Search

Very little is known about the impacts of Anthropocene environmental change on aquatic systems in the mountains of southern Africa. The Maloti-Drakensberg region forming the border between South Africa and Lesotho is not generally associated with natural, permanent lakes, but there are dammed wetland lakes with evidence that natural water bodies were present before lake levels were raised, including Mountain Lake in the Eastern Cape in South Africa. In order to address a regional lack of long-term monitoring data, here we present evidence from lake sediment records spanning over 50 years from Mountain Lake that industrial signals of contamination associated with distant coal fired power stations are transported across the region, including trace metals, mercury (reaching 95 ng·g−1) and spheroidal carbonaceous particles. In addition, high concentrations of the organochlorine pesticides DDT (ΣDDT = 166.3 ng·g−1) and methoxychlor (39.3 ng·g−1), most likely from catchment sources, are recorded in recent sediments. Finally, the diatom record indicates shifts in assemblages within the last 20 years indicative of possible nutrient enrichment, which is consistent with known intensification of agricultural and other human activity within the catchment, shown by increasing sediment enrichment of P, Mn, Fe, As and Co. Hence there are multiple lines of evidence for increasing environmental pressures on the ecosystems of Mountain Lake and its catchment over the period of the proposed Anthropocene. Further studies are required to assess the magnitude of threats to the unique but largely unstudied biodiversity associated with lakes in the region, including those in protected areas. [ABSTRACT FROM AUTHOR]

The relative roles of anthropogenic nitrogen (N) deposition and climate change in causing ecological change in remote Arctic ecosystems, especially lakes, have been the subject of debate over the last decade. Some palaeoecological studies have cited isotopic signals (δ.15N)) preserved in lake sediments as evidence linking N deposition with ecological change, but a key limitation has been the lack of co-located data on both deposition input fluxes and isotopic composition of deposited nitrate (NO-3 /. In Arctic lakes, including those in western Greenland, previous palaeolimnological studies have indicated a spatial variation in δ.15N) trends in lake sediments but data are lacking for deposition chemistry, input fluxes and stable isotope composition of NO-3 . In the present study, snowpack chemistry, NO-3 stable isotopes and net deposition fluxes for the largest ice-free region in Greenland were investigated to determine whether there are spatial gradients from the ice sheet margin to the coast linked to a gradient in precipitation. Late-season snowpack was sampled in March 2011 at eight locations within three lake catchments in each of three regions (ice sheet margin in the east, the central area near Kelly Ville and the coastal zone to the west). At the coast, snowpack accumulation averaged 181mm snow water equivalent (SWE) compared with 36mm SWE by the ice sheet. Coastal snowpack showed significantly greater concentrations of marine salts (Na+, Cl-, other major cations), ammonium (NH-4 ; regional means 1.4-2.7 μmol L-1), total and non-sea-salt sulfate (SO2-4 ; total 1.8-7.7, non-sea-salt 1.0-1.8 μmol L-1/ than the two inland regions. Nitrate (1.5- 2.4 μmol L-1/ showed significantly lower concentrations at the coast. Despite lower concentrations, higher precipitation at the coast results in greater net deposition for NO-3 as well as NHC 4 and non-sea-salt sulfate (nss-SO2-4 / relative to the inland regions (lowest at Kelly Ville 6, 4 and 3; highest at coast 9, 17 and 11 mol ha-1 a-1 of NO-3, NHC 4 and nss-SO2-4 respectively). The δ.15N) of snowpack NO-3 shows a significant decrease from inland regions (-5.7‰ at Kelly Ville) to the coast (-11.3 ‰). We attribute the spatial patterns of δ.15N) in western Greenland to post-depositional processing rather than differing sources because of (1) spatial relationships with precipitation and sublimation, (2) withincatchment isotopic differences between terrestrial snowpack and lake ice snowpack, and (3) similarities between fresh snow (rather than accumulated snowpack) at Kelly Ville and the coast. Hence the δ.15N) of coastal snowpack is most representative of snowfall in western Greenland, but after deposition the effects of photolysis, volatilization and sublimation lead to enrichment of the remaining snowpack with the greatest effect in inland areas of low precipitation and high sublimation losses. [ABSTRACT FROM AUTHOR]

Snowpack chemistry, nitrate stable isotopes and net deposition fluxes for the largest ice-free region in Greenland were investigated to determine whether there are spatial gradients from the ice sheet margin to the coast linked to a gradient in precipitation. Late-season snowpack was sampled in March 2011 at 8 locations within 3 lake catchments in each of 3 regions (ice sheet margin in the east, central area near Kelly Ville and the coastal zone to the west). At the coast, snowpack accumulation averaged 181 mm snow water equivalent (SWE), compared with 36 mm SWE by the ice sheet. Coastal snowpack showed significantly greater concentrations of marine salts (Na+, Cl-, other major cations), ammonium (regional means 1.4-2.7 μmol L-1), total and non-sea salt sulfate (total 1.8-7.7, non-sea salt 1.0-1.8 μmol L-1) than the two inland regions. Nitrate (1.5-2.4 μmol L-1) showed significantly lower concentrations at the coast. Despite lower concentrations, higher precipitation at the coast results in a strong deposition gradient for NO3- as well as NH4+ and non-sea salt sulfate (nss-SO42 -) increasing from the inland regions to the coast (lowest at Kelly Ville 6, 4 and 3; highest at coast 9, 17 and 11 mol ha-1 yr-1 of NO3-, NH4+ and nss-SO42 - respectively). The δ(15N) of snowpack NO3- shows a significant decrease from the ice sheet margin (-7.5 ‰) to the coast ( -11.3 ‰). We attribute the spatial gradient of δ(15N) in SW Greenland to post-deposition processing rather than differing sources because of (1) the climatic gradient from ice sheet margin to coast, (2) within-catchment isotopic differences between terrestrial snowpack and lake-ice snowpack, and (3) similarities between fresh snow (rather than accumulated snowpack) at Kelly Ville and the coast. Hence the δ(15N) of coastal snowpack is most representative of snowfall in SW Greenland, but after deposition the effects of photolysis, volatilization and sublimation lead to enrichment of the remaining snowpack with the greatest effect in inland areas of low precipitation and high sublimation losses. [ABSTRACT FROM AUTHOR]

Abstract: Upland waters are located upstream of the areas of direct human disturbance and intensive land use through industry, agriculture and urbanisation and are valued particularly as sources of potable water and as biodiverse freshwater habitats. Nonetheless, the impact of human activity can be detected even in some of the most remote lakes on the planet due to the effects of long-range transport of air pollutants and global climate change. In the UK, upland waters are threatened by a range of pressures including not only atmospheric deposition of acidic compounds, trace metals and organic pollutants, but also climate change, nutrient enrichment by deposited nitrogen and changing land-use or land management regimes. The threat from acid deposition has declined sharply since the 1980s but its legacy remains a major concern; recovery is taking place but even assuming a complete chemical and biological recovery to a pre-industrial baseline were possible, dynamic models suggest that this could take another 100 years. However, current climate change projections suggest that by then, UK upland waters will become much warmer, with lower summer streamflows, higher winter streamflows and a much reduced or even absent influence of snowfall and lake ice-cover. Hence there is no rationale for aspiring to the return of pre-industrial “reference” conditions because climate change is likely to shift the climatic baseline at an unprecedented rate. Meanwhile, expansion of forest planting, changing grazing regimes and management measures for peatland restoration, among other land-use pressure, will affect upland catchments in the UK with potentially major repercussions for aquatic ecosystems, both positive and negative. The challenge for scientists, policymakers and other stakeholders in the uplands is to determine not only the trajectory of change in upland waters, but also to define the ecological endpoints needed to provide the optimum range of ecosystem services for society. Integrated monitoring of the kind exemplified by the papers in this volume is a fundamental prerequisite in this regard. [Copyright &y& Elsevier]

Abstract: Previous analyses of deposition trends in the UK have used traditional linear methods, but recognised that neither emissions nor acid deposition had followed linear trends. Here we employ a non-linear technique, an additive model, to determine trends in both concentrations and bulk deposition loads (precipitation-weighted) at 12 Acid Deposition Monitoring Network (ADMN) sites most closely co-located with sites in the UK Acid Waters Monitoring Network (AWMN). Bulk deposition data were collected weekly or two-weekly over the 20 year period from 1988 to 2007 and all samples were analysed according to common protocols. Periods of significant increase or decrease over the period of monitoring were identified using the first derivative of the fitted trend, computed using finite differences. Results of the trend analysis show that: [1.] 11 out of 12 bulk deposition sites show significant increasing trends in pH. [2.] Concentrations of non-marine sulphate (xSO4 2−) show significant decreasing trends at ten out of 12 sites and appear to be the main driver of changes in bulk deposition pH since the late 1990s, though earlier trends in bulk deposition pH are so far unexplained. [3.] Trends in concentrations of nitrogen (N) species are mixed with many sites showing no significant trend. For NO3 − three sites show a general decline while four sites show a short period of significant increase in the early 1990s which in three cases reverses to a significant declining trend in the late 1990s. For NH4 + five sites show some periods of significant decline in concentration but these are only prolonged at three sites. [4.] Precipitation-corrected deposition loads show very similar trends to concentrations for xSO4 2− and N species, but for N species there are more sites with significant trends. [5.] For total Cl− concentrations, seven sites show declining trends but only four of these remain significant with precipitation weighting. Non-marine chloride (xCl−) concentrations decline significantly at nine sites, reducing to six sites with precipitation weighting. Hence reductions in xCl− are acting alongside xSO4 2− as drivers of declining acidity in bulk deposition. [6.] Small declining trends in precipitation measured in the bulk deposition collectors may reflect changes in sampling methodology as sampling frequency changed from weekly to 2-weekly during the ADMN monitoring period. These non-linear trends explain the lack of significant trends using linear methods on shorter data series in previous analyses and may help to explain non-linear patterns in chemical recovery in surface waters. [Copyright &y& Elsevier]

Abstract: Nitrate (NO3 −) is often observed in surface waters draining terrestrial ecosystems that remain strongly nitrogen (N) limited. It has been suggested that this occurs due to hydrological bypassing of soil or vegetation N retention, particularly during high flows. To test this hypothesis, artificial rain events were applied to 12 replicate soil blocks on a Welsh podzolic acid grassland hillslope, labelled with 15N-enriched NO3 − and a conservative bromide (Br−) tracer. On average, 31% of tracer-labelled water was recovered within 4h, mostly as mineral horizon lateral flow, indicating rapid vertical water transfer through the organic horizon via preferential flowpaths. However, on average only 6% of 15N-labelled NO3 − was recovered. Around 80% of added NO3 − was thus rapidly immobilised, probably by microbial communities present on the surfaces of preferential flowpaths. Transitory exceedance of microbial N-uptake capacity during periods of high water and N flux may therefore provide a mechanism for NO3 − leaching. [Copyright &y& Elsevier]

For the Western North America Mercury Synthesis, we compiled mercury records from 165 dated sediment cores from 138 natural lakes across western North America. Lake sediments are accepted as faithful recorders of historical mercury accumulation rates, and regional and sub-regional temporal and spatial trends were analyzed with descriptive and inferential statistics. Mercury accumulation rates in sediments have increased, on average, four times (4 ×) from 1850 to 2000 and continue to increase by approximately 0.2 μg/m 2 per year. Lakes with the greatest increases were influenced by the Flin Flon smelter, followed by lakes directly affected by mining and wastewater discharges. Of lakes not directly affected by point sources, there is a clear separation in mercury accumulation rates between lakes with no/little watershed development and lakes with extensive watershed development for agricultural and/or residential purposes. Lakes in the latter group exhibited a sharp increase in mercury accumulation rates with human settlement, stabilizing after 1950 at five times (5 ×) 1850 rates. Mercury accumulation rates in lakes with no/little watershed development were controlled primarily by relative watershed size prior to 1850, and since have exhibited modest increases (in absolute terms and compared to that described above) associated with (regional and global) industrialization. A sub-regional analysis highlighted that in the ecoregion Northwestern Forest Mountains, < 1% of mercury deposited to watersheds is delivered to lakes. Research is warranted to understand whether mountainous watersheds act as permanent sinks for mercury or if export of “legacy” mercury (deposited in years past) will delay recovery when/if emissions reductions are achieved. [ABSTRACT FROM AUTHOR]

Abstract: In this special issue we present papers based on data from the UK's Acid Waters Monitoring Network (UK AWMN) and other UK acid waters. The AWMN was set up in 1988. It was designed to monitor the chemical and biological response of acidified surface waters in the UK to the planned reduction in the emission of acidic sulphur and nitrogen gases as required by the UNECE Convention on Long Range Transboundary Air Pollution. Most papers in the volume are concerned with the changes that have taken place at the 22 AWMN sites during 20 years of monitoring from 1988 to 2008. They show that significant changes in deposition chemistry, in water chemistry and, to a lesser extent, in biology have taken place, consistent with a recovery from acidification. However, when compared with pre-acidification conditions inferred from lake sediment records, the extent of biological recovery so far is shown to be quite limited. The volume also contains papers on other aspects of surface water acidification in the UK. They include evidence for persistent highly acidic conditions of streams in the North York Moors, data from Scotland showing how afforestation is modifying recovery from acidification and the results of chemical speciation modelling in explaining the relationship between acidification and macroinvertebrate species richness at AWMN and other sites in the UK. The final papers are concerned with projections for the future and the extent to which acidified sites will continue to improve. They conclude that recovery will continue albeit slowly during this century but that other pressures principally from climate and land-use change are likely to alter the recovery pathways towards novel ecological endpoints potentially quite different from past baselines. [Copyright &y& Elsevier]