Spatial variations in nutrients and other physicochemical variables in the topographically closed Lake Baringo freshwater basin (Kenya)

Spatial physicochemical parameters were determined from 39 sampling sites distributed throughout Lake Baringo during December 2010. Mean values of temperature, dissolved oxygen concentration and electrical conductivity decreased successively with depth, while the pH remained constant. Only the turbidity values increased marginally with depth. Of the surface water parameters, mean (range) values of dissolved oxygen (DO), pH, electrical conductivity, water transparency and turbidity were 6.9 (4.5–8.4) mg L^?1, 8.3 (7.8–8.5), 573 (556–601)μS cm^?1, 33 (28–37) cm and 43.3 (32.7–54.6) NTU, respectively. Mean and range values of total nitrogen (TN), nitrate‐nitrogen(NO₃‐N), ammonia nitrogen (NH₄‐N), total phosphorus (TP) and soluble reactive phosphorus (SRP) were 788.4 (278–4486) μg L^?1, 4.5 (2.4–10.0) μg L^?1, 42.6 (33.8–56.3) μg L^?1, 102.9 (20.3–585.3) μg L^?1 and 23.5 (15.2–30.5) μg L^?1, respectively. Dissolved silica concentrations ranged from 19.7 to 32.7 mg L^?1, with a mean value of 24.7 mg L^?1. The chlorophyll‐a concentrations were quite low, ranging from 1.4 to 4.9 μg L^?1, with a mean value of 4.2 μg L^?1. In contrast to previous reported values, a key finding in the present study is a relatively high water transparency, indicating a relatively clear water column, due possibly to the fact that the sampling was conducted during the dry period. The nutrient levels remained low, and the chlorophyll‐a concentration also was an almost all time low value. A TP value of 20 μg L^?1 and higher confirms strongly eutrophic conditions prevailing in the lake, with an extremely low potential for fish production and low species diversity, consistent with other studies. The results of the present study, therefore, reinforce the database for future management and monitoring plans for the Lake Baringo ecosystem, which lies adjacent to known geothermally active zones and a saline Lake Bogoria.     

A case study of water retention and ecosystem functioning restoration in Wenying Lake (China)

Wenying Lake in Datong, China, has been drying for the last several years. Analysis of standard penetration test data revealed that a missing waterproof layer of silt soil and silty clay in the south part of the lake, resulting from frequent flood flushing, was responsible for the water loss from the lake. Accordingly, 6.7 × 10⁵ m² of geosynthetic clay liner (GCL) was used in May 2010 to repair the area of sediment exhibiting the water leakage, equivalent to 15.6% of the total lake bottom area. Approximately 4.1 × 10⁶ m³ of floodwater was then diverted from upstream rivers to the lake. Eight months later, about 0.9 × 10⁶ m³ of the water was retained, with the water loss being reduced from 4.0 to 1.1 m³ m^?2 year^?1. Ecologically safe and cost‐effective clay materials also can be used to furthermore improve the water retention characteristics. Modelling results indicated that capping the whole lake with a 2 cm layer of bentonite with a permeability coefficient of 5.0 × 10^?9 cm s^?1 could reduce the sediment water leakage to 0.04 m³ m^?2 year^?1. The quality of the retained water after GCL treatment project was poor, with a total nitrogen concentration of 11.0 mg L^?1 and sulphate 307.0 mg L^?1, which were 5 and 300 times higher, respectively, than the Chinese class V surface water standard. Restoration of aquatic vegetation in the lake and constructed wetlands near the lake inlets could be helpful to improve the lake’s water quality over the long term.     

Estimates of the remineralization and burial of organic carbon in Lake Baikal sediments

Sediment cores collected from several stations throughout Lake Baikal in water depths from 100 m off the Selenga River delta to the deepest basin of the lake (~1640 m), have been analyzed for sedimentary organic carbon, nitrogen, and the remineralized components in pore water. The organic carbon content of surface sediments generally varied from 2.3 to 3.2% by weight, and profiles typically showed an exponential decrease in both organic carbon and nitrogen in the upper 20–30 cm of the sediment column. Steady state models of organic matter diagenesis yield first order decomposition rate constants which range from 0.0009 to 0.022 y⁻¹. The calculated residence times for the metabolizable fraction of the organic matter in these sediments increases roughly with increasing water depth and is on the order of 50–300 years. Pore water concentration profiles were determined for dissolved inorganic carbon, dissolved organic carbon (DOC), methane, and dissolved ammonium. At depth (25–30 cm) methane concentrations ranged from 50 to 800 μmol L_pw⁻¹ and DOC from 400 to 900 μmol L_pw⁻¹. Estimation of carbon recycling rates based upon diffusion along pore water concentration gradients at the sediment-water interface, indicate that combined DOC and methane fluxes generally contribute <15% of the overall turnover of sedimentary organic carbon. Comparisons to Laurentian Great Lakes environments show trends in sediment deposition, organic matter remineralization, and the time scales of carbon recycling across nearly two orders of magnitude with the fraction of organic content buried generally decreasing with decreasing sedimentation rates.     

Fate of phosphorus from a point source in the Lake Michigan nearshore zone

Nutrient loading into Lake Michigan can produce algal blooms which in turn can lead to hypoxia, beach closures, clogging of water intakes, and reduced water quality. The Great Lakes Water Quality Agreement targets for Lake Michigan are 5600 MT annually for total phosphorus (TP) loading, 7 μg L^?1 lake-wide mean TP concentration, and a chlorophyll-a concentration of 1.8 μg L^?1. However, in light of the recent resurgence of nuisance algal (Cladophora sp.) growth in the nearshore zone, the validity of these targets is now uncertain. The occurrence and abundance of Cladophora in the nearshore area depends primarily on the availability of dissolved phosphorus, light, and temperature. The availability of dissolved phosphorus is a potentially useful indicator of nearshore areas susceptible to excessive Cladophora growth and impaired water quality. Regulating agencies are looking for guidance in determining phosphorus loading rates that minimize local exceedance of the lake target concentration. In this study, the lake assimilative capacity was quantified by applying a biophysical model to estimate the area required for mixing and diluting wastewater treatment plant outfall TP loadings to the level of the lake target concentration during the Cladophora growing season. Model results compared well with empirical measurements of particulate and dissolved phosphorus as well as Cladophora biomass and phosphorus content. The model was applied to test scenarios of wastewater treatment plant phosphorus loading in two different years, in order to help establish phosphorus discharge limits for the plant.     

The occurrence of microcystin-LR in Lake Chivero, Zimbabwe

Lake Chivero is a eutrophic reservoir, initially constructed to supply drinking water to the City of Harare, Zimbabwe. Blooms of blue‐green algae have been a problem in the lake for many years and concern has been expressed about the toxins produced by Microcystis spp. The concentrations of the toxin, microcystin‐LR, produced in cultures of Microcystis aeruginosa from Lake Chivero, were investigated from March–April 2003. Microcystin‐LR was found in algal cells cultured from the lake water in concentrations ranging between 18.02 and 22.48 µg L^?1, with a mean concentration of 19.86 µg L^?1. These concentrations are the highest recorded to date for the lake, raising concerns about the possible effects of the toxin on the health of people who are drinking the water. Based on these study results, there is a need to control eutrophication, reducing algal blooms in order to prevent their potentially detrimental effects from blue‐green algal toxins produced under such conditions.     

Use of TXRF and Convectional Energy Dispersive X‐ray Fluorescence Analysis (EDXRF) to determine trace metal concentrations in waters of Nakivubo Channel and Lake Victoria

To understand better the pollution levels in the waters of the Nakivubo Channel and Lake Victoria, the concentrations of manganese (Mn), iron (Fe), cobalt (Co), copper (Cu), zinc (Zn) and lead (Pb) were determined using convectional Energy Dispersive X‐ray Fluorescence Analysis (EDXRF) and Total X‐ray Fluorescence (TXRF) analysis. Particulate deposits were analysed for trace metals with a convectional EDXRF spectrometer. Extracted dissolved metals contents were analysed with Total Reflection X‐Ray Fluorescence. The analyses indicated higher copper concentrations in the filtrate samples collected at the rivermouths and inshore stations than on the particulate matter. Samples from battery manufacturing industry‐1 indicated copper concentrations in the filtrate exceeding the National Environmental management Authority (NEMA) drinking water standard of 1.0 mg L^?1. Free zinc concentrations were measured for almost all the sampling sites, but at concentrations below the 3 mg L^?1 NEMA standard. High concentrations of iron in the labile form measured at the lake shores were above NEMA drinking water standards of 0.3–3.5 mg L^?1 in 2006, except for the April 2006 Murchison Bay rivermouth, and for low manganese concentrations in the lake waters. The iron and manganese concentrations on the particulate matter at the upstream end of the Channel, but were lower in the lake waters. Effluents from soap manufacturing industries exhibited elevated total iron concentrations, ranging from 19.038 ± 0.190 to 63.129 ± 6.248 mg L^?1 throughout the 2‐year study period. The manganese concentrations were the highest for the battery manufacturing industry‐2 site in April 2006. The total iron and manganese concentrations were generally higher upstream along the Nakivubo Channel than in the lake waters. Cobalt and lead concentrations were below detection limits for most of the sampling sites. Generally, most metal concentrations along the Nakivubo Channel exceeded acceptable limits, illustrating the need for mitigation measures.     

Long‐term irreversible changes in a lake ecosystem affected by the Indian Ocean Tsunami

This study focused on ecosystem responses to the environmental perturbations caused by the 2004 Indian Ocean Tsunami in a small lake that was a freshwater body in 1996, prior to the tsunami. The physicochemical and biological characteristics of Kokilamedu Lake (KKM) revealed drastic changes, compared with pretsunami conditions. Monthly average observations on water quality indicated the electrical conductivity of the water increased steeply to 17.41 mS cm^?1 in 2009, from the lowest pretsunami value of 1.83 mS cm^?1 (range of 1.83–5.25 mS cm^?1). Simultaneously, the nitrate + nitrite (NO₃ + NO₂) values increased significantly from 0.49 μmol L^?1 in 1996 to 74.47 μmol L^?1 in 2006. Silicate (SiO₄‐Si) exhibited a dramatic increase in concentration, from an average of 64.87 μmol L^?1 in the pretsunami period to 309.71 μmol L^?1 the post‐tsunami period (2009–2010). Inorganic phosphate had increased to a maximum of 9.59 μmol L^?1 from a pretsunami maximum of 1.09 μmol L^?1. The chlorophyll‐α concentrations did not respond to the increased nutrient stoichiometry of the lake. There was a decreased chlorophyll‐α concentration under post‐tsunami conditions. The recent infilling of the lake with sediment during the tsunami, associated with wind‐driven resuspension reduced the light penetration. There was a significant improvement in dissolved oxygen concentrations (2006–2010 average of 8.27 mg L^?1) in the lake, however, compared with the pretsunami values (1994–1995 average of 5.94 mg L^?1). The algal component is now dominated by blue‐green algae, while green algae had dominated in the pretsunami period. Pre‐ and post‐tsunami observations from a control site did not exhibit such dramatic shifts from the 1995 and 1996 conditions, whereas a shift was apparent in the case of KKM. Certain marine fishes have adapted to this altered ecosystem. These marine species encountered (Elops machnata, Cociella punctata, Sphyraena jello, Platycephalus indicus, Glossogobius giuris) might have been recruited during the intrusion of the tsunami waves.     

Using 223Ra and 224Ra to estimate discharges of groundwater and associated nutrients into southeast of Qinghai Lake,in Qinghai–Tibet Plateau

With its important geographical location and status as the largest saltwater body in China, Qinghai Lake plays a vital role in the ecological environment of the northeastern part of the Qinghai-Tibet Plateau. Due to climate change and the subsequent adjustment of Qinghai Lake’s tourism policy, it is necessary to understand groundwater discharges in southeast of Qinghai lake both for ecological protection and risk prevention. This study used radium isotopes ²²³Ra and ²²⁴Ra to trace groundwater discharges and nutrients carried into the lake. The spatial characteristics of Ra isotopes with greater activity in the upper and bottom layers in the lake indicated that they were influenced by inputs of shallow groundwater and diffusion from sediments. The average ²²⁴Ra diffusion flux of the sediments in the Lake was 33.54 dpm m^?2 d^?1. Based on the ²²⁴Ra mass balance model, the discharge flux of shallow groundwater in this region was estimated to be 3.49 × 10⁶ ～ 3.68 × 10⁶ m³ d^?1. The PO₄^3? and SiO₂ fluxes carried into the southeastern of the lake by groundwater were 1.78 × 10¹¹ ～ 1.88 × 10¹¹ mg/y and 2.22 × 10¹² ～ 2.34 × 10¹² mg/y, respectively. It is thus essential to monitor shallow groundwater discharge into Qinghai Lake for the protection of the water environment and prevention of potential ecological risks.     

Physicochemical characteristics of Lake IRAD, an artificial lake in Wakwa region, Cameroon

Wakwa is a region in north Cameroon characterized by intensive cattle production. This study evaluated the physicochemical characteristics of the waters in Lake IRAD, located near Wakwa, which is the main water source for cattle grazing in this area. Water samples were collected at four sampling sites during the rainy and dry seasons (April, July, October and February). The chemical composition of the water samples was analysed for various constituents, including nitrate (NO₃^–), chloride (Cl^?), phosphate (PO₄^3?), bicarbonate (HCO₃^?), calcium (Ca), magnesium (Mg), manganese (Mn), aluminium (Al), zinc (Zn), copper (Cu), iron (Fe), nickel (Ni), cadmium (Cd), ammonia–nitrogen (NH₄–N) and organic matter (OM). The mineral composition varied significantly (P < 0.05) with the sampling period. High concentrations of zinc (0.96 mg L^?1) and dissolved iron (1.23 mg L^?l) were observed during the dry season. Total iron (3.25 mg L^?1), OM (15.4 mg of O₂ L^?1), nitrate (28.82 mg L^?1) and NH₄–N (1.05 mg L^?1) concentrations were highest during the rainy season. The iron, OM and NH₄–N concentrations were higher than the USEPA‐recommended values (0.2 mg L^?1, 4 mg of O₂ L^?1 and 0.5 mg L^?1, respectively). The phosphate, copper, nickel and cadmium concentrations, considered as the polluting substances, were present in negligible concentrations, being below the detection limits of the analytical techniques used to measure them. The high iron, OM and nitrogen concentrations were attributed to water‐leached soil run‐off, as well as the activity of animals in the lake. Sampling sites 1 and 2, which were used mostly by cattle, were observed to have the highest concentrations of NH₄–N, compared with sites 3 and S (exit point). It will be necessary to delimit cattle access points to the lake to reduce this type of contamination of drinking water.     

Risk assessment for organochlorines and organophosphates pesticide residues in water and Sediments from lower Nyando/Sondu‐Miriu river within Lake Victoria Basin,Kenya

The objective of this study was to survey and document pesticide residue levels in the lower Nyando/Sondu‐Miriu catchment areas of Lake Victoria, Kenya, during the dry and rainy seasons of 2009. Water and sediment samples from the Nyando/Sondu‐Miriu Basin were analysed for selected pesticide residues, using gas chromatography equipped with Ni⁶³ and CP‐SIL 8CB‐15m and TSD detectors for organochlorine and organophosphorus pesticide residues, respectively. The findings indicated that banned organochlorines are still being used in the catchment. Dieldrin and p,p′‐DDD were notably higher (P < 0.05) in concentrations than their metabolically formed analogues of aldrin and DDT, respectively. Notably, organophosphorus was below detection levels in water samples, whereas diazinon and malathion were at higher levels in sediment samples. The total residues of DDT, HCH, methoxychlor and endrin generally were below WHO drinking water limits of 2, 2, 20 and 0.01 μg L^?1, respectively, whereas aldrin and dieldrin were above the recommended values of 0.03 μg L^?1. Agricultural activities in the Lake Victoria Basin are influencing accumulation of the pesticide residues in the basin rivers and the lake. The study recommends creation of buffer zones around the natural water bodies to reduce the inflow of pesticides into water bodies. An integrated pest management approach that encourages reduced usage of chemical compounds also should be encouraged.     

Evidence of lake trout (Salvelinus namaycush) spawning and spawning habitat use in the Dog River,Lake Superior

Lake trout spawn primarily in lakes, and the few river-spawning populations that were known in Lake Superior were believed to be extirpated. We confirmed spawning by lake trout in the Dog River, Ontario, during 2013–2016 by the collection of and genetic identification of eggs, and we describe spawning meso- and microhabitat use by spawning fish. Between 2013 and 2016, a total of 277 lake trout eggs were collected from 39 of 137 sampling locations in the river. The majority of eggs (220) were collected at the transition between the estuary and the river channel crossing the beach. Lake trout eggs were most often located near the downstream end of pools in areas characterized by rapid changes in depth or slope, coarse substrates, and increased water velocities, where interstitial flows may occur. Depths in wadeable areas where eggs were found averaged 0.9?m (range: 0.4 to 1.3?m) and substrate sizes consisted of large gravel, cobble, and boulder; comparable to spawning characteristics noted in lakes. Water velocities averaged 0.66?m·s^?1 (range: 0.33 to 1.7?m³·s^?1) at mid-depth. This information on spawning habitat could be used to help locate other remnant river-spawning populations and to restore river-spawning lake trout and their habitat in rivers that previously supported lake trout in Lake Superior. The Dog River population offers a unique opportunity to understand the ecology of a river spawning lake trout population.     

Sediment greenhouse gases (methane and carbon dioxide) in the Lobo-Broa Reservoir, São Paulo State, Brazil: Concentrations and diffuse emission fluxes for carbon budget considerations

Carbon gases (methane, CH₄, and carbon dioxide, CO₂) were measured for the first time in sediments of the Lobo‐Broa Reservoir, near São Carlos in São Paulo State, Brazil. It is believed these are the first measurements of this kind in any of the many reservoirs located in Brazil. Even though the Lobo‐Broa Reservoir is classified as oligotrophic, the sediment gas concentrations were exceedingly high, ranging from 0.4–3 mmol L^?1 for CH₄ and 1–9 mmol L^?1 for CO₂. Both gases exceeded their in situ gas saturation values at these shallow water depths (7 m in central basin; 11 m at dam), resulting in numerous sediment bubbles. Organic matter was highly concentrated in the reservoir sediments, averaging 25.5% loss on ignition (LOI) (dam) to 26.9% LOI (central basin) for the 0–12 cm depth interval, with values as high as 29–30% LOI (12% organic carbon) in the surface 0–5 mm layer. The theoretical flux of dissolved pore water carbon gases to the sediment–water interface (SWI) averaged 3.4 mmol L^?1 m^?2 day^?1 CH₄ and 7.3 mmol L^?1 m^?2 day^?1 CO₂ for the surface 0–10 mm. From gas emission measurements at the water surface, it was calculated that 90% of CH₄ is consumed either at the SWI or in the water column, resulting in a loss of 0.31 mmol L^?1 m^?2 day^?1 of CH₄ to the atmosphere. However, only 20% of the total CO₂ gas transported across the water–atmosphere interface (36.3 mmol L^?1 m^?2 day^?1, or 1600 mg CO₂ m^?2 day^?1) was produced in the sediments. The remaining 80% of CO₂ probably comes from other carbon sources. With CH₄ oxidation in the aerobic water column, close to 30% of the carbon gas flux to the atmosphere could be accounted for by gas production of CO₂ and CH₄ in the sediments and their diffuse transport to the water column.     

Eutrophication of lakes in urbanized areas: The case of Yaounde Municipal Lake in Cameroon, Central Africa

A 1 year qualitative and quantitative evaluation of phytoplankton and chlorophyll‐a, as well as some physicochemical parameters, was recorded in a shallow tropical lake in Cameroon: the Yaounde Municipal Lake. Physicochemical measurements also were regularly made in its main tributary (Mingoa Stream). These analyses aimed to assess the lake's trophic status and to propose measures for controlling its degradation process. The Secchi disk transparency was low and rarely exceeded 100 cm. Conductivity was higher near the lake bottom. The oxygen deficiency, and sometimes anoxia, recorded from a 2.5 m depth leads to high quantities of ammonium‐nitrogen. The total phosphorus concentrations varied from 80–2290 µg P L^?1 and the total Kjeldhal nitrogen concentrations fluctuated between 3 and 15 mg  L^?1. Upstream to the lake, in the Mingoa Stream, total phosphorus concentrations ranged from 0.6–3.8 mg P L^?1 and total Kjeldhal nitrogen concentrations ranged from 10–22 mg  L^?1. There are up to 102 phytoplankton‐specific taxa, with Euglenophyta and Chlorophyta particularly more diversified. The phytoplankton biomass and chlorophyll‐a concentrations reached 225 µg mL^?1 and 566 mg m^?3, respectively. The analyses pointed out the allogenic nature of the functioning of this ecosystem as a result of bad waste management in the surrounding landscape. Urgent actions need to be undertaken in order to rehabilitate this lake, which rapidly shifted to a hypertrophic status.     

First estimation of the diffusive methane flux and concentrations from Lake Winnipeg,a large,shallow and eutrophic lake

Freshwater lakes are increasingly recognized as significant sources of atmospheric methane (CH₄), potentially offsetting the terrestrial carbon sink. We present the first study of dissolved CH₄ distributions and lake-air flux from Lake Winnipeg, based on two-years of observations collected during all seasons. Methane concentrations across two years had a median of value of 24.6 nmol L^-1 (mean: 41.6 ± 68.2 nmol L^-1) and ranged between 5.0 and 733.8 nmol L^-1, with a 2018 annual median of 24.4 nmol L^-1 (mean: 46.8 ± 99.3 nmol L^-1) and 25.1 nmol L^-1 (mean: 38.8 ± 45.2 nmol L^-1) in 2019. The median lake-air flux was 1.1 µmol m^?2 h^?1 (range: 0.46–70.1 µmol m^?2h^?1, mean: 2.9 ± 10.2 µmol m^?2 h^?1) in 2018, and 5.5 µmol m^?2h^?1 (range: 0.0–78.4 µmol m^?2 h^?1, mean: 2.7 ± 8.5 µmol m^?2 h^?1) in 2019, for a total diffusive emission of 0.001 Tg of CH₄-C yr^?1. We found evidence of consistent spatial variability, with higher concentrations near river inflows. Significant seasonal trends in CH₄ concentrations were not observed, though fluxes were highest during the fall season due to strong winds. Our findings suggest Lake Winnipeg is a CH₄ source of similar mean magnitude to Lake Erie, with lower concentrations and fluxes per unit area than smaller mid- to high-latitude lakes. Additional work is needed to understand the factors underlying observed spatial variability in dissolved gas concentration, including estimations of production and consumption rates in the water column and sediments.     

Variations in zooplankton community structure and water quality conditions in three habitat types in northern Lake Victoria

Lake Victoria is vulnerable to increasing eutrophication, which has become manifested in ecological changes not yet fully understood. From October 2009 to January 2010, the influence of water quality on zooplankton community structure in three habitats in northern Lake Victoria, including sewage lagoons at the lake shores, Napoleon Gulf (NG) and the interface between the lake and the Nile River (also known as Source of the Nile River), was examined. Selected physico‐chemical parameters (dissolved oxygen concentration; water temperature; electrical conductivity; water depth) were measured in‐situ, while water samples were collected for chlorophyll‐a determinations. Zooplankton was sampled with conical plankton net (mesh size 60 μm; 0.25‐m mouth diameter). The NG and Source of the River Nile (SN) sampling sites exhibited significantly higher species richness, relative to the Sewage Lagoons (SL) site (F_2,69 = 68.533; P < 0.05). Higher mean densities and dry biomass of zooplankton was generally a characteristic of the SL site (8715 ± 3241 ind L^?1; 1862 ± 451 μg L^?1), compared to the NG (119 ± 24 ind L^?1; 53 ± 8 μg L^?1) and SN sites (151 ± 26 ind L^?1; 58 ± 9 μg L^?1). Copepoda constituted a high numerical composition of the zooplankton at the NG and SN sites (>90% for both sites), while Rotifera dominated the zooplankton community at the SL site (97%). The mean values (±SE) of soluble reactive phosphorus (4060.7 ± 776.6 μg L^?1) and nitrate–nitrogen (2121.7 ± 355.5 μg L^?1) were much higher for the SL site, compared with the SN (8.2 ± 1.1 μg L^?1; 28.6 ± 5.3 μg L^?1, respectively), and NG site (7.8 ± 0.8 μg L^?1; 32.7 ± 5.4 μg L^?1, respectively). This study indicated the nutrient‐rich conditions observed at the SL site suppress the zooplankton species diversity, but favour species‐specific abundance and biomass. These study results indicate the zooplankton community structure can be used as a biological indicator of water quality in the Lake Victoria region.     

Geomorphic response to river flow regulation: Case studies and time-scales

River regulation imposes primary changes on flow and sediment transfer, the principal factors governing the alluvial channel regime. In this study, the effect of flow regulation is isolated from sediment delivery. Peace River (Q? = 1080m³s^?1, increasing to 2110m³s^?1 downstream) was regulated in 1967 for hydropower. The gravel-bed reach immediately downstream from the dam has become stable. Gravel accumulates at major tributary junctions, so the river profile is becoming stepped. Further downstream, the river has a sand bed. It can still transport sand, so morphological changes along the channel include both aggradation and channel narrowing by lateral accretation. In the gravel-bed Kemano River (Q? = 150m³s^?1), the addition of water by diversion from another river caused degradation when additional bed material was entrained below the inflow point. However, the effect became evident only after many years, when a competent flood occurred. The short-term response was channel widening. The time-scale for the response depends on the size of the river and the nature and severity of regulation. In both rivers, significant adjustment will require centuries and will intimately involve the riparian forest.     

Assessing the Potential Efficacy of Glutaraldehyde for Biocide Treatment of Un-ballasted Transoceanic Vessels

Treating the ballast water of oceanic vessels with a biocide is one potential management strategy to reduce the number of nonindigenous species released into the Laurentian Great Lakes from NOBOB (no ballast on board) vessels. To evaluate biocide effectiveness, glutaraldehyde, a five-carbon dialdehyde widely used for its antimicrobial properties, was investigated. Biocide effectiveness was assessed for various organisms using 24 h acute toxicity bioassays in water-only and water-sediment environments. Acute studies indicate a 24 h LC₉₀ value of 100 mg glutaraldehyde L^–1 or less for most of the freshwater organisms tested. The main exception was the freshwater amphipod, Hyalella azteca, which was much more resistant to glutaraldehyde (24 h LC₉₀ = 550 mg glutaraldehyde L⁻¹; 95% CI: 476–681). Biocide efficacy was also evaluated in water-sediment exposures. The presence of a test sediment (3% organic carbon) greatly increased lethal concentration estimates for the oligochaete Lumbriculus variegatus, but not for H. azteca: The 24 h LC₉₀ for L. variegatus varied depending on the water-sediment ratio, and ranged from 61 mg glutaraldehyde L⁻¹ (95% CI 52–78) for an 8:1 water-sediment ratio to 356 mg glutaraldehyde L⁻¹ (95% CI 322–423) for a 2:1 water-sediment ratio. This indicates that the amount of sediments present in NOBOB vessels may have a significant impact on biocide efficacy. Experiments using material from actual NOBOB vessels generally corroborated data from the water-sediment experiments and suggest a potential treatment concentration of approximately 500 mg glutaraldehyde L⁻¹ for short exposure periods (e.g., 24 h).     

Factors influencing microplastic abundances in nearshore,tributary and beach sediments along the Ontario shoreline of Lake Erie

Sediment samples were collected from nearshore, tributary and beach environments within and surrounding the northern part of Lake Erie, Ontario to determine the concentrations and distribution of microplastics. Following density separation and microscopic analysis of 29 samples, a total of 1178 microplastic particles were identified. Thirteen nearshore samples contained 0–391 microplastic particles per kg dry weight sediment (kg^?1), whereas 4 tributary samples contained 10–462?kg^?1 and 12 beach samples contained 50–146?kg^?1. The highest concentrations of nearshore microplastics were from near the mouths of the Detroit River in the western basin and the Grand River in the eastern basin, reflecting an urban influence. The highest microplastic concentrations in beach samples were determined from Rondeau Beach in the central basin where geomorphology affects plastics concentration. The Welland Canal sample in the eastern basin contained the greatest concentration of microplastics of the tributary samples, which is consistent with high population density and shipping traffic. The overall abundance of microplastic in northern Lake Erie nearshore, tributary and beach samples is 6 times lower than in sediment sampled from northern Lake Ontario. The nearshore and beach sample results potentially reflect the transport patterns of floating plastics modeled for Lake Erie, which predict that the majority of plastic particles entering the lake are transported to southern shoreline regions rather than northern areas.     

Episodic nearshore-offshore exchanges of hypoxic waters along the north shore of Lake Erie

We investigate the nearshore-offshore exchange of hypoxic waters during episodic coastal upwelling events in the nearshore waters of northern Lake Erie using intensive field observations and a validated hydrodynamic and water quality model. We observe wind-induced coastal upwelling events to be the dominant nearshore physical process in the lake which are energized every 5–10 days. When the winds were predominantly blowing from the west or south-west, epilimnetic waters were transported to the offshore bringing in hypolimnetic waters with low temperature (8–10 °C), dissolved oxygen (DO: 0–6 mg L^?1) and pH (6–7) to the nearshore zones. During these events, vertical diffusivity coefficients decreased from 10^?2 m² s^?1 to values as low as ~ 10^?7 m² s^?1. In late summer, the coastal upwelling events in the nearshore waters lower the near bottom DO to hypoxic levels (DO < 2 mg L^?1). Lake-wide observations of DO and pH show that they are positively and linearly correlated while in the nearshore DO and pH experience spatial and temporal variability where upwelling events were developed, which were further assessed using a three-dimensional model. The model accuracy to reproduce offshore hypoxia was first assessed on a lake-wide basis using a coarse resolution model for a five-year period (2008–2012) and in nearshore waters using a higher resolution model for 2013. We use the model results to delineate the near bottom areas experiencing hypoxia at time scales longer than 48 h.     

From River to Lake: Phosphorus partitioning and algal community compositional changes in Western Lake Erie

The Maumee River is an important source of phosphorus (P) loading to western Lake Erie and potentially a source of Microcystis seed colonies contributing to the development of harmful algal blooms in the lake. Herein, we quantified P forms and size fractions, and phytoplankton community composition in the river–lake coupled ecosystem before (June), during (August), and after (September) a large Microcystis bloom in 2009. Additionally, we determined the distribution and density of a newly emergent cyanobacterium, Lyngbya wollei, near Maumee Bay to estimate potential P sequestration. In June, dissolved organic phosphorus (DOP) was the most abundant P form whereas particulate P (partP) was most abundant in August and September. Green algae dominated in June (44% and 60% of total chlorophyll in river and lake, respectively) with substantial Microcystis (17%) present only in the river. Conversely, in August, Microcystis declined in the river (3%) but dominated (32%) the lake. Lake phytoplankton sequestered < 6% of water column P even during peak Microcystis blooms; in all lake samples < 112 μm non-algal particles dominated partP. Lyngbya density averaged 19.4 g dry wt/m², with average Lyngbya P content of 15% (to 75% maximum) of water column P. The presence of Microcystis in the river before appearing in the lake indicates that the river is a potential source of Microcystis seed colonies for later lake blooms, that DOP is an important component of early summer total P, and that L. wollei blooms have the potential to increase P retention in nearshore areas.