207
15 Biogeochemical Indicators of Nutrient Enrichments in Wetlands …
15.4 Microbial Structure and Function as
Indicators for Wetland Trophic Status
Although soil microorganisms regulate biogeochemical
processes, their distribution and abundance is controlled by
environmental and anthropogenic factors. With this premise
studies have focused on linking microbial groups with the
trophic status of wetlands (Hartman et al. 2008). It is also
known that both extrinsic (regional scale including climate
change, geographic location) and intrinsic (local scale including nutrient inputs) factors affect in regulating the microbial communities therefore studies that aim to narrow
down the specific microbial species as an indicator of trophic status are still very few. Nevertheless, few studies have
explained the presence of certain microbial groups at specific sites with varying nutrient content (Castro et al. 2002,
2004; Bowen et al. 2009; Inglett et al. 2011). These studies
have defined the potential role of microbial structure (species richness and distribution of the microbial community),
and function (metabolic status of microbial groups, carbon
utilization patterns) as indicators for the ecological status of
the ecosystems including aquatic soils and sediments. Application of techniques such as nucleic acid fingerprinting (denaturing gradient gel electrophoresis, DGGE; terminal restriction length fragment polymorphism, tRFLP; fluorscence
in situ hybridization, FISH), lipid biomarkers (phospholipid
fatty acid, PLFA; phospholipid ether lipid, PLEL) and community-level physiological profile (CLPP) have been used
in several aquatic soil and sediments including freshwater
and coastal wetlands (Kowalchuck et al. 1998; Sizova et al.
2003; Castro et al. 2004; Costa et al. 2007; Zhou et al. 2009;
Inglett et al. 2011).
A study by Hartman et al. (2008) showed that wetland restoration resulted in a decrease of bacterial diversity, which is
an opposite response to that of the terrestrial systems. The
bacterial taxa Acidobacteria and Proteobacteria were reported to be potential indicators of restoration and trophic
status. Although specific microbial groups that have been
linked to Acidobacteria are oligotrophs and they are characterized by slow growth and use of more refractory carbon
substrates in their metabolism (Eichorst et al. 2007). Studies
with sediments from reservoirs revealed abundance of β Proteobacteria in eutrophic regions and γ-Proteobacteria in dystrophic regions. The ratio of Proteobacteria to Acidobacter
has been suggested to be a broad indicator of trophic status
of terrestrial soils. Whether this could be applied in wetland
systems is yet to be seen. In another study by Jackson and
Vallaire (2009) in sediments of the Louisiana wetlands with
N enrichment a reduction of the microbial diversity and a decreased proportion of α-Proteobacteria and Planctomycetes
were reported.
Studies on specific microbial groups across the phosphorus gradient in the Florida Everglades have shown differences in sulfate reducing bacteria and methanogenic communities. Eutrophic regions have shown the dominance of
Desulfotomaculum with ability to completely oxidize substrates in the eutrophic areas relative to the oligotrophic region that was dominated with species that incompletely oxidize substrates (Castro et al. 2002). The Florida Everglades
are characterized by high number of methanogens that belong to the order of Methanomicrobiales with higher abundance in the nutrient-enriched regions (Castro et al. 2004).
Higher abundance of cellulolytic bacteria in P-enriched sites
has been reported, being Clostridium assemblages in soils
significantly correlated with the soil nutrient status. (Uz and
Ogram 2006).
Both the shift in the microbial community of periphyton
mats from cyanobacteria and large number of epiphytic diatoms to green algae and the declined abundance of epiphytic diatoms have also been noted across a P gradient in the
Florida Everglades (McCormick and O’Dell 1996). Within
the periphyton mats the shift from cyanobacteria dominated
system to a filamentous green algae system has been a common response to phosphorus enrichment in the Everglades
(McCormick et al. 1996). Dramatic decreases of cyanobacteria species richness as a result of eutrophication have also
been reported by Rejmankova et al. (2004).
Wetland restoration studies also have shown linkages of
the microbial community structure and function to biogeochemical parameters including nutrient changes. By comparing phospholipid biomarkers of the overall microbial
community in wetland soils, Inglett et al. (2011) have shown
increased fungal population and higher ratio of Gram negative to Gram positive bacteria in high sites with OC:N ratio
(newly restored sites). Low phosphorus sites (native sites)
were characterized with a higher abundance of Gram positive bacteria. Biomarkers for Actinomycetes was also found
to be positively correlated to the P concentration in soils.
Phospholipid fatty acids (PLFA) are present in both eukaryotic and prokaryotic membranes and thereby give a complete
extraction efficiency (k EC ) factor of 0.37. The values
of total organic carbon for the nonfumigated (control) samples were defined as extractable or labile C.
MBN is determined by subtracting the extractable
NH 4 -N concentrations of the triplicate nonfumigated
samples from triplicate fumigated samples, applying
a combined extraction efficiency value (k EN ) of 0.54
(Brookes et al. 1985). Finally, the difference in total P
between the treated and untreated samples constitutes
the MBP, without using any extraction efficiency factor (Ivanoff et al. 1998).
15 Biogeochemical Indicators of Nutrient Enrichments in Wetlands …
15.4 Microbial Structure and Function as
Indicators for Wetland Trophic Status
Although soil microorganisms regulate biogeochemical
processes, their distribution and abundance is controlled by
environmental and anthropogenic factors. With this premise
studies have focused on linking microbial groups with the
trophic status of wetlands (Hartman et al. 2008). It is also
known that both extrinsic (regional scale including climate
change, geographic location) and intrinsic (local scale including nutrient inputs) factors affect in regulating the microbial communities therefore studies that aim to narrow
down the specific microbial species as an indicator of trophic status are still very few. Nevertheless, few studies have
explained the presence of certain microbial groups at specific sites with varying nutrient content (Castro et al. 2002,
2004; Bowen et al. 2009; Inglett et al. 2011). These studies
have defined the potential role of microbial structure (species richness and distribution of the microbial community),
and function (metabolic status of microbial groups, carbon
utilization patterns) as indicators for the ecological status of
the ecosystems including aquatic soils and sediments. Application of techniques such as nucleic acid fingerprinting (denaturing gradient gel electrophoresis, DGGE; terminal restriction length fragment polymorphism, tRFLP; fluorscence
in situ hybridization, FISH), lipid biomarkers (phospholipid
fatty acid, PLFA; phospholipid ether lipid, PLEL) and community-level physiological profile (CLPP) have been used
in several aquatic soil and sediments including freshwater
and coastal wetlands (Kowalchuck et al. 1998; Sizova et al.
2003; Castro et al. 2004; Costa et al. 2007; Zhou et al. 2009;
Inglett et al. 2011).
A study by Hartman et al. (2008) showed that wetland restoration resulted in a decrease of bacterial diversity, which is
an opposite response to that of the terrestrial systems. The
bacterial taxa Acidobacteria and Proteobacteria were reported to be potential indicators of restoration and trophic
status. Although specific microbial groups that have been
linked to Acidobacteria are oligotrophs and they are characterized by slow growth and use of more refractory carbon
substrates in their metabolism (Eichorst et al. 2007). Studies
with sediments from reservoirs revealed abundance of β Proteobacteria in eutrophic regions and γ-Proteobacteria in dystrophic regions. The ratio of Proteobacteria to Acidobacter
has been suggested to be a broad indicator of trophic status
of terrestrial soils. Whether this could be applied in wetland
systems is yet to be seen. In another study by Jackson and
Vallaire (2009) in sediments of the Louisiana wetlands with
N enrichment a reduction of the microbial diversity and a decreased proportion of α-Proteobacteria and Planctomycetes
were reported.
Studies on specific microbial groups across the phosphorus gradient in the Florida Everglades have shown differences in sulfate reducing bacteria and methanogenic communities. Eutrophic regions have shown the dominance of
Desulfotomaculum with ability to completely oxidize substrates in the eutrophic areas relative to the oligotrophic region that was dominated with species that incompletely oxidize substrates (Castro et al. 2002). The Florida Everglades
are characterized by high number of methanogens that belong to the order of Methanomicrobiales with higher abundance in the nutrient-enriched regions (Castro et al. 2004).
Higher abundance of cellulolytic bacteria in P-enriched sites
has been reported, being Clostridium assemblages in soils
significantly correlated with the soil nutrient status. (Uz and
Ogram 2006).
Both the shift in the microbial community of periphyton
mats from cyanobacteria and large number of epiphytic diatoms to green algae and the declined abundance of epiphytic diatoms have also been noted across a P gradient in the
Florida Everglades (McCormick and O’Dell 1996). Within
the periphyton mats the shift from cyanobacteria dominated
system to a filamentous green algae system has been a common response to phosphorus enrichment in the Everglades
(McCormick et al. 1996). Dramatic decreases of cyanobacteria species richness as a result of eutrophication have also
been reported by Rejmankova et al. (2004).
Wetland restoration studies also have shown linkages of
the microbial community structure and function to biogeochemical parameters including nutrient changes. By comparing phospholipid biomarkers of the overall microbial
community in wetland soils, Inglett et al. (2011) have shown
increased fungal population and higher ratio of Gram negative to Gram positive bacteria in high sites with OC:N ratio
(newly restored sites). Low phosphorus sites (native sites)
were characterized with a higher abundance of Gram positive bacteria. Biomarkers for Actinomycetes was also found
to be positively correlated to the P concentration in soils.
Phospholipid fatty acids (PLFA) are present in both eukaryotic and prokaryotic membranes and thereby give a complete
extraction efficiency (k EC ) factor of 0.37. The values
of total organic carbon for the nonfumigated (control) samples were defined as extractable or labile C.
MBN is determined by subtracting the extractable
NH 4 -N concentrations of the triplicate nonfumigated
samples from triplicate fumigated samples, applying
a combined extraction efficiency value (k EN ) of 0.54
(Brookes et al. 1985). Finally, the difference in total P
between the treated and untreated samples constitutes
the MBP, without using any extraction efficiency factor (Ivanoff et al. 1998).