The flux of reduced substances, such as methane and ammonium, from the sediment to the bottom water (Fred) is one of the major factors contributing to the consumption of oxygen in the hypolimnia of ...lakes and thus crucial for lake oxygen management. This study presents fluxes based on sediment porewater measurements from different water depths of five deep lakes of differing trophic states. In meso- to eutrophic lakes Fred was directly proportional to the total organic carbon mass accumulation rate (TOC-MAR) of the sediments. TOC-MAR and thus Fred in eutrophic lakes decreased systematically with increasing mean hypolimnion depth (zH), suggesting that high oxygen concentrations in the deep waters of lakes were essential for the extent of organic matter mineralization leaving a smaller fraction for anaerobic degradation and thus formation of reduced compounds. Consequently, Fred was low in the 310 m deep meso-eutrophic Lake Geneva, with high O2 concentrations in the hypolimnion. By contrast, seasonal anoxic conditions enhanced Fred in the deep basin of oligotrophic Lake Aegeri. As TOC-MAR and zH are based on more readily available data, these relationships allow estimating the areal O2 consumption rate by reduced compounds from the sediments where no direct flux measurements are available.
Strandlines document the former presence of lakes and a sea in east-central North America along the southern margin of the retreating Laurentide Ice Sheet (LIS). The strandlines of these formerly ...level water bodies are uplifted to the north and provide evidence of glacial isostatic adjustment (GIA) of the Earth's crust to the former ice load. We compile published ages and measurements of the present elevation and location of shore features in the strandlines of eight major paleo-water bodies from the St. Lawrence Valley to the northern Great Plains in digital format as an aid for the numerical modelling of GIA. Data for eastern water bodies were extracted and digitized from publications during the past 120 years. Digital position coordinates were scaled from published maps of survey sites or were determined using Google Earth Pro software. Published data for paleo-lakes Duluth and Agassiz were mainly obtained from field measurements and digital elevation models. Two-sigma or 95% probability values are provided for the strandline ages and for isobase (contour) positions representing the deformed water surfaces. Peak strandline gradients reported here were largest at about ca. 13 000 years ago. Lower strandline gradients for older shores may reveal areas closer to the peripheral bulge and areas of thinner ice (lighter crustal loads). Concave upward strandline profiles characterize most paleo-basins, whereas a linear uplift profile characterizes the Champlain Sea strandline. Directions of strandline maximum uplift within the former water body basins point toward the thickest part of the LIS near the Quebec-Labrador ice dome.
To study the fluvial interaction between Changjiang River and Poyang Lake, we analyze the observed changes of riverine flux of the mid-upstream of Changjiang River catchment, the five river systems ...of Poyang Lake and Poyang Lake basin. Inter-annual and seasonal variations of the water discharge and sediment exchange processes between Changjiang River and Poyang Lake are systematically explored to determine the influence of climate change as well as human impact (especially the Three Gorges Dam (TGD)). Results indicate that climate variation for the Changjiang catchment and Poyang Lake watershed is the main factor determining the changes of water exchanges between Changjiang River and Poyang Lake. However, human activities (including the emplacement of the TGD) accelerated this rate of change. Relative to previous years (1956–1989), the water discharge outflow from Poyang Lake during the dry season towards the Changjiang catchment increased by 8.98km3y−1 during 2003–2010. Evidently, the water discharge flowing into Poyang Lake during late April–late May decreased. As a consequence, water storage of Poyang Lake significantly reduced during late April–late May, resulting in frequent spring droughts after 2003. The freshwater flux of Changjiang River towards Poyang Lake is less during the flood season as well, significantly lowering the magnitude and frequency of the backflow of the Changjiang River during 2003–2010. Human activities, especially the emplacement and operation of the TGD and sand mining at Poyang Lake impose a major impact on the variation of sediment exchange between Changjiang main river and Poyang Lake. On average, sediments from Changjiang River deposited in Poyang Lake before 2000. After 2000, Changjiang River no longer supplied sediment to Poyang Lake. As a consequence, the sediment load of Changjiang River entering the sea increasingly exists of sediments from Lake Poyang during 2003–2010. As a result, Poyang Lake converted from a depositional to an erosional system, with a gross sediment loss of 120.19Mty−1 during 2001–2010, including sand mining.
•The river–lake interaction greatly changed after 2003.•Climate change exerted greater influence on water exchange between river and lake.•Human activities imposed more impact on sediment exchange between river and lake.•The forcing of Changjiang River on Poyang Lake significantly weakened after 2003.•The sediment contribution of Lake Poyang to Changjiang River greatly increased.
18th World Lake Conference
Lakes & Reservoirs : Science, Policy and Management for Sustainable Use,
December 2019, 2019-12-00, 20191201, Letnik:
24, Številka:
4
Journal Article
Between January 2013 and December 2014, water levels on Lake Superior and Lake Michigan‐Huron, the two largest lakes on Earth by surface area, rose at the highest rate ever recorded for a 2 year ...period beginning in January and ending in December of the following year. This historic event coincided with below‐average air temperatures and extensive winter ice cover across the Great Lakes. It also brought an end to a 15 year period of persistently below‐average water levels on Lakes Superior and Michigan‐Huron that included several months of record‐low water levels. To differentiate hydrological drivers behind the recent water level rise, we developed a Bayesian Markov chain Monte Carlo (MCMC) routine for inferring historical estimates of the major components of each lake's water budget. Our results indicate that, in 2013, the water level rise on Lake Superior was driven by increased spring runoff and over‐lake precipitation. In 2014, reduced over‐lake evaporation played a more significant role in Lake Superior's water level rise. The water level rise on Lake Michigan‐Huron in 2013 was also due to above‐average spring runoff and persistent over‐lake precipitation, while in 2014, it was due to a rare combination of below‐average evaporation, above‐average runoff and precipitation, and very high inflow rates from Lake Superior through the St. Marys River. We expect, in future research, to apply our new framework across the other Laurentian Great Lakes, and to Earth's other large freshwater basins as well.
Key Points
Between January 2013 and December 2014, the two largest lakes on Earth rose at a record‐setting rate
We developed a Bayesian MCMC routine for inferring estimates of the water budget for this period
The cold 2013–2014 winter contributed to reduced evaporation rates and rising water levels
After 200 years of reclaiming shallow lakes to expand cultivated land in Europe and North America, recent decades have been marked by the establishment of new lakes, this time to stop the decline of ...freshwater biodiversity and help reduce nutrient transport from land to sea. However, new lakes risk becoming eutrophic and turbid, because they are established mainly on fertile agricultural soils. Minimizing internal nutrient loading from sediments can be accomplished by relocating nutrient-rich sediment to deep water with low release, rapidly exporting nutrients by washout, or immobilizing soil-nutrients before inundation. We studied sediment relocation in relation to sediment shear stress and phosphorus decline in sediment in new Lake Birke, Denmark (area 125 ha, mean water depth 0.56 m, retention time ca. 193 days). Evaluating core samples and other data on two occasions, 116 and 530 days after establishment, we found that sediment density changed towards harder materials in the middle of the lake, which is characterized by high bottom shear stress, while islands and shores exposed to short fetches from the prevailing winds experienced low bottom shear stress and accumulated softer, nutrient-rich organic material. After 530 days, sediment density had become a highly significant linear function of bottom shear stress (P < 0.001, R2 = 0.59). Daily mean sediment P in surface sediment (0–10 cm) decreased by 20.1 mg P m−2 sediment during the first 116 days and 7.9 mg P m−2 during the next 414 days. Overall, 69% of the phosphorus pool in surface sediments was lost and likely washed out over the first 530 days. Managing a lake by keeping initially shallow water and short water retention time, and locating the lake outlet in a wind-exposed area of high particle concentration, may facilitate loss of sediment nutrients and thus promote desired ecological qualities. Moreover, deeper sedimentation areas that are easily accessible to mechanical dredging may be planned to reduce nutrient release of fine, nutrient-rich organic particles.
This study investigated a series of dammed lakes and downstream‐adjacent alluvial fans in the upstream to middle reaches of the Golmud River in the eastern Kunlun Mountain, on the north‐eastern ...Qinghai‐Tibetan Plateau (QTP). An optically stimulated luminescence (OSL) chronology shows the sediments of five dammed lakes developed from c. 45–40, 30–25, 18–14, and 12–8 ka, corresponding to MIS 3b, late MIS 3a, Last Deglaciation, and early Holocene, respectively. The remote sensing data show these dammed lakes have a total area of 109.4 km2, with the lake volume of more than 4.0 km3. Symmetric alluvial fans from north–south tributary valleys produced OSL ages of c. 61–52, 42–31, 26–20, and 16–10 ka, corresponding to glaciation periods: the MIS 3c and MIS 3a, MIS 2, and the Last Deglaciation. This suggests that glacial activity is responsible for the alluvial fan development, where dammed rivers occurred first, but lake formation did not take place synchronously until later periods of strong hydrologic activity, resulting from northward intrusions of the Indian summer monsoon (ISM) or glacier melt. Thus, the blocking pattern is that river valleys were dammed during periods of glacial activity and lakes formed during wet periods. The lake formation and subsequent drainage may have resulted in: (i) impeded headwater incision and strengthening of downstream dissection; (ii) enriched the halite and potash in the distal Qarhan Salt Lake through hydrologic and hydrochemical processes of abundant water input, the salt lake expansion, salt redissolution from playa and final resedimentation during later dry periods. The alluvial‐dammed lake pattern in the mountain‐basin systems of eastern Kunlun Mountain offers a model for assessing the linkages between monsoon dynamics, geomorphic processes and distal salt lake evolutions in other arid regions.
Landscape evolution processes in the mountain‐basin system of the Golmud River catchment: (a) During glacial advance stages, massive outwash‐origin detritus is produced by glacier cascades to lateral alluvial fans in tributary valleys. Coalescence of north‐south symmetric alluvial fans forms dams in the main river valley, and the distal salt lake shrinks; (b) During wet stages, the Indian summer monsoon intrudes northward and abundant precipitation forms surface runoff. Dammed lakes develop behind the preexisting alluvial dams; (c) After subsequent dam failure, high runoff input causes salt lake expansion, clast input and salt minerals redissolution from playa; (d) During later dry climatic stages, salt minerals accumulate from the playa owing to shrinkage of the salt lake.
PDF
