Biomagnification & Watersheds

 Remember from our last notes that generally only 10% of the previous trophic levels’ energy gets passed up to the next level, while 90% of energy is given off to the environment in the form of waste, heat energy:

 Unfortunately, if the organism that the predator consumes contains a non-biodegradable toxin, the same ratio for the reduction of the toxin is not followed as for food. Due to the fact that such a toxin is non-biodegradable, this means that biological functions can not get rid of it. Thus, the only choice that remains is that the organism consuming the toxin will incorporate it into its body tissues, normally fat stores (Most of these accumulating toxins are fat soluble, and thus stored in fats for good).  When that organism is captured and consumed, its predator will consume the toxin and again will not be able to break it down biologically and so will either have to get rid of it through its waste (provided that the body can identify the toxin and get rid of it) or build it into its fat reserves (which is generally the case).

 In other words, instead of having only 10% of the food consumed passed on to the next trophic level, the opposite occurs and the toxin is in fact magnified approximately by 10% as it moves into the next trophic level. This is known as biomagnification. The food chain below illustrates this concept. The producer starts off with 0.01% of its body containing a non-biodegradable toxin like DDT or mercury  Producer (0.01%) ==> primary consumer (0.1%) ==> secondary consumer (1%) ==> tertiary consumer (10%)  This of course assumes that there is very little contact with other ecosystems (possibly a closed system) that would dilute the concentration of the toxin with food sources that are not contaminated.

 DDT is a powerful pesticide which was not biodegradable and influenced (in particular ocean based food webs) a large variety of ecosystems. Marine ecosystems were particularly a vulnerable target due to the amount of DDT that was being washed off of (through run-off) cultivated land into streams and eventually found concentrated in lake and ocean deltas where this contaminated sediment was deposited. DDT Case Study

 Implications for organisms that live on the top of the food chain, is that they will become vulnerable and generally die out due to the toxins effect. This happens also because organisms in the lower trophic levels that are affected to a lesser degree by the toxin can survive, but in a weakened state. This makes organisms with larger amounts of contamination easy prey for the higher levels.  Persistence is how long a chemical remains in the environment  scientists usually measure this in terms of a half-life (how long it takes for a chemical to degrade to half its original concentration). The half-life for DDT is 30 years, so even after the US has banned its use, it will still remain in the environment for several decades later.  Although the US has banned the use of DDT in our country, many countries still use it, especially those who have high levels of malaria (caused by mosquitos).

 Disturbances – any event caused by physical, chemical, or biological agents that results in changes in population size or community composition  Natural -> hurricanes, tornadoes, tsunamis, volcanoes, fires  Anthropogenic -> human settlements/development, agriculture, air pollution, clear-cutting forests, etc.  Watershed is an important place to conduct disturbance studies.  A Watershed = all the land of a given landscape that DRAINS into a particular stream, river, lake or wetland.  Ex. Chesapeake Bay Watershed Watershed Studies

What is a watershed?  A watershed is an area of land that drains to a particular body of water. We all live in a watershed: some, like the Chesapeake Bay's, are large, while others are small. Watersheds are sometimes called "basins" or "drainage basins."

 The Chesapeake Bay watershed stretches across more than 64,000 square miles, encompassing parts of six states — Delaware, Maryland, New York, Pennsylvania, Virginia and West Virginia — and the entire District of Columbia.  The Chesapeake's land-to-water ratio (14:1) is the largest of any coastal water body in the world. This is why our actions on the land have such a significant influence on the health of the Bay.

 Threading through the Chesapeake watershed are more than 100,000 streams and rivers — called tributaries — that eventually flow into the Bay

VA Rivers

 Largest estuary in the U.S. and faces some of the biggest environmental challenges:  Abundance of nutrients -> (esp. N & P) from sewage, animal waste, and fertilizers running off into streams. These increased nutrients cause algae growth to get out of hand (algal bloom) which can lead to even worse problems!  Increased Sediments -> from soil being washed away. Tiny sediments can stay suspended, causing water to be cloudy, which prevents sunlight from getting to aquatic plants (important habitat for blue crabs).  Chemicals from pesticides and pharmaceuticals (passing through human bodies). Some of these chemicals mimic the hormone estrogen -> scientists have noticed higher rates of “feminized” fish in the bay, as well as possible increased cancer rates in humans. Chesapeake Bay Status

 Action Plan : Developed in 2000 to reduce nutrients, sediments and chemicals entering bay!  As of 2010, all goals were being met, including reduced N, increased water clarity and increased blue crabs -> blue crab population increased 60% between 2009 and 2010 (largest in 13 years!)  Great inter-state collaboration and teamwork!  However, the 2014 data is not looking good. The blue crab populations are at their lowest (stock is said to be depleted, and minimum thresholds are barely met) in a long time. However, they are not being over-fished. Causes for this include the unusually cold winter, change in coastal currents, weather patterns, and natural predators. Management strategies are continuing to help populations increase this year! CB Action Plan

Resistance versus Resilience  Resistance- A measure of how much a disturbance can affect its flows of energy and matter. (If a disturbance does not affect the flow of E and matter much, it is very resistant!)  Resilience- The rate at which an ecosystem returns to its original state after a disturbance. (One that returns “quickly” would be very resilient!)  Restoration ecology- A new scientific discipline that is interested in restoring damaged ecosystems.

 Provisions - Goods that humans can use directly. Ex. Lumber, food, and medicine  Regulating services- The service provided by natural systems that helps regulate environmental conditions. Ex. Carbon storage (trees, etc)  Support systems- The support services that natural ecosystems provide such as pollination, natural filters and pest control.  Resilience - Resilience of an ecosystem ensures that it will continue to provide benefits to humans. This greatly depends on species diversity. (Ability to overcome disturbances).  Cultural services- Ecosystems provide cultural or aesthetic benefits to many people. Ex. Aesthetic beauty of nature/hike, intellectual gain from research Types of Ecosystem Services