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.     

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.     

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.     

Processes regulating temporal and longitudinal variations in the chemistry of a low-order woodland stream in the Adirondack region of New York

Watershed processes influence the acid neutralizing capacity of surface waters by mediating changes in concentration of ionic solutes. Acidification of surface waters by atmospheric deposition of mineral acids and the extent to which ecosystem transformations neutralize this acidity are of particular concern. Seasonal variations in flow paths of water through soil and biological processes result in short-term changes in chemistry that may be critical to surface water ecology. In this study, we assessed longitudinal and temporal variations in the chemistry of a low-order stream, Pancake-Hall Creek, located in the west-central Adirondack region of New York. By quantifying changes in ionic solute concentration (e.g. Ca²⁺, Al^a+, SO ₄ ^2– , NO ₃ ^– ) we were able to evaluate processes responsible for short-term fluctuations in acid/base chemistry.In the headwater sites, stream water was acidic; changes in pH, acid neutralizing capacity (ANC) and Al were primarily due to seasonal variations in basic cation and NO ₃ ^– concentrations. At the downstream sites, water migrated through a large beaver impoundment and thick till resulting in higher pH, acid neutralizing capacity and basic cation concentrations, and lower concentrations of Al. Neutralization of acidity was particularly evident during the low flow summer period and coincided with retention of SO ₄ ^2– in the beaver impoundment. During the high flow non-summer (October to June) period, depressed pH and ANC, and elevated Al concentrations were observed in the downstream sites. Acidic conditions during the non-summer period were not due to the oxidation of reduced sulfur deposits (e.g. SO ₄ ^2– events) but rather the resumption of conservative SO ₄ ^2– transport through the beaver impoundment (e.g. minimal SO ₄ ^2– retention) coupled with increases in NO ₃ ^– .     

Buffering an Acidic Stream in New Hampshire with a Silicate Mineral

Ground and pelletized Wollastonite (Wo; CaSiO₃) was added to a 50‐m reach of an anthropogenically acidified stream within the Hubbard Brook Experimental Forest, New Hampshire, to evaluate its buffering and restoration potential. The Wo was highly effective in raising the pH, acid‐neutralizing capacity (ANC), dissolved inorganic carbon (DIC), and Ca²⁺ concentrations of the stream water, but during the short duration of the experiment had no discernable effect on the stream biota. After initial, spike‐like fluctuations in pH and concentrations of ANC, DIC, and Ca²⁺, the relatively slow dissolution rates of the Wo dampened extreme concentrations and contributed to relatively long‐lasting (4 months) amelioration of streamwater acidity. Changes in concentrations of Ca²⁺, dissolved Si, ANC, and DIC were inversely related to streamflow. After several high, stream‐discharge events, concentrations quickly and consistently returned to pre‐event conditions.     

Comparative suitability of binocular observation, burrow counting and excavation for the quantification of the mangrove fiddler crab Uca annulipes (H. Milne Edwards)

Insect emergence from three different sections of a small mountain brook in Germany was studied: a free-flowing section (`brook'), a section impounded by beavers (`beaver pond') and a beaver dam. The three sections had very different faunas with that of the dam being more similar to that of the brook than that of the pond. The heterogeneity of the fauna was greatest in the dam and lowest in the pond. Median emergence density in the dam was 443 specimens m^–2 d^–1. This was 3.2 times higher than median emergence density in the brook section and 5.5 times higher than median emergence density in the pond section. In particular, the density of emerging Trichoptera (especially filter-feeding species) was increased. Mean annual number of emerging EPTC species was 32.3/trap (779 cm² ground area) in the dam, 18.4/trap in the brook and 11.0/trap in the pond. Emerging biomass was highest in the dam (18.0 – 26.7 g m^–2 yr^–1; 5.0 times higher than in the free flowing section and 5.4 times higher than in the pond section). The composition of a recently broken beaver dam is described by measuring all pieces of wood used in building the dam and analysing sediment samples. The dam consisted of a framework of wood pieces almost entirely of a diameter <5 cm, in which cavities are partly filled with fine sediment (mean organic content = 20%). The `inner surface' of the dam was 2.09 times higher than the dam's ground area and 1.63 times higher than the dam's surface. Beavers, therefore, significantly increase the heterogeneity of faunal composition and productivity of small brooks.     

Nitrogen fixation in subarctic streams influenced by beaver (Castor canadensis)

Nitrogen fixation was measured in four subarctic streams substantially modified by beaver (Castor canadensis) in Quebec. Acetylene-ethylene (C₂H₂ C₂H₄) reduction techniques were used during the 1982 ice-free period (May–October) to estimate nitrogen fixation by microorganisms colonizing wood and sediment. Mean seasonal fixation rates were low and patchy, ranging from zero to 2.3 × 10^–3 µmol C₂H₄ · cm^–2 · h^–1 for wood, and from zero to 7.0 × 10^–3 µmol C₂H₄ · g AFDM^–1 · h^–1 for sediment; 77% of all wood and 63% of all sediment measurements showed no C₂H₂ reduction. Nonparametric statistical tests were unable to show a significant difference (p > 0.05) in C₂H₂ reduction rates between or within sites for wood species or by sediment depth.Nitrogen contributed by microorganisms colonizing wood in riffles of beaver influenced watersheds was small (e.g., 0.207 g N · m^–2 · y^–1) but greater than that for wood in beaver ponds (e.g., 0.008 g N · m^–2 · y^–1) or for streams without beaver (e.g., 0.003 g N · m^–2 · y^–1). Although mass specific nitrogen fixation rates did not change significantly as beaver transform riffles into ponds, the nitrogen fixed by organisms colonizing sediment in pond areas (e.g., 5.1 g N · m^–2 · y^–1) was greater than that in riffles (e.g., 0.42 g N · m^–2 · y^–1). The annual nitrogen contribution is proportional to the amount of sediment available for microbial colonization. We estimate that total nitrogen accumulation in sediment, per unit area, is enhanced 9 to 44 fold by beaver damming a section of stream.     

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.     

Phosphorus and nitrogen retention in five Precambrian shield wetlands

Phosphorus and nitrogen mass balances of five wetlands (two beaver ponds, two conifer-Sphagnum swamps and one sedge fen) situated in three catchments in central Ontario, Canada, were measured. Monthly and annual input-output budgets of total phosphorus (TP), total nitrogen (TN), total organic nitrogen (TON), total inorganic nitrogen (TIN), ammonium ion (NH₄ ⁺ -N), nitrate (NO ₃ ^– -N) and dissolved organic carbon (DOC) were estimated for the five wetlands during the 1982–83 and 1983–84 water years. Except for the deepest beaver pond (3.2 m) which had annual TP retention of –44% (–0.030 ± 0.015 g m^–2 yr^–1), the wetlands retained < 0.001 to 0.015 g M^–2 yr^–1 ; however, this wasless than 20% of the inputs and the estimated budget uncertainties were equal to or greater than the retention rates. Annual TN retentions ranged from –0.44 to 0.56 g m^–2 yr^–1 (–12 to 4%) but were not significantly different from zero. The wetlands transformed nitrogen by retaining TIN (16 to 80% RT) and exporting an equivalent amount as TON (–7 to 102% RT). The beaver ponds, however, retained NO ₃ ^– while NH ₄ ⁺ was passed through or the outputs exceeded the inputs. In contrast, the conifer swamps retained both NH ₄ ⁺ and NO ₃ ^– . DOC fluxes into and out of the beaver ponds were equal (–18 and 4% RT) but output from the conifer swamps exceeded input by > 90%. Marked seasonal trends in nutrient retention were observed. Nutrient retention coincided with low stream flow, increased evapotranspiration and biotic uptake during the summer. Net nutrient export occurred during the winter and spring when stream flows were highest and biotic uptake was low.     

Calcium content of liming material and its effect on sulphur release in a coniferous forest soil

Soil columns with O + A (Experiment I) or Ohorizons (Experiment II) from a Haplic Podsol wereincubated at 15 °C for 368 and 29 + 106 days,respectively. Three types of liming material differingin Ca²⁺ content, i.e. calcium carbonate(CaCO₃), dolomite (CaMg(CO₃)₂) andmagnesium carbonate (MgCO₃), were mixed into theO horizons in equimolar amounts corresponding to 6000kg of CaCO₃ per ha. In the limed treatments ofExperiment I, the leaching of dissolved organic carbon(DOC) and the net sulphur mineralization (estimated asaccumulated SO ₄ ^2– leaching corrected forchanges in the soil pools of adsorbed and waterextractable SO ₄ ^2– ) increased with decreasingCa²⁺ content of the lime and increasing degree oflime dissolution. In relation to the controltreatment, only the MgCO₃ treatment resulted ina significantly higher net sulphur mineralization. InExperiment I the net sulphur mineralization was 4.06,1.68, 0.57, and 2.14 mg S in the MgCO₃,CaMg(CO₃)₂, CaCO₃ and control treatment,respectively. The accumulated SO ₄ ^2– leachingin Experiment II during the first 29 days was 1.70,0.74 and 0.48 mg S in the MgCO₃,CaMg(CO₃)₂ and control treatment,respectively. In the two experiments there wereconsistently significant positive correlations betweenleached amounts of SO ₄ ^2– and DOC. It wasconcluded that net sulphur mineralization was stronglyconnected to the solubilization of the organic matter(DOC formation) and that pH and/or Ca²⁺ ionsaffected the net sulphur mineralization through theireffects on organic matter solubility.     

The chemistry and transport of mercury in a small wetland in the Adirondack region of New York, USA

The biogeochemistry of Hg was evaluated in a small wetland in the Adirondack region of New York. Concentrations of total Hg (Hg_T) in streamwater draining the wetland showed little temporal variation. The annual areal watershed flux of Hg_T (2.2 µg/m²-yr) was considerably smaller than regional inputs of atmospheric deposition of Hg_T, indicating that the terrestrial environment is a net sink for atmospheric deposition of Hg_T. Drainage inputs of Hg_T were conservatively transported through the beaver impoundment. The annual flux of total methyl mercury (CH₃Hg⁺ _T was greater than literature values of atmospheric deposition suggesting that the watershed is a net source of CH₃Hg⁺ _T . Stream concentrations of CH₃Hg⁺ _T increased during low-flow summer conditions in a riparian wetland, and particularly at the outlet of the beaver impoundment. Net production of CH₃Hg⁺ _T occurred in the beaver impoundment (0.45 µg/m²-yr). Rates of net methylation for the beaver impoundment were comparable to values reported in the literature for wetlands.     

Dissolved organic carbon and its utilization in a riverine wetland ecosystem

Variations in dissolved organic carbon (DOC) concentrations of surface waters and subsurface interstitial groundwater of riparian and wetland soils to 1.2 m depth were evaluated in a riverine wetland ecosystem over one year. DOC was monitored at seven sites within the wetland pond, two sites on the inflow stream, and one site on the outflow stream. Surface concentrations in the inflow stream ranged from 0.74 to 11.6 mg C L^–1 and those of the outflow from 2.1 to 8.0 mg C L^–1 Average DOC from stream floodplain hydrosoils (3.1 to 32.1 mg C L^–1 was greater than DOC from the sediments below the stream channel (1.6 to 6.8 mg C L^–1 Surface DOC within the wetland varied seasonally, with greatest fluctuations in concentrations through the summer and autumn (range 4.8 to 32.6 mg C L^–1 ) during intensive macrophyte growth and bacterial production. DOC was less variable during the winter months (1.7 to 3.3 mg C L^–1 Within the wetland pond, average DOC concentrations (7.1 to 48.2 mg C L^–1) in the subsurface waters were significantly greater (p < 0.05) than average surface concentrations. The microbial availability of surface and subsurface DOC to bacteria was evaluated from losses of DOC by wetland bacteria grown on the DOC. Bacterial growth efficiencies ranged from 5 to 20% and were negatively correlated to the percentage of DOC removed by bacteria (r²=0.93). Throughout the ecosystem, DOC concentrations were greatest in the subsurface waters, but at most depths this DOC was a less suitable substrate than surface DOC for utilization by bacteria.     

A comparison of calcium binding inCallinectes sapidus premolt and postmolt cuticle homogenates: Implications for regulation of biomineralization

Cuticle tissue homogenates (CTHs) fromCallinectes sapidus premolt cuticle bound approximately 367% more Ca²⁺ ions than did those from the postmolt cuticle. ThepH-stat assay which was used to comparein vitro CaCO₃ nucleation times confirmed that the premolt CTHs had greater inhibitory activity than did the postmolt CTHs. This inhibitory activity was indicated by CaCO₃ nucleation times in excess of control values. Premolt nucleation times exceeded those of postmolt samples by approximately 340%. A positive correlation was observed between Ca²⁺ binding and calcification inhibitory activity for both premolt and postmolt CTHs. Heat pretreatment of CTHs at 70°C for a 24-hr period had no significant effect on their Ca²⁺ binding. However, this heat pretreatment decreased their calcification inhibitory activity. Pretreatment of CTHs with Ca²⁺ diminished their calcification inhibitory activity. These results are consistent with a mechanism for inhibition of biocalcification by these proteins which involves their initial reversible binding to nascent calcite nuclei growth steps and kinks, rather than theirin vivo interaction with free Ca²⁺ ions in solution.     

Seasonal variations of pH, pCO2, pO2, HCO3- and Ca2+ in the haemolymph: implications on the calcification physiology in Anodonta cygnea

A study about the relationship between the physical–chemical parameters and the calcium carbonate balance between the haemolymph fluid and mantle calcareous structures was carried out in Anodonta cygnea. An intense peak of HCO₃ ⁻ and a highest pH in December–January months may be understood as a preparation period for creating alkaline conditions. An intense pH decrease from January to February in parallel with the HCO₃ ⁻ reduction seems to indicate the beginning process of carbonate precipitation. On the other hand, the following calcium and HCO₃ ⁻ increases in February–May associated with a continuous and gradual pH fall profile may infer two combined aspects: calcium and HCO₃ ⁻ absorption from external environment and a simultaneous intense calcium carbonate deposition in the haemolymph. So, the pCO₂ peak in this period reflects a subsequent result on equilibrium balance between HCO₃ ⁻ absorption and deposition. The only significant pO₂ increase in the next period, from February to June, is related with an energetic increase to support the metabolic activity favouring the posterior intense pCO₂ peaks. The extended time of CO₂ production in the haemolymph from May to November should induce an increased metabolic acidosis with subsequent intense formation of both HCO₃ ⁻ and Ca²⁺ ions in the same period. This seems to result from CaCO₃ deposits dissolution in the haemolymph, the most direct calcareous source. Additionally, the later increase of metabolic succinic acid during autumn may greatly potentiate this acidosis increasing the dissolution process. Consequently, the pH profile present two simultaneous alkaline peaks in July and October, probably due to a strong HCO₃ ⁻ release from the CaCO₃ dissolution. So, the present seasonal results indicate that in the freshwater bivalve A. cygnea, the low metabolism with higher pH from the early winter is the main cause which may favour a calcareous precipitation, while the high metabolism with lower pH from the early summer may function as an inductor of calcareous dissolution in the haemolymph.     

Pond-Breeding Amphibian Species Richness and Habitat Selection in a Beaver-Modified Landscape

ABSTRACT Beaver (Castor canadensis) activity creates wetland habitats with varying hydroperiods important in maintaining habitat diversity for pond-breeding amphibians with significantly different breeding habitat requirements. We documented pond-breeding amphibian assemblages in 71 freshwater wetlands in Acadia National Park, Maine, USA. Using 15 variables describing local pond conditions and wetland landscape characteristics, we developed a priori models to predict sites with high amphibian species richness and used model selection with Akaike's Information Criterion to judge the strength of evidence supporting each model. We developed single-species models to predict wood frog (Rana sylvatica), bullfrog (R. catesbeiana), and pickerel frog (R. palustris) breeding site selection. Sites with high species richness were best predicted by 1) connectivity of wetlands in the landscape through stream corridors and 2) wetland modification by beaver. Wood frog breeding habitat was best predicted by temporary hydroperiod, lack of fish, and absence of current beaver activity. Wood frog breeding was present in abandoned beaver wetlands nearly as often as in nonbeaver wetlands. Bullfrog breeding was limited to active beaver wetlands with fish and permanent water. Pickerel frog breeding sites were best predicted by connectivity through stream corridors within the landscape. As beavers have recolonized areas of their former range in North America, they have increased the number and diversity of available breeding sites in the landscape for pond-breeding amphibians. The resulting mosaic of active and abandoned beaver wetlands both supports rich amphibian assemblages and provides suitable breeding habitat for species with differing habitat requirements. Land managers should consider the potential benefits of minimal management of beavers in promoting and conserving amphibian and wetland diversity at a landscape scale.     

Beaver population fluctuations and tropospheric methane emissions in boreal wetlands

Measurements of net methane flux were made during the 1988 ice-free season (May–October) at a beaver-meadow complex in northern Minnesota, USA. The site included upland boreal forest, sedge meadow, submerged aquatic plants, and the open water of a beaver pond. Annual fluxes were 8–11 g C/m² in the permanently wetted zones and 0.2–0.4 g C/m² at the occasionally inundated meadow and forest sites. These data, when coupled with long-term (46 yr) data on beaver (Castor canadensis) population size and habitat alteration, suggest that about 1% of the recent rise in atmospheric methane may be attributable to pond creation by beaver in North America.     

Nitrate transformation and water movement in a wetland area

The NO₃ ^– transformation capacity of a riparian zone at Rabis stream, Denmark, was investigated for a period of 2 years. The riparian zone of 15–25 m received NO₃ ^–-containing groundwater from the adjoining agricultural areas. The water flows as surface runoff along the surface of the wetland and in the root zone towards the stream. Changes in water chemistry, water balance and mass transport were investigated. The riparian zone acted as a buffer zone for NO₃ ^–, PO₄ ^3– and dissolved Fe²⁺. The NO₃ ^–-transformation capacity of the wetland was about 400 kg N ha^–1 y^–1, but varied seasonally. A simple rearrangement of drain systems in wetland areas can probably reduce the NO₃ ^– content of Danish surface waters by 20 000–50 000 t N y^–1.     

Contrasting stream water NO3− and Ca2+ in two nearly adjacent catchments: the role of soil Ca and forest vegetation

Two nearly adjacent subcatchments, located in the Adirondack Mountains of New York State, US, with similar atmospheric inputs of N (0.6 kmol ha^?1 yr^?1), but markedly different stream water solute concentrations, provided a unique opportunity to evaluate the mechanisms causing this variation. Subcatchment 14 (S14) had much greater stream water Ca²⁺ and NO₃^? concentrations (851 and 73 μmol_c L^?1, respectively) than Subcatchment 15 (S15) (427 and 26 μmol_c L^?1, respectively). To elucidate factors affecting the variability in stream water concentrations, soil and forest floor samples from each subcatchment were analyzed for total elemental cations and extractable N species. Mineral soil samples were also analyzed for exchangeable cations. Tree species composition was characterized in each subcatchment and potential differences in land use history and hydrology were also assessed. Compared with S15, soils in S14 had significantly higher total elemental Ca²⁺ in the forest floor (380 vs. 84 μmol g^?1), Bs horizon (e.g. 1361 vs. 576 μmol g^?1) and C horizon (1340 vs. 717 μmol g^?1). Exchangeable Ca²⁺ was also significantly higher in the mineral soil (64 μmol g^?1 in S14 vs. 8 μmol g^?1 in S15). Extractable NO₃^? was higher in S14 compared with S15 in both the forest floor (0.1 vs. 0.01 μmol g^?1) and Bs horizon (0.2 vs. 0.07 μmol g^?1) while extractable NH₄⁺ was higher in S14 vs. S15 in the forest floor (7 vs. 5 μmol g^?1). The total basal area of ‘base‐rich indicator’ tree species (e.g. sugar maple, American basswood, eastern hophornbeam) was significantly greater in S14 compared with S15, which had species characteristic of sites with lower base concentrations (e.g. American beech and eastern white pine). The disparity in stream water Ca²⁺ and NO₃^?, concentrations and fluxes between S14 and S15 were explained by differences in tree species composition and soil properties rather than differences in land use or hydrology. The marked difference in soil Ca²⁺ concentrations in S14 vs. S15 corresponded to the higher stream water Ca²⁺ and the larger contribution of base‐rich tree species to the overstory biomass in S14. Soil under such species is associated with higher net mineralization and nitrification and likely contributed to the higher NO₃^? concentrations in the drainage waters of S14 vs. S15. Studies investigating differences in spatial and temporal patterns of the effects of chronic N deposition on surface water chemistry need to account for changes in tree species composition and how vegetation composition is influenced by soil properties, as well as climatic and biotic changes.     

Influencing factors and formation mechanism of CaCO3 precipitation induced by microbial carbonic anhydrase

Microbial carbonic anhydrase promotes carbonate deposition, which is important in the formation and evolution of global carbon cycle and geological processes. A kind of bacteria producing extracellular carbonic anhydrase was selected to study the effects of temperature, pH value and Ca²⁺ concentration on bacterial growth, carbonic anhydrase activity and calcification rate in this paper. The results showed that the activity of carbonic anhydrase at 30 °C was the highest, which was beneficial to the calcification reaction, calcification rate of CaCO₃ was the fastest in alkaline environment with the initial pH value of 9.0. When the Ca2+ concentration was 60 mM, compared with other Ca²⁺ concentration, CA bacteria could grow and reproduce best, and the activity of bacteria was the highest, too low Ca²⁺ concentration would affect the generation of CaCO₃, while too high Ca²⁺ concentration would seriously affect the growth of bacteria and reduce the calcification rate. Finally, the mechanism of CaCO₃ precipitation induced by microbial carbonic anhydrase was studied. Carbonic anhydrase can accelerate the hydration of CO₂ into HCO₃⁻, and react with OH⁻ and Ca²⁺ to form CaCO₃ precipitation in alkaline environment and in the presence of calcium source.     

Ecosystem engineering by beavers affects mayfly life histories

1. The North American beaver has been studied as a model ecosystem engineer for many decades. Previous studies have documented physical, chemical and biological impacts attributed to beaver engineering in both aquatic and terrestrial environments. This study focused on the effects of ecosystem engineering by beavers on life histories of a common mayfly and on the potential consequences for mayfly populations. 2. We studied 18 montane beaver ponds of varying size and shape in western Colorado near the Rocky Mountain Biological Laboratory. Our goal was to test whether variation in beaver pond morphology (pond size and shape) explains downstream changes in stream temperature, mayfly size and timing of emergence. 3. Downstream water temperatures varied predictably with pond morphology, being colder downstream of high‐head dams and warmer downstream of low‐head dams. Pond morphology was also a significant predictor of variation in the size of mature female Baetis bicaudatus (the most abundant mayfly), with larger females emerging downstream of high‐head dams and smaller females downstream of low‐head dams. The size of male B. bicaudatus was not significantly related to pond morphology or stream temperature. There was no relationship between pond morphology and variation in the timing of emergence of Baetis (males or females) between upstream and downstream reaches. 4. Our results have implications for the effects of beaver ponds on Baetis individual fitness because large Baetis females are more fecund. Therefore, predictable female size variation associated with beaver pond morphology makes it possible to model the effects of beaver activity on local contributions of Baetis to the regional pool of reproductive adults at the catchment scale. Additionally, predictable changes in the size of emerging mayflies may have important consequences for the magnitude of aquatic to terrestrial resource subsidies in beaver‐modified systems.