Lake Retention Research Articles

Estimated microplastic stress and potential affiliated toxic elements on phytoplankton in a floodplain-lake system.

Hazards associated with microplastics (MPs) and the pollutants they absorb in freshwater lake ecosystems have become a hot research topic in academia. In this study, in order to investigate potential affiliated MP hazards, lake MP samples were collected from a typical subtropical freshwater lake system in China (Poyang Lake) during the dry season (here, you should show the specific months) to explore their potential toxic element (PTE) response (i.e., exposure to Cu, Pb, and Zn) respective to the ecological environment and resident phytoplankton. Results show that average MP abundance in surface water can reach up to 1800 items m-3, which higher in the Nanjishan Wetland National Nature Reserve (NWNNR) (1175 items m-3). Polyester (i.e., purified terephthalic acid [PTA]) and polyethylene (PE) were the main polymer types found in surface water, fiber was the main MP shape, and most of the MP particle sizes are greater than 100 μm. Moreover, phytoplankton biomass was significantly higher in the NWNNR compared to Poyang Lake's retention basin and water channel. It indicated that MP pollutant status of Poyang Lake is mild; however, the ecological risks that MPs pose should not be ignored. The significant positive correlation between MPs and PTEs indicated that PTE absorption and desorption by MPs may cause potential ecological stress. Although we anticipate no direct link between ecotoxicity and phytoplankton, MPs may have indirect effects on phytoplankton through their regulatory effects on PTE levels in water.

Measurement of microplastic settling velocities and implications for residence times in thermally stratified lakes

AbstractMicroplastics residence times in lakes are currently poorly understood. In this work, settling experiments with pristine and biofilm‐colonized microplastic particles were combined with model calculations to evaluate settling velocities, particle distributions, and residence times in the epilimnion, metalimnion, and hypolimnion of a hypothetical stratified lake broadly based on Upper Lake Constance. Settling velocities of various biodegradable and nonbiodegradable polymers of various shapes, sizes, and biofilm colonization were measured in a settling column. The settling velocities ranged between ~ 0.30 and ~ 50 mm s−1. Particle sizes and polymer densities were identified as primary controls on settling rates. Microplastic particles that had been exposed to a lake environment for up to 30 weeks were colonized by a range of biofilms and associated extracellular polymeric substances; surprisingly, however, the settling velocity did not vary significantly between pristine and colonized microplastic particles. Simulated microplastic residence times in the model lake varied over a wide range of time scales (10−1 to 105 d) and depended mainly on the size of the particles and depth of the lake layer. Long residence times on the order of 105 d (for 1‐μm microplastic particles) imply that for small microplastic particles there is a high probability that they will be taken up at some stage by lake organisms. As the lake retention time (~ 4.5 years) is considerably shorter than the residence time of small microplastics, negligible quantities of these microplastic particles should be found in the lake sediment unless some other process increases their settling velocity.

Retention time of lakes in the Larsemann Hills oasis, East Antarctica

Abstract. This study provides first estimates of the water transport timescale for five lakes located in the Larsemann Hills oasis (69∘23′ S, 76∘20′ E) in East Antarctica. We estimated lake retention time (LRT) as a ratio of lake volume to the inflow and outflow terms of a lake water balance equation. The LRT was evaluated for lakes of epiglacial and landlocked types, and it was assumed that these lakes are monomictic, with water exchange occurring during the warm season only. We used hydrological observations collected in four seasonal field campaigns to evaluate the LRT. For the epiglacial lakes Progress and Nella/Scandrett, the LRT was estimated at 12–13 and 4–5 years, respectively. For the landlocked lakes Stepped, Sarah Tarn and Reid, our results show a great difference in the LRT calculated from the outflow and inflow terms of the water balance equation. The LRTs for these lakes vary depending on the methods and errors inherent to them. We relied on the estimations from the outflow terms, since they are based on hydrological measurements with better quality. Lake Stepped exchanged water within 1.5 years. Sarah Tarn and Lake Reid are endorheic ponds, with water loss mainly through evaporation. Their LRTs were estimated as 21–22 and 8–9 years, respectively. To improve the LRT estimates, special hydrological observations are needed to monitor the lakes and streams during the warm season with a uniform observational programme.

Quantifying the dependence of cyanobacterial growth to nutrient for the eutrophication management of temperate-subtropical shallow lakes

The increasing global occurrence of cyanobacterial blooms, attributed primarily to human-induced nutrient enrichment, significantly degrades freshwater ecosystems and poses serious risks to human health. The current study examined environmental variables and cyanobacterial biovolume (BCyano) of 28 shallow lakes in the eastern China plains during the spring and summer of 2018. We used a 95% quantile regression model to explore season-specific response of BCyano to total nitrogen (TN), or total phosphorus (TP), and robust linear relationships were observed between log(BCyano+0.001) and log(TN), or log(TP) in both spring and summer periods. Based on these regressions, regional-scale and season-specific TN and TP thresholds are proposed for these lakes to ensure the safety for recreational waters and drinking water source. However, actual BCyano for a given concentration of TN (or TP) for many observations were considerably lower than the results of the 95% regression model predict, indicating that other factors significantly modulated nutrient limitation of BCyano. Generalized additive model and quantile regression model were used together to explore potentially significant modulating factors, of which lake retention time, macrophytes cover and N: P ratio were identified as most important. Thus, it is necessary to develop type-specific nutrient thresholds with the consideration of these significant modulating factors. Furthermore, nutrient-BCyano relationships of our studied lakes with lake retention time>100 days and no macrophyte were further explored and nutrient thresholds of this lake type were proposed. Nutrient thresholds proposed in this study may play an essential role in achieving a cost-effective eutrophication management for shallow lakes both in the eastern China plains and elsewhere with similar climatic background. On a broader scale, the approaches and findings of this study may provide valuable reference to formulate reasonable nutrient reduction targets for other ecoregions with different climatic conditions.

Quantitative comparison of river inflows to a rapidly expanding lake in central Tibetan Plateau

AbstractThe recent rapid expansion of inland lakes on the Tibetan Plateau (TP) are a good indicator of the consequences of climate change. Quantifying the hydrological cycle of the lake basin is fundamentally important to understand the causes of lake growth. However, the hydrological processes of the TP interior are very complex and difficult to investigate because of the lack of observations. This is especially true for estimating the lake changes when run‐off inflows are affected by small lakes located in the flow routes within drainage areas. We used an integrated hydrological model, in combination with glacier melt and lake retention models, to analyse the run‐off inflows to Lake Siling Co, the largest endorheic lake in Tibet. It includes four subdrainage basins: Zhajiazangbu, Zhagenzangbu, Alizangbu, and Boquzangbu. Lake Siling Co was characterized by considerable increases during warm season from 1981 to 2012, due to the increased run‐off from Zhajiazangbu accounting for about 51–62% of the total run‐off inflows. Moreover, the dramatic increases exhibited during cold seasons were related to the increased retention water released from the small lakes within Zhagenzangbu and Alizangbu. Of the studied subdrainage basins, Boquzangbu contributed the least during both warm and cold seasons. On average, the annual amount of evaporation from lakes within the drainage area was about 2 times greater than that of glacier melt run‐off. Our results suggest that the retention effects of lakes on river inflows should receive more attention, because understanding these effects is potentially crucial to improved understanding of lake variations in the TP.

Erratum to: Suspended solids and total phosphorus loads and their spatial differences in a lake-rich river basin as determined by automatic monitoring network

Turbidity datasets recorded by sensors during 2009-2012 were collected in five observation sites in the 2046-km2 Karjaanjoki River Basin in southern Finland. From these and water sample-based data, total phosphorus (TP) and total suspended solids (TSS) fluxes were determined. Based on calculations made with combined sensor- and water sample-based dataset, the annual loading from the Karjaanjoki Basin in 2009-2012 varied between 11,300 and 23,900[corrected] kg of TP and 3300-8400 t of TSS. As compared with two other river basins discharging into the Baltic Sea in southern Finland, the TP loading from Karjaanjoki was low because the summed retention in the two major lakes Hiidenvesi and Lohjanjarvi was high: 48 and 49% of the TSS and TP loadings generated in their upstream catchments, respectively. Depending on how water sampling took place in relation to peak flow events, differences of annual fluxes as determined by "water samples only" vs. "sensors and water samples" data varied between -22 and 26 for TP and -31 and 39% for TSS. This study proved automatic monitoring being useful when spatial differences and lake retention of riverine fluxes are explored. Moreover, the loading estimates calculated on the base of well-functioning and well-maintained automatic monitoring system, supported with water sampling during periods when devices were off, are undoubtedly more accurate than those based on manual grab water sampling only. The findings of this study were in line with, and well contribute to, earlier Finnish and international research on automatic water quality monitoring.

Suspended solids and total phosphorus loads and their spatial differences in a lake-rich river basin as determined by automatic monitoring network.

Turbidity datasets recorded by sensors during 2009-2012 were collected in five observation sites in the 2046-km2 Karjaanjoki River Basin in southern Finland. From these and water sample-based data, total phosphorus (TP) and total suspended solids (TSS) fluxes were determined. Based on calculations made with combined sensor- and water sample-based dataset, the annual loading from the Karjaanjoki Basin in 2009-2012 varied between 11,300 and 23,900[corrected] kg of TP and 3300-8400 t of TSS. As compared with two other river basins discharging into the Baltic Sea in southern Finland, the TP loading from Karjaanjoki was low because the summed retention in the two major lakes Hiidenvesi and Lohjanjärvi was high: 48 and 49% of the TSS and TP loadings generated in their upstream catchments, respectively. Depending on how water sampling took place in relation to peak flow events, differences of annual fluxes as determined by "water samples only" vs. "sensors and water samples" data varied between -22 and 26 for TP and -31 and 39% for TSS. This study proved automatic monitoring being useful when spatial differences and lake retention of riverine fluxes are explored. Moreover, the loading estimates calculated on the base of well-functioning and well-maintained automatic monitoring system, supported with water sampling during periods when devices were off, are undoubtedly more accurate than those based on manual grab water sampling only. The findings of this study were in line with, and well contribute to, earlier Finnish and international research on automatic water quality monitoring.

Lake retention of manufactured nanoparticles

For twenty-five world lakes and three engineered nanoparticles (ENP), lake retention was calculated using a uniformly mixed lake mass balance model. This follows similar approaches traditionally used in water quality management. Lakes were selected such that lake residence times, depths and areal hydraulic loadings covered the widest possible range among existing lakes. Sedimentation accounted for natural colloid as well as suspended solid settling regimes. An ENP-specific mixed sedimentation regime is proposed. This regime combines ENP sedimentation through slow settling with natural colloids from the water column, with faster settling with suspended solids from a selected part of the water column. Although sedimentation data and hydrodynamic concepts as such were not new, their first time combination for application to ENPs shows in which cases lake retention is important for these particles. In combination with ENP emission data, lake retention translates directly into potential risks of ENPs for lake benthic communities.

Saving the Baltic Sea, the inland waters of its drainage basin, or both? spatial perspectives on reducing P-loads in eastern Sweden.

Nutrient loads from inland sources to the Baltic Sea and adjacent inland waters need to be reduced in order to prevent eutrophication and meet requirements of the European Water Framework Directive (WFD) and the Baltic Sea Action Plan (BSAP). We here investigate the spatial implications of using different possible criteria for reducing water-borne phosphorous (P) loads in the Northern Baltic Sea River Basin District (NBS-RBD) in Sweden. Results show that most catchments that have a high degree of internal eutrophication do not express high export of P from their outlets. Furthermore, due to lake retention, lake catchments with high P-loads per agricultural area (which is potentially of concern for the WFD) did not considerably contribute to the P-loading of the Baltic Sea. Spatially uniform water quality goals may, therefore, not be effective in NBS-RBD, emphasizing more generally the need for regional adaptation of WFD and BSAP-related goals.

Distributed conceptual modelling in a Swedish lowland catchment: a multi-criteria model assessment

Operational management and prediction of water quantity and quality often requires a spatially meaningful simulation of environmental flows and storages at the catchment scale. In this study, the performance of a fully distributed conceptual hydrologic model was evaluated based on the HBV (Hydrologiska Byråns Vattenbalansavdelning) and TACD (Tracer Aided Catchment model – Distributed) model concept in the meso-scale Fyrisån catchment in the Central Swedish lowlands. For a more spatially explicit representation of runoff generation processes of small landscape elements such as wetlands, a new sub-grid parameterization scheme was implemented in the model. In addition, a simple flow distribution and lake retention routine was introduced to better conceptualize the flow routing. During intensive model evaluation and comparison the model underwent conventional split-sample and proxy-basin tests. In this process, shortcomings of the model in the transferability of parameter sets and in the spatial representation of runoff generating processes were found. It was also demonstrated how a detailed comparison with a lumped benchmark model and the additional use of synoptic stream flow measurements allowed further insights into the model performance. It could be concluded that such a thorough model assessment can help to detect shortcomings in the spatial representation of the model and help facilitate model development.

Modelling the response of phytoplankton in a shallow lake (Loch Leven, UK) to changes in lake retention time and water temperature

The phytoplankton community of Loch Leven in 2005 was modelled and subjected to a combination of different flushing rates and water temperatures in order to assess the lake’s sensitivity to these two climatic drivers. Whilst the simulated annual mean total chlorophyll a proved relatively insensitive to these changes, at the species level marked changes were recorded. Some species responded positively to increased temperature (e.g. Aulacoseira), some negatively (e.g. Asterionella), whilst others were negatively affected by increased flow (e.g. Aphanocapsa) and others enhanced (e.g. Stephanodiscus). However, this relationship with flow was season dependent with, for example, a simulated increase in summer inflows actually benefiting some species through increased nutrient supply, whereas an equivalent increase in flow in wetter seasons would have negatively affected those species (i.e. through flushing loss). Overall, the simulations showed that the range of species types simulated in the community was sufficient for one species to always benefit from the changing niches created by the multiple climatic drivers applied in this study. The level of exploitation by such a species was only constrained by the nutrient carrying capacity of the system, which led to the overall dampened response in the total chlorophyll a measure, both at the annual and season scale. Thus, whilst overall biomass showed relatively little reaction to the two climatic drivers tested, the phytoplankton community composition responded markedly.

Global spatial distribution of natural riverine silica inputs to the coastal zone

Abstract. Silica, SiO2, in dissolved (DSi) and particulate (PSi) form, is both a major product of continental weathering as well as an essential nutrient in terrestrial and aquatic systems. Here we present estimates of the spatial distribution of riverine silica fluxes under natural conditions, i.e. without human influence, to ~140 segments of the global coastal zone. Focussing on the construction of the DSi budget, natural DSi concentration is multiplied with discharge of rivers for each segment for documented basins and segments. Segments with no documentation available are estimated using clustered information based mainly on considerations of local lithology, climate, and lake retention. We approximate fluxes of particulate silica in various forms (PSi) from fluxes of suspended matter, calculated from existing models. Results have been established for silica fluxes, concentrations and yields for drainage basins of the different continents, oceans basins as well as coastal segment basins. For the continental surfaces actually draining into the oceans (exorheic regions, representing 114.7 million (M) km2), 371 M t y−1 of DSi and 8835 M t y−1 of PSi are transported, corresponding to a mean concentration of 9.5 mg l−1 and 226 mg l−1, and to a mean yield of 3.3 t km−2 y−1 and 77 t km−2 y−1, respectively. DSi yields exceeding 6.6 t km−2 y−1, i.e. >2× the global average, represent 17.4% of the global continental ice-free exorheic area but correspond to 56.0% of DSi fluxes. Pacific catchments hold most of the hyper-active areas (>5× global average), suggesting a close connection between tectonic activity and DSi fluxes resulting from silicate weathering. The macro-filters of regional and marginal seas intercept 33% and 46% of the total dissolved and particulate silica fluxes. The mass of DSi received from rivers per unit square area of various oceans ranges over more than one order of magnitude. When expressed per unit volume and when individual regional seas are considered this figure ranges over two to three orders of magnitude, an illustration of the heterogeneity of the land to sea connection.

Northern Canada in a Changing Climate: Major Findings and Conclusions

Northern Canada in a Changing Climate: Major Findings and Conclusions

Larval Fish Transport and Retention and the Importance of Location for Juvenile Fish Recruitment in Upper Klamath Lake, Oregon

AbstractIn the Upper Klamath Lake basin of Oregon, we applied the member‐vagrant hypothesis to larval lake fishes, documented marsh and hydrographic retention for larval shortnose suckers Chasmistes brevirostris and Lost River suckers Deltistes luxatus, and examined the effect of larval retention on the shoreline abundance of the juveniles of five species of fish in August. Emigration of larval suckers was highest from natal rivers, and immigration was highest in nonnatal areas downstream of the lake. Lake retention was facilitated by a wind‐generated gyre and advection by an eastern boundary current. Marshes and other shoreline irregularities acted as traps that slowed river and eastern boundary current advection and retained larvae, especially for shortnose suckers, for up to 3 weeks. The interaction of behavior, seasonal spawning, and seasonal system dynamics appears to drive retention patterns. For both species of suckers and three minnow species (fathead minnow Pimephales promelas, blue chub Gila coerulea, and tui chub G. bicolor), the abundance of juveniles along the shoreline increased with distance from the lake outlet and was weakly related to lake elevation, a surrogate for available habitat. For these five species, 45.5% of the variation in August juvenile abundance was determined by distance from the lake outlet. This work suggests that the nonbehavioral component of freshwater retention is complex and depends on hydrographic features, the boundary conditions of hydrographic features, and shoreline habitat.

Nitrogen in river basins: Sources, retention in the surface waters and peatlands, and fluxes to estuaries in Finland

Nitrogen export from diffuse and point sources and its retention in the major river basins of Finland is quantified and discussed. The estimated total export from river-basins in Finland was 119 000 tonnes N a − 1 for the period 1993 to 1998 based on N export from different land use types defined in a GIS-based assessment model, incorporated with estimates of N inputs from atmospheric deposition and point sources. Agriculture contributes 38% of the total export, varying in the range 35–85% in the south-western basins and 0–25% in the northern basins. This estimate of N export from agriculture was based on regional N balances together with data from small agricultural research catchments. Forestry contributes on average 9%, with increasing dominance towards eastern and northern parts of the country: from 2% to 15% in the southern–mid-western Finland basins to 10–30% in the large northern basins. ‘Background’ N export from forests on both mineral and organic soils contributes 27% on average; in the northern basins it may contribute from 40% up to 90% of the total load. The estimate was calculated based on practically all data available from 42 small, experimental catchments in Finland. Of the total N input to Finnish river-systems, 0% to 68% was retained in surface waters and/or peatlands, with a mean retention of 22%. The highest retention of N (36–61%) was observed in the basins with the highest lake percentages. The lowest retention (0–10%) of N was in the coastal basins with practically no lakes. In the national N mass balance, 38 000 tonnes N a − 1 (32%) was estimated as lake retention and 4000 tonnes N a − 1 (3%) as retention in peatlands. On the basis of mass balances and sensitivity analysis, retention was in most cases estimated to be in the range of 7.5–12.5 kg ha − 1 a − 1 in lakes and 0–1.5 kg ha − 1 a − 1 in peatlands. The model results were tested using the split-sample technique and uncertainty estimates for different data sources are provided and discussed.

Long‐term trends in catchment export and lake retention of dissolved organic carbon, dissolved organic nitrogen, total iron, and total phosphorus: The Dorset, Ontario, study, 1978–1998

Annual catchment export of total phosphorus (TP), dissolved organic carbon (DOC), total iron (Fe), and dissolved organic nitrogen (DON) to seven lakes in central Ontario was measured between 1978 and 1998. Fluctuations in annual water discharge and total DOC load (including precipitation) to the lakes over the 20‐year period were similar in the seven study lakes. DOC export to the lakes responded proportionally to changes in discharge, decreasing during drier and warmer years. There were similar but less accentuated variations in annual DOC lake concentrations. There were no clear regional trends evident during the 20‐year period toward drier or wetter conditions, less DOC load, clearer lakes, etc., that could be interpreted as signaling a shift toward a different equilibrium state. The fraction of the DOC load retained by lakes (transferred to sediments and the atmosphere) increased during an extended dry period. Fe, TP, and DON export decreased more than DOC export during the extended dry period. Runoff appears to affect Fe, TP, and DON export first by controlling export of organic matter and second by affecting water table position and thus redox levels in the surface layer of peatlands. Permanently drier conditions with less runoff would likely lead to clearer lakes that are less productive. Conversely, increased runoff would lead to more colored and productive lakes. Both scenarios have implications for subsistence and sport fishing economies.

Reconstruction of the total N and P inputs from the IJsselmeer into the western Wadden Sea between 1935–1998

In this paper we reconstruct the Total Nitrogen (TN) and Total Phosphorus (TP) inputs into the western Wadden Sea from its major freshwater source the lake IJsselmeer between 1935–1998. The reconstruction is based on the TN and TP loads of the river Rhine at the German/Dutch border and follows the aquatic continuum approach to calculate loads further downstream in (1) the river IJssel feeding the IJsselmeer, and (2) the discharge of this lake into the western Wadden Sea. Our objectives are to determine (1) how the signal of changing nutrient loads of the Rhine is transferred downstream, and (2) how hydrological changes in the rivers-and-lake system affected the TN and TP discharges into the western Wadden Sea. Observational data from which TN and TP loads of the river Rhine could be calculated date back to the 1960s and we used background loads for European rivers for the period before World War II. The period in between was interpolated using the historic scenarios of watershed land use and management tested for the hypothetical Phison river (Billen and Garnier, 1997, Aquat. Microb. Ecol. 13, 3–17), adapted for the hydrology of the Rhine. The interpolations were constrained by loads of dissolved inorganic N and P compounds, for which data go back to the 1930s. Using the reconstructed loads of the river Rhine, TN and TP loads of the river IJssel and the lake IJsselmeer were calculated with simple mass balance models that were calibrated against data available from 1972–1993 onwards. Results show a gradual 12-fold increase of the TN discharge of the IJsselmeer into the Wadden Sea from 1935 to 1988, after which it decreased to levels still ∼5 fold those in 1935. The discharge of TP increased more abruptly in the early 1960s to values in 1983 ∼10 fold those before 1965, followed by a sharp decrease to values still ∼2.5 fold those before 1965. These patterns resemble those in the river Rhine, but are modified due to (1) variability of other sources to the lake, and (2) reduction of the retention capacity of the lake due to enormous land reclamation. TN:TP atomic ratios in the freshwater input to the Wadden Sea as high as 100 in 1995 were caused by successful P reduction programmes, less successful N reduction and N-rich inputs from smaller rivers and land runoff into the lake IJsselmeer. Land reclamation caused the lake's retention of TN to decrease step-wise from ∼70% to ∼45–50% and that of TP from 85% to 55–60% between 1950 and 1980.

Application of Static Critical Load Models for Acidity to High Mountain Lakes in Europe

Critical load models for acidityprovide a measure of the sensitivity of surfacewaters to acid deposition, and can be used todetermine critical load exceedance and potentiallong-term harmful effects. Three static models,the Steady-State Water Chemistry model, diatommodel and First-order Acidity Balance model, arehere applied to 11 high mountain lakes in Norway,Scotland, the Alps, the Pyrenees and the Tatras.Between five and seven of the lakes show criticalload exceedance, depending on the model used.Nitrogen as well as sulphur deposition isimportant in causing exceedance. Since soil andvegetation cover are generally sparse, geologyand lake retention time appear to be key factorsin the determination of critical load. Retentionof nitrogen is observed, but it is unclearwhether this occurs within the lake or theterrestrial part of the catchment.

Colour - mass balances and colour - dissolved organic carbon relationships in lakes and streams in central Ontario

Colour and dissolved organic carbon (DOC) concentrations and mass balances were measured for seven unproductive lakes and 20 tributary streams between June 1980 and May 1992. Individual observations of colour, which measures an unknown DOC fraction assumed to be principally humic, were not good predictors of discrete DOC concentrations for any of the study sites. Long-term mean colour was, however, strongly correlated with long-term mean DOC concentrations in streams and lakes. Colour behaved differently from the total DOC pool in lakes. Lake retention and loss coefficients for colour were always higher than corresponding values for the total DOC pool, and the mean annual colour/DOC ratios in lake outflows were always less than the corresponding ratios in lake inputs, indicating that the coloured fraction was preferentially removed or photooxidized. A steady-state mass balance model was used to estimate the upper bound for the average coloured fraction of DOC in each lake. The upper bound for the seven lakes ranged from 34 to 88%, increasing with increasing colour, DOC, and total phosphorus.

Precipitation Chemistry and Chemical Limnology of Fertilized and Natural Lakes at Saqvaqjuac, N.W.T.

Precipitation at Saqvaqjuac (northwest coast of Hudson Bay, 60°39′N) had high concentrations of sea salts, was moderately acidic, and had less SO4 and total N than lower latitude precipitation, although SO4 sources were distant. Watershed retention was high for H+, but negative for other elements as a consequence of isostatic rebound. Annual element runoff was a function of the timing of melt runoff and summer rain events because of permafrost. Lake retention of Si was higher than P because of the different times of loading, late summer versus spring. Conservative element mass did not change overwinter except in low-elevation Spring Lake, where residual Cl, Na, and K diffused from the sediments. Phosphorus and N were the only elements incorporated into black ice. As a result of freezeout and incomplete meltwater mixing beneath lake ice, element concentrations were 1.6 times higher in lakes than inflows, and major ion turnover times were 1.5–2.0 times higher than water turnover times.