Environmental impact of urban life on watershed

Hello steemians,
hope we are all doing fine and I hope you enjoyed my last write-up.Today I will be talking to us about watershed as regards our geographic environment and its relation to us.

^{Image source Pixabay. CC0 creative commons. Contributed by Free Photos}

Nature is very beautiful and as such we are fascinated by it. When we travel along the road or visit some natural reserves, have we ever noticed water coming out from a particular natural source? It could be a rock or directly from the ground. Have you ever wondered where is the water coming from and where it is going to? Well these are watershed paths.

Watershed is that part of the land that contributes water to a particular destination such as rivers, lakes, streams, ponds etc. Watershed depicts areas of land and water which is surrounded by a central drainage which acts as a receptacle for surface runoff and empties through a single outlet into a larger water body. It is a catchment area which is normally surrounded by topographic features like hills, mountains, ridge tops.

Watershed represents a unique physical unit within the milieu which water moves continuously in a cycle that begins with rain or snow. Within the watershed landscape, plant leaves will intercept some rain and snow, where it will either evaporate back into the air or drop to the earth’s surface. Rain water and melted snows may infiltrate the soil or flow over land to be stored temporally in depressions, wetlands and lakes.

^{Wolf -river watershed, the river isn't that wide. The blue part indicates the extent of the Wolf River's floodplain. Image source Flickr. CC BY 2.0 license. Contributed by Gary Bridgeman}

Watershed can be of different varying sizes as regards the geographic location where they are found in the environment but generally, the larger the water body the larger the watershed. This is because for every water body we see, there is a watershed associated with it no matter how small the water body maybe. Watershed can be classified depending on the size, drainage, shape and land use patterns and these are

• Macro watershed (<50,000 hect)
• Sub-watershed (10000 to 50,000 hect)
• Milli-watershed (1000 to 10000 hect)
• Micro-watershed (100to 1000 hect)
• Mini-watershed (1 to 100 hect)

Groundwater forms when surface water seeps through the soil to varying depths and collects in aquifers. Groundwater can remain stored underground and then re-emerges as springs after a long time or discharges into nearby rivers, lakes or wetlands .this process is usually within few days which can also lead to thousands of years. Eventually, every water flowing over the surface or through the ground makes its way into rivers and lakes or is taken up by vegetation, where evaporation or transpiration to begin the cycle again.

^{Ground-water flow paths vary greatly in length, depth, and traveltime from points of recharge to points of discharge in the groundwater system. Image source Wikimedia. A creative commons license. contributed by T.C. Winter, J.W. Harvey, O.L. Franke, and W.M. Alley}

Precipitation will dissipate through several routs once it reaches the earth’s surface .some will be absorbed into the ground. Once the top soil has reached its saturation point, the excess may begin to run off the land as surface flow following the force of gravity. Runoff will eventually find its way into surface waters.

Watershed is a very important aspect of the environment and that is why there are so many factors affecting the quality and functions of resources in a watershed. Such factors include the quality of water, flow regime of the watershed, habitat (structures and functions),climate and energy sources.

Water quality

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When we talk about the term water quality, we refer to the physical, chemical and biological characteristics of the water and these include temperature, ph., turbidity, dissolved oxygen, nutrients, and presence of organic and inorganic chemicals, heavy metals and toxic substances that are present within the water. In addition to these, there are also micro-invertebrates, fishes and plants living in the water are also considered in assessing the water quality of a watershed. Water quality is impaired by land uses that contributes pollutants to ground water and runoff.

^{Population that uses improved water sources as percent of total population. Green: 100-95; yellow: 75-94.9; red: 74.9 and below. Source: UNDP (2006). Image source Wikimedia. Creative Commons Attribution 3.0 Unported license. Contributed by Ionut Cojocaru}

The factors affecting the quality include but not limited toelevated nutrient inputs, too many solids such as sediments, Pathogens that are present in the water, toxic substances such as heavy metals, pesticides, oils and road salts, high level of organic matter, Litter and trash along stream banks, Lower levels of dissolved oxygen and the alteration of stream temperature as a result of the climate of the area

Flow regime

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Flow regime comprises of surface runoffs which may eventually turn to flash floods and flow at a very high speeds, size of the water body and normal water flow (non-turbulent). Flow regime is determined using physical characteristics of watersheds like the size of vegetation within the area, land orientations and surface types. In addition, structures like gutters, pipes and ditches can affect flow. Changes in any of these factors can have the effects on the watershed of the region.

An increase in velocity may also increase the frequency and severity of flooding in the said region and in such case accelerate channel erosion both locally and downstream. The flow regime of a watershed contribute to sedimentation of particles in the water and alter stream bed composition and structure which means it will increase the size of the water bed in the geographic location.

An increase in volume of water when combined with higher velocity of flow can accelerate channel erosion rates and change stream bed composition, destroy habitat and disrupt stream ecology as well. A reduced infiltration into the ground, commonly called a decrease in base flow, will decrease ground water recharge, which in turn can lower the level of surface water in surrounding lakes, streams and wetlands
Habitat

^{A River flow regime shifts which has been projected to occur until the 2050s as a result of climatic change. River flow regimes are either perennial represented with P, transitional represented with T or intermittent represented withI. The brown color shows that rivers flowing all the time could shift to regimes without flow for a period of time, while the green color indicates the opposite. This model was put forward by WaterGAP. Image source Wikimedia. Creative Commons Attribution-Share Alike 3.0 Unported license. Author Petra Döll}

Aquatic and near-shore habitat structure include substrate, water depth, current, velocity, spawning and nursery places, riparian stability and habitat diversity. Changes in habitat structure and function can be caused by modifications in the shapes of an area (morphology), condition of banks and upland areas, presence or absence of vegetation and quality of substrates.

Any Change in habitat structure can affect the diversity and amount of plant and animal species present in the habitat (species composition and abundance).change in habitat structure can affect the nearest and resting areas for aquatic and water dependent species since most species depend on these water source for survival and procreation. Also any change in habitat can affect the stream flow or meander, from relatively curvy to straight channels. Water is known to create their own path way if there is no path way for them to flow or if the path way is small and by so doing water changes its routes sometimes thereby causing new landmarks to form.

Energy source

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Source of energy include organic materials entering a water resource from banks to upland area, referred to as the riparian zone, the process of photosynthesis and the seasonal pattern of available energy from sunlight.

The energy sources within a watershed depends on two processes which are mainly photosynthesis and metabolism. Photosynthesis which is the conversion of light energy to chemical energy takes place in plants. Metabolism (which is the use of chemical energy to sustain life form) occurs in all living things.

These processes are disrupted when light energy is not effectively transmitted or when chemical energy in the form of organic materials and nutrients is not present in large quantities enough to sustain the food web.

The food web depends on maintaining a sufficient supply of energy in the system. Changes to the energy source within the system may have serious consequences which include food scarcity, genetic deterioration of fish and animal species, invertebrate’s deficit and plant and animal species distribution.

Even As we consider land use changes within the watershed, remember that each modification to watershed sources can influence one or more of these factors. There is a huge out flow from rural areas to urban areas for various reasons, the most important being occupation.

Therefore, there is an intense pressure on urban areas for infrastructure and related development, sometimes, it becomes difficult to have a planned growth of cities of which the most affected are the water sector, which include water supply, storm water and sewage. As cities expand, more and more natural streams and water bodies are ill-treated and these become the most neglected water courses.

Climate

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Climate of an area affects the watershed of that area directly by the distribution of rainfall and temperature. The variations in rainfall can be described by the intensity and type of storms that occur in the geographic region because they play a big role in influencing the ground water recharge, the stream flow and the flooding pattern of the geographic area. If the rainfall is light and extends over a long duration, it will have more time to infiltrate the soil and help to replenish the already used-up ground water supply.

^{Classification of climate. Image source Wikimedia. Creative Commons Attribution-Share Alike 2.5 Generic, 2.0 Generic and 1.0 Generic license. Contributed by Peter Halasz}

However, high intensity thunderstorms that deposits large volumes of rainfall in a relatively short period of time can cause rapid overland runoff and flash flooding of rivers and streams

Conclusion

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There are countless treats to water sources today globally especially its quality and habitat due to urbanization and these include the non-point source pollutants which is critical to watershed and the health of man. The urban environment contributes to the majority of non-point source pollution into the receiving water bodies. Pollutants that originates from diffuse source are known as non-point source pollutants because the exact point where the pollutant originated from cannot be identified. Such pollutant remain a major issue for water ways because the inability to trace their sources hinders any attempt to limit or stop the pollution.

In urban topography, issues of soil loss through erosion, from construction site for example and nutrient enhancement from lawn fertilizers is a big issue today in our immediate environment. Point source pollution, such as effluents from waste water treatment plants and other industries play a much larger role in non-point pollution. Water and its contaminants are also quickly transported from urban areas into water bodies, this usually occurs when the surface runoff occurs on hard surfaces like tarred and concrete surfaces (example, roads). When this happens, the streams are polluted.

The all round effects emanating from all urban residential activities are also significant nonpoint source direct and indirect pollutants which includes household chemicals , paints and solvents, fertilizers, pesticides and herbicides used on gardens and lawns ,nutrients and fecal matters from septic systems, domestic animals waste ,metals and toxins from wash water, oil and grease , antifreeze agents, transmission and brake fluids and fuels from automobile maintenance all affect watershed sources.
Water plays a huge part of human survival here on earth and as such we need to protect all our sources of water.

Till I come your way next time, keep steeming and keep winning.

Gracias @prettyprecy

REFERENCES

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1. Watershed -Wikipedia
2. Watershed -usgs
3. Groundwater -Wikipedia
4. Natural flow regimes -silverchair

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