Relative importance of phosphorus,invasive mussels and climate for patterns in chlorophyll a and primary production in Lakes Michigan and Huron

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Macrophyte effects on algal turbidity in subtropical versus temperate lakes: a comment on Wang et al. (2014)

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Quantitative relationships between oligochaete communities and phosphorus concentrations in lakes

SUMMARY.

• 1 The relative abundance of oligotrophic species in tubificid and lumbriculid communities was related to phosphorus concentration in eight lakes of Western Europe and three large lakes of North America.
• 2 Mean annual concentrations of total phosphorus, recorded in the whole lake during the 5 years preceding the sampling of worms, were averaged and this mean was used to indicate the trophic state.
• 3 Mean relative abundance (%) of oligotrophic species (OS) was negatively correlated with mean concentrations (mg m^?3) of total phosphorus (TP): OS = 80.29 – 8.35 TP^0.5r²= 0.81
• 4 Location and depth from which worms were sampled also influenced values of OS.

     

Lake‐type‐specific seasonal patterns of nutrient limitation in German lakes,with target nitrogen and phosphorus concentrations for good ecological status

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A comparison of diatom phosphorus transfer functions and export coefficient models as tools for reconstructing lake nutrient histories

1. We compared the baseline phosphorus (P) concentrations inferred by diatom‐P transfer functions and export coefficient models at 62 lakes in Great Britain to assess whether the techniques produce similar estimates of historical nutrient status. 2. There was a strong linear relationship between the two sets of values over the whole total P (TP) gradient (2–200 μg TP L^?1). However, a systematic bias was observed with the diatom model producing the higher values in 46 lakes (of which values differed by more than 10 μg TP L^?1 in 21). The export coefficient model gave the higher values in 10 lakes (of which the values differed by more than 10 μg TP L^?1 in only 4). 3. The difference between baseline and present‐day TP concentrations was calculated to compare the extent of eutrophication inferred by the two sets of model output. There was generally poor agreement between the amounts of change estimated by the two approaches. The discrepancy in both the baseline values and the degree of change inferred by the models was greatest in the shallow and more productive sites. 4. Both approaches were applied to two lakes in the English Lake District where long‐term P data exist, to assess how well the models track measured P concentrations since approximately 1850. There was good agreement between the pre‐enrichment TP concentrations generated by the models. The diatom model paralleled the steeper rise in maximum soluble reactive P (SRP) more closely than the gradual increase in annual mean TP in both lakes. The export coefficient model produced a closer fit to observed annual mean TP concentrations for both sites, tracking the changes in total external nutrient loading. 5. A combined approach is recommended, with the diatom model employed to reflect the nature and timing of the in‐lake response to changes in nutrient loading, and the export coefficient model used to establish the origins and extent of changes in the external load and to assess potential reduction in loading under different management scenarios. 6. However, caution must be exercised when applying these models to shallow lakes where the export coefficient model TP estimate will not include internal P loading from lake sediments and where the diatom TP inferences may over‐estimate TP concentrations because of the high abundance of benthic taxa, many of which are poor indicators of trophic state.     

Total phosphorus thresholds for regime shifts are nearly equal in subtropical and temperate shallow lakes with moderate depths and areas

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Light limitation of phytoplankton development in an oligotrophic lake - Loch Ness, Scotland

• 1 The underwater light climate in Loch Ness is described in terms of mixing depth (Z_m) and depth of the euphoric zone (Z_eu). During periods of complete mixing, Z_m equates with the mean depth of the loch (132 m), but even during summer stratification the morphometry of the loch and the strong prevailing winds produce a deep thermocline and an epilimnetic mixed layer of about 30 m or greater. Hence, throughout the year the quotient Z_m/Z_eu is exceptionally high and the underwater light climate particularly unfavourable for phytoplankton production and growth.
• 2 Phytoplankton biomass expressed as chlorophyll a is very low in Loch Ness, with a late summer maximum of less than 1.5 mg chlorophyll a m^-3 in the upper 30 m of the water column. This low biomass and the resulting very low photosynthetic carbon fixation within the water column are evidence that a severe restraint is imposed on the rate at which phytoplankton can grow in the loch.
• 3 The chlorophyll a content per unit of phytoplankton biovolume and the maximum, light-saturated specific rate of photosynthesis are both parameters which might be influenced by the light climate under which the phytoplankton have grown. However, values obtained from Loch Ness for both chlorophyll a content (mean 0.0045 mg mm^-3) and maximum photosynthetic rate (1–4 mg C mg Chla^-1 h^-1) are within the range reported from other lakes.
• 4 Laboratory bioassays with the natural phytoplankton community from Loch Ness on two occasions in late summer when the light climate in the loch is at its most favourable, suggest that even then limitation of phytoplankton growth is finely balanced between light and phosphorus limitation. Hence, for most of the year, when the light climate is less favourable, phytoplankton growth will be light limited.
• 5 Quotients relating mean annual algal biomass as chlorophyll a (c. 0.5 mg Chla m^-3) and the probable annual specific areal loading of total phosphorus (0.4–1.7 g TP m^-2 yr^-1) suggest that the efficiency with which phytoplankton is produced in Loch Ness per unit of TP loading is extremely low when compared with values from other Scottish lochs for which such an index has been calculated. This apparent inefficiency can be attributed to suppression of photosynthetic productivity in the water column due to the unfavourable underwater light climate.
• 6 These several independent sources of evidence lead to the conclusion that phytoplankton development in Loch Ness is constrained by light rather than by nutrients. Loch Ness thus appears to provide an exception to the generally accepted paradigm that phytoplankton development in lakes of an oligotrophic character is constrained by nutrient availability.

     

Deriving nutrient targets to prevent excessive cyanobacterial densities in U.S. lakes and reservoirs

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Macrophyte effects on algal turbidity in subtropical versus temperate lakes: a reply to Dolman (2014)

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Phosphorus recycling in lakes: evidence from large limnetic enclosures for the importance of shallow sediments

• 1 The dynamics of phosphorus in large field enclosures are described from a series of experimental manipulations directed primarily to the study of phytoplankton populations. The enclosures were similar in size but differed in their depth contours. The aim of the present analysis was to detect systematic differences in the phosphorus budgets of deep and shallow systems.
• 2 The sequence of events in each of six year-long experiments is described in terms of algal production. The values are compared with water-column measurements of total phosphorus (TP), the reactive fraction (SRP) and changes in the particulate fraction (PP, assumed to be TP minus SRP). Stoichiometric ratios for larger phytoplankton crops were in the range 85–110 C/P (molar).
• 3 The annual aggregate of new carbon produced in the two uniformly deep enclosures (11.5 m) in relation to the phosphorus supplied was also remarkably close to Redfield stoichiometry, with between 87 and 97mol C yielded per mol P added. However, in the graded enclosure (< 4–13.5 m), the yield was up to twice as great (maximum: 197 mol C mol^-1 P available).
• 4 There are two possible mechanisms. A graded surface permits a greater area of sediment to be in contact with the hypolimnion and for the sediment oxygen demand to deplete a greater hypolimnetic volume; the associated fall in redox would have been adequate to explain the observed increment of dissolved phosphorus to the hypolimnion, associated with the Einsele–Mortimer model (ferric → ferrous iron reduction). There was no clear evidence that this phosphorus supported autotrophic production until late in the year.
• 5 The alternative mechanism is based on the association of phosphorus ‘injection’ to the epilimnion during wind-mixed episodes, when the enhanced shear stress on shallow sediments resuspends fine, superficial deposits and their interstitial waters into the full circulation. Circumstantial evidence suggests this second pathway predominated in the graded enclosure but was ineffective in the uniformly deep enclosures.
• 6 The role of mechanical, aerobic phosphorus cycling in the nutrient economy of lakes, especially small or shallow ones, may have been underestimated in the past but it must be considered when evaluating any proposal to reduce the external nutrient loads to lakes.

     

Mechanisms preventing a decrease in phytoplankton biomass after phosphorus reductions in a German drinking water reservoir—results from more than 50 years of observation

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Historical changes in epilimnetic phosphorus concentrations in six rural lakes in Northern Ireland

1. Sediment cores were taken from six lakes in Northern Ireland: Loughs Heron, Ballywillin, Corbet, Patrick, Brantry and Creeve. The present-day total phosphorus (TP) concentrations of these lakes range from around 30 to 400 μg TP l^–1. None of the lakes have sewage point-sources disposing into them, and all have primarily agricultural catchments. 2. Sediment cores were dated using ²¹⁰Pb. The cores cover time periods ranging from about 100 years at Lough Corbet to periods considerably greater than the range of ²¹⁰Pb (more than 150 years), Lough Patrick. 3. Diatom stratigraphies indicate considerable ecological change at all the lakes, regardless of their current nutrient status. Epilimnetic phosphorus concentrations were inferred using weighted averaging regression and calibration. Diatom-inferred TP values for the core surface samples agreed reasonably well with the contemporary values. Pre-1900 TP concentrations range from about 10 μg TP l^–1 at Lough Patrick to 80 μg TP l^–1 at Lough Corbet. The higher values prior to 1900 are assumed to relate to land-clearance activities and the expansion of agriculture associated with the Plantation period. 4. Although there are increasing diatom-inferred TP concentrations between 1850 and 1900 at some sites, there is a final and more marked increase at all lakes after 1950. Phosphorus concentrations have increased at all lakes, by between a factor of three to five, over an average 50-year period. At four of the lakes, TP concentrations have been increasing linearly from around 1950 to the present day, suggesting that, in general, there is little sign of amelioration of the eutrophication problem. 5. The post-1950 increases are assumed to relate to changes in agricultural activity within their catchments, notably the continued improvement in field drainage, which has facilitated transfer of nutrients to water courses and lakes and increasing soil-P concentration due to a positive annual-P balance. Another factor, probably associated with increased animal grazing densities and improvement of grassland, is the application of animal slurries, which appears to be a largely unquantified factor.     

Depth distribution of the native freshwater mussel (Echyridella menziesii) in warm monomictic lakes: Towards a general model for mussels in lakes

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Limnology of naturally acidic,oligotrophic dune lakes in subtropical Australia,including chlorophyll — phosphorus relationships

This study provides the most comprehensive physico-chemical and phytoplankton data yet available for Australian dune lakes, which are among the world's most naturally acidic and oligotrophic freshwaters. Seasonal and spatial variations were examined in Blue Lagoon and Lake Freshwater, two ‘water-table window’ lakes in south-east Queensland. Like other dune lakes, they are acidic (minimum pH 4.20 and 4.55, respectively), polymictic water bodies with low concentrations of marine-derived major ions and almost undetectable levels of trace metals. While linmologically similar in winter, during spring-summer Lake Freshwater has significantly higher levels of chlorophyll-a, total phosphorus (TP) and turbidity than Blue Lagoon and other dune lakes, indicating seasonal mesotrophy. The key nutrient is TP, which has recently increased to a maximum of 17 μ· l⁻¹, due either to inputs from recreational sources, or to the death and decomposition of littoral vegetation resulting from falling water levels over the last decade. Inorganic nitrogen, though present only in small amounts, does not appear to limit the eutrophication process because of a shift in phytoplankton dominance from the usual desmids and dinoflagellates to N₂-fixing blue-green algae. A chlorophyll - TP linear regression derived for dune lakes indicates that at TP < 20 μg · l⁻¹ chlorophyll ‘yield’ is higher than in other lake types represented by regressions from the literature. This may be due to a more efficient utilization of the limited available phosphorus by dune lake algae which have adapted to the naturally oligotrophic environment. The implications of these findings for lake management are discussed.     

Assessing Seasonal and Inter-Annual Variations of Lake Surface Areas in Mongolia during 2000-2011 Using Minimum Composite MODIS NDVI

A minimum composite method was applied to produce a 15-day interval normalized difference vegetation index (NDVI) dataset from Moderate Resolution Imaging Spectroradiometer (MODIS) daily 250 m reflectance in the red and near-infrared bands. This dataset was applied to determine lake surface areas in Mongolia. A total of 73 lakes greater than 6.25 km²in area were selected, and 28 of these lakes were used to evaluate detection errors. The minimum composite NDVI showed a better detection performance on lake water pixels than did the official MODIS 16-day 250 m NDVI based on a maximum composite method. The overall lake area detection performance based on the 15-day minimum composite NDVI showed -2.5% error relative to the Landsat-derived lake area for the 28 evaluated lakes. The errors increased with increases in the perimeter-to-area ratio but decreased with lake size over 10 km². The lake area decreased by -9.3% at an annual rate of -53.7 km² yr^-1 during 2000 to 2011 for the 73 lakes. However, considerable spatial variations, such as slight-to-moderate lake area reductions in semi-arid regions and rapid lake area reductions in arid regions, were also detected. This study demonstrated applicability of MODIS 250 m reflectance data for biweekly monitoring of lake area change and diagnosed considerable lake area reduction and its spatial variability in arid and semi-arid regions of Mongolia. Future studies are required for explaining reasons of lake area changes and their spatial variability.     

Resistance to drought affects persistence of alternative regimes in shallow lakes of the Boreal Plains (Alberta,Canada)

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Plant community structure determines primary productivity in shallow,eutrophic lakes

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Patterns and controls of seasonal variability of carbon stable isotopes of particulate organic matter in lakes

Carbon stable isotopes (δ¹³C) of particulate organic matter (POM) have been used as indicators for energy flow, primary productivity and carbon dioxide concentration in individual lakes. Here, we provide a synthesis of literature data from 32 freshwater lakes around the world to assess the variability of δ¹³C_POM along latitudinal, morphometric and biogeochemical gradients. Seasonal mean δ¹³C_POM, a temporally integrated measure of the δ¹³C_POM, displayed weak relationships with all trophic state indices [total phosphorus (TP), total nitrogen (TN), and chlorophyll a (Chl a)], but decreased significantly with the increase in latitude, presumably in response to the corresponding decrease in water temperature and increase in CO₂ concentration. The seasonal minimum δ¹³C_POM also correlated negatively with latitude while seasonal maximum δ¹³C_POM correlated positively with all trophic state indices, pH, and δ¹³C of dissolved inorganic carbon (DIC). Seasonal amplitude of δ¹³C_POM (the difference between seasonal maximum and minimum values) correlated significantly with pH, TP and Chl a concentrations and displayed small variations in oligotrophic, mesotrophic and low latitude eutrophic lakes, which is attributed to low primary productivity and abundant non-living POM in the low trophic state lakes and relatively stable environmental conditions in the subtropics. Seasonal amplitude of δ¹³C_POM was the greatest in high latitude eutrophic lakes. Greater seasonal changes in solar energy and light regime may be responsible for the large seasonal variability in high latitude productive lakes. This synthesis provides new insights on the factors controlling variations in stable carbon isotopes of POM among lakes on the global scale.     

The influence of iron,siderophores and refractory DOM on cyanobacterial biomass in oligotrophic lakes

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Phosphorus dynamics in Danish lakes and the implications for diatom ecology and palaeoecology

SUMMARY 1. Seasonal phosphorus variability may be considerable in eutrophic lakes and patterns are influenced by internal, as well as external, nutrient loading. The strong seasonality of planktonic diatoms, with main growth periods in the spring and also in the autumn in meso‐ to eutrophic lakes, means that the measure of total phosphorus (TP) that is most relevant for diatom ecology may not be adequately assessed by single or few measurements during the year. 2. The diatom species assemblage of surface sediments can be used to infer in‐lake nutrient concentrations. Weighted averaging (WA) and weighted averaging partial least squares (WAPLS) regression and calibration models for diatoms and annual mean TP were developed for a 29‐site data set of Danish lakes based on (a) all diatom species and (b) planktonic species only. Jack‐knifed error statistics were: =0.37, root mean squared error of prediction (RMSEP)=0.28 log₁₀μg TP L^?1 and mean bias=0.04 log₁₀μg TP L^?1 for the WAPLS 2‐component model based on all species; =0.23, RMSEP= 0.32log₁₀μg TP L^?1 and mean bias=0.07 log₁₀μg TP L^?1 for the WA model with tolerance downweighting based on planktonic species only. These are comparable with similar, published data sets. 3. A subset of 23 sites was used to develop models based on seasonal TP measurements. Mean spring TP concentrations gave only slightly improved RMSEP values for models based on all species and plankton‐only (0.24 log₁₀μg TP L^?1 and 0.29 log₁₀μg TP L^?1, respectively). 4. Weighted averaging models derive environmental optima, for individual species, which are not necessarily of ecological relevance. However, good water chemistry data are required to model species' responses adequately and to develop calibration data sets.