Lake Trophic Status Research Articles

Recent sedimentary legacy of sockeye salmon (Oncorhynchus nerka) and climate change in an ultraoligotrophic, glacially turbid British Columbia nursery lake

Paleolimnological studies of sockeye salmon ( Oncorhynchus nerka ) nursery lakes have shown that lake trophic status is often regulated by climate and harvest via marine-derived nutrients (MDN) from adult spawners. However, these controls are not well understood for sockeye nursery lakes in coastal British Columbia, many of which are ultraoligotrophic and glacially turbid. We examined climate, sockeye population dynamics, and sedimentary indicators of lake algal production from 1958 to 2005 using a radioisotope-dated sediment core from Kitlope Lake, British Columbia. Despite high sedimentation rates (~4.7 mm·year–1), significant influence of terrestrial and aquatic organic matter from the main tributary, and the lowest mean (± standard deviation) δ15N (–0.28‰ ± 0.79‰; a proxy for MDN flux) yet reported from a sockeye nursery lake, sedimentary δ15N, C–N ratio, and fossil pigments were coherent with order-of-magnitude changes in sockeye escapements. Moreover, air temperatures were positively correlated with δ15N, indicating a climate influence counteracting declines of MDN import related to declining spawner returns. Despite elevated production potential, Kitlope Lake remains nutrient-limited with a declining sockeye population, and the productivity of this system would benefit from increased sockeye returns.

A multi-proxy paleolimnological reconstruction of trophic state reference conditions for stratified carbonate-rich lakes in northern Germany

This study aims to identify reference conditions (nutrient status and diatom assemblages) as required by the European Water Framework Directive (WFD) for stratified, carbonate-rich lowland lakes with a large watershed area (watershed area to lake volume ratio (WV) > 1.5 km2 10−6 m−3) and a retention time (RT) from 0.1 to 10 years (Central Baltic Lake-Type 1, German Lake-Type 10) in European ecoregion 14. Diatoms, pollen and geochemistry were analysed from sediment cores of six lakes from northern Germany representing different subtypes of Lake-Type 10 (varying WV and RT) and covering the past 290–1,750 years. Historic total phosphorus levels were inferred using diatom-based transfer functions selected from a merged European data set and from optimised data sets identified with the moving-window approach. Pollen and geochemical proxies were used to identify occurrence and intensity of anthropogenic catchment usage. Lake trophic state reference conditions and associated diatom assemblages were identified for three of the six study lakes. In contrast, according to fossil pollen assemblages, two lakes were already strongly impacted by intensive catchment usage when the oldest investigated sediments were laid down. Thus, reference conditions of these already eutrophic lakes could not be identified. Similarly, the lowermost samples of a core from the sixth lake showed signs of impact, and it remains unclear whether the identified dystrophic conditions occurred naturally or if they were due to the drainage of wetlands in Medieval times. Lakes with a relatively small WV (1.5–5.0 km2 10−6 m−3) and RT > 1 year were naturally oligotrophic to low mesotrophic and a typical, representative diatom assemblage was identified. In contrast, typical reference conditions or diatom assemblages for lakes with higher WV (5–18.6 km2 10−6 m−3) and RT < 1 year could not be identified as chemical precipitation and upstream lakes (nutrient sinks or sources) additionally influenced natural nutrient levels. Therefore, the reference situation of both trophic state and diatom assemblages in a lake may be strongly influenced by other modifying, limnological processes in addition to WV and RT. Overall, this study helps to implement the WFD by identifying reference conditions and by discussing the level of differentiation of lake types required to set reference conditions.

Lability of organic carbon in lakes of different trophic status

Summary1. We used first‐order kinetic parameters of biological oxygen demand (BOD), the constant of aerobic decomposition (k) and the asymptotic value of BOD (BODult), to characterise the lability of organic carbon pools in six lakes of different trophic state: L. Naroch, L. Miastro and L. Batorino (Belarus), L. Kinneret (Israel), L. Ladoga (Russia) and L. Mendota (U.S.A.). The relative contributions of labile and refractory organic carbon fractions to the pool of total organic carbon (TOC) in these lakes were quantified. We also determined the amounts of labile organic carbon within the dissolved and particulate TOC pools in the three Belarus lakes.2. Mean annual chlorophyll concentrations (used as a proxy for lake trophic state) ranged from 2.3 to 50.6 μg L−1, labile organic carbon (OCL = 0.3BODult) from 0.75 to 2.95 mg C L−1 and k from 0.044 to 0.14 day−1.3. Our data showed that there were greater concentrations of OCL but lower k values in more productive lakes.4. In all cases, the DOC fraction dominated the TOC pool. OCL was a minor component of the TOC pool averaging about 20%, irrespective of lake trophic state.5. In all the lakes, most (c. 85%) of the DOC pool was refractory, corresponding with published data based on measurements of bacterial production and DOC depletion. In contrast, a larger fraction (27–55%) of the particulate organic carbon (POC) pool was labile. The relative amount of POC in the TOC pool tended to increase with increasing lake productivity.6. Long‐term BOD incubations can be valuable in quantifying the rates of breakdown of the combined particulate and dissolved organic carbon pools and in characterising the relative proportions of the labile and recalcitrant fractions of these pools. If verified from a larger number of lakes our results could have important general implications.

The Planktonic Index of Biotic Integrity (P-IBI): An approach for assessing lake ecosystem health

Using historical (1970) and more recent (1996) Lake Erie plankton and trophic status data, we developed a Planktonic Index of Biotic Integrity (P-IBI) to measure changes in lake ecosystem health. We used discriminant analysis to determine phytoplankton and zooplankton community characteristics (metrics) that distinguished among levels of impairment. Traditional measures of lake trophic status classes (i.e., oligotrophic, mesotrophic, eutrophic), such as chlorophyll a and total phosphorus concentrations, were used to classify sites on a gradient of impairment. We then judged the ability of plankton metrics to distinguish among trophic status classes. Because of the temporal variability found in plankton communities, we conducted analyses on a monthly basis (May–September). For June, July and August we found five unique metrics that could distinguish among trophic status classes. The P-IBI showed an increase in water quality in Lake Erie between 1970 (<3 = eutrophic) and the mid-1990s (1996 and 1997) (3–4 = mesotrophic) (which reflected mean (±standard error) total phosphorus concentrations (μg/L) 1970 > 1996; western basin (41.53 ± 2.68 > 29.75 ± 1.39), eastern basin (14.84 ± 0.82 > 7.74 ± 0.28) and mean (±standard error) chlorophyll a concentrations (μg/L) uncorrected for pheophytin 1970 > 1996; western basin (12.58 ± 1.82 > 5.40 ± 0.22), central basin (5.90 ± 0.36 > 3.17 ± 0.54), and eastern basin (5.17 ± 0.38 > 1.67 ± 0.18)), with declining water quality in the late 1990s (1998 and 1999) (∼3) and 2002 (<3). We recommend that the techniques used in creating the P-IBI be investigated for determining ecosystem health of other lakes.

Development of predictive models for geosmin-related taste and odor in Kansas, USA, drinking water reservoirs

The presence of taste and odor compounds can greatly reduce the quality of drinking water supplies. Because the monetary costs associated with the removal of these compounds can be high, it is impractical for most facilities to continuously treat their raw water. Instead, new tools are needed to help predict when taste and odor events may be most likely to occur. Water quality data were collected between June and October in 2006–2007 from five Kansas (USA) reservoirs in order to develop predictive models for geosmin, a major taste and odor compound; two of these reservoirs were also sampled during specific taste and odor events in December 2006 and January 2007. Lake trophic state alone was not a good predictor of geosmin concentrations as the highest average geosmin concentration was observed in the reservoir with the lowest nutrient and chlorophyll a concentrations. In addition, taste and odor events were not confined to summer months; elevated geosmin concentrations were observed in several reservoirs during the winter. Growth limitation by inorganic phosphorus appeared to be the primary determinant of geosmin production by algal cells in these reservoirs.

Variations and controls of nitrogen stable isotopes in particulate organic matter of lakes

Nitrogen stable isotope (delta(15)N) data of particulate organic matter (POM) from the literature were analyzed to provide an understanding of the variations and controls of delta(15)N(POM) in lakes at the global scale. The delta(15)N(POM) variability characterized by seasonal mean, minimum, maximum, and amplitude (defined as delta(15)N(POM) maximum -- delta(15)N(POM) minimum) from 36 lakes with seasonal data did not change systematically with latitude, but was significantly lower in small lakes than in large lakes. The seasonal mean delta(15)N(POM) increased from oligotrophic lakes to eutrophic lakes despite large variations that are attributed to the occurrences of nitrogen fixation across the trophic gradient and the differences in delta(15)N of dissolved inorganic nitrogen (DIN) in individual lakes. Seasonal mean delta(15)N(POM) was significantly correlated with DIN concentration and delta(15)N(DIN) in two subsets of lakes. Seasonal minimum delta(15)N(POM) in individual lakes is influenced by nitrogen fixation and delta(15)N(DIN) while seasonal maximum delta(15)N(POM) is influenced by lake trophic state and delta(15)N(DIN). As a result of the dominance of non-living POM in the unproductive surface waters, seasonal delta(15)N(POM) amplitude was small (mean = 4.2 per thousand) in oligotrophic lakes of all latitudes. On the other hand, seasonal delta(15)N(POM) amplitude in eutrophic lakes was large (mean = 10.3 per thousand), and increased from low to high latitudes, suggesting that the seasonal variability of delta(15)N in the phytoplankton-dominated POM pool was elevated by the greater spans of solar radiation and thermal regimes at high latitudes. The delta(15)N(POM) from 42 lakes with no seasonal data revealed no consistent patterns along latitude, lake area, and trophic gradients, and a greater than 2 per thousand depletion compared to the lakes with seasonal data. Along with the large seasonal variability of delta(15)N(POM) within lakes, these results provide insightful information on sampling design for the studies of food web baseline in lakes.

The effects of residential docks on light availability and distribution of submerged aquatic vegetation in two Florida lakes

Campbell, K.R. and R.Baird. 2009. The effects of residential docks on light availability and distribution of submerged aquatic vegetation in two Florida lakes. Lake Reserv. Manage. 25:87–101. This study was conducted to determine the effects of residential docks on the density and diversity of submerged aquatic vegetation (SAV) within two freshwater lakes in Orange County, Florida: Lake Butler and Lake Jessamine. From a lake manager's perspective, an improved understanding of the effects of docks should result in better planning and management to help ensure that additional docks do not harm the aquatic environment, while still providing reasonable access to the water. Major issues considered in this study included whether the amount of light penetrating beneath a dock affected the density and diversity of SAV growing beneath it, and whether other variables affected the density and diversity of SAV beneath docks, including lake trophic status. Ten docks and 10 reference sites were surveyed in each lake in June and July 2007. During each survey, we collected numbers and species of SAV, field water quality, surface and underwater light, dock measurements, and surrounding condition information. We documented a reduction in available light under docks with a corresponding decrease in plant density. Density of SAV was higher under docks oriented north/south compared to those oriented east/west. Overall, turbidity had the most influence on SAV diversity, while Secchi depth had the most influence on SAV diversity under docks. For this investigation overall, including beneath docks, SAV density was most affected by the percent of surface light above the SAV/bottom, while SAV diversity was most affected by the clarity of the water.

Effect of Lake Trophic Status and Rooted Macrophytes on Community Composition and Abundance of Ammonia-Oxidizing Prokaryotes in Freshwater Sediments

Communities of ammonia-oxidizing archaea (AOA) and bacteria (AOB) in freshwater sediments and those in association with the root system of the macrophyte species Littorella uniflora, Juncus bulbosus, and Myriophyllum alterniflorum were compared for seven oligotrophic to mesotrophic softwater lakes and acidic heathland pools. Archaeal and bacterial ammonia monooxygenase alpha-subunit (amoA) gene diversity increased from oligotrophic to mesotrophic sites; the number of detected operational taxonomic units was positively correlated to ammonia availability and pH and negatively correlated to sediment C/N ratios. AOA communities could be grouped according to lake trophic status and pH; plant species-specific communities were not detected, and no grouping was apparent for AOB communities. Relative abundance, determined by quantitative PCR targeting amoA, was always low for AOB (<0.05% of all prokaryotes) and slightly higher for AOA in unvegetated sediment and AOA in association with M. alterniflorum (0.01 to 2%), while AOA accounted for up to 5% in the rhizospheres of L. uniflora and J. bulbosus. These results indicate that (i) AOA are at least as numerous as AOB in freshwater sediments, (ii) aquatic macrophytes with substantial release of oxygen and organic carbon into their rhizospheres, like L. uniflora and J. bulbosus, increase AOA abundance; and (iii) AOA community composition is generally determined by lake trophy, not by plant species-specific interactions.

Do spectrally inferred determinations of chlorophyll a reflect trends in lake trophic status?

Visible reflectance spectroscopy (VRS) has been used to reconstruct lake sediment chlorophyll a concentrations. Despite good concordance between inferred and measured chlorophyll a values, questions remain as to whether this spectral technique is tracking past changes in aquatic primary production, or simply recording a diagenetic signal. In this study, we critically evaluate how well VRS chlorophyll a determinations track past trends in aquatic primary production using sediment cores from several lake systems with well-known trophic histories. Our study sites include Arctic, boreal and prairie lakes that encompass a gradient of trophic states. In general, our spectrally inferred chlorophyll a values tracked past trends in lake trophic status consistent with historical measurements of production, or as inferred by independent proxies of primary production. We conclude that VRS chlorophyll a inferences indeed track histories of lake production trends and that this method is widely applicable as a rapid, inexpensive and non-destructive alternative to wet-chemical analyses of sediment chlorophyll a concentrations.

“Karelian lakes” expert system: 1. Ordinal and nominal characteristics of lakes

An expert system is proposed for the assessment of characteristic and the trophic status of lakes for which little or no direct observational data are available. The system is based on the mathematical apparatus of fuzzy logic and applied to the best studied in Russia Karelian lake region. The created database on the morphometry, hydrology, hydrochemistry, and hydrobiology for 100 best studied lakes is described. The lakes are classified by methods of multidimensional statistics, factor, cluster, and logical-information analysis with the use of multidimensional scaling technique. Serious drawbacks of different classifications are demonstrated, in particular, because of the lack of a constructive algorithm for the recovery of unknown characteristics of a lake once it is referred to a certain class. In such cases, the mathematical apparatus of fuzzy sets and fussy logic should be used.

Growing season variability of nitrate along a trophic gradient – contrasting patterns between lakes and streams

We studied the growing season (May to October) variability of NO3-N across Swedish lakes and streams. We found that NO3-N concentrations showed the highest growing season variability among all water chemical variables tested, both in lakes and in streams. However, the growing season variability of NO3-N increased with increasing trophic status in lakes while it decreased in streams. We attributed the contrasting pattern between lakes and streams to the relative importance of biological uptake and denitrification with increasing trophic status. Our results highlight the relation between growing season NO3-N variability and trophic status, which is positive in lakes but negative in streams. The findings of this study have important ramifications for ecosystem studies as well as water management. We suggest that the assessment of growing season variability of NO3-N in aquatic systems can be improved by considering the effect of trophic status.

Dynamic of phytoplankton size-class and photosynthetic activity in a tropical hypereutrophic lake: the Yaounde municipal lake (Cameroon)

This study carried out within the framework of a multi-disciplinary project, aimed at highlighting the fundamental processes governing the functioning of the hypertrophic Yaounde Municipal Lake. It was based on the hypothesis that, even within a small range of lake trophic status, important variations can occur in the species composition, biomass and photosynthetic activity of the phytoplankton size-fractions. For this purpose, samples were taken at weekly intervals from November 1996 to December 1997 at a fixed set of depths in the water column. Spatial-temporal fluctuations of some physical–chemical variables, associated with biological variables such as phytoplankton size-class species composition, phytoplankton size-class biomass, phytoplankton primary production and chlorophyll-a were analysed. The water transparency was low and rarely exceeded 100 cm. Conductivity values relatively higher increased generally from the top to the lake bottom. The oxygen deficiency, and sometimes anoxia, recorded from 2.5 m depth resulted in high quantities of ammonium nitrogen. Total phosphorus and total Kjeldahl nitrogen concentrations were characteristics of hypertrophic lakes. The fertility of this biotope favoured the development of a high phytoplanktonic community with remarkable physiological adaptations to the variations of the nutritive potentials of the lake, characterized by the size-structure of these organisms. Cells of small size ( 45 μm), mainly Euglenophyta, maintained the relatively most important biomass, accounting for up to 89.85% of the total phytoplanktonic biomass. Chlorophyll-a concentrations are among the highest reported for both fresh water and sea water, being a consequence of high proportions of Chlorophyta and Euglenophyta. This led to intense phytoplanktonic photosynthetic activity which continued throughout the year, even though it was confined to the upmost first meter of the water column. Analyses pointed out the allogenic nature of the functioning of this urban lake ecosystem, due to a poor waste management on the surrounding landscape.

Zooplankton-based assessment of the trophic state of a tropical forest river in Nigeria

In this study, we explore the usefulness of zooplankton as a tool for assessing the trophic status of a Nigerian forest river. The river was sampled monthly and investigated for water physico-chemistry and zooplankton community structure using basic statistical measurement of diversity indices to characterize the zooplankton fauna. The trophic sta?tus of the river evaluated from its physico-chemical parameters indicates that the river is oligotrophic. The zooplankton composition was typical of a tropical freshwater river, with a total of 40 species, made up of 16 rotifers, 12 cladocerans, and 12 copepods and their developing stages in the following order of dominance: Rotifera &gt; Cladocera &gt; Cyclopoida &gt; Calanoida. There were strong correlations between the lake's trophic status and its zooplankton communities. The zoo?plankton community was dominated by numerous species of rotifers and crustaceans, which are typical of oligotrophic to mesotrophic systems, such species including Conochilus dossuarius and Synchaeta longipes. However, the most dominant zooplankton species in West African freshwater ecosystems, viz., Keratella tropica, Keratella quadrata, Brachionus angularis, Trichocerca pusilla, Filinia longiseta, Pompholyx sulcata, and Proales sp., and others that are indicator species of high trophic levels, were not recorded in the river. The river is very clear and can be used for all manner of recreational activities.

Long-term changes in commercial fish catches in Lake Mamry Północne (northeastern Poland) on the background of physical, chemical, and biological data

Lake Mamry Po³nocne, a part of the Great Masurian Lake System in northeastern Poland, is a valuable body of water from environmental, recreational, and economic points of view. The paper evaluates long-term physical, chemical, and biological parameters as well as commercial fisheries data. Nitrogen and phosphorus influx data as well as physical and chemical data indicate that the trophic state of Lake Mamry Po³nocne can be described as moderate from 1967 to 2006, making the lake borderline -mesotrophic and eutrophic. The lake's trophic state increased with time, manifesting itself in an increasing concentration of biogenic substances, decreasing water transparency, and worsening oxygen conditions in the hypolimnion. Changes in physical, chemical, and biological parameters generally corresponded with changes in the commercial fish catches of selected species and groups of species indicative of the process of eutrophication.

Littoral zones as sources of biodegradable dissolved organic carbon in lakes

A survey of 12 lakes in Minnesota, USA, was conducted to examine the factors controlling variability in biodegradable dissolved organic carbon (BDOC) concentration. The principal question addressed was whether BDOC concentration was more strongly related to lake trophic status or morphometric parameters. BDOC concentration was determined by incubating filtered lake water for a period of 15 months and fitting an exponential decay curve to measured DOC concentrations. BDOC concentrations varied from 73 to 427 µmol C·L–1 and composed 15%–63% of the total DOC pool. There were no significant correlations between BDOC and measures of lake trophic status. Instead, BDOC was most closely associated with the percentage of lake area covered by littoral zone, suggesting a significant source of BDOC from aquatic macrophytes and lake surface sediments.

Shallow lake trophic status linked to late Holocene climate and human impacts

Lake Mattamuskeet, North Carolina, USA is a large (162 km 2 ) and shallow (mean depth = 1m ) coastal lake, which was significantly modified to support agricultural activities following European settlement in 1850. Paleolimnological proxies mea- sured on a 400-cm sediment core collected from Lake Mattamuskeet reveal shifts in organic matter input and primary producer community structure in response to climatic and human impacts on the lake during the late Holocene. Stratigraphic changes in organic matter content, nutrients, metals, lignin phe- nols and photosynthetic pigments were used to divide the sediment core into three intervals. Interval I includes sediment deposited between A.D. 360-1584 and indicates a clear-water, sand-bottom state with low algal abundance. In addition, the lake catchment area experienced two significant fires during this interval that were recorded as charcoal layers in the core around A.D. 360 and A.D. 1435 (calibrated 14 C AMS dates). Trophic structure changed with the onset of Interval II (A.D. 1584-1860) when total algal abundance increased, and the primary producer com- munity was comprised primarily of diatoms, chrysophytes, cryptophytes and cyanobacteria. Dur- ing this interval there was also an increase in terrestrial organic material input into the lake as well as a shift in plant type from woody gymnosperms to non-woody angiosperms as determined from lignin data. Sediment deposited in Lake Mattamuskeet following European settlement (Interval III, A.D. 1860-present) suggests a dramatic increase in organic- matter deposition, metals, primary-producer abun- dance and the onset of cyanobacterial dominance. Sedimentary evidence indicates that shallow-water primary producers can respond rapidly to climate change and human development.

Biomarker evidence of macrophyte and plankton community changes in Zeekoevlei, a shallow lake in South Africa

Zeekoevlei is the largest freshwater lake in South Africa and has a century-long history of anthropogenic impact that caused hyper-eutrophic conditions. We used biomarkers (alkanes and pigments), stable isotopes (δ 13 C and δ 15 N), rates of primary palaeoproduction and total inorganic carbon (TIC) accumulation rates in the lake sediments to investigate changes in plankton and macrophyte communities in response to anthropogenic activities in this shallow lake. Specific alkanes (ΣC 15,17,19 , pristane, phytane and n-C 29 /n-C 17 ratio) and pigment (chlorophyll a, β,β-carotene, echinenone, fucoxanthin and zeaxanthin) concentrations in lake waters indicated the present-day hyper-eutrophic condition and seasonal fluctuations of cyanobacteria, zooplankton and diatom populations. Eutrophic conditions were initiated in the lake with the start of recreational activities and construction of a sewage treatment plant in the early 1920s. The lake transformed from a eutrophic to a hyper-eutrophic waterbody following damming, pondweed eradication and accelerated catchment-derived nutrient input. The change in lake trophic state was recorded by a sharp decline in the terrestrial to aquatic ratio (TAR) of specific n-alkanes, low carbon preference index (CPI) and increased δ 13 C values in the sediment core. In addition, the aquatic macrophyte n-alkane proxy (P aq ) values (~1) indicated a slow takeover by floating macrophytes after the eradication of submerged pondweeds in 1951. Elevated n-alkane (ΣC 15,17,19 ), total alkane and pigment (chlorophyll a, β,β-carotene, zeaxanthin and zeaxanthin to β,β-carotene ratio) concentrations, low δ 15 N values and low TIC accumulation rates in the upper middle section of the core indicated the beginning of intense cyanobacterial blooms after the dredging in 1983. Although the cyanobacterial population has decreased in recent years, hyper-eutrophic conditions are reflected by low CPI <0.04 and TAR <1 values at the top of the sediment core.

Screening for Organic Phosphorus Compounds in Aquatic Sediments by Liquid Chromatography Coupled to ICP-AES and ESI-MS/MS

The structures of organic phosphorous (P) compounds in aquatic sediments are to a large extent unknown although these compounds are considered to play an important role in regulating lake trophic status. To enhance identification of these compounds, a liquid chromatography (LC) method for their separation was developed. The stationary phase was porous graphitic carbon (PGC), and the mobile phases used in the gradient elution were compatible with both inductive coupled plasma atomic emission spectroscopy (ICP-AES) and electrospray ionization tandem mass spectrometry (ESI-MS/MS). With LC-ICP-AES, eight different P containing peaks could be observed in the P chromatogram indicating that at least eight different P compounds were separated. With the setup of an information dependent acquisition (IDA) with ESI-MS/MS, the mass over charge ( m/ z) of compounds containing a phosphate group (H 2PO 3 (-), m/ z 97) could be measured and further fragmentation experiments gave additional information on the structure of almost 40 separated P compounds, several were verified to be nucleotides. ICP-AES was very suitable in the development of the LC method and allowed screening and quantification of P compounds. The presented LC-ESI-MS/MS technique was able to identify several sediment organic P compounds.

Ecological variation within Sellaphora species complexes (Bacillariophyceae): specialists or generalists?

The genus Sellaphora has become a model system for studies of the species concept, speciation and automated identification in diatoms. Three species, S. pupula, S. bacillum and S. laevissima, have proved to be complexes containing several or many species, which are difficult to distinguish morphologically but which are genetically differentiated and (where tested) reproductively isolated. Until now, however, there has been little information about the ecology of the species within this complex, except in relation to parasite sensitivity. In order to test whether semi- and pseudo-cryptic Sellaphora species are ecologically differentiated with respect to trophic status, we used tools recently developed in the UK in response to the EU Water Framework Directive (WFD). Diatom samples from three substrata (plants, rocks, sediment) were taken from 22 lakes in Scotland and England, covering a gradient from oligotrophic mountain lakes to eutrophic lowland ponds. The epilithic and epiphytic diatom assemblages were used to evaluate lake trophic status according to the UK WFD assessment system and showed that there was a strong environmental gradient in the dataset. Sellaphora species occurred in the sediment-derived epipelon and their distributions were analysed in relation to the trophic gradient. A total of 28 Sellaphora phenodemes (putative species) were found, and some of them differed in their environmental demands. Two groups were distinguished: (1) a group indicating rather oligotrophic conditions and containing several demes with linear valves and subcapitate or capitate poles (referred to here as S. [pupula] cap-A, cap-B and cap-C and (2) a group occurring in eutrophic lakes and containing the recently described species S. blackfordensis, S. capitata and S. obesa, as well as S. [pupula] Φ ‘small lanceolate’. The data obtained are also discussed with respect to Finlay’s hypothesis on microalgal cosmopolitanism.

Monitoring periphyton in lakes experiencing shoreline development

Early detection of degradation is crucial in previously pristine lakes experiencing residential development along their shores. Despite suggestions that the littoral zone responds to anthropogenic disturbance before open water, the use of periphyton for monitoring lake trophic status has been hindered by the heterogeneous distribution of this community. We examined the response of periphyton growing on different natural substrata — rocks, wood, sediments, and macrophytes — as well as on introduced plastic strips along a gradient of residential development in the Laurentian lakes (Quebec). We measured periphyton biomass as chlorophyll a and as thickness estimated with a ruler with the goal to evaluate the best method to monitor the incipient degradation of these lakes. Our findings suggest that rocks are the best substratum to sample because they are ubiquitous, and epilithic algae show a stronger response to shoreline residential development than algae on other substrata. Measurement of epilithon thickness appears a fast and reliable tool for estimating epilithon biomass. If measurements of chlorophyll a require several field and laboratory manipulations that are not readily available for voluntary lake monitoring by residents, measurement of periphyton thickness on rocks may allow examining spatial and temporal changes in a large number of lakes.