[Show abstract][Hide abstract] ABSTRACT: The photochemical release of inorganic nitrogen from dissolved organic matter is an important source of bio-available nitrogen (N) in N-limited aquatic ecosystems. We conducted photochemical experiments and used mathematical models based on pseudo-first-order reaction kinetics to quantify the photochemical transformations of individual N species and their seasonal effects on N cycling in a mountain forest stream and lake (Plešné Lake, Czech Republic). Results from laboratory experiments on photochemical changes in N speciation were compared to measured lake N budgets. Concentrations of organic nitrogen (Norg; 40-58 µmol L-1) decreased from 3 to 26% during 48-hour laboratory irradiation (an equivalent of 4-5 days of natural solar insolation) due to photochemical mineralization to ammonium (NH4+) and other N forms (Nx; possibly N oxides and N2). In addition to Norg mineralization, Nx also originated from photochemical nitrate (NO3-) reduction. Laboratory exposure of a first-order forest stream water samples showed a high amount of seasonality, with the maximum rates of Norg mineralization and NH4+ production in winter and spring, and the maximum NO3- reduction occurring in summer. These photochemical changes could have an ecologically significant effect on NH4+ concentrations in streams (doubling their terrestrial fluxes from soils) and on concentrations of dissolved Norg in the lake. In contrast, photochemical reactions reduced NO3- fluxes by a negligible (<1%) amount and had a negligible effect on the aquatic cycle of this N form.
PLoS ONE 12/2014; 9(12):e116364. · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Mountain lakes in the Bohemian Forest, on both the Czech and German sides, were atmospherically acidified mainly in the 1960s–1980s and have since been recovering from acidification. In 2007, we performed the first complete study on littoral macroinvertebrates in all eight lakes. The goals of the study were to 1) compare macroinvertebrates in the lakes during the process of recovery and 2) investigate relations between the occurrence of taxa and water chemistry. Lake water pH varied from 4.6 to 5.7, concentrations of dissolved reactive Al and labile Al ranged from 118–601 and 11–470 μg l-1, respectively, and DOC concentrations were <6 mg l-1. Altogether 73 taxa were identified from all lakes; a positive relationship was found between pH and the number of macroinvertebrate taxa. The highest number of taxa was found in the least acidic lakes Laka and Grosser Arbersee, including the mollusk Pisidium casertanum. In contrast, the lowest diversity was found in the most acidified Čertovo jezero. Cluster analyses of macroinvertebrates and water chemistry suggested pH as the key factor influencing the occurrence of macroinvertebrate taxa. An interesting finding was the occurrence of the boreo-montane water beetle Nebrioporus assimilis in Prášilské jezero, which is the first documented record of this species in the Czech Republic since 1960.
[Show abstract][Hide abstract] ABSTRACT: Anthropogenically derived nitrogen (N) has a central role in global environmental changes, including climate change, biodiversity loss, air pollution, greenhouse gas emission, water pollution, as well as food production and human health. Current understanding of the biogeochemical processes that govern the N cycle in coupled human-ecological systems around the globe is drawn largely from the long-term ecological monitoring and experimental studies. Here, we review spatial and temporal patterns and trends in reactive N emissions, and the interactions between N and other important elements that dictate their delivery from terrestrial to aquatic ecosystems, and the impacts of N on biodiversity and human society. Integrated international and long-term collaborative studies covering research gaps will reduce uncertainties and promote further understanding of the nitrogen cycle in various ecosystems.
AMBIO A Journal of the Human Environment 07/2014; · 2.97 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We examined long-term data on water chemistry of Lake Rachelsee (Germany) following the changes in acidic depositions in central Europe since 1980s. Despite gradual chemical recovery of Rachelsee, its biological recovery was delayed. In 1999, lake recovery was abruptly reversed by a coincident forest die-back, which resulted in elevated terrestrial export of nitrate and ionic aluminum lasting ~5 years. This re-acidification episode provided unique opportunity to study plankton recovery in the rapidly recovering lake water after the abrupt decline in nitrate leaching from the catchment. There were sudden changes both in lake water chemistry and in plankton biomass structure, such as decreased bacterial filaments, increased phytoplankton biomass, and rotifer abundance. The shift from dominance of heterotrophic to autotrophic organisms suggested their substantial release from severe phosphorus stress. Such a rapid change in plankton structure in a lake recovering from acidity has, to the best of our knowledge, not been previously documented.
AMBIO A Journal of the Human Environment 02/2014; 43(2):207-217. · 2.97 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Ionic and nutrient compositions of tributaries to Plešné Lake (PL, 4 inlets, granite bedrock) and Čertovo Lake (CT, 7 inlets, mica schist and quartzite bedrock) were analyzed in 3-week intervals from October 1997 to November 2012. Norway spruce stands, dominating both catchments, were damaged during this study: 93% of the PL mature trees died due to bark beetle infestation between 2004–2011; 14% of the CT forest was seriously damaged by windthrows and bark beetle in 2007–2011. Almost all dead biomass remained in the catchments. Prior to the forest damage, water chemistry of tributaries exhibited trends typical for areas recovering from strong atmospheric acidification, such as decreasing concentrations of strong acid anions, base cations, ionic aluminium (Al i), and protons (increasing pH). Chemistry of tributaries draining the af-fected sub-catchments rapidly changed after the forest damage. Concentrations of nitrate immediately in-creased, reaching the maximum values (up to 350 μmol.l –1) within 3–6 years after the forest dieback, then started to decline. Nitrate became the dominant anion and its leaching was accompanied by similar trends in Al i and potassium (K +) concentrations, and decreasing pH. Increases in magnesium (Mg 2+) and calcium (Ca 2+) leaching were less steep than those of Al i and K + , but continued at elevated rates until the end of the study. The elevated leaching of phosphorus (P) and dissolved organic carbon (DOC) and nitrogen (DON) occurred immediately after forest dieback. The DON concentrations increased more steeply than DOC, resulting in decreasing DOC:DON ratios. Because almost no biomass was removed from the damaged fo-rest, leaching of K +
[Show abstract][Hide abstract] ABSTRACT: Using dynamic, mass budget, and empirical models, we quantified sulphate-sulphur (SO4-S) leaching from soils in a large central European catchment (upper Vltava river, Czech Republic) over a 110-year period (1900-2010). SO4-S inputs to soils with synthetic fertilisers and atmospheric deposition increased in the 1950s-1980s, then rapidly decreased (~80%), and remained low since the middle 1990s. The proportion of drained agricultural land rapidly increased from 4 to 43% between the 1950s and 1990s; then the draining ability of the system slowly decreased due to its ageing. Sulphate concentrations in the Vltava exhibited similar trends as the external SO4-S inputs, suggesting that they could be explained by changes in atmospheric and fertiliser S inputs. The available data and modelling, however, showed that (i) internal SO4-S sources (mineralization of soil organic S in the drained agricultural land), (ii) a hysteresis in SO4-S leaching from forest soils (a net S retention at the high S inputs and then a net release at the lowered inputs), and (iii) hydrology must be taken into account. An empirical model was then employed, based on parameters representing hydrology (discharge), external SO4-S sources (inputs by synthetic fertilisers and atmospheric deposition), and internal SO4-S sources (mineralization related to soil drainage). The model explained 84% of the observed variability in annual SO4-S concentrations in the Vltava river during 1900-2010 and showed that forest soils were a net sink (105kgha(-1)) while agricultural land was a net source (55kgha(-1)) of SO4-S during 1960-2010. In the late 1980s, forest soils changed from a sink to a source of S, and the present release of SO4-S accumulated in forest soils thus delays recovery of surface waters from acidification, while S losses from agricultural soils increase the risk of future S deficiency in S-demanding crops.
Science of The Total Environment 10/2013; 470-471C:543-550. · 3.16 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Using mass budget and hydrological models, we quantified the contribution of major diffuse nitrogen (N) sources to surface water loading in a large heterogeneous catchment (upper Vltava river, Czech Republic, about 13,000 km2) over the last 52 years. The catchment reflects the typical development in central and eastern European countries, which witnessed socio-economic shifts from a market to a planned economy in the 1950s and back to a market economy in the 1990s. The former shift was accompanied by increasing N inputs to agricultural and forest areas with ranges for the 1950–1980s of 60–160 and 14–30 kg ha−1 year−1, respectively, and with intensive draining of waterlogged farmland. The shift in the 1990s resulted in ~40 and ~50 % reduction of N inputs to agricultural areas and forests, respectively, and farmland draining ceased. The N exports from agricultural land (E
) and from forests (E
) varied within 3–45 and 1.6–7.1 kg ha−1 year−1, respectively (with maxima in the 1980s). The E
fluxes exhibited several similar patterns, being dominated by NO3-N, increasing with N inputs, and having similar inter-annual variability related to hydrology. The N losses from forests were stable (19 % of N input on average), while those from agricultural land increased from ~10 % in the 1960s up to 32 % in the 2000s, due probably to the previous extensive drainage and tillage of waterlogged fields and pastures. These land use changes reduced the water residence time in agricultural land and induced mineralization of soil organic matter. Continuing mineralization of soil organic N pools thus was the most probable reason for the remaining high E
fluxes despite a ~40 % reduction in N inputs to agricultural land, while the E
fluxes decreased proportionally to the decreasing N deposition during 1990–2010.
[Show abstract][Hide abstract] ABSTRACT: In some of the eight glacial lakes in the Bohemian Forest we have observed first signs of zooplankton reco- very from acidity. The recovery has followed a drop in atmospheric sulphur and nitrogen deposition and consequent reversal in water chemistry of the lakes during the last decade. At present, stable populations of Ceriodaphnia quadrangula have returned to Lake Černé and Prášilské, and two circumneutral rotifers have recently occurred in the lakes with positive alkalinity: Laka, Großer Arbersee (Keratella testudo) and Kleiner Arbersee (K. valga). Moreover, in the mesotrophic, strongly acidified Lake Plešné, we documented increase in both phytoplankton and planktonic rotifers during the 1990s. A statistical comparison of seaso- nal data (1994, 1998, 2001 and 2003; Kruskal-Wallis test) showed a significant increase in pH and a signi- ficant drop in total reactive aluminium (Al T ). In parallel, a significant increase in chlorophyll a concentra- tion suggested the recovery of phytoplankton. In consequence, summer abundance of planktonic rotifers in Lake Plešné rose by more than two orders of magnitude during the 1990s.
Aktuality šumavského výzkumu II. Sborník z konference, 4.–7. 10. 2004, Srní, Česko. 07/2013;
[Show abstract][Hide abstract] ABSTRACT: We evaluated changes in the chemistry of the uppermost soil horizons in an unmanaged spruce forest (National Park Bohemian Forest, Czech Republic) for 3 years after dieback caused by a bark beetle infestation, and compared these changes with a similar undisturbed forest area. The soils below the disturbed forest received 2–6 times more elements via litter fall compared to the unaffected plot. The subsequent decomposition of litter and reduced nutrient uptake by trees resulted in a steep increase in soil concentrations of soluble N (NH4-N, organic-bound N) and P forms in the disturbed plot. The average concentrations of NH4-N and soluble reactive P increased from 0.8 to 4.4 mmol kg−1 and from 0.04 to 0.9 mmol kg−1, respectively, in the uppermost soil horizon. Decomposition of litter at the disturbed plot elevated soil concentrations of Ca2+, Mg2+ and K+, which replaced Al3+ and H+ ions from the soil sorption complex. Consequently, soil concentrations of exchangeable base cations increased from 120 to 200 meq kg−1, while exchangeable Al3+ and H+ decreased 66 and 50 %, respectively, and soil base saturation increased from 40 to 70 %. The Al3+ liberation did not elevate concentrations of ionic Al in the soil solution, because most of the liberated Al3+ was rapidly complexed by dissolved organic carbon (DOC) and transformed to DOC–Al complexes. The chemical parameters investigated at the unaffected plot remained stable during the study.
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[Show abstract][Hide abstract] ABSTRACT: Elevated and chronic nitrogen (N) deposition to N-limited terrestrial ecosystems can lead to ‘N saturation’, with resultant ecosystem damage and leaching of nitrate (NO3 −) to surface waters. Present-day N deposition, however, is often a poor predictor of NO3 − leaching, and the pathway of the ecosystem transition from N-limited to N-saturated remains incompletely understood. The dynamics of N cycling are intimately linked to the associated carbon (C) and sulphur (S) cycles. We hypothesize that N saturation is associated with shifts in the microbial community, manifest by a decrease in the fungi-to-bacteria ratio and a transition from N to C limitation. Three mechanisms could lead to lower amount of bioavailable dissolved organic C (DOC) for the microbial community and to C limitation of N-rich systems: (1) Increased abundance of N for plant uptake, causing lower C allocation to plant roots; (2) chemical suppression of DOC solubility by soil acidification; and (3) enhanced mineralisation of DOC due to increased abundance of electron acceptors in the form of SO42− SO 4 2 − and NO3 − in anoxic soil micro-sites. Here we consider each of these mechanisms, the extent to which their hypothesised impacts are consistent with observations from intensively-monitored sites, and the potential to improve biogeochemical models by incorporating mechanistic links to the C and S cycles.
[Show abstract][Hide abstract] ABSTRACT: Biological response of aquatic macrophytes to changes in water chemistry
and temperature has been studied on a background of the long-term
research of Bohemian Forest lakes recovery from acid stress.
Isoëtes lacustris and I. echinospora are common aquatic macrophytes
adapted for living in soft-water lakes widely distributed in European
lake districts; however, in central Europe they are rare glacial
relicts. In Černé and Plešné lakes, two
populations survived a thirty-year period of severe acidification but
failed to reproduce. In our experimental and field studies on
Isoëtes reproduction we identified early ontogenetic stages to be
most vulnerable to changes in lake water pH, temperature, and aluminium
(Al) toxicity .We described specific symptoms on plantlets reflecting
various lake water acidity and Al-toxicity and defined critical limits
of the stressors for plant survival. Using a mathematical model we also
described temperature-related changes in species reproductive phenology
and revealed their narrow temperature tolerance. The knowledge of
critical environmental factors and their limits for species survival
allows us to infer changes in species reproduction in response to both
historical and ongoing changes in climate and lake water chemistry. Due
to species-specific ecological traits, we can now explain the recent
population recovery of I. echinospora contrasting with the poor
reproduction of I. lacustris that will be constrained by environmental
stressors for at least during the next 20 years.
[Show abstract][Hide abstract] ABSTRACT: Over recent decades, palaeolimnological records from remote sites have provided convincing evidence for the onset and development of several facets of global environmental change. Remote lakes, defined here as those occurring in high latitude or high altitude regions, have the advantage of not being overprinted by local anthropogenic processes. As such, many of these sites record broad-scale environmental changes, frequently driven by regime shifts in the Earth system. Here, we review a selection of studies from North America and Europe and discuss their broader implications. The history of investigation has evolved synchronously with the scope and awareness of environmental problems. An initial focus on acid deposition switched to metal and other types of pollutants, then climate change and eventually to atmospheric deposition-fertilising effects. However, none of these topics is independent of the other, and all of them affect ecosystem function and biodiversity in profound ways. Currently, remote lake palaeolimnology is developing unique datasets for each region investigated that benchmark current trends with respect to past, purely natural variability in lake systems. Fostering conceptual and methodological bridges with other environmental disciplines will upturn contribution of remote lake palaeolimnology in solving existing and emerging questions in global change science and planetary stewardship.
Journal of Paleolimnology 03/2013; 49(3):513-535. · 2.21 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This study describes the origin, bedrock geology, geomorphology, hydrological stability and physical and chemical characteristics of a representative set of 29 lakes in the ice-free parts of the Ulu Peninsula, James Ross Island, located close to the northern tip of the Antarctic Peninsula. Based on these features, six different types of lakes were defined: stable shallow lakes on higher-altitude levelled surfaces, shallow coastal lakes, stable lakes in old moraines, small unstable lakes in young moraines, deep cirque lakes and kettle lakes. We observed a significant relationship between lake type and water chemistry. Bedrock, lake age and morphometry together with altitude were the most important factors underlying the observed limnological variability. Our results further suggested possible nitrogen limitation in the lake ecosystems. However, physical factors such as low temperature and light were also likely to be limiting.
[Show abstract][Hide abstract] ABSTRACT: The 1998–2012 average composition of bulk precipitation was dominated by NH4+ (25 μmol.l–1) among cations and NO3 – (21 μmol.l–1) among anions in catchments of Plešné (PL) and Čertovo (CT) lakes in the Bohemian Forest. Concentrations of other ions averaged between 0.8 and 8.3 μmol.l–1. The average precipitation amount was 1372 mm, bulk deposition fluxes of major nutrients were 5.0, 4.7, and 3.5 kg.ha.yr–1 of NH4-N, NO3-N, and TON, respectively, and 22, 4.5, 2.6, 1.9, 0.5, 0.23 kg.ha.yr–1 of TOC, SO4-S, Ca2+, K+, Mg2+, and TP, respectively. Prior to bark beetle infestation in the PL catchment in 2004–2006, the average throughfall fluxes (TF) of Na+, H+, SO4 2–, NO3 –, Cl–, and TP, were on average 1.5–2.1 fold higher than their precipitation fluxes (PF). Higher TF:PF ratios (2.1–9.8) were observed for Mn, K+, Mg2+, Ca2+, and organic C, N, and P forms, while lower ratios (0.6–1.3) occurred for dissolved reactive P and NH4 +. After the forest infestation, throughfall deposition of ions and nutrients started to decrease in the PL catchment compared to the CT catchment. The greatest and most rapid changes occurred for K+, DOC, Mg2+, and Ca2+. Their fluxes rapidly decreased to values similar to precipitation fluxes within 6–8 years after the infestations. Slower changes occurred in throughfall fluxes of SO4 2–, NO3 –, and Cl–, and negligible changes so far occurred in the throughfall fluxes of NH4 +. The major reason for differing response of throughfall deposition of individual elements to forest dieback (and reduced surface area of canopies) was different contribution of canopy leaching (export from living and decaying canopy tissue) and microbial transformations to the elemental throughfall fluxes.
[Show abstract][Hide abstract] ABSTRACT: Correct identification of P forms together with their main Fe and Al binding partners in non-calcareous sediments is of crucial importance for evaluation of P cycling in water bodies. In this paper, we assess extraction methods frequently used for this purpose, i.e., a sequential five-step fractionation (water, bicarbonate buffered dithionite solution (BD), NaOH, HCl, nitric-perchloric acid), ascorbate extraction (pH ∼7.5), and oxalate extraction (pH ∼3), directly on a range of laboratory prepared Fe and Al minerals enriched with adsorbed P. Extraction selectivity and efficiency for particular P, Fe and Al forms were also verified by specific combinations of these extraction methods applied on freshwater sediment samples. In the sequential fractionation, BD was highly effective in dissolving both amorphous and crystalline Fe (hydr)oxides and the associated P, while neither FeS nor Al (hydr)oxides were dissolved. The following NaOH extraction effectively dissolved both amorphous and crystalline Al (hydr)oxides. The high solubilizing power of BD and NaOH to dissolve crystalline Fe and Al oxides that have only a small P-sorption ability prevents the use of resulting Fe/P and Al/P ratios as simple predictors of total P sorption capacity of sediments and soils. Ascorbate non-selectively extracted small proportions of FeS and amorphous Fe and Al (hydr)oxides, but significant amounts of adsorbed P, which hinders its use for the characterization of P forms in non-calcareous sediments. Similar nonselective characteristics were found for oxalate extractions. As oxalate extracts most of the adsorbed phosphate, it is not possible to use it unambiguously to determine specific Fe/P and Al/P ratios of active complexes. However, this method is convenient (and more selective than NaOH step in the sequential fractionation) for the determination of amorphous Al (hydr)oxides.
[Show abstract][Hide abstract] ABSTRACT: Outflows from two atmospherically acidified lakes in the Bohemian Forest were studied in 2005 and 2007. While Lake Čertovo has been strongly acidified (∼pH 4.6), Lake Laka was only slightly acidified in the past and is recovering now (∼pH 5.2). The water chemistry and macrozoobenthos composition were analysed along longitudinal gradients of both lake outflows to determine the present status of their streams. A certain progression in stream chemistry to more neutral conditions was observed along the longitudinal gradients of both streams. However, a possible recovery of macrozoobenthos was evident only in the Lake Laka outflow, mainly via an increasing number of Ephemeroptera and Trichoptera taxa, and an increasing number of Gammarus fossarum, both along the longitudinal gradient and during the period of study. In contrast, no considerable changes were observed in the macrozoobenthos composition of the Lake Čertovo outflow, presumably because its chemistry was harmful for acidosensitive taxa such as Ephemeroptera and Trichoptera. Plecoptera and Chironomidae were the most numerous groups in this stream. The biological recovery of both streams will depend on further chemical improvement in their catchments as well as on the dispersal ability of benthic organisms.
[Show abstract][Hide abstract] ABSTRACT: We developed and tested a regression model, interpolating long-term sequences of observed atmospheric deposition of SO42−, NO3−, and NH4+ in the upper Vltava river catchment (Czech Republic) to its three sub-regions, differing in elevation and forest cover. The model provides more realistic estimates of wet and total S and N depositions and their inter-annual variability in the study catchment than the available European deposition sequences, especially in the case of wet S deposition prior to 1997. In the model, ion fluxes are calculated as the product of the precipitation volume and ion concentrations, which both are derived as empirical functions of elevation and time. The long-term sequences of ion concentrations are based on measured deposition data at 19 stations and their relationships with central European emission trends of SO2, NOx, and NH3 for years with no measurements. Exponential relationships between elevation and precipitation volume (positive) and elevation and ion concentrations (negative) are used to convert the long-term sequences of precipitation and concentrations into values for individual elevations. Throughfall fluxes (TF) of S and N in the forest areas are calculated from their fluxes in precipitation (PF), using long-term sequences of TF:PF ratios, based on measured fluxes and the S and N emission trends. The calculated fluxes of S and reactive nitrogen (NO3–N and NH4–N) explain 80% and 56% of the variability in their measured fluxes, respectively, along an elevation gradient from 275 to 1334 m.
[Show abstract][Hide abstract] ABSTRACT: We present a new formulation of the acidification model MAGIC that uses decomposer dynamics to link nitrogen (N) cycling to carbon (C) turnover in soils. The new model is evaluated by application to 15-30 years of water chemistry data at three coniferous-forested sites in the Czech Republic where deposition of sulphur (S) and N have decreased by >80% and 40%, respectively. Sulphate concentrations in waters have declined commensurately with S deposition, but nitrate concentrations have shown much larger decreases relative to N deposition. This behaviour is inconsistent with most conceptual models of N saturation, and with earlier versions of MAGIC which assume N retention to be a first-order function of N deposition and/or controlled by the soil C/N ratio. In comparison with earlier versions, the new formulation more correctly simulates observed short-term changes in nitrate leaching, as well as long-term retention of N in soils. The model suggests that, despite recent deposition reductions and recovery, progressive N saturation will lead to increased future nitrate leaching, ecosystem eutrophication and re-acidification.