hey everybody it's mr smeeds and today we'll be covering topic 1.6 which is the phosphorous cycle just like with the carbon cycle and the nitrogen cycle we'll be talking about how phosphorus moves between sources and sinks but we'll also be making some comparisons between the carbon cycle and the nitrogen cycle as we go through the phosphorus cycle today our objective today is to be able to explain the steps and reservoir interactions in the phosphorus cycle and the skill we'll practice at the end of the video is the one that we've been practicing the past couple days which is explaining relationships between characteristics of an environmental concept in a visual model setting so just like in the carbon cycle in the nitrogenous cycle the phosphorus cycle is the movement of phosphorus containing elements between sources and sinks so the two major reservoirs of phosphorus are rocks and phosphorus containing sediments so if we look at the diagram here we can see rocks that could be found in mountains or really in any ecosystem contain phosphorus in them and also sediments at the bottom of bodies of water or even sediments found in soil an important point to know is that the phosphor cycle is extremely slow when compared to the carbon cycle and nitrogen cycle this is for a couple reasons which we'll talk about now so the first one is that the two main reservoirs of phosphorus which again are rocks and sediments release phosphorus very slowly it's a process called weathering where wind and rain break down the rock and release phosphorus in a form called phosphate so that phosphate then has to be washed away from that rock or those sediments and into either aquatic ecosystems or into soil on land so that process takes a long time another reason that this is such a slow process is there's no gas form of phosphorus on earth and so what that means is that phosphorus has to be moving in this solid form in phosphate which has to be weathered from rocks and carried by water and that's just really slow so when we compare that again to the nitrogen carbon cycles there are gas phases of both of those cycles which move faster then finally an important point to understand is that because phosphorus cycles so slowly it's often a limiting nutrient in ecosystems so because it takes so long for the rocks to be weathered and for them to release their phosphorus which is then carried through runoff into either bodies of water or in the soil that's a really slow process and organisms therefore have less access to phosphorus now all organisms need phosphorus because it's a key element in atp which is an energy source for every living thing in dna and then for many animals it's a source of strength for their bones and for the enamel in their teeth now we'll talk about both natural and synthetic sources of phosphorus so the major natural source of phosphorus is the weathering of phosphorus containing rocks by the wind and the rain so the wind in the rain beat down on these rocks over time breaking them into smaller bits which results in the release of phosphate from these rocks the phosphate then dissolves into the rainwater and it's washed either into aquatic ecosystems or into terrestrial ecosystems so into the soil in an area so you can see this here in the diagram if we look at this big green circle again the phosphates are worn down from those rocks and then the wind and the rain will carry them either into a body of water or into a terrestrial ecosystem it's important to remember that this process is very slow and because of that phosphorus is a limiting nutrient in many different ecosystems meaning plant growth is dependent on how much phosphorus is available in terms of synthetic or human-made sources of phosphorus humans mine phosphate containing rocks out of the ground and then they add phosphates to either synthetic fertilizers or other products like detergents and cleaners so we can see this diagram here we'll dig up rocks that contain phosphorus take out the phosphorus and add phosphates to these products such as fertilizers or detergents so this creates an issue because when we have runoff from agricultural fields it can carry the phosphates that were in the soil into nearby bodies of water the same thing can happen if we're talking about detergents and cleaners because those can leave homes via their waste water and the phosphates in those detergents and cleaners can eventually enter natural bodies of water just like nitrogen phosphorus is absorbed from the soil by plant's roots and it's assimilated into plant tissues animals just like in the nitrogen cycle have to eat plants to take in phosphorus to their bodies or eat other animals that have eaten plants then we also have the excretion of animal waste or the decomposition of dead organic matter by soil bacteria and decomposers and that's going to return phosphorus to the soil so just like in the nitrogen cycle we have this mini loop that's formed here where we have assimilation of phosphorus into plants and then we have animals that eat those plants to take the phosphorus into their bodies when the animals and plants die that phosphorus is returned to the soil by decomposition just like in the nitrogen cycle next we'll talk about sedimentation and geological uplift so phosphorus does not dissolve super well into water which means that much of it precipitates out or forms solid phosphate sediments at the bottom of a body of water think about when you make kool-aid and you add too much sugar the water can only hold so much of that sugar so a lot of it forms crystallized sugar at the bottom that you can actually see and so this is similar to the way that phosphate will precipitate out of a water source and we call this act sedimentation so the act of forming phosphate sediments at the bottom of a body of water over time what we can see is that the weight of the water above those phosphate containing sediments will compress those sediments into sedimentary rock like limestone or sandstone geological uplift then is the process where tectonic plates collide and force new rock layers up to form mountains so this allows new rock to be exposed to the elements like wind and rain which then starts the weathering of phosphorus and we're basically back at the beginning of the cycle and lastly today we'll talk about a problem called eutrophication which results when a body of water receives too much nitrogen and phosphorus so because these elements are usually so limited having extra inputs of nitrogen or phosphorus can lead to eutrophication which literally means excess growth or excess nutrients and this can in turn lead to an algae growth or an algae bloom that covers up the surface of the water now these nitrogen inputs can often come from things like synthetic fertilizers that are applied to lawns or agricultural fields or when a body of water becomes contaminated with waste from humans or waste from animals because this waste is an organic compound they often contain both phosphorus and nitrogen so because the surface of the water is covered by these algae that blocks the sunlight from reaching the plants below the surface of the water and those plants die the algae themselves eventually die off and then the bacteria in the water use up oxygen to break down the algae and the other dead plants the reason that they use up the oxygen is because decomposition is an aerobic process so it requires them to use oxygen this loss of oxygen as the bacteria use it up results in the death of other aquatic species especially larger fish species that have high oxygen requirements then the bacteria break down those dead organisms and that uses up even more oxygen so pretty quickly we have something called a positive feedback loop positive feedback loop is where the outcome of the process drives the process to continue forward at an even faster rate so as we have less oxygen we have more organisms die which results in more bacteria breaking down those dead bodies using up even more oxygen and you can see how this quickly spirals out of control to create something called a dead zone where the water contains such little oxygen that virtually no life can be supported there anymore our practice frq for topic 1.6 today will involve the skill of using a visual model to explain relationships between different characteristics of an environmental concept so i want you to look at this model and choose two reservoirs that are shown in the model then i want you to describe how phosphorus moves between those two reservoirs alright everybody thanks for tuning in today don't forget to like this video if it was helpful subscribe for future apes video updates and check out other notes over here to the side and as always think like a mountain write like a scholar