Quantifying the Human Induced Water Level Decline of China’s Largest Freshwater Lake from the Changing Underlying Surface in the Lake Region

In recent years, dramatic decline in China’s largest freshwater lake, Poyang Lake, has raised wide concerns about water supply and ecological crises in the middle–lower Yangtze River reaches. To assist in resolving the debates regarding the low water regime of the lake, the current study quantitatively assessed the enhanced water level decline from the changing underlying surface in the Poyang Lake region. It is the first time that the magnitude, temporal–spatial difference, trend development and background mechanism of lake water level variation and its causes are studied comprehensively. The results revealed that the changing underlying surface in the lake region has caused an average decline of annual water level of 0.26 m ~ 0.75 m across the lake during 2000–2014, which shows great seasonal and spatial differences. The enlarged outflow cross–section due to extensive sand mining was the major reason for the effect on water level decline in the northern lake. While, increased water surface gradient should be attributed to water level decline in the southern lake. The long–term increasing trend of annual lake water level decline reflects the cumulative effects of lake bottom topography change caused by the continuous south movement of sand mining activities.     

Studies of Large-Scale Currents in Lake Erie, 1979–80

Currents and water temperatures were recorded at a large-scale grid of fixed moorings in Lake Erie from May 1979 through June 1980. Currents measured in the lower half of the central basin water column were mostly return flows (beneath the surface wind drift) driven by the surface pressure gradient. Often observed was a complex system of Lake Erie circulation gyres as predicted by models. Another common occurrence was for one of the central basin gyres to become dominant and envelop the whole basin in either uniform clockwise or anticlockwise flow. It is not fully certain why one of the circulation cells grows as opposed to the others, but the curl of the wind stress had influence. The currents were more barotropic than predicted by full Ekman layer current models. Tidal-like currents driven by the longitudinal seiches of Lake Erie dominate the island-filled passages between the western and central Lake Erie basins, with currents across the whole island chain very closely in phase. Processes of hypolimnion volume entrainment are suggested from the central basin temperature recordings. Large volume water exchanges between the central and eastern basins occurred after the water mass in the vicinity of the shallow ridge that separates them had become unstratified. These and other topics are discussed as the large data set generated from the experiment is explored.     

Reproductive Potential and Fecundity of Lake Trout Strains in Southern and Eastern Waters of Lake Ontario, 1977–1994

We assessed the reproductive potential of various genetic strains of hatchery lake trout (Salvelinus namaycush) in southern and eastern Lake Ontario from indices of fecundity and indices of male abundance. Indices were constructed from catches of mature lake trout in gill nets during September 1980 to 1994 after correcting for mortality from sea lampreys (Petromyzon marinus) which occurred between September sampling and late fall spawning. Strain and age were assigned to individual lake trout based on clipped fins and maxillary bones or coded wire tags. Fecundity-length relationships for fish of the same age, determined from mature females collected in 1977 to 1981 and 1994, were not different (P > 0.05) among genetic strains. For all strains combined, fecundity-length relationships in 1977 to 1981 were not different among fish of various ages but in 1994, age-5 and -6 fish had fewer eggs (P < 0.003) than age-7 fish, and age-7 fish had fewer eggs (P < 0.003) than fish of age 8, 9, or 10. Annual indices of fecundity varied 19 fold and indices of mature males varied 11 fold; both indices were low in the early 1980s, increased sharply in the mid 1980s, and peaked in 1993. The strain which dominated fecundity and mature male indices shifted during the study from Seneca Lake strain to Lake Superior strain and then back to Seneca Lake strain. However, changes in either reproductive potential or genotypes do not appear responsible for the abrupt appearance of naturally-produced yearling lake trout throughout southern and eastern Lake Ontario in 1994–1995, the first widespread occurrence of juveniles produced by hatchery lake trout in Lake Ontario.     

Occurrence and distribution of organochlorine pesticides and polycyclic aromatic hydrocarbons in surface sediments from Qinghai Lake,northeast Qinghai–Tibet plateau,China

Organochlorine pesticides (OCPs) and polycyclic aromiatic hydrocarbons (PAHs) were analyzed in surface sediment samples collected from Qinghai Lake, the largest lake in China, which is situated in the northeast Qinghai–Tibet plateau at an altitude of 3200 m. The concentrations of these pollutants ranged from 0.02 to 1.00 ng/g for hexachlorocyclohexanes (HCHs), from not detected to 0.86 ng/g for dichlorodiphenyltrichloroethanes (DDTs), from 0.26 to 1.73 ng/g for OCPs, and from 366 to 966 ng/g for PAHs. The predominance of α-HCH suggests that long-range atmospheric transport is an important source for HCHs. A low α- to γ-HCH ratio (3.87 on average) indicates the possible usage of lindane in the drainage basin. The high percentage of p,p′-DDE and p,p′-DDD and the low percentage of o,p′-DDT indicated significant degradation from previous inputs, and no recent inputs of dicofol derived DDT. Based on the analysis of the component ratios, PAHs were found to be primarily from the combustion of biomass and coal-based fossil fuels. Using the Canadian sediment guidelines, PAHs are of greater ecological concern than OCPs in Qinghai Lake.     

Development and Analytical Verification of an Integrated 2-D Surface Water—Groundwater Model

DIVAST is a two-dimensional hydrodynamic and water quality numerical model developed for estuarine and coastal modelling. The original model enables the simulation of problems such as pollution and flooding in surface waters. In this paper the existing model is extended to allow the modelling of 2-D groundwater as well as surface water in the same model, using an integrated approach rather than two disparate models. The changes to the original model are summarised and the method of implementation is outlined. The new extended model (DIVAST-SG) is then tested against an analytical solution to verify that the model solves the equations correctly. The model is shown to predict the analytical solution for two different scenarios to within approximately 1 % of the height of flood wave.     

Status of the amphipod Diporeia spp. in Lake Superior, 2006–2016

The amphipod Diporeia spp. has historically been an important component of the benthic food web of the Laurentian Great Lakes. The Great Lakes Water Quality Agreement included its population density as an indicator of ecological condition for Lake Superior, with target values of 220–320 m^?2 in nearshore areas (≤100 m depth) and 30–160 m^?2 in offshore areas (>100 m). To assess the status of Diporeia in Lake Superior, we used a probability-based lake-wide survey design to obtain estimates of Diporeia density and biomass in 2006, 2011 and 2016. A PONAR grab sampler was used to collect Diporeia at 50–53 sites each year, with approximately half in the nearshore (<100 m depth) region of the lake and half in the offshore. The mean area-weighted lake-wide density was 395 ± 56 (SE) m^?2 in 2006, 756 ± 129 m^?2 in 2011, and 502 ± 60 m^?2 in 2016. For all years, both density and biomass were greater in the nearshore than in the offshore stratum. The densities for 2006–2016 were 3–5 times higher than those reported from a lake-wide survey conducted in 1973 by the Canada Centre for Inland Waters. The severe declines in Diporeia populations observed in the other Great Lakes during recent decades have apparently not occurred in Lake Superior. Further research is needed to understand spatial and temporal variability of Diporeia populations in Lake Superior to enhance the utility of Diporeia density as an indicator of benthic condition.     

Sudden Disappearance of the Amphipod Diporeia from Eastern Lake Ontario, 1993–1995

Diporeia, Oligochaeta, and Sphaeriidae were sampled at three sites (28 to 35 m depth) in the east basin of Lake Ontario, and at one mid-lake site (125 m) from 1982 and 1996. In addition, Diporeia was sampled at 14 more sites located in the south and eastern part of the lake in 1990 and 1995. Before 1991, densities of all three macroinvertebrate taxa fluctuated with peaks occurring between 1988 and 1991. Between 1992 and 1995, Diporeia declined rapidly from > 6,000 per m² to 0 at all three sites in the east basin, while increasing from 1,050 to 5,230 per m² at the mid lake site. Samples from the south and eastern part of the lake confirmed the decline was extensive at depths < 100 m. Abundance and biomass of the Oligochaeta and Sphaeriidae also fluctuated, but remained more similar before 1991 and after 1993. Direct cause for the disappearance of Diporeia is unknown but declines occurred after establishment of nearshore Dreissena colonies. Lake circulation patterns suggest that the nearshore mussel populations may intercept diatoms and other material that had been consumed by Diporeia located further offshore. A substantial biomass of Diporeia (3 g/m² dry) has been lost from the food web of eastern Lake Ontario, with serious consequences to the coldwater fisheries of the lake.     

Life on a seamount: Lake charr at Stannard Rock,Lake Superior, 2011–2015

Lake Superior has four extant lake charr ecotypes including the ubiquitous lean (shallow-water form), the deep-water siscowet, and the less common, mid-depth redfin and humper forms. Stannard Rock is a distant seamount in Michigan waters that is a coveted recreational lean lake charr fishing destination. Lake charr at Stannard Rock were surveyed during 2011–2015 using gill nets set in waters <80 and ≥80 m to assess population status. All four ecotypes were found at Stannard Rock with leans being most abundant at depths <80 m and humpers and siscowets most abundant in waters ≥80 m. Few redfins were found. Total annual mortality was estimated to be 24% for leans, 18% for humpers, and 15% for siscowets. Population age and size structure of lake charr were broad with many fish older than 20 years and >700 mm. Asymptotic length was 891 mm for leans, 459 mm for humpers, and 938 mm for siscowets. Female length at 50% maturity was 547 mm for leans, 382 mm for humpers, and 453 mm for siscowets. Recreational fishery total harvest of leans peaked at 5,000 fish per year during 2011–2015. Overall, lake charr populations at Stannard Rock were healthy. Caution must be exercised because harvest levels were modest at Stannard Rock, which has a small area relative to nearshore lake charr habitat. These findings support the concept put forth by progressive recreational fishers that have advocated assigning Stannard Rock as a heritage fishery area with restrictive regulations to maintain its sustainability.     

Fleet Dynamics of the Commercial Lake Trout Fishery in Michigan Waters of Lake Superior during 1929–1961

Understanding fishing fleet dynamics is important when using fishery dependent data to infer the status of fish stocks. We analyzed data from mandatory catch reports from the commercial lake trout (Salvelinus namaycush) fishery in Michigan waters of Lake Superior during 1929–1961, a period when lake trout populations collapsed through the combined effects of overfishing and sea lamprey (Petromyzon marinus) predation. The number of full-time fishermen increased during 1933–1943 and then decreased during 1943–1957. Addition of new fishermen was related to past yield, market prices, World War II draft exemptions, and lost fishing opportunities in Lake Huron and Lake Michigan. Loss of existing fishermen was related to declining lake trout density. Large mesh (≥ 114-mm stretch-measure) gill net effort increased during 1929–1951 because fishermen fished more net inshore as lake trout density declined, even though catch per effort (CPE) was often higher in deeper waters. The most common gill net mesh size increased from 114-mm to 120-mm stretch-measure during 1929–1957, as lake trout growth increased. More effort was fished inshore than offshore and the amount of inshore effort was less variable over time than offshore effort. Relatively stable yield was maintained by increasing gill net effort and by moving some effort to better grounds. Because fishing-up caused yield and CPE to remain high despite declining lake trout abundance, caution must be used when basing goals for lake trout restoration on historical fishery indices.     

Diet complexity of Lake Michigan salmonines: 2015–2016

In Lake Michigan, the unintended introduction of invasive species (e.g., zebra mussel, Dreissena polymorpha; quagga mussel, D. rostriformis bugensis; round goby, Neogobius melanostomus) and reduced nutrient loading has altered nutrient dynamics, system productivity, and community composition over the past two decades. These factors, together with sustained predation pressure, have contributed to declines of several forage fish species, including alewife (Alosa pseudoharengus), which has dominated diets of the five primary salmonine species of Lake Michigan for the last 50 years. Salmonines that have inflexible, less complex diets may struggle if alewife declines continue. We analyzed stomach contents of salmonines collected throughout the main basin of Lake Michigan in 2015 and 2016 to investigate diet composition, diet diversity, and individual variation of alewife lengths consumed. Chinook salmon (Oncorhynchus tshawytscha) almost exclusively consumed alewife and had lower diet diversities compared to the other four species, which consumed relatively high frequencies of round goby (brown trout, Salmo trutta; lake trout, Salvelinus namaycush), aquatic invertebrates (coho salmon, Oncorhynchus kisutch) and terrestrial invertebrates (rainbow trout, Oncorhynchus mykiss) along with alewife. Although clear spatio-temporal feeding patterns existed, much of the variation in diet composition and diet diversity was expressed at the individual level. Salmonine populations consumed the entire size range of alewife that were available, whereas individual stomachs tended to contain a narrow range of alewife sizes. Due to their reliance on alewife, it is likely that Chinook salmon will be more negatively impacted than other salmonine species if alewife abundance continues to decline in Lake Michigan.     

Trends of PCB concentrations in Lake Michigan coho and chinook salmon, 1975–2010

The manufacture and use of polychlorinated biphenyls (PCBs) was banned in the United States in 1977 after it was determined that these compounds adversely affect animals and humans. The Wisconsin Department of Natural Resources has quantified total PCB concentrations in Lake Michigan chinook (n = 765) and coho (n = 393) salmon (Oncorhynchus tshawytscha and Oncorhynchus kisutch, respectively) filets since 1975. We analyzed these data to estimate trends in PCB concentrations in these fish (1975–2010). We used generalized linear models with a gamma error distribution and log link fit to the untransformed concentrations. Trend patterns were examined using graphical smoothing and generalized additive models. We identified a candidate set of models that included time trend and other predictor variables. Using the Akaike Information Criterion to select among models we found the best models for both species included piecewise linear time trends, total body length, % lipid, and collection season as predictor variables. The intersection of the two trends was 1985 for chinook salmon and 1984 for coho salmon. PCB concentrations in both species increased with body length and % lipid, and were higher for individuals caught in the fall. Our data reveals a dramatic decline in PCB concentrations of − 16.7% and − 23.9% per year for chinook and coho, respectively, up until the intersection year likely reflecting implementation of restrictions on Aroclor-based PCBs. After the intersection year to 2010, PCB concentrations declined at an annual rate of − 4.0% (95% CI: − 4.4% to − 3.6%) and − 2.6% (95% CI: − 3.3% to − 1.9%) for chinook and coho, respectively.     

Results of the collaborative Lake Ontario bloater restoration stocking and assessment, 2012–2020

Bloater, Coregonus hoyi, are deepwater planktivores native to the Laurentian Great Lakes and Lake Nipigon. Interpretations of commercial fishery time series suggest they were common in Lake Ontario through the early 1900s but by the 1950s were no longer captured by commercial fishers. Annual bottom trawl surveys that began in 1978 and sampled extensively across putative bloater habitat only yielded one individual (1983), suggesting that the species had been locally extirpated. In 2012, a multiagency restoration program stocked bloater into Lake Ontario from gametes collected in Lake Michigan. From 2012 to 2020, 1,028,191 bloater were stocked into Lake Ontario. Bottom trawl surveys first detected stocked fish in 2015, and through 2020 ten bloater have been caught (total length mean = 129 mm, s.d. = 44 mm, range: 96–240 mm). Hatchery applied marks and genetic analyses confirmed the species identification and identified stocking location for some individuals. Trawl capture locations and acoustic telemetry suggested that stocked fish dispersed throughout the main lake within months or sooner, and the depth distribution of recaptured bloater was similar to historic distributions in Lake Ontario and other Great Lakes. Predicted bloater trawl catches, based on modeled population abundance and trawl survey efficiency, were similar to observed catches, suggesting that post-stocking survival is less than 20% and contemporary bottom trawl surveys can quantify bloater abundance at low densities and track restoration.     

Resuspension of Bottom Sediments in Lake Ontario During the Unstratified Period, 1992–1993

Time-series measurements of current velocity and water temperature made at a station in southwestern Lake Ontario between October 1992 and June 1993 are combined with analyses of material collected in a sequencing sediment trap moored at the same location. The results show that local resuspension of bottom material occurred several times during November and December. Analyses of total PCBs and Mirex concentrations were used to infer the origins of the material collected in the traps. Material collected during the fall has multiples sources; in addition to material already in suspension and bottom material resuspended from the immediate area, some material appears to be derived from the Niagara River delta. This is the first reported instance of bottom resuspension in the Great Lakes at depths below wave base during the unstratified period that has been confirmed by current velocity measurements.     

Water Quality Changes in Lake Erie, 1968–1980

Data on chlorophyll a, total phosphorus, and hypolimnetic dissolved oxygen concentration, which were collected by Canada Centre for Inland Waters during the period 1968 to 1980, are statistically analyzed to evaluate the changes in the water quality of Lake Erie. There are strong evidences of a decreasing trend in the value of chlorophyll a and total phosphorus in the western, central, and eastern basins of the lake between 1970 and 1980. Furthermore, a statistical model is developed for the hypolimnetic dissolved oxygen concentration in the central basin. The model shows that the increase in depletion is related to the increase in the level of total phosphorus. Hence, it is possible to improve the anoxic conditions in the lake by controlling total phosphorus loadings.     

Study of Drawdown–Drain Discharge Relationship and its Application in Design of Cost Effective Subsurface Drainage System in Mugogo Swamp, Busogo, Rwanda

Mostly the swamps in Rwanda are surrounded by volcanic hills with small streams flowing to discharge runoff and seepage water. Mugogo swamp is located in Busogo sector, Musanze district, North province. Total area of the swamp is approximately 50 ha. The swamp is surrounded by hills and elevated volcanic rocky terrains. Potato is the main crop cultivated in the swamp. The average production rate of potato is 7 MT/ha which is very low compared to 12 MT/ha in well drained areas. During rainy season seepage water and runoff water from the surrounding hills cause the waterlogged condition of the swamp and affecting the potato cultivation and land productivity. The remedial measure for this swamp is to divert separately the runoff and seepage water from surrounding catchment area and then remove the recharge water by pumping through a system of subsurface drains. Hydraulic head–drain discharge relationship can be fitted with quadratic equation. Equivalent drainable porosity and equivalent hydraulic conductivity are determined as 0.105 m/day and 0.34% respectively for drain depth of 40 cm from soil surface. Effective hydraulic conductivity in the soil profile shows that its average value in the top 15 cm of soil layer is 0.17 m/day and that in the remaining depth up to impermeable layer is 0.015 m/day. Third degree polynomial expressions are made for Head–hydraulic conductivity and head–drainable porosity relationships. The nonlinear relation of hydraulic conductivity and drainable porosity with drawdown shows that the proximity of Kinoni stream does not affect drainage parameters of the area because of less seepage from the stream. The study also reveals that adoption of 7 m drain spacing is very less if crop parameter is not considered and will result higher drain cost. Drainage coefficient of 5 mm/day is arrived considering the rainfall distribution, infiltration rate of soil, allowable water logging tolerance of potato crop. Required drain spacings are calculated for different drainage coefficients of 1, 2, 3, 4 and 5 mm/day under different drawdown conditions to plot subsurface drainage characteristic curves of the swamp. These curves are useful to directly read the drain spacing and drain depth for the required drainage coefficient without going for tedious calculations. Cost analysis shows that the ratio of drain spacing to drain depth can be a decisive factor to select best combination of drain depth and drain spacing. For drainage coefficient of 5 mm/day, optimum drain spacing-depth ratio is found as 7.2 with a cost of 0.689 million Frw/ha. For different drainage coefficients in the swamp, the drain depth of 1.5 m is crucial and optimum cost occurs at this depth. It is also found that any increase in drawdown beyond the drawdown at critical drain depth will not reduce the cost significantly.     

Parasites of Lake Trout,Salvelinus namaycush,from the Great Lakes: a Review of the Literature 1874–1994

A comparative summary of the literature on parasites reported from lake trout, Salvelinus namaycush, from the Great Lakes is presented. Twenty-four studies on parasites infecting lake trout in these lakes have been published since 1874 with 32 parasite species (1 Monogenea, 3 Digenea, 9 Cestoidea, 6 Nematoda, 6 Acanthocephala, 1 Annelida, 5 Crustacea, 1 Fungi) being reported. The most common parasites are Eubothrium salvelini and Echinorhynchus salmonis in the intestine, and Cystidicola stigmatura in the swim bladder. Most of the parasites occur in the gastrointestinal tract. Twenty (80%) of the 25 helminth species reported from lake trout are represented by adults. The dominance of these helminth species is attributable to the position of lake trout in the food web of the Great Lakes as top predators. Parasitological data from splake, Salvelinus namaycush X Salvelinus fontinalis, from Lake Huron are also presented.     

In-use Pesticide Concentrations in Surface Waters of the Laurentian Great Lakes, 1994–2000

Pesticides are heavily used in agricultural production in the Great Lakes basin. Large-volume surface water samples were collected between 1994 and 2000 from Lakes Ontario, Erie, Huron (including Georgian Bay), and Superior and analyzed for neutral and phenoxy-acid herbicides, and organophosphorus insecticides. Thirty-nine pesticides from these three pesticide classes, including analytes and some metabolites, were measured. Six pesticides—barban, diallate-2, triallate, phorate, phosmet, and disulfoton—were not detected. Atrazine, metolachlor, simazine, and 2,4-D were detected in greater than 50% of the samples. The highest maximum concentrations were observed for atrazine (1,039 ng/L), metolachlor (736 ng/L), and D-simazine (281 ng/L). No pesticide concentrations exceeded water quality guidelines/criteria for the protection of aquatic life and drinking water. In general, an increasing concentration gradient from north to south was observed with Superior < Huron < Ontario < Erie. The spatial and seasonal variability of selected pesticides are discussed in relation to their use and application.     

Fifty Years of Physical Investigations and Related Limnological Studies on Lake Erie, 1928–1977

To set the scene for the papers which follow, this review presents the principal findings of hydrodynamic and related chemical and sedimentological studies in Lake Erie beginning with the 1928/29 cooperative surveys of the central and eastern basins (Fish 1929, 1960) and ending with the (also cooperative) “Project Hypo” (Burns and Ross 1972) and the papers assembled in the 1976 special number, “Lake Erie in the Early Seventies” (J. Fish. Res. Board Canada, Vol. 33). Attention is also drawn to the far-reaching and interweaving influence of the physical phenomena on biological and sedimentological processes operating in the lake. Where needed to place the half-century's findings in context or to lead into the papers which follow in this issue, some references to work published before 1928 or after 1977 are also included. After an introduction, the review examines: surface surges and seiches; thermal stratification and its coupling with the distribution of oxygen and phosphorus in bottom water; long-term and short-term circulation patterns; sedimentation and sediment transport.     

Pink Salmon Populations in the U.S. Waters of Lake Superior, 1981–1984

Pink salmon were introduced to Lake Superior in very small numbers at Thunder Bay, Ontario, Canada in 1956. Since that time, they have established themselves as permanent members of the Lake Superior ecosystem. Peak spawner densities were observed in the U.S. tributaries of Lake Superior in 1979 when many streams experienced runs of 10,000 fish or more. To better understand the population dynamics of pink salmon, population characteristics, fecundity and egg deposition of spawners, egg and larval survival, and fry outmigration were studied in several Michigan and Minnesota tributaries in 1980. Population estimates indicate a significant decline of pink salmon in the U. S. waters of Lake Superior since 1979. This decline appears to be related to instream fry survival, which is in turn related to the hydrological conditions of the streams in fall and winter. Lake Superior pink salmon are phenotypically similar to their Pacific Coast counterparts, the major difference being age structure and smaller size of adults. Approximately 90% of the adults mature as 2-year-olds while the remaining 10% mature as 3-year-olds. Pink salmon maturing as 3-year-olds have different growth patterns than those maturing at 2 years of age. Two-year-old pink salmon average 390 mm in length, which is about 30% smaller than 2-year-olds from the Pacific Ocean. Three-year-old females have a lower fecundity and a poorer egg quality than 2-year-old females.