Nutrient-chlorophyll trajectories across trophic gradients

We estimate the response of chl-a (mg · m^–3) to changes in concentrations of total phosphorus (TP) by calculating the slopeS = chl-a/TP in chl-a =f(TP) graphs. Results show that in years where algae are P-limited oligotrophic lakes respond less (median slope 0.21) to changes in nutrient concentrations than eutrophic lakes, (median slope 0.31) and these again less than hypereutrophic lakes, (median slope 1.02). We find no saturation value for the slope within the TP range considered (6–480 mg · m^–3). Chl-a in eutrophic lakes responds more frequently to non-nutrient factors than oligotrophic and hypereutrophic lakes. Results obtained by replacing TP with a new nutrient parameter, TP = 0.056 · TP · IN^0.226, in which inorganic nitrogen, IN, is factored in, suggest that nitrogen has an influence on chl-a in oligotrophic lakes. Blue-green algae respond less to changes in TP than other algal species, e.g., diatoms.     

Prediction of dissolved inorganic nitrogen (DIN) concentrations in deep,seasonally stratified lakes based on rates of DIN input and N removal processes

Mean dissolved inorganic nitrogen concentrations ([DIN]) in deep, seasonally stratified lakes with comparable DIN inputs can differ by up to a factor of 3 depending on hydraulic and morphometric properties and/or different trophic states of the lakes. In such lakes, net N sedimentation rates were estimated with two independent methods (sediment core analysis and input-output mass balances). They were higher in eutrophic lakes (Mean: 5.1; SD: ± 1.6 g m^–2 yr^–1; n = 13) than in oligotrophic lakes (1.6 ± 1.0 g m^–2 yr^–1; n = 3), but independent of [DIN]. Gaseous N loss rates to the atmosphere, as calculated from combined N- and P-mass balances from selected lakes, ranged from 0.9 to 37.4 g m^–2 yr^–1 (n = 10) and were positively correlated with [DIN]. Reduction of NO ₃ ^- to N₂ is assumed to be the main cause for gaseous N losses. A simple one-box mass balance model for [DIN], based on DIN input and rates and kinetics of N removal processes (net sedimentation and gaseous N loss) is proposed, and validated with a data base on [DIN] and DIN input in 19 deep, seasonally stratified lakes of central Europe. The model illustrated that the amount of water loading per unit surface area of a lake (called water discharge height q) is the critical parameter determining mean lake [DIN] relative to mean input [DIN]. Lakes with a q > 50 m yr^–1 have average [DIN] similar to the [DIN] of the inflows regardless of their trophic states, because input and outflow exceed lake-internal N removal processes. A high primary production favors DIN removal in lakes with q < 50 m yr^–1. It is concluded that measures to decrease primary production, e.g. by means of P removal programs, lead to an increase of [DIN] in lakes.     

Dissolved organic carbon in a eutrophic lake; dynamics,biodegradability and origin

The seasonal and spatial changes in dissolved organic carbon (DOC) in Lake Kasumigaura, a shallow, eutrophic lake, were analyzed and the lability of DOC was tested by long-term incubations. There was a nearly 1 mgCl^–1 downstream increase in refractory DOC in the lake; at the center it fluctuated little seasonally. The characteristic UV-absorbance: DOC ratios were determined for samples from the influent rivers (pedogenic: used interchangeably with allochthonous) and outdoor experimental ponds (autochthonous) during incubations. These ratios were then used to calculate the proportion of total measured lake water DOC in each of four components: pedogenic-refractory (PR), pedogenic-labile (PL), autochthonous-refractory (AR) and autochthonous-labile (AL). PR was uniform (around 1.5 mgCl^–1) or diminished very slightly over time. AR increased from nearly zero at the station closest to an influent river to 1 mgCl^–1 at the lake center. PL declined downstream from 0.3 mgCl^–1 to zero. AL was virtually constant at 0.8 mgCl^–1 except at the station closest to the influent river. The constancy of the UV-absorbance: DOC ratio during the biodegradation process was confirmed for Lake Kasumigaura; hence a two-component model (pedogenic-autochthonous) could be applied here without consideration of DOC lability. However, this assumption is not always met for other water bodies, and therefore it should be checked before applying a two-component model elsewhere.     

MELIMEX,an experimental heavy metal pollution study: Chemical speciation and biological availability of copper in lake water

The chemical speciation of dissolved copper was investigated in waters from the limno-corrals of the MELIMEX project and compared with speciation data from other Swiss lakes. Copper is complexed primarily by organic ligands having molecular sizes between 10⁴ and 10³ daltons. The mean concentration of the ligands is approximately 5×10⁻⁷ mole/mg DOC. The conditional stability constants (pH=8.8) are about 10¹¹. An increased metal load did not induce an increase of binding ligands. A comparison of calculated Cu²⁺ concentration with corresponding copper contents in the biomass leads to the conclusion that organic ligands and pH are the most important factors in deciding the biological availability of copper. However the sorption capacity of the biomass depends as well on the variety of plankton species.     

Population dynamics of autotrophic picoplankton in relation to environmental factors in a productive lake

Spatial and seasonal fluctuations in autotrophic picoplankton (APP) abundance in a eutrophic, dimictic lake (Lake Aydat, France) were measured concurrently with a variety of environmental variables. Cell number ranged from 0.03 to 2.36×10⁶ cells·ml^–1 (highest concentrations were >5-fold higher than in oligotrophic lakes) and averaged 24 ± 7% of total picoplankton abundance (APP + heterotrophic bacteria). APP abundance (1) peaked in spring simultaneously with heterotrophic flagellate and ciliate densities, (2) decreased during the nitrogen-limited and summer stratification period, and (3) increased with fall turnover. In summer-autumn, the contribution of single-cell eukaryotic (up to 66%) and colonial prokaryotic (18%) forms to total abundance peaked in the bottom waters. Multivariate regression analyses suggest that >40% variance in APP number changes may be explained by ciliate abundance (at 0–4 m depth-range), heterotrophic flagellate number and oxygen concentration (5–9 m), and ciliate carbon biomass (10–14 m). The model accounting for changes in heterotrophic bacterial abundance (5–9 m) indicates chlorophylla concentration (r ²=58%) and ciliate abundance (r ²=34%) as dominant covariates. The data presented here suggest that micrograzers control APP abundance in Lake Aydat.     

Eutrophisation du Léman indiquée par les communautés d'oligochètes: campagnes 1982–1985

Oligochaete communities (tubificid and lumbriculid worms) were studied between 1982 and 1985 in 23 areas of the mesoeutrophic Lake Geneva (Switzerland). Species numerically dominant in eutrophic lakes (mostlyPotamothrix hammoniensis), in mesotrophic lakes (mostlyP. vejdovskyi) and in oligotrophic lakes (mostlyStylodrilus heringiamus) constituted 52%, 36% et 12% of the worm communities, respectively (means across the 23 areas). The relative abundance of eutrophic species increased (15 to 94%) according to depth or to external organic inputs. In this case, the mean biomass (wet weight) of oligochaetes per area was higher than 15 g·m⁻² (up to 210 g). Mesotrophic species decreased (65 to 1%) along the same gradients of depth or of sedimentation. Oligotrophic species increased (0 to 31%) only in areas where the organic sedimentation was lessened by steep bottom slope and by currents. Thus, the structure of oligochaete communities reflected the patterns of sedimentation and the trophic state of Lake Geneva.      

Comparisons of wetland and drainage lake influences on stream dissolved carbon concentrations and yields in a north temperate lake-rich region

Processes occurring at various scales interact to influence the export of organic carbon from watersheds to freshwater ecosystems and eventually the ocean. The goal of this study was to determine if and how differences in wetland extent and presence of lakes influenced dissolved organic carbon (DOC) concentrations and yields in streams. We monitored stream flow, DOC and dissolved inorganic carbon concentrations periodically for 2 years at four sites with forested watersheds, four sites with wetland watersheds, and four sites with wetland watersheds that also contained in-network lakes. As expected, the presence of wetlands resulted in higher DOC concentrations and yields, but the impact of lakes was less clear on the magnitude of DOC concentrations and yields. With respect to temporal dynamics, we found positive relationships between stream flow and DOC concentration (median r² = 0.89) in streams without upstream lakes. The relationships for forested sites are among the strongest reported in the literature, and suggest a clear shift in hydrologic flowpath from intersecting mineral soils at low flow, to organic soils at high flow. In streams with upstream lakes, the relationship between flow and concentration was non-significant for three of four sites unless time lags with flow were applied to the concentration data, after which the relationship was similar to the non-lake streams (median r² = 0.95). These findings suggest that lakes buffering temporal patterns in streams by hydrologically delaying pulses of carbon, but provide little support that in-line lakes have a net effect on carbon exports in this region.     

Methane levels in shallow subtropical lake sediments: Dependence on the trophic status of the lake and allochthonous input

The vertical sediment profiles (10 cm) of the margins of three shallow subtropical lakes (Rio Grande, Brazil) with different trophic states and surrounding areas were evaluated to identify the effects of the allochthonous input on the methane concentration in the sediment. Sediment cores were collected to quantify the organic matter content (OM) and total carbon (TC), total nitrogen (TN), total phosphorous (TP) and methane (CH₄) concentrations.The three lakes were distinguished according to the trophic status and classified as oligotrophic, dystrophic and eutrophic. The natural characteristics of the dystrophic and eutrophic lakes have been changed due to the allochthonous input of leaves and twigs (Eucalyptus sp.) and the excreta of birds, respectively. In the eutrophic lake, the allochthonous input contributed to high autochthonous production. The highest values of OM, TC, TN and TP were found in the superficial sediments of the dystrophic and eutrophic lakes. The accumulation of allochthonous organic matter in the littoral zone promoted changes in the vertical sediment profiles and contributed to increases in the CH₄ concentrations in the sediment.     

Fluxes and seasonal changes in composition of organic matter in the English Channel

Dissolved and particulate organic matter (DOM and POM) have been investigated along a transect between Cherbourg and the Isle of Wight. In addition, the relative contribution of different sources of POM have been assessed by the use of lipid biomarkers (e.g. fatty acids). Seawater samples were collected at two depths (subsurface and above the bottom) at five stations located on the transect during five cruises (from September 1994 to July 1995). Particulate organic carbon (POC) and dissolved organic carbon (DOC) concentrations vary between 30–530 μg l⁻¹ and 0.5–2.7 mg l⁻¹, respectively, for all the cruises. Fluxes of POM and DOM have been estimated at 0.6×10¹² g yr⁻¹ and 6.5×10¹² g yr⁻¹ of carbon, respectively. General fluxes of water and therefore of DOC and POC are oriented eastward. However, around the Isle of Wight a westward oriented flux exists due to a gyre located in the area. The major DOC and POC fluxes occur in the central part of the Channel where the water column is deepest. Seasonal variations of different sources of POM (algal, bacterial and terrigenous) have been examined for the five cruises. The fresh algal organic fraction is relatively important in September in coastal waters with a predominance of diatom species on the English side, whereas it has a low or undetectable contribution during winter months. The bacterial fraction generally varies in concert with the algal component. It is low during the winter period and more important in bloom or post-bloom conditions, as for example in May. Terrestrial organic matter is restricted to coastal areas in September, and is present at low levels in May and July. Nevertheless, in November and February, terrigenous inputs have been clearly identified for the whole transect even in central waters.     

On the use of UV spectrophotometry to assess dissolved organic carbon origin variations in the Upper Rhône River

To detect temporal changes and the origin of the refractory dissolved organic matter in the Upper Rhône River, UV light absorbance (A) at 285 nm and quantitative dissolved organic carbon (DOC) measurements were carried out. Data from 63 visits to the main channel over a period of two years and from visits to different waterbodies in the alluvial plain before and after a flood are presented. There was a good correlation between A (0.019–0.160) and the DOC content (1.40–9.81 mg/L) for the waterbodies, but not for the river axis with lower A (0.013–0.044) and DOC content (1.13–2.20 mg/L). Due to this good correlation, the DOC content could be quantified for the waterbodies by absorbance measurements only. For the river water this indirect determination of the DOC content was not possible. However, the A/DOC ratio showed changes in the composition of DOC of river water and provided indications about the origin of the dissolved organic matter in the Upper Rhône River.     

Long-term variations of the trophic state index in the Narochanskie Lakes and its relation with the major hydroecological parameters

Variations of the trophic status of lakes Batorino, Myastro, and Naroch were analyzed over a long period of 1978–2013. The lakes form a system of interconnected water bodies with a wide range of trophic states. In the period under consideration, the trophic conditions in the lakes varied from highly eutrophic (Lake Batorino) to oligotrophic (Lake Naroch), making it possible to analyze the long-term changes in the trophic state of the lakes with the use of different variants of evaluating the Carlson index (trophic state index, TSI), to assess the relationship between the three versions of the index with one another, with phytoplankton biomass, and with hydroecological characteristics, such as the concentrations of total N, seston, and organic matter and biochemical oxygen demand. The possibility to evaluate the index by other characteristics, including phytoplankton biomass, was also considered.     

Organic Trace Components Extractable by Chloroform from Swamp and River Waters in the Middle Ob Basin

For the first time in the Middle Ob Basin, new data of importance for evaluating the quality of swamp and river water were obtained, characterizing the microcomponent composition of extractive organic compounds. More than 150 compounds of natural genesis were identified. The water of oligotrophic and mesotrophic bogs shows widest diversity and maximal, almost equal masses of extractable organic substances, averaging 13357 ng/L. In the water of eutrophic bogs and taiga rivers, this characteristic is five times lower; and that in lakes is lower by more than an order of magnitude. The amount of extractive trace components is closely correlated with the concentration of water-soluble carbon of humic nature. It was established that the natural water of taiga zone identical in terms of the fulvate type differs in the composition of organic trace components and can be grouped into four clusters: (a) water of oligotrophic bogs, (b) water of mesotrophic bogs, (c) river water, and (d) water of eutrophic bogs and bog lakes.     

A hydrobiological study to interpret the presence of desmids in Lake Zirahuén, México

Monthly collections of phytoplankton were supported by physical–chemical data and measures of chlorophyll a concentrations in the search for particular environmental factors that could explain the constant presence of desmids in a Mexican tropical lake, a characteristic not common among the phytoplanktic communities of Mexican lakes. Samplings were taken from the water column in the deepest part of the lake (40 m) and intensified in the metalimnetic zone, whose establishment was monitored by observations of temperature and oxygen profiles. The general behavior of Lake Zirahuén was typical of warm monomictic tropical lakes at high elevation: a short mixing phase during the hemispheric winter. The depth of Z_MIX and Z_eu revealed a well-illuminated epilimnion, suggesting that phytoplankton communities are not likely to be light-limited. The oligotrophic nature of the lake is indicated by discrete concentrations of inorganic nutrients, P_TOT in the interval of 0.01–0.03 mg l⁻¹ and chlorophyll a between 0.23 and 3.98 μg l⁻¹. These characteristics together with a low concentration of calcium, define a lacustrine environment different from other Mexican lakes, and one that could be suitable for desmids communities.     

Complexation of aqueous elements by DOC in a clay aquitard

The extent of partitioning of several elements (Cu, Mn, Mo, Ni, Sr, U, and Zn) on dissolved organic carbon (DOC) was investigated in pore water samples collected from a clay-rich aquitard. High DOC concentrations in the aquitard, ranging from 21 to 143 mg C/L, and natural aqueous metal concentrations higher than in most ground water environments facilitated complexation studies at this site. Analyses were conducted using on-line coupling of asymmetrical flow field-flow fractionation with ultraviolet, total organic carbon, and inductively coupled plasma-mass spectrometry detectors. Of the elements investigated, only U and Zn were complexed with all DOC samples, ranging from 2.2 to 60 microg U/g DOC (0.4% to 3% of the total U in the pore water) and 0.04 to 0.5 microg Zn/g DOC (0.1% to 0.9% of the total Zn in the pore water), respectively. Laboratory experiments conducted over a range in pH (1.3 to 9.7) and geochemical modeling supported the measured complexation of U and Zn on the DOC. The in situ association constant, K(d), for U decreased with depth from 76 mL/g C for pore water samples at 2.2 m below ground (BG) to 24 mL/g C at 9.7 m BG. The decrease was attributed to a decrease in aromaticity of the DOC with depth. Zn K(d)constants ranged from 2 to 12 mL/g C and exhibited no trend with depth. Results of the current study suggest minor masses of U and Zn (less than or equal to 4% of total) complex with this DOC under in situ pH conditions. Our data suggest that competitive complexation by other ligands may limit the importance of DOC-facilitated transport of the elements studied in water of similar chemical composition.     

Biosilicium (BSi) in Sedimenten Mecklenburger Seen (Deutschland) und das Calciumcarbonat-Biosilicium-Verhältnis als Trophie- und Wasserstandsindikator Biogenic Silica (BSi) in Sediments of the Mecklenburgian Lake District (Germany) and the Calcite-Silica-Relation as Indicator for Trophy and Water Level

The BSi content has been investigated in the surface sediments of lakes of different trophic state in the Mecklenburgian Lake District. The BSi content differs between 1 to 1000 mg BSi/g dry matter. High values were found in deep eutrophic lakes. Litoral sediments and shallow eutrophic lakes have lower contents. BSi content was found to be correlated with lake morphometry, depth, trophic level, sediment composition and especially with calcite. With the CaCO₃/BSi-value, 3 groups of lakes can be characterized:

• CaCO₃/BSi = 0 oligotrophic and dystrophic lakes
• CaCO₃/BSi ≤ 10 mesotrophic and eutrophic deep lakes
• CaCO₃/BSi ≤ 10 eutrophic shallow lakes

The results from the recent sediments have been compared with those from older sediments. Using the CaCO₃/BSi-value, climatic change, trophic state, and sea level can be detected.     

The effect of light on the release of organic compounds by the cyanobacteriumOscillatoria rubescens

The effect of light intensity on the release of dissolved organic carbon during photosynthesis on NaH¹⁴CO₃ was investigated using the phytoplanktonic CyanobacteriumOscillatoria rubescens. The released products were fractionated by molecular size and chemical identifications attempted using combined thin-layer electrophoresis and chromatography, and high pressure liquid chromatography.Within the range of irradiances tested (from 6 to 60 µmole m^–2 sec^–1), though the upper one inhibited photosynthesis ofO. rubescens, light had little effect on the quantity and composition of the excreted products. The released carbon was always lower than 3% of the incorporated carbon, and mainly composed (62 to 86%) by small molecular weight compounds. The prevailing identified compounds were amino acids which represented more than 20% of the excreted carbon. Among organic acids, glycolic acid accounted for less than 2% of the recovered radioactivity. Glucose was the only identified sugar.Abbreviations EOC excreted organic carbon - DOC dissolved organic carbon - PER percent extracellular release - LMW low molecular weight - HMW high molecular weight - AA amino acids - µmoles m^–2 sec^–1 = µEinsteins m^–2 sec^–1     

Pelagic trophic transfer efficiency in an oligotrophic, dimictic deep lake (Lake Stechlin, Germany) and its relation to fisheries yield

We investigated trophic transfer efficiency in the pelagic food chain of deep, oligotrophic Lake Stechlin (Germany) by analyses of the primary, secondary, and fish production. Primary production between April and November 2000 was estimated at 78 g C m⁻², pelagic secondary production at 14 g C m⁻², and production of the main planktivorous fish species [European cisco, Coregonus albula (L.)] at 0.77 g C m⁻². Thus, trophic transfer efficiency between primary and pelagic secondary production was around 18%, whereas between pelagic and fish production around 6%. The high efficiency at the first step of the chain is discussed to be due to the high food quality in oligotrophic lakes due to the dominance of Bacillariophyceae and Chlorophyceae rich in essential fatty acids. In turn, the relatively low trophic transfer efficiency between the secondary and the fish production is mainly explained by the avoidance of calanoid copepods as food source by the ciscoes. Concerning the trophic transfer efficiency, results from this study support the general assumption of a 10% transfer between neighbouring trophic levels within ecosystems.     

Association between trophic state,watershed use,and blooms of cyanobacteria in south-central Chile

An increase in the distribution and frequency of cyanobacterial blooms has been reported for many regions worldwide. Due to this fact, we studied the variables that influence the abundance of natural populations of planktonic cyanobacteria in temperate lakes of central and southern Chile. These lakes differed in trophic state and watershed use. Cyanobacteria dominated in meso- and eutrophic systems and their occurrence correlated to watershed use (tree plantations and urban). Ochrophyta and Bacillariophyta were dominant in oligotrophic lakes, where native forest dominated land usage. In these lakes, the maximum depth of the euphotic zone influenced the community structure and the genera of cyanobacteria. Dolichospermum was the most abundant, frequent, and widely distributed genus, found in oligotrophic and eutrophic lakes, forming blooms in eutrophic systems.The concentration of total phosphorus and total nitrogen positively influenced cyanobacterial abundance and bloom formation, mainly by Aphanizomenon, Aphanocapsa, Aphanothece, and Dolichospermum, and Microcystis.In contrast to many reports on their occurrence in the northern hemisphere, these genera occurred widely at less than 20 °C, forming dispersive blooms, at low temperatures in autumn and winter (10.8–15.6 °C). This shows that eutrophication is the main factor for bloom formation and these genera can form blooms independent of temperature. However, some genera, such as Microcystis, increased their abundance and presented more intense blooms (scums) at high temperatures. Our study provides baseline data to document long-term changes in lentic systems of the western south-central area of South America, including genera that could respond by increasing their abundance with eutrophication and projected climatic changes.