Hydrologic & Nutrients Cycle Department of Civil Engineering College of Engineering King Saud University GE 302 – Industry and the Environment Topic 2 Hydrologic & Nutrients Cycle

What Happens to Matter in an Ecosystem? Matter, in the form of nutrients and water, cycles within and among ecosystems and the biosphere, and human activities are altering these cycles.

Nutrients Cycle within and among Ecosystems The elements and compounds that make up nutrients move continually through air, water, soil, and living organisms within ecosystems, as well as in the biosphere in cycles called nutrient cycles, or biogeochemical cycles. These cycles include the hydrologic (water), carbon, nitrogen, and phosphorus cycle. These cycles driven directly or indirectly by incoming solar energy and the earth’s gravity

The hydrologic cycle The hydrologic cycle, or water cycle, collects, purifies, and distributes the earth’s fixed supply of water. The water cycle is powered by energy from the sun and involves three major processes: evaporation, precipitation, and transpiration. When precipitation fall on terrestrial ecosystems it: can become surface runoff that flows into streams. seeps into the upper layers of soils where it is used by plants. some evaporate from top soil to atmosphere. sinks through soil to underground layers of rock, sand, and gravel called aquifers, where it is stored as groundwater.

A small amount of the earth’s water ends up in the living components of ecosystems. As producers, plants absorb some of this water through their roots, most of which evaporates from plant leaves back into the atmosphere during transpiration. Because water dissolves many nutrient compounds, it is a major medium for transporting nutrients within and between ecosystems. Only about 0.024% of the earth’s vast water supply is available to humans and other species as liquid freshwater

Simplified model of the hydrologic cycle, in which water circulates in various physical forms within the biosphere. Major harmful impacts of human activities are shown by the red arrows and boxes

Schematic diagram of the natural hydrologic cycle Schematic diagram of the natural hydrologic cycle. The constant circulation of water is powered by energy from the sun and by gravity.

Human Activity Alter Water Cycle We alter the water cycle in three major ways (see the red arrows and boxes in Figure): First, we withdraw large quantities of freshwater from streams, lakes, and aquifers sometimes at rates faster than nature can replace it. Second, we clear vegetation from land for agriculture, mining, road building, and other activities, and cover much of the land with buildings, concrete, and asphalt. This increases runoff, reduces infiltration that would normally recharge groundwater supplies, accelerates topsoil erosion, and increases the risk of flooding. Third, we also increase flooding when we drain and fill wetlands for farming and urban development. wetlands provide the natural service of flood control, acting like sponges to absorb and hold overflows of water from drenching rains or rapidly melting snow.

Jeddah floods, 2009

Natural Water Purification Processes Throughout the hydrologic cycle, many natural processes purify water. Evaporation and subsequent precipitation act as a natural distillation process that removes impurities dissolved in water. Water flowing above ground through streams and lakes is partially purified by chemical and biological processes (due to natural aeration and decomposer bacteria). Water flowing below ground in aquifers is naturally filtered by soil. The hydrologic cycle can be viewed as a cycle of natural renewal of water quality.

The Carbon Cycle Carbon is the basic building block organic compounds necessary for life. Various compounds of carbon circulate through the biosphere, the atmosphere, and parts of the hydrosphere, in the carbon cycle. The carbon cycle is based on carbon dioxide (CO2) gas, which makes up 0.039% of the volume of the earth’s atmosphere and is also dissolved in water. Carbon dioxide (along with water vapor in the water cycle) is a key component of the atmosphere’s thermostat. If the carbon cycle removes too much CO2 from the atmosphere (Cooler) if the carbon cycle generates too much CO2 to the atmosphere (Warmer)

The Carbon Cycle Decomposers release the carbon stored in the bodies of dead organisms on land back into the air as CO2. In water, decomposers release carbon that can be stored as insoluble carbonates in bottom sediment. Marine sediments are the earth’s largest store of carbon. Over millions of years, buried deposits of dead plant matter and bacteria are compressed between a layers of sediment, where high pressure and heat convert them to carbon-containing fossil fuels such as coal, oil, and natural gas. We have extracted and burned huge quantities of fossil fuels that took millions of years to form. This is why, on a human time scale, fossil fuels are nonrenewable resources.

Simplified model illustrates the circulation of various chemical forms of carbon in the global carbon cycle, with major harmful impacts of human activities shown by the red arrows.

Simplified diagram of the carbon cycle Simplified diagram of the carbon cycle. The arrows show the various directions of carbon transfer through the biosphere.

The Nitrogen Cycle The major reservoir for nitrogen is the atmosphere. Chemically unreactive nitrogen gas (N2) makes up 78% of the volume of the atmosphere. Nitrogen is a crucial component of proteins, many vitamins, and nucleic acids such as DNA. N2 cannot be absorbed and used directly as a nutrient by plants or animals. Two natural processes convert, or fix, N2 into compounds that plants and animals can use as nutrients. Electrical discharges, or lightning, taking place in the atmosphere. (Nitrogen, N2  Ammonia, NH3) Nitrogen fixation takes place in aquatic systems, in soil, and in the roots of some plants, where specialized bacteria, called nitrogen-fixing bacteria, complete this conversion. (Nitrogen, N2  Ammonia, NH3)

Nitrate ions are easily taken up by the roots of plants N2 and O2 combine as we burn any fuel at high temperatures, such as in car, truck, and jet engines. A simplified model of the circulation of various chemical forms of nitrogen in the nitrogen cycle in a terrestrial ecosystem, with major harmful human impacts shown by the red arrows.

Simplified diagram of the nitrogen cycle Simplified diagram of the nitrogen cycle. Molecular nitrogen must first be fixed (combined with oxygen) into the form of nitrate nitrogen before it can be used by plants as a nutrient.

The Phosphorus Cycle Compounds of phosphorous (P) circulate through water, the earth’s crust, and living organisms in the phosphorus cycle. The phosphorus cycle does not include the atmosphere. phosphate ions (PO43 –) serve as an important nutrient. The major reservoir for phosphorous is phosphate salts containing phosphate ions in terrestrial rock formations and ocean bottom sediments. The phosphorus cycle is slow compared to the water, carbon, and nitrogen cycles. For both producers and consumers, phosphates are a component of biologically important molecules such as nucleic acids. Because most soils contain little phosphate, the lack of it often limits plant growth on land unless phosphorus is applied to the soil as a fertilizer.

Nitrate ions are easily taken up by the roots of plants N2 and O2 combine as we burn any fuel at high temperatures, such as in car, truck, and jet engines. a simplified model of the circulation of various chemical forms of phosphorus (mostly phosphates) in the phosphorus cycle, with major harmful human impacts shown by the red arrows.

Eutrophication Eutrophication is a process whereby water bodies, such as lakes, estuaries, or slow-moving streams receive excess nutrients (nitrogen and phosphorus) that stimulate excessive growth of algae or phytoplankton (algae blooms). This algae bloom reduces dissolved oxygen in the water and after dying its decomposition consume more oxygen and makes water hypoxic (water with low concentration of dissolved oxygen). Hyperoxic water is the water with high concentration of oxygen.