Effects of watershed liming on the soil chemistry of Woods Lake,New York

The effects of watershed liming on the exchange complex of a forest soil were investigated at Woods Lake, in the west-central Adirondack Park, New York. Attempts to neutralize lake acidity via direct application of calcite during the 1980"s were short-lived due to a short hydraulic retention time. The Experimental Watershed Liming Study (EWLS) was initiated to investigate watershed base addition as a potentially more long-term strategy for mitigation of lake acidity. In this paper we discuss the changes in the exchangeable soil complex which occurred in response to the calcite addition and attempt a mass balance for calcite applied to the watershed.An extensive sampling program was initiated for the watershed study. Soil samples were collected from pits prior to and in the two years following treatment to evaluate changes in soil chemistry. Calcite addition significantly altered the exchange complex in the organic horizon. Increases in pH caused deprotonation of soil organic matter and increases in cation exchange capacity, providing additional exchange sites for the retention of added calcium. Exchangeable acidity decreased to very low values, allowing the base saturation of upper organic horizons to increase to nearly 100 percent.Post-treatment sampling found that approximately 48 percent of the calcite remained undissolved in the soil"s Oe horizon two years later. Dissolution of the calcite was affected by field moisture conditions, with greater dissolution in wetter areas of the watershed. Mass balances calculated for calcium applied to the watershed suggest that only 4 percent of the calcium was removed through the lake outlet. Approximately 96 percent of the calcium applied remained within the watershed; as undissolved calcite, on soil exchange sites or stored in the vegetation, groundwater or surface waters of the watershed.     

The experimental watershed liming study: Comparison of lake and watershed neutralization strategies

The Experimental Watershed Liming Study (EWLS) was initiated to evaluate the application of CaCO₃ to a forested watershed in an effort to mitigate the acidification of surface water. The objective of the EWLS was to assess the response of the Woods Lake watershed to an experimental addition of CaCO₃. During October 1989, 6.89 Mg CaCO₃/ha was applied by helicopter to two subcatchments comprising about 50% (102.5 ha) of the watershed area. The EWLS involved individual investigations of the response of soil and soil water chemistry, forest and wetland vegetation, soil microbial processes, wetland, stream and lake chemistry, and phytoplankton and fish to the CaCO₃ treatment. In addition, the Integrated Lake/Watershed Acidification (ILWAS) model was applied to the site to evaluate model performance and duration of the treatment. The results of these studies are detailed in this volume. The purposes of this introduction and synthesis paper are to: 1) present the overall design of the EWLS, 2) discuss the linkages between the individual studies that comprise the EWLS, and 3) summarize the response of the lakewater chemistry to watershed addition of CaCO₃ and compare these results to previous studies of direct lake addition. An analysis of lake chemistry revealed the watershed treatment resulted in a gradual change in pH, acid neutralizing capacity (ANC) and Ca²⁺ in the water column. This pattern was in contrast to direct lake additions of CaCO₃ which were characterized by abrupt changes following base addition and subsequent rapid reacidification. Over the three-year study period, the supply of ANC to drainage waters was largely derived from dissolution of CaCO₃ in wetlands. Relatively little dissolution of CaCO₃ occurred in freely draining upland soils. The watershed treatment had only minor effects on forest vegetation. The watershed treatment eliminated the episodic acidification of streamwater and the near-shore region of the lake during snowmelt, a phenomenon that occurred during direct lake treatments. Positive ANC water in the near-shore area may improve chemical conditions for fish reproduction, and allow for the development of a viable fish population. The watershed CaCO₃ treatment also decreased the transport of Al from the watershed to the lake, and increased the concentrations of dissolved organic carbon (DOC) and dissolved silica (H₄SiO₄) in stream and lakewater. The watershed treatment appeared to enhance soil nitrification, increasing concentrations of NO₃ ^– in soilwater and surface waters. However, the acidity associated with this NO₃ ^– release was small compared to the increase in ANC due to CaCO₃ addition and did not alter the acid-base status of Woods Lake. Acid neutralizing capacity (ANC) budgets for 12-month periods before and after the watershed treatment showed that the lake shifted from a large source of ANC to a minor source due to retention of SO₄ ^2–, NO₃ ^–, Al and the elevated inputs of Ca²⁺ associated with the watershed CaCO₃ application. In contrast to the direct lake treatments, Ca²⁺ inputs from the watershed application were largely transported from the lake.     

Forest soil solutions: Acid/base chemistry and response to calcite treatment

Soil solution chemistry was investigated at a forested watershed draining into Woods Lake. N.Y. as part of the Experimental Watershed Liming Study (EWLS). The objective of this study was to assess the response of soil water to watershed treatment of calcite (CaCO₃). This material was applied in an effort to mitigate the effects of acidic atmospheric deposition. Soil solutions draining Oa and Bs horizons in reference subcatchments were characterized by low pH and acid neutralizing capacity (ANC) due to elevated concentrations of SO ₄ ^2– , NO ₃ ^– and organic anions relative to the sum of base cation (C_B Ca²⁺, Mg²⁺, Na⁺, K⁺) concentrations. Seasonal and spatial variation of pH andANC in soil solutions appeared to belargely controlled by variations in the concentrations of dissolved organic acids which, in turn, were regulated by reactions of Al with soil organic matter. Nitrate was positively correlated and SO²⁺ was negatively correlated with Ca²⁺ and Al concentrations in reference soil solutions, indicating that changes in NO ₃ ^– influences spatial and seasonal variations in Ca²⁺ and Al concentrations. On this basis, NO ₃ ^– appears to be important in soil acidification and the dynamics of drainage water acidity. Comparison of our results with historical data for the site showed declines in concentrations of SO ₄ ^2– , which are consistent with decreases in emissions of SO₄, in the eastern U.S. and atmospheric deposition of SO ₄ ^2– , to the Adirondack region. Mineral soil solutions have shown large increases in concentrations of NO ₃ ^– . Declines in concentrations of C_B and increases in concentrations of Al have occurred over the last ten years, suggesting depletion of soil pools of exchangeable basic cations and increased sensitivity to acidic deposition. Calcite (CaCO₃) treatment of 6.89 Mg/ha resulted in a significant increase of Ca²⁺, ANC and pH in both Oa and Bs horizon soil solutions. Soil water response to CaCO₃ addition was most evident during the first year after treatment, apparently due to macropore transport of particulate and dissolved CaCO₃ However, increases in ANC and pH in the mineral soil waters were not sustained and appeared insufficient to result in substantial improvement in surface water quality over the 43 month study period.     

Effect of whole catchment liming on the episodic acidification of two adirondack streams

During the fall of 1989 7.7Mg/ha of calcium carbonate was applied on two tributary catchments (40 ha and 60 ha) to Woods Lake, a small (25 ha) acidic headwater lake in the western Adirondack region of New York. Stream-water chemistry in both catchment tributaries responded immediately. Acid-neutralizing capacity (ANC) increased by more than 200 eq/L in one of the streams and more than 1000 eq/L in the other, from pre-liming values which ranged from –25 to +40 eq/L. The increase in ANC was primarily due to increases in dissolved Ca²⁺ concentrations. Most of the initial response of the streams was due to the dissolution of calcite that fell directly into the stream channels and adjacent wetlands. A small beaver impoundment and associated wetlands were probably responsible for the greater response observed in one of the streams.After the liming of subcatchmentIV (60 ha), Ca²⁺ concentrations increased with increasing stream discharge in the stream during fall rain events, suggesting a contribution from calcite dissolved within the soil and transported to the stream by surface runoff or shallow interflow. Concentrations of other ions not associated with the calcite (e.g. Na⁺) decreased during fall rain events, presumably due to mixing of solute-rich base flow with more dilute shallow interflow. The strong relation between changes in Ca²⁺ and changes in NO ₃ ^– concentrations during spring snowmelt, (r² = 0.93, slope = 0.96, on an equivalent basis) suggests that both solutes had a common source in the organic horizon of the soil. Increases in NO ₃ ^– concentrations during snowmelt were balanced by increases in Ca²⁺ that was released either directly from the calcite or from exchange sites, mitigating episodic acidification of the stream. However, high ambient NO ₃ ^– concentrations and relatively low ambient Ca²⁺ concentrations in the stream during the spring caused the stream to become acidic despite the CaCO₃ treatment.In stream WO2 (40ha), Ca²⁺ concentrations were much higher than in stream WO4 because of the dissolution of calcite which fell directly into the upstream beaver pond and its associated wetlands. Calcium concentrations decreased as both NO ₃ ^– concentrations and stream discharge increased, due to the dilution of Ca-enriched beaver pond water by shallow interflow. Despite this dilution, Ca²⁺ concentrations were high enough to more than balance strong acid anion (SO ₄ ^– , NO ₃ ^– , Cl^–) concentrations, resulting in a positive ANC in this stream throughout the year. These data indicate that liming of wetlands and beaver ponds is more effective than whole catchment liming in neutralizing acidic surface waters.     

Limestone Treatment of Whetstone Brook, Massachusetts. I. Treatment Methodology and Water-Chemistry Changes during Treatment

Whetstone Brook is a trout stream located in north-central Massachusetts that is degraded by acid precipitation. The stream was treated with 56 tonnes of powdered limestone by a prototype, water-powered doser as part of the U.S. Fish and Wildlife Service's Acid Precipitation Mitigation Program. The goal of liming Whetstone Brook was to raise the pH to 6.5 and acid neutralizing capacity (ANC) to at least 50 μeq/1 in a 3.2-km reach. This goal was achieved despite the fact that during the 31 months of treatment stream flow was 37% higher than during the pretreatment period. During the treatment period, pH averaged 6.54 and ANC averaged 69.75. During the pretreatment period average pH was 5.97 and average ANC was 20.26. In the control section of Whetstone Brook, both pH and ANC were lower during the treatment period than during the pretreatment period. During treatment, monomeric aluminum, a form toxic to fish, declined in the treated section and increased in the control section. Total calcium, sediment calcium, and pore-water calcium increased in the treated section during treatment but declined in the control section. The other base anions and cations, nutrients, and physical parameters were not significantly affected by liming.     

The effects of liming an Adirondack lake watershed on downstream water chemistry

Calcite treatment of chronically acidic lakes has improved fish habitat, but the effects on downstream water quality have not previously been examined. In this study, the spatial and temporal effects of watershed CaCO₃ treatment on the chemistry of a lake outlet stream in the Adirondack Mountains of New York were examined. Before CaCO₃ treatment, the stream was chronically acidic. During spring snowmelt before treatment, pH and acid-neutralizing capacity (ANC) in the outlet stream declined, and NO ₃ ^– and inorganic monomeric aluminum (Al_IM) concentrations increased sharply. During that summer, SO ₄ ^– and NO ₃ ^– concentrations decreased downstream, and dissolved organic carbon (DOC) concentrations and ANC increased, in association with the seasonal increase in decomposition of organic matter and the attendant SO ₄ ^– -reduction process. A charge-balance ANC calculation closely matched measured downstream changes in ANC in the summer and indicated that SO ₄ ^– reduction was the major process contributing to summer increases in ANC. Increases in Ca²⁺ concentration and ANC began immediately after CaCO₃ application, and within 3 months, exceeded their pretreatment values by more than 130 eq/L. Within 2 months after treatment, downstream decreases in Ca²⁺ concentration, ANC, and pH, were noted. Stream mass balances between the lake and the sampling site 1.5 km downstream revealed that the transport of all chemical constituents was dominated by conservative mixing with tributaries and ground water; however, non-conservative processes resulted in significant Ca²⁺ losses during the 13-month period after CaCO₃ treatment. Comparison of substrate samples from the buffered outlet stream with those from its untreated tributaries showed that the percentage of cation-exchange sites occupied by Ca²⁺ as well as non-exchangeable Ca, were higher in the outlet-stream substrate than in tributary-stream substrate. Mass-balance data for Ca²⁺ H⁺, Al_IM, and DOC revealed net downstream losses of these constituents and indicated that a reasonable set of hypothesized reactions involving Al_IM, HCO ₃ ^– , Ca²⁺, SO ₄ ^– NO ₃ ^– , and DOC could have caused the measured changes in stream acid/base chemistry. In the summer, the sharp decrease in ANC continued despite significant downstream decreases in SO₄ ^2– concentrations. After CaCO₃ treatment, reduction of SO ₄ ^– was only a minor contributor to ANC changes relative to those caused by Ca²⁺ dilution from acidic tributaries and acidic ground water, and Ca²⁺ interactions with stream substrate.     

Changes in Aquatic Macrophytes after Liming Thrush Lake, Minnesota

Thrush Lake, Minnesota, was treated with limestone in 1988 to evaluate the efficacy of protective base addition against the loss of sport fisheries in a sensitive, mildly acidic lake. Prior to treatment, the lake was stressed (pH 6.46, ANC 64 μeq/L) but not severely degraded by acidic deposition and had a macrophyte community typical of lakes in northeastern Minnesota with low acid-neutralizing capacity (ANC). This paper describes the changes observed in aquatic plant communities during the 5 years after treatment, as pH and ANC slowly returned to pretreatment levels. Sphagnum platyphyllum, intolerant of non-acid conditions, was completely eliminated from the lake. The charo-phyte, Nitella, that originally shared dominance in the deep littoral zone with S. platyphyllum, decreased in importance during the first 2 years after treatment. Two vascular plants, Potamogeton pusillus and Najas flexilis, were first found in the lake the year after treatment and were abundant for 2 years after liming, probably in response to a combination of more neutral pH and reduced cover of Nitella. As the ANC and pH slowly returned to pretreatment conditions, Nitella again increased in coverage and depth range, with a concomitant decrease in P. pusillus and N. flexilis. The moss, S. platyphyllum, had not reinvaded the lake by 1993, 2 years after its dramatic decline.     

Longitudinal and temporal trends in the water chemistry of the North Branch of the Moose River

Surface water acidification is potentially a problem in regions with low ionic strength drainage waters. Atmospheric deposition of sulfuric acid has generally been implicated as the causative agent of this problem, although other sources of acidity may contribute. The Adirondack region of New York State is an area with acid-sensitive surface waters and an abundance of acidic lakes. The intent of this study was to evaluate the processes regulating the acid/base chemistry of a series of lakes draining a large heterogeneous watershed in the Adirondack region of New York.The study site, the North Branch of the Moose River, is heterogeneous in its soil and geological characteristics. This variability was reflected through differences in water chemistry that occurred within the basin. The northern headwaters generally drain subcatchments with shallow, acidic soils. The resulting water chemistry was acidic (equivalence of acidic anions exceeded equivalence of basic cations) with high concentrations of Al and dissolved organic carbon (DOC). As this water migrated through a large lake (Big Moose Lake) with a moderate hydrologic retention time (0.5 yr), considerable loss of DOC was evident.As acidic water was transported through the drainage area, it mixed with waters that were enriched in concentrations of basic cations from the eastern subbasins. As a result, there was a successive increase in the acid neutralizing capacity (ANC) and a decrease in Al concentrations as water migrated from the northern reaches to the outlet of the watershed.In addition to these general trends, short-term changes in water chemistry were evident. During low flow summer periods concentrations of basic cations were elevated, while concentrations of SO ₄ ^2– and NO ₃ ^– were relatively low. These conditions resulted in less acidic waters (higher ANC) with relatively low concentrations of Al. During high flow winter/spring conditions, elevated concentrations of SO ₄ ^2– and NO ₃ ^– were evident, while concentrations of basic cations were reduced resulting in low pH (low ANC) waters with high concentrations of Al.Variability in the processes regulating the pH buffering of waters was apparent through these short-term changes in water chemistry. In the northern subbasin short-term fluctuations in ANC were minimal because of the buffering of Al under low pH conditions. Seasonal changes in the ANC were more pronounced in the eastern subbasin because of the predominance of inorganic carbon buffering in the circumneutral pH waters.Lakes in the west-central Adirondacks have characteristically short hydraulic residence times and elevated nitric acid inputs. As a result these waters may be more susceptible to surface water acidification than other acid-sensitive lake districts in eastern North America. Given the apparent interregional differences, extrapolation of chemical trends in the Adirondacks to other areas may be tenuous.     

Calcium and Magnesium Levels in Agricultural Soil and Sewage Sludge in an Industrial Area from Southeastern Spain: Relationship with Plant (Saccharum officinarum) Disposition

This investigation was initiated to assess the following objectives: (1) to measure the total calcium and magnesium content in agricultural soil and sewage sludge from the Mediterranean coastal area of Motril (southeastern Spain); (2) to determine the pH values of indicated samples in order to evaluate first their influence on calcium and magnesium content, and second on levels of these minerals in the main crop (sugar cane: Saccharum officinarum) grown in the area; (3) to study the influence of industrial activities, first on calcium and magnesium cantents and pH values in agricultural soil, and second on calcium and magnesium concentrations present in sugar cane samples; (4) to check if the calcium and magnesium levels existing in agricultural soil exert any influence on corresponding element uptake by sugar cane plants. Calcium levels found in agricultural soil were significantly higher (p < 0.05) than those found in sewage sludge. Significant linear relationships between calcium and magnesium concentrations in agricultural soil and sewage sludge (p < 0.005) were found. Calcium concentrations found in soil from the industrialized area (39.2 ± 7.2 mg g^?1) were significantly higher than those corresponding to the non-industrialized area (31.0 ± 6.6 mg g^?1). The pH values determined in agricultural soil were significantly influenced by industrial activity (p < 0.05). The industrial activity and pH values measured in agricultural soil did not statistically influence either calcium or magnesium levels in the sugar cane plants. Calcium and magnesium concentrations existing in agricultural soil did not significantly influence the element uptake by sugar cane plants.     

Calcite supersaturation in some subtropical,Kashmir, Himalayan lakes

Results of a two year study of the detailed water chemistry of three productive, Kashmir, Himalayan lakes, Khanpur, Trigam and Tilwan (average alt. 1580 m), are used to provide an appreciation of the role of calcite precipitation. Two extreme behaviours are apparent. The least productive lake is close to saturation throughout the year, with the concentrations of calcium and alkalinity being controlled by temporary excursions in pH accompanying increased photosynthetic activity. The most productive lake is always greatly and uniformly supersaturated, the ion activity product being more than seven times the stability constant, and the concentrations of calcium and alkalinity are lowest at higher temperatures when calcite is less soluble. It appears that the saturation index has a critical level, above which precipitation proceeds more rapidly. The third lake shows behaviour intermediate between these two extremes.     

Watershed-Level Responses to Calcium Silicate Treatment in a Northern Hardwood Forest

Watershed 1 (W1) at the Hubbard Brook Experimental Forest in New Hampshire, with chronically low pH and acid neutralizing capacity (ANC) in surface water, was experimentally treated with calcium silicate (CaSiO₃; wollastonite) in October 1999 to assess the role of calcium (Ca) supply in the structure and function of base-poor forest ecosystems. Wollastonite addition significantly increased the concentrations and fluxes of Ca, dissolved silica (Si), and ANC and decreased the concentrations and fluxes of inorganic monomeric Al (Al_i) and hydrogen ion (H⁺) in both soil solution and stream water in all sub-watersheds of W1. Mass balances indicate that 54% of the added Ca remained undissolved or was retained by vegetation during the first 6 years after treatment. Of the remaining added Ca, 44% was retained on O horizon cation exchange sites. The Ca:Si ratio in the dissolution products was greater than 2.0, more than twice the molar ratio in the applied wollastonite. This suggests that Ca was preferentially leached from the applied wollastonite and/or Si was immobilized by secondary mineral formation. Approximately 2% of the added Ca and 7% of the added Si were exported from W1 in streamwater in the first 6 years after treatment. Watershed-scale Ca amendment with wollastonite appears to be an effective approach to mitigating effects of acidic deposition. Not only does it appear to alleviate acidification stress to forest vegetation, but it also provides for the long-term supply of ANC to acid-impacted rivers and lakes downstream.     

Interactions between calcite precipitation (natural and artificial) and phosphorus cycle in the hardwater lake

The influence of calcite precipitation on the phosphorus cycle in stratified hardwater lake was studied before and during experiments with a new restoration technique. Surveys of the chemical composition of water column and monitoring of settling particles of Lake Luzin (North–East) showed that calcite precipitation occurs each year over 2–3 periods during spring and summer. The change of the phosphorus content influenced the calcite precipitation intensity. The sedimentation fluxes of phorphorus and the calcite precipitation were closely associated. Based on the hypothesis that calcite precipitation acts as an improvement to the trophic state by enhancing the internal phosphorus sink, this new technology for lake restoration was developed. The hypolimnetic Ca(OH)₂ addition during summer stratification in 1996–1997 induced the calcite precipitation in the deep water layer of Basin Carwitz of Lake Schmaler Luzin. The treatment also supported the natural calcite precipitation in the epilimnion. The annual total phosphorus content decreased from 0.46 tons in 1995 to 0.35 tons in 1997. The annual SRP content decreased from 0.02 tons in 1996 to 0.01 tons in 1997 after beginning the artificial calcite precipitation in 1996. The decrease of the annual Chl-a concentration in 1998 on 38% compared with that in 1996 pointed out the lake recovering. According to the one box model, the artificial calcite precipitation affected the P cycle in the lake by suppressing the P release from the sediments.     

Limestone to Mitigate Lake acidification: macrozoobenthos response in treated and reference lakes

The littoral macrozoobenthos (MZB) of two low acid neutralizing capacity (ANC = 50.0 µeq l^–1) northeastern Pennsylvania lakes (treatment and reference) were sampled each ice free season, 1984 through 1988, to evaluate response to limestone addition. Following addition of 100 tons agricultural limestone (CaCO₃) to the treatment lake in February 1985, mean annual ANC rose from 20 µeq l^–1 to 668 µeq l^–1 then decreased. In October 1987, ANC in the treatment lake was decreasing, so 15 additional tons of limestone were added. Pre- limestoning there were few significant (p<0.05) differences between MZB assemblages in the two lakes, but 4 years post treatment the following differences (p<0.05) were detected in the treatment lake: more Chironomidae, Ephemeroptera, Odonata, Hyalella azteca, total MZB numbers and higher Mollusca wet weight than in the reference lake. From 1984 to 1988 in the treatment lake the annual means of the following community characteristics increased (p<0.05): totals of Chironomidae, Ephemeroptera (including Caenis spp.), Odonata, Trichoptera, Sphaeriidae, collectors and MZB numbers; Chironomidae and Ephemeroptera taxa richness and total taxa richness; total and Mollusca wet weight. However, the treatment lake ecosystem is neither self-sustaining nor stable because limestone must be added every 2 to 3 years to maintain ANC above 50 µeq l^–1 In the reference lake annual means of ANC, specific conductance, calcium and magnesium decreased (p<0.05) while Secchi depth increased (p<0.05), suggesting continuing acidification.     

施肥和增水对弃耕草地土壤酸中和容量的影响

大气氮沉降增加是草地土壤酸化的主要原因。土壤酸缓冲性能作为评估土壤酸化的重要指标,对氮输入的响应受到降水与其他限制养分含量的影响。本研究以我国北方温带弃耕草地氮、磷、水添加试验13年后的土壤为对象,利用二次多项式模型拟合酸滴定曲线,计算了土壤酸缓冲容量(ABC)以及以pH 5.0和4.0为参比的土壤酸中和容量(ANC)。结果表明: 不增水处理下,单独加氮和同时添加氮磷均显著降低土壤pH,降低以pH 5.0和4.0为参比时的酸中和容量(ANC_pH5.0和ANC_pH4.0);单独加磷对土壤pH、ANC_pH5.0和ANC_pH4.0均无显著影响。增水处理下,加氮及加氮磷显著降低土壤pH、ANC_pH5.0和ANC_pH4.0;加磷显著降低土壤pH,但增加了ANC_pH4.0,而对ANC_pH5.0无显著影响。与不增水处理相比,增水处理对土壤pH、酸中和容量均具有显著的正效应。对于初始pH值不同的土壤,采用土壤酸中和容量比酸缓冲容量能更好地指示土壤抗酸化能力。     

Interaction of mineral elements in sea water and shell of oysters (Crassostrea virginica (Gmelin)) cultured in controlled and natural systems

The interaction is reported of selected chemical elements (cadmium, calcium, copper, iron, magnesium, manganese, strontium, and zinc) in cultured sea water, with soft tissues, prismatic calcite of the right valve, and foliated calcite of right and left valves of genetically similar American oysters, Crassostrea virginica (Gmelin) grown in a natural habitat and in two environmentally controlled experimental systems (flow-through and recycle). The addition of trace elements as algal nutrients in ambient sea water was reflected in higher concentrations of trace metals in shells and soft tissues of oysters grown in experimental systems. Calcium was relatively uniformly distributed in major regions of valves from the three habitats, even though its concentration fluctuated widely in sea water in experimental systems. Magnesium and strontium were most concentrated in valves of oysters grown in the recycle system (magnesium in the prismatic layer of the shell and strontium in the foliated calcite). Iron was uniformly distributed. Cadmium, copper, manganese, and zinc were most concentrated in the prismatic calcite of valves from the flow-through system. In soft tissues, calcium was more concentrated in oysters from experimental systems than in those from the natural habitat. Manganese was about equally distributed in soft tissues from the three habitats, whereas copper and iron were more concentrated in soft tissues in experimental systems than in the natural habitat, and were many times more concentrated in soft tissues than in valves from all three habitats. As concentrations of magnesium, strontium, mangenese, zinc, and cadmium increased in valves in experimental systems, pigmentation of valves decreased. The study confirmed the capacity of oysters to concentrate several elements in their valves as concentration of these elements increased in ambient sea water and disclosed the heterogeneous distribution of these elements in major regions of the valves.     

Fungi,bacteria and soil pH: the oxalate–carbonate pathway as a model for metabolic interaction

The oxalate–carbonate pathway involves the oxidation of calcium oxalate to low‐magnesium calcite and represents a potential long‐term terrestrial sink for atmospheric CO ₂. In this pathway, bacterial oxalate degradation is associated with a strong local alkalinization and subsequent carbonate precipitation. In order to test whether this process occurs in soil, the role of bacteria, fungi and calcium oxalate amendments was studied using microcosms. In a model system with sterile soil amended with laboratory cultures of oxalotrophic bacteria and fungi, the addition of calcium oxalate induced a distinct pH shift and led to the final precipitation of calcite. However, the simultaneous presence of bacteria and fungi was essential to drive this pH shift. Growth of both oxalotrophic bacteria and fungi was confirmed by qPCR on the frc (oxalotrophic bacteria) and 16S rRNA genes, and the quantification of ergosterol (active fungal biomass) respectively. The experiment was replicated in microcosms with non‐sterilized soil. In this case, the bacterial and fungal contribution to oxalate degradation was evaluated by treatments with specific biocides (cycloheximide and bronopol). Results showed that the autochthonous microflora oxidized calcium oxalate and induced a significant soil alkalinization. Moreover, data confirmed the results from the model soil showing that bacteria are essentially responsible for the pH shift, but require the presence of fungi for their oxalotrophic activity. The combined results highlight that the interaction between bacteria and fungi is essential to drive metabolic processes in complex environments such as soil.     

The impacts of a watershed CaCO3 treatment on stream and wetland biogeochemistry in the Adirondack Mountains

Temporal and longitudinal variations in the chemistry of two tributary streams of Woods Lake in the Adirondack Mountains of New York were monitored before and after a watershed CaCO₃ application. One subcatchment of the lake had a large beaver pond and wetland at its headwaters, while the second was free-flowing. Treatment of both subcatchments with CaCO₃ resulted in an immediate increase in acid neutralizing capacity (ANC) associated with Ca²⁺ release. The extent and duration of the response to the treatment were greater in the wetland-impacted stream. Aluminum was retained and complexed with organic solutes generated within the beaver-pond. In the free-flowing stream, NO ₃ ^– concentration increased significantly after the manipulation; this pattern was not evident in the wetland-impacted stream. Net retention of SOkinf4/sup2– was evident in the beaver pond prior to and following treatment, and this response was enhanced after the watershed liming. Comparisons of beaver pond inlet/outlet concentrations, mass balance calculations, and in-pond profiles of chemical parameters revealed patterns of retention of SO ₄ ^2– , NO ₃ ^– and Al, and release of Fe²⁺, dissolved organic carbon (DOC) and NH ₄ ⁺ in the wetland during the summer before CaCO₃ treatment. Post-treatment releases of Ca²⁺ from the near-sediment zone in the beaver pond corresponded to anoxic periods in mid- to late-summer and under ice in winter. These findings demonstrate the importance of increased microbial processing of organic matter, along with high partial pressure Of CO₂ (Pco₂) in facilitating the dissolution of the applied CaCO₃. Dissolved silica (H₄SiO₄) was retained in the wetland during the summer prior to treatment but was released after the manipulation. This phenomenon may reflect the dissolution of diatom frustules or silicate minerals in the wetland at higher pH and DOC concentrations. Within two years of the CaCO₃ treatment 60% of the CaCO₃ applied to the beaver pond and surrounding wetland was dissolved and transported from the pond, in contrast to only 2.2% of the CaCO₃ applied to the upland subcatchment draining into the wetland. These results, coupled with high quantities of exchangeable Ca²⁺ found in sediments and onSphagnums mosses in the pond, demonstrate the importance of hydrologic source areas and wetlands in facilitating the dissolution of added CaCO₃ and in regulating the production of chemical species important in ANC generation.     

Microbially Induced Calcite Precipitation for Seepage Control in Sandy Soil

Microbially induced calcite precipitation (MICP) can reduce the permeability of soil by reducing the pore volumes. A MICP-based soil improvement method to control water leakage in irrigation channels and reservoirs built on sandy soil grounds is presented in this article. Using this method, a low-permeable hard crust can be formed at the soil surfaces. An experimental study was carried out to evaluate the effect of this method. Sandy soil samples were treated using four different schemes, namely, (1) surface spray, (2) surface spray with the addition of fibers, (3) surface spray and bulk stabilization, and (4) immersion stabilization. By applying around 2.6?L treatment liquid (consisting of ureolytic bacteria, 0.5?mol/L calcium chloride and 0.5?mol/L urea) to the top 2-cm thick soil, the seepage rates of the samples treated by the four different schemes could be reduced by up to 379 times. The conversion rates of calcium source in the tests were up to 89.7%. The results showed that a method of treating the soil in bulk before the formation of a crust on top of the soil layer was effective in reducing the seepage rates. After the bio-treatment, the formed low-permeable hard crust layer was 10 to 20?mm thick with a calcite content higher than 5%. Below the hard crusts, the calcite content was less than 5% and the soil was not properly cemented. Using the mercury intrusion test, it was found that both pore volumes and pore sizes of the bio-treated soil reduced significantly as compared with the untreated soil. Penetration tests using a flat-bottom penetrometer were used to assess the mechanical behavior of the bio-treated soil. The results indicated that the penetration resistance of the bio-treated soil layer was much higher than that of the untreated soil.     

Effects of ammonium sulphate application on the rhizosphere,fine-root and needle chemistry in aPicea abies (L.) Karst. stand

Rhizosphere, fine-root and needle chemistry were investigated in a 28 year old Norway spruce stand in SW Sweden. The uptake and allocation pattern of plant nutrients and aluminium in control plots (C) and plots repeatedly treated with ammonium sulphate (NS) were compared. Treatments started in 1988. Current year needles, one-year-old needles and cylindrical core samples of the LFH-layer and the mineral soil layers were sampled in 1988, 1989 and 1990. Compared to the control plots, pH decreased significantly in the rhizosphere soil in the NS plots in 1989 and 1990 while the SO₄-S concentration increased significantly. Aluminium concentration in the rhizosphere soil was generally higher in the NS plots in all soil layers, except at 0–10 cm depths, both in 1989 and 1990. Calcium, Mg and K concentrations also increased after treatment with ammonium sulphate. Ammonium ions may have replaced these elements in the soil organic matter. The NS treatment significantly reduced Mg concentrations in fine roots in all layers in 1990. A similar trend was found in the needles. Ca concentrations in fine roots were significantly lower in the NS plots in the LFH layer in 1990 and the same pattern was found in the current needles. The N and S concentrations of both fine roots and needles were significantly higher in the NS plots. It was suggested that NS treatment resulted in displacement of Mg, Ca and K from exchange sites in the LFH layer leading to leaching of these cations to the mineral soil. Further application of ammonium sulphate may damage the fine roots and consequently adversely affect the water and nutrient uptake of root systems.     

Calcium and temperature effects on seedling exudation and root rot infection of common bean on an acid sandy soil

Soil born fungi such as Phytium ultimum, Fusarium ssp., and Rhizoctonia solani (Kühn) severely restrict stand establishment of common bean (Phaseolus vulgaris L.) on acid soils of the Tropics. Calcium application is known to alleviate fungal infection in many legumes but the causes are still unclear. To investigate environmental factors and physiological mechanisms involved, growth chamber experiments were conducted with an acid sandy soil from Mexico. Treatments were soil liming at a rate of 0.67 g Ca(OH)₂ kg^-1, gypsum application at 0.49 g CaSO₄ 2H₂O kg^-1 soil placed around the seed, and an untreated control. Beans were grown under three temperature regimes with constant night and one constant day vs. two sinusoidal day temperatures. To examine patterns of seed and seedling exudation at regular intervals leachates of germinating seeds were collected on filter paper soaked with equilibrium solutions from soils of the three treatments. The severity of root rot in the control treatment was highest when plants were stressed by temperature extremes. At a sinusoidal day temperature peaking at 40°C soil liming and gypsum application to the seed increased the number of healthy seedlings similarly by over 60%. However, only liming which effectively eliminated growth constraints by low pH and high aluminum concentrations led to an increase in hypocotyl elongation by 22% and in total root length by 8%. Both calcium amendments increased the calcium and potassium contents in the hypocotyl tissue. From seeds exposed to the equilibrium solution of unlimed soil with pH 3.7, 1 mM Ca, and 0.6 mM Al considerable amounts of amino acids and carbohydrates were leached. In contrast, exposure to the equilibrium solution from limed soil with pH 4.3, 3 mM Ca, and negligible concentrations of Al led to a net uptake of amino acids and decreased leaching of carbohydrates. Exposure to the equilibrium solution of the gypsum treatment with pH 3.6, 20 mM Ca, and 1.2 mM Al resulted in a somewhat smaller net uptake of amino acids compared to liming. During germination pH around the seeds steeply increased in the untreated control but significantly less with both amendments. The results indicate that pH and the Ca/Al ratio in the soil solution around bean seeds determine their pattern of exudation and solute uptake. For bean germination and early growth on acid soils locally placed application of small amounts of gypsum as seed pelleting seems as effective as soil liming in reducing the incidence of root rot. The results indicate that this may be accomplished by decreasing the amount of leachates available for fungal development.