Cation Budgets Research Articles

Long Term Trends of Base Cation Budgets of Forests in the UK to Inform Sustainable Harvesting Practices

There is growing concern in the UK that available base cation pools in soil are declining due to the combined effects of acid deposition and forest harvesting. To help inform the issue, elemental mass balances for calcium (Ca), magnesium (Mg) and potassium (K) were calculated using more than 10-years (10–24 years) of data from the UK’s ICP Forest Intensive Monitoring Network (Level II) of plots, covering a range of soil types and three tree species—oak, Scots pine and Sitka spruce. Out of the ten sites investigated, small negative Ca balances were observed at three sites and negative K balances on two sites, all on acid geology and nutrient poor soils, which were previously heavily acidified due to acid deposition. There is sufficient Ca and K in the soil exchangeable pool to sustain forest growth on these sites, however, if the present rate of Ca and K loss continues forest health and productivity are likely to be threatened within a few forest rotations. Magnesium showed a positive balance at all but one site, partly sustained by marine deposition. Base cation budgets were significantly (p < 0.01) positively related to soil exchangeable cations and soil base saturation status. Six of the sites showed an increasingly statistically significant positive cation balance with time, attributed to a decline in leaching linked to recovery from acidification. This included the three sites with negative Ca balance, although Ca remained in deficit. One site (Alice Holt) exhibited a decreasing cation balance, driven by a continued significant decline in base cation deposition thought to be related to pollutant emission control. The results were used to simulate the impact of different forest biomass harvesting scenarios involving the removal of brown (extracted after needle drop) or green (extracted before needle drop) brash. Podzols and deep peats were found to be the most vulnerable to brash harvesting causing Ca and K imbalance, but problems also occurred on brown earths. Impacts were greatest for the extraction of green brash from higher productivity stands. Base cation balance calculations remain highly uncertain due to the restricted nature of available measurements and wide variation of some estimates, particularly inputs from mineral weathering. More data are required to check and improve model predictions to better guide forest harvesting practice and ensure sustainable forest management.

Base cation budgets under residue removal in temperate maritime plantation forests

The removal of harvest residues—branches, treetops and needles—has the potential to impact the long-term sustainability of forest soils. In this study we used mass balance calculations to predict the impact of harvesting on ecosystem balances of calcium (Ca), magnesium (Mg), potassium (K) as well as on soil acidification (ANCle) for forests in Ireland. Balances were determined for three harvesting scenarios: stem-only harvest (SOH), stem plus branch harvest (SBH) and whole-tree harvest (WTH). The study was carried out at forty sites—selected on a grid across the country. The sites were plantations of Sitka spruce (Picea sitchensis (Bong.) Carr), Norway spruce (Picea abies (L.) Karst.) and provenances of lodgepole pine (Pinus contorta (Dougl. var. latifolia)). Flux calculations were based on site measurements of standing biomass and soil properties as well as regional maps of atmospheric deposition. Under SOH and SBH, inputs were predicted to be sufficient to meet outputs for Ca, Mg and K budgets. Atmospheric deposition was the most important input to Ca and Mg balances. For K, inputs from mineral weathering were as important as deposition. Under WTH, Ca output was greater than input at 19 of the 40 study sites. However, the difference was small relative to the size of soil Ca pools; at these sites, exchangeable pools could support WTH removal for a median of 220years. Magnesium and K removal under WTH was supported by inputs in deposition and weathering. For soil acidification budgets (ANCle), base cation (BC) removal in harvesting under all scenarios was much greater than that BC generated by weathering, suggesting that soils will become acidified over the long term. There was considerable uncertainty around the calculation of fluxes. For Ca balances, confidence intervals spanned positive and negative values at many sites such that it was not possible to predict the balance of Ca budgets. In addition, uncertainty in flux calculations was particularly important for K budget because soil exchangeable pools were small and could be depleted within one to two rotations.

Estimating weathering rates using base cation budgets in a Norway spruce stand on podzolised soil: Analysis of fluxes and uncertainties

Since forestry is often allocated to soils with a low weathering capacity, reliable estimates of weathering rates are crucial in analyses of sustainability, e.g. of whole-tree and stump harvesting. In the present study, weathering rates (kgha−1yr−1) for base cations were estimated using cation budgets in a replicated (n=4) experimental Norway spruce (Picea abies (L.) Karst.) plantation situated on a nutrient-poor glacial till in south-west Sweden and aged 25–39years during the study period. Weathering rates (central values) were 2.4, 1.4, 0.3 and 2.3kgha−1yr−1 for Ca, Mg, K and Na, respectively. However, weathering was a minor flux in the overall cycling of these cations in the ecosystem, and the confidence intervals of the weathering estimates had amplitudes that generally were greater than the central values. The overall uncertainties were divided into (i) regular standard errors of the mean, expressing spatial variability, sampling errors and random method-related errors in data from measurements replicated over the experimental plots (‘Type A’ uncertainties), and (ii) estimated standard uncertainties accounting for systematic errors of methods, and of uncertainties in variables, functions and factors not replicated over the plots (‘Type B’ uncertainties). For Ca and K, bioaccumulation dominated the overall uncertainty. Most (>90 %) of this uncertainty, in turn, was of Type A (between-plot variability in measured stem diameters and cation concentrations); the remainder resulted from Type B uncertainties in allometric functions etc. Hence, regular standard errors over plots yielded a correct level of uncertainty of weathering estimates for these ions at the studied site. For Mg and Na, however, deposition and leaching were large terms in the cation budget. Whereas the uncertainty in deposition was mostly taken into account by plot-wise replicated measurements of throughfall (Type A uncertainty), Type B uncertainties were crucial to the estimates of leaching. Due to the fact that uncertainties accumulate when terms are added and subtracted in a cation budget, it is difficult to predict the sustainability of the pools of exchangeable cations from estimated weathering rates; it may be better to measure them directly in the soil. However, in the studied ecosystem these had a rapid turnover (mean residence time, 1–4years), and underwent abrupt fluctuations over only a few years. A study performed during a limited time may therefore suffer from considerable temporal uncertainties, if the results are to be generalised for a longer period.

Partitioning the impact of environmental factors on lake concentrations and catchment budgets for base cations in forested ecosystems

Seventy-two forested lake catchments were studied in Quebec (Canada) to examine the influence of climate, atmospheric deposition and catchment characteristics on base cation (BC) concentrations in lake waters (BCC) and base cation budgets at the catchment scale (BCQ). The catchments are located along a bioclimatic gradient in a vast (180000km2) study area underlained by the Canadian Shield. Multivariate statistical approaches are used to simultaneously assess the effects of multiple environmental factors on cation fluxes. Mean annual BCC were 132, 40, 24 and 7μmolcl−1 for Ca, Mg, Na and K, respectively. Mean annual BCQ estimates showed exports of 0.826, 0.251, 0.135 and 0.043kmolcha−1an−1 for Ca, Mg, Na and K, respectively. There were strong similarities in the spatial variation of BCC and BCQ, and also in their links with environmental factors. We hypothesized that the spatial variability of both, BCC and BCQ, were strongly influenced by the spatial variability in the rates of mineral weathering reactions. Variance partitioning indicated that climate-related effects accounted for 51.6% and 52.7% of the variation in BCQ and BCC, respectively. Nonetheless, lake/catchment morphometry and variables linked to solutes sources (lithology, atmospheric deposition and soil properties) were also included in some models. Overall, BCC and BCQ were positively affected by temperature, precipitation as rain and sulphate depositions, and negatively influenced by precipitation as snow and the number of frost days. Multivariate models explaining up to 69% of variation in BCC and BCQ were developed. This study shows the strong impact of climatic drivers on base cation budgets and, thus, on mineral weathering at the regional scale on the Canadian Shield.

Long-term changes in the chemical properties of Japanese cedar (Cryptomeria japonica) forest soils under high precipitation in southwest Japan

There is insufficient direct evidence of long-term changes in the chemical properties of forest soils to provide information for forestry management plans for sustainable site productivity. To understand changes in the chemical properties of forest soils in a specific high-precipitation climate in Japan, we re-investigated, in 1997, soil pits within a Japanese cedar (Cryptomeria japonica) forest in the Yanase region of Kochi Prefecture which had previously been surveyed in 1976. Comparison of the 1976 and 1997 results revealed significantly lower pH of surface and subsurface soils, and fewer exchangeable cations over time. In contrast, subsoil pH, concentrations of total carbon and nitrogen, and cation-exchange capacity (CEC) had not changed over the 21-year period. Estimation of proton and cation budgets in the forest ecosystem over 21 years, using data for the amounts in soil, biomass accumulation, and input through precipitation, revealed that biomass accumulation did not explain the cation depletion in soils. This suggests that cations were leached from the ecosystem. In contrast with previous reports, which showed Ca accumulation in Japanese cedar forest soils, our results indicated that high precipitation of more than 4,000 mm combined with acid deposition resulted in soil acidification and leaching of cations from soils, following the decrease in base saturation.

Seasonal variability of element fluxes in two Central Siberian rivers draining high latitude permafrost dominated areas

In order to constrain the origin and fluxes of elements carried by rivers of high latitude permafrost-dominated areas, major and trace element concentrations as well as Sr and U isotopic ratios were analyzed in the dissolved load of two Siberian rivers (Kochechum and Nizhnyaya Tunguska) regularly sampled over two hydrological cycles (2005–2007). Large water volumes of both rivers were also collected in spring 2008 in order to perform size separation through dialysis experiments. This study was completed by spatial sampling of the Kochechum watershed carried out during summer and by a detailed analysis of the main hydrological compartments of a small watershed. From element concentration variations along the hydrological cycle, different periods can be marked out, matching hydrological periods. During winter baseflow period (October to May) there is a concentration increase for major soluble cations and anions by an order of magnitude. The spring flood period (end of May-beginning of June) is marked by a sharp concentration decrease for soluble elements whereas dissolved organic carbon and insoluble element concentrations strongly increase. When the spring flood discharge occurs, the significant increase of aluminum and iron concentrations is related to the presence of organo-mineral colloids that mobilize insoluble elements. The study of colloidal REE reveals the occurrence of two colloid sources successively involved over time: spring colloids mainly originate from the uppermost organic-rich part of soils whereas summer colloids rather come from the deep mineral horizons. Furthermore, U and Sr isotopic ratios together with soluble cation budgets in the Kochechum river impose for soluble elements the existence of three distinct fluxes over the year: (a) at the spring flood a surface flux coming from the leaching of shallow organic soil levels and containing a significant colloidal component (b) a subsurface flux predominant during summer and fall mainly controlled by water–rock interactions within mineral soils and (c) a deep groundwater flux predominant during winter which enters large rivers through unfrozen permafrost-paths. Detailed study of the Kochechum watershed suggests that the contribution of this deep flux strongly depends on the depth and continuous nature of the permafrost.

IMPACT OF NUTRIENT REMOVAL THROUGH HARVESTING ON THE SUSTAINABILITY OF THE BOREAL FOREST

The cycling of base cations (K, Ca, Mg, and Na) was investigated in a boreal balsam fir forest (the Lake Laflamme Watershed) between 1999 and 2005. Base cation budgets were calculated for the soil rooting zone that included atmospheric deposition and soil leaching losses, two scenarios of tree uptake (whole-tree and stem-only harvesting), and three scenarios of mineral weathering, leading to six different scenarios. In every scenario there was a net accumulation of Mg within the soil exchangeable reservoir, while Ca accumulated in four scenarios. Potassium was lost in five of the six scenarios. Contrary to Ca and Mg, immobilization of K within tree biomass (69 mol x ha(-1) x yr(-1)) was the main pathway of K losses from the soil exchangeable reservoir, being five times higher than losses via soil leaching (14 mol x ha(-1) x yr(-1)). The amounts of K contained within the aboveground biomass and the exchangeable soil reservoir were 3.3 kmol/ha and 4.2 kmol/ha, respectively. Whole-tree harvesting may thus remove 44% of the K that is readily available for cycling in the short term, making this forest sensitive to commercial forestry operations. Similar values of annual K uptake as well as a similar distribution of K between tree biomass and soil exchangeable reservoirs at 14 other coniferous sites, distributed throughout the boreal forest of Quebec, suggest that the Lake Laflamme Watershed results can be extrapolated to a much larger area. Stem-only harvesting, which would reduce K exports due to biomass removal by 60%, should be used for these types of forest.

The ecological significance of the coarse soil fraction for Picea abies (L.) Karst. seedling nutrition

Recent studies showed that the coarse fraction of soils can have a considerable stock of short-term available nutrients. However, a direct proof that coarse soil fragments have significant nutritional functions in forest ecosystems is missing. In a 23 week microcosm experiment with controlled in- and output, mycorrhizal (Laccaria bicolor S238N) and non-mycorrhizal Norway spruce seedlings (Picea abies (L.) Karst.) were grown on either coarse soil fragments (dark paragneiss, Black Forest, S-W Germany) or quartz only. The microcosms were irrigated with a solution adjusted to the mean ionic composition of the soil solution in the reference profile, but devoid of Ca and Mg. The uptake rates of Ca and Mg by spruce seedlings were sufficient to allow normal root and shoot growth. Mycorrhization was low and did not have a significant influence on seedling nutrition. The oxalic anion was found in concentrations below 1.5 mg L−1 in the leachate, approximately corresponding to a C2O42−-saturation in equilibrium with precipitated calcium oxalate. Cation budgets and relationships among the cation species suggest that exchange processes were the main trigger of Ca and Mg mobilisation and uptake rather than protolytic weathering by exudation of carboxylic acids. The exchange processes may be attributed to weathering cracks filled with fine material of high base saturation. Therefore it is concluded that the short-term nutritional functions of coarse soils in forest sites are significant, and exchange mechanisms in the “stone protected fine earth” are in principal the same as they are known for the “free fine earth”.

Solute geochemical mass-balances and mineral weathering rates in small watersheds: Methodology, recent advances, and future directions

Solute-based geochemical mass balance methods are commonly used in small-watershed studies to estimate rates of a variety of geochemical processes at the Earth’s surface, including primary-mineral weathering and soil formation, and the quantitative contribution of these elemental transfer processes to cation budgets, nutrient cycling, and landscape susceptibility to acid deposition. Weathering rates of individual minerals in watershed mass-balance studies are determined by solving a system of simultaneous linear geochemical mass-balance equations with constant (stoichiometric) coefficients. These equations relate the measured net fluxes to the (known) stoichiometries and (unknown) rates of weathering reactions for multiple minerals in the weathering profiles. Solving the system of equations requires petrologic, mineralogic, hydrologic, botanical, and aqueous geochemical data. The number of mineral-weathering rates that can be determined is limited by the number of elements for which solute mass-balance equations can be written. In addition to calculating mineral weathering rates, elemental transfer into or out of the biomass may also be calculated. Elemental uptake by aggrading forest vegetation can act as an intrawatershed sink for at least some mineral-derived cations, producing mineral weathering rates higher than would be estimated from solute fluxes alone; similarly, element release from decaying forest biomass can result in higher solute fluxes than are produced by weathering alone. The mathematics of, significant contributions from, role of biomass in, and recent advances in, watershed geochemical mass-balance methods are discussed using examples from the Appalachian headwaters watersheds of the Coweeta Hydrologic Laboratory in the southern Blue Ridge Physiographic Province of North Carolina, USA.

Impact of Harvest Intensity on Long-Term Base Cation Budgets in Swedish Forest Soils

The effects of harvesting on the long-term mass balances of calcium (Ca), magnesium (Mg) and potassium (K) were evaluated on a regional level in Sweden. A new high-resolution weathering database was used together with estimates of total deposition, losses through harvest and leaching. Estimates were made for pine and spruce separately and for two harvesting intensity scenarios: stem harvesting and whole-tree harvesting. The mass balance calculations showed net losses of Ca and Mg in almost the whole country for both scenarios. The losses were smaller for pine than for spruce. The K balances were mainly positive for pine but negative for spruce. Leaching was a main factor in the mass balances, especially for Ca and Mg. Whole-tree harvesting in spruce forests led to substantially higher net losses of K and Ca than stem harvesting, according to the calculations. In the whole-tree harvesting scenario in spruce forests the estimated yearly net losses of Ca, Mg and K corresponded to at least 5%, 8% and 3% of the pools of exchangeable base cations, respectively, at 25% of the analysed sites. If losses of this magnitude continue the depletion of the pools of Ca, Mg and K may lead to very low base saturation of the soils, possibly accompanied by negative effects on soil fertility, runoff water quality, tree vitality and tree growth within a forest rotation in parts of Sweden. Avoiding whole-tree harvesting can improve the situation substantially for K, but the losses of Ca and Mg will still be significant.

Sulphate, Nitrogen and Base Cation Budgets at 21 Forested Catchments in Canada, the United States and Europe

To assess the concern over declining base cation levels in forest soils caused by acid deposition, input-output budgets (1990s average) for sulphate (SO(4)), inorganic nitrogen (NO(3)-N; NH(4)-N), calcium (Ca), magnesium (Mg) and potassium (K) were synthesised for 21 forested catchments from 17 regions in Canada, the United States and Europe. Trend analysis was conducted on monthly ion concentrations in deposition and runoff when more than 9 years of data were available (14 regions, 17 sites). Annual average SO(4) deposition during the 1990s ranged between 7.3 and 28.4 kg ha(-1) per year, and inorganic nitrogen (N) deposition was between 2.8 and 13.8 kg ha(-1) per year, of which 41-67% was nitrate (NO(3)-N). Over the period of record, SO(4) concentration in deposition decreased in 13/14 (13 out of 14 total) regions and SO(4) in runoff decreased at 14/17 catchments. In contrast, NO(3)-N concentrations in deposition decreased in only 1/14 regions, while NH(4)-N concentration patterns varied; increasing at 3/14 regions and decreasing at 2/14 regions. Nitrate concentrations in runoff decreased at 4/17 catchments and increased at only 1 site, whereas runoff levels of NH(4)-N increased at 5/17 catchments. Decreasing trends in deposition were also recorded for Ca, Mg, and K at many of the catchments and on an equivalent basis, accounted for up to 131% (median 22%) of the decrease in acid anion deposition. Base cation concentrations in streams generally declined over time, with significant decreases in Ca, Mg and K occurring at 8, 9 and 7 of 17 sites respectively, which accounted for up to 133% (median 48%) of the decrease in acid anion concentration. Sulphate export exceeded input at 18/21 catchments, likely due to dry deposition and/or internal sources. The majority of N in deposition (31-100%; median 94%) was retained in the catchments, although there was a tendency for greater NO(3)-N leaching at sites receiving higher (<7 kg ha(-1) per year) bulk inorganic N deposition. Mass balance calculations show that export of Ca and Mg in runoff exceeds input at all 21 catchments, but K export only exceeds input at 16/21 sites. Estimates of base cation weathering were available for 18 sites. When included in the mass balance calculation, Ca, Mg and K exports exceeded inputs at 14, 10 and 2 sites respectively. Annual Ca and Mg losses represent appreciable proportions of the current exchangeable soil Ca and Mg pools, although losses at some of the sites likely occur from weathering reactions beneath the rooting zone and there is considerable uncertainty associated with mineral weathering estimates. Critical loads for sulphur (S) and N, using a critical base cation to aluminium ratio of 10 in soil solution, are currently exceeded at 7 of the 18 sites with base cation weathering estimates. Despite reductions in SO(4) and H(+) deposition, mass balance estimates indicate that acid deposition continues to acidify soils in many regions with losses of Ca and Mg of primary concern.

Base Cation and Nitrogen Budgets for a Mixed Hardwood Catchment in South-central Ontario

There is growing concern that available base cation pools in soil are declining in eastern North America and that some forests are approaching nitrogen (N) saturation due to the combined effects of acid deposition and harvesting. To assess these concerns, elemental mass balances for calcium (Ca), magnesium (Mg), potassium (K), and N were conducted over a 17-year period in a representative mixed hardwood forest (HP4) in the Muskoka-Haliburton region in central Ontario, Canada. On average, 76% of the N measured in bulk deposition, which is a conservative estimate of total N deposition, was retained in HP4, with tree uptake accounting for over half of the retained N. Year-to-year variations in annual NO3 export were affected by climate variations, although the low annual NO3-N concentrations (80–156 μg/L) suggest that HP4 is not approaching N saturation. Losses of Ca, Mg, and K in stream export plus accumulation in trees (more than 12 cm in diameter at breast height) exceeded inputs in deposition by 296, 76.2, and 53.6 kg/ha, respectively, over the 17-year period. Inclusion of mineral weathering estimates obtained using PROFILE, zirconium (Zr) depletion, and total analysis correlation failed to balance Ca losses from HP4, and calculations indicate that between 98 and 145 kg/ha (depending on mineral weathering estimate) was lost from the soil exchangeable pool between 1983 and 1999. These losses were supported by repeated field measurements, which showed that the exchangeable Ca concentrations and soil pH decreased over the 17-year period, particularly in the upper soil horizons. When mineral weathering estimates are included, mass balance calculations generally indicated that there was no net loss of Mg and K from HP4, which was confirmed by our soil measurements. At present, there is sufficient Ca in the soil exchangeable pool to sustain forest growth at HP4; however, continued losses of Ca due to leaching and harvesting at the present rate may ultimately threaten the health and productivity of the forest within just a few decades.

Biogeochemical modelling of EXMAN research sites: A comparison

The Experimental Manipulation of Forest Ecosystems in Europe (EXMAN) project was conducted to assess the effects caused by atmospheric deposition on forest ecosystems. The dynamic biogeochemical model, Soil Acidification in Forest Ecosystems (SAFE), was used to simulate the soil and soil solution chemistry at Ballyhooly (IR), Höglwald (DE), Klosterhede (DK) and Solling (DE) from 1800 to 2000. The model considers soil processes (cation exchange, weathering, solution equilibria) and external forcing function (deposition, hydrology, nutrient uptake). The model was successfully calibrated to all EXMAN sites. Base cation budgets were evaluated, and they demonstrate the importance of nutrient cycling for the element fluxes in the rooting zone. The vital stands Ballyhooly and Höglwald have higher litterfall rates and the lowest canopy leaching rates than Klosterhede and Solling. SAFE suggests that the soils at Höglwald and Ballyhooly are still being depleted of base cations, while Klosterhede and Solling are close to a steady-state or show slight recovery. Comparison with soil solution data show that SAFE reproduces the pH insolution in the most soil layers. One exception was the O-layer in Höglwald, where underpredicted pH resulted from overestimation of nitrification. Base cation concentrations were well reproduced for all layers for all sites. SAFE predicts that base cation concentrations at all sites have reached a peak, and will decline. Calculated aluminium concentrations were within the range of the observations. The model shows that nutrient cycling dominates O-layer chemistry. N-uptake appears to follow the fine root biomass distribution. To reproduce base cation fluxes correctly, base cation uptake had to be allocated to lower soil layers. Al-solubility was similar for comparable sites. The effects of shortcoming in the SO 4 2− chemistry of SAFE on model predictions was discussed. The model predicted the major effects of the ‘clean rain’ manipulation on soil solution at Solling, decreased Al and base cation concentrations and increased pH. The model application to the Klosterhede manipulation was difficult to evaluate due to the temporal variability in experimental data, caused by the marine influence.

The role of surface and sub-surface runoff processes in controlling cation export from a wetland watershed

Water and cation budgets were calculated for two sub-basins within a small low relief watershed in South-Central Ontario during a period of ephemeral runoff which was initiated by spring snow melt. The hydrology of one (upland) sub-basin was strongly influenced by seasonal fluctuations in the level of regional ground water. Saturated contributing areas formed in low lying regions adjacent to the stream channel where the water table rose to the surface, and stream discharge was a mixture of ground water and saturation overland flow. In the second sub-basin a wetland provided a large and spatially less variable saturated contributing area. Clay soils underlying the wetland resulted in a shallow perched water table, poorly drained and highly organic soils, and greatly reduced inputs of regional ground water. Stream discharge was largely the result of surface runoff from the wetland and adjacent areas of saturated soil.

Geochemical mass balances and weathering rates in forested watersheds of the southern Blue Ridge; III, Cation budgets and the weathering rate of amphibole

The geochemical mass balance of alkali and alkaline- earth elements in a southern Blue Ridge watershed underlain by amphibolite (Carroll Knob Complex; Watershed 3 of the U.S. Forest Service Coweeta Hydrologic Laboratory, Otto, North Carolina) can be explained by weathering of plagioclase (oligoclase-andesine), horn- blende (ferroan pargasite), biotite, and calcite, and elemental uptake by forest biota. Feldspar and biotite weathering rates (calculated from geochemical mass balance) in the amphibolitic watershed are similar to previously calculated rates for compositionally similar minerals in the surrounding gneissic/schistose watersheds. However, the similarity of feldspar weathering rates despite significant differences in modal abun- dance suggests that feldspar in the Carroll Knob Complex is somewhat less reactive per unit modal abundance than is plagioclase in the surrounding rocks. Textural differences between the Carroll Knob Complex and the surrounding rocks (smaller surface—area—to—volume- ratio of coarser crystals in the Carroll Knob Complex) could be respon- sible. Hornblende and plagioclase weathering rates in Coweeta Water- shed 3 are approximately equal (when normalized for differences in modal abundance of the two minerals), consistent with experimentally determined rates and empirical weathering series.

Geochemical mass balances and weathering rates in forested watersheds of the southern Blue Ridge II. Effects of botanical uptake terms

Geochemical mass balance methods are commonly used in small-watershed studies to estimate rates of primary-mineral weathering and soil formation, and the contribution of these processes to cation budgets, nutrient cycling, and landscape susceptibility to acid deposition. Many researchers employ the “balance sheet” approach, a system of simultaneous linear equations with constant coefficients which represent the steady-state behavior of the modelled system. Most workers also assume that the steady-state assumption for the entire system means that botanical factors can be ignored; in other words, that there is no net elemental transfer between biomass and inorganic compartments of the system. However, the widely invoked assumption that biomass is at steady-state is mathematically a second, explicit assumption, not a built-in mathematical consequence of the assumption of overall steady-state. The common assumption that the biomass is necessarily at steady-state in a steady-state system ignores the possibility of uptake of elements into the forest biomass. To quantify the implications of the separate mathematical assumptions, weathering rates for seven forested watersheds in the southern Blue Ridge mountains are calculated twice, once allowing for net element exchange with biomass, and once assuming no net exchange with biomass. Our calculations show that misunderstanding the mathematical constraints which are built into the most widely used geochemical mass balance equations commonly causes errors (underestimates) of up to a factor of 4 in the calculated rates of mineral weathering and soil formation. This problem is most pronounced for minerals which contain major nutrient elements, and for rates calculated from mass balances of those nutrient elements.

Groundwater chemistry and cation budgets of tropical karst outcrops, Peninsular Malaysia, I. Calcium and magnesium

The discharge and chemical properties of 217 autogenic groundwaters were monitored over a 1-yr period in the tower karsts of central Selangor and the Kinta Valley, and in the Setul Boundary Range. Because of differences in soil P CO 2 , calcium concentrations are significantly higher in the Boundary Range (mean, 82.5 mg l −1) than in the tower karst terrain (44.6 mg l −1). Local differences in both source area P CO 2 and amounts of secondary deposition underground cause marked intersite variability, particularly in the tower karst. Dilution occurs during flood peaks in certain conduit and cave stream waters. Generally, however, calcium correlates positively with discharge, since the amount of secondary deposition per unit volume of water decreases at higher flows. Magnesium concentrations and Mg:Ca + Mg ratios of groundwaters are strongly influenced by bedrock composition, though bedrock heterogeneity and the kinetics and equilibria of carbonate dissolution reactions preclude extremely low or high Mg:Ca + Mg values. Net chemical denudation rates range from 56.6 to 70.9 m 3km 2yr −1. The results are considered in relation to cation fluxes in surface runoff, soil throughflow and nutrient cycling. Preliminary calcium and magnesium budgets show that (1) dissolutional activity is largely confined to the near-surface zone; and (2) the annual uptake of calcium and magnesium by tropical limestone forests is similar in magnitude to the net solute output in groundwaters.

The Effects of Leaching and Whole‐tree Harvesting on Cation Budgets of Several Forests

AbstractThe effects of acid deposition, natural leaching, and harvesting on base cation export from forests in Maine, Tennessee, South Carolina, North Carolina, and Washington were compared. Based on previous literature, we hypothesized that base cation export via whole‐tree harvesting (WTH) would be nearly independent of soil exchangeable base cation supplies; base cation export via leaching would be strongly dependent on the exchangeable cation supplies as well as the input, production, and mobility of anions. This hypothesis was supported by the data: mixed deciduous sites in Tennessee had among the highest base cation (principally Ca) exports via WTH (1.2 kmolc ha−1 yr−1), yet the lowest soil exchangeable supplies (35 kmolc ha−1), whereas the Washington sites had by far the highest base cation leaching (5–41 kmolc ha−1 yr−1, due to very high levels of naturally produced HCO−3) and soil exchangeable supplies, yet only relatively moderate base cation exports via WTH (0.4 kmolc ha−1 yr−1). Sulfate was either the dominant or a major anion in soil solutions from the eastern sites, suggesting that atmospheric deposition was a major factor in soil leaching from these sites (0.2–2.1 kmolc ha−1 yr−1), but total leaching rates from these sites were much lower than at the Washington sites. Indeed, some of the eastern sites showed a net annual accumulation of one or more base cations from atmospheric deposition. Some of the southeastern sites with Ultisols showed the expected net retention of SO2−4, but the sites in the Tennessee Valley near Oak Ridge showed surprisingly little ecosystem SO2−4 retention, perhaps due to lower soil SO2−4 adsorption in these soils than in other Ultisols.

Growth and Major Inorganic Cation Budgets of Atlantic Salmon Alevins at Three Ambient Acidities

Abstract Budgets of Ca++, Mg++, Na+, and K+ were determined for alevins of Atlantic salmon Salmo salar incubated at pH 6.8, 5.1, or 4.5. Accumulation of Ca++, K +, and Na + by larvae was reduced at pH 4.5 whereas Mg++ accumulation was unaffected. The extrapolated dry weight of larvae at terminal yolk resorption was reduced from 27 mg at pH 6.8 and 5.1 to 20 mg at pH 4.5. The findings support the hypothesis that high acidity affects ion uptake from the ambient water more than yolk-to-larva transfer of cations.

Studies of Cation Budgets in the Southern Appalachians on Four Experimental Watersheds with Contrasting Vegetation

Nutrient fluxes within and through watershed ecosystems at the Coweeta Hydrologic Laboratory are under study. This paper describes the annual budgets and seasonal fluctuations for selected cations. Concentrations and flux of cations moving through a hardwood forest stand, a weed to forest succession, a hardwood coppice stand and an eastern white pine stand on steep mountain topography are compared. Stream discharge was greater by 6% for the successional weed stand, and 10% for the second hardwood coppice, but 15% less for the young pine stand in contrast to pretreatment levels. Although concentrations for Ca(++), Mg(++), K+ and Na+ combined were usually less than 3.5 ppm, over 98% of the loss of each cation was in dissolved form on all four watersheds. Regression analysis showed that 50 to 60% of the variation in monthly weighted average concentration was accounted for by monthly discharge amounts. Annual losses of the four cations from the mature hardwood stand were in the amounts of approximately 7, 3, 5, and 10 kg/ha respectively for the Ca(++), Mg(++), K+ and Na+. Annual budgets showed net changes to be —0.8, —2.0, and —4.3 kg/ha, respectively, for this mature hardwood ecosystem. In contrast, the weed stand lost significantly greater amounts, and the young pine and hardwood coppice watersheds showed a net gain in Ca(++) and significantly lower losses than the mature ecosystem for the other three ions. These budgets show that major alterations to these forest ecosystems are not now producing a substantial out—flux for these cations.