Distribution of chironomids (Diptera) in low arctic West Greenland lakes: trophic conditions, temperature and environmental reconstruction

1. Surface sediment samples of subfossil chironomid head capsules from 47 lakes in southern West Greenland were analysed using multivariate numerical methods in order to explore the relationship between chironomid assemblages and selected environmental variables. The study lakes are located along a climate gradient ranging from coastal maritime conditions near the Davis Strait to a continental climate near the margin of the Greenland ice sheet. 2. High‐resolution surface water temperatures were measured through the summer season using automatic data loggers in 21 of the study lakes. The mean July surface water temperature (1999) ranged from 7.3 to 16.5 °C in the data set. 3. In all lakes, a total of 24 chironomid taxa were recorded; Micropsectra, Psectrocladius, Chironomus and Procladius were the dominant genera. There was a strong correlation between the trophic variables [total nitrogen and total phosphorus (TN, TP)] and temperature, and in redundancy analysis (RDA) the three variables explained almost equal significant amounts of variation in the chironomid data (19.8–22.3%). However, temperature lost significant explanatory power when the effect of TN was partialled out in RDA. 4. The lakes were classified using two‐way indicator species analysis (TWINSPAN ) into eight groups defined by temperature, trophic variables, salinity (conductivity) and lake‐morphometric data. Fourteen chironomid taxa showed significant differences in percentage abundances among groups, with Heterotrissocladius, Micropsectra, Ablabesmyia and Chironomus as the most robust group‐indicator taxa. Forward selection of taxa in multiple discriminant analysis was used to fit chironomid assemblages into lake groups. Using only eight taxa, 95% of lakes were correctly classified at a second TWINSPAN division level (four groups) and 85% of lakes at a third division level (eight groups). 5. This study showed that there is considerable potential in using subfossil chironomid head capsules as paleoenvironmental indicators in both short‐ and long‐term (down‐core) studies of lake ontogeny and palaeoclimate conditions in West Greenland. However, because of the strong correlation between temperature and trophic variables, a quantitative reconstruction of lake‐ and habitat‐type is recommended, in combination with direct reconstruction of single variables such as temperature.     

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.     

Chironomid-based inference models for estimating end-of-summer hypolimnetic oxygen from south-central Ontario shield lakes

1. Subfossil chironomid head capsules were sampled from surficial sediments from 86 boreal shield lakes in south‐central Ontario, Canada. Lake characteristics ranged from shallow to very deep (> 80 m), ultraoligotrophic to mesotrophic, and with end‐of‐summer hypolimnetic oxygen conditions ranging from near‐saturation to anoxic. 2. Subfossil chironomid assemblages, comprising 44 taxa from 59 lakes, were analysed using multivariate ordination techniques such as redundancy analysis (RDA) and canonical correspondence analysis (CCA). Forward selection in RDA and CCA both showed that measures of oxygen, such as end‐of‐summer volume‐weighted hypolimnetic oxygen concentration (VWHO) and bottom oxygen concentration (botO₂), were the strongest explanatory variables for the chironomid data. Maximum depth and major ion chemistry were also important explanatory variables. 3. Oxygen inference models were developed using partial‐least‐squares regression (PLS), weighted‐averaging partial‐least‐squares regression (WA‐PLS), and weighted averaging regression (WA). Models were developed using both the full 44 taxa assemblage (which included littoral taxa) and using only 15 profundal‐type taxa. 4. Cross‐validated models (jackknifing) using full‐assemblage or profundal‐only taxa had similar statistical power (similar root mean squared error of prediction, RMSEP). The best models had moderate predictive power, with an r²_jack as high as 0.56, and an RMSEP as low as 2.15 mg L^–1 for [VWHO], and an r²_jack of 0.49 and an RMSEP of 0.24 for log([botO₂] + 1). 5. Reconstruction of [VWHO] and [botO₂] using a previously published chironomid profile that showed strong lake response to land‐clearance and logging suggests that oxygen inference models are reliable and accurate, reflecting the qualitative changes occurring in subfossil assemblages. However, the profundal‐only models may be misleading in situations where the ratio of littoral‐to‐profundal subfossils changes drastically in response to lake disturbance.     

Respiration of midges (Diptera; Chironomidae) in British Columbian lakes: oxy-regulation, temperature and their role as palaeo-indicators

1. The specific respiration rate of 13 chironomid taxa and Chaoborus were measured to test the hypothesis of the relation between a species' ability to regulate their oxygen uptake and their distributional patterns among nine study lakes in British Columbia, Canada.
2. Respiration patterns of individual taxa were modelled using piecewise linear regression with break point and simple hyperbolic functions. Three types of respiration curves were identified: (i) classical oxy-conformers (e.g. littoral Cricotopus ) which cannot sustain a sufficient oxygen uptake with decreasing oxygen availability; (ii) oxy-regulators (e.g. profundal Chironomus ) which can regulate and maintain a constant respiration until a certain critical point and (iii) oxy-stressors ( Micropsectra ) which increase their respiration rate with decreasing oxygen availability until a critical point.
3. Respiration was measured at two different temperatures (10 and 20 °C), and over the range of oxygen saturation conditions studied here (0–90%) mean Q ₁₀ values varied from 1.3 to 2.5.
4. The results show that different chironomid taxa have varying sensitivity to low oxygen concentrations and different respiratory responses to increased temperature. The critical point increased to higher oxygen saturation for six taxa, decreased for one taxon and was unchanged for two taxa.
5. The results illustrate one of the possible biological mechanisms behind the use of chironomids as temperature and climate indicators in palaeoecological studies by exploring the link between temperature and respiration physiology.     

Reconstructing the historical trophic status of northwestern Pennsylvania lakes using GIS

From each of 46 watersheds in glaciated northwestern Pennsylvania we estimated phosphorus export (kg P/ha/yr) from weekly or twice-weekly measured stream phosphorus concentrations and measured stream discharges, and determined land covers using GIS. Simple and step-down multiple regression analyses yielded models that explained 24% of the variation in P export using land cover within whole watersheds, and 64% of the variation using land cover within 200 m riparian buffers. We used these models to predict P loading to seven lakes and found that predicted lake [P] was consistent with measured lake [P]. To estimate pre-settlement lake [P] we reapplied the P export models with the assumption that human-impacted land covers were originally forests. Predicted (hindcast) pre-settlement lake [P] indicated that six of the seven lakes were edaphically mesotrophic (10 < [P] < 20 μg/l). Lake remediation targets set on the assumption that area lakes were historically oligotrophic ([P] < 10 μg/l) will be unattainable.     

Ecological sensitivity of marl lakes to nutrient enrichment: evidence from Hawes Water,UK

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Weichselian chironomid and cladoceran assemblages from maar lakes

Sediments from maar lakes in the periglacial area were analysed to obtain information about the limnetic fauna of Pleniglacial lakes. On the basis of abundance and species composition of the subfossil chironomid and cladoceran assemblages, three major zones were biostratigraphically separated: the Upper Pleniglacial, the Middle Pleniglacial, and the Eem Interglacial.     

Indicator value of midge larvae (Diptera: Nematocera) in shallow boreal lakes with a focus on habitat,water quality,and climate

Identification of indicator species is invaluable for lake management and long-term environmental change assessments. In this study, multi- and intralake datasets were investigated for their fossil midge assemblages (mostly Chironomidae) in the surface sediment layers representing the modern faunal composition. The aim was to examine taxon-specific responses to selected key variables and to assign indicator taxa for these environmental factors. Taxon-specific optima and tolerances were calculated and the significance of a particular environmental variable in explaining the distribution patterns was tested for each taxa. The results showed that numerous taxa had significant relationship with the environmental variables of interest. Thus, several midge indicator taxa were identified for the key variables. For the interest of palaeolimnology, the present results imply that when reconstructing long-term changes in a single environmental variable, variability in other regional, local or in-lake variables can distort the inference due to the complex taxon-specific responses to multiple environmental factors.     

Classification of the Tatra Mountain lakes (Slovakia) using chironomids (Diptera,Chironomidae)

Chironomid assemblages in thirty-three mountain lakes situated above tree line in the Slovakian part of the Tatra Mountains were studied during 2000–2002. Chironomid species/taxa, collected as pupal exuviae, were correlated with physical, chemical, and lake morphometry variables of 22 lakes. Two-way indicator species analysis (TWINSPAN) was used to classify the lakes into four distinct groups: higher situated alpine lakes, lower situated alpine lakes, subalpine lakes and acidified lakes. Presence/absence of eight taxa was identified as indicative for this classification. In discriminant function analysis, pH, dissolved organic carbon, altitude and lake area were the most significant variables reflecting differences among groups of lakes. This model of four variables allowed 77% success in the prediction of group membership. A multiple regression model with lake area, concentration of magnesium and total phosphorus accounted for 37% of the variance in taxa richness. Lakes with greater area contained more chironomid taxa than smaller ones. Lakes with higher alkalinity and higher trophic status tend to support more taxa. Canonical correspondence analysis (CCA) indicated that most variation in the composition of chironomid assemblages was related to pH and to altitude. The results can be used as reference data for long-term monitoring of the Tatra lakes, especially in connection with a recovery from acidification and global climatic change.     

Recovery from acidification in boreal lakes inferred from macroinvertebrates and subfossil chironomids

Acidification of waters and soils caused by emissions and the long-range transport of air pollutants has been a serious worldwide problem during the last decades. The extent of the acidification problem in Finnish acid-sensitive forest lakes was examined in the Acidification Research Project (HAPRO) in the mid-1980s. The recent decline in the emissions of air pollutants has resulted in the chemical recovery of watersheds in many regions, and the present work on the recovery processes in acidified Finnish headwater lakes (REPRO) was launched to examine whether the chemical recovery has already been accompanied by biological recovery. The patterns of recovery were studied by re-sampling littoral macrozoobenthos in a subset of the previously sampled HAPRO lakes. Paleolimnological samples were taken in order to assess the possible dependence of lacustrine chironomid communities on the changing degree of acidification. Acid sensitive and moderately acid sensitive benthic species revealed slight recovery in the formerly most acidic (pH 5.5) but recently recovered lakes. The most significant factors affecting the response of benthic communities were increased mean lake pH and decreased labile aluminium concentration. Paleolimnological chironomid analysis revealed a slight response along the pH gradient, but also significant structural similarity between the present and pristine chironomid assemblages. This implies that no major changes in chironomid communities of these acidic lakes have occurred during the past centuries. The alternative future trends and threats to biological recovery in small headwater lakes are discussed.     

Impact of eutrophication on the carbon stable‐isotopic baseline of benthic invertebrates in two deep soft‐water lakes

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Rotifer occurrence in relation to age,depth and trophic state of quarry lakes

An effect of age of quarry lakes on rotifer abundance and species composition has been evaluated. Rotifers occurred in all lakes under study. They were even found in the youngest (2 years of age) one, Rogonica 4, but both rotifer density and species richness were low there. Rotifer communities of much higher density and species diversity were noted in lakes only 4–6 years older. Lakes of over 30 years of age were strongly differentiated in rotifer numbers and species structure. In general, age of quarry lakes has an impact on rotifer communities only at the very beginning of the process of colonization. Several years later other factors become more important, e.g., depth or trophic state of the lakes.     

城市河湖生态系统健康评价——以北京市“六海”为例

健康的城市河湖才能发挥生态环境功能,体现景观和人文价值。城市河湖健康评价是城市河湖科学管理和生态恢复的前提和基础。对城市河湖生态系统健康概念和内涵进行了探讨,建立了评价指标体系和评价模型。以北京“六海”为例,对各子湖的健康状况进行比较评价。结果表明,中海和南海处于不健康向临界转化的状态,其余4个湖均处于不健康状态;水环境质量、水生态系统结构和功能以及水滨空间结构是影响“六海”健康水平的制约因素;除南海外,各湖的健康程度都处于很差的级别。中海和南海的整体生态环境好于其余4湖,对健康和临界状态的隶属度之和接近0.6,可恢复程度处于中等水平;其余4湖对健康和临界状态的隶属度之和均小于0.3,恢复困难。对“六海”的生态恢复和科学管理提出建议:①控制点源、面源污染,改善入湖和湖水水质;②改善“六海”的水文条件;③恢复水生态系统结构和水滨空间。     

Bioturbation enhances the aerobic respiration of lake sediments in warming lakes

While lakes occupy less than 2% of the total surface of the Earth, they play a substantial role in global biogeochemical cycles. For instance, shallow lakes are important sites of carbon metabolism. Aerobic respiration is one of the important drivers of the carbon metabolism in lakes. In this context, bioturbation impacts of benthic animals (biological reworking of sediment matrix and ventilation of the sediment) on sediment aerobic respiration have previously been underestimated. Biological activity is likely to change over the course of a year due to seasonal changes of water temperatures. This study uses microcosm experiments to investigate how the impact of bioturbation (by Diptera, Chironomidae larvae) on lake sediment respiration changes when temperatures increase. While at 5°C, respiration in sediments with and without chironomids did not differ, at 30°C sediment respiration in microcosms with 2000 chironomids per m² was 4.9 times higher than in uninhabited sediments. Our results indicate that lake water temperature increases could significantly enhance lake sediment respiration, which allows us to better understand seasonal changes in lake respiration and carbon metabolism as well as the potential impacts of global warming.     

Benthic community metabolism and trophic conditions of four South American lakes

Oxygen uptake rates of undisturbed sediment columns have been used as an integrative measure of the metabolic activities of benthic communities. Since the intensity of metabolic processes of profundal lake is dependent on the production of organic matter in the pelagic zone, oxygen uptake rates reflect the trophic condition of the whole lake. Four small lakes of central Chile, differing strongly in trophic conditions, provided a possibility to compare benthic oxygen uptake rates, under different oxygen conditions (Quiñenco, Grande, Chica and Lleulleu). Our objective was to establish the relationship between the oxygen uptake rates and bottom characteristics of lakes with different trophic conditions. At 8 mg O₂ l^-1 in the overlying water of the cores studied, the oxygen uptake rates of the sediment were: Quiñenco 51.2–56.0 mg O₂ m² h^-1 (eutrophic), Grande 41.2–46.4 mg O₂ m² h^-1 (mesotrophic), Chica 23.2–18.1 mg O₂ m² h^-1 (mesotrophic) and Lleulleu 11.7–16.0 mg O₂ m² h^-1 (oligotrophic). By exposing the sediments to different oxygen levels in the laboratory, it was found that benthic community metabolism decreased with oxygen concentrations. The slope of regression lines, relating oxygen uptake rates to oxygen concentrations, differed for the different sites investigated, closely related with the trophic conditions of the lakes. It was positively correlated with the organic matter content of the sediment of the cores (r ²= 0.78, p<0,05) and the nutrients of the bottom waters (total-P: r ²= 0.73, p<0,05; total-N: r ²= 0.73, p<0,05), and negatively with the redox potential of the sediments (r ²= 0.88, p<0,05).     

Factors influencing the variability of pigments in the surface sediments of mountain lakes

1. Surface sediment biofilm samples from 82 Pyrenean lakes were analysed for marker pigment composition using high performance liquid chromatography (HPLC). 2. Variability in the pigment composition among lakes was investigated by multivariate statistical analyses using a large data set of factors describing lake chemical, physical, morphological and catchment characteristics. 3. Due to the widely varying light penetration in the lakes, the most significant gradient of pigment composition extended from a benthic to a planktonic signal. The most important pigments in the gradient were alloxanthin (cryptophytes marker pigment, planktonic signal) and diatoxanthin (diatoms marker pigment, benthic signal). The molar ratio between these two marker pigments was positively correlated with lake depth. 4. Chlorophyll‐a preservation was found to be positively related to light penetration and the development of an autothrophic biofilm on the surface sediment and negatively related to decreasing pH and the percentage of alpine meadows in the lake catchments. 5. Zooplankton marker pigments in the surface sediment, including grazing by‐products (e.g. phaeophorbides) and carotenoids (astaxanthin, canthaxanthin, echinenone) incorporated into their tissues, were correlated with the areal abundance of zooplankton. 6. Marker pigments for photosynthetic bacteria, BChl‐e and okenone, were found mainly in relatively shallow lakes with large catchments that are forested, probably because of their higher loading of allochthonous organic matter. 7. The evaluation of a preservation index (Chl‐a expressed as a percentage of a‐phorbins) and the alloxanthin/diatoxanthin ratios throughout the sediment record of mountain lakes can provide evidence of historical changes in the relative importance of planktonic versus benthic primary production and might ultimately be interpreted in terms of climatic or environmental changes.     

The eutrophication of shallow coastal lakes in Southwest England — understanding and recommendations for restoration,based on palaeolimnology,historical records,and the modelling of changing phosphorus loads

Palaeolimnological studies of sediments from Slapton Ley and Loe Pool, two coastal freshwater lakes in Southwest England, show that in the period since 1945, they have been eutrophicated by nutrient inputs from intensification of agriculture, but also from sewage effluent. Two simple models have been used to identify the main sources of catchment outputs, and in the case of Slapton Ley, to evaluate historical changes in land use, and their likely effect on lake trophic status.Restoration strategies may also be evaluated using the same models. They suggest that in order to reduce loads on either lake to within OECD permissible limits, not only will all sewage inputs need to be prevented, and non-phosphate detergents used, but also losses from agricultural land must be reduced. This could take the form of the keeping of fewer cattle (the main source of organic nitrogen and phosphorus in both catchments), or the zoning of the respective catchments so that steep slopes close to riparian zones are not used, as at present, for the grazing of livestock.A better option, however, would appear to be the establishment along most of the rivers draining into these lakes, of buffer strips of woodland at least 15 m wide. According to the models, this measure, along with treatment or diversion of sewage effluent, would reduce phosphorus loads upon the lakes to within acceptable limits.     

Subfossil chironomid assemblages in deep,stratified European lakes: relationships with temperature,trophic state and oxygen

1. The distributions of subfossil remains of chironomid larvae in 28 large, deep and stratified lakes in Europe were examined in surface sediments along a latitudinal transect ranging from northern Sweden to southern Italy. 2. Canonical correspondence analysis (CCA) showed that summer surface water and July air temperature, as well as total phosphorus (TP) concentrations, hypolimnetic oxygen availability and conductivity were statistically significant (P < 0.05) explanatory variables explaining between 11 and 14% of the variance in the chironomid data. 3. Owing to the spatial scale covered by our study, many environmental variables were covarying. Temperature, TP concentration and oxygen availability were positively or negatively correlated with the first axis of a detrended correspondence analysis (DCA) of chironomid assemblages, suggesting that climatic and trophic conditions influenced profundal chironomid assemblages either in a direct (food and oxygen) or in an indirect (temperature) way. Parameters related to local environmental conditions, lake morphology and bedrock geology, such as organic matter content of the sediment, maximum lake depth, Secchi depth and pH, were not significant in explaining the distribution of chironomid assemblages in our study lakes. 4. The strong relationship between chironomid assemblages and summer temperature may be related to the covariation of temperature with parameters, such as nutrient and oxygen availability, known to affect chironomid assemblages in deep, stratified lakes. However, summer temperature explained a statistically significant proportion of the variance in the chironomid assemblages even when effects of oxygen availability and TP concentrations were partialled out. This suggests that summer temperature has an effect on chironomid assemblages in deep lakes, which is not related to its covariation with trophic state. 5. The potential of fossil chironomid analysis for quantitatively reconstructing past nutrient conditions in deep, stratified lakes was examined by calculating the Benthic Quality Index (BQI) based on subfossil chironomids and by comparing BQI values with observed TP concentrations. BQI was linearly related to log‐transformed TP. Applying this relationship to fossil chironomid assemblages from Lake Päijänne (Finland) produced a TP reconstruction in agreement with measured TP during the period 1970–1990, demonstrating that this approach can provide quantitative estimates of past nutrient concentrations in deep, stratified lakes.     

The trophic state of shallow lakes in The Netherlands

A study has been carried out on the development of an ecological assessment method for shallow lakes in The Netherlands. Analyses of eutrophication characteristics of 93 lakes with, in total, 127 sampling localities gave insight into some of the steering variables, such as total-P, total-N, chlorophyll-a and transparency. On the basis of phytoplankton species composition, three main groups of lakes could be distinguished. The first group, characterized by persistent filamentous Cyanobacteria, had the highest summer means of chlorophyll-a and total-P. The second group was characterized by non-persistent filamentous Cyanobacteria, occurring in low abundancies, and at lower chlorophyll-a and total-P concentrations. The third group of lakes was characterized by the absence or very low abundance of the filamentous Cyanobacteria. As a result of these analyses, criteria for the abatement of eutrophication in shallow lakes could be refined.