Top Causes of Lake Pollution

Top Causes of Lake Pollution In an extensive sampling effort, the Environmental Protection Agency, with the help of state and tribal agencies, coordinated water quality assessments for the country’s lakes. They evaluated 43% of the lake surface area or about 17.3 million acres of water. The study concluded that: Fifty-five percent of the study’s water acreage was judged to be of good quality. The other 45% had waters impaired for at least one type of use (for example as drinking water supply, for recreational fishing, swimming, or aquatic life support). When considering man-made lakes alone, the proportion that was impaired jumped to 59%.Water quality is sufficiently high to allow swimming in 77% of the waters assessed.Aquatic life was not supported adequately by 29% of lake waters.For 35% of the lake waters surveyed, fish consumption was not recommended. For the impaired lakes, the top types of pollution were: Nutrients (problematic in 50% of impaired waters). Nutrient pollution occurs when excess nitrogen and phosphorus make their way into a lake. These elements are then picked up by algae, allowing them to grow rapidly to the detriment of the aquatic ecosystem. Overabundant cyanobacterial algae blooms can lead to toxin build-up, oxygen level drops, fish kills, and poor conditions for recreation. Nutrient pollution and the subsequent algae blooms are to blame for Toledo’s drinking water shortage in the summer of 2014. Nitrogen and phosphorus pollution comes from inefficient sewage treatment systems and from some agricultural practices.Metals (42% of impaired waters). The two main culprits here are mercury and lead. Mercury accumulates in lakes mostly from atmospheric deposition of pollution coming from coal-fired power plants. Lead pollution is often the result of accumulated fishing tackle like sinkers and jig heads, and from lead shot in shotgun shells.Sediment (21% of impaired w aters). Fine-grained particles like silt and clay may occur naturally in the environment but when they enter lakes in large quantity, they become a serious pollution problem. Sediments come from the many ways soil can be eroded on land and carried into streams then lakes: erosion can originate from road construction, deforestation, or agricultural activities. Total Dissolved Solids (TDS; 19% of impaired waters). TDS measurements can be interpreted as how salty the water is, generally due to high concentrations of dissolved calcium, phosphates, sodium, chloride, or potassium. These elements most often enter the roadways as road salt, or in synthetic fertilizers. Where do these pollutants come from? When assessing the source of pollution for the impaired lakes, the following findings were reported: Agriculture (affecting 41% of impaired waters). Many agricultural practices contribute to lake water pollution, including soil erosion, manure and synthetic fertilizer management, and the use of pesticides,Hydrologic modifications (18% of impaired waters). These include the presence of dams and other flow regulation structures and dredging activities. Dams have extensive effects on a lake’s physical and chemical characteristics, and on aquatic ecosystems.Urban runoff and storm sewers (18% of impaired waters). Streets, parking lots, and rooftops are all impervious surfaces that do not allow water to percolate through. As a result, water runoff speeds up to storm drains and picks up sediments, heavy metals, oils, and other pollutants, and carries it into lakes. What Can You Do? Use soil erosion best practices whenever you disturb soil near a lake.Project lake shorelines on your property by preserving the natural vegetation. Replant shrubs and trees if needed. Avoid fertilizing your lawn close to a lake’s edge.Encourage the use of sustainable farming methods like cover crops and no-till farming. Talk to farmers at your local farmers market to find out more about their practices.Keep septic systems in good working order, and have regular inspections conducted.Encourage local authorities to use alternatives to road salt in winter.Consider your nutrient inputs from soaps and detergents, and reduce their use whenever possible.In your yard, slow down water runoff and allow it to be filtered by plants and soil. To accomplish this, establish rain gardens, and keep drainage ditches well vegetated. Use rain barrels to harvest roof runoff.Consider using pervious pavement in your driveway. These surfaces are designed to let water percolate into the soil below, p reventing runoff. Choose alternatives to lead when selecting fishing tackle.   Sources: EPA. 2000. National Lake Assessment Report. EPA. 2009. National Lake Assessment: A Collaborative Survey of the Nation’s Lakes.

The Periodic Properties of the Elements

The Periodic Properties of the Elements The periodic table arranges the elements  by periodic properties, which are recurring trends in physical and chemical characteristics. These trends can be predicted merely by examing the periodic table and can be explained and understood by analyzing the electron configurations of the elements. Elements tend to gain or lose valence electrons to achieve stable octet formation. Stable octets are seen in the inert gases, or noble gases, of Group VIII of the periodic table. In addition to this activity, there are two other important trends. First, electrons are added one at a time moving from left to right across a period. As this happens, the electrons of the outermost shell experience increasingly strong nuclear attraction, so the electrons become closer to the nucleus and more tightly bound to it. Second, moving down a column in the periodic table, the outermost electrons become less tightly bound to the nucleus. This happens because the number of filled principal energy levels (whi ch shield the outermost electrons from attraction to the nucleus) increases downward within each group. These trends explain the periodicity observed in the elemental properties of atomic radius, ionization energy, electron affinity, and electronegativity. Atomic Radius The atomic radius of an element is half of the distance between the centers of two atoms of that element that are just touching each other. Generally, the atomic radius decreases across a period from left to right and increases down a given group. The atoms with the largest atomic radii are located in Group I and at the bottom of groups. Moving from left to right across a period, electrons are added one at a time to the outer energy shell. Electrons within a shell cannot shield each other from the attraction to protons. Since the number of protons is also increasing, the effective nuclear charge increases across a period. This causes the atomic radius to decrease. Moving down a group in the periodic table, the number of electrons and filled electron shells increases, but the number of valence electrons remains the same. The outermost electrons in a group are exposed to the same effective nuclear charge, but electrons are found farther from the nucleus as the number of filled energy shells increases. Therefore, the atomic radii increase. Ionization Energy The ionization energy, or ionization potential, is the energy required to remove an electron from a gaseous atom or ion completely. The closer and more tightly bound an electron is to the nucleus, the more difficult it will be to remove, and the higher its ionization energy will be. The first ionization energy is the energy required to remove one electron from the parent atom. The second ionization energy is the energy required to remove a second valence electron from the univalent ion to form the divalent ion, and so on. Successive ionization energies increase. The second ionization energy is always greater than the first ionization energy. Ionization energies increase moving from left to right across a period (decreasing atomic radius). Ionization energy decreases moving down a group (increasing atomic radius). Group  I elements have low ionization energies because the loss of an electron forms a stable octet. Electron Affinity Electron affinity reflects the ability of an atom to accept an electron. It is the energy change that occurs when an electron is added to a gaseous atom. Atoms with stronger effective nuclear charge have greater electron affinity. Some generalizations can be made about the electron affinities of certain groups in the periodic table. The Group IIA elements, the alkaline earths, have low electron affinity values. These elements are relatively stable because they have filled s subshells. Group VIIA elements, the halogens, have high electron affinities because the addition of an electron to an atom results in a completely filled shell. Group VIII elements, noble gases, have electron affinities near zero since each atom possesses a stable octet and will not accept an electron readily. Elements of other groups have low electron affinities. In a period, the halogen will have the highest electron affinity, while the noble gas will have the lowest electron affinity. Electron affinity decreases moving down a group because a new electron would be further from the nucleus of a large atom. Electronegativity Electronegativity is a measure of the attraction of an atom for the electrons in a chemical bond. The higher the electronegativity of an atom, the greater its attraction for bonding electrons. Electronegativity is related to ionization energy. Electrons with low ionization energies have low electronegativities because their nuclei do not exert a strong attractive force on electrons. Elements with high ionization energies have high electronegativities due to the strong pull exerted on electrons by the nucleus. In a group, the electronegativity decreases as the atomic number increases, as a result of the increased distance between the valence electron and nucleus (greater atomic radius). An example of an electropositive (i.e., low electronegativity) element is cesium; an example of a highly electronegative element is fluorine. Summary of Periodic Table Properties of Elements Moving Left → Right Atomic Radius DecreasesIonization Energy IncreasesElectron Affinity Generally Increases (except Noble Gas Electron Affinity Near Zero)Electronegativity Increases Moving Top → Bottom Atomic Radius IncreasesIonization Energy DecreasesElectron Affinity Generally Decreases Moving Down a GroupElectronegativity Decreases