Predicting concentration of total phosphorus and chlorophyll a in a lake with short hydraulic residence time

The relationship between total phosphorus and chlorophyll a concentration was determined for Skinner Lake, Indiana over an annual cycle in 1978–79. Total nitrogen:total phosphorus ratios in the epilimnion ranged from 19 to 220 suggesting a phosphorus-dependent algal yield in the epilimnion. Approximately 90% of annual TP loading reached the lake via streamflow, and 93% of this entered during snowmelt and spring-overturn periods. At that time incoming water flushed the lake 2.4 times. Atmospheric loading accounted for 1.4% of annual TP load. Internal hypolimnetic TP loading occurred during summer stratification. Mean [chl a] for the ice-free period was 15.15 mg m^–3, within the range expected for eutrophic lakes.The 1978–79 data were used in conjuction with the Vollenweider & Kerekes (1980) model to produce a model specific for the Skinner Lake system. The model predicted mean epilimnetic total phosphorus and chlorophyll a concentrations from mean total phosphorus concentration in inlet streams and from lake water residence time during the period of spring overturn and summer stratification. The Skinner-specific model was tested in 1982 and it closely predicted observed mean epilimnetic [TP] and [chl a] during the ice-free period. This study shows that variability in lake models which average data over an annual period can be reduced by considering lake-specific seasonal variation in hydrology and external TP loading.     

Lake sturgeon population attributes and reproductive structure in the Namakan Reservoir,Minnesota and Ontario

Quantified were the age, growth, mortality and reproductive structure of lake sturgeon (Acipenser fulvescens) collected in the US and Canadian waters of the Namakan Reservoir. The hypotheses were tested that (i) age and growth of lake sturgeon in the Namakan Reservoir would differ by sex and reproductive stage of maturity, and (ii) that the relative strength of year‐classes of lake sturgeon in the reservoir would be affected by environmental variables. To quantify age, growth and mortality of the population, existing data was used from a multi‐agency database containing information on all lake sturgeon sampled in the reservoir from 2004 to 2009. Lake sturgeon were sampled in the Minnesota and Ontario waters of the Namakan Reservoir using multi‐filament gillnets 1.8 m high and 30–100 m long and varying in mesh size from 178 to 356 mm stretch. Reproductive structure of the lake sturgeon was assessed only during spring 2008 and 2009 using plasma testosterone and estradiol‐17β concentrations. Ages of lake sturgeon >75 cm ranged from 9 to 86 years (n = 533, mean = 36 years). A catch‐curve analysis using the 1981–1953 year classes estimated total annual mortality of adults to be 4.8% and annual survival as 95.2%. Using logistic regression analysis, it was found that total annual precipitation was positively associated with lake sturgeon year‐class strength in the Namakan Reservoir. A 10 cm increase in total annual precipitation was associated with at least a 39% increase in the odds of occurrence of a strong year class of lake sturgeon in the reservoir. Plasma steroid analysis revealed a sex ratio of 2.4 females: 1 male and, on average, 10% of female and 30% of male lake sturgeon were reproductively mature each year (i.e. potential spawners). Moreover, there was evidence based on re‐captured male fish of both periodic and annual spawning, as well as the ability of males to rapidly undergo gonadal maturation prior to spawning. Knowledge of lake sturgeon reproductive structure and factors influencing recruitment success contribute to the widespread conservation efforts for this threatened species.     

Models to predict lake annual mean total phosphorus

A lake is a product of processes in its watershed, and these relationships should be empirically quantifiable. Yet few studies have made that attempt. This study quantifies and ranks variables of significance to predict annual mean values of total phosphorus (TP) in small glacial lakes. Several new empirical models based on water chemistry variables, on map parameters of the lake and its catchment, and combinations of such variables are presented. Each variable provides only a limited (statistical) explanation of the variation in annual mean values of TP among lakes. The models are markedly improved by accounting for the distribution of the characteristics (e.g., the mires) in the watershed. The most important map parameters were the proportion of the watershed lying close to the lake covered by rocks and open land (as determined with the drainage area zonation method), relief of the drainage area, lake area and mean depth. These empirical models can be used to predict annual mean TP but only for lakes of the same type. The model based on map parameters (r ²=0.56) appears stable. The effects of other factors/variables not accounted for in the model (like redox-induced internal loading and anthropogenic sources) on the variation in annual mean TP may then be estimated quantitatively by residual analysis. A new mixed model (which combines a dynamic mass-balance approach with empirical knowledge) was also developed. The basic objective was to put the empirical results into a dynamic framework, thereby increasing predictive accuracy. Sensitivity tests of the mixed model indicate that it works as intended. However, comparisons against independent data for annual mean TP show that the predictive power of the mixed model is low, likely because crucial model variables, like sedimentation rate, runoff rate, diffusion rate and precipitation factor, cannot be accurately predicted. These model variables vary among lakes, but this mixed model, like most dynamic models, assumed that they are constants.     

Historical water level change of Lake Weishan in East China from 1758–1902 AD: relationship with the flooding of the Yellow River

In order to understand high-resolution environmental changes, historical water level changes on decadal and centennial scales have been conventionally analyzed employing documentary records and lake sediments. However, annual records are still limited. Here we report the discovery of water level observations (up to monthly) in the historical literature of the Qing Dynasty (1644–1912 AD). We reconstruct the chronologies of annual mean, maximum and minimum water level changes of Lake Weishan from 1758–1902 AD. The chronologies are compared with the precipitation data (dryness/wetness index data) of four stations in the vicinity of Lake Weishan (i.e., Heze, Jinan, Linyi and Xuzhou). We suggest that the annual water level changes are related to the amount of precipitation at the four stations. In addition, the flooding of the Yellow River significantly affects Lake Weishan, always resulting in extremely high annual mean, maximum and minimum water levels in the lake. The flooding in 1871 and 1873 AD even destroyed the banks between Lake Weishan-Zhaoyang-Nanyang and Lake Dushan, thus forming a united lake. In particular, we identify a high water level interval from 1851–1855 AD, just prior to the Yellow River channel change event in 1855 AD.     

Thermal regimes of Florida lakes

Water column temperatures were determined monthly for 24 lakes and bimonthly for 5 lakes in peninsular Florida during 1979. Three geographical groups (north, central, south) were delineated from mean monthly water column temperatures for individual lakes. On a monthly basis, northern lakes were least similar to southern lakes, while central Florida lakes displayed greater affinity to the southern than to the northern lake group. Temperature differences between lake groups broke down during late summer. Subtropical lakes have been defined tentatively as those Florida lakes south of 28° latitude which possess warm monomictic circulation and a mean annual temperature of 24.2 ± 4.8 °C with minimum water column temperature rarely less than 14 °C and summer maxima rarely exceeding 31 °C. While all lakes in Florida are clearly warm monomictic annual nutrient cycling and productivity patterns may be influenced by inter-group differences in the timing and duration of water column circulation.     

基于能值分析的洞庭湖区退田还湖生态补偿标准

基于能值分析理论,对1999-2010年洞庭湖区退田还湖的各项主要生态服务价值的能值及其货币价值进行计算,确立了根据每年生态服务功能能值总量相对于退田还湖生态恢复起始年份的增量来确定生态补偿标准的计算方法,分析了1999-2010年的生态补偿标准和补偿范围.结果表明： 1999-2010年,洞庭湖区退田还湖年补偿标准在40.31～86.48元·m^-2,均值为57.33元·m^-2;生态补偿标准呈逐年增加趋势,这反映了退田还湖生态恢复工程的成效逐渐显现.研究区生态补偿标准2005年以后呈现出稳步快速增长的态势,这主要是湖南省集约型经济发展的结果,进一步说明随着经济社会的发展,自然生态资源价值将日益凸显.能值分析应用于生态补偿标准能反映补偿标准的动态变化,解决了物质流、能量流与经济流对接困难的问题,克服了以往环境经济学方法主观随意性较大的弊端,研究表明了能值分析的可行性与先进性.     

Total Mercury Concentrations in Lake and Streams Sediments Related to Wet-Area Coverage and Geogenic Sources within Upslope Basins

Total mercury concentrations (THg) in lake and stream sediments generally decrease with wet-area coverage (A_W) per upslope basin area (A_B). This was determined by delineating the wet-area component of 12,653 basins above as many sediment-sampling locations of the Geological Survey of Canada. These locations represent four climate regions (maritime, boreal, arctic, alpine) comprising six stream and six lake study areas. The dependence of sediment THg on A_W/A_B was examined by dividing the 0 < A_W/A_B < 1 range into 40 equal segments, and obtaining the mean sediment THg value for each segment. The results were evaluated by way of regression analysis using the following equation: mean sediment THg = a (1 ? A_W/A_B)^b + c A_W/A_B, with a, b and c as area-specific coefficients. The “a” and “c” coefficients could – in part – be inferred from bedrock type, annual atmospheric Hg deposition, and mean monthly air temperatures, and mean annual precipitation. Both “a” and “c” increased with increasing atmospheric Hg deposition for lake sediments. For stream sediments, only “a” did so. The geogenic influence on the THg variations per study area was addressed through multiple regression analyses, using sediment concentrations of other heavy elements and organic matter as independent variables.     

Hydrology of Lake Atnsjøen and River Atna

The hydrological investigations in the Atna basin started in 1917 with discharge measurements at the outlet of Lake Atnsjøen. Ice data are available from the lake since 1950 and water temperature data from 1980. With the start of the FORSKREF program in 1986 the number of hydrological stations increased substantially and included also snow measurements. During the FORSKREF period 1986–98 the annual mean discharge was 8% lower than during the normal period 1931–60. The annual flood is highest during the snow melt in spring, an exception was 1987 when a rain flood in October was the annual high. The spring flood in early June 1995 was the largest ever recorded and had a 100–200 year return period. The water temperature is low above tree-line at 1000 m a. s. l., rarely exceeding 7–8?°C. The temperature increases gradually with decreasing altitude and is periodically above 15?°C at 400 m a. s. l. The Atna Lake is an important heat source for the river downstream. In this lake, wind mixing normally prevents the development of a strong summer thermocline. The lake usually freezes over in late November and has a stable ice cover of 50–90 cm thickness in early spring. The ice normally breaks up in late May; thus the mean ice-covered period is 6 months. The ice cover on the river is less stable and rather large ice-runs are common on the lower part of River Atna. The snow measurements are carried out in April in a small subbasin between 800 and 1200 m a. s. l. The snow cover is unevenly distributed due to strong wind transport, but the pattern is more or less the same from one season to another. The mean snow accumulation in this basin is equivalent to 205 mm of precipitation.     

Analysis of macrophyte indicator variation as a function of sampling,temporal, and stressor effects

Biological indicators that signal changes in lake condition are essential tools for guiding resource management decisions. Macrophyte-based indicators have traditionally been selected and evaluated in the context of nutrient-based stressors, although the need to evaluate indicators that are sensitive to climate stressors has been increasingly relevant. Moreover, indicators should ideally exhibit minimal sampling variation and have low natural temporal variation so there is high power to detect changes in the mean value over time. Eight macrophyte indicators were estimated in 23 Minnesota (USA) lakes using four years of repeated surveys to estimate sampling and temporal variation, response to development (phosphorus concentration) and climate stress (annual growing degree days), and power to detect significant change at various annual sampling intervals. Indicators included a macrophyte index of biotic integrity, floristic quality index, maximum depth of growth, total species richness, common species richness, mean richness, and frequency occurrence of rooted species and Chara sp. Overall, regression and smoothed additive models indicated significant relationships of indicators to total lake phosphorus and mean annual growing degree days. The macrophyte index of biotic integrity, floristic quality index, and the frequency rooted species had minimal sampling variation in this study, were responsive to development or climate stress, and had low annual variation (coefficients of variation 0.08, 0.10, and 0.19, respectively) resulting in high to moderate power (>50%) for detecting significant change over a 20 year period. Results from these analyses will facilitate the use of precise and powerful indicators that respond to stressors that are of concern for the management of freshwater glacial lakes.     

The major cations in Lake Maryût waters

Summary The concentrations of sodium, potassium, calcium and magnesium in Lake Maryût water are determined at six stations representing the different regions of the lake during the year 1966. The sodium content varies seasonally and regionally with an annual average value of 1.0332 g/kg. The potassium content varies also seasonally and regionally following the sodium variation, with an annual average content of 0.0585 g/kg. The potassium concentration in the lake water forms about 4.5% that of sodium, compared with 3.6% in sea water and 21.6% in fresh water. The average Na/Cl ratio varies between a maximum in autumn and a minimum in summer. Contrary to the Na/Cl ratio, the K/Cl ratio is more or less correlated with salinity variations where it increases in summer and decreases in winter. The annual average Na/Cl ratio of 0.6345 for the lake water is higher than the average ratio of 0.5555 given for sea water. The K/Cl ratio has an annual average value of 0.0339 which is again higher than the average ratio of 0.0208 for sea water. The sodium and potassium chlorinity ratios decrease with the increase of chlorinity.The calcium content in the lake water reaches its maximum in summer and its minimum in autumn with an annual average content of 0.0549 g/kg. The Ca/Cl ratio for the lake water has an average value of 0.0335 which is higher than the ratio of 0.02126 for oceanic water. It increases by the increase of chlorinity and subsequently follows the salinity variation in the lake water. It also varies regionally following the distribution of carbonates in the bottom sediments.The magnesium content in the lake water has an annual average of 0.1201 g/kg. The Mg/Cl ratio increases by the increase of chlorinity, with an annual average value of 0.0733 which is higher than the average ratio of 0.06692 for sea water. Similar to calcium, the Mg/Cl ratio follows more or less the seasonal variation of salinity. The Mg/Cl ratio varies slightly from one region to another, with a slight westward increase in the lake. The average Mg/Cl ratios are the same at the six stations and the annual average ratio is 0.0733.     

Organic Carbon Flux to a Large Salt Lake: Pyramid Lake,Nevada, USA

Energy flux to a large, deep, salt lake from phytoplankton, periphyton and macrophyte primary production as well as fluvial transport and wind-transported terrestrial vegetation and dust were quantified. Average areal phytoplankton net photosynthesis was 511 mg C m⁻² d⁻¹. Highest rates were during water-blooms of the bluegreen alga, Nodularia spumigena. Although areal daily net photosynthesis by periphyton in Pyramid Lake was comparable to other salt lakes, annual carbon influx by periphyton was small due to the lake's graben morphology and moderate euphotic depth (mean, 11.9 m). Macrophytes were uncommon and, therefore a minor source of energy. Truckee River is the only major fluvial discharge to Pyramid Lake and dissolved organic carbon was the principal organic carbon fraction in river water. Large upstream water diversions coupled with several drought years resulted in an average fluvial organic carbon load of only 7.3 g Cm⁻²y⁻¹ or 4% of median phytoplankton net photosynthesis. Tumbleweeds were the most common terrestrial plant material observed in Pyramid Lake comprising a maximum projected importance of 6% of total annual carbon input. Windborne dust represented < .1% of annual carbon input. Phytoplankton primary production is the predominant energy source to Pyramid Lake, accounting for over 80% of annual carbon influx. The relative magnitude of autochthonous and allochthonous vectors to the annual carbon budget of this desert salt lake are comparable to those of the few other large lakes for which detailed energy input budgets have been calculated.     

A northern Italian shallow lake as a case study for eutrophication control

Lake Varese (northern Italy) has shown deterioration in water quality since the 1960s and, as a result of the long duration of direct discharge of untreated sewage into the lake, it was classified as being hypertrophic. To recover the lake water quality, a series of externally and internally remedial actions were implemented in subsequent years. The applied sewage collecting system induced a reduction of the external P loads from 50 t P year⁻¹ to 16t P year⁻¹ and the weighted mean annual TP concentration decreased from 352 μg P l⁻¹ to 85 μg P l⁻¹, typical of eutrophic conditions. The hypolimnetic water withdrawals, adopted in the years 2000–2003, allowed a reduction of the internal P loads of about 3–5 t P. In the same years, 500t O₂ were injected at depths of 4.5–8 m during the summer months. In spite of these internal remedial actions, no significant reduction of the weighted mean annual concentration of the TP could be observed, and during the summer stratification period no significant reduction of the volumes of anoxic water and of the duration of the anoxia were detected. The anoxic conditions are still the prevailing force driving the lake P-budget, maintaining the lake in eutrophic status.     

Climatic governance of the latitudinal cline in seasonality of freshwater phytoplankton production

Data on the intra-annual variation in phytoplankton production for 114 southern and northern hemisphere lakes (42°S to 75° N) were combined to examine broad-scale latitudinal trends. Much of the seasonal variation in production can be statistically explained through the climatic factors of mean annual range of atmospheric temperature and annual variance in incident solar radiation, of which the amplitude of both increases with distance from the equator. Quantification of this latitudinal-climatic trend is an important step in understanding the hierarchial regulation of variability in lake trophic dynamics.     

Carbon,phosphorus and nitrogen budgets of the littoral Equisetum belt in an oligotrophic lake

Stores and flows of carbon, phosphorus and nitrogen in a littoral Equisetum stand were studied in 1978–1980 in the oligotrophic, mesohumic lake Pääjärvi, southern Finland. The major carbon and nutrient stores were sediment and Equisetum. The seasonal cycle of the macrophyte vegetation had a profound influence on the whole littoral ecosystem. In spring, when only dead remains of Equisetum were present above ground, there were few differences in nutrient, chlorophyll a and zooplankton concentrations between the littoral and the open lake; phytoplankton and epiphytes were the major producers.In early June, when new shoots of Equisetum reached the water surface, water exchange between the littoral and the open lake started to diminish, and the characteristic features of a closed macrophyte zone gradually developed: by August the P, Chl a and zooplankton concentrations in the littoral were 5–10 times those in the open lake. From late June until autumn Equisetum was overwhelmingly dominant both in biomass and in production.The measured total primary production and respiration values indicated a high rate of internal cycling of carbon and nutrients. The daily P requirements of plant growth exceeded the total P stored in the water by a factor of 2–4, and also exceeded the release of nutrients in excretion. High N:P ratios in the water (total 10–64, inorganic 18–171) suggested that P was probably always the limiting nutrient.The P content of the annual production of Equisetum in Pääjärvi was 2.3% of the mean annual P load, and 5.3% of the mean total P storage in the water volume of the lake.     

Temporal dynamics in epipelic, pelagic and epiphytic algal production in a clear and a turbid shallow lake

SUMMARY 1. Pelagic and epipelic microalgal production were measured over a year in a pre-defined area (depth 0.5 m) in each of two lakes, one turbid and one with clear water. Further estimates of epiphytic production within reed stands were obtained by measuring production of periphyton developed on artificial substrata.
2. Total annual production of phytoplankton and epipelon was 34% greater in the turbid lake (190 g C m⁻² year⁻¹) than in the clearwater lake (141 g C m⁻² year⁻¹). However, the ratio of total production to mean water column TP concentration was two fold greater in the clearwater lake.
3. Phytoplankton accounted for the majority of the annual production (96%) in the turbid lake, while epipelic microalgal production dominated (77%) in the clear lake. The relative contribution of epipelic algae varied over the year, however, and in the turbid lake was higher in winter (11–25%), when the water was relatively clear, than during summer (0.7–1.7%), when the water was more turbid. In the clearwater lake, the relative contribution of epipelon was high both in winter, when the water was most clear, and in mid-summer, when phytoplankton production was constrained either by nutrients or grazing.
4. Compared with pelagic and epipelic primary production, epiphytic production within a reed stand was low and did not vary significantly between the lakes.
5. The study supports the theory of a competitive and compensatory trade-off between primary producers in lakes with contrasting nutrient concentrations, resulting in relatively small differences in overall production between clear and turbid lakes when integrating over the season and over different habitats.     

Ecosystem services of Lake Võrtsjärv under multiple stress: a case study

This study is the first attempt at the European scale to make an inventory of ecosystem services (ESS) of a large lake. We analysed a set of ESS indicators against the annual mean values of environmental parameters for 2006–2013. According to principal component analysis, the trophic state- and hydrology-related factors explained about 70% of the environmental variability of the lake and showed strong relationships with some ESS. Among the provisioning ESS, the annual eel catch and the total fish catch were positively related to different eutrophication indicators while the catches of pike, bream, and burbot depended rather on hydrological factors. Reed harvesting efficiency was related to the lake’s water level. The indicators of regulating, maintenance, and cultural ESS showed very high variability in different years, the latter depending on socio-economic conditions rather than environmental factors. We discovered numerous trade-offs between ESS benefitting from higher trophic state or regulated water level of the lake and the goals of good ecological status of the lake. Our analysis showed a clear need for rules prioritizing life supporting regulatory services against other ESS.     

Vegetation abundance in lowland flood plan lakes determined by surface area, age and connectivity

SUMMARY 1. We analysed the vegetation structure of 215 lakes in the flood plain of the river Lower Rhine in relation to environmental variables related to hydrological connectivity, lake morphometry, lake age and land use on adjacent land. 2. The frequency distribution of the cover of submerged macrophytes was not normal, implying that submerged macrophytes in any one lake were either scarce or abundant. 3. We observed clear water lakes with submerged macrophyte dominance over a wide range of total P concentration (0.020–0.40 mg total P L^?1). 4. Multiple logistic regression indicated that the probability of dominance by submerged macrophytes decreased markedly with the surface area, depth and age of the lakes. The surface area effect occurred independently of the depth. Further, there was a negative relationship between submerged macrophyte dominance and the long‐term annual duration of inundation by the river. 5. Nymphaeid cover showed a distinct optimum with respect to mean lake depth, being almost absent in lakes shallower than 0.5 m. In contrast to what was found for submerged plants, the probability of occurrence of nymphaeids increased with lake age. 6. The probability of helophyte occurrence increased with lake age, and decreased with the presence of trees, cattle grazing, surface area, use of manure and mean lake depth. 7. In all cases the critical level of one factor (e.g. mean lake depth) depended on other factors (e.g. surface area or age of lake). Thus, in the present study, small lakes tended to remain dominated by submerged macrophytes up to a greater depth than large lakes, and helophytes colonised smaller lakes in an earlier phase. 8. The effect of inundation by the river was modest. This could be because most of our lakes are rarely inundated during the growing season and experience only moderate current velocities while flooded. 9. The results have practical implications for future management of flood plains for conservation purposes. In new water bodies, macrophyte domination will be promoted if many small shallow lakes, rather than few large deep ones, are excavated.     

Lake water acidification and temperature have a lagged effect on the population dynamics of Isoëtes echinospora via offspring recruitment

The aquatic quillwort, Isoëtes echinospora, survived the strong water acidification during 1960s–1990s in Plešné Lake (Bohemian Forest, Central Europe), but failed to reproduce. We studied the relationships between a recent population recovery and an improvement of lake water quality. We used correlation analysis to evaluate lagged seasonal effects of lake water quality on population dynamics during the past decade, and factor analysis to determine the independent factors responsible for population recovery. We also provided a water-quality-based reconstruction of population growth from the beginning of the lake recovery two decades ago, using a partial least squares regression (PLSR) model of population growth. We identified three independent controlling factors: nutrients (nitrate, phosphorus, calcium, potassium, magnesium), stressors (pH, ionic aluminium) and temperature. Of these, nutrient availability did not limit the quillwort growth, but annual mean pH and winter mean concentrations of toxic ionic aluminium influenced population growth through negative effects on sporeling establishment until the age of one year, while cumulative temperature in spring and summer controlled the later plant growth. Thus, water quality in the acidified Plešné Lake mainly controls recruitment success rather than adult survival of Isoëtes echinospora. This study provides the first in situ evidence that the recruitment success, namely the annual increment in the adult quillwort population, indicates the degree of recovery from acidification, however further extensive investigation is required to more accurately quantify, and therefore understand, the relationships between recruitment, water quality and other factors.     

Production and Ecology of Benthic Chironomid Larvae (Diptera) in Lake Hayes,New Zealand,a Warm-monomictic Eutrophic Lake

The distribution and abundance of larval chironomids in Lake Hayes were studied from December 1973 to March 1975. The mean annual production of the two dominant species, Chironomus zealandicus and Chironomus sp. a, was 29.2 g m⁻² dry weight which is approximately 4.3 % of the average annual phytoplankton production in the lake. A high annual P/B ratio of 18.5 is consistent with the multivoltine life cycle of C. zealandicus. Larval chironomid production in the second summer when Anabaena blooms were absent was only one quarter of that in the first summer and is consistent with the hypothesis that the production of benthic chironomids in Lake Hayes is closely linked to that of the phytoplankton through the sedimentation of autochthonous organic matter.