Freshwater ecosystems streams

In 1947, Patrick established a new department of limnology (the study of lakes, ponds, and streams) at the academy, a department that is now known as the Patrick Center for Environmental Research. The purpose of the department has been to study the structure and function of freshwater ecosystems, including rivers, lakes, and wetlands, along with the impact of human activities on these systems. Patrick served as curator of the center and chair of the Department of Limnology at the academy for more than decades. In 2003, at the age of 94, she still held the titles of Senior Scientist and Francis Boyer Chair of Limnology at the academy. 

In freshwater ecosystems, particularly streams and wetlands, biofilms account for a large portion of heterotrophic metabolism, as well as primary production (Edwards etal., 1990 see Chapter 12), acting as both sources and sinks for DOM. As the depth of the overlying water in the system increases, attached communities account for a declining share of system metabolism. 

Freshwater ecosystems range in size from large lakes and rivers to small streams and ponds. All can be exposed to environmental contaminants, but risk assessment tends to focus on static water bodies, the rationale being that these provide a realistic worse case. But do they ... 

Surface freshwater ecosystems consist of wetlands (e.g., bogs, fens, marshes, swamps, prairie potholes, etc.), streams, lakes (and artificial reservoirs), and rivers. Surface freshwater ecosystems receive most of their Nr from their associated watersheds, from atmospheric deposition, and from BNF within the system. There is hmited potential for Nr to accumulate within surface-water ecosystems, because the residence time of Nr within surface waters, like the water itself, is very brief. Residence times may be relatively longer in the sediments associated with wetlands and some larger lakes but are still short when compared to terrestrial ecosystems or the oceans. 

About 70% of the Earth s surface is covered by water much of which occurs in the oceans, estuaries, and freshwaters (ponds, streams, rivers, and lakes). These waters are used for many purposes such as recreation and transportation, as sources of drinking water (sometimes without any form of treatment, particularly in developing countries), and for industrial activities and irrigation on farmlands. Surface waters are also important ecosystems from which finfish, shellfish, and macroalgae are harvested, and in which a variety of organisms are cultured. 

The most evident damage from acid depositions is to freshwater lake and stream ecosystems. Acid depositions can lower the pH of the water, with potentially serious consequences for fish, other animal, and plant life. Lakes in areas with soils containing only small amounts of calcium or magnesium carbonates that could help neutralize acidified rain are especially at risk. Few fish species can survive the sudden shifts in pH (and the effects of soluble... 

Kaplan and Newbold (2003) have provided an updated review of the abundances of low-molecular-weight organic compounds in freshwaters, with emphasis on their metabolism in stream ecosystems. They reported that the DOC in an average river includes —1% free sugars, 0.05% free amino acids, 3.3% carboxylic acids, 0.02% phenols, and 0.2% hydrocarbons. Collectively, these identifiable compounds account for less than 7% of the DOC in unpolluted freshwaters. 

The estimated primary production (in terms of C content) for various aquatic ecosystems is shown in Table 3.3. Freshwater primary production, in lakes and streams, amounts to a little over 1% of total aquatic primary production. Phytoplankton account for c.95% of marine primary production, which totals c.40GtCyr-1, whereas coastal ecosystems make relatively minor contributions. Important macrophytes in intertidal zones include Rhizophora in mangrove swamps, turtle grass... 

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