Transport and loss of nitrous oxide in soil water after forest clear-cutting.

Whole-tree harvesting increased the concentration of nitrous oxide dissolved in soil water by two orders of magnitude over the concentration expected in equilibrium with the atmosphere. In contrast, the nitrous oxide content of soil water in an intact, second-growth forest was close to the expected theoretical value. Nitrous oxide, produced at active sites in the soil, dissolves in soil water and is transported to seeps and streams where it rapidly degasses from the solution and is released into the atmosphere. This loss of nitrous oxide after clear-cutting is not important to the nitrogen economy of the site; however, it may be important to the global atmospheric budget of nitrous oxide. Sources of nitrous oxide may have been overlooked because nitrous oxide emissions can be separated in time and space from the sites of the most intense production of nitrous oxide.

Phosphorus cycling in a northern hardwood forest: biological and chemical control.

Phosphorus is tightly conserved within the northern hardwood forest ecosystems at Hubbard Brook, New Hampshire. Detailed analyses of the soil system indicate that biological and geochemical processes, stratified within the profile, regulate phosphorus retention.

Natural disturbance and the steady state in high-altitude balsam fir forests.

Wind-induced, cyclic waves of death, regeneration, and maturation constantly move through the high-altitude balsam fir forests in the northeastern United States. Biomass and productivity relations, species diversity, and nutrient cycling patterns are closely tied to this cycle of disturbance. Disturbance is thus an integral part of the long-term maintenance of this ecosystem. Since forests of this type normally include all phases of the disturbance-regeneration cycle, they may constitute a steady-state ecosystem in equilibrium with the surrounding environment.

Nitrogen budget for an aggrading northern hardwood forest ecosystem.

Long-term analyses of the structure and function of a northern hardwood ecosystem have resulted in measurement of the salient features of the nitrogen cycle. These data allow an evaluation of the importance of the various components and provide a framework for more efficient forest management.

Role of Erythronium americanum Ker. in Energy Flow and Nutrient Dynamics of a Northern Hardwood Forest Ecosystem.

The aboveground activity of the spring herb, Erythronium americanum, is restricted to the period between snowmelt and forest canopy development. Its phenology and production capacity closely adapt the species to this temporal niche in northern deciduous forests. While E. americanum has a minor effect on energy flow, it may reduce losses of potassium and nitrogen from the ecosystem during the period of maximum removal by incorporating these elements in accumulating biomass. Later, during the summer, these nutrients are made available when the above-ground, nonperennating tissues decay.

Acid rain: a serious regional environmental problem.

At present, acid rain or snow is falling on most of the northeastern United States. The annual acidity value averages about pH 4, but values between pH 2.1 and 5 have been recorded for individual storms. The acidity of precipitation in this region apparently increased about 20 years ago, and the increase may have been associated with the augmented use of natural gas and with the installation of particle-removal devices in tall smokestacks. Only some of the ecological and economic effects of this widespread introduction of strong acids into natural systems are known at present, but clearly they must be considered in proposals for new energy sources and in the development of air quality emission standards.

Barrier island forest ecosystem: role of meteorologic nutrient inputs.

The Sunken Forest, located on Fire Island, a barrier island in the Atlantic Ocean off Long Island, New York, is an ecosystem in which most of the basic cation input is in the form of salt spray. This meteorologic input is sufficient to compensate for the lack of certain nutrients in the highly weathered sandy soils. In other ecosystems these nutrients are generally supplied by weathering of soil particles. The compensatory effect of meteorologic input allows for primary production rates in the Sunken Forest similar to those of inland temperate forests.

Revegetation following Forest Cutting: Mechanisms for Return to Steady-State Nutrient Cycling.

Dense stands of a woody, successional species, Prunus pensylvanica L., develop rapidly, with early closure of canopy and rapid attainment of high values of net annual production and nutrient accumulation. Such rapid growth following disturbance tends to minimize losses of nutrients from the ecosystem, thus promoting a return to steady-state cycling characteristic of a mature forest.

Nitrification: importance to nutrient losses from a cutover forested ecosystem.

The nitrate concentration (weighted average) in stream water from an experimentally deforested watershed increased from 0.9 milligram per liter before removal of the vegetation to 53 milligrams per liter 2 years later. This nitrate mobilization, presumably due to increased microbial nitrification, was equivalent to all of the other net cationic increases and anionic decreases observed in tae drainage water.

Nutrient loss accelerated by clear-cutting of a forest ecosystem.

The forest of a small watershed-ecosystem was cut in order to determine the effects of removal of vegetation on nutrient cycles. Relative to undisturbed ecosystems, the cut ecosystem exhibited accelerated loss of nutrients: nitrogen lost during the first year after cutting was equivalent to the amount annually turned over in an undisturbed system, and losses of cations were 3 to 20 times greater than from comparable undisturbed systems. Possible causes of the pattern of nutrient loss from the cut ecosystem are discussed.

Nutrient cycling.

The small-watershed approach to problems of nutrient cycling has these advantages. (i) The small watershed is a natural unit of suitable size for intensive study of nutrient cycling at the ecosystem level. (ii) It provides a means of reducing to a minimum, or virtually eliminating, the effect of the difficult-to-measure variables of geologic input and nutrient losses in deep seepage. Control of these variables makes possible accurate measurement of nutrient input and output (erosion) and therefore establishes the relationship of the smaller ecosystem to the larger biospheric cycles. (iii) The small-watershed approach provides a method whereby such important parameters as nutrient release from minerals (weathering) and annual nutrient budgets may be calculated. (iv) It provides a means of studying the interrelationships between the biota and the hydrologic cycle, various nutrient cycles, and energy flow in a single system. (v) Finally, with the small-watershed system we can test the effect of various land-management practices or environmental pollutants on nutrient cycling in natural systems.

The Calcium, Magnesium, Potassium, and Sodium Budgets for a Small Forested Ecosystem.

The balance of calcium, magnesium, potassium, and sodium was studied in six watersheds of the Hubbard Brook Experimental Forest at West Thornton, New Hampshire. These watersheds are characterized by a near climax, northern hardwoods ecosystem, humid continental climate, and acid metamorphic rock. Bedrock in the area is considered to be watertight. Weekly samples of precipitation and stream water were collected from June 1963 through May 1965. Cation analyses were made by atomic absorption spectrophotemetry. Precipitation was about 117 cm during 1963-64 and 95 cm during 1964-65 and did not differ significantly in amount with elevation. Loss of water by runoff from the system was about 68 cm during 1963-64 and 49 cm during 1964-65. Evapotranspirational losses were calculated at 49 cm in 1963-64 and 46 cm in 1964-65. About 37% of the total annual runoff ocurred in April and less than 0.2% in September. Concentration of Ca+ + , Mg+ + , K+ , and Na+ in weekly precipitation samples was variable. The annual weighted average values (mg/liter) were : 1963-64, Ca 0.26, mg 0.06, K 0.21, Na 0.09; 1964-65, Ca 0.30, Mg 0.12, K 0.19, Na 0.22. Differences were not related to elevation. The contribution of cations from dry fallout was negligible. Cation content of stream water was relatively very low. The weighted average content for the entire area (mg/liter) was Ca 1018, Mg 0.38, K 0.26, Na 0.87 during 1963-64; and Ca 0.80, Mg 0.38, K 0.22, Na 0.91 during 1964-65. In general, the cationic concentrations in drainage water were constant although discharge or water varied greatly. Statistically, the relationship between concentration and discharge was not significant for Ca+ + and Mg+ + in any of the watersheds, but was inversely significant for Na+ , and was possibly direct for K+ in a few instances. The budget for dissolved cations was calculated from determinations of input (cation concentration times volume of precipitation) and output (cation concentration times volume of runoff.) During 1963-64 the average inputs in kg/ha were 3.0 Ca+ + , 0.7 Mg+ + , 2.5 K+ , and 1.0 Na+ , while the output averaged 8.0 Ca+ + , 2.6 Mg+ + , 1.8 K+ , and 5.9 Na+ . During 1964-65 the values were: input, 2.8 Ca+ + , 1.1 Mg+ + , 1.8 K+ , and 2.1 Na+ ; and output, 3.9 Ca+ + , 1.8 Mg+ + , 1.1 K+ , and 4.5 Na+ . Assuming that the vegetation is near dynamic equilibrium, the net losses of Ca+ + , Mg+ + , and Na+ represent conservative measurements of geochemical weathering in the system. The K+ budget is probably near balance.