this is the preview video for chapter 29 on energy flow and nutrient cycling in ecosystems we'll start with a brief introduction to nutrients and energy and then think more specifically about how energy flows through ecosystems and how nutrients cycle within ecosystems and then we'll finish up by looking at what happens when humans disrupt some of these natural processes in this chapter we'll be thinking about both biotic components those are things that are living and abiotic components those are all of the non-living aspects of an environment so climate light temperature water minerals those would all be abiotic one of the Key T homes in this chapter is that nutrients are going to be cycling both within ecosystems and between ecosystems and so if you look at the picture here if we follow the purple arrows we can see that they are both C cycling within and moving between different ecosystems energy in contrast flows through ecosystems and so it starts from the Sun and um it flows in a one-way Direction Through the ecosystems okay so when we think about how energy moves specifically um you probably already know that the main source of energy is coming from the Sun and we'll talk about how much of that sunlight actually reaches Earth how much is visible I how much is useful a lot of it actually is reflected back what does reach Earth is primarily used for photosynthesis so this is how plants convert solar energy into things like sugars which are then used by all of the other consumers in an ecosystem we'll be discussing how energy passes through ecosystems um in different levels these are called trophic levels and so each category of organism that uses energy has its own separate level and we'll be talking about the producers that are at the bottom these are typically the green plants we call these autotrofos they make their own energy and then everything above them is a consumer these are heterotrofos organisms that have to eat something else to get their energy the consumers that are directly eating the producers these are called the primary consumers we have secondary consumers tertiary consumers um Etc as keep going up higher in the trophic levels we'll be thinking about how much energy um different ecosystems contain and the amount of Life an ecosystem supports is determined by how much energy the producers in that particular place can capture um the energy that those photosynthetic organisms store is called net primary production and it varies between something like a grassland or a tropical rainforest or a Tundra we count the biomass as the dry biological material that's usually a good measure of how much energy is stored in the organism's bodies in that particular place and when you're trying to add all of this up total um a lot of things um influence it but mostly how productive a particular ecosystem is and how much area it actually covers we have um different food chain to describe the feeding relationships within communities and these happen both on land and in the water and so if you're thinking about a terrestrial ecosystem the plants are going to be the primary producer um and then things move up again primary consumer might be a caterpillar gets eaten by a bird um you know which might be um the secondary consumer eating the caterpillar the primary consumer um Etc in water-based ecosystems um you have uh some different uh sources of energy so the photosynthetic protests and bacteria are typically called phytoplankton and those are consumed by Zoo Plankton uh other protests and small shrimp-like crustations and then those Zoo Plankton get consumed by um lots of other consumers again moving up the food chain when we talk about a food web this is just showing a lot of the interconnect Ed food chains and actual feeding relationships in a community we'll be talking about omnivores so these are organisms that eat um a lot of different things and they can act both as you know primary and secondary and tertiary consumers and they're often you know eating um both plants and animals we'll talk about DET travores and these are debris eaters like this dung beetle and they are really important for helping to recycle materials um and then we'll also be mentioning decomposers so these are primarily fungus and bacteria they're often consuming the same um material as you know uh a Davore um and again they're just helping break things down um so they can be reused we'll mention how the energy transfer within ecosystems is terribly inefficient um so when you think about the number of calories that a producer makes and again producers are a tropes like this grass here um we can visualize this in an energy pyramid so the producers may make a lot the primary consumers consume a lot of it but they only store um a smaller section of it the secondary consumers then get a small fraction of what the primary consumers have and by the time you go up in the trophic levels only a very small amount of energy actually reaches the higher level consumers and so we call this the the 10% law for the energy uh transfer between trophic levels we'll also talk about biological magnification and how if there is a a substance especially in this producer level um it can be um concentrated as it moves up the food chain so we'll talk about this in the context of mercury um especially in uh marine ecosystems um and it's relevant to human health um as we are thinking about eating some of those um marine organisms the next section looks at nutrient Cycles at these Pathways that different nutrients follow as they move from their main um sources in the abiotic parts of the ecosystem through the living communities the biotic parts and and back again one of the Cycles we'll talk about is the water cycle moving from the reservoirs in the ocean um through the atmosphere to other reservoirs like lakes and rivers groundwater and back for the oceans again we'll also talk about the carbon cycle um how it has short-term reservoirs in the atmosphere and the oceans and then it moves through um producers uh you know we know plants capture carbon dioxide and they build it into sugars and then that carbon is going to move into the consumers um like this rabbit and then eventually um be exhaled and back into some of these reservoirs like the atmosphere and the oceans again and remember carbon atoms form the basis of all organic molecules on Earth so the carbon cycle is particularly important we'll also be looking at the nitrogen cycle the primary Reservoir is in the atmosphere and there are smaller reservoirs in things like the soil or water we'll talk again about uh ammonia um and how that's important both um as something that is a waste product excreted by consumers um and again how this is moving back and forth and cycling through different ecosystems nitrogen is also really important um it's the backbone of carbon um sorry not of carbon of proteins a lot of vitamins nucleotides like ATP and um DNA like nucleic acids we'll also mention the phosphorus cycle um one of its primary reservoirs is actually in rock and it's important in biological molecules um phol lipids and nucleic acids and it's really important in making the teeth and bones of different consumers we'll finish up this chapter by looking at some of the things that happen when humans muck up these nitrogen Cycles so um ancient peoples with uh small populations and relatively limited technology didn't have very much impact on nutrient Cycles worldwide but as human populations grow and we have the technology to now make very um dramatic alterations to our landscape we're really changing a lot of these nutrient Cycles so we'll be talking about the use of fossil fuels um the use of chemical fertilizers like you see um being sprayed on these fields and how those can disrupt the global nutrient cycles of things like nitrogen and phosphorus sulfur and carbon we'll be mentioning dead zones um which are these areas that can form in waters um here's pictured um off the Gulf of Mexico off the coast of Louisiana and these are often the result of enormous quantities of fertilizer that run off so fertilizer contains nitrates and phosphates they create an alal Bloom and then when those algae die the bacteria that break them down use up a lot of oxygen in the water which other species need they need that oxygen and the water and so um this is something that um the United States in particular has been battling for a long time and we'll also mention some other consequences of overloading nitrogen and phosphorous Cycles um in 2023 there is a giant seaweed Mass um that's been making the news um this particular type of seaweed um always uh grows in the Atlantic Ocean um in 2023 it is particularly large um spanning about 5,000 miles um and it's starting to wash up on beaches um in Florida and it's um uh proposed that runoff from the Mississippi River the Amazon and from uh Congo those extra nutrients are contributing um to that extra growth of the seaweed we'll also be talking about um acid rain um this is when sulfur and nitrogen cycle um H are overloaded and so the rain is actually a little bit more acidic than it used to be um part of this is from burning of fossil fuels and we'll be talking about some of the consequences both um to when that rain um hits forests whose plants can be particularly sensitive to pH and um even other things like man-made materials that are more degraded with acid rain we'll mention the Greenhouse Effect and so if you want the temperature to remain constant on planet Earth the amount of energy coming in has to be equal to the amount of energy leaving and we'll talk about how different greenhouse gases in the atmosphere can actually trap some extra heat and what the consequences are for that global warming um that we see evidence of occurring and that will lead us directly into climate change and we'll mention some of the consequences so um the warming atmosphere can cause things like more severe storms stronger hurricanes more rain or snow occurring in single storms um more frequent or longer droughts um more carbon dioxide um acidifying our oceans melting sea ice really imperiling species that depend on sea us like these polar bears that rely on those ice um chunks to raise their young all right that is it for the preview of chapter 29