Chemical recovery of acidified Bohemian lakes between 1984 and 2012: the role of acid deposition and bark beetle induced forest disturbance

Assessment of temporal trends and rates of change in hydrochemical parameters and forest cover has been conducted to elucidate key drivers of surface water acidification in glacial lakes in the Czech Republic. Since 1984, the key driver in acidification reversal was sulphate (SO₄) concentration (median decrease of ?3.58 μeq L^?1 yr^?1) which fell in line with reductions in sulphur (S) deposition. Reduction of nitrogen (N) deposition was followed by proportional reduction in nitrate (NO₃) leaching although decline in NO₃ concentrations was more pronounced at two sites, the ?ertovo Lake (CT) and Prá?ilské Lake (PR) until 2006; only ??árské pond showed effective catchment N immobilization. Coherent decline of chloride concentration was detected across all sites. The decrease of strong mineral acids was partly compensated by decrease of inorganic aluminium (Al_in), especially at sites most acidified in the beginning of observations (ANC_1984–1986 between ?160 and ?90 μeq L^?1 at CT, ?erné Lake—CN and Ple?né lake—PL) and by reductions of base cations and increases of pH. All lakes (CN, CT, PL, PR and LK) moved to the ANC range between ?29 and 30 μeq L^?1 (2010–2012) where sensitivity of pH to further reductions in acid anions may be expected. Concurrently, charge of weak organic acids (OAs) increased and partly balanced the strong mineral acid decrease as a consequence of (i) significant DOC (dissolved organic carbon) increase (median change of 0.13 mgC L^?1 yr^?1 since 1993) and (ii) deprotonation of weak OAs caused by pH rise. Since 2000s, bark beetle induced forest decline accelerated NO₃ leaching at most of the catchments (by 200 % at LK, PL and PR). However, elevated N leaching was effectively neutralized by base cations (K, Mg, Ca) originating from decaying fresh litter, thus acidification recovery was not reversed, but slowed down. After cessation of NO₃ leaching we hypothesise that collapsed tree canopy across catchments (from 12 to 87 % compared to 1984) will cause lower total acid input in precipitation (S + N) and regrowth of vegetation may stimulate higher N immobilization (in biomass and soil); processes which could lead to further increase of ANC and pH, key indicators for biological recovery.     

长白山森林生态系统大气氮素湿沉降通量和组成的季节变化特征

2009—2010年期间,利用雨量计收集法在长白山森林生态系统定位站开展定位观测,分析降水中氮素浓度,研究了该区域大气氮素湿沉降通量和组成的季节变化特征。结果表明,各形态氮素月均浓度之间差别较大,具有明显的季节性;其降水中浓度主要受降水量和降水频次的影响。全年氮素湿沉降中TN、TIN和TON的沉降量分别为27.64 kg N hm-2a-1、11.05 kg N hm-2a-1和16.59 kg N hm-2a-1,TON为沉降主体,占60.02%;其大气氮沉降量主要由降水量和降水中氮素浓度共同决定。该地区氮湿沉降量已处于我国中等水平,考虑到氮素的干湿沉降比例,本区域的年氮沉降量已接近或超过本区域的营养氮沉降临界负荷,存在一定的环境风险。该地区生长季(5—10月)的氮沉降量(16.59 kg N hm-2a-1)占全年氮沉降量的比例达到73.20%。生长季的氮沉降对于促进植物生长直接生态意义重大,而非生长季的氮沉降对于大量补充次年植物生长初期所需养分的间接生态意义明显。     

Palaeolimnological evidence for recent chemical and biological changes in U.K. Acid Waters Monitoring Network sites

1. Palaeolimnological evidence is presented for the long-term (post-1850) and recent (post-1970) trends in acidity of eleven sites in the U.K. Acid Waters Monitoring Network.
2. Sites are located throughout the U.K. in areas sensitive to acidification, and results show that all have been acidified since pre-industrial times. Although there is considerable variation in the timing and magnitude of these changes the results are consistent with other evidence of the widespread and severe acidification of sensitive U.K. freshwaters as a result of acidic deposition.
3. The most severely acidified sites generally have the highest critical load exceedance, although there is a only a poor relationship between exceedance and post-1850 pH change ( r = 0.58, P = 0.06) or diatom floristic change ( r = 0.52, P = 0.1). These results highlight the difficulty of inferring biological change or 'damage' in freshwater ecosystems from current national maps of critical load exceedances.
4. Evidence of chemical and biological response to the post-1970 reduction in U.K. S emissions is variable: seven lakes show continued acidification in the 1970s and early 1980s while four appear to have been in steady state. One afforested site shows continued acidification until at least 1990, the year of coring, suggesting that at this site increased scavenging of acid anions following canopy closure and/or increased nitrate leaching have offset the benefits of reduced S deposition.
5. Five sites appear to have been in steady state since the early to mid-1980s, and two show unambiguous evidence for a recent increase in pH and a reversal in the diatom assemblages to that of earlier levels. The results support and extend the findings of other studies and show that biological recovery is occurring in at least two chronically acidified areas of the U.K. (Galloway, SW Scotland, and north Wales), and that natural recovery can lead to the re-establishment of biota previously present at the site.     

Palaeolimnological evidence for recent chemical and biological changes in U.K. Acid Waters Monitoring Network sites

1. Palaeolimnological evidence is presented for the long-term (post-1850) and recent (post-1970) trends in acidity of eleven sites in the U.K. Acid Waters Monitoring Network.
2. Sites are located throughout the U.K. in areas sensitive to acidification, and results show that all have been acidified since pre-industrial times. Although there is considerable variation in the timing and magnitude of these changes the results are consistent with other evidence of the widespread and severe acidification of sensitive U.K. freshwaters as a result of acidic deposition.
3. The most severely acidified sites generally have the highest critical load exceedance, although there is a only a poor relationship between exceedance and post-1850 pH change ( r = 0.58, P = 0.06) or diatom floristic change ( r = 0.52, P = 0.1). These results highlight the difficulty of inferring biological change or 'damage' in freshwater ecosystems from current national maps of critical load exceedances.
4. Evidence of chemical and biological response to the post-1970 reduction in U.K. S emissions is variable: seven lakes show continued acidification in the 1970s and early 1980s while four appear to have been in steady state. One afforested site shows continued acidification until at least 1990, the year of coring, suggesting that at this site increased scavenging of acid anions following canopy closure and/or increased nitrate leaching have offset the benefits of reduced S deposition.
5. Five sites appear to have been in steady state since the early to mid-1980s, and two show unambiguous evidence for a recent increase in pH and a reversal in the diatom assemblages to that of earlier levels. The results support and extend the findings of other studies and show that biological recovery is occurring in at least two chronically acidified areas of the U.K. (Galloway, SW Scotland, and north Wales), and that natural recovery can lead to the re-establishment of biota previously present at the site.     

Contrasting responses of two Sitka spruce forest plots in Ireland to reductions in sulphur emissions: results of 20 years of monitoring

Long-term trends in ion concentrations of bulk precipitation, throughfall, forest floor leachate (humus water) and shallow and deep soil water were assessed at two Sitka spruce (Picea sitchensis) stands—one on an Atlantic peat bog in the west of Ireland (Cloosh), the other on the east coast on a peaty podzol (Roundwood). Deposition at Cloosh was dominated by marine ions (sodium, [Na⁺], chloride [Cl^?], and magnesium [Mg²⁺]), whereas bulk precipitation and throughfall at Roundwood was characterized by inputs of non-marine sulphate (nmSO₄ ^2?), acidity and inorganic nitrogen (NH₄ ⁺, NO₃ ^?). Significant declines in concentrations of nmSO₄ ^2? and acidity in bulk precipitation and throughfall were observed at both sites. The decline in throughfall nmSO₄ ^2? was significantly related to reductions in European sulphur dioxide (SO₂) emissions. At Roundwood, SO₄ ^2? declined significantly in humus, shallow and deep soil water. In deep soil water this was accompanied by a long-term increase in pH and a reduction in total aluminum (Al_tot). The recovery from acidification was delayed by high concentrations of NO₃ ^?, which strongly influenced acidity and Al_tot concentrations. At Cloosh, there was a significant decline in SO₄ ^2? in humus water but long-term trends were not evident in shallow or deep soil water; SO₄ ^2? concentrations at these depths fluctuated in response to drought-events. Marine ions strongly influenced soil water chemistry at both sites; at Cloosh soil water acidity was strongly related to Na⁺ and Cl^?, while at Roundwood, Na⁺, Cl^? and Mg²⁺ influenced Al_tot concentrations. Dissolved organic carbon increased significantly in humus and soil water at Roundwood, where it was associated with declining acidity. Soil water at both sites was influenced by a combination of anthropogenic sulphur (S) and nitrogen (N) deposition, drought and sea-salt events. The study highlights the value of long-term monitoring in assessing the response of forest soils to S and N deposition against a background of climate influences on soil water through drought and sea-salt events.     

Molecular mechanisms of water table lowering and nitrogen deposition in affecting greenhouse gas emissions from a Tibetan alpine wetland

Rapid climate change and intensified human activities have resulted in water table lowering (WTL) and enhanced nitrogen (N) deposition in Tibetan alpine wetlands. These changes may alter the magnitude and direction of greenhouse gas (GHG) emissions, affecting the climate impact of these fragile ecosystems. We conducted a mesocosm experiment combined with a metagenomics approach (GeoChip 5.0) to elucidate the effects of WTL (?20 cm relative to control) and N deposition (30 kg N ha^?1 yr^?1) on carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) fluxes as well as the underlying mechanisms. Our results showed that WTL reduced CH₄ emissions by 57.4% averaged over three growing seasons compared with no‐WTL plots, but had no significant effect on net CO₂ uptake or N₂O flux. N deposition increased net CO₂ uptake by 25.2% in comparison with no‐N deposition plots and turned the mesocosms from N₂O sinks to N₂O sources, but had little influence on CH₄ emissions. The interactions between WTL and N deposition were not detected in all GHG emissions. As a result, WTL and N deposition both reduced the global warming potential (GWP) of growing season GHG budgets on a 100‐year time horizon, but via different mechanisms. WTL reduced GWP from 337.3 to ?480.1 g CO₂‐eq m^?2 mostly because of decreased CH₄ emissions, while N deposition reduced GWP from 21.0 to ?163.8 g CO₂‐eq m^?2, mainly owing to increased net CO₂ uptake. GeoChip analysis revealed that decreased CH₄ production potential, rather than increased CH₄ oxidation potential, may lead to the reduction in net CH₄ emissions, and decreased nitrification potential and increased denitrification potential affected N₂O fluxes under WTL conditions. Our study highlights the importance of microbial mechanisms in regulating ecosystem‐scale GHG responses to environmental changes.     

Leiocolea fitzgeraldiae sp. nov. in Britain and Ireland

Abstract

Leiocolea fitzgeraldiae sp. nov. from Wales, Scotland and Ireland is described and illustrated. Comparisons between it and the related species L. bantriensis and L. alpestris are outlined. Its cytology and habitat preferences are discussed and a distribution map is given.     

Geochemistry and health in the United Kingdom.

Before the 1960s, comparisons between the distribution of trace elements in the environment and health in the United Kingdom were primarily confined to ad hoc studies in areas associated with particular agricultural disorders or with unusual human mortality or morbidity records. More recently, increasing interest in the importance of trace elements in crop and animal production and in the hazards of environmental pollution have created a need for more systematic geochemical data. Geochemical reconnaissance maps for England, Wales, Northern Ireland and parts of Scotland have demonstrated the extent of many known clinical trace element problems in agriculture and have also been valuable in delineating areas within which subclinical disorders may occur. Their application to studies on the composition of soils, food crops and surface waters in relation to public health has proved encouraging. Current knowledge and present investigations into environmental geochemistry and human health in the U.K. are reviewed, together with future research requirements.     

Nitrous oxide emission factors for agricultural soils in Great Britain: the impact of soil water-filled pore space and other controlling variables

Measurements were made of nitrous oxide (N₂O) emissions from N‐fertilised ungrazed grassland and arable land at sites widely distributed across Great Britain during 1999–2001. The closed static chamber method was used throughout. Emissions varied widely throughout the year at each site, and between sites. Daily fluxes up to 1200 g N₂O–N ha ^{? 1} d ^{? 1} were recorded. The highest annual flux was 27.6 kg N₂O–N ha ^{? 1} at a grassland site in Wales, whereas the lowest, 1.7 kg N₂O–N ha ^{? 1}, occurred on a soil overlying chalk in southern England. The key factors affecting N₂O emissions from agricultural soil were soil WFPS, temperature and soil NO₃^––N content. On grassland, rainfall (particularly around the time of N application), with its consequent effect on water‐filled pore space (WFPS), was the main driving factor during the growing season. Annual emission factors (EFs), uncorrected for background emission, varied from 0.4 to 6.5% of the nitrogen (N) applied, covering a similar range for grassland to that found previously for sites restricted to Scotland. Continued monitoring at a grassland reference site near Edinburgh showed that annual EFs vary greatly from year to year, even with similar management, and that several years' data are required to produce a robust mean EF. The overall distribution of EFs in this and previous studies was log‐normal. The EFs for small‐grain cereals (and oilseed rape) peaked at a much lower value than those for grassland, whereas the values for leafy vegetables and potato crops fitted well into the grassland distribution. These differences in EF between various types of crop should be taken into account when compiling regional or national N₂O emission inventories.     

Spatial and temporal variation of atmospheric nitrogen deposition in the North China Plain

A monitoring network of nine sites was established to determine the spatial and temporal variation of atmospheric nitrogen (N) deposition in the North China Plain (NCP) over a two-year period. The annual bulk deposition of inorganic N in the North China Plain ranged from 18.4 to 38.5 kg/hm² and averaged 28.0 kg/hm². The concentration of NH₄⁺-N and NO₃^?-N in rainwater averaged 3.76 and 1.85 mg/L, respectively, which were significantly higher than the values at background sites in China (normally less than 0.5 mg/L). Annual bulk deposition of inorganic N in the Beijing area (32.5 kg/hm²) was higher than that in Shandong and Hebei provinces (21.2 kg/hm² on an average). Also bulk N deposition was much greater in Dongbeiwang and Fangshan than in Yanqing and Shunyi counties. Significant spatial variation of bulk deposition was observed in the Beijing area because of variation of precipitation, and 60% of bulk deposition occurred from June to September. Bulk deposition of NH₄⁺-N was 2.0 times that of NO₃^?-N deposition at the rural monitoring sites. However, the situation was reversed at the Beijing Academy of Agricultural-Forestry Sciences (BAAFS), the unique urban monitoring site. The results suggest that reduced N in precipitation is dominant in rural regions, but oxidized N is the major form in urban regions. The positive relationship between inorganic N deposition and precipitation can be fitted by a power equation (r²= 0.67), showing an increase of NH₄⁺-N and NO₃^?-N inputs with increased precipitation. Wet deposition of N accounted for 73% of the bulk deposition, implying that dry deposition of N, particularly NH₄⁺-N from dust, is important in the North China Plain.     

Fluxes and transformations of nitrogen in a high-elevation catchment,Sierra Nevada

The fluxes and transformations of nitrogen (N) were investigated from 1985 through 1987 at the Emerald Lake watershed (ELW), a 120 ha high-elevation catchment located in the southern Sierra Nevada, California, USA. Up to 90% of annual wet deposition of N was stored in the seasonal snowpack; NO ₃ ^– and NH ₄ ⁺ were released from storage in the form of an ionic pulse, where the first fraction of meltwater draining from the snowpack had concentrations of NO ₃ ^– and NH ₄ ⁺ as high as 28 eq L^–1 compared to bulk concentrations of <5 eq L^–1 in the snowpack. The soil reservoir of organic N (81 keq ha^–1) was about ten times the N storage in litter and biomass (12 keq ha^–1). Assimilation of N by vegetation was balanced by the release of N from soil mineralization, nitrification, and litter decay. Mineralization and nitrification processes produced 1.1 keq ha^–1 yr^–1 of inorganic N, about 3 1/2 times the loading of N from wet and dry deposition. Less than 1% of the NH ₄ ⁺ in wet and dry deposition was exported from the basin as NH ₄ ⁺ . Biological assimilation was primarily responsible for retention of NH ₄ ⁺ in the basin, releasing one mode of H⁺ for every mole of NH ₄ ⁺ retained and neutralizing about 25% of the annual acid neutralizing capacity produced by mineral weathering in the basin. Nitrate concentrations in stream waters reached an annual peak during the first part of snowmelt runoff, with maximum concentrations in stream water of 20 eq L^–1, more than 4 times the volume-weighted mean annual concentrations of NO ₃ ^– in wet deposition. This annual peak in stream water NO ₃ ^– was consistent with the release of NO ₃ ^– from the snowpack in the form of an ionic pulse; however soil processes occurring underneath the winter snowpack were another potential source of this NO ₃ ^– . Concentrations of stream water NO ₃ ^– during the summer growing season were always near or below detection limits (0.5 eq L^–1).     

Effects of extreme experimental drought and rewetting on CO2 and CH4 exchange in mesocosms of 14 European peatlands with different nitrogen and sulfur deposition

The quantitative impact of intense drought and rewetting on gas exchange in ombrotrophic bogs is still uncertain. In particular, we lack studies investigating multitudes of sites with different soil properties and nitrogen (N) and sulfur (S) deposition under consistent environmental conditions. We explored the timing and magnitude of change in CO₂ (Respiration, Gross Primary Production – GPP, and Net Exchange – NE) and CH₄ fluxes during an initial wet, a prolonged dry (~100 days), and a subsequent wet period (~230 days) at 12 °C in 14 Sphagnum peat mesocosms collected in hollows from bogs in the UK, Ireland, Poland, and Slovakia. The relationship of N and S deposition with GPP, respiration, and CH₄ exchange was investigated. Nitrogen deposition increased CO₂ fluxes and GPP more than respiration, at least up to about 15 kg N ha^?1 yr^?1. All mesocosms became CO₂ sources during drying and most of them when the entire annual period was considered. Response of GPP to drying was faster than that of respiration and contributed more to the change in NE; the effect was persistent and few sites recovered “predry” GPP by the end of the wet phase. Respiration was higher during the dry phase, but did not keep increasing as WT kept falling and peaked within the initial 33 days of drying; the change was larger when differences in humification with depth were small. CH₄ fluxes strongly peaked during early drought and water table decline. After rewetting, methanogenesis recovered faster in dense peats, but CH₄ fluxes remained low for several months, especially in peats with higher inorganic reduced sulfur content, where sulfate was generated and methanogenesis remained suppressed. Based on a range of European sites, the results support the idea that N and S deposition and intense drought can substantially affect greenhouse gas exchange on the annual scale.     

On the tracks of Nitrogen deposition effects on temperate forests at their southern European range – an observational study from Italy

We studied forest monitoring data collected at permanent plots in Italy over the period 2000–2009 to identify the possible impact of nitrogen (N) deposition on soil chemistry, tree nutrition and growth. Average N throughfall (N‐NO₃+N‐NH₄) ranged between 4 and 29 kg ha^?1 yr^?1, with Critical Loads (CLs) for nutrient N exceeded at several sites. Evidence is consistent in pointing out effects of N deposition on soil and tree nutrition: topsoil exchangeable base cations (BCE) and pH decreased with increasing N deposition, and foliar nutrient N ratios (especially N : P and N : K) increased. Comparison between bulk openfield and throughfall data suggested possible canopy uptake of N_, levelling out for bulk deposition >4–6 kg ha^?1 yr^?1. Partial Least Square (PLS) regression revealed that ‐ although stand and meteorological variables explained the largest portion of variance in relative basal area increment (BAI_rel 2000–2009) ‐ N‐related predictors (topsoil BCE, C : N, pH; foliar N‐ratios; N deposition) nearly always improved the BAI_rel model in terms of variance explained (from 78.2 to 93.5%) and error (from 2.98 to 1.50%). N deposition was the strongest predictor even when stand, management and atmosphere‐related variables (meteorology and tropospheric ozone) were accounted for. The maximal annual response of BAI_rel was estimated at 0.074–0.085% for every additional kgN. This corresponds to an annual maximal relative increase of 0.13–0.14% of carbon sequestered in the above‐ground woody biomass for every additional kgN, i.e. a median value of 159 kgC per kgN ha^?1 yr^?1 (range: 50–504 kgC per kgN, depending on the site). Positive growth response occurred also at sites where signals of possible, perhaps recent N saturation were detected. This may suggest a time lag for detrimental N effects, but also that, under continuous high N input, the reported positive growth response may be not sustainable in the long‐term.     

Some effect of sodium application on the yield and chemical composition of pasture grown under differing conditions of potassium and moisture supply

The effects of Na fertiliser (supplied as an NPK-Na compound) on herbage yield and composition were examined at two different sites to see if pasture responses to Na were affected by differences in K and moisture availability. At one site, pasture was grown under conditions of moisture stress and limited K availability, whereas at the other site the pasture was grown under comparatively non-stress conditions.The results were interesting in that Na fertilisation appeared to be detrimental to pasture yield and quality under conditions of moisture stress and suboptimal K supply, whereas under the non-stress conditions it actually increased herbage N offtake, marginally improved the nutritional quality of the pasture and produced appreciable (albeit non-significant) increases in DM yield. It was suggested that an important effect of Na on grass production may have been its ability to enhance the rate of NO₃ ^– uptake by plants, thereby minimising NO₃ ^–-N losses from the soil-plant system by denitrification. However, because the amount of N fertiliser used in the experiments (i.e. 390 kg N ha^–1 yr^–1) was close to that normally required for maximum yield production (N max) under Northern Ireland conditions, the scope for yield increases in response to Na-elicited improvements in N offtake were thought to have been very limited at both experimental sites.On the basis of results from both the present study and previous field trials, a unifying theory is presented to explain the differential effects of Na on NO₃ ^– uptake and herbage growth under different sets of circumstances.     

Landscape-level nitrogen import and export in an ecosystem with complex terrain, Colorado Front Range

Knowledge of import, export, and transport of nitrogen (N) in headwater catchments is essential for understanding ecosystem function and water quality in mountain ecosystems, especially as these ecosystems experience increased anthropogenic N deposition. In this study, we link spatially explicit soil and stream data at the landscape scale to investigate import, export and transport of N in a 0.89?km² site at the alpine-subalpine ecotone in the Front Range of the Rocky Mountains, Colorado, U.S.A. For two of the major N inputs to our site, N deposition in the snowpack and N fixation, a complementary relationship was found across the study site, with greater abundance of N-fixing plants in areas with less snow and substantial snow inputs in areas with low N fixer abundance. During the initial phases of snowmelt, mixing model end members for oxygen isotopes in nitrate (NO₃ ^?) indicated that a substantial quantity of NO₃ ^? is transported downhill into the forested subalpine without being assimilated by soil microbes. After this initial pulse, much less NO₃ ^? entered the stream and most but not all of it was microbial in origin. Rising δ¹⁵N in stream NO₃ ^? indicated greater influence of fractionating processes such as denitrification later in the season. NO₃ ^? from both atmospheric and microbial sources was not exported from our site because it was consumed within the first several hundred meters of the stream; ultimately, N exports were in the form of dissolved organic nitrogen (DON) and particulate N (PN). The results of this study suggest that the highest elevation dry alpine meadows rely more heavily on N fixation as an N source and experience less of the effects of anthropogenic N deposition than mid and lower elevation areas that have more snow. Our data also suggest that mid-elevation krummholz, moist meadows, and talus slopes are exporting N as NO₃ ^? shortly after the onset of snowmelt, but that this NO₃ ^? is rapidly consumed as the stream flows through the subalpine forest. This consumption by assimilation and/or denitrification currently provides a buffer against increased inorganic N availability downstream.     

The spread of the Bank vole Clethrionomys glareolus in Ireland

The discovery of the Bank vole Clethrionomys glareolus in Ireland and the published information on its spread are reviewed, and the results of a complete resurvey of its distribution, in 1 982 , presented. The rate of spread is extremely variable and somewhat unpredictable. Over suitable habitat—agricultural land with hedges and other cover (and sometimes mountain valleys)—spread may average 2–4.5 kmyr^-1 but can sometimes be very much slower. This might be influenced by the type and extent of hedges and of permanent pasture. High ground and moorland usually prevent spread but there have been dramatic exceptions. In 1982 Bank voles occupied probably the whole of Co. Limerick; most of Co. Kerry, with the exception of substantial parts of the mountainous peninsulas in the southwest and contiguous interior; a large part of Co. Cork, though not the south-east and again excepting portions of the mountainous south-west, together with a substantial strip of east Co. Tipperary, and the south-east quarter of Co. Clare.     

An ecological basis for the conservation management of Polygonatum verticillatum (L.) All. (Convallariaceae)

Summary

Populations of Polygonatum verticillatum were studied in Scotland and south-west Scandinavia. Soil fertility and light appear to be the most important factors determining vegetative vigour and reproductive potential affecting rhizome size and flower production. Differences between the two geographic areas and between different habitats are discussed in the context of the rarity of P. verticillatum in Scotland and the need for informed conservation.     

A ground water nitrogen budget for a headwater swamp in an area of permanent ground water discharge

Ground water inputs and outputs of N were studied for a small ground water discharge swamp situated in a headwater drainage basin in southern Ontario, Canada. Darcy's equation with data for piezometers was used to measure inputs of shallow local ground water at the swamp margin and deep regional ground water beneath the swamp. Ground water flux was also quantified by measuring ground water discharge to the outlet stream draining the swamp in combination with a chemical mixing model to separate shallow and deep ground water components based on chloride differences. Estimates of shallow ground water flux determined by these two approaches agreed closely however, the piezometer data seriously underestimated the deep ground water input to the swamp. An average ground water input-output budget of total N (TN) total organic nitrogen (TON) ammonium (NH₄ ⁺-N) and nitrate (NO₃ ^--N) was estimated for stream base flow periods which occurred on an average of 328 days each year during 1986–1990. Approximately 90% of the annual NO₃ ^--N input was contributed by shallow ground water at the swamp margin. Deep ground water represented about 65% of the total ground water input and a similar proportion of TON and NH₄ ⁺-N inputs. Annual ground water NO₃ ^--N inputs and outputs were similar whereas NH₄ ⁺-N retention was 4 kg ha^-1 representing about 68% of annual ground water input. Annual TON inputs in ground water exceeded outputs by 7.7 kg ha (27%). The capacity of the swamp to regulate ground water N fluxes was influenced by the N chemistry of ground water inputs and the hydrologic pathways of transport within the swamp.     

The Effect of Increased N Deposition on Nitrous oxide, Methane and Carbon dioxide Fluxes from Unmanaged Forest and Grassland Communities in Michigan

Atmospheric nitrogen deposition is anticipated to increase over the next decades with possible implications for future forest-atmosphere interactions. Increased soil N₂O emissions, depressed CH₄ uptake and depressed soil respiration CO₂ loss is considered a likely response to increased N deposition. This study examined fluxes of N₂O, CH₄ and CO₂ over two growing seasons from soils in unmanaged forest and grassland communities on abandoned agricultural areas in Michigan. All sites were subject to simulated increased N-deposition in the range of 1–3 g N m⁻² annually. Nitrous oxide fluxes and soil N concentrations in coniferous and grassland sites were on the whole unaffected by the increased N-inputs. It is noteworthy though that N₂O emissions increased three-fold in the coniferous sites in the first growing season in response to the low N treatment, although the response was barely significant (p<0.06). In deciduous forests, we observed increased levels of soil mineral N during the second year of N fertilization, however N₂O fluxes did not increase. Rates of methane oxidation were similar in all sites with no affect of field N application. Likewise, we did not observe any changes in soil CO₂ efflux in response to N additions. The combination of tillage history and vegetation type was important for the trace gas fluxes, i.e. soil CO₂ efflux was greater in successional grassland sites compared with the forested sites and CH₄ uptake was reduced in post-tillage coniferous- and successional sites compared with the old-growth deciduous site. Our results indicate that short-term increased N availability influenced individual processes linked to trace gas turnover in the soil independently from the ecosystem N status. However, changes in whole system fluxes were not evident and were very likely mediated by competitive N uptake processes.     

Status of the Hen Harrier Circus cyaneus in the UK and Isle of Man in 2016

Capsule: The fifth UK and the Isle of Man survey of Hen Harrier in 2016 showed varying trends by country and region.

Aim: To estimate the size of the breeding Hen Harrier population (with associated 95% confidence intervals) in the UK and Isle of Man, constituent countries and Scottish regions, in 2016 and calculate population change over the five surveys to date.

Methods: Complete surveys were made of all 10-km squares likely to be occupied by breeding Hen Harriers in England, Wales, Northern Ireland and the Isle of Man, using standard methods developed for previous national surveys. In Scotland, self-selected 10-km squares were surveyed by volunteers and a stratified random selection of the remaining 10-km squares within the known breeding range was surveyed.

Results: The UK and Isle of Man Hen Harrier population was estimated at 575 territorial pairs (95% confidence limits, 477–694), a non-significant decline of 13% since 2010 but a significant decline of 24% since 2004. Scotland held the majority (80%) of the population with 460 (359–573) territorial pairs. Elsewhere, 46 territorial pairs were recorded in Northern Ireland, 35 in Wales, 30 in the Isle of Man and four in England. Significant decreases were recorded in the number of pairs in Scotland using grouse moor (?57%) and young forest (?54%).

Conclusion: The combined breeding population of Hen Harriers in the UK and Isle of Man has shown a non-significant decline between 2010 and 2016. There were notable decreases in England, Northern Ireland and Wales since 2010.