2y ago
3.71 MB
22 Pages
Last View : 29d ago
Last Download : 1y ago
Upload by : Aiyana Dorn

EFFECTS OF HUMAN ACTIVITIESON THE INTERACTION OFGROUND WATER AND SURFACE WATERHuman activities commonly affect the distribution, quantity, and chemical quality of waterresources. The range in human activities that affectthe interaction of ground water and surface water isbroad. The following discussion does not providean exhaustive survey of all human effects butemphasizes those that are relatively widespread. Toprovide an indication of the extent to whichhumans affect the water resources of virtually alllandscapes, some of the most relevant structuresand features related to human activities are superimposed on various parts of the conceptual landscape (Figure 25).The effects of human activities on the quantity and quality of water resources are felt overa wide range of space and time scales. In thefollowing discussion, “short term” implies timescales from hours to a few weeks or months, and“long term” may range from years to decades.“Local scale” implies distances from a fewfeet to a few thousand feet and areas as large as afew square miles, and “subregional and regionalscales” range from tens to thousands of squaremiles. The terms point source and nonpoint sourcewith respect to discussions of contamination areused often; therefore, a brief discussion of themeaning of these terms is presented in Box M.Agricultural DevelopmentAgriculture has been the cause of significantmodification of landscapes throughout the world.Tillage of land changes the infiltration and runoffcharacteristics of the land surface, which affectsrecharge to ground water, delivery of water andsediment to surface-water bodies, and evapotranspiration. All of these processes either directly orindirectly affect the interaction of ground water andsurface water. Agriculturalists are aware of thesubstantial negative effects of agriculture on waterresources and have developed methods to alleviatesome of these effects. For example, tillage practices have been modified to maximize retention ofwater in soils and to minimize erosion of soil fromthe land into surface-water bodies. Two activitiesrelated to agriculture that are particularly relevantto the interaction of ground water and surfacewater are irrigation and application of chemicals tocropland.54

Figure 25. Human activities and structures, as depictedby the distribution of various examples in the conceptual landscape, affect the interaction of ground waterand surface water in all types of landscapes.55

MPoint and NonpointSources of ContaminantsContaminants may be present in water or in air asa result of natural processes or through mechanisms ofdisplacement and dispersal related to human activities.Contaminants from point sources discharge either into groundwater or surface water through an area that is small relative tothe area or volume of the receiving water body. Examples ofpoint sources include discharge from sewage-treatmentplants, leakage from gasoline storage tanks, and seepagefrom landfills (Figure M–1).Nonpoint sources of contaminants introducecontaminants to the environment across areas that arelarge compared to point sources, or nonpoint sources mayconsist of multiple, closely spaced point sources. A nonpointsource of contamination that can be present anywhere, andaffect large areas, is deposition from the atmosphere, bothby precipitation (wet deposition) or by dry fallout (dry deposition). Agricultural fields, in aggregate, represent large areasthrough which fertilizers and pesticides can be released to theenvironment.The differentiation between point and nonpoint sourcesof contamination is arbitrary to some extent and may dependin part on the scale at which a problem is considered. Forexample, emissions from a single smokestack is a pointsource, but these emissions may be meaningless in a regionalanalysis of air pollution. However, a fairly even distribution oftens or hundreds of smokestacks might be considered as anonpoint source. As another example, houses in suburbanareas that do not have a combined sewer system have individual septic tanks. At the local scale, each septic tank maybe considered as point source of contamination to shallowground water. At the regional scale, however, the combinedcontamination of ground water from all the septic tanks ina suburban area may be considered a nonpoint source ofcontamination to a surface-water body.Figure M–1. The transport of contamination from a pointsource by ground water can cause contamination of surfacewater, as well as extensive contamination of ground water.Waste me56

IRRIGATION SYSTEMSSurface-water irrigation systems representsome of the largest integrated engineering worksundertaken by humans. The number of thesesystems greatly increased in the western UnitedStates in the late 1840s. In addition to dams onstreams, surface-water irrigation systems include(1) a complex network of canals of varying sizeand carrying capacity that transport water, in manycases for a considerable distance, from a surfacewater source to individual fields, and (2) a drainagesystem to carry away water not used by plants thatmay be as extensive and complex as the supplysystem. The drainage system may include underground tile drains. Many irrigation systems thatinitially used only surface water now also useground water. The pumped ground watercommonly is used directly as irrigation water, butin some cases the water is distributed through thesystem of canals.Average quantities of applied water rangefrom several inches to 20 or more inches of waterper year, depending on local conditions, over theentire area of crops. In many irrigated areas, about75 to 85 percent of the applied water is lost toevapotranspiration and retained in the crops(referred to as consumptive use). The remainder ofthe water either infiltrates through the soil zone torecharge ground water or it returns to a localsurface-water body through the drainage system(referred to as irrigation return flow). The quantityof irrigation water that recharges ground waterusually is large relative to recharge from precipitation because large irrigation systems commonly arein regions of low precipitation and low naturalrecharge. As a result, this large volume of artificialrecharge can cause the water table to rise (seeBox N), possibly reaching the land surfacein some areas and waterlogging the fields. For thisreason, drainage systems that maintain the level ofthe water table below the root zone of the crops,generally 4 to 5 feet below the land surface, are anessential component of some irrigation systems.The permanent rise in the water table that is maintained by continued recharge from irrigation returnflow commonly results in an increased outflow ofshallow ground water to surface-water bodiesdowngradient from the irrigated area.57

NEffects of Irrigation Developmenton the Interaction ofGround Water and Surface WaterNebraska ranks second among the States with respectto the area of irrigated acreage and the quantity of water usedfor irrigation. The irrigation water is derived from extensivesupply systems that use both surface water and ground water(Figure N–1). Hydrologic conditions in different parts ofNebraska provide a number of examples of the broad-scaleeffects of irrigation development on the interactions of groundwater and surface water. As would be expected, irrigationsystems based on surface water are always located nearstreams. In general, these streams are perennial and (or)have significant flow for at least part of the year. In contrast,irrigation systems based on ground water can be locatednearly anywhere that has an adequate ground-waterresource. Areas of significant rise and decline in ground-waterlevels due to irrigation systems are shown in Figure N–2.Ground-water levels rise in some areas irrigated with surfacewater and decline in some areas irrigated with ground water.Rises in ground-water levels near streams result in increasedground-water inflow to gaining streams or decreased flow fromthe stream to ground water for losing streams. In some areas,it is possible that a stream that was losing water before development of irrigation could become a gaining stream followingirrigation. This effect of surface-water irrigation probablycaused the rises in ground-water levels in areas F and G insouth-central Nebraska (Figure N–2).EXPLANATIONSurface-waterirrigation project02040 MILESFigure N–1. Nebraska is one of the most extensively irrigated States in the Nation. The irrigation water comes fromboth ground-water and surface-water sources. Dots are irrigation wells. (Map provided by the University of Nebraska,Conservation and Survey Division.)58

Average annual precipitation ranges from less than15 inches in western Nebraska to more than 30 inches ineastern Nebraska. A large concentration of irrigation wells ispresent in area E (Figure N–2). The ground-water withdrawalsby these wells caused declines in ground-water levels thatcould not be offset by recharge from precipitation and thepresence of nearby flowing streams. In this area, the withdrawals cause decreases in ground-water discharge to thestreams and (or) induce flow from the streams to shallowground water. In contrast, the density of irrigation wells inareas A, B, and C is less than in area E, but water-leveldeclines in these three western areas are similar to area E.The similar decline caused by fewer wells in the westcompared to the east is related to less precipitation, lessground-water recharge, and less streamflow available forseepage to ground water.DAHFEXPLANATION 50-foot rise 20 to 50 10 to 20–5 to 10–5 to –10–10 to –15–15 to –20–20 to –25–25 to –30 –30-foot declineGBEC02040 MILESFigure N–2. The use of both ground water and surface water for irrigation in Nebraska has resulted in significant rises anddeclines of ground-water levels in different parts of the State. (Map provided by the University of Nebraska, Conservationand Survey Division.)59

Although early irrigation systems made useof surface water, the development of large-scalesprinkler systems in recent decades has greatlyincreased the use of ground water for irrigation forseveral reasons: (1) A system of supply canals isnot needed, (2) ground water may be more readilyavailable than surface water, and (3) many types ofsprinkler systems can be used on irregular landsurfaces; the fields do not have to be as flat asthey do for gravity-flow, surface-water irrigation.Whether ground water or surface water was usedfirst to irrigate land, it was not long before watermanagers recognized that development of eitherwater resource could affect the other. This is particularly true in many alluvial aquifers in arid regionswhere much of the irrigated land is in valleys.Significant changes in water quality accompany the movement of water through agriculturalfields. The water lost to evapotranspiration is relatively pure; therefore, the chemicals that are leftbehind precipitate as salts and accumulate in thesoil zone. These continue to increase as irrigationcontinues, resulting in the dissolved-solids concentration in the irrigation return flows being significantly higher in some areas than that in the originalirrigation water. To prevent excessive buildup ofsalts in the soil, irrigation water in excess of theneeds of the crops is required to dissolve and flushout the salts and transport them to the ground-watersystem. Where these dissolved solids reach highconcentrations, the artificial recharge from irrigation return flow can result in degradation of thequality of ground water and, ultimately, the surfacewater into which the ground water discharges.“Whether ground water or surface water wasused first to irrigate land, it was notlong before water managers recognizedthat development of either waterresource could affect the other”60

USE OF AGRICULTURALCHEMICALSApplications of pesticides and fertilizersto cropland can result in significant additions ofcontaminants to water resources. Some pesticidesare only slightly soluble in water and may attach(sorb) to soil particles instead of remaining in solution; these compounds are less likely to causecontamination of ground water. Other pesticides,however, are detected in low, but significant,concentrations in both ground water and surfacewater. Ammonium, a major component of fertilizerand manure, is very soluble in water, and increasedconcentrations of nitrate that result from nitrification of ammonium commonly are present in bothground water and surface water associated withagricultural lands (see Box O). In addition to thesenonpoint sources of water contamination, pointsources of contamination are common in agricultural areas where livestock are concentrated insmall areas, such as feedlots. Whether the initialcontamination is present in ground water or surfacewater is somewhat immaterial because the closeinteraction of the two sometimes results in bothbeing contaminated (see Box P).“Whether the initial contamination is presentin ground water or surface water issomewhat immaterial because the closeinteraction of the two sometimes resultsin both being contaminated”61

OEffects of Nitrogen Use on the Quality ofGround Water and Surface WaterNitrate contamination of ground water and surfacewater in the United States is widespread because nitrate isvery mobile in the environment. Nitrate concentrations areincreasing in much of the Nation’s water, but they are particularly high in ground water in the midcontinent region of theUnited States. Two principal chemical reactions are importantto the fate of nitrogen in water: (1) fertilizer ammonium can benitrified to form nitrate, which is very mobile as a dissolvedconstituent in shallow ground water, and (2) nitrate can bedenitrified to produce nitrogen gas in the presence of chemically reducing conditions if a source of dissolved organiccarbon is available.High concentrations of nitrate can contribute to excessive growth of aquatic plants, depletion of oxygen, fishkills,and general degradation of aquatic habitats. For example, astudy of Waquoit Bay in Massachusetts linked the decline ineelgrass beds since 1950 to a progressive increase in nitrateinput due to expansion of domestic septic-field developmentsin the drainage basin (Figure O–1). Loss of eelgrass is aconcern because this aquatic plant stabilizes sediment andprovides ideal habitat for juvenile fish and other fauna incoastal bays and estuaries. Larger nitrate concentrationssupported algal growth that caused turbidity and shading,which contributed to the decline of eelgrass.Waquoit Bay, MassachusettsMorgan Creek, MarylandFigure O–1. The areal extent of eelgrassin Waquoit Bay, Massachusetts, decreasedmarkedly between 1951 and 1987 becauseof increased inputs of nitrogen related todomestic septic-field developments. (Modifiedfrom Valiela, I., Foreman, K., LaMontagne, M.,Hersh, D., Costa, J., Peckol, P., DeMeoAndeson, B., D’Avanzo, C., Babione, M.,Sham, C.H., Brawley, J., and Lajtha, K.,1992, Couplings of watersheds and coastalwaters—Sources and consequencesof nutrient enrichment in Waquoit Bay,Massachusetts: Estuaries, v. 15, no. 4,p. 433–457.) (Reprinted by permission ofthe Estuarine Research Federation.)Eelgrass195162WaquoitBay197119781987

Significant denitrification has been found to takeplace at locations where oxygen is absent or present atvery low concentrations and where suitable electron-donorcompounds, such as organic carbon, are available. Suchlocations include the interface of aquifers with silt and clayconfining beds and along riparian zones adjacent to streams.For example, in a study on the eastern shore of Maryland,nitrogen isotopes and other environmental tracers were usedto show that the degree of denitrification that took placedepended on the extent of interaction between ground-waterand the chemically reducing sediments near or below thebottom of the Aquia Formation. Two drainage basins werestudied: Morgan Creek and Chesterville Branch (Figure O–2).Ground-water discharging beneath both streams had similarnitrate concentration when recharged. Significant denitrification took place in the Morgan Creek basin where a largefraction of local ground-water flow passed through thereducing sediments, which are present at shallow depths(3 to 10 feet) in this area. Evidence for the denitrificationincluded decreases in nitrate concentrations along the flowpath to Morgan Creek and enrichment of the 15N isotope.Much less denitrification took place in the Chesterville Branchbasin because the top of the reducing sediments are deeper(10 to 20 feet) in this area and a smaller fraction of groundwater flow passed through those sediments.EXPLANATIONNITRATE (NO3–), IN MILLIGRAMS PER LITER AS NGreater than 10RechargeNO3 – 3 to 20 milligrams per liter15N(NO –) 2 to 6 per mil5 to 102 to 53Less than 2Morgan CreekNO3– 2 to 3 milligrams per liter15N(NO –) 7 to 10 per milChesterville BranchNO 3– 9 to 10 milligrams per liter15N(NO –) 4 to 5 per mil3South3Northler tabWateBase of AGround waterquia FormationNO3– 0 milligrams per liter15N(excess N 2) 2 to 5 per milGround waterNO 3– 3 to 5 milligrams per liter15N(NO –) 4 to 5 per mil3Figure O–2. Denitrification had a greater effect on ground water discharging to Morgan Creek than to Chesterville Branch inMaryland because a larger fraction of the local flow system discharging to Morgan Creek penetrated the reduced calcareoussediments near or below the bottom of the Aquia Formation than the flow system associated with the Chesterville Branch.(Modified from Bolke, J.K., and Denver, J.M., 1995, Combined use of ground-water dating, chemical, and isotopic analysesto resolve the history and fate of nitrate contamination in two agricultural watersheds, Atlantic coastal plain, Maryland: WaterResources Research, v. 31, no. 9, p. 2319–2337.)63

PEffects of Pesticide Application toAgricultural Lands on the Quality ofGround Water and Surface WaterPesticide contamination of ground water and surfacewater has become a major environmental issue. Recentstudies indicate that pesticides applied to cropland cancontaminate the underlying ground water and then movealong ground-water flow paths to surface water. In addition,as indicated by the following examples, movement of thesepesticides between surface water and ground water can bedynamic in response to factors such as bank storage duringperiods of high runoff and ground-water withdrawals.A study of the sources of atrazine, a widely usedherbicide detected in the Cedar River and its associatedalluvial aquifer in Iowa, indicated that ground water was themajor source of atrazine in the river during base-flow conditions. In addition, during periods of high streamflow, surfacewater containing high concentrations of atrazine movedinto the bank sediments and alluvial aquifer, then slowlydischarged back to the river as the river level declined.Reversals of flow related to bank storage were documentedusing data for three sampling periods (Figure P–1). The firstsampling (Figure P–1A) was before atrazine was applied tocropland, when concentrations in the river and aquifer wererelatively low. The second sampling (Figure P–1B) was afteratrazine was applied to cropland upstream. High streamflow atthis time caused the river stage to peak almost 6 feet above itsbase-flow level, which caused the herbicide to move withthe river water into the aquifer. By the third sampling date(Figure P–1C), the hydraulic gradient between the riverand the alluvial aquifer had reversed again, and atrazinecontaminated water discharged back into the river.A680ALTITUDE, IN FEETSampling period February 20 to 22CedarRiver690Sand(0.12)Water table6700.30.3660Sand6500. till630CedarRiverB690ALTITUDE, IN FEET680(0.51)6700.56600.5Sampling period March 20 to 22SandWater table0.560. 0.6 till630CSampling period April 3 to 5CedarRiverALTITUDE, IN FEET690680(0.21)0.

the stream to ground water for losing streams. In some areas, it is possible that a stream that was losing water before devel-opment of irrigation could become a gaining stream following irrigation. This effect of surface-water irrigation probably caused the rises in ground-water levels in areas F and G in south-central Nebraska (Figure N–2).

Related Documents:

Hour of Code—30 Activities for K-8 2 30 Hour of Code K-8 Activities Organized by Grade Kindergarten o Online activities o Misc. coding websites o Human robot o Human algorithm 1st Grade o Online activities o Misc. coding websites o Human robot o Human algorithm 2nd Grade o Online activities o Misc. coding websites o Sequencing o Animation 3rd Grade o Online activities

you learn what the full range of media effects are and how the media influence contributes to those many effects. Need to Organize Media Effects Because this definition is so broad as to capture the full range of media effects, it encom-passes a great many such effects. See a partial list of those effects in Exhibit 3.1.

Social Studies Textbook Effects 3 study focused on the effects of social studies textbooks on stu-dent achievement.1 To our knowledge, all prior empirical studies on the effects of textbooks on student learning focused on the dif-ferential effects of mathematics textbooks. Several recent reviews included studies of mathematics textbook effects in

Health Impact Assessment for EJ Cumulative Effects Combined and incremental effects of human activities on environmental resources, human communities, or ecosystems (40 CFR §1508.7.; USEPA 1999). Cumulative effects on human communities may be combined Two or more sources of the same physical exposure

1. Colors - 16 activities 2. Numbers - 18 activities 3. Time - 36 activities 4. Weather - 17 activities 5. Food - 16 activities 6. Clothes - 23 activities 7. School Words - 20 activities Everyday English Everyday English Essential

Human Resource Management Question Answer Bank MBA-203 Q.1 What is Human Resource Management Human Resource Management is a process, which consists of four main activities, namely, acquisition, development, motivation, as well as maintenance of human resources. Scott, Clothier and Spriegel have defined Human Resource Management as that

Ans Human resource planning can be defined as the process of identifying the number of people required by an organization in terms of quantity and quality. All human resource management activities start with human resource planning. So we can say that human resource planning is the principle/primary activity of human resource management.

Human migration has traditionally been studied without the application of a human development approach. By using this approach to the study of human migration, UNDP's Human Development Report 2009, sets itself apart from other postcolonial studies. The report, Overcoming Barriers: Human Mobility and Development, gives a