Upland Lakes Research Articles

Recovery of UK lakes from acidification: An assessment using combined palaeoecological and contemporary diatom assemblage data

We assess the recovery of UK lakes from acidification using the combined data from sediment cores and sediment traps to track changes in diatom assemblages in 11 UK upland lakes from pre-acidification times (prior to ca. 1850 AD) to the present (2008 AD). We projected the data into a Principal Component Analysis (PCA) of diatom assemblage data from 121 low-alkalinity lakes in the UK to show how the floristic composition of the core and trap diatom assemblages for each site has changed through time. The results show that the degree of recovery from acidification varies amongst sites but in all cases its extent is limited when compared with the pre-acidification reference. In most cases the recovery, although usually slight, is characterised by a decline in acid tolerant taxa and a return towards taxa that occurred previously at each respective site. In a few cases, however, the floristic composition of recent samples is different from those that occurred during and before the acidification phase. The reasons for this are not yet clear but it is possible that nutrient enrichment from atmospheric N deposition and/or climate change is beginning to play a role in driving water quality as acidity decreases. More generally the results show that annually recovered samples from sediment traps can be successfully combined with sediment core data to provide a continuous record of environmental change in lake systems, and that diatoms collected in sediment traps can be used to provide a very powerful lake monitoring tool.

The impacts of prescribed moorland burning on water colour and dissolved organic carbon: A critical synthesis

Discolouration of natural surface waters due to the humic component of dissolved organic carbon (DOC) is a costly problem for water supply companies. This paper reviews what is known about the impacts of prescribed moorland vegetation burning on water colour. Relevant research has taken place at three scales: laboratory experiments on peat cores, plot scale sampling of soil waters and catchment scale sampling of stream waters. While laboratory studies suggest burning increases colour production, the evidence from catchment and plot studies is contradictory. Plot studies suggest colour production may decrease or remain unchanged following burning although there is evidence for some transient changes. Catchment studies suggest prescribed moorland burning causes stream water colour to increase, although in most cases the evidence is not clear cut since most studies could not clearly disentangle the effects of burning from those of vegetation cover. The differences in findings between plot and catchment studies may be explained by: i) the short-term nature of some studies which do not measure long-term response and recovery times to burning; ii) the lack of colour measurements from shallow soil depths which contribute more to streamflow than soil water from deeper in the peat; and iii) the possibility of hydrological interactions occurring between different experimental plots at some sites. Additionally, the increase in recent patch burning in some catchments that has been statistically attributed by some authors to increases in stream water colour cannot be reconciled with theoretical calculations. When dilution with waters derived from other parts of the catchment are taken into account, large values of colour have to be theoretically derived from those recently burnt areas that occupy a small proportion of the catchment area in order to balance the change in stream water colour observed in recent years. Therefore, much further process-based work is required to properly investigate whether prescribed vegetation burning is a direct driver of enhanced colour and DOC in upland streams, rivers and lakes.

An assessment of the mechanisms for the transfer of lead and mercury from atmospherically contaminated organic soils to lake sediments with particular reference to Scotland, UK

While the sediment records of upland lakes are known to be valuable natural archives of depositional changes, recent studies in the UK have shown that full basin records of trace metals are not showing the decline expected as a result of the massive reduction in emissions since the 1970s. As trends in metal deposition across Europe are known to be declining, this ‘additional’ trace metal input to upland lakes can only be the result of mobilisation from catchment storage. We undertook a multiple sediment core, multi-pollutant study at nine lakes across Scotland to test hypotheses that this additional input was a result of (i) a simple time-lag; (ii) catchment soil erosion; (iii) leaching with dissolved organic carbon. We constructed decadally resolved full basin inventories for Pb, Hg and spheroidal carbonaceous particles (SCPs), a particulate component of fly-ash, at lakes with thin soils, lakes with eroded soils and lakes with non-eroded soils in their catchments to assess temporal trends. The use of both trace metals and SCPs allowed a comparison between erosive (SCPs and metals) and leaching (metals only) processes. Our results showed that the full basin inventories for Hg, Pb and SCPs for lakes with thin catchment soils had similar temporal trends to those of atmospheric emissions and deposition. For lakes with significantly eroded catchment soils, increasing trends in inventories continued to the most recent decades while those with non-eroded soils showed an intermediate pattern with some similarity to atmospheric deposition patterns, but with a reduced recent decline. We conclude that catchment soil erosion is the main transfer mechanism for trace metals at these sites and that although the leaching of metals bound to dissolved organic carbon (DOC) may play a role this appears to be less significant. The processes that lead to soil erosion and leaching of DOC from the catchment are exacerbated by increased winter rainfall, prolonged summer drought and increased frequency of high intensity rain events. Hence, predicted climatic changes will increase pollutant transfer from catchment to surface waters. The catchment storage of deposited pollutants is a massive potential reservoir that could keep fluxes of contaminants to surface waters elevated for many decades to come. This would counteract the benefits of reductions in deposition resulting from policy implementations over recent decades and may elevate exposure of aquatic biota to these contaminants.

Atmospheric pollution histories of three Cumbrian surface waters

1. The CHemistry of the Uplands Model (CHUM), driven by measured and estimated atmospheric deposition, was used to simulate the chemical compositions of three upland Lake District surface waters, Devoke Water (DW), Levers Water (LW) and Mosedale Beck (MB) over several hundred years. 2. “Natural acidification” combined with human activities, notably forest clearance, was assumed to have brought about chemically stable acid moorlands by the period 1000–1500 A.D. Deposition of sulphur, nitrogen, chlorine and heavy metals, released into the atmosphere by coal-burning and industrial processes, then took place, gradually increasing to maximum levels in the late 20th century. 3. Surface water concentrations of chloride are consistent with depositional inputs, whereas the transfer of atmospherically deposited sulphur to the surface waters is delayed by temporary retention processes within the catchment. Over the last 40 years, concentrations of pollutant (non-marine) sulphate in the surface waters declined to one-third of their maximum levels. Atmospherically deposited pollutant N continues to accumulate in catchment soils, although a significant fraction appears in surface waters as nitrate. Annual average surface water bicarbonate concentrations were 20 - 60 µmol L-1 in the pristine past, fell nearly to zero in all three waters when acidification was most intense, but now are increasing. 4. Combined data from several Lake District upland waters suggest substantial recent increases in concentrations of dissolved organic carbon (DOC). If this can be attributed to acidification reversal, a corresponding decline in DOC concentrations would have occurred as acidification intensified, and pristine surface waters would have been comparatively rich in DOC. 5. Major cationic elements enter the soil-water system in deposition (H+, Na, Mg, K, Ca), from organic matter decomposition (H+), or by chemical weathering (Mg, Al, Ca), and are much affected by sorption to soil organic matter (SOM). The surface soils of all three catchments are acid (current pH ~ 4.5) and so variations in surface water chemistry among sites reflect differences in mineral dissolution rates deeper in the soil-rock profile. The simulations indicate pH values of 6.9, 6.1 and 6.4 for DW, LW and MB respectively in the period up to 1800, followed by declines to minima of c. 6.0, 4.7 and 5.0 in around 1980, then acidification reversal in agreement with observations. 6. The transfer of atmospherically deposited heavy metals to surface waters depends upon their sorption by SOM. Nickel, zinc and cadmium adsorb relatively weakly and therefore are quite readily leached, and sensitive to changes in acidification status. The higher affinities of organic matter to Cu and Pb promote retention and these two metals are continuing to accumulate in soil, despite major declines in deposition over the past several decades. 7. The WHAM-FTOX model was used to estimate the maximum number of Ephemeroptera, Plecoptera and Trichoptera species in MB through time, as influenced by chemical variability. The maximum number is estimated to have fallen from 14-15 under pristine conditions to 9-10 when acidification was greatest and a modest recovery to 10-11 species since then.

Holocene sediment dynamics in an upland temperate lake catchment: climatic and land-use impacts in the English Lake District

Accelerated erosion and transport of fine sediment from upland temperate catchments can reflect increased erosivity and/or erodibility, due in turn to climatic and/or human forcing. Identification of sediment fluxes and sources over Holocene timescales can both enable understanding of the relative impacts of these forcings and provide perspective on recent sediment fluxes. Here we present a ~ 5500 yr record of sediment fluxes and sources from Lake Bassenthwaite in the English Lake District, utilizing magnetic measurements and fuzzy clustering, coupled with independent pollen and archaeological records, to identify the timing and impact of catchment disturbance. This record shows that recent sediment flux increases (ie, within the last 150 years) are unprecedented in scale throughout the mid—late Holocene and appear to be in response to specific human changes occurring within the catchment. Earlier episodes of human activity, from the mid Holocene onwards, show no link with increased lake sediment fluxes, indicating either limited catchment impact and/or `buffering' through within-catchment sediment storage. Increasingly intensive land use and reduction of sediment storage through revetment construction on a key inflow, Newlands Beck, have resulted in 3 × increases in lake sediment flux. These data may be significant for other upland temperate areas, as increasing land-use pressures and reduced sediment storage capacity may not only increase contemporary sediment flux, but increase sensitivity to predicted increases in rainfall and storminess as a result of global climate change.

Spatial and temporal distribution of the cyanotoxin microcystin-LR in the Lake Ontario ecosystem: Coastal embayments, rivers, nearshore and offshore, and upland lakes

Cyanotoxins, a group of hepatotoxins and neurotoxins produced by cyanobacteria, pose a health risk to those who use surface waters as sources for drinking water and for recreation. Little is known about the spatial and seasonal occurrence of cyanotoxins in Lake Ontario and other lakes and ponds within its watershed. Within the embayments, ponds, rivers, creeks, shoreside, and nearshore and offshore sites of Lake Ontario, microcystin-LR concentrations were low in May, increased through the summer, and reached a peak in September before decreasing in October. Considerable variability in microcystin-LR concentrations existed between and within habitat types within the Lake Ontario ecosystem. In general, the average microcystin-LR concentration was two orders of magnitude lower in embayment (mean = 0.084 μg/L), river (mean = 0.020 μg/L), and shoreside (mean = 0.052 μg/L) sites compared to upland lakes and ponds (mean = 1.136 μg/L). Concentrations in the nearshore sites (30-m depth) and offshore sites (100-m depth) were another order of magnitude lower (mean = 0.006 μg/L) than in the creek/river, bay/pond, and shoreside habitats. Only 0.3% (2 of 581) of the samples taken in Lake Ontario coastal waters exceeded the World Health Organization (WHO) Drinking Water Guideline of 1 μg microcystin/L for humans. In contrast, 20.4% (20 of 98) of the samples taken at upland lakes and ponds within the watershed of Lake Ontario exceeded WHO Guidelines. No significant relationship between nitrate and microcystin-LR concentrations was observed in Lake Ontario even though a significant positive relationship existed between phosphorus and phycocyanin and microcystin-LR concentrations. At an upland lake site (Conesus Lake) in the Ontario watershed, the development of a littoral Microcystis population was not observed despite high nutrient loading (P and N) into the nearshore zone, well-developed nearshore populations of filamentous Spirogyra and Zygnema, the occurrence of Dreissena spp., and the known occurrence of Microcystis and microcystin production in the pelagic waters of Conesus Lake.

Proglacial sediment trapping in recently formed Silt Lake, upper Lillooet Valley, Coast Mountains, British Columbia

AbstractThe sedimentology of proglacial Silt Lake was assessed by lake sediment coring and monitoring of lacustrine processes during a late‐summer period of high glacier melt to characterize sediment delivery from the heavily glacierized catchment and investigate the sediment trapping dynamics of this upland lake. A complete varve chronology was established for a distal basin of the lake which was exposed by Lillooet Glacier retreat between 1947 and 1962. The varve record showed decreasing sedimentation rates in the basin while the glacier retreated, and as the lake became free of ice contact in the early 1970s. Although recession has continued over recent decades, and glacier proximity to the lake has, therefore, continued decreasing, lacustrine sedimentation rates are now accelerating due to changing basin morphometry caused by delta progradation. Over shorter time scales, lake sedimentation patterns respond to changing runoff conditions, including late‐summer glacier melt intensity, intra‐annual flooding events, diumal runoff fluctuations, and within‐lake turbidity currents. Turbidity currents included quasi‐regular flows during high diurnal discharges and an episodic flushing of temporarily stored sediment from the sandur or delta at a time of low stage. Suspended sediment yield to Silt Lake is estimated to exceed 103 Mg km−2 a−1, a magnitude that surpasses previous local and regional yield estimates for the glacierized headwaters of the Lillooet River valley. Since Silt Lake currently traps a significant prooportion of that upland sediment supply, and the trapping efficiency of the basin has been variable at decadal time scales, the formation and continued development of Lilt Lake has likely had a significant influence on downstream sediment delivery. Lacustrine sediment‐based proxies of long‐term hydroclimatic variability being developed in glacially distal settings should include provisions for dynamic sediment trapping effects in upstream water bodies that often form in the active proglacial environment. Copyright © 2008 John Wiley & Sons, Ltd.

Spiggin levels are reduced in male sticklebacks infected with Schistocephalus solidus

Using an enzyme‐linked immunosorbent assay (ELISA) based technique, Schistocephalus solidus infection was shown to considerably reduce levels of spiggin in the kidney of male three‐spined sticklebacks Gasterosteus aculeatus from an oligotrophic upland lake. These results suggested a graduated effect of the infection on the reproductive physiology of male three‐spined sticklebacks.

Two-layer shallow water computation of mud flow intrusions into quiescent water

The present computational study addresses two-layer shallow flows in which the superposed layers differ in velocity, density and rheology. The geomorphological phenomena motivating this model are confluence problems in which mud and debris surges slump into upland lakes and rivers. Specifically, the flows of interest are assumed to be sharply stratified, with a clear water layer flowing over a moving layer of mud modelled as a Herschel–Bulkley fluid.A finite volume computational scheme suitable for the simulation of such flows is presented and applied to various validation cases. The scheme extends to two-layer flows the robust method of Harten, Lax and Van Leer. Special care is devoted to the following numerical issues: the treatment of pressure along interfaces, the ”contact points“ at which the thickness of either layer can vanish, and the finite yield stress characterizing the mud rheology. Results are presented for the intrusion of mud surges into shallow quiescent water.

Spatial variation in concentrations of dissolved nitrogen species in an upland blanket peat catchment

The concentration of nitrogen (N), particularly as nitrate (NO3-N), in upland streams, lakes and rivers is frequently used as a diagnostic of the vulnerability of upland ecosystems to increased atmospheric nitrogen deposition and N saturation. The N content of running waters, however, is generally assessed on the basis of sampling at a limited number of points in space and time within the catchment under investigation. The current study was conducted at Trout Beck, an 11.5 km2 blanket peat-dominated catchment in the North Pennine uplands of the UK. Results from sampling at 33 sites within this catchment demonstrated that the concentrations of all dissolved N species were highly variable, even over short distances. Statistical relationships between the concentrations of NO3-N and dissolved organic nitrogen (DON) and percentage catchment cover of Calluna/Eriophorum and Eriophorum vegetation were found. However, it was also noted that in catchments containing limestone outcrops, NO3-N concentration was much higher than in catchments where runoff was sourced directly from the blanket peat surface. It is possible that NH4-N and DON leached from the blanket peat are mineralised and nitrified, providing a source for the NO3-N found in the river channels. Overall, the current study suggests that interpretations of N-saturation based on river water chemistry measurements at a single point must be treated cautiously, and that the influence of catchment-scale physical factors, such as vegetation and geology cover on the concentration of dissolved N species in upland river waters should not be ignored.

Vegetation communities of British lakes: a revised classification scheme for conservation

AbstractA revised classification scheme is described for standing waters in Britain, based on the TWINSPAN analysis of a dataset of aquatic plant records from 3447 lakes in England, Wales and Scotland, which is held by the Joint Nature Conservation Committee.Separate ecological descriptions of 11 distinct lake groups (A–J) are presented with summary environmental data, macrophyte constancy tables and maps showing their distribution. These lake groups include small dystrophic waters dominated bySphagnumspp.; large, acid, upland lakes supporting a diversity of plant species, includingJuncus bulbosus,Littorella uniflora,Lobelia dortmannaandMyriophyllum alterniflorum; low‐altitude, above‐neutral lakes with a high diversity of plant species, characterized by the presence ofPotamogetonspp.,Charaspp. or water‐lilies and other floating‐leaved vegetation; and coastal, brackish lakes, with macroalgae.The Plant Lake Ecotype Index (PLEX) is presented as an indicator of changing lake environments. PLEX scores reflecting the new classification scheme have been developed for individual plant species and lakes. Applications of the index are demonstrated.There is discussion of possible applications of the data collected and the resultant classification, in the context of the Habitats Directive, the Water Framework Directive and other conservation requirements.© Crown copyright 2006. Reproduced with the permission of Her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd.

Peat erosion and atmospheric deposition impacts on an oligotrophic lake in eastern Ireland

The Holocene diatom and pollen records from Kelly’s Lough have been analysed to determine the timing and extent of the acidification in this upland lake. The pollen data during the early Holocene reflect the typical vegetation changes that occur in sediments throughout Ireland during this period. The diatom record begins by being dominated by circumneutral and acidophilous benthic forms. Later tychoplanktonic Aulacoseira species begin to expand and dominate indicating increased water transparency following the stabilization of catchment soils. Peatland development in the catchment is evident from approximately 6,450 cal year BP. The main change in the diatom assemblages at this time is the decline of Aulacoseira species and expansion of periphytic species. At around 1,450 cal year BP, loss-on-ignition (LOI) values, Calluna pollen and microscopic charcoal all increase suggesting the initiation of a major phase of peat erosion and an increased inwash of organic matter to the lake. Lake acidity changed significantly although the initial acidification is very subtle as indicated by the diatom-inferred pH record. Changes in the diatom assemblages might be largely the result of increasing erosion and inwash of organic matter from the catchment to the lake leading to reduced water transparency and more acidic conditions. The diatom flora remains relatively stable until the mid-twentieth century when more acidibiontic species increase. These diatom changes result in the reconstructed pH curve showing a moderate recent acidification from pH 5.7 to 5.1. About half of the total change in pH took place by around the late 1960s. The lowest diatom-inferred pH value occurs in the late 1970s, and parallels the peak in SO2 emissions in Ireland. Acidic conditions seem to have prevailed in Kelly’s Lough throughout its entire history and alkalinity has been low or absent for much of the time. However, soil acidification and inwash of organic acids from peatlands are not a sufficiently effective mechanism to explain the low pH levels found today in Kelly’s Lough. The effect of acid deposition on the waters of Kelly’s Lough is clear and it has probably caused these already naturally acid waters to acidify further.

Use of created wetlands to improve water quality in the Midwest—Lake Bloomington case study

Agricultural watersheds of the Midwest typically export nitrogen (N) and phosphorus (P) to surface waters causing contamination of drinking water reservoirs and, ultimately, hypoxia in the Gulf of Mexico. Two agricultural runoff wetlands, W1 (area 0.16 ha, volume 660 m 3) and W2 (area 0.4 ha, volume 1780 m 3), intercepting surface and tile drainage in the Lake Bloomington, Illinois, watershed were constructed in 1996 on forest soils (alfisols) between upland cropland and Lake Bloomington. They were created to determine whether wetlands could reduce agricultural nonpoint source pollution before it entered the Lake Bloomington drinking water reservoir. Water (precipitation, tile inflow, surface inflow, outflow, seepage and evaporation) and nutrient (N, P and carbon [C]) budgets were determined from 1 April 1998 to 30 December 1999 for each wetland. Combined, the wetlands received 746 kg NO 3-N as tile loading, 104 kg as surface loading and exported 545 kg of NO 3-N as outflow and seepage. Mass NO 3-N retention was 36%. Following wetland treatment, overall volume-weighted NO 3 −-N concentrations were reduced by 42% (W1) and 31% (W2). Combined P mass retention was 53%, and combined total organic carbon (TOC) mass retention was 9%. Wetlands were constructed in a sloping drainage (5%) where surface runoff was a major component of flow. Nutrient dynamics of P and C were affected by site slopes. Calculations made by extrapolating these results indicate that a wetland area of 450 ha would be required in the Lake Bloomington watershed to reduce N loading by 46%, at a construction cost ranging from 3 to 3.5 million dollars. Results support the growing evidence that agricultural runoff wetlands can effectively reduce NPS pollution loading in the Mississippi River Basin.

Nesting, courtship and kidney hypertrophy inSchistocephalus‐infected male three‐spined stickleback from an upland lake

The effect ofSchistocephalus solidusinfection on reproductive development and behaviour of male three‐spined sticklebackGasterosteus aculeatusfrom an upland lake (Llyn Frongoch, Wales, U.K.) was investigated. Uninfected and infected males were collected on two separate occasions during the 2005 breeding season and encouraged to build nests under favourable laboratory conditions. Male nuptial colouration, courtship levels and nesting activity were recorded daily over two separate 21 day studies. Completed nests were removed, encouraging males to build multiple nests. On termination of each study, males were dissected and the kidney and anyS. solidusplerocercoids were removed and weighed. In contrast to uninfected males, which readily built multiple nests, no infected males completed a nest during either study. Infected males also exhibited significantly reduced courtship levels, nesting activity, nuptial colouration, kidney development and body condition, compared with uninfected fish. Among infected three‐spined stickleback, courtship and nesting behaviours tended to be more severely impacted in fish harbouring heavier plerocercoid burdens. In contrast to other populations, male three‐spined stickleback from Llyn Frongoch appear to be unable to overcome the negative impacts of infections on reproductive development and behaviour when provided with short‐term favourable conditions. Discrepancies between populations might have been related to the trophic status at the site of capture, emphasizing the importance of studying the biological effects of infections under different environmental conditions.

Interglacial and Holocene temperature reconstructions based on midge remains in sediments of two lakes from Baffin Island, Nunavut, Arctic Canada

Midge remains (Insecta: Diptera: Chironomidae and Chaoboridae) from two upland lake basins on the Cumberland Peninsula of Baffin Island were analyzed and the results used in a transfer function to reconstruct paleotemperatures. This upland region remained ice-free throughout the last glacial cycle and the two lake basins retain sediments deposited during the previous interglacial period as well as during the Holocene period, but they did not accumulate sediment during most of the glacial period. Midge remains are abundant and well preserved at both sites. Midge-inferred summer surface water temperatures and mean July air temperatures were estimated using an inference model built on modern samples spanning a geographic range extending from Devon Island, Canada to Maine, USA. Data from twenty-nine new surface samples from Baffin Island were added to an existing inference model. The new weighted averaging (WA) model for summer surface water temperature yields r 2 jack = 0.88 and RMSEP = 2.22 °C for summer water temperatures, and r 2 jack = 0.88 and RMSEP = 1.53 °C for mean July air temperatures. Reconstructions at both sites indicate that summer temperatures during the last interglacial were higher than at any time in the Holocene, and 5 to 10 °C higher than present. Peak Holocene temperatures occurred in the first half of the period, and have decreased since about the mid-Holocene.

Lake Sediments Record Sensitivity of Two Hydrologically Closed Upland Lakes in Mexico to Human Impact

We provide evidence of rapid, recent environmental change in two lakes in the highlands of central Mexico. Multiple sediment cores were obtained from Lago de Zirahuén (Michoacán) and Laguna de Juanacatlán (Jalisco). Analysis of diatom assemblages, magnetic susceptibility, and metal concentrations was carried out, with the chronology provided by 210Pb dating, 14C dating, and tephrochronology. There is evidence of catchment disturbance during the colonial period in both basins, but the most striking feature at both sites is the rapid change in diatom assemblages during the last 20 y, indicating the onset of eutrophication. Limnological data from Lago de Zirahuén support this interpretation, although none are available from Laguna de Juanacatlán. Paleolimnology is a powerful tool in tracking recent change, particularly in the absence of regular limnological monitoring programs. These lakes appear to be highly sensitive to changes in catchment exploitation, which must be considered in future drainage basin management.

The Role of Northern Lakes in a Regional Energy Balance

Abstract There are many lakes of widely varying morphometry in northern latitudes. For this study region, in the central Mackenzie River valley of western Canada, lakes make up 37% of the landscape. The nonlake components of the landscape are divided into uplands (55%) and wetlands (8%). With such abundance, lakes are important features that can influence the regional climate. This paper examines the role of lakes in the regional surface energy and water balance and evaluates the links to the frequency–size distribution of lakes. The primary purpose is to examine how the surface energy balance may influence regional climate and weather. Lakes are characterized by both the magnitude and temporal behavior of their surface energy balances during the ice-free period. The impacts of combinations of various-size lakes and land–lake distributions on regional energy balances and evaporation cycles are presented. Net radiation is substantially greater over all water-dominated surfaces compared with uplands. The seasonal heat storage increases with lake size. Medium and large lakes are slow to warm in summer. Their large cumulative heat storage, near summer’s end, fuels large convective heat fluxes in fall and early winter. The evaporation season for upland, wetland, and small, medium, and large lakes lasts for 19, 21, 22, 24, and 30 weeks, respectively. The regional effects of combinations of surface types are derived. The region is initially treated as comprising uplands only. The influences of wetland, small, medium, and large lakes are added sequentially, to build up to the energy budget of the actual landscape. The addition of lakes increases the regional net radiation, the maximum regional subsurface heat storage, and evaporation substantially. Evaporation decreases slightly in the first half of the season but experiences a large enhancement in the second half. The sensible heat flux is reduced substantially in the first half of the season, but changes little in the second half. For energy budget modeling the representation of lake size is important. Net radiation is fairly independent of size. An equal area of medium and large lakes, compared with small lakes, yields substantially larger latent heat fluxes and lesser sensible heat fluxes. Lake size also creates large differences in regional flux magnitudes, especially in the spring and fall periods.

Influence of moderate phosphate addition on nitrogen retention in an acidic boreal lake

Inorganic phosphorus (P) fertilizer was added to a small, acidic lake in southernmost Norway to test the potential of this technique to increase the retention of total inorganic nitrogen (TIN) and thereby mitigate the effects of elevated leaching of atmospherically derived N. The experiment was conducted over 4 years (1 pretreatment year followed by 3 years with weekly P additions during the growing season). To avoid any undesirable eutrophication effects, the total P concentration was increased from 4–5 µg P·L–1 to a moderate level of 10–12 µg P·L–1. Compared with the pretreatment year, the P additions increased the average TIN retention in the experimental lake by nearly 70% (from 53 to 88 mmol·m–2·year–1) during three growing seasons. However, when considering that the reference lake experienced a 55% decrease in TIN retention during the same period, the increase might have been even larger. This underlines the role of P (both natural and anthropogenic) as an important regulator of N retention in upland lake districts that in large parts of southernmost Norway contribute significantly to the N loading on coastal marine areas.

The influence of thermokarst disturbance on the water quality of small upland lakes, Mackenzie Delta region, Northwest Territories, Canada

Chemical data are presented for water from 22 lakes in small upland catchments (< 20 ha) between Inuvik and Richards Island, Northwest Territories, Canada. Eleven of the basins appear pristine and 11 are affected by thermokarst slumping. The mean dissolved organic carbon (DOC) concentration of the pristine lakes (16.3 mg/l) is greater than the mean concentration of lakes disturbed by thermokarst slumping (10.5 mg/l). In pristine lakes, mean concentrations of Ca, Mg and SO4 are 9.6, 3.6 and 11.1 mg/l, but in lakes affected by thermokarst, mean concentrations are 72.6, 26.8 and 208.2 mg/l, respectively. Soluble materials released from degrading permafrost are transported to lakes by surface runoff, elevating concentrations in lake water. The percentage of total basin area influenced by thermokarst is positively associated with ionic concentrations in lake water and inversely related to DOC. Thermokarst occupying as little as 2% of catchment area may modify the chemistry of lake water, and water quality may remain affected for several decades after slump development has ceased. Aerial photographs indicate that 5 to 15% of all lakes and ponds in four 49 km2 areas between Inuvik and Richards Island are small (median size < 2 ha) with catchments affected by thermokarst. Copyright © 2005 John Wiley & Sons, Ltd.

Lake Sediments Record Sensitivity of Two Hydrologically Closed Upland Lakes in Mexico to Human Impact

Lake Sediments Record Sensitivity of Two Hydrologically Closed Upland Lakes in Mexico to Human Impact