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The Omaha District has collected water quality data at Corps projects in the District since the late 1970's. The data have been assessed and summarized in water quality reports prepared by the District. The data collected are stored in the U.S. Environmental Protection Agency's national STORET and WQX water quality database. The data can be accessed and downloaded online from the STORET/WQX website at www.epa.gov/storet.
Recent water quality data collected by the District may not have been entered into STORET/WQX and can be obtained by contacing the District. The U.S. Geological Survey collects water quality data throughout the United States. Water quality data have been collected at Corps project areas in the District. These data can be accessed online through the U.S. Geological Survey's website "Surface-Water Data for the Nation" at http://waterdata.usgs.gov/usa/nwis/sw. State environmental agencies responsible for surface water quality management routinely collect surface water quality data within their State. Water quality data have been collected by the States at Corps projects in the District. This information may be stored and accessible through the U.S. Environmental Protection Agency's STORET/WQX database. State water quality agency websites may publish water quality information on their web sites. The State of Nebraska, during the recreation season, publishes weekly bacteria and cyanobacteria toxin levels at District reservoirs with swimming beaches. Local Watershed Management Authorities have been established to protect and improve water quality at the three Colorado Tributary Projects in the District: Bear Creek, Chatfield, and Cherry Creek Reservoirs. Each of these Watershed Authorities has adopted local water quality regulations and water quality management plans to protect and manage water quality at the respective reservoirs. As part of these water quality management plans, the Watershed Authorities are implementing comprehensive water quality monitoring programs. For efficiency purposes, the Corps ceased its water quality monitoring activities at the three Colorado Tributary Projects in 2002, and now defers to the respective Watershed Authorities for assessment of water quality conditions at Bear Creek, Chatfield, and Cherry Creek Reservoirs. Persons interested in water quality conditions at the three Colorado tributary projects can visit the websites maintained by the following groups:
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Reservoirs are commonly classified or grouped by trophic or nutrient status. The natural progression of reservoirs through time is from an oligotrophic (i.e., low nutrient/low productivity) through a mesotrophic (i.e., intermediate nutrient/intermediate productivity) to a eutrophic (i.e., high nutrient/high productivity) condition. The tendency toward the eutrophic or nutrient-rich status is common to all impounded waters. The eutrophication, or enrichment process, can be accelerated by nutrient additions to the lake resulting from cultural activities.
As deeper, temperate lakes warm in the spring and summer they typically become thermally stratified, due to the density differences of the water, into three vertical zones: 1) epilimnion, 2) metalimnion, and 3) hypolimnion. The epilimnion is the upper zone of less dense, warmer water in the lake that remains relatively mixed due to wind action and convection. The metalimnion is the middle zone that represents the transition from warm surface water to cooler bottom water. The hypolimnion is the bottom zone of more dense, colder water that is relatively quiescent.
A significant water quality concern that can occur in reservoirs that thermally stratify in the summer is the depletion of dissolved oxygen levels in the hypolimnion. The depletion of dissolved oxygen is attributed to the differing density of water with temperature, the utilization of in-lake dissolved oxygen in the decomposition of organic matter, and the oxidation of reduced inorganic substances. When density differences become significant, the deeper colder water is isolated from the surface and re-oxygenation from the atmosphere. In eutrophic lakes, the decomposition of the abundant organic matter can significantly reduce dissolved oxygen in the quiescent hypolimnetic zone. Anoxic conditions in the hypolimnion can result in the release of sediment-bound substances (e.g., phosphorus, metals, sulfides, etc.) as the reduced conditions intensify and result in the production of toxic and caustic substances (e.g., hydrogen sulfide, etc.). Most fish and other intolerant aquatic life cannot inhabit water with less than 4 to 5 mg/l dissolved oxygen for extended periods. These conditions can impact aquatic life in the lake and also in waters downstream of the reservoir if its releases are from a bottom outlet. Sedimentation is a process that reduces the usefulness of reservoirs. In the design and construction of reservoirs, the Corps will commonly allow for additional volume to accommodate sedimentation. The incoming sediment can seriously affect the reservoir ecology, fisheries, and benthic aquatic life. The reservoir can suffer ecological damage before a volume function such as flood control is impacted. The influx of sediment eliminates fish habitat, adds nutrients, increases turbidity, destroys aesthetics, and decreases biodiversity. Working closely with Local agencies and the public in an effort to manage sediment input could ultimately prolong reservoir life. Wetlands or sediment traps could be constructed at the headwaters of a reservoir, either upstream of the reservoir or by taking a portion of the reservoir’s upper end. Shoreline erosion is a major problem occurring on nearly all reservoirs located in areas of erodible soils such as the Midwest. Over 6,000 miles of reservoir shoreline exist at Corps projects in the District, and it is estimated that over 70 percent of this shoreline is eroding. Some locations have been protected, such as recreational and archaeological sites, but most of the shoreline continues to erode. Continued loss of the shoreline habitat (littoral zone) results in the loss of fishery habitat as well as loss of habitat for other biota such as aquatic vegetation and benthic invertebrates. Shoreline erosion can degrade water quality by increasing turbidity and suspended solids levels in the effected waterbody. Pollutants associated with the eroded material (e.g., nutrient, metals, pesticides, etc) can also degrade water quality. Past shoreline erosion control efforts should be evaluated for effectiveness so that successful control measures can be identified for future application. Bioaccumulation is the accumulation of contaminants in the tissue of organisms through any route, including respiration, ingestion, or direct contact with contaminated water or sediment. Bioavailable, for chemicals, is the state of being potentially available for biological uptake by an aquatic organism when that organism is processing or encountering a given environmental medium (e.g., the chemicals that can be extracted by the gills from the water as it passes through the respiratory cavity or the chemicals that are absorbed by internal membranes as the organism moves through or ingests sediment). In the aquatic environment, a chemical can exist in three different basic forms that affect availability to organisms: 1) dissolved, 2) sorbed to biotic or abiotic components and suspended in the water column or deposited on the bottom, and 3) incorporated (accumulated) into organisms. Bioconcentration is a process by which there is a net accumulation of a chemical directly from water into aquatic organisms resulting from simultaneous uptake (e.g., by gill or epithelial tissue) and elimination. Biomagnification is the result of the process of bioconcentration and bioaccumulation by which tissue concentrations of bioaccumulated chemicals increase as the chemical passes up through two or more trophic levels. The term implies an efficient transfer of a chemical from food to consumer so that residual concentrations increase systematically from one trophic level to the next.
Bioaccumulation of contaminants can have a direct effect on aquatic organisms. These effects can be chronic (reduced growth, fecundity, etc.) and acute (lethality). The bioaccumulation of contaminants can also be a concern to human health when the contaminated tissue of aquatic organisms is consumed by humans. Pesticides are widely applied to lands throughout the District. Pesticides detected in water quality samples collected at Corps projects in the District over the past 5 years include: acetochlor, alachlor, atrazine, chloropyrifos, deethylatrazine, deisopropylatrazine, dimethenamid, metolachlor, metribuzin, oxyfluorfen, profluralin, prometon and propazine. Many of these pesticides do not have State or Federal numeric water quality criteria established. Urbanization around many District reservoirs is occurring at a rapid pace. Reservoirs with urbanizing watersheds include Cherry Creek, Chatfield, and Bear Creek in the Denver, Colorado area; Holmes in the Lincoln, Nebraska area; and Ed Zorinsky, Glen Cunningham, Standing Bear, and Wehrspann in the Omaha, Nebraska area. Urbanization, to a much lesser degree, is occurring at other Corps projects in the District.
Construction methods used to develop urban areas disturb the land and allow sediment-laden runoff to impact nearby streams and lakes. Best management practices (BMPs) to minimize construction associated sedimentation damages are used ineffectively in many cases. BMPs to control the impact of construction practices include; sediment retention basins, phased “grading”, and runoff control (e.g. hay bales, silt fences, vegetative ground cover, terracing, etc). Efforts need to be made to prevent sedimentation from off-project construction activities from causing impacts to Corps projects. This could be accomplished by the appropriate State, County, or City agencies working with developers.
Post-construction problems are commonly associated with storm drainage and urban pollution. The conversion of grasslands or forests to roads, rooftops, sidewalks, and other water impervious surfaces make stream flows more variable and increases the frequency of high flow events. In addition, pollutants associated with urban drainage can cause impacts to downstream water bodies. Storm sewer exits can be allowed on project lands provided detention in the form of ponds, swales, or wetlands exist on private property. A developer may be asked to construct a series of wetlands to slow downhill flows and provide time for bacterial die-off, chemical degradation, reduced flow rates, and sediment settling.
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