This study demonstrates that the amount of nutrients leaving an intact forest ecosystem is controlled by the plants. Results of the Hubbard Brook studies assess natural ecosystem dynamics and provide insight into the mechanisms by which human activities affect ecosystem processes. Concept 54.5 The human population is disrupting chemical cycles throughout the biosphere activities and technologies have disrupted the trophic structure, energy flow, and chemical cycling of ecosystems worldwide. The human population moves nutrients from one part of the biosphere to another. Human activity intrudes in nutrient cycles. • Nutrients from farm soil may run off into streams and lakes, depleting nutrients in one area, causing excesses in another, and disrupting chemical cycles in both places. Humans also add entirely new materials—many toxic—to ecosystems. In agricultural ecosystems, a large amount of nutrients are removed from the area as crop • biomass. After a while, the natural store of nutrients can become exhausted. The soil cannot be used to grow crops without nutrient supplementation. Nitrogen is the main nutrient lost through agriculture. • Plowing and mixing the soil increase the decomposition rate of organic matter, releasing usable nitrogen that is then removed from the ecosystem when crops are harvested. Recent studies indicate that human activities have approximately doubled the worldwide • supply of fixed nitrogen, due to the use of fertilizers, cultivation of legumes, and burning. This may increase the amount of nitrogen oxides in the atmosphere and contribute to atmospheric warming, depletion of ozone, and possibly acid precipitation. The key problem with excess nitrogen seems to be critical load, the amount of added • nitrogen that can be absorbed by plants without damaging the ecosystem. Nitrogenous minerals in the soil that exceed the critical load eventually into groundwater or run off into freshwater and marine ecosystems, contaminating water supplies, choking waterways, and killing fish. Lakes are classified by nutrient availability as oligotrophic or eutrophic. • In an oligotrophic lake, primary productivity is relatively low because the mineral nutrients required by phytoplankton are scarce. Overall productivity is higher in eutrophic lakes. Human intrusion has disrupted freshwater ecosystems by cultural eutrophication. • Sewage and factory wastes and runoff of animal wastes from pastures and stockyards have overloaded many freshwater streams and lakes with nitrogen. This results in an explosive increase in the density of photosynthetic organisms, released from nutrient limitation.
This study demonstrates that the amount of nutrients leaving an intact forest ecosystem is controlled by the plants. Results of the Hubbard Brook studies assess natural ecosystem dynamics and provide insight into the mechanisms by which human activities affect ecosystem processes. Concept 54.5 The human population is disrupting chemical cycles throughout the biosphere activities and technologies have disrupted the trophic structure, energy flow, and chemical cycling of ecosystems worldwide. The human population moves nutrients from one part of the biosphere to another. • Human activity intrudes in nutrient cycles. Nutrients from farm soil may run off into streams and lakes, depleting nutrients in one area, causing excesses in another, and disrupting chemical cycles in both places. Humans also add entirely new materials—many toxic—to ecosystems. • In agricultural ecosystems, a large amount of nutrients are removed from the area as crop biomass. After a while, the natural store of nutrients can become exhausted. The soil cannot be used to grow crops without nutrient supplementation. • Nitrogen is the main nutrient lost through agriculture. Plowing and mixing the soil increase the decomposition rate of organic matter, releasing usable nitrogen that is then removed from the ecosystem when crops are harvested. • Recent studies indicate that human activities have approximately doubled the worldwide supply of fixed nitrogen, due to the use of fertilizers, cultivation of legumes, and burning. This may increase the amount of nitrogen oxides in the atmosphere and contribute to atmospheric warming, depletion of ozone, and possibly acid precipitation. • The key problem with excess nitrogen seems to be critical load, the amount of added nitrogen that can be absorbed by plants without damaging the ecosystem. Nitrogenous minerals in the soil that exceed the critical load eventually into groundwater or run off into freshwater and marine ecosystems, contaminating water supplies, choking waterways, and killing fish. • Lakes are classified by nutrient availability as oligotrophic or eutrophic. In an oligotrophic lake, primary productivity is relatively low because the mineral nutrients required by phytoplankton are scarce. Overall productivity is higher in eutrophic lakes. • Human intrusion has disrupted freshwater ecosystems by cultural eutrophication. Sewage and factory wastes and runoff of animal wastes from pastures and stockyards have overloaded many freshwater streams and lakes with nitrogen. This results in an explosive increase in the density of photosynthetic organisms, released from nutrient limitation.
AP%20Biology%20SUMMER%20WORK1.docx