Copper complexation in eutrophic and humic Lake Tjeukemeer, The Netherlands

SUMMARY. 1. Copper(II) complexation in the eutrophic. humus-rich Lake Tjeukemeer was measured fortnightly for several years by copper titration (Ion Selective Electrode) and by copper solubilization. Additionally, the copper speciation during titration was followed by ultrafiltration.
2. The Tjeukemeer showed high ligand concentrations able to complex up to 8.5X10^-5 M Cu.
3. Scatchard plots and affinity spectra of the titration data allowed the discrimination of at least three different binding sites. In Scatchard plots log K values ranged from 5 to 9, in affinity spectra from 4.5 to 8.
4. The highest log K values coincided with relatively low humus concentrations and blooms of algae, mainly Cyanobacteria.
5. The ultrafiltration experiments indicated that relatively small size fractions (<10 nm) have the highest copper binding affinity.     

Biological availability and humic properties of dissolved organic carbon in Lake Balaton (Hungary)

The nursery role of the Mondego estuary for marine fish species was studied between June 2003 and May 2004. The spatial and temporal distribution and abundance patterns of 0-group Dicentrarchus labrax (Linnaeus, 1758), Platichthys flesus (Linnaeus, 1758) and Solea solea (Linnaeus, 1758) were analyzed based on monthly sampling surveys in five stations along the estuarine gradient. Fishing took place during the night at low water of spring tides, using a 2 m beam trawl. The spatial patterns of estuarine colonization were different according to species. D. labrax showed a wider distribution, but the main nursery ground was the same as for S. solea. Highest densities of S. solea juveniles were found in oligohaline areas, with muddy bottoms and high benthic invertebrates availability, while P. flesus occurred mainly in the sandy uppermost areas. D. labrax was found in both these areas. Fish abundance in the estuary mainly reflected seasonal changes.     

Distribution of dissolved organic carbon and dissolved fulvic acid in mesotrophic Lake Biwa, Japan

The dissolved organic carbon (DOC) concentrations in mesotrophic Lake Biwa were determined by a total organic carbon (TOC) analyzer, and DOC molecular size distributions were determined by size exclusion chromatography (SEC) using a fluorescence detector at excitation/emission (Ex/Em) levels of 300/425 nm with the eluent at pH 9.7. The fluorescence wavelengths for detection were chosen from the result of excitation–emission matrix spectrometry (EEM) analysis for dissolved fulvic acid (DFA) extracted from Ado River (peak A, Ex/Em = 260–270/430–440 nm; peak B, Ex/Em = 300–310/420–430 nm). Ado River DFA was eluted with a retention time (RT) of 7.4–8.9 min and the apparent molecular weight was estimated at 22–87 kDa based on the elution curve for the spherical protein molecular weight standard. A DFA peak eluted at the same retention time as Ado River DFA also appeared in all the samples of Lake Biwa water. From the linear relationship between the peak areas with an RT of 7.4–8.9 min by SEC analysis and DOC values of DFA by TOC analysis of a series of DFA samples (r² = 0.9995), the concentrations of DFA in the lake water were roughly calculated. DFA was distributed within the range 0.25–0.43 mg C l⁻¹ and accounted for 15%–41% of DOC, with the highest ratios observed at a depth of 70 m in August and the lowest at 2.5 m in May.     

Distribution of dissolved organic carbon in Lake Baikal and its watershed

 Concentrations of dissolved organic carbon (DOC) in Lake Baikal ranged from 90 to 110 μM C, considerably higher than those in oceanic environments. The DOC concentrations in the epilimnion were higher than those in the hypolimnion. Since particulate organic carbon (POC) concentrations in the pelagic waters of Lake Baikal were <10–40 μM C in the epilimnion and 2–5 μM C in the hypolimnion, DOC constitutes a major component of the organic carbon pool in Lake Baikal, especially in the deep layers. The DOC concentrations downstream of the Barguzin and Selenga Rivers were quite high (400–500 μM C). Probably because of the high concentrations of DOC in these rivers, the DOC levels in Barguzin Bay and offshore at the mouth of the Selenga River were higher than those in the pelagic regions of the central and south basins of Lake Baikal. The relationship between DOC and electric conductivity revealed the transport of DOC from rivers to the pelagic area in Lake Baikal. The spatial distribution of DOC suggested that a major part of DOC in the lake was allochthonous (land-derived). Received: July 26, 2002 / Accepted: September 16, 2002 Present address:Research Institute for Humanity and Nature, 335 Takashima-cho, Marutamachi Kawaramachi, Kamigyo-ku, Kyoto 602-0878, Japan Tel. +81-75-229-6167; Fax +81-75-229-6150 e-mail: yos@chikyu.ac.jp Acknowldgments The authors wish to thank Director Prof. M. Grachev and Dr. O. Timoshkin of the Limnological Institute, Siberian Branch, Academy of Science, Russia, for arranging the cruise on Lake Baikal. We are also indebted to Drs. V. Sinyukovich, I. Khanaev, and A. Zhdanov for their kind assistance during the expeditions. We wish to thank Ms. Y. Ito for measuring the DOC concentrations. This work was supported and financed by Grants-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan (No. 09041159) and for Scientific Research of Priority Area B (No. 11213101) and by the International Geosphere-Biosphere Programme (IGBP) at Nagoya University. Correspondence to:T. Yoshioka     

Distribution patterns of zooplankton in Tjeukemeer, The Netherlands

The vertical and horizontal distribution of Copepoda and Cladocerain Tjeukemeer were studied. Indices of dispersion are discussed,the sample variance of log-transformed data proved to be anappropriate way to quantify patchiness. Indices of dispersionwere calculated to express species specific differences. Onlyduring short periods of the year the population densities appearedto be influenced by canals and pumping stations that bring waterto the lake. Dispersion values were influenced by windspeed,inhomogenities in the chlorophyll-a concentrations and by thepopulation densities of the populations studied. Sample variancesare relatively low, compared with those of other lakes.     

Availability of dissolved organic carbon for planktonic bacteria in oligotrophic lakes of differing humic content

Bacterioplankton from 10 oligotrophic lakes, representing a gradient from clearwater to polyhumic, were grown in dilution cultures of sterile filtered lake water. The bacterial biomass achieved in the stationary phase of the dilution cultures was positively correlated with the amount of both humic matter and dissolved organic carbon (DOC) in the lakes. About the same fraction of the total DOC pool was consumed in the dilution cultures of all lakes (average 9.5%, coefficient of variation (CV) 24%), with approximately the same growth efficiency (average 26%, CV 28%). Thus, humic lakes could support a higher bacterial biomass than clearwater lakes due to their larger DOC pools. The relevance of the results to planktonic food webs of humic and clearwater lakes is discussed.     

The relation of biotic and abiotic interactions to eutrophication in Tjeukemeer,The Netherlands

During the summer months of 1974–1985 chlorophyll-a and total P concentration, biomass of Daphnia hyalina, smelt Osmerus eperlanus, bream Abramis brema and pikeperch Stizostedion lucioperca, water temperature and water intake from lake IJsselmeer were monitored in Tjeukemeer. During this period there were manipulations with the bream and pikeperch stocks as a consequence of the termination of a gill-net fishery in 1977, and larval smelt immigrated each year from the large lake IJsselmeer and contributed largely to the yearly smelt recruitment.The correlation matrix of the nine variables mentioned above showed a positive correlation between bream and chlorophyll-a, but surprisingly a negative one between smelt and chlorophyll-a. The latter can only be explained when smelt is the dependent variable. In a multi-linear regression there was a negative effect of temperature, chlorophyll a and pikeperch on smelt and a positive effect of water intake. Daphnia hyalina was negatively influenced by the biomass of smelt and the water intake of lake IJsselmeer. The positive relation of Daphnia hyalina and chlorophyll-a was probably related to better survival chances of D. hyalina in an Oscillatoria-rich environment when smelt is the most important predator. An increasing biomass of bream coincided with higher total-P levels and probably contributed to higher chlorophyll-a levels.     

The relation between bacterial carbon and dissolved humic compounds in oligotrophic lakes

Abstract The mean annual biomass of planktonic bacteria showed large variations both within and between lakes. The lowest bacterial biomass was found in acidified lakes (7.8–12.1 μg C · 1⁻¹), and tended to increase with increasing water colour (up to 44.1 μg C · 1⁻¹). The highest recorded bacterial biomass was 138 μg C · 1⁻¹. The mean annual bacterial biomass equalled 23–45% of the algal biomass. Zooplankton biomass was high, compared to algal biomass (40–50%). Multiple regression analysis of 10 variables showed a strong positive correlation between bacterial biomass and humic content ( r = 0.74, P < 0.001), while other parameters, except pH, showed no correlation. The observation thus strongly supports the role of humic compounds in aquatic secondary production.     

Influence of soil temperature and moisture on the dissolved carbon,nitrogen, and phosphorus in organic matter entering lake ecosystems

Concentrations of terrestrially derived dissolved organic matter (DOM) have been increasing in many north temperate and boreal lakes for over two decades. The concentration of DOM in lakes is influenced by a number of environmental factors, but there is still considerable debate about how the availability of terrestrial DOM, and associated dissolved nitrogen and phosphorus, may be affected by drivers of climatic change. Using experimental and observational methods, we considered how changes in soil temperature and moisture affected the composition of carbon, nitrogen, and phosphorus entering freshwater lakes. In our experiment, organic soil cores were collected from the wetland shoreline of a darkly-stained seepage lake in northern Wisconsin, USA and manipulated in laboratory with temperature and moisture treatments. During the 28-day study, soil leachate was sampled and analyzed for optical properties of DOM via UV/Vis absorbance, as well as concentrations of dissolved organic carbon (DOC), total dissolved nitrogen, and total dissolved phosphorus (TDP). DOM optical properties were particularly sensitive to moisture, with drier scenarios resulting in DOM of lower molecular weight and aromaticity. Warmer temperatures led to lower DOC and TDP concentrations. To consider long-term relationships between climate and lake chemical properties, we analyzed long-term water chemistry data from two additional Wisconsin lakes from the long term ecological research (LTER) project in a cross correlation analysis with Palmer drought severity index data. Analysis of the LTER data supported our experimental results that soil moisture has a significant effect on the quality of DOM entering lakes and that climate may significantly affect lake chemical properties. Although unexpected in terms of DOM loading for climate change scenarios, these results are consistent with patterns of decomposition in organic soils and may be attributed to an increase in soil DOM processing.     

Quantification and characterization of dissolved organic carbon and iron in sedimentary porewater from Green Bay,WI, USA

Both dissolved organic carbon (DOC) and iron play an important role in biogeochemical processes in lacustrine benthic environments. Moreover, recent evidence has shown that both substances can act as active reductants in the redox transformation of organic pollutants. This paper examines the nature and abundance of DOC and dissolved ferrous iron (Fe^II) in porewaters from a sediment core collected in Green Bay, WI, USA. The concentration of dissolved Fe^II and the abundance, absorbance at 280 nm (A _{280 nm}), molar absorptivities (_{280 nm}), molecular weights, and polydispersities of DOC were measured as a function of depth in porewaters. Dissolved Fe^II concentrations increased from 3.6 M near the sediment–water interface to 163 M at a depth of 11 cm, then gradually declined. The DOC distribution varied with sediment depth, with the greatest variation in porewater DOC content and properties occurring in the transitional zone between oxic and suboxic conditions. The down-core porewater DOC profile was characterized by an increase in DOC concentration with depth from 0.64 mM OC at 1 cm to 1.23 mM OC at 13 cm, below which it remained relatively constant. A strong correlation was observed between Fe^II and DOC concentrations, suggesting that these constituents co-accumulate in these porewaters. The correlation between the DOC concentration of the porewaters and A _{280 nm} was significant, making this parameter a good predictor for DOC concentrations in these waters. The molecular weight distributions of the porewater DOC were primarily monomodal, with relatively low polydispersivities. Weight-average molecular weights ranged from 1505 to 1949 Da. This data set is unique in that it is the first detailed study of a relatively highly resolved DOC profile of benthic porewater in surficial sediment from the Laurentian Great Lakes.     

Dissolved organic carbon and fluorescence in Lake Hovsgol: factors reducing humic content of the lake water

 Lake Hovsgol is a large tectonic lake located in northern Mongolia, which has extremely transparent lake water. In our survey, the dissolved organic carbon of the lake water was 80–100 μM-C, and the fluorescence intensity in an excitation and emission matrix was very low. The brown color and high content of humic substances in river water flowing from a watershed consisting of grassland and forests rapidly declined in the coastal area of the lake. The decrease in humic content may be due not only to dilution by the lake water but also to flocculation and photobleaching. Among tectonic lakes in Asia, Lake Hovsgol would appear to have unique biological and hydrological features that reduce humic content and help to maintain water transparency. Received: June 25, 2002 / Accepted: January 10, 2003 Acknowledgments The authors acknowledge helpful discussion with Dr. J. Urabe. We thank Dr. T. Galbaatar, Mongolian Academy of Science, Mongolia, for his arrangements on the expeditions in 1999. We are also indebted to Mr. D. Hadbaatar, B. Ganbat, and the cruise staff of the R/V Suchbaatar for their assistance in the course of the study. This study was supported by Grant-in-Aid No. 09041159 and 13575034 for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology of Japan. Correspondence to:K. Hayakawa     

The role of dissolved organic matter, particularly free amino acids and humic substances, in freshwater ecosystems

1. Although the mass of dissolved organic matter (DOM) often exceeds that of living organisms in freshwaters, little is known about the roles of its constituent molecules as sources of energy and information for aquatic organisms. In the present review attention is focused on free amino acids (FAA) and humic substances (HS) as examples of labile and refractory components within DOM. 2. The following questions are addressed. (i) What are spatiotemporal patterns in the distribution of DOM, HS and FAA? (ii) What are the origins of the components of DOM and how are their concentrations regulated? (iii) What is the significance of the spatial and temporal distributional patterns of DOM, HS and FAA to detritivorous invertebrates and other organisms associated with them? (iv) What is the relevance of DOM to the food web concept and to the biochemical ecology of freshwater ecosystems? 3. Concentrations of DOM, FAA and HS within lentic ecosystems are ranked as follows: Sediment pore water > Air–water interface > Midwater column. Comparisons between water bodies show that the concentrations of labile constituents of DOM, such as FAA, are usually positively correlated with base cations, nutrients and biological activity. In contrast, HS concentrations are negatively correlated with base cations or nutrients but positively correlated with the rate of biological degradation (the maximum values occurring in the autumn). The FAA : HS ratios might serve therefore as an indicator of the potential productivity of a water body. 4. External sources of DOM in general, and FAA and HS in particular, include rainwater, windborne material, surface flow and groundwater. The relative importance of these allochthonous sources of DOM decreases along the length of lotic ecosystems and also with increase in size of lentic ecosystems. Internal sources of FAA and HS include synthesis or polymerization from existing organic matter, degradation of organic matter and release from both living and dead organisms. The net accumulation of DOM released by living bacteria, phytoplankton, epilithon, macrophytes and invertebrates is much reduced due to heterotrophic uptake. Hence, most of the allochthonous DOM in freshwater originates from dead organic matter deposited on the sediment. Phytoplankton-dominated ecosystems may, however, differ, as most of their DOM may be recycled within the water column. 5. The factors that determine the external concentrations of DOM, FAA and HS are discussed. Evidence is cited in support of the following testable hypotheses. (i) The rates of production of DOM components will be favoured by increasing base cation and nutrient concentrations. (ii) Colloidal clay, base cations, biopolymers and living organisms, particularly bacteria, facilitate the removal of HS. Consequently, base-rich eutrophic waters tend to have lower HS concentrations than oligotrophic, base-deficient waters. (iii) As a result of higher productivity and selective removal of FAA, eutrophic waters tend to have higher FAA concentrations than those that are oligotrophic. 6. Labile DOM components, such as FAA, act as sources of information for aquatic organisms. More research is needed in this field. There is a consensus that DOM acts as an important source of energy for aquatic bacteria, thus forming the microbial loop. However, higher eukaryotic organisms also utilize DOM, including components released by bacteria and plants as metabolic end-products and photoassimilates, respectively. As a result, these DOM components may be more important as food for macrodecomposers than the microdecomposers themselves. HS may also benefit aquatic organisms by promoting their growth and protecting them from inimical forces. Conversely, the removal of photons and the release of toxins by HS may be detrimental to aquatic organisms. 7. It is concluded that the central dogma of the foodweb, and its implicit assumption that the energy flow in aquatic ecosystems can be quantified solely by measuring rates of photosynthesis, ingestion of solid food and its digestion by higher organisms, is invalid. To extend our understanding of the role of DOM as a source of nutrition and information to aquatic organisms it is suggested that the subject should be studied within the context of ‘modules’ which have the following properties: (i) the components have co-evolved; (ii) the more vulnerable components will have protective mechanisms; (iii) the components will derive mutual benefits from co-existence; (iv) sedentary components will release kairomonal attractants or developmental primers; (v) living components will exchange energy and information; (vi) the module will collapse following the removal of strongly interactive keystone species. An example of a three-component, three-subset module, is provided by tubificid worms, epilithic bacteria and algae. A more complex module consisting of pulmonate snails, associated macrophytes, their epiphytic bacteria and algae has four components and six subsets. The elucidation of the interactive mechanisms within such modules demands an interdisciplinary approach, involving microbiology, biochemistry and behavioural biology.     

Fluctuation of algal alkaline phosphatase activity and the possible mechanisms of hydrolysis of dissolved organic phosphorus in Lake Barato

For freshwater cyanobacteria, the autofluorescence of phycocyanin is quite high while the in vivo fluorescence (IVF) yield of chlorophyll-a is relatively low, apparently because of low chlorophyll concentrations associated with photosystem II. In eucaryotic phytoplankton, even those with phycobili-protein accessory pigments (e.g. some cryptophytes), the opposite is true. Thus, an IVF ratio which relates phycocyanin to chlorophyll-a signals could be a good index of relative cyanobacterial abundance in the field. Spectrofluorometric scans of whole cells from laboratory cultures indicated that the ratio Em₆₆₀ @ Ex₆₃₀/Em₆₈₀ @ Ex₄₃₀ could be a very sensitive cyanobacterial indicator. Tandem flowthrough fluorometers were then fitted with the appropriate interference filters and their discriminatory power was evaluated with mixtures of cyanobacterial and eucaryotic phytoplankton. Although subject to many of the constraints of other IVF assays, tandem fluorometry should be particularly appropriate for real-time mapping of the relative spatial and temporal distributions of broad phytoplankton taxa in continuous vertical of horizontal profiles in lakes.     

Transport and fate of dissolved organic carbon in the Lake Pontchartrain esutary,Louisiana, U.S.A.

Cycling dynamics of dissolved organic carbon (DOC) were examinedin Lake Pontchartrain estuary, Louisiana, in relation to changesin freshwater inputs. DOC concentrations ranged from 5.3 to 8.5mg C L-1 reaching their highest during high river inflow.The percentage of DOC represented by HMW DOC (or colloidal material)was greatest (ca. 11%) at stations where freshwaterdischarge from rivers and surrounding wetlands was most significant.Moreover, the lignin-phenol content of this material (ranged from 0.09 to 0.33 and from 0.11 to 0.39)confirmed that a significant fraction of colloidal organic carbon wasderived from terrestrial sources. Riverine and benthic fluxes representedthe dominant sources of DOC to the estuary. On an annual basis, riverineand benthic DOC concentrations were estimated to be 2.8 ×10 10 g C yr-1 and 8.8 × 10 10 g C yr-1, respectively, while the totalDOC pool in the estuary was 3.8 × 10 10 gC. Annual average concentrations of dissolved inorganic carbon (DIC)(1298 M) and pCO2 (5774 atm)were comparable to those found in other freshwater systems that reachedCO2 saturation levels. Net losses of DOC in the LakePontchartrain estuary appeared to be primarily controlled by heterotrophicconsumption (conversion of CO2) – whichmay have been amplified by the long residence time (approximately 120days) of DOC in this system.     

Bioavailability and size-fraction of dissolved organic carbon, nitrogen, and sulfur at the Arbutus Lake watershed, Adirondack Mountains, NY

The heterogeneity of DOM is closely linked with the various sources and the diversity of biogeochemical processes. We studied the spatial and temporal patterns of the quantity (bioavailable [B-] and refractory concentrations by laboratory incubations) and quality (δ¹³C, aromaticity, and size-fraction by ultrafiltration [low molecular weight (LMW) < 1 kDa and high molecular weight (HMW) > 1 kDa]) of dissolved organic C (DOC), N (DON), and S (DOS) for surface waters (two upland streams, two wetland-affected streams, and lake outlet) over a 14-month period within the Arbutus Lake watershed in the Adirondack Mountains of New York State, USA. The % BDOC and % BDON of this watershed averages ranged from 6 to 18 % and from 12 to 43 %, respectively. The DOC and DON concentrations increased as water was transported through wetland areas of the Arbutus Lake watershed. DOC and DON constituents in the surface waters passing through a wetland were composed mostly of refractory HMW components (% HMWDOC: 55 %, % HMWDON: 60 %) with a higher level of aromaticity compared to upland streams (% HMWDOC: approximately 35 %, % HMWDON: approximately 30 %). DOS was dominated by the refractory (% BDOS range 6–13 %) and LMW (% LMWDOS range 62–96 %) form and we suggest that bacterial dissimilatory sulfate reduction might play an important role in generating this distinct DOS biogeochemistry. The aromaticity was positively related to total DOC concentration, but negatively to % BDOC. Arbutus Lake DOM was dominated by bioavailable and LMW characteristics, compared to wetland-affected streams where refractory and HMW DOM fractions were more prevalent. Our study suggests the different variability of DOM characteristics among elements (C, N, S) using a “bioavailability-molecular size model” showing a diagenetic perspective due to the relative refractoriness of the LMW DOS. This study also highlights the importance of multiple approaches for understanding DOM biogeochemistry with respect to molecular size, bioavailability, aromaticity, stoichiometry, isotopic values, and elemental concentrations.     

Size distribution of dissolved (<200 nm) organic carbon and aluminium in alkaline and humic lakes

Chemical equilibrium calculations treating humic substances as the simple diprotic phtalic acid, predicted no Al-humus at pH>6.5 in humic lake water. However, dissolved (<200 nm) organic carbon (DOC) and dissolved Al appeared to be linearly (r=0.597, P<0.001) correlated in samples from five different humic surface waters in The Netherlands with a DOC range of 10–36 mg.l^–1 and a (mean) pH range of 6.85–8.47. Yet, organic carbon (C_org) and Al did no exhibit similar size distributions between 5 and 200 nm revealed by ultrafiltration. Averaged 25% of the C_org and >50% of the Al occurred in the fraction <5 nm. Only in this fraction the C_org and Al were linearly correlated (r=0.515, P<0.001). This result suggests the presence of organic ligands in the DOC pool of humic waters having smaller molecular sizes and higher Al stability constants than the humic substances used to model aquatic Al speciation.     

Essential fatty acids and phosphorus in seston from lakes with contrasting terrestrial dissolved organic carbon content

1. It is often assumed that lakes highly influenced by terrestrial organic matter (TOM) have low zooplankton food quality because of elemental and/or biochemical deficiencies of the major particulate organic carbon pools. We used the biochemical [polyunsaturated fatty acids, especially eicosapentaenoic acid (EPA) – 20:5ω3] and elemental (C : P ratio) composition of particulate matter (PM) as qualitative measures of potential zooplankton food in two categories of lakes of similar primary productivity, but with contrasting TOM influence (clear water versus humic lakes). 2. C : P ratios (atomic ratio) in PM were similar between lake categories and were above 400. The concentration (μg L⁻¹) and relative content (μg mg C⁻¹) of EPA, as well as the particulate organic carbon concentration, were higher in the humic lakes than in the clear‐water lakes. 3. Our results show high fatty acid quality of PM in the humic lakes. The differences in the biochemical quality of the potential zooplankton food between lake categories can be attributed to the differences in their phytoplankton communities. 4. High biochemical quality of the food can result in high efficiency of energy transfer in the food chain and stimulate production at higher trophic levels, assuming that zooplankton are able to ingest and digest the resource available.