes are polymictic with a considerable area of the shallowest zone (1 m depth). This favors the vegetation succession and, consequently, shallowing of the lake basins. Moreover, direct connection with the Baltic Sea contributes to the fact that the materials of marine origin deposited in the form of a reverse delta also contribute to a decrease in the open water surface area.

The short-term impact of wetland restoration on the genetic diversity of a predominantly clonal plant species

Genetic diversity plays a major role in ensuring the adaptive capacity and long-term viability of populations. Recent studies have shown that evaluations of the ecological benefits of ecosystem restoration should incorporate the impact of restoration on population genetic variability to accurately guide restoration priorities. This study aimed to analyse the population genetic diversity of an aquatic plant, Berula erecta, in wetlands restored by sediment dredging using natural local wetlands as a reference to assess the impact of ecological restoration on genetic diversity. The analyses were performed using microsatellite markers. Restoration led to a considerable increase in the open water surface area at the site, and the restored areas were efficiently colonised by B. erecta. The populations exhibited a high level of genetic diversity, even though clonal propagation is the major reproductive mode of this species. Two years after restoration, population genetic diversity (AR allelic richness, FIS and PG) was very similar between the restored and natural wetlands. For one restored wetland, the individuals in the restored area of the wetland showed greater allelic richness than those in the unrestored areas of the same wetland. In addition, most of the multilocus genotypes observed in the restored wetlands only occurred as single individuals, suggesting that clonal propagation is not the only mode of recolonisation after restoration. The source of the new genotypes that appeared after restoration may have been a local relict population, seeds remaining in the seed bank after restoration (cryptic genetic diversity), or propagules (seed or vegetative fragments) that migrated into the wetland. These results suggest that the benefits of restoration may depend strongly on the genetic diversity of established relict and dormant populations. Population diversity, in turn, may partly depend on the ecological characteristics of the site (i.e., connectivity of the water body to the surrounding wetlands, successional stage and site history).

Contemporary changes in open water surface area of Lake Inle, Myanmar

From 1935 to 2000, the net open water area of Inle Lake in Central Shan State, Myanmar decreased from 69.10 to 46.69 km2, a loss of 32.4% during this 65-year period. Local beliefs are that losses in lake area have been even greater within the last 100–200 years. Various activities, including timber removal, shifting agriculture in the uplands by various ethnic groups, and unsustainable cultivation practices on the low- and mid-level hillslopes around the lake, have been blamed for both historical and ongoing sedimentation. We take issue with attributing loss of lake area to these activities, and propose instead that ongoing “in-lake” and “near-lake” agricultural practices are the main sources of contemporary sediment and loss of open water area. About 93% (i.e., 20.84 km2) of the recent loss in open water area of the lake is due to the development of floating garden agriculture, largely along the west side of the lake. Direct environmental impacts associated with this practice and with other agriculture activities within the wetlands and margins of the lake include sedimentation, eutrophication, and pollution. Whilst the sustainability of hillslope agriculture and past forestry practices can indeed be questioned, a more urgent need is to address these "in-lake" and "near-lake" practices.

Controls on evapotranspiration in a west Siberian bog

This study analyzed controls on evapotranspiration (E) from a western Siberian bog, from a perspective that surface constraints limit the E available for atmospheric evapotranspiration demands. Ratios of E to potential evapotranspiration (EP) ranged from 0.2 to 0.9, and were clearly related to changes in surface constraints represented by the bulk transfer coefficient for latent heat CE (= βCH where β is the surface moisture availability and CH is the bulk transfer coefficient for sensible heat). Both EP and equilibrium evaporation (EEQ) showed similar seasonal trends, suggesting the importance of radiation to the seasonal variation of EP. The atmospheric drying power (Ea) was a minor factor in EP and showed less seasonal change during most of the growing season. However, the presence of a dry air mass caused by synoptic scale advection (most frequently observed in May 1999) significantly enhanced Ea; consequently, the seasonal maximum of EP occurred earlier than the seasonal maximum of EEQ. Values for CH (0.004–0.011) increased with leaf area index except Sphagnum moss (LAIg), indicating that vegetation growth contributes to changes in bog roughness through canopy height changes. The β value gradually decreased with decreases in the water table position (zwt); the open water surface area and water content of Sphagnum moss depended on zwt. Furthermore, the absence of a significant relationship between β and phenology implies that changes in evaporation contribute to variations in E more than changes in transpiration. Hence roughness change created by vegetation growth and surface wetness limit evapotranspiration to less than the potential evapotranspiration.

Evapotranspiration Crop Coefficients for Cattail and Bulrush

Accurate estimates of evapotranspiration from constructed wetlands are required to establish design flow estimates and to assess the effectiveness of wetland water quality amelioration. Water consumption by two wetland plant species, Typha latifoilia (broadleaf cattail) and Scoenoplectus acutus (hardstem bulrush), was measured in a greenhouse for eight months. Measurements of actual evapotranspiration (ETC) from replicates of both plant treatments were related to potential evaporation (ET0) as approximated by evaporation from saturated gravel beds. Ratios of ETC to ET0 were used to develop crop coefficients (Kc) for each plant species. The relationship between cattail ETC/ET0 and the ratio of vegetative to open water surface area (SV/S0) agreed with previous investigations. A linear relationship was used to account for advective energy fluxes due to peripheral canopy area. Cattail crop coefficients were scaled according to this relationship. The resulting scaled crop coefficient curve may be transferable ...

Bacteria and fungi in aerosols generated by two different types of wastewater treatment plants

Raw wastewater is a potential carrier of pathogenic microorganisms and may pose a health risk when pathogenic microorganisms become aerosolized during aeration. Two different types of wastewater treatment plants were investigated, and the amounts of cultivable bacteria and fungi were measured in the emitted aerosols. Average concentrations of 17000 CFU m −3 of mesophilic, 2100 CFU m −3 of TSA-SB bacteria (bacteria associated with certain waterborne virulence factors), 1700 CFU m −3 of mesophilic and 45 CFU m −3 of thermotolerant fungi, were found in the aerosol emitted by the aeration tank of the activated sludge plant. In the aerosol of the fixed-film reactor 3000 CFU m −3 mesophilic and 730 CFU m −3 TSA-SB bacteria, and 180 CFU m −3 mesophilic and 14 CFU m −3 thermotolerant fungi were measured. The specific emissions per population equivalent between the two types of treatment plants differed by two orders of magnitude. The microbial flux based on the open water surface area of the two treatment plants was similar. The aerosolization ratios of cultivable bacteria (expressed as CFU m −3 aerosol/m −3 wastewater) ranged between 8.4×10 −11 and 4.9×10 −9. The aerosolization ratio of fungi was one to three orders of magnitude higher and a significant difference between the two types of treatment plants could be observed.

Wetland vegetation colonization and expansion in small impoundments in Yaounde, Cameroon, West Africa

Temporal changes in the pattern and distribution of tropical wetland vegetation in four small impoundments over a 28-year period were documented for a wetland ecosystem in the Olezoa drainage basin in Yaounde, Cameroon, West Africa. These impoundments were constructed along the Olezoa stream for the purpose of aquaculture and ranged in size from 1.4 to 3.0 ha, had depths between 200 to 400 cm, and were devoid of vegetation. Evaluation of the impoundments and the surrounding catchment was accomplished using low altitude aerial photographs for the years 1964, 1974, and 1986 and field surveys for the periods 1985 through 1992. The results reveal a progressive decline in open water surface area of the impoundments ranging from 70 to 100% due to plant colonization and expansion. Measured impoundment depths along profiles show more than 50% reduction from original depths of 300–400 cm to less than 150–200 cm in 1992. We suggest that vegetation colonization and expansion in the impoundments is a function of the reduction of water depth due to siltation accompanying increasing urbanization. During the period of evaluation, urbanization in the surrounding catchment tripled. Siltation in the impoundments resulted mainly from the accumulation of soil eroded from the upland accompanying devegetation and construction activities. The shallowing of the impoundments by siltation provided a favorable water-depth regime and substrate for colonization by aquatic and emergent wetland vegetation. Continued shallowing resulted in development of vegetation zones along a water-depth gradient, and the migration of these zones toward the interior of the impoundments. The history of degradation of the catchment area and siltation of the impoundments is thus recorded by temporal changes in vegetation.

Ice cover melting in a shallow river

The heat transfer coefficients computed from field data on both ice cover melting and water temperature attenuation are higher than the values one would compute based on extrapolation of previous laboratory flume data. The computed heat transfer coefficients were relatively consistent when calculated from the water temperature decay data. Consistent results were also obtained with one set of very detailed ice cover melting data.The diurnal fluctuation in water temperature from the freezing point to values of 0.4–0.6 °C was associated with the incoming solar radiation and the open water surface area. The measured water temperature distribution beneath the ice cover at a particular cross section varied from 0.2 to 0.6 °C due to the influence of frazil ice and flow distribution. In the open water reaches the water temperature was essentially fully mixed vertically but lateral variation across the river ranged from 0.1 to 0.3 °C.The average daily melting of the ice cover often exceeded 5.0 cm and at some locations the rate was as high as 8 cm/d. The melt was not uniform across the section but was highly dependent upon the flow conditions, velocity, and depth. The ice cover melting for this year only occurred during the daylight hours as the air temperatures dropped below 0 °C at night and the water temperature likewise decayed to its freezing point.

THE EFFECTIVENESS OF BMP'S AND SEDIMENT CONTROL STRUCTURES AND THEIR RELATIONSHIP TO IN-LAKE WATER QUALITY

ABSTRACT Lake Herman is a nitrogen limited, hypereutrophic, shallow (mean depth 1.7m), warm water lake located in Lake County, S.D. The lake has experienced extensive blue-green algal blooms, fish winterkills, and receives a high sediment load. Algal and macrophyte growth has diminished the open water surface area. The predominant land use is agriculture with permanent homes, small businesses, and public recreation areas surrounding the lake's shoreline. On January 13, 1978, Lake Herman and its associated watershed were selected to participate in the U.S. Department of Agriculture and U.S. Environmental Protection Agency sponsored Model Implementation Program. The primary objective of the project was to improve the water quality of Lake Herman by reducing phosphorus, nitrogen, and sediment loads through voluntary application of Best Management Practices (BMP's) and construction of sediment control structures. Approximately 5 years of water quality data from the lake, the tributaries, the outlet, and above and below the BMP's, and the sediment control structures are available from this project. Although the results of t-test analyses indicated that the sediment control structures are reducing the sediment and nutrient load, a corresponding reduction has not been observed in the lake. Therefore, two phosphorus mass budget models were used to predict the phosphorus concentrations in the lake: neither predicted the high phosphorus concentrations observed in the lake. It is assumed that another nonpoint source of phosphorus affects the lake (internal loading from resuspended sediments or aquatic macrophytes). The next step in the Lake Herman restoration project is to dredge selected areas to deepen them and reduce the resuspension of sediments.

Response Characteristics of an Ebb-Dominated Tidal Inlet Channel

ABSTRACT A three-year study (July 1974 to July 1977) of Price Inlet, South Carolina, monitored inlet hydraulics and channel morphology. The inlet is strongly ebb-dominant. Both the peak and mean current velocities during ebb exceed the corresponding velocities during flood. The velocity asymmetry is caused by changes in inlet efficiency during the tidal cycle. The intertidal marsh of the Price Inlet drainage area experiences a change in open water surface area of about 670 percent during an average tidal cycle. At high tide, the large water surface of the marsh is responsible for inefficient exchange of water through the inlet. This causes a long time lag between ocean and bay tides. The small surface area of open water in the marsh at low tide, on the other hand, yields nearly no time lag. These differential time lags cause longer flood durations than ebb durations in the inlet throat and, consequently, stronger ebb elocities. Monitoring of the cross-sectional flow area of the inlet throat demonstrates rapid adjustment to changing flow conditions. The 1159 m2 cross sectional area of the inlet throat varied as much as 8.3 percent during one tidal cycle. The cross sectional area varied in phase with the tidal range. Long-term changes in the dimensions of the channel appear to be a direct result of changes in the size of ebb-tidal delta shoals. During the study period, the growth of the linear bars in the channel margin gradually reduced wave energy along the inlet shoreline and on the inner ebb-tidal delta platform. This in turn reduced sediment transport into the inlet, which resulted in a gradual increase in the cross-sectional area of the channel. Seasonal fluctuations in mean sea level appear t have little effect on the inlet channel.