Allochthonous organic carbon is increasing and leading to browning of freshwaters in the northern hemisphere. It is already known that an increase in allochthonous dissolved organic carbon (DOC) affects benthic primary production and respiration negatively via light limitation, however, little is known about the impact on benthic bacteria. This report aims at examining how DOC and other environmental variables affect the production and growth of benthic bacteria. This was done by analyzing data from 18 lakes in northern Sweden with different DOC concentrations. This analysis was divided into two datasets: one including data at the whole lake scale and the other including data over depth within the lakes. The result showed that DOC, average depth, and the light extinction coefficient all had a negative impact on bacterial production on a whole lake scale. The light extinction coefficient was also affecting the whole lake bacterial growth efficiency (BGE) negatively. Over depth within the lakes a higher light input increased the bacterial production. In the same dataset, light was also affecting the BGE positively, while temperature had a negative effect. The results can thus be linked to the increase in allochthonous carbon and brownification. Because allochthonous DOC have a negative effect on benthic primary production, there will be less autochthonous DOC available for benthic bacteria. Allochthonous DOC is considered less degradable than autochthonous DOC. The increase in allochthonous DOC therefore has a negative impact on benthic bacterial production, likely connected to a decrease in production of autochthonous DOC by benthic algae.

Sedimentos de regiões costeiras são caracterizados por altas concentrações de matéria de orgânica. As bactérias desempenham um fator chave na decomposição da matéria orgânica e na reciclagem de nutrientes inorgânicos essenciais. Além de representar um dos mais importantes recursos alimentares para a meio- e macrofauna. O presente estudo teve por objetivo avaliar a abundância e biomassa da comunidade bacteriana bêntica de duas enseadas na região costeira de Ubatuba (SP), relacionando-as ao aporte de matéria orgânica de diferentes fontes (marinha, terrestre e antrópica) e à estrutura da comunidade bêntica. Foram realizadas seis coletas bimensais em quatro estações por enseada ao longo de um transecto costa-oceano. O sedimento de cada testemunho foi fatiado a bordo em três camadas (0-2, 2-5 e 5-10 cm). A análise bacteriana foi conduzida através de contagem direta em microscópio de epifluorescência e a atividade através da freqüência de células em divisão. A análise dos parâmetros sedimentares como granulometria, qualidade e quantidade de matéria orgânica, bem como dados de macro e meiofauna foram obtidos através do Projeto DIAGEN, do qual o presente estudo faz parte. Os resultados de densidade e biomassa bacteriana mostraram valores sempre maiores na enseada de Ubatuba em relação à Fortaleza, acompanhado por teores mais elevados de matéria orgânica total, clorofila-a, feopigmentos e biomassa microbiana. O padrão de deposição das enseadas provavelmente teve papel decisivo nos altos valores de biomassa e densidade bacteriana nas regiões centrais e rasas das enseadas. Densidades e biomassas bacterianas mais elevadas foram encontradas no inverno (junho de 2005), não sendo observadas relações direta com os valores de matéria orgânica total ou clorofila-a. O estudo mostrou uma alta atividade bacteriana na camada superficial do sedimento, em especial no outono, com valores sempre maiores na enseada de Fortaleza, contrastando com os valores de densidade e biomassa. / Coastal sediments are characterized by high organic matter contents. Bacteria play a key role in organic matter decomposition and are essential in the nutrient recycling process. Moreover, represent an important food source for meio- and macrofaunal organisms. The present study aimed to evaluate the abundance and biomass of the benthic bacterial community in two bays of the coastal region of Ubatuba (SP). Bacterial abundance and biomass were compared with the distribution and abundance of different organic matter sources (marine, terrestrial and anthropogenic) and with the structure of the benthic community. We collected samples every two months for a period of one year in four stations on each bay along a coast-ocean transect. Tube cores were used to collect sediment samples, which were sliced on board in three layers (0-2, 2-5 and 5-10 cm). Bacterial abundance and biomass were counted and measured under epifluorescence microscopy and bacterial activity was estimated by the frequency of dividing cells. Information on sediment grain size distribution, quality and quantity of organic matter, as well as macro- and meiofauna were available from Project DIAGEN, from which this study is part. Bacterial density and biomass were always higher in Ubatuba bay, which appeared to be related to larger amounts of total organic matter, chlorophyll-a, pheopigments and microbial biomass. The differential deposition pattern observed in both bays was probably important determining the higher values of bacterial biomass and density found in the central and shallow portions of the bays. Despite higher bacterial density and biomass were found during the winter (June 2004) in most stations, this seemed not to be related to total organic matter or chlorophyll-a. Bacterial activity was high in surficial sediments, especially during autumn, with consistently larger values in Fortaleza bay.

Sedimentos de regiões costeiras são caracterizados por altas concentrações de matéria de orgânica. As bactérias desempenham um fator chave na decomposição da matéria orgânica e na reciclagem de nutrientes inorgânicos essenciais. Além de representar um dos mais importantes recursos alimentares para a meio- e macrofauna. O presente estudo teve por objetivo avaliar a abundância e biomassa da comunidade bacteriana bêntica de duas enseadas na região costeira de Ubatuba (SP), relacionando-as ao aporte de matéria orgânica de diferentes fontes (marinha, terrestre e antrópica) e à estrutura da comunidade bêntica. Foram realizadas seis coletas bimensais em quatro estações por enseada ao longo de um transecto costa-oceano. O sedimento de cada testemunho foi fatiado a bordo em três camadas (0-2, 2-5 e 5-10 cm). A análise bacteriana foi conduzida através de contagem direta em microscópio de epifluorescência e a atividade através da freqüência de células em divisão. A análise dos parâmetros sedimentares como granulometria, qualidade e quantidade de matéria orgânica, bem como dados de macro e meiofauna foram obtidos através do Projeto DIAGEN, do qual o presente estudo faz parte. Os resultados de densidade e biomassa bacteriana mostraram valores sempre maiores na enseada de Ubatuba em relação à Fortaleza, acompanhado por teores mais elevados de matéria orgânica total, clorofila-a, feopigmentos e biomassa microbiana. O padrão de deposição das enseadas provavelmente teve papel decisivo nos altos valores de biomassa e densidade bacteriana nas regiões centrais e rasas das enseadas. Densidades e biomassas bacterianas mais elevadas foram encontradas no inverno (junho de 2005), não sendo observadas relações direta com os valores de matéria orgânica total ou clorofila-a. O estudo mostrou uma alta atividade bacteriana na camada superficial do sedimento, em especial no outono, com valores sempre maiores na enseada de Fortaleza, contrastando com os valores de densidade e biomassa. / Coastal sediments are characterized by high organic matter contents. Bacteria play a key role in organic matter decomposition and are essential in the nutrient recycling process. Moreover, represent an important food source for meio- and macrofaunal organisms. The present study aimed to evaluate the abundance and biomass of the benthic bacterial community in two bays of the coastal region of Ubatuba (SP). Bacterial abundance and biomass were compared with the distribution and abundance of different organic matter sources (marine, terrestrial and anthropogenic) and with the structure of the benthic community. We collected samples every two months for a period of one year in four stations on each bay along a coast-ocean transect. Tube cores were used to collect sediment samples, which were sliced on board in three layers (0-2, 2-5 and 5-10 cm). Bacterial abundance and biomass were counted and measured under epifluorescence microscopy and bacterial activity was estimated by the frequency of dividing cells. Information on sediment grain size distribution, quality and quantity of organic matter, as well as macro- and meiofauna were available from Project DIAGEN, from which this study is part. Bacterial density and biomass were always higher in Ubatuba bay, which appeared to be related to larger amounts of total organic matter, chlorophyll-a, pheopigments and microbial biomass. The differential deposition pattern observed in both bays was probably important determining the higher values of bacterial biomass and density found in the central and shallow portions of the bays. Despite higher bacterial density and biomass were found during the winter (June 2004) in most stations, this seemed not to be related to total organic matter or chlorophyll-a. Bacterial activity was high in surficial sediments, especially during autumn, with consistently larger values in Fortaleza bay.