Magnitude Of Water Level Fluctuations Research Articles

Changes in mobility of trace metals at the sediment-water-biota interfaces following laboratory drying and reimmersion of a lacustrine sediment.

Alterations in the timing, frequency, and magnitude of water level fluctuations (WLF) in lakes may result in important changes in abiotic parameters that can affect sediment-borne contaminant mobility at the sediment-water-biota interfaces in littoral zones. This study aims to assess the mobility of trace metals (TMs)-Cd, Cr, Cu, Ni, Pb, and Zn-under laboratory-simulated WLF (i.e., drying and reimmersion of sediments) through a three-pronged approach. One surficial sediment was sampled from the shoreline of a large French lake exhibiting an artificially limited WLF. A sample was enriched with a solution of TMs to ensure significant measurements of mobility. The spiked and naturally contaminated sediments were dried and reimmersed. The first approach consisted in measuring the mobility of TMs from the sediment to the water column under resuspensions of particles through leaching tests. The second approach assessed the partitioning of TMs between the different binding forms within the sediments through sequential extraction tests. The last approach tested the changes in TM bioconcentration in organisms exposed to sediment through microcosm assays. The hypothesis was that WLF may increase mobility from the sediment to the water column relative to mobility from the residual to easily mobilizable fractions within the sediments and consequently increase the bioconcentration of less inert trace metals, mostly Cd and Zn. This hypothesis was partly rejected as TM binding forms mainly increased toward the residual fractions within the sediment, especially for Cd and Zn, and bioconcentration mainly decreased following WLF. However, TM concentration increased in the water column when WLF included great resuspension of particles. The study also provides insights into the complex relationships among contaminant mobility to the water column, bioavailability, and bioconcentration, especially in the context of large abiotic disturbances such as WLF. These findings may be useful for further management strategies for WLF-regulated lakes and reservoirs.

Littoral benthic macroinvertebrate response to water‐level fluctuations in three reservoirs of the Willamette River Basin, Oregon

AbstractHigh‐head dams throughout the Willamette River Basin, Oregon create deep reservoirs that undergo inter‐seasonal and intra‐seasonal water‐level fluctuations (WLFs). The magnitude of WLFs is dependent on competing objectives of flood control, recreation, and water releases to maintain downstream habitat and facilitate migration of Endangered Species Act–listed salmonids. These reservoirs are drawn down to minimum conservation pool in winter, refilled to full pool by late spring and undergo variable WLFs, typically between 4 and 15 m, throughout summer. Here, we investigate the impact of seasonal WLFs on the density, biomass, and species composition of littoral benthic macroinvertebrates at Fall Creek, Hills Creek, and Lookout Point reservoirs. We sampled the submerged littoral zone during spring and summer using an adapted quadrat sampling method and assessed differences in species assemblages using a non‐parametric multivariate statistical technique. Descriptors of variation in substrate, WLF, temperature, and depth were incorporated to identify environmental variables associated with variation in assemblage composition. We hypothesized that density and biomass would decrease and assemblage composition would shift between seasons in response to WLFs. We found statistically significant differences in assemblage composition between seasons and among reservoirs, but density and biomass did not respond similarly. Observed variation in assemblages was associated with surface water temperature, water depth, substrate, and WLF. None of these variables alone explained observed variation. We provide evidence that seasonal WLFs influence macroinvertebrate assemblage composition and alter habitat characteristics. Our procedure effectively quantifies changes in species assemblages in impounded systems with low densities and dynamic littoral zones and can inform water management decisions with relatively modest costs.

Assessment of remnant unionid assemblages in a selection of Great Lakes coastal wetlands

Populations of native unionids have been in steady decline over the past century. The invasion of dreissenid mussels (Dreissena polymorpha and Dreissena rostriformis bugensis) in the mid-1980's impacted already imperiled unionid populations by greatly increasing their regional extinction rates. A selection of Great Lakes coastal wetlands around Michigan was surveyed to locate remnant populations of native unionids. Physical and chemical parameters were measured in coastal wetlands to evaluate the importance of these habitat parameters to remnant unionid assemblages. We assessed fouling rates by dreissenids on unionids and used artificial substrates to estimate dreissenid colonization densities. Live unionids were found in coastal wetlands of the Les Cheneaux Islands, the Lake St. Clair delta, and North Maumee Bay with significantly higher unionid fouling in the Les Cheneaux Islands compared to the other two sampling areas (F2,76=4.97, p=0.0095). No live unionids were documented in Beaver Island, Garden Island, Grand Traverse Bay, or Saginaw Bay wetlands. Dreissena colonization densities on artificial substrates averaged 19,213m−2 at one site in North Maumee Bay, and 10,425m−2 in Saginaw Bay, but no colonization occurred in the wetlands of Beaver Island, Garden Island, the Les Cheneaux Islands, or Grand Traverse Bay while Dreissena presence in the open water of these regions was evident. Dreissena colonization densities on artificial substrates increased with measures of anthropogenic disturbance and decreased with higher water level fluctuations and aerial exposure. Specific conductance, turbidity, and magnitude of water level fluctuations were important predictors of Dreissena colonization on artificial substrates.

Simulating smallmouth bass reproductive success in reservoirs

An individual-based model of nesting smallmouth bass, Micropterus dolomieu, is used to predict the effects of water level fluctuations on reproductive success. The model simulates daily nest site selection, spawning, nest guarding, and development and survival of eggs, embryos, and larvae until dispersal. The model was configured for Brownlee Reservoir, Idaho-Oregon. Each reservoir bank is represented as a rectangular grid of cells, with each cell characterized by an assigned slope, substrate, and elevation, and by a water depth that varied daily. Nest site (cell) selection is determined from a habitat suitability index (HSI) based on substrate, slope, and depth. Development of young is temperature-dependent. Mortality of young occurs via attrition, abandonment by the guarding male, and probabilistic whole-nest catastrophe. Simulations were performed that used observed data for 1991 to 1996. Model predicted nest habitat selection and egg-to-dispersal survival rates were similar to observed values. Additional model simulations showed that: (1) nest habitat selection was best predicted when depth, slope, and substrate were considered together rather than singly, (2) egg-to-dispersal survival was related to the magnitude of water level fluctuations during the peak spawning period, (3) relating mortality to HSI values resulted in lower survival, while relating growth to HSI values resulted in higher survival, and (4) spawning habitat is not limiting in Brownlee Reservoir. Suggestions for future monitoring of reservoir-based smallmouth bass populations are discussed.

Induced and natural sinkholes in Alabama — A continuing problem along highway corridors : Newton, J G Transp Res Rec, N612, 1976, P9–16

Sinkholes are divided into two categories, induced (man-related) and natural. Since 1900, an estimated 4000 induced sinkholes or related features have formed in Alabma,; fewer than 50 natural sinkholes have been reported. Most induced sinkholes are caused by water-level declines due to pumpage; others result from factors associated with construction. Almost all occur where cavities develop in unconsolidated deposits overlying openings in bedrock. The downward migration of the deposits and the development of the cavities are caused or accelerated by a water-level decline that results in the loss of buoyant support and increases the velocity of water movement, the magnitude of water-level fluctuations, and the induced recharge. Most sinkholes caused by construction are due to the diversion of drainage over openings in bedrock. Many natural sinkholes are caused by the collapse or downward migration of unconsolidated deposits into openings in bedrock. The downward migration that sometimes creates cavities in the deposits results from natural declines in the water table, progressive enlargement by solution of openings in the top of bedrock, or a combinstion of both. The failure of bedrock roofs over solutionally enlarged openings is a rare occurrence. The time required for the development of natural sinkholes is far greater than that associated with induced sinkholes. /Author/