Contrasting nutrient exports from a forested and an agricultural catchment in south-eastern Australia

Dissolved organic carbon (DOC) and total and inorganic nitrogen and phosphorus concentrations were determined over 3 years in headwater streams draining two adjacent catchments. The catchments are currently under different land use; pasture/grazing vs plantation forestry. The objectives of the work were to quantify C and nutrient export from these landuses and elucidate the factors regulating export. In both catchments, stream water dissolved inorganic nutrient concentrations exhibited strong seasonal variations. Concentrations were highest during runoff events in late summer and autumn and rapidly declined as discharge increased during winter and spring. The annual variation of stream water N and P concentrations indicated that these nutrients accumulated in the catchments during dry summer periods and were flushed to the streams during autumn storm events. By contrast, stream water DOC concentrations did not exhibit seasonal variation. Higher DOC and NO₃ ⁻ concentrations were observed in the stream of the forest catchment, reflecting greater input and subsequent breakdown of leaf-litter in the forest catchment. Annual export of DOC was lower from the forested catchment due to the reduced discharge from this catchment. In contrast however, annual export of nitrate was higher from the forest catchment suggesting that there was an additional NO₃ ⁻ source or reduction of a NO₃ ⁻ sink. We hypothesize that the denitrification capacity of the forested catchment has been significantly reduced as a consequence of increased evapotranspiration and subsequent decrease in streamflow and associated reduction in the near stream saturated area.     

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.     

Proton production from nitrogen transformation drives stream export of base cations in acid-sensitive forested watersheds

The biogeochemical cycles of nitrogen (N) and base cations (BCs), (i.e., K⁺, Na⁺, Ca²⁺, and Mg²⁺), play critical roles in plant nutrition and ecosystem function. Empirical correlations between large experimental N fertilizer additions to forest ecosystems and increased BCs loss in stream water are well demonstrated, but the mechanisms driving this coupling remain poorly understood. We hypothesized that protons generated through N transformation (PPR_N)—quantified as the balance of NH₄⁺ (H⁺ source) and NO₃⁻ (H⁺ sink) in precipitation versus the stream output will impact BCs loss in acid-sensitive ecosystems. To test this hypothesis, we monitored precipitation input and stream export of inorganic N and BCs for three years in an acid-sensitive forested watershed in a granite area of subtropical China. We found the precipitation input of inorganic N (17.71 kg N ha⁻¹ year⁻¹ with 54% as NH₄⁺–N) was considerably higher than stream exported inorganic N (5.99 kg N ha⁻¹ year⁻¹ with 83% as NO₃⁻–N), making the watershed a net N sink. The stream export of BCs (151, 1518, 851, and 252 mol ha⁻¹ year⁻¹ for K⁺, Na⁺, Ca²⁺, and Mg²⁺, respectively) was positively correlated (r = 0.80, 0.90, 0.84, and 0.84 for K⁺, Na⁺, Ca²⁺, and Mg²⁺ on a monthly scale, respectively, P < 0.001, n = 36) with PPR_N (389 mol ha⁻¹ year⁻¹) over the three years, suggesting that PPR_N drives loss of BCs in the acid-sensitive ecosystem. A global meta-analysis of 15 watershed studies from non-calcareous ecosystems further supports this hypothesis by showing a similarly strong correlation between ∑BCs output and PPR_N (r = 0.89, P < 0.001, n = 15), in spite of the pronounced differences in environmental settings. Collectively, our results suggest that N transformations rather than anions (NO₃⁻ and/or SO₄²⁻) leaching specifically, are an important mediator of BCs loss in acid-senstive ecosystems. Our study provides the first definitive evidence that the chronic N deposition and subsequent transformation within the watershed drive stream export of BCs through proton production in acid-sensitive ecosystems, irrespective of their current relatively high N retention. Our findings suggest the N-transformation-based proton production can be used as an indicator of watershed outflow quality in the acid-sensitive ecosystems.     

TOC fluctuations in a humic lake as related to catchment acidification, season and climate

Studies of fluctuations in total organic carbon (TOC) were performedin both the reference basin and the acidified basin of experimental LakeSkjervatjern, in order to separate effects of various catchment and in-lakeprocesses. Nearly five years of catchment acidification did not inducesignificant changes in TOC. TOC concentrations was not related clearly toprecipitation or runoff. In both basins, there was a regular, seasonal patternwith a gradual increase in TOC concentrations from spring to late autumn.Minima in concentrations occurred during periods with frozen ground inwinter, irrespective of discharge patterns. The decrease from 10 mg C l^-1 in autumn to 1--2 mg C l^-1 in latewinter, was only seen in surface layers. Runoff was the major loss routefor surface TOC in the lake. Photo-oxidation, bacterial oxidation, andsedimentation combined yielded maximum loss rates of 3%of surface TOC d^-1. Below a depth of 1 m 0.5%d^-1 was lost to these same processes. The surface microlayerhad 5--10 times more TOC than the bulk water on average, and could haveeffects on gas exchange and sub-surface light. Despite the oxidation ofTOC, the short residence time of the lake and rapid replacement of TOCfrom the catchment was the major determinant of lake water TOC.     

Changes of soil organic carbon,nitrogen and phosphorus concentrations under different land uses in marshes of Sanjiang Plain

Wetlands provide a large pool of organic matter and nutrients, and are important for maintaining material cycle balances in terrestrial ecosystems, and also help retard climate change. Land use changes in wetlands have greatly disturbed the natural evolution of wetland ecosystems. Wetland drainage and reclamation alters the physical, chemical and biological conditions of the wetland, thus significantly disturbing the material cycles, leading to significant changes in the biogeochemical processes of carbon, nitrogen and phosphorus in the wetland. The wetlands in the Sanjiang Plain are the largest area of fresh wetlands in China. However, the area has experienced major land uses changes since the 1950s; areas of the wetland have been drained and converted to arable land. Some studies have been conducted into the effects of land use change on material cycles in the Sanjiang Plain wetlands but few reports have discussed the C/N and C/P ratios and pH values as indicators of wetland degradation due to land use changes. We selected eight land uses: humus marsh (HM), marshy meadow (MM), drained humus marsh (DHM), drained marshy meadow (DMM), tillage land (TL), abandoned land (AL), natural secondary forest (NSF) and artificial forest (AF), in the Honghe area of the Sanjiang Plain. We studied changes in the total organic carbon (TOC), total nitrogen (TN), total phosphorus (TP), C/N and C/P ratios and pH values in topsoil (0–20 cm) of these eight different land uses. The possible mechanisms underlying the changes, and the significance of the C/N and C/P ratios as indicators of soil quality were also discussed. In the natural wetland, the TOC, TN and TP concentrations in the soil were high, with values of 203.5 g/kg, 20.2 g/kg and 1.44 g/kg, respectively, in HM; and 59.2 g/kg, 5.28 g/kg and 0.83 g/kg, respectively, in MM. Drainage of the HM has led to decreases in the TOC, TN and TP concentrations of about 50%. Significant decreases were also observed in TOC, TN and TP for NSF and AF compared to HM. Drained MM led to decreases in the TOC and TN of about 45%, but had little effect on TP. Marshy meadow that had been drained for more than 10 years experienced an exponential decline in TOC, TN and TP, with decreases of more than 60% for TOC and TN, and 20% for TP. However, after being abandoned for a short time (5 years), the TOC, TN and TP concentrations in soil experienced little change because poor water conditions combined with low productivity led to a large loss of soil organic matter. Land use change in the marsh areas has led to a decrease in C/N and C/P ratios of the soil, which are positively related to TOC and TN with different land uses (P < 0.05). Marsh reclamation has led to decreasing C/N and C/P ratios in soil and increasing pH values, which are negatively related to TOC, TN and TP (P < 0.05). Changes in carbon, nitrogen and phosphorus in soil with different land uses were mainly regulated by water-heat conditions and microbial activity, while the C/N and C/P ratios were mainly regulated by substrate availability. Our results suggest that C/N and C/P ratios and the pH value could be used as indicators to evaluate the quality and nutrient status of wetland soil under different land uses.     

Post-restoration development of organic carbon and nutrient leaching from two ecohydrologically different peatland sites

Restoration of drained peatland forests is an important tool in maintaining and improving biodiversity in the boreal region. It has been shown to cause leaching of nutrients from the restoration area to lower waterbodies. Two drained peatland systems of different ecohydrological types in the Nuuksio (60°18′N, 24°27′E) and Seitseminen (61°56′N, 23°26′E) national parks were restored and total organic carbon, nitrogen and phosphorus leaching was monitored for 6 years after restoration. The richer site proved to leach more nitrogen and less total organic carbon and phosphorus than the poor site although the per-treatment-area excess leaching of organic carbon caused by restoration was higher in the richer site. The pattern of excess leaching was more stable in the poor site. The differences in leaching reflect the ecohydrological differences between these two peatland basins.     

Nutrient additions generate prolific growth of Lyngbya majuscula (cyanobacteria) in field and bioassay experiments

Nutrients such as bioavailable iron, phosphorus and nitrogen have been hypothesised to stimulate nuisance blooms of the toxic, marine cyanobacterium Lyngbya majuscula. The current study used two laboratory based biological assay techniques to test whether the addition of iron, phosphorus and nitrogen enhanced L. majuscula growth. A three-way analysis of variance showed all nutrients stimulated L. majuscula filament growth and biomass under laboratory conditions, with organically chelated iron (FeEDTA)  phosphorus > nitrogen. An in situ field experiment was also conducted concurrently on naturally occurring L. majuscula in eastern Moreton Bay (Amity Banks), Australia, to determine any growth response to phosphorus and iron additions. Field results showed substantial and significant increases in biomass occurred with the addition of organically chelated iron and phosphorus (15.9 and 6.4 times the control, respectively)—confirming the laboratory responses to iron and phosphorus. Furthermore, results from the field and laboratory experiments were highly correlated, showing the applicability of results obtained in laboratory experiments to the natural environment. These results show that nutrients, particularly organically chelated iron, phosphorus and nitrogen can promote prolific growth of the bloom forming cyanobacterium L. majuscula. The current study shows that a precautionary approach should be taken to limit or reduce nutrient additions to streams, estuaries and coastal waters, otherwise the magnitude of L. majuscula blooms is likely to increase in Moreton Bay in the future.     

Sources and sinks of dissolved organic carbon in a forested swamp catchment

Concentrations of dissolved organic carbon (DOC) were measured in precipitation, throughfall, stemflow, and soil, peat and stream water in a 50 ha catchment with a central 5 ha swamp at Mont St. Hilaire, Quebec. DOC concentrations in precipitation were low (2.0 mg L^–1), but increased in passage through the tree canopies as throughfall (9.1–14.6 mg L^–1) and stemflow (23.1–30.1 mg L^–1). For the period July 1–November 15, 1987, 0.5 g DOC m^–2 was imported as precipitation, and forest canopies contributed a further 1.4–1.7 g m^–2 2 to the soil surface. DOC concentrations were higher (46.0 and 67.6 mg L^–1) in upland soil organic horizons, but decreased with depth because subsoil mineral horizons acted as a major sink of DOC. A laboratory experiment using leaf leachate revealed that subsoil horizons were able to adsorb DOC, with equilibrium DOC concentrations ranging from 3 to 19 mg L^–1. Soil organic carbon appeared to be an important determinant of equilibrium DOC concentrations. The swamp was a major source of DOC, with an overall average DOC concentration of 58.6 mg L^–1 and showed strong spatial and temporal variations related to hydrologic and thermal regimes. During base flow periods, stream DOC concentrations were small (< 3 mg L^–1), dominated by water fed from springs draining upland soils. During high flows, stream DOC concentrations increased through the contribution of DOC-rich water originating in the swamp. Sources, sinks and transport of DOC are thus a function of a complex set of inter-related biotic and abiotic process.     

The relationships of vegetation to surface water chemistry and peat chemistry in fens of Alberta,Canada

The relationships between vegetation components, surface water chemistry and peat chemistry from 23 fens in boreal Alberta, Canada, substantiate important differences along the poor to rich fen gradient. Each of the three fen types have their own characteristic species. The extreme-rich fens are characterized by Calliergon trifarium, Drepanocladus revolvens, Scirpus hudsonianus, S. cespitosus, Scorpidium scorpioides, and Tofieldia glutinosa. Moderate-rich fens are characterized by Brachythecium mildeanum, Carex diandra, Drepanocladus vernicosus, D. aduncus, and D. polycarpus. Poor fens are characterized by Carex pauciflora, Drepanocladus exannulatus, Sphagnum angustifolium, S. jensenii, and S. majus. Moderate-rich fens have fewer species in common with poor fens than with extreme-rich fens, while species richness is highest in the moderate-rich fens and lowest in poor fens. Variation in vascular plant occurrence appears to be more associated with nutrient levels, while bryophytes are more affected by changes in acidity and mineral elements. Based on chemical criteria, the three fen types are clearly separated by surface water pH, calcium, magnesium, and conductivity, but are less clearly differentiated by the nitrogen and phosphorus components of the surface waters. Moderate-rich fens are chemically variable both temporally and spatially, whereas poor fens and extreme-rich fens are more stable ecosystems. Whereas components of alkalinity-acidity are the most important factors that distinguish the three fen types in western Canada, nutrient concentrations in the surface waters generally do not differ appreciably in the three fen types.     

Acid sensitivity and water chemistry correlates of amphibian breeding ponds in northern Wisconsin,USA

Fifty-one amphibian breeding sites in northern Wisconsin were sampled in two surveys, in 1986 and 1987, to determine the chemical conditions and amphibian inhabitants present. All twenty-one ponds in 1986 and twenty-eight in 1987 were mildly acidic and sensitive to acidification. The pH levels encountered were generally not toxic to the resident amphibians, and may have been related to levels of phenolics in some cases. Soil type and forest canopy coverage appeared to influence the chemistry of these ponds and a direct relationship of amphibian species richness with pond size was found. Only larger ponds were long-lived enough for metamorphosis of amphibian larvae, suggesting an importance for recruitment. They were also the most sensitive ponds and the only ones to enter the chronically toxic pH range for ambystomatid salamanders, possibly placing them at risk to future acid inputs.     

Declining water yield from forested mountain watersheds in response to climate change and forest mesophication

Climate change and forest disturbances are threatening the ability of forested mountain watersheds to provide the clean, reliable, and abundant fresh water necessary to support aquatic ecosystems and a growing human population. Here, we used 76 years of water yield, climate, and field plot vegetation measurements in six unmanaged, reference watersheds in the southern Appalachian Mountains of North Carolina, USA to determine whether water yield has changed over time, and to examine and attribute the causal mechanisms of change. We found that annual water yield increased in some watersheds from 1938 to the mid‐1970s by as much as 55%, but this was followed by decreases up to 22% by 2013. Changes in forest evapotranspiration were consistent with, but opposite in direction to the changes in water yield, with decreases in evapotranspiration up to 31% by the mid‐1970s followed by increases up to 29% until 2013. Vegetation survey data showed commensurate reductions in forest basal area until the mid‐1970s and increases since that time accompanied by a shift in dominance from xerophytic oak and hickory species to several mesophytic species (i.e., mesophication) that use relatively more water. These changes in forest structure and species composition may have decreased water yield by as much as 18% in a given year since the mid‐1970s after accounting for climate. Our results suggest that changes in climate and forest structure and species composition in unmanaged forests brought about by disturbance and natural community dynamics over time can result in large changes in water supply.     

The effect of afforestation with Scots pine (Pinus silvestris L.) of sandy post-arable soils on their selected properties. II. Reaction, carbon, nitrogen and phosphorus

Despite the extensive literature on the effect on soil properties of afforestation of former arable land, we still lack full understanding of whether the changes proceed in the same direction and at the same rate, and of how long is required to achieve a state of soil equilibrium typical of a natural forest ecosystem. Therefore, as part of a study comparing post-arable sandy soils (Dystric Arenosols) afforested with Scots pine (Pinus silvestris L.) with arable soils and soils of continuous coniferous forests, the range and direction of changes in pH, organic carbon (C_org), total nitrogen (N_tot), ammonium (N-NH₄) and nitrates (N-NO₃) in soil solution, total (P_tot) and available (P_av) phosphorus were determined. The studies were carried out in south-east Poland (51°30′-51°37′N, 22°20′-22°35′E). Ten paired sites of afforested soils (five with 14- to 17-year-old stands and five with 32- to 36-year-old stands) with adjacent cultivated fields, and five sites of continuous forest with present stands of ca. 130–150 years old were selected. Soil samples were taken from the whole thickness of master horizons and, in the case of the A horizon of the afforested soils, from three layers: 0–5 (A_0–5), 5–10 (A_5–10) and 10–20 cm (A_10–20). The cultivated soils in the Ap horizon showed higher pH (by ca. 1.0 unit), lower C_org and C:N, similar N_tot, lower N-NH₄, higher N-NO₃, higher P_tot and P_av contents compared with the Ah horizon of continuous forest soils. The results indicated decreased soil pH in the former plough layer of the afforested soils, with the greatest decrease observed in the 0–5 cm layer. In these soils, the C_org content was considerably higher in the A_0–5 layer, but lower in the two deeper layers and in the whole A horizon (0–20 cm) compared with the Ap horizon of the arable soils. The results indicate that the C_org content, after an initial phase of decline, again achieved a level characteristic of arable soils. The N_tot content in all layers of the A horizon of the afforested soils was lower than in the Ap horizon of the arable soils, and showed a reduction with stand age, especially in deeper layers. The C:N ratios in the mineral topsoil increased with stand age. N-NH₄ content increased and N-NO₃ decreased after afforestation. The P_tot and P_av contents in all layers and in the whole A horizon of the afforested soils, on stands of both ages, was lower than in the Ap of the cultivated soils. From the results, it could be concluded that, after more than 30 years of tree growth, the soils of the A horizon were still more similar to arable than to continuous forest soils with respect to C_org, P_tot and P_av. With respect to pH, N-NH₄ and N-NO₃, especially in the 0–5 cm layer, they were more similar to continuous forest soils than to cultivated soils, but with respect to N_tot and C:N ratio they were somewhere in between.     

Fate and Transport of Organic Nitrogen in Minimally Disturbed Montane Streams of Colorado,USA

In two montane watersheds that receive minimal deposition of atmospheric nitrogen, 15–71% of dissolved organic nitrogen (DON) was bioavailable in stream water over a 2-year period. Discharge-weighted concentrations of bulk DON were between 102 and 135 μg/l, and the C:N ratio differed substantially between humic and non-humic fractions of DON. Approximately 70% of DON export occurred during snowmelt, and 40% of that DON was biologically available to microbes in stream sediments. Concentrations of bioavailable DON in stream water were 2–16 times greater than dissolved inorganic nitrogen (DIN) during the growing season, and bioavailable DON was depleted within 2–14 days during experimental incubations. Uptake of DON was influenced by the concentration of inorganic N in stream water, the concentration of non-humic DON in stream water, and the C:N ratio of the non-humic fraction of dissolved organic matter (DOM). Uptake of DON declined logarithmically as the concentration of inorganic N in stream water increased. Experimental additions of inorganic N also caused a decline in uptake of DON and net production of DON when the C:N ratio of non-humic DOM was high. This study indicates that the relative and absolute amount of bioavailable DON can vary greatly within and across years due to interactions between the availability of inorganic nutrients and composition of DOM. DOM has the potential to be used biotically at a high rate in nitrogen-poor streams, and it may be generated by heterotrophic microbes when DIN and labile DOM with low relative nitrogen content become abundant.     

The effects of dissolved organic carbon,acidity and seasonality on metal geochemistry within a forested catchment on the Precambrian Shield,central Ontario,Canada

Metal pollution, in combination with other environmental stressors such as acid deposition and climate change, may disturb metal biogeochemical cycles. To investigate the influence of dissolved organic carbon, acidity and seasonality on metal geochemistry, this study has described concentrations of 19 metals as they pass through an acidified forested catchment on the Precambrian Shield in south-central Ontario, Canada. Metal, dissolved organic carbon (DOC) and sulphate (SO₄ ²⁻) concentrations fluctuate throughout the catchment compartments as the water passes through and interacts with vegetation, soils and bedrock. Relationships among metals, DOC and SO₄ ²⁻ are most pronounced in compartments where DOC and SO₄ ²⁻ exhibit high variability, namely in the throughfall, organic horizon soil water, and wetland-draining stream. Metal, DOC and SO₄ ²⁻ concentrations varied seasonally in the streams, and temporal coherence occurred among metal, DOC and SO₄ ²⁻ concentrations in the organic horizon soil water and the wetland-draining stream (PC1). In the wetland-draining stream, the highest DOC, Cr, Cu, Fe, Pb, and V concentrations occur in the summer, whereas concentrations of SO₄ ²⁻ and most other metals peak in the fall after a period of drought. Despite the rural location, provincial water quality objectives for surface water were exceeded for many metals when the peak fall values occurred.     

Formation of biofilms in drinking water distribution networks,a case study in two cities in Finland and Latvia

The formation of biofilms in drinking water distribution networks is a significant technical, aesthetic and hygienic problem. In this study, the effects of assimilable organic carbon, microbially available phosphorus (MAP), residual chlorine, temperature and corrosion products on the formation of biofilms were studied in two full-scale water supply systems in Finland and Latvia. Biofilm collectors consisting of polyvinyl chloride pipes were installed in several waterworks and distribution networks, which were supplied with chemically precipitated surface waters and groundwater from different sources. During a 1-year study, the biofilm density was measured by heterotrophic plate counts on R2A-agar, acridine orange direct counting and ATP-analyses. A moderate level of residual chorine decreased biofilm density, whereas an increase of MAP in water and accumulated cast iron corrosion products significantly increased biofilm density. This work confirms, in a full-scale distribution system in Finland and Latvia, our earlier in vitro finding that biofilm formation is affected by the availability of phosphorus in drinking water.     

The chemistry,physiology and pathology of pH in cancer

Cell survival is conditional on the maintenance of a favourable acid–base balance (pH). Owing to intensive respiratory CO₂ and lactic acid production, cancer cells are exposed continuously to large acid–base fluxes, which would disturb pH if uncorrected. The large cellular reservoir of H⁺-binding sites can buffer pH changes but, on its own, is inadequate to regulate intracellular pH. To stabilize intracellular pH at a favourable level, cells control trans-membrane traffic of H⁺-ions (or their chemical equivalents, e.g. ) using specialized transporter proteins sensitive to pH. In poorly perfused tumours, additional diffusion-reaction mechanisms, involving carbonic anhydrase (CA) enzymes, fine-tune control extracellular pH. The ability of H⁺-ions to change the ionization state of proteins underlies the exquisite pH sensitivity of cellular behaviour, including key processes in cancer formation and metastasis (proliferation, cell cycle, transformation, migration). Elevated metabolism, weakened cell-to-capillary diffusive coupling, and adaptations involving H⁺/H⁺-equivalent transporters and extracellular-facing CAs give cancer cells the means to manipulate micro-environmental acidity, a cancer hallmark. Through genetic instability, the cellular apparatus for regulating and sensing pH is able to adapt to extracellular acidity, driving disease progression. The therapeutic potential of disturbing this sequence by targeting H⁺/H⁺-equivalent transporters, buffering or CAs is being investigated, using monoclonal antibodies and small-molecule inhibitors.     

Trends in aluminium export from a mountainous area to surface waters, from deglaciation to the recent: Effects of vegetation and soil development, atmospheric acidification, and nitrogen-saturation

We reconstructed the history of terrestrial export of aluminium (Al) to Plešné Lake (Czech Republic) since the lake origin 12,600 year BC, and predicted Al export for 2010–2050 on the basis of previously published and new data on mass budget studies, palaeolimnological data, and MAGIC modelling. We focused on three major Al forms; ionic Al (Al_i), organically-bound Al (Al_o), and particulate Al hydroxide [Al(OH)₃]. In early post-glacial time, Plešné Lake received high terrestrial export of Al, but with a minor proportion of Al(OH)₃ (4–25 μM), and concentrations of Al_i and Al_o were negligible. Since the forest and soil development (9900–9000 year BC), erosion has declined and soil organic acids increased export of Al_o from soils. The terrestrial Al_o leaching (7.5 μM) persisted throughout the Holocene until the industrial period. Then, Al_i concentrations continuously increased (up to 28 μM in the mid-1980s) due to atmospheric acidification; the Al_i leaching was mostly associated with sulphate. The proportion of Al_i associated with nitrate has been increasing since the beginning of lake recovery from acidification after 1990 due to reduction in sulphur deposition and nitrogen-saturation of the catchment, leading to persistent nitrate leaching. Currently, nitrate has become the dominant strong acid anion and the major Al_i carrier. Al_o (5.5 μM) is predicted to dominate Al concentrations around 2050, but the predicted Al_i concentrations (4 μM) are uncertain because of uncertainty associated with the future nitrate leaching and its effect on soils.     

Effect of catchment characteristics on aquatic carbon export from a boreal catchment and its importance in regional carbon cycling

Inland waters transport and emit into the atmosphere large amounts of carbon (C), which originates from terrestrial ecosystems. The effect of land cover and land‐use practises on C export from terrestrial ecosystems to inland waters is not fully understood, especially in heterogeneous landscapes under human influence. We sampled for dissolved C species in five tributaries with well‐determined subcatchments (total size 174.5 km²), as well as in various points of two of the subcatchments draining to a boreal lake in southern Finland over a full year. Our aim was to find out how land cover and land‐use affect C export from the catchments, as well as CH₄ and CO₂ concentrations of the streams, and if the origin of C in stream water can be determined from proxies for quality of dissolved organic matter (DOM). We further estimated the gas evasion from stream surfaces and the role of aquatic fluxes in regional C cycling. The export rate of C from the terrestrial system through an aquatic conduit was 19.3 g C m^?2(catchment) yr^?1, which corresponds to 19% of the estimated terrestrial net ecosystem exchange of the catchment. Most of the C load to the recipient lake consisted of dissolved organic carbon (DOC, 6.1 ± 1.0 g C m^?2 yr^?1); the share of dissolved inorganic carbon (DIC) was much smaller (1.0 ± 0.2 g C m^?2 yr^?1). CO₂ and CH₄ emissions from stream and ditch surfaces were 7.0 ± 2.4 g C m^?2 yr^?1 and 0.1 ± 0.04 g C m^?2 yr^?1, respectively, C emissions being thus equal with C load to the lake. The proportion of peatland in the catchment and the drainage density of peatland increased DOC in streams, whereas the proportion of agricultural land in the catchment decreased it. The opposite was true for DIC. Drained peatlands were an important CH₄ source for streams.