The effect of forest type on throughfall deposition and seepage flux: a review

Converting deciduous forests to coniferous plantations and vice versa causes environmental changes, but till now insight into the overall effect is lacking. This review, based on 38 case studies, aims to find out how coniferous and deciduous forests differ in terms of throughfall (+stemflow) deposition and seepage flux to groundwater. From the comparison of coniferous and deciduous stands at comparable sites, it can be inferred that deciduous forests receive less N and S via throughfall (+stemflow) deposition on the forest floor. In regions with relatively low open field deposition of atmospheric N (<10 kg N ha⁻¹ year⁻¹), lower NH₄⁺ mean throughfall (+stemflow) deposition was, however, reported under conifers compared to deciduous forest, while in regions with high atmospheric N pollution (>10 kg N ha⁻¹ year⁻¹), the opposite could be concluded. The higher the open field deposition of NH₄⁺, the bigger the difference between the coniferous and deciduous throughfall (+stemflow) deposition. Furthermore, it can be concluded that canopy exchange of K⁺, Ca²⁺ and Mg²⁺ is on average higher in deciduous stands. The significantly higher stand deposition flux of N and S in coniferous forests is reflected in a higher soil seepage flux of NO₃⁻, SO₄²⁻, K⁺, Ca²⁺, Mg²⁺ and Al(III). Considering a subset of papers for which all necessary data were available, a close relationship between throughfall (+stemflow) deposition and seepage was found for N, irrespective of the forest type, while this was not the case for S. This review shows that the higher input flux of N and S in coniferous forests clearly involves a higher seepage of NO₃⁻ and SO₄²⁻ and accompanying cations K⁺, Ca²⁺, Mg²⁺ and Al(III) into the groundwater, making this forest type more vulnerable to acidification and eutrophication compared to the deciduous forest type.     

Hillslope Nutrient Dynamics Following Upland Riparian Vegetation Disturbance

We investigated the effects of removing near-stream Rhododendron and of the natural blowdown of canopy trees on nutrient export to streams in the southern Appalachians. Transects were instrumented on adjacent hillslopes in a first-order watershed at the Coweeta Hydrologic Laboratory (35°03′N, 83°25′W). Dissolved organic carbon (DOC), K⁺, Na⁺, Ca²⁺, Mg²⁺, NO₃ ⁻-N, NH₄ ⁺-N, PO₄ ³⁻-P, and SO₄ ²⁻ were measured for 2 years prior to disturbance. In August 1995, riparian Rhododendron on one hillslope was cut, removing 30% of total woody biomass. In October 1995, Hurricane Opal uprooted nine canopy trees on the other hillslope, downing 81% of the total woody biomass. Over the 3 years following the disturbance, soilwater concentrations of NO₃ ⁻-N tripled on the cut hillslope. There were also small changes in soilwater DOC, SO₄ ²⁻, Ca²⁺, and Mg²⁺. However, no significant changes occurred in groundwater nutrient concentrations following Rhododendron removal. In contrast, soilwater NO₃ ⁻-N on the storm-affected hillslope showed persistent 500-fold increases, groundwater NO₃ ⁻-N increased four fold, and streamwater NO₃ ⁻-N doubled. Significant changes also occurred in soilwater pH, DOC, SO₄ ²⁻, Ca²⁺, and Mg²⁺. There were no significant changes in microbial immobilization of soil nutrients or water outflow on the storm-affected hillslope. Our results suggest that Rhododendron thickets play a relatively minor role in controlling nutrient export to headwater streams. They further suggest that nutrient uptake by canopy trees is a key control on NO₃ ⁻-N export in upland riparian zones, and that disruption of the root–soil connection in canopy trees via uprooting promotes significant nutrient loss to streams. Received 30 January 2001; accepted 25 July 2002.     

Ecophysiological differences between fringe and dwarf Avicennia marina mangroves

In this investigation, morphological and physiological differences between fringe and dwarf Avicennia marina (Forsk.) Vierh. growing in seawater and hypersalinity were compared along a tree height and productivity gradient in Richards Bay, South Africa. Dwarf trees had thicker leaves and cuticles, lower specific leaf area and salt gland frequency, while the concentrations of total chlorophyll and chlorophylls a and b were lower by 26, 23 and 39%, respectively, compared to fringe trees. Soil ψ and soil salinity were −3.04 ± 0.09 MPa and 36 ± 3 psu in the fringe zone, compared to −7.24 ± 0.38 MPa and 58 ± 5 psu, respectively, in the dwarf zone. Midday minimum xylem ψ was −4.3 ± 0.23 MPa in the fringe zone and −6.4 ± 0.28 MPa in the dwarf zone. In leaves of dwarf trees, the concentration of Na⁺ was 30% higher, while those of K⁺, Ca²⁺ and Mg²⁺ were lower by 41, 38 and 55%, respectively, than fringe trees. The Na⁺/K⁺ ratio of leaves was 2.1 ± 0.03 for fringe and 5.6 ± 0.05 for dwarf trees. Rates of secretion of Na⁺, Cl⁻, K⁺, Ca²⁺ and Mg²⁺ over 24 h were significantly lower in dwarf trees by 44, 45, 78, 66 and 54%, respectively. In fringe trees, the rate of secretion of Na⁺ and Cl⁻ was about 28% higher during the night than during the day, while in dwarf trees the corresponding increase was about 174%. CO₂ exchange, leaf conductance, quantum yield of PS II, ETR through PSII and intrinsic photochemical efficiency of PS II were significantly lower in dwarf trees by 50, 83, 39, 33 and 12%, respectively.     

Relationship between river water quality and land use in a small river basin running through the urbanizing area of Central Japan

In this study, the relationship between water quality (as represented by major inorganic ion concentrations) and land use characteristics is examined for a small river basin which runs through the urbanizing area of central Japan. Water samples were taken from 24 sites at base flow and analyzed, and the proportions of the various land uses associated with the respective drainage basins were calculated using a digital land-use map (scale: 1:25000). The electrical conductivity (EC) of the water ranged from 84.5 to 600 μS cm⁻¹. Ca²⁺ and Na⁺ were the major cations, accounting for 77% of all cations. Among the anions, HCO₃ ⁻ was dominant (56%), followed by Cl⁻ (24%), SO₄ ²⁻ (13%) and NO₃ ⁻ (7%). Applying principal component analysis to land use in the drainage basin yielded three principal components. The first principal component expressed the degree of occupation by residential areas, the second indicated the degree of urban developing area (i.e., fast-developing and industrial areas), and the third showed the degree of coverage with farmland and green space. The residential area showed significant positive correlations with K⁺, Mg²⁺, Ca²⁺, NO₃ ⁻, HCO₃ ⁻, EC and TMI (total major ions). Urban developing area showed significant positive correlations with Ca²⁺, Cl⁻, HCO₃ ⁻, EC and TMI as well as weak negative correlations with NO₃ ⁻ and SO₄ ²⁻. Industrial area showed weak positive correlations with Na⁺ and Cl⁻ and a moderate negative correlation with NO₃ ⁻. Farmland showed significant positive correlations with NO₃ ⁻ and SO₄ ²⁻; these ions are present due to fertilizers and the biological activity of plants. Forest area is inversely related to almost all ions, indicating the need for this form of land use in order to maintain river water quality.     

Magnesium Transport Across the Basolateral Plasma Membrane of the Fish Enterocyte

In tilapia (Oreochromis mossambicus) intestine, Mg²⁺ transport across the epithelium involves a transcellular, Na⁺- and Na⁺/K⁺-ATPase dependent pathway. In our search for the Mg²⁺ extrusion mechanism of the basolateral compartment of the enterocyte, we could exclude Na⁺/Mg²⁺ antiport or ATP-driven transport. Evidence is provided, however, that Mg²⁺ movement across the membrane is coupled to anion transport. In basolateral plasma membrane vesicles, an inwardly directed Cl⁻ gradient stimulated Mg²⁺ uptake (as followed with the radionuclide ²⁷Mg) twofold. As Cl⁻-stimulated uptake was inhibited by the detergent saponin and by the ionophore A23187, Mg²⁺ may be accumulated intravesicularly above chemical equilibrium. Valinomycin did not affect uptake, suggesting that electroneutral symport activity occurred. The involvement of anion coupled transport was further indicated by the inhibition of Mg²⁺ uptake by the stilbene derivative, 4,4′-diisothiocyanato-stilbene-2,2′-disulfonic acid. Kinetic analyses of the Cl⁻-stimulated Mg²⁺ uptake yielded a K _m (Mg²⁺) of 6.08 ± 1.29 mmol · l⁻¹ and a K _m (Cl⁻) of 26.5 ± 6.5 mmol · l⁻¹, compatible with transport activity at intracellular Mg²⁺- and Cl⁻-levels. We propose that Mg²⁺ absorption in the tilapia intestine involves an electrically neutral anion symport mechanism. Received: 19 January 1996/Revised: 1 August 1996     

Fifteen-year Change in Forest Floor Organic and Element Content and Cycling at the Turkey Lakes Watershed

To assess the long-term effects of atmospheric deposition on forest floor chemical composition, we took quantitative samplings of L-(Oi), F-(Oe), and H-(Oa) layers at an old-growth sugar maple–yellow birch stand on a till soil at the Turkey Lakes Watershed near Lake Superior, Ontario, Canada, in 1981 and 1996. We then assessed these samples for contents of organic matter (OM), total N, K, Ca, Mg, S, and Na, and exchangeable NH₄ ⁺, NO₃ ⁻, K⁺, Ca²⁺, Mg²⁺, SO₄ ²⁻, and Na⁺. Over the 15-year period, total OM and element contents remained unchanged, with the exception of N, which increased significantly from 61.3 kmol/ha in 1981 to 78.4 kmol/ha in 1996. On an area basis, there were significant increases in exchangeable Ca²⁺ (from 3.8 to 4.6 kmol/ha) and Na⁺ (from 0.05 to 0.08 kmol/ha) and decreases in exchangeable NH₄ ⁺-N (from 1.41 to 0.95 kmol/ha) and SO₄ ²⁻-S (from 1.29 to 0.96 kmol/ha). There were no significant differences in average annual litterfall OM, N, Ca, Mg, S or Na inputs between 1980 and 1985 and between 1992 and 1997. Average annual wet-only SO₄ ²⁻-S deposition during 1981–86 was 0.30; during 1992–97, it was 0.21 kmol/ha. Annual wet-only NO₃ ⁻-N averaged 0.33 kmol/ha during 1981–86 and was similar during 1992–97. Throughfall was less rich in SO₄ ²⁻ and Ca²⁺, Mg²⁺, and Na⁺ during 1992–97 than earlier. Throughfall NH₄ ⁺ and NO₃ ⁻ fluxes were unchanged. Efflux of cations from the forest floor reflected reduced throughput of SO₄ ²⁻. Overall, the results suggest that in spite of atmospheric inputs, active biological processes—including litter input, fine-root turnover, and tree uptake—serve to impart stability to the mineral composition of mature sugar maple forest floor. Received 5 October 1999; accepted 25 October 2000.     

Accumulation of inorganic and organic osmolytes and their role in osmotic adjustment in NaCl-stressed vetiver grass seedlings

The accumulation of inorganic and organic osmolytes and their role in osmotic adjustment were investigated in roots and leaves of vetiver grass (Vetiveria zizanioides) seedlings stressed with 100, 200, and 300 mM NaCl for 9 days. The results showed that, although the contents of inorganic (K⁺, Na⁺, Ca²⁺, Mg²⁺, Cl⁻, NO₃⁻, SO₄²⁻ and H₂PO₃⁻)) and organic (soluble sugar, organic acids, and free amino acids) osmolytes all increased with NaCl concentration, the contribution of inorganic ions (mainly Na⁺, K⁺, and Cl⁻) to osmotic adjustment was higher (71.50–80.56% of total) than that of organic solutes (19.43–28.50%). The contribution of inorganic ions increased and that of organic solutes decreased in roots with the enhanced NaCl concentration, whereas the case in leaves was opposite. On the other hand, the osmotic adjustment was only effective for vetiver grass seedlings under moderate saline stress (less than 200 mM NaCl).     

Soil solution chemistry of two reclamation sites in the Lusatian lignite mining district as influenced by organic matter application

Due to a large reclamation (recultivation) demand in the Lusatian lignite mining district, efficient strategies for the rehabilitation of abandoned mine sites are needed. A field study was conducted for comparing the effects of three different fertilizer treatments (mineral fertilizer, sewage sludge and compost) on soil solution chemistry of both a lignite and pyrite containing spoil as well as a lignite and pyrite free spoil. The lignite and pyrite containing spoil was ameliorated with fly ash from a lignite power plant (17–21 t ha⁻¹ CaO), whereas the lignite and pyrite free site received 7.5 t ha⁻¹ CaO in form of limestone. Fertilizer application rates were: mineral fertilizer 120 N, 100 P and 80 K kg ha⁻¹. 19 t ha⁻¹ sewage sludge and 22 t ha⁻¹ compost were applied. Soil solution was sampled in 20, 60 and 130 cm depth for the period of 16 months. Solution was collected every fortnight and analysed for pH, EC, Ca²⁺, Mg²⁺, K⁺, Na⁺, Feⁿ⁺, Alⁿ⁺, Mn²⁺, Zn²⁺, NO₃ ⁻, NH₄ ⁺, SO₄ ²⁻, Cl⁻, PO₄ ³⁻, C_inorg and DOC. Lignite and pyrite containing spoil differed clearly from lignite and pyrite free spoil regarding soil solution concentrations and composition. Acidity (H⁺) produced by pyrite oxidation led to an enhanced weathering of minerals and, therefore, to at least 10 fold higher soil solution concentrations compared to the lignite and pyrite free site. Major ions in solution of the lignite and pyrite containing site were Ca²⁺, Mg²⁺, Feⁿ⁺, Alⁿ⁺ and SO₄ ²⁻, whereas soil solution at the lignite and pyrite free site was dominated by Ca2+, Mg²⁺ and SO₄ ²⁻. At both sites application of mineral fertilizer led to an immediate but short term (about 1 month) increase of NO₃ ⁻, NH₄ ⁺ and K+ concentrations in soil solution down to a depth of 130 cm. Application of sewage sludge caused a long term (about 16 months) increase of NO_{3 3} ⁻ in the topsoil, whereas NO₃ ⁻ concentrations in the subsoil were significantly lower compared to the mineral fertilizer plot. Compost application resulted in a strong long-term increase of K+ in soil solution, whereas NO₃ ⁻ concentrations did not increase. Concentrations of PO₄ ³⁻ in soil solution depend on solution pH and were not correlated with any treatment. This revised version was published online in June 2006 with corrections to the Cover Date. This revised version was published online in June 2006 with corrections to the Cover Date. This revised version was published online in June 2006 with corrections to the Cover Date.     

The role of ion regulation in the control of the distribution of Gammarus tigrinus (Sexton) in salt-polluted rivers

Fluctuating salinities at different sites on the German salt-polluted rivers Werra and Weser were compared with extracellular ion levels of specimens of Gammarus tigrinus (Sexton; Amphipoda, Crustacea), collected at the same sites. G. tigrinus regulated haemolymph concentrations of inorganic anions (Cl⁻, SO²⁻ ₄, PO³⁻ ₄) and cations (Na⁺, K⁺, Mg²⁺, Ca²⁺) during fluctuations of salt pollution in the upper Weser. This capacity to regulate varying levels of salt pollution in the upper Weser, correlated well with the distribution of the brackish amphipods in this river ecosystem. G. tigrinus tolerated periods of Na⁺ and Cl⁻ stress (>380 mmol l⁻¹) without compensating these maxima by regulating extracellular Na⁺ and Cl⁻. However, during such bursts of Na⁺ and Cl⁻ stress in Werra and Weser, the ability to regulate extracellular [K⁺] at river water K⁺ stress of ≥6.0 mmol l⁻¹ may explain why this brackish species has been more successful in these rivers than its competitors like Gammarus pulex. The present investigation demonstrates that the water salinity affects the [NO⁻ ₃] in the haemolymph of G. tigrinus. With increasing hypo-osmotic stress the animals accumulate increasing amounts of NO⁻ ₃. A simultaneous increase in stream water [NO⁻ ₃] causes an additional accumulation of NO⁻ ₃ in the haemolymph. The high extent of accumulation indicates that active ion transport systems may be involved. The accumulation of NO⁻ ₃ in the haemolymph has low physiological consequences to G. tigrinus, but when hypo-osmotically stressed under anoxic conditions, nitrite formed by the reduction of nitrate may have an adverse affect on the metabolism of G. tigrinus. Accepted: 4 October 1999     

Effects of Anions on the Capacity and Affinity of Copper Adsorption in Two Variable Charge Soils

Effects of nitrate,(NO₃⁻) chloride (Cl⁻), sulfate (SO₄^2-, and acetate (Ac⁻) on Cu²⁺ adsorption and affinity of the adsorbed Cu²⁺ were evaluated in two Fe and Al enriched variable charge soils from Southern China. The maximum adsorption of Cu²⁺ (M, a parameter from the Langmuir isotherm model) in the presence of different anions decreased in the order Cl⁻ > Ac⁻ > NO₃⁻ > SO₄^2- for both soils. The clayey loamy soil (mixed siliceous thermic Typic Dystrochrept, TTD), developed on the Arenaceous rock, adsorbed less Cu²⁺ than the clayey soil (kaolinitic thermic Plinthudults, KTP), derived from the Quaternary red earths, regardless of anion type present in the medium. The affinity of adsorbed Cu²⁺ to both soils could be characterized by the Kd (distribution coefficient) values and successive extraction of the adsorbed Cu²⁺ with 1-mol NH₄Ac L⁻¹. The log₁₀Kd value was smaller for the TTD soil than for the KTP soil and decreased in the order of Cl⁻ > NO₃⁻ > SO₄^2- > Ac⁻ at low initial Cu²⁺ concentrations (≤40 mg Cu²⁺L⁻¹), whereas at 80 mg Cu²⁺L⁻¹, the log₁₀Kd value was similar for NO₃⁻, SO₄^2-, and Ac⁻, but was slightly higher for Cl⁻. Complete extraction of Cu²⁺ adsorbed in the presence of Ac⁻ was achieved. Influence of NO₃⁻ and SO₄^2- on the affinity of adsorbed Cu²⁺ was similar, but the effects of Cl⁻ depended on the initial Cu²⁺ concentrations. The extracted percentage of the adsorbed Cu²⁺ in the presence of NO₃⁻ or SO₄^2- increased with increasing Cu²⁺ adsorption saturation. The presence of Cl⁻, NO₃⁻, or SO₄^2- markedly decreased the equilibrium solution pH for both soils with increasing initial Cu²⁺ concentrations, and the delta pH values at the highest Cu²⁺ level were 0.5, 0.63, and 0.55 U for the TTD soil and 0.79, 0.84, and 0.93 U for the KTP soil, respectively for the three anions. The presence of Ac⁻ had a minimal influence on the equilibrium solution pH because of the buffering nature of the NaAc/HAc medium which buffered the released protons. The effects of anions on Cu²⁺ adsorption and affinity of the adsorbed Cu²⁺ were dependent on anion types and were apparently related to the altered surface properties caused by anion adsorption and/or the formation of anion– Cu²⁺ complexes.     

Spatial distributions and net deposition rates of mineral elements in the elongating wheat (Triticum aestivum L.) leaf under saline soil conditions

Wheat leaf growth is known to be spatially affected by salinity. The altered spatial distribution of leaf growth under saline conditions may be associated with spatial changes in tissue mineral elements. The objective of this study was to evaluate the spatial distributions of mineral elements and their net deposition rates in the elongating and mature zones of leaf 4 of the main stem of spring wheat (Triticum aestivum L. cv. Lona) during its linear growth phase under saline soil conditions. Plants were grown in an illitic-chloritic silty loam with 0 and 120 mM NaCl. Three days after emergence of leaf 4, sampling was begun at 3 and 13 h into the 16-h light period. Spatial distributions of fresh weight (FW), dry weight (DW), and Na⁺, K⁺, Cl⁻, NO⁻ ₃, Ca²⁺, Mg²⁺, total P, and total N in the elongating and mature tissues were determined on a millimeter scale. The patterns of spatial distribution of Na⁺, Cl⁻, K⁺, NO₃ ⁻, and Ca²⁺ in the growing leaves were affected by salinity, while those of Mg²⁺, total P, and total N were not. Sodium, K⁺, Cl⁻, Ca²⁺, Mg²⁺, and total N concentrations (mmol · kg⁻¹ FW) were consistently higher at 120 mM NaCl than at 0 mM NaCl along the leaf axis from the leaf base, whereas NO₃ ⁻ concentration was lower at 120 mM NaCl. Deposition rates of all nutrients were greatest in the elongation zone. The elongation zone was the strongest sink for mineral elements in the leaf tissues. Local net deposition rates of Na⁺, Cl⁻, Ca²⁺, and Mg²⁺ (mmol · kg⁻¹ FW · h⁻¹) in the most actively elongating zone were enhanced by 120 mM NaCl, whereas for NO₃ ⁻ this was depressed. The lower supply of NO⁻ ₃ to growing leaves may be responsible for the inhibition of growth under saline conditions. Higher tissue concentrations of Na⁺ and Cl⁻ may cause ion imbalance but probably did not result in ion toxicity in the growing leaves. Potassium, Ca²⁺, Mg²⁺, total P, and total N are less plausibly responsible for the reduction in leaf growth in this study. Higher tissue K⁺ and Ca²⁺ concentrations at 120 mM NaCl are probably due to the presence of high Ca²⁺ in the soil of this study. Received: 13 March 1997 / Accepted: 9 June 1997     

Distribution of nitrogen-15 tracers applied to the canopy of a mature spruce-hemlock stand,Howland, Maine,USA

In N-limited ecosystems, fertilization by N deposition may enhance plant growth and thus impact C sequestration. In many N deposition–C sequestration experiments, N is added directly to the soil, bypassing canopy processes and potentially favoring N immobilization by the soil. To understand the impact of enhanced N deposition on a low fertility unmanaged forest and better emulate natural N deposition processes, we added 18 kg N ha⁻¹ year⁻¹ as dissolved NH₄NO₃ directly to the canopy of 21 ha of spruce-hemlock forest. In two 0.3-ha subplots, the added N was isotopically labeled as ¹⁵NH₄ ⁺ or ¹⁵NO₃ ⁻ (1% final enrichment). Among ecosystem pools, we recovered 38 and 67% of the ¹⁵N added as ¹⁵NH₄ ⁺ and ¹⁵NO₃ ⁻, respectively. Of ¹⁵N recoverable in plant biomass, only 3–6% was recovered in live foliage and bole wood. Tree twigs, branches, and bark constituted the most important plant sinks for both NO₃ ⁻ and NH₄ ⁺, together accounting for 25–50% of ¹⁵N recovery for these ions, respectively. Forest floor and soil ¹⁵N retention was small compared to previous studies; the litter layer and well-humified O horizon were important sinks for NH₄ ⁺ (9%) and NO₃ ⁻ (7%). Retention by canopy elements (surfaces of branches and boles) provided a substantial sink for N that may have been through physico-chemical processes rather than by N assimilation as indicated by poor recoveries in wood tissues. Canopy retention of precipitation-borne N added in this particular manner may thus not become plant-available N for several years. Despite a large canopy N retention potential in this forest, C sequestration into new wood growth as a result of the N addition was only ~16 g C m⁻² year⁻¹ or about 10% above the current net annual C sequestration for this site.     

Analysis of salts transport affected by root absorption capacity in surface — irrigated fields in the upper Yellow River basin

In order to analyze the salt transport affected by roots and its effects on soil salinity in an experimental irrigated field newly established in an alluvial valley of the Yellow River in China, spatial distribution of ions contained in waters, soils and crops relevant to these phenomena were evaluated there. During the intensive surveys conducted in year 2007–2008, the Yellow River water, irrigation canal water, groundwater, field soils and crops, etc. were sampled and their chemical characteristics such as electrical conductivity, concentrations of ions Na⁺, Ca²⁺, Mg²⁺, K⁺, Cl⁻, SO₄²⁻and NO₃⁻ were measured. Irrigation seemed to cause increases in the concentrations of ions Na⁺, Cl⁻ and SO₄²⁻ in the groundwater. Although those were also major ions contained in the field soil, the soil was classed as saline but not sodic according to the standard classification. On the other hand, K⁺, which is one of the major essential nutrients for plant growth, was highly concentrated in the crops, while Na⁺ was not concentrated because of crop’s poor ability to absorb it. The ion concentration within the plant body seemed to be reflected by the active and selective ion uptake by roots and the transpiration stream. Furthermore, salt accumulation in the surface-irrigated field largely depended on the upward transport of water and ions in the soil profile affected by root absorption capacity. The information obtained in this study will contribute to the development of scientific methods for sustainable and effective plant production in irrigated fields.     

Atmospheric Deposition to the Turkey Lakes Watershed: Temporal Variations and Characteristics

We investigated the atmospheric concentrations and deposition fluxes of major ions to the Turkey Lakes Watershed (TLW) between 1980 and 1996. During that time, daily SO₄ ²⁻ concentrations in precipitation decreased markedly, while NO₃ ⁻, NH₄ ⁺, and H⁺ concentrations remained roughly constant. It appears that precipitation acidity did not decrease in spite of declining SO₄ ²⁻ concentrations due to a concurrent and counterbalancing decrease in the concentrations of Ca²⁺, Mg²⁺, and K⁺ in precipitation. The reasons for the decline in base cations are unknown, but this decline is probably related to decreasing emissions of soil-derived particles from agricultural, industrial, and road sources. A similar situation was seen during the same period in other parts of Canada, the eastern United States, and Europe. Wet, dry, and total (wet + dry) deposition fluxes of sulphur (S) and nitrogen (N) were estimated annually for the years 1980–96. The 17-year mean annual total (wet + dry) deposition of S to the watershed was estimated at 38.5 mmol m⁻² y⁻¹ (range 24.3–50.3). Total S deposition decreased by 35% from the early 1980s (1982–84) to the mid-1990s (1994–96), a decline consistent with the 23% decline in annual SO₂ emissions in eastern North America during the same period. In contrast, the annual total (wet + dry) deposition of oxidized N ranged from 39.8 to 60.4 mmol m⁻² y⁻¹, with a 15-year mean of 50.1 mmol m⁻² y⁻¹ and a net increase of 10% between the early 1980s (1983–85) and the mid-1990s (1994–96). This is in keeping with a 10% increase in NO_x emissions in eastern North America during the same period. For both S and N (oxidized), wet deposition dominated over dry deposition as the major mechanism for atmospheric input to the watershed. Annually, wet deposition accounted for approximately two-thirds of the total atmospheric deposition of both S and N. Dry S deposition was due more to gaseous SO₂ deposition (two-thirds of dry S deposition) than to particulate SO₄ ²⁻ deposition (one-third of dry S deposition). Dry deposition of oxidized N, however, was dominated (95%) by gaseous HNO₃ deposition, with minimal input from particulate NO₃ ⁻ deposition. Compared to several selected watershed/forest sites in Canada, the United States, and Europe, the estimated total deposition of S and N at the TLW was relatively high during the measurement period. Received 5 October 1999; accepted 1 March 2001.     

Correlations between projection area of ectomycorrhizae and H<Subscript>2</Subscript>O extractable nutrients in organic soil layers

Most of the fine root tips of boreal and temperate forests are colonized by ectomycorrhizal fungi. Thus ectomycorrhizal (ECM) symbiosis is an important factor in supplying trees with water and a wide range of nutrients. ECM are frequently patchily distributed and often form dense systems in small areas. One of the reasons for this uneven distribution might be a heterogeneous and patchy distribution of nutrients. The present study compares the occurrence of ECM of Cortinarius obtusus, Lactarius decipiens, L. theiogalus, and Russula ochroleuca and soil nutrient concentrations at a micro-scale (1 cm²) in the O_F layer of a pure Norway spruce stand. In addition to the macronutrients K⁺, Mg²⁺, Ca²⁺, NO₃ ⁻, NH₄ ⁺, the concentrations of Na⁺, Fe³⁺+Mn²⁺, Al³⁺, Cl⁻, SO₄ ²⁻ are studied, as well as pH. Whereas Russula ochroleuca and Lactarius decipiens did not reveal any significant correlation with any of the tested nutrients or pH, the occurrence of L. theiogalus was significantly (p < 5 %) positively correlated with NH₄ ⁺, K⁺, Na⁺, Mg²⁺, Fe³⁺+Mn²⁺, and pH. Cortinarius obtusus was positively correlated at the same significance level only with NH₄ ⁺ and Mg²⁺.     

Kinetic analysis of gill (Na⁺,K⁺)-ATPase activity in selected ontogenetic stages of the Amazon River shrimp, Macrobrachium amazonicum (Decapoda, Palaemonidae): interactions at ATP- and cation-binding sites

We investigated modulation by ATP, Mg²⁺, Na⁺, K⁺ and NH₄ ⁺ and inhibition by ouabain of (Na⁺,K⁺)-ATPase activity in microsomal homogenates of whole zoeae I and decapodid III (formerly zoea IX) and whole-body and gill homogenates of juvenile and adult Amazon River shrimps, Macrobrachium amazonicum. (Na⁺,K⁺)-ATPase-specific activity was increased twofold in decapodid III compared to zoea I, juveniles and adults, suggesting an important role in this ontogenetic stage. The apparent affinity for ATP (K _M = 0.09 ± 0.01 mmol L⁻¹) of the decapodid III (Na⁺,K⁺)-ATPase, about twofold greater than the other stages, further highlights this relevance. Modulation of (Na⁺,K⁺)-ATPase activity by K⁺ also revealed a threefold greater affinity for K⁺ (K _0.5 = 0.91 ± 0.04 mmol L⁻¹) in decapodid III than in other stages; NH₄ ⁺ had no modulatory effect. The affinity for Na⁺ (K _0.5 = 13.2 ± 0.6 mmol L⁻¹) of zoea I (Na⁺,K⁺)-ATPase was fourfold less than other stages. Modulation by Na⁺, Mg²⁺ and NH₄ ⁺ obeyed cooperative kinetics, while K⁺ modulation exhibited Michaelis-Menten behavior. Rates of maximal Mg²⁺ stimulation of ouabain-insensitive ATPase activity differed in each ontogenetic stage, suggesting that Mg²⁺-stimulated ATPases other than (Na⁺,K⁺)-ATPase are present. Ouabain inhibition suggests that, among the various ATPase activities present in the different stages, Na⁺-ATPase may be involved in the ontogeny of osmoregulation in larval M. amazonicum. The NH₄ ⁺-stimulated, ouabain-insensitive ATPase activity seen in zoea I and decapodid III may reflect a stage-specific means of ammonia excretion since functional gills are absent in the early larval stages.     

Seasonal variation in nutrient limitation of microbial biofilms colonizing organic and inorganic substrata in streams

Humans have increased the availability of nutrients including nitrogen and phosphorus worldwide; therefore, understanding how microbes process nutrients is critical for environmental conservation. We examined nutrient limitation of biofilms colonizing inorganic (fritted glass) and organic (cellulose sponge) substrata in spring, summer, and autumn in three streams in Michigan, USA. Biofilms were enriched with nitrate (NO₃ ⁻), phosphate (PO₄ ³⁻), ammonium (NH₄ ⁺), NO₃ ⁻ + PO₄ ³⁻, NH₄ ⁺ + PO₄ ³⁻, or none (control). We quantified biofilm structure and function as chlorophyll a (i.e., primary producer biomass) and community respiration on all substrata. In one stream, we characterized bacterial and fungal communities on cellulose in autumn using clone library sequencing and denaturing gradient gel electrophoresis to determine if community structure was linked to nutrient limitation status. Despite oligotrophic conditions, primary producer biomass was infrequently nutrient limited. In contrast, respiration on organic substrata was frequently limited by N + P combinations. We found no difference between biofilm response to NH₄ ⁺ versus NO₃ ⁻ enrichment, although the response to both N-species was positively related to water column PO₄ ³⁻ concentrations and temperature. Molecular analysis for fungal community composition suggested no relationship to nutrient limitation, but the dominant members of the bacterial community on cellulose were different on NO₃ ⁻, PO₄³, and NO₃ ⁻ + PO₄ ³⁻ treatments relative to control, NH₄ ⁺, and NH₄ ⁺ + PO₄ ³⁻ treatments, which matched patterns for biofilm respiration rates from each treatment. Our results show discrete patterns of nutrient limitation dependent upon substratum type and season, and imply changes in bacterial community structure and function may be linked following nutrient enrichment in streams.     

Effects of different ionic compositions on survival and growth of <Emphasis Type="Italic">Physa acuta</Emphasis>

Most inland saline waters in southern Australia predominantly contain Na⁺ and Cl⁻ as major ions. The proportions of Ca²⁺, Mg²⁺, SO₄ ²⁻, HCO₃ ⁻ and CO₃ ²⁻ in these waters somewhat vary and might influence salinity tolerance of freshwater organisms. Here the salinity stress of five ionic compositions to the freshwater snail Physa acuta Draparnaud (Gastropoda: Physidae) was compared: commercial sea salt Ocean Nature (ON), synthetic Ocean Nature (ONS) and three saline water types that are common in southern Australia (ONS but without [1]: SO₄ ²⁻, HCO₃ ⁻ and CO₃ ²⁻, [2]: Ca²⁺, HCO₃ ⁻ and CO₃ ²⁻, [3]: Ca²⁺, Mg²⁺), Milli-Q water was used as a negative control. The 96-h LC₅₀ values for all treatments did not differ. However in prolonged sub-lethal exposures, results varied depending on the ionic composition. Growth was negative and shell strength reduced in treatments lacking Ca. Though the content of major cationic elements (Ca, Mg, Na and K) did not differ per unit dry weight of snail across the treatments, the total load of these elements per individual snail varied among treatments. Furthermore, at the sub-lethal salinities tested, 1 and 5 mS cm⁻¹, ionic compositions had more effect on the snail’s growth than salinity. The long-term effects on freshwater animals, especially taxa with calcium-based exoskeletons, from exposure to common saline water types with low calcium concentrations will likely be greater than from exposure to saline waters with an ionic composition similar to seawater.     

NO<Subscript>3</Subscript><Superscript>−</Superscript>-Driven SO<Subscript>4</Subscript><Superscript>2−</Superscript> Production in Freshwater Ecosystems: Implications for N and S Cycling

Massive anthropogenic acceleration of the global nitrogen (N) cycle has stimulated interest in understanding the fate of excess N loading to aquatic ecosystems. Nitrate (NO₃ ⁻) is traditionally thought to be removed mainly by microbial respiratory denitrification coupled to carbon (C) oxidation, or through biomass assimilation. Alternatively, chemolithoautotrophic bacterial metabolism may remove NO₃ ⁻ by coupling its reduction with the oxidation of sulfide to sulfate (SO₄ ²⁻). The NO₃ ⁻ may be reduced to N₂ or to NH₄ ⁺, a form of dissimilatory nitrate reduction to ammonium (DNRA). The objectives of this study were to investigate the importance of S oxidation as a NO₃ ⁻ removal process across diverse freshwater streams, lakes, and wetlands in southwestern Michigan (USA). Simultaneous NO₃ ⁻ removal and SO₄ ²⁻ production were observed in situ using modified “push-pull” methods in nine streams, nine wetlands, and three lakes. The measured SO₄ ²⁻ production can account for a significant fraction (25–40%) of the overall NO₃ ⁻ removal. Addition of ¹⁵NO₃ ⁻ and measurement of ¹⁵NH₄ ⁺ production using the push–pull method revealed that DNRA was a potentially important process of NO₃ ⁻ removal, particularly in wetland sediments. Enrichment cultures suggest that Thiomicrospira denitrificans may be one of the organisms responsible for this metabolism. These results indicate that NO₃ ⁻-driven SO₄ ²⁻ production could be widespread and biogeochemically important in freshwater sediments. Removal of NO₃ ⁻ by DNRA may not ameliorate problems such as eutrophication because the N remains bio-available. Additionally, if sulfur (S) pollution enhances NO₃ ⁻ removal in freshwaters, then controls on N processing in landscapes subject to S and N pollution are more complex than previously appreciated. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Seasonal nutrient fluxes variability of northern salt marshes: examples from the lower St. Lawrence Estuary

This study presents the tidal exchange of ammonium, nitrite + nitrate, phosphate and silicate between two salt marshes and adjacent estuarine waters. Marsh nutrient fluxes were evaluated for Pointe-au-Père and Pointe-aux-épinettes salt marshes, both located along the south shore of the lower St. Lawrence Estuary in Rimouski area (QC, Canada). Using nutrients field data, high precision bathymetric records and a hydrodynamic numerical model (MIKE21-NHD) forced with predicted tides, nutrients fluxes were estimated through salt marsh outlet cross-sections at four different periods of the year 2004 (March, May, July and November). Calculated marsh nutrient fluxes are discussed in relation with stream inputs, biotic and abiotic marsh processes and the incidence of sea ice cover. In both marshes, the results show the occurrence of year-round and seaward NH₄ ⁺ fluxes and landward NO₂ ⁻ + NO₃ ⁻ fluxes (ranging from 9.06 to 30.48 mg N day⁻¹ m⁻² and from −32.07 to −9.59 mg N day⁻¹ m⁻², respectively) as well as variable PO₄ ³⁻ and Si(OH)₄ fluxes (ranging from −3.73 to 6.34 mg P day⁻¹ m⁻² and from −29.19 to 21.91 mg Si day⁻¹ m⁻², respectively). These results suggest that NO₂ ⁻ + NO₃ ⁻ input to marshes can be a significant source of NH₄ ⁺ through dissimilatory nitrate reduction to ammonium (DNRA). This NH₄ ⁺, accumulating in marsh sediment rather than being removed through coupled nitrification–denitrification or biological assimilation, is exported toward estuarine waters. From average P and Si tidal fluxes analysis, both salt marshes act as a sink during high productivity period (May and July) and as a source, supplying estuarine water during low productivity period (November and March).