Effects of arsenic on nutrient dynamics of grassland microcosms and field plots

Grassland field plots were compared to two sizes of excised microcosms (15 and 30 cm diameter) and 30-cm diameter homogenized microcosms to assess the effects of As on soil-plant nutrient dynamics. The goal of this experiment was to determine the feasibility of using microcosms for screening chemicals which are potentially toxic to terrestrial ecosystems. All experimental units were treated with As, at rates of 0, 0.5, and 5.0 mg cm^?2, by superficial application of dissolved Na₂AsO₄. Calcium, PO₄-P, NO₃-N, dissolved organic carbon (DOC), and NH₄-N were determined in soil leachate and soil extracts. Greater loss of PO₄-P, NO₃-N, NH₄-N, and DOC occurred via soil leachate from microcosms treated with the greatest level of As relative to untreated microcosms. Field plots were unaffected by As treatment. Excised microcosms were found to be more representative of field plots in reflecting microbial dynamics than were homogenized microcosms. Thus excised microcosms were recommended for testing potentially hazardous chemicals.     

Loss of Ca and NO3-N from terrestrial microcosms as an indicator of soil pollution

Ion separation of acid air pollutants out of snow causes sudden, deep pH-drops in lakes and running waters at an early stage of snowmelting. These pH-drops have drastic effects on fish populations and are suggested to be the main cause of Sphagnum invasion and changes in the microflora already at an early stage of acidification, i.e. when summer pH-values are about 6. These effects in turn reduce the nutrient recycling and accelerate the acidification process.     

Behavior of heavy metals in forest microcosms: II. Effects on nutrient cycling processes

Effects of heavy metals on forest nutrient cycling processes were investigated using intact forest microcosms. Baghouse dust from a primary Pb smelter in southeastern Missouri was applied on the microcosms to approximate one annual deposition of metals at 0.4 km from the smelter. Contaminated litter from a forest adjacent to the smelter was also placed on the microcosms. Total dosage of Pb, Cd, Zn, and Cu was 11.0, 0.128, 0.748, and 0.161 mg cm^?2, respectively. Sustained increases in leaching rates of Ca and NO₃-N were found in microcosms amended with heavy metals. After 20 mo, extractable Ca, NH3-N, NO₃-N and dissolved organic carbon (DOC) were significantly lower in treated soil to a depth of 5 cm. In addition, extractable NH₃-N, NO₃-N and DOC were significantly lowered to a depth of 10 cm. Results from this experiment indicate that forest microcosms can be used for determining the effect of heavy metals on forest ecosystems.     

Behavior of heavy metals in forest microcosms

Transport and distribution of heavy metals were determined in soil and vegetation (Acer Rubrum) of intact forest microcosms. Litter from a contaminated forest and baghouse dust from a primary Pb smelter were applied to three of the microcosms, while three uncontaminated microcosms served as controls. Total dosages for Ph, Cd, Zn, and Cu on the treated microcosms were 11.0, 0.128, 0,748, and 0.161 mg cm^?2, respectively. All metals were mobilized in soil and were enriched in at least one tissue component of Acer rubrum. Enrichment of Pb, Cd, and Zn occurred in all Acer tissues; Cu enrichment was found only in leaves. Uptake of metals by Acer rubrum was similar to a contaminated forest in southeastern Missouri and decreased in order: Zn, Cu, Cd, and Pb. Results of this experiment indicate that intact microcosms may be useful in assessing uptake and mobility of toxic chemicals which may be applied to forest ecosystems.     

Monitoring terrestrial ecosystems by analysis of nutrient export

Current methodology for environmental impact assessment relies heavily on population parameters to detect ecological effects of perturbation. We believe that recent advances in ecosystem analysis permit the identification of monitoring points that reflect changes in the total system. Focusing on mechanisms of ecosystem homeostasis, we suggest soil nutrient loss as a sensitive, holistic measure of ecological effects. In three separate studies, attempts were made to detect the effects of toxic substances by monitoring relevant population parameters. In each case, disturbance could be detected in nutrient cycling, but no significant change was evident in the population/community parameters. These results indicate that indices of total ecosystem function may be feasible.     

Comparison of carbon dynamics of three microcosm substrates

Microcosms are being examined as potential tools to assess toxic chemical effects on populations, trophic chains, processes, and ecosystems. The suitability of three microcosm substrates (intact soil, homogenized soil, and sand-soil) as analogs of soil was tested by comparing CO₂ efflux, dissolved C turnover, and soil C pool turnover among microcosm substrates. Carbon dynamics of intact soil microcosms were more predictable than those of other substrates. Microcosm units constructed from intact soil cores excised from the ecosystem of interest are recommended for assessment of soil processes or their potential disruption. Total C dynamics, rather than CO₂ efflux alone, should be monitored in soil microcosms to provide an accurate measure of soil processes.