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pH’s were greater than 4.8, and, in western Minnesota, they were greater than 7.0. The samples that had high pH’s also had high concentrations of total inorganic carbon and calcium and were in the area that received the lowest amount of precipitation. These high pH’s may, therefore, reflect acid neutralization by dustfall derived from the alkaline soils in the area. Patterns for nitrate, lead, and iron loading are similar to those of ph and may reflect some interrelationship. Many constituents showed local anomalies, although it was not the original intent of this study to assess them. Local deviation from regional patterns is exemplified by fluoride deposition (fig. 2). High fluoride deposition generally occurred downwind from urban and industrial centers where the prin
cipal users of flouride are the iron and steel, electronics, and chemical industries.
Finally, the validity and usefulness of these data may be tested by comparing them to the distribution of atmospheric deposition reported from other networks. The deposition pattern of hydrogen ion (mass per unit area) from this study agrees with that for wet deposition (averaged for 1978) from the Canadian Network for Sampling Precipitation. Furthermore, during late fall 1979 and winter 1980, the regional pattern for wet deposition from the Geological Survey study is similar to that of the National Atmospheric Deposition Program, excluding Minnesota and western Wisconsin where, as mentioned previously, the acidic atmospheric deposition may have been neutralized by dustfall.
l l l 94° 92° 90“ Figure 1.— The spatial distri
bution of ph in bulk precipitation in the NorthCentral and Eastern United States during the 1980-81 winter. (Modified from fig. 14A, U. 8. Geological Survey Circular 874.)
Trends in Quality of U.S. Streams:
A search for evidence of effects of acid precipitation on stream waters was made by the U.S. Geological Survey using data from Benchmark Network sites of the Geological Survey. (This "network” was established in 1958 to gather data on streams in basins which are little affected by manmade changes in the environment. It was determined that data obtained from these basins could be used to document natural changes with time and thereby provide a better understanding of the hydrologic structure of natural basins. in addition, the network could provide a comparative base for studying the effects of man on the environment.) The data gathered from the 51 streams and lakes of the network would not be as likely to be affected by population growth, industrial development, or other human activities as would data gathered from less isolated sites; however, they might show the effects of acid precipitation or other atmospheric fallout.
Although a number of the stream basins had high enough buffering capacity to mask the effects of precipitation acidity, evidence for small, but geographically, widespread changes in sulfate and alkalinity was noted (fig. 3). The pattern observed in streams expected to be sensitive to the effects of precipitation on water quality was that of no change or small increases in sulfate in the
western, central, and southeastern parts of the country, and no change or small decreases in alkalinity in the same regions. This pattern would be consistent with a picture of slightly increased contributions of sulfuric acid to precipitation and a resulting slight loss of buffering capacity in the streams. The opposite pattern was exhibited in the Northeast-sulfate either did not change or decreased slightly, while alkalinity either did not change or increased slightly. This pattern would be consistent with a picture of slightly decreased contributions of sulfuric acid to precipitation and a resulting slight recovery of buffering capacity in the streams in the Northeast.
Acidification of surface waters due to acid precipitation can be expected to occur only in watersheds that have little buffering capacity, either natural or provided by human activities. Even in these sensitive waters, little change in acidity will be observed during the period when the buffering capacity of the watershed is being exhausted. When this has occurred, however, acidification of the water body will progress much more rapidly, even with precipitation acidity remaining the same. Measurement of alkalinity probably is the best way to detect a progressive change in the buffering capacity of a body of water.
Drainage basin of the Apalachiuo/a, Chattahoochee, and Flint Rivers in Florida, Georgia, and Alabama.
Apalachicola River-Quality Assessment
The Apalachicola was one of the rivers selected for study under the U.S. Geological Survey’s River-Quality Assessment Program. The program was established to define the character, interrelationships, and causes of existing river-quality conditions and to devise and demonstrate the approaches needed for developing technically sound information for use by planners to evaluate alternatives for river-quality management.
The quality of water in a river is affected by two factors: the unique hydrology of a river basin and man's development and use of the land and the water resources. In the broadest context, the river-quality assessments carried out by the Geological Survey are problem-oriented approaches for obtaining the needed information.
The Apalachicola River meanders 106 miles through northwestern Florida to Apalachicola Bay on the Gulf of Mexico. It is a good example of a multi use waterway system. The area's principal commercial activities, barge traffic, timber harvest, land development, and commercial fishing in the Apalachicola Bay, often require different management practices for optimum returns in this river basin.
A flood-plain forest of 175 square miles borders the Apalachicola River in Florida. It has sustained a viable timber industry since the early 1800's. The bottom-land hardwood forest contains over 40 species of trees in a largely undisturbed wetland. This forest was an integral part of the broad interdisciplinary scientific investigation conducted as part of the Geological Survey’s assessment. Statistical surveys of tree abundance and distribution were coupled with measurements of leaf production to provide estimates of total production of organic litter in the flood-plain environment.
Annual flooding overflows the natural levees and covers the flood plain. In many areas, the water velocities are sufficient to transport the decaying leaf litter into the river and ultimately to Apalachicola Bay. The nutrients and litter material form the basis for one of the most productive estuarine systems in North America. Oysters, shrimp, blue crab, and fish depend on the seasonal materials transported by the floods coming out of the Apalachicola River wetland system. The Apalachicola RiverQuality Assessment developed methods and techniques to quantify the flood-plain contribution to the 1980-81 annual load of nutrients and detritus (organic particulate material) to the bay. Results obtained in the river were compared with estimates of litterfall transported in the flood plain. Such estimates were based on new methods developed during the study. During a 1-year period, approximately 30,000 tons of organic carbon entered the river from the flood plain.