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ENV CHAPTER 7-1: FRESHWATER ECOSYSTEMS
The kinds of things that live in an aquatic ecosystem are mainly determined by the water’s salinity – the amount of salt in the water. Freshwater – no salt – lakes, ponds, rivers, streams, wetlandsSaltwater (marine) – salt – marshes, swamps, reefs, oceans Temperature, amount of O2, and nutrients determine which organisms live where There are 3 groups of aquatic organisms:1. Plankton – tiny organisms that float near the surface of the watera. phytoplankton – plants – producers of the aquatic ecosystemb. zooplankton – animals2. Nekton – free-swimming organisms like fish, turtles, whales.3. Benthos – bottom-dwellers like mussels and worms. Often live attached to things. Lakes and pondsCan be structured into horizontal and vertical zones1. Littoral zone – nutrient-rich, near the shore, lots of light, life is diverse and abundant2. Benthic zone – bottom, cooler, darker water, lots of decaying material and decomposers Animals that live in the different regions have adaptations that allow them to do well there. Nutrients affect lakes.Eutrophication – an increase in the amount of nutrients in an aquatic ecosystem. If there are lots of nutrients, there are lots of plants, then decaying things, and bacteria. The bacteria use a lot of the O2 and eventually suffocate the orgs that need O2.Eutrophication is accelerated by runoff that contains fertilizers, waste, etc. Freshwater wetlandsAreas of land covered w/ fresh water for at least part of the year – marshes and swamps.Most are located in the southeast US. Occur on low, flat lands.1. marshes – contain non-woody plants. Benthic zones are nutrient rich, contain plants, decomposers and scavengers-brackish – has slightly salty water-salt marshes – saltier water2. swamps – dominated by woody plants. Occur on flat, poorly drained land often near streams important environmental functions of wetlands:-they act like filters – they remove pollutants from water that flows through them and improve the quality of water downstream-control flooding – they absorb extra water when rivers overflow-many fish species use these areas for feeding and spawning- they provide homes for migratory animals- the vegetation traps C which would otherwise be released as CO2 into the atmosphere RiversMany originate from snow melt in the mountains.-at the head (where it starts) – water is colder, full of O2, runs fast, and the riverbed is shallow-downstream – becomes wider, warmer, slower, less O2 A river changes w/ the land and climate it goes through. Runoff from the surrounding land also affects the river.Life in a river:Near the beginning – mosses anchored by rhizoids, trout, minnows, no plankton b/c the current is too strongFarther down – plankton, plants, lots of sediment, and other fish.Rivers are in danger from industries dumping in them, runoff of pollutants, dams that alter the ecosystem.ENV CHAPTER 7-2: MARINE ECOSYSTEMS
Marine ecosystems are located in costal areas and open oceans-Costal – organisms adapt to different water levels and salt levels-Ocean – organisms adapt to diff temps, sunlight, nutrients Costal wetlands – areas covered by salt water for all or part of the time- provide habitat for fish and wildlife-absorb excess rain to prevent flooding- filter the water- provide recreation areasEstuaries - where freshwater from a river mixes w/ salt water from the ocean- They are very productive ecosystems b/c they constantly receive fresh nutrients form the river and ocean. - The surrounding land protects the estuary from the force of ocean waves - They support many orgs b/c the water is shallow and so receives plenty of light for photosynthesis, and there are plenty of nutrients.- Organisms that live there are able to tolerate variations in salinity b/c the salt content of the water varies as fresh and salt water mix and as tides go in and out. - threatened by pollution from sewage, industrial waste, agricultural runoff. Salt marshes – along the Gulf of Mexico and the Atlantic coast. -they develop in estuaries where rivers deposit mineral-rich mud. -Dominated by marsh grasses. -Provide breeding and feeding grounds. Mangrove swamps – along the coastal areas of tropical and subtropical zones. -Dominated by mangrove trees. -Help prevent erosion and damage from storms. Rocky and sandy shores-Rocky shores have more plants. - Sandy shores dry out when the tide goes out Barrier islands run parallel to the shore and help protect the mainland and coastal wetlands. Coral reefs – Limestone ridges built by tiny coral animals called coral polyps that secrete limestone skeletons.-Are among the most diverse ecosystems- Live in clear warm salt water where there is plenty of light for photosynthesis – so in shallow tropical seas.-The reef forms cracks and crevices that act as habitats for tons of orgs- Fragile ecosystems – extremely sensitive to temperature, nutrient level, disturbance. Oceans- Most of the life is in the shallow coastal waters b/c that’s where all the light is (remember producers need light for photosynthesis) so producers and the consumers that eat them are all concentrated there. - Phytoplankton, zooplankton, fish, marine mammals live there.- As a result, open ocean is among the least productive ecosystems.- Deep in the ocean it’s dark so most food consists of dead things that fall from the surface. - Decomposers, filter-feeders and the orgs that eat them live on the bottom.
-Threats – pollution, overfishing
Arctic and antacrtic ecosystems – depend on marine ecosystems b/c nearly all the food comes from the ocean. Too cold for plants to grow so the plankton are the producers that start off the food chain.
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