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In northern lakes, which are often stained and productive, the impacts of dissolved organic carbon (DOC) on sediment phosphorus (P) release are largely unexplored. Here we elucidated the factors behind experimentally-derived sediment release rates of P by diffusion (DF) in four Finnish lakes with a range of colour. Next, we extended our analysis to a larger set of northern lakes for further insights regarding possible implications of organic substances on sediment P release. The significant correlation between pore-water soluble reactive P and dissolved iron, and a positive effect of iron-bound sedimentary P (Fe-P) on DF supports the classic paradigm of redox-dependent P release in the four Finnish lakes studied. Nevertheless, the P release from Fe-P may be inhibited by humic substances, as we observed lower Fe-P and negative DF in two humic rich lakes (high DOC). The analysis of a larger set of northern lakes supported the negative effect of humic substances on P release rate (RR) determined by in situ P increases. In this dataset, DOC correlated positively with water colour and negatively with RR. Furthermore, multiple stepwise regression analysis selected sediment total P and organic matter content in sediments (LOI) as the best predictors of RR, similar to a previously published model by Nürnberg (1988). While the model predictions (RRpred) were correlated to RR in the present study, they tended to overestimate RR that was determined in closed experimental systems. The inhibiting effects of humic substances on RR may be manifested in both internal P loading and primary production.

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Abstract One aquatic coleopteran species from family Dytiscidae and two aquatic coleopteran genera from family Hydrophilidae were recorded in the summer period and represent first records in the Egyptian lakes. Beetles were collected from two northern lakes, Lake Idku and Lake Burullus. They were identified by morphological characteristics as well as the mtDNA barcoding method. A molecular phylogenetic approach was used to determine the genetic identity of the collected samples based on the mitochondrial cytochrome oxidase I (COI). Prodaticus servillianus (Dytiscidae) from Egypt showed no significant difference in the COI region and they are highly similar to P. servillianus from Madagascar. The phylogenetic analysis revealed that the other two coleopteran genera belong to family Hydrophilidae. Based on COI only, there is no clear evidence for their genetic identity at the species level. So, we defined them to the closest taxon and denoted them as Cymbiodyta type A and B. The results indicated that resolving the molecular identity of the aquatic beetles from northern lakes of Egypt need more considerations in the field of biological conservation. We concluded that utilization of COI as a barcoding region for identifying some coleopteran species is not sufficient and additional molecular markers are required to uncover the molecular taxonomy at deep levels.

Resumo Uma espécie de coleópteros aquático da família Dytiscidae e dois gêneros de coleópteros aquáticos da família Hydrophilidae foram registrados no período de verão e representam os primeiros registros nos lagos egípcios. Os besouros foram coletados em dois lagos do norte, o lago Idku e o lago Burullus, e identificados por características morfológicas e pelo método de código de barras mtDNA. Uma abordagem filogenética molecular foi usada para determinar a identidade genética das amostras coletadas com base no citocromo oxidase I mitocondrial (COI). Prodaticus servillianus (Dytiscidae) do Egito não mostrou diferença significativa na região COI e é altamente semelhante a P. servillianus de Madagascar. A análise filogenética revelou que os outros dois gêneros de coleópteros pertencem à família Hydrophilidae. Com base apenas no COI, não há evidências claras de sua identidade genética no nível da espécie. Assim, nós os agrupamos no táxon mais próximo e os denominamos Cymbiodyta tipo A e B. Os resultados indicaram que a identidade molecular dos besouros aquáticos dos lagos do norte do Egito precisa de mais considerações no campo da conservação biológica. Concluímos que a utilização de COI como região de código de barras para identificar algumas espécies de coleópteros não é suficiente, sendo necessários marcadores moleculares adicionais para descobrir a taxonomia molecular em níveis profundos.

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The interacting effects of global changes-including increased temperature, altered precipitation, reduced acidification and increased dissolved organic matter loads to lakes-are anticipated to create favourable environmental conditions for cyanobacteria in northern lakes. However, responses of cyanobacteria to these global changes are complex, if not contradictory. We hypothesized that absolute and relative biovolumes of cyanobacteria (both total and specific genera) are increasing in Swedish nutrient-poor lakes and that these increases are associated with global changes. We tested these hypotheses using data from 28 nutrient-poor Swedish lakes over 16 years (1998-2013). Increases in cyanobacteria relative biovolume were identified in 21% of the study sites, primarily in the southeastern region of Sweden, and were composed mostly of increases from three specific genera: Merismopedia, Chroococcus and Dolichospermum. Taxon-specific changes were related to different environmental stressors; that is, increased surface water temperature favoured higher Merismopedia relative biovolume in low pH lakes with high nitrogen to phosphorus ratios, whereas acidification recovery was statistically related to increased relative biovolumes of Chroococcus and Dolichospermum. In addition, enhanced dissolved organic matter loads were identified as potential determinants of Chroococcus suppression and Dolichospermum promotion. Our findings highlight that specific genera of cyanobacteria benefit from different environmental changes. Our ability to predict the risk of cyanobacteria prevalence requires consideration of the environmental condition of a lake and the sensitivities of the cyanobacteria genera within the lake. Regional patterns may emerge due to spatial autocorrelations within and among lake history, rates and direction of environmental change and the niche space occupied by specific cyanobacteria.

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Abstract One aquatic coleopteran species from family Dytiscidae and two aquatic coleopteran genera from family Hydrophilidae were recorded in the summer period and represent first records in the Egyptian lakes. Beetles were collected from two northern lakes, Lake Idku and Lake Burullus. They were identified by morphological characteristics as well as the mtDNA barcoding method. A molecular phylogenetic approach was used to determine the genetic identity of the collected samples based on the mitochondrial cytochrome oxidase I (COI). Prodaticus servillianus (Dytiscidae) from Egypt showed no significant difference in the COI region and they are highly similar to P. servillianus from Madagascar. The phylogenetic analysis revealed that the other two coleopteran genera belong to family Hydrophilidae. Based on COI only, there is no clear evidence for their genetic identity at the species level. So, we defined them to the closest taxon and denoted them as Cymbiodyta type A and B. The results indicated that resolving the molecular identity of the aquatic beetles from northern lakes of Egypt need more considerations in the field of biological conservation. We concluded that utilization of COI as a barcoding region for identifying some coleopteran species is not sufficient and additional molecular markers are required to uncover the molecular taxonomy at deep levels.

Resumo Uma espécie de coleópteros aquático da família Dytiscidae e dois gêneros de coleópteros aquáticos da família Hydrophilidae foram registrados no período de verão e representam os primeiros registros nos lagos egípcios. Os besouros foram coletados em dois lagos do norte, o lago Idku e o lago Burullus, e identificados por características morfológicas e pelo método de código de barras mtDNA. Uma abordagem filogenética molecular foi usada para determinar a identidade genética das amostras coletadas com base no citocromo oxidase I mitocondrial (COI). Prodaticus servillianus (Dytiscidae) do Egito não mostrou diferença significativa na região COI e é altamente semelhante a P. servillianus de Madagascar. A análise filogenética revelou que os outros dois gêneros de coleópteros pertencem à família Hydrophilidae. Com base apenas no COI, não há evidências claras de sua identidade genética no nível da espécie. Assim, nós os agrupamos no táxon mais próximo e os denominamos Cymbiodyta tipo A e B. Os resultados indicaram que a identidade molecular dos besouros aquáticos dos lagos do norte do Egito precisa de mais considerações no campo da conservação biológica. Concluímos que a utilização de COI como região de código de barras para identificar algumas espécies de coleópteros não é suficiente, sendo necessários marcadores moleculares adicionais para descobrir a taxonomia molecular em níveis profundos.

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Lakes are a major component of boreal landscapes, and whereas lake CO2 emissions are recognized as a major component of regional C budgets, there is still much uncertainty associated to lake CH4 fluxes. Here, we present a large-scale study of the magnitude and regulation of boreal lake summer diffusive CH4 fluxes, and their contribution to total lake carbon (C) emissions, based on in situ measurements of concentration and fluxes of CH4 and CO2 in 224 lakes across a wide range of lake type and environmental gradients in Québec. The diffusive CH4 flux was highly variable (mean 11.6 ± 26.4 SD mg m(-2)  d(-1) ), and it was positively correlated with temperature and lake nutrient status, and negatively correlated with lake area and colored dissolved organic matter (CDOM). The relationship between CH4 and CO2 concentrations fluxes was weak, suggesting major differences in their respective sources and/or regulation. For example, increasing water temperature leads to higher CH4 flux but does not significantly affect CO2 flux, whereas increasing CDOM concentration leads to higher CO2 flux but lower CH4 flux. CH4 contributed to 8 ± 23% to the total lake C emissions (CH4  + CO2 ), but 18 ± 25% to the total flux in terms of atmospheric warming potential, expressed as CO2 -equivalents. The incorporation of ebullition and plant-mediated CH4 fluxes would further increase the importance of lake CH4 . The average Q10 of CH4 flux was 3.7, once other covarying factors were accounted for, but this apparent Q10 varied with lake morphometry and was higher for shallow lakes. We conclude that global climate change and the resulting shifts in temperature will strongly influence lake CH4 fluxes across the boreal biome, but these climate effects may be altered by regional patterns in lake morphometry, nutrient status, and browning.

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